Jack Blanton, Julie Amft, Peter Verity. Georgia Marine Science Center University System of Georgia Skidaway Island, Georgia

Transcription

1 Tehnial Report Series Number94-1 TheMay93 North Edisto Ingress Experiment (NED1) Jak Blanton, Julie Amft, Peter Verity Georgia Marine Siene Center University System of Georgia Skidaway Island, Georgia

2 The May 93 North Edisto Ingress Experiment (NEDl) Tehnial Report 94-1 J. Blanton, J. Amft, and P. Verity Skidaway Institute of Oeanography 10 Oean Siene Cirle Savannah, Georgia The Tehnial Report Series of the Georgia Marine Siene Center is issued by the Georgia Sea Grant College Program and the Marine Extension Servie of the University of Georgia on Skidaway Island (30 Oean Siene Cirle, Savannah, Georgia 31411). It was established to provide dissemination of tehnial information and progress reports resulting from marine studies and investigations mainly by staff and faulty of the University System of Georgia. In addition, it is intended for the presentation of tehniques and methods, redued data, and general information of interest to industry, loal, regional, and state governments and the publi. Information ontained in these reports is in the publi domain. If this pre-publiation opy is ited, it should be sited as an unpublished manusript. This work was sponsored by joint grants from the Georgia Sea Grant Program (Grant No. RJEA-15) to the Skidaway Institute of Oeanography and the South Carolina Sea Grant Consortium (Grant No ) to the South Carolina Marine Resoure Researh Institute.

3 ACKNOWLEDGEMENTS We wish to express our appreiation to the several individuals without whose help this projet would not have been possible. First, our thanks go to Marsha Ward who partiipated in the ruises and Lane Mitham of Skidaway Institute who developed muh of the instrumentation and software used in the ODIS system aboard the BLUE FIN. Next, we thank Charlie Barans, Betty Wenner, Brue Stender and David Knott of the South Carolina Marine Resoures Researh Institute, our sientifi partners in this projet We also appreiate the able support of Captain Jay Fripp and rew Raymond Sweatte and Chris Knight of the R/V BLUE FIN, and Captain Paul Tuker of the R/V ANITA. This work was sponsored by joint grants from the Georgia Sea Grant Program (Grant No. R/EA-15) to the Skidaway Institute of Oeanography and the South Carolina Sea Grant Consortium (Grant No ) to the SC Marine Resoure Researh Institute. i

4 ABSTRACT The ingress of postlarval rustaeans through inlets is a potential bottlenek to reruitment. A joint oeanographi and fishery program was designed to identify the physial oeanographi transport proesses that ontrol the ingress of postlarval blue rab and white shrimp through an inlet. A 14-day experiment was onduted in and off the South Carolina oast utilizing a ombination of moored instrumentation and shipboard surveys. Two researh vessels operated in the inlet and offshore to measure vertial profiles of ondutivity, temperature, depth, and hl a as well as larval abundane. The estuary was essentially well-mixed during upwelling with stratified water offshore. The abrupt salinity disonnetion from vertially well-mixed to stratified between offshore waters and estuarine waters suggests weak oupling between estuarine and oastal waters. The estuary was also well-mixed during downwelling but hl a onentrations were higher. Salinity on the shelf was vertially uniform, onsistent with strong vertial mixing. Coupling of oastal and estuarine waters was optimized during this period when downwelling-favorable winds plus spring tides effiiently transported oeani water into the estuary. Both salinity and hlorophyll a inreased most rapidly in the inlet during downwelling winds and the onset of spring tidal onditions. Chl a onentration generally inreased with depth suggesting a benthi soure. A near-bottom hl a maxima was present along the ebb tide delta between the inlet mouth and the oastal front. It was positively orrelated with salinity refleting higher hl a in the more-saline water where the oastal front intersets the bottom along the offshore portion of the inlet delta. ii

5 Abundanes of postlarval Penaeus were usually greatest in surfae samples. Peaks abundanes in the inlet oinided with downwelling onditions suggesting that larval ingress is enhaned then. Keywords: Shrimp, Coastal, Estuaries, Fisheries, South Carolina, Hydrodynamis, Hdyrography, Inlet, Larvae, Meteorology, Oeanography, Plankton, Reruitment, Upwelling, Downwelling, Fronts iii

6 LIST OF TABLES Table I. Moored instrumentation used during NEDl in May p. 31 Table 2a. R/V BLUE FIN station log for NED 1. p. 32 Table 2b. R/V ANITA station log for NED I. p. 34 Table 3. First order statistis for parameters measured during NED 1. The station loation and depth above bottom are designated for eah sensor. All parameters with x- and y-omponents have been rotated 50 degrees ounter-lokwise. Series with a length of 15. days begin 13 May 1993 at 18 GMT and end 29 May 1993 at 00 GMT; series with a length of days begin 15 May 1993 at 00 GMT and end 26 May 1993 at 18 GMT. (a) 3hlp data; (b) 40hlp data. p. 36 Table 4. First order statistis using 3hlp data for parameters measured for 2 tidal yles eah during the neap and spring tide of NED 1. The station loation and depth above bottom are designated for eah sensor. All parameters with x- andy-omponents have been rotated 50 degrees ounter-lokwise. (a) Neap tide iv

7 data begin 15 May 1993 at 09 GMT and end 16 May 1993 at 09 GMT; (b) spring tide data begin 22 May 1993 at 14 GMT and end 23 May 1993 at 14 GMT. p. 37 Table 5. First order statistis using 40hlp data for parameters measured for two events (one upwelling and one downwelling) during NED 1. The station loation and depth above bottom are designated for eah sensor. All parameters with x- andy-omponents have been rotated 50 degrees ounter-lokwise. (a) The upwelling event begins 16 May 1993 at 12 GMT and ends 19 May 1993 at 12 GMT; (b) the downwelling event begins 21 May 1993 at 00 GMT and ends 23 May 1993 at 00 GMT. p. 38 v

8 LIST OF FIGURES Fig. 1. Loation maps showing bathymetry and station loations for moorings and ship sampling. (a) Offshore domain overed by RN BLUE FIN; (b) inlet domain overed primarily by Fig. 2. Fig. 3. Fig. 4. RN ANITA. Mooring design for stations Ml and M2 during NEDl. Sampling times of offshore and inlet surveys in relation to yles of tide and darkness. Predited flood urrents are positive and time is Eastern Daylight Savings Time. Calibration urves of CTD fluorometer voltage versus p. 39 p. 41 p. 42 extrated hlorophyll a. (a) RN ANITA; (b) R/V BLUE FIN. p. 43 Fig. 5. Time series of rotated wind stress at FBIS 1. Hourly data have been smoothed with a 40-hour low-pass filter and rotated 50 degrees ounter-lokwise. (a) Alongshelf and ross-shelf omponents; (b) vetor plot p. 44 Fig. 6. Time series of 3hlp urrent data from Ml. (a) Wind stress omponent at FBISl; (b) along-inlet urrent omponent (positive seaward); () ross-inlet urrent omponent (positive northeastward). p. 45 Fig. 7. Time series of 3hlp urrent data from M2. (a) Wind stress omponents at FBISl; (b) ross-shelf omponent (positive offshore); () alongshelf omponent Vl

9 (positive northeastward). p. 46 Fig. 8. Time series of 3hlp data from Ml and M2. (a) Temperature; (b) salinity; () rt; (d) subsurfae pressure. p. 47 Fig. 9. Vetor plots of 40hlp wind stress at FBIS 1 and oastal urrents at M2. p. 49 Fig. 10. Component plots of 40hlp wind stress at FBIS 1 and oastal urrents at M2. p. 50 Fig. 11. Time series plots of 40hlp data from M 1 and M2. (a) Temperature; (b) salinity; () rt; (d) subsurfae pressure. p. 51 Fig. 12. Oeanographi and larval survey OSl: May (a) Salinity; b) hlorophyll a; () temperature (d) r 1 See Figure 1 for station loations. p. 53 Fig. 13. Oeanographi and larval survey OS2: May (a) Salinity; (b) hlorophyll a; () temperature (d) rt. See Figure 1 for station loations. p. 54 Fig. 14. Oeanographi and larval survey OS3: 20 May (a) Salinity; (b) hlorophyll a; () temperature (d) rt. See Figure 1 for station loation. p. 55 Fig. 15. Oeanographi and larval survey OS4: May (a) Salinity; (b) hlorophyll a; () temperature (d) rt. See Figure 1 for station loations. p. 56 vii

10 Fig. 16. Oeanographi and larval survey OS5: 22 May (a) Salinity; (b) not available; () temperature (d) not available. See Figure 1 for station loations. Note: The InterOean Systems S4 CID used for this survey did not have a fluorometer and salinities for this survey have not yet been alibrated. p. 57 Fig. 17. Oeanographi and larval survey OS6: 23 May (a) Salinity; (b) hlorophyll a; () temperature (d) rt. See Figure 1 for station loations. p. 58 Fig. 18. Oeanographi and larval survey OS7: 24 May (a) Salinity; (b) hlorophyll a; () temperature (d) at. See Figure 1 for station loations. p. 59 Fig. 19 Oeanographi and larval survey OS8: May (a) Salinity; (b) hlorophyll a; () temperature (d) at" See Figure 1 for station loations. p. 60 Fig. 20. Oeanographi and larval survey OS9: -26 May (a) Salinity; (b) hlorophyll a; () temperature (d) (Jt See Figure 1 for station loations. p. 61 Fig. 21. Oeanographi and larval survey OSlO: 26 May (a) Salinity; (b) hlorophyll a; () temperature (d) a,. See Figure 1 for station loations. p. 62 Vlll

11 Fig. 22. Offshore oeanographi surveys onduted during high water and low water neap tide of 15 May See Figure 1 for station loations. p. 63 Fig. 23. Estuarine survey in the North Edisto River during low water neap tide of 15 May See Figure 1 for station loations. p. 64 Fig. 24. Estuarine surveys in the North Edisto River during high water and low water spring tide of 22 May See Figure 1 for station loations. p. 65 Fig.. Time versus depth plots during nighttime maximum flood urrent in the throat of North Edisto Inlet. (a) Salinity; (b) hlorophyll a; () temperature (d) rt. p. 66 Fig. 26. (a) Chlorophyll a versus salinity; (b) hlorophyll a versus rt and () hlorophyll a versus optial baksatter ( 400*volts) for all offshore stations. p. 67 Fig. 27. (a) Chlorophyll a versus salinity; (b) hlorophyll a versus r 1 and () hlorophyll a versus optial baksatter (400*volts) for all North Edisto Inlet stations. p. 68 Fig. 28. Density (No./100 m 3 ) of postlarval Penaeus from surfae and bottom plankton samples taken during NED1, May Colletions were made at night during flood tide. p. 69 lx

12 Fig. 29. Composite setions of salinity and hlorophyll a during (a) neap tide on 15 May and (b) spring tide on 22 May. The shallow inlet delta is in the break between zones overed by the R/V ANITA in the estuary and those overed by R/V BLUE FIN offshore. See Figure 1 for station loations. p. 70 Fig. 30. Near-surfae salinity and temperature data on 5 traverses between Ml and A6 using the ODIS flow-through system. The numbers for eah line denote the May date of the survey. See Figure 1 for loation of M1 and A6. p. 72 X

13 Table of Contents Aknowledgements.... Abstrat List of Tables List of Figures Table of Contents ii iv vi xi 1.0 Purpose and Objetives Oeanographi Methods Used Results and Disussion Summary Referenes xi

14 The May 93 North Edisto Ingress Experiment (NEDl) by J. Blanton, J. Amft, and P. Verity 1.0 Purpose and Objetives This report summarizes data and results. from NEDl, the May 1993 North Edisto Ingress Experiment. This was the first of a series of ruises designed to relate the spatial and temporal distribution of postlarval blue rab and white shrimp in inner shelf water entrained through an inlet to periodi (tidal, diel, lunar) and stohasti (wind, urrent) events. Our hypothesis is that the physial flow field interats with the behavior and population biology of white shrimp and blue rab larvae to disontinuously transport developmental larval stages from offshore sites to estuarine nurseries. From a oneptual perspetive, we view this transport as omprising two steps, eah likely dominated by a different mehanism: (1) transport from seaward spawning or larval development sites into the oastal frontal zone (as for blue rab), and (2) transport from the oastal frontal region into the estuary. Postlarvae are entrained into an inlet by an interation of the alongshore oastal urrent with a landward influx of oastal water aused by alongshore wind stress and tidal urrents. Detennination of the portion of the oastal urrent from whih landward withdrawal ours requires a study of the onfiguration and extent of the oastal frontal zone. Cirulation will differentially influene ingress of blue rab and white shrimp depending upon the vertial distribution of the postlarvae. The strength of the tidal urrent 1

15 over the lunar yle has a neap-spring modulation. The ability of larvae to maintain themselves at a ertain depth an be nullified by strong vertial mixing indued by strong tidal urrents. The degree of vertial mixing enountered by the larvae will depend upon urrent frition at the seabed and the degree of vertial density stratifiation. The vertial density stratifiation is imposed by the ambient density struture of the oastal frontal zone and loal freshwater disharges. NEDl was designed to determine: (1) the hydrography of the oastal frontal zone adjaent to a study site and orresponding abundanes of larvae or megalopae, (2) the hydrographi state of the inlet water and orresponding abundanes of larvae or megalopae, and (3) the response of shelf and inlet waters to wind and tides. NEDl was onduted in and off the North Edisto Inlet on the South Carolina oast (Fig. la) in May During spring, prevailing winds favor upwelling, and the oastal frontal zone is vertially stratified beause of seasonally high freshwater disharge. White shrimp postlarvae are usually present in oastal waters at this time. The sampling period overed 14 days. Beause the tidal yle is hrs (2 yles in hrs) and the diurnal yle is 24 hrs, a sampling of the same tidal stage over the 14-day period overs a full yle of spring-neap tides and half-yle of sunlight. 2.0 Oeanographi methods used We utilized a ombination of moored instrumentation and shipboard sampling. One mooring was was positioned on the inner ontinental shelf to assess the response of the alongshelf urrent to wind foring and another mooring was deployed within the deep inlet 2

16 hannel to monitor the strong tidal urrents there. Instruments at both moorings were plaed in the lower half of the water olumn to measure urrents, temperature, salinity and density, and subsurfae pressure. The temporal resolution of urrents and water masses at a few disrete points was supplemented by frequent hydrographi and larval abundane SUIVeys both in the inlet and offshore. Thus, the ombined synthesis of in situ data and shipboard data from NED 1 provided us the means to detennine: (1) the temporal variations in oastal water adveted into the inlet; (2) the loation of larval populations relative to the oastal front; and (3) temporal variations in larval abundane adveted into the inlet during flood tide. 2.1 Moored instruments Oeanographi information was olleted from two moored instrument arrays, designated as 'Ml' and 'M2' (Fig. la) for approximately two weeks in May Ml was plaed on a relatively flat ledge to the south of the main hannel of the North Edisto River in water 14.5 meters deep (the main hannel is 21 meters deep). M2 was loated about 10 nautial miles (18 km) offshore at the 14-meter isobath. Two InterOean Systems, In. S4 urrent meters and two Sea-Bird Eletronis, In. SEACAT data loggers were deployed at eah site to measure urrents, temperature and ondutivity at 2 levels in the vertial and subsurfae pressure at the bottom (Fig. 2; Table 1). Salinity and density (rj were derived from ondutivity, temperature and pressure values. The sampling rate for all the moored instruments was six minutes (0.1 hour). The temperature and ondutivity values reorded by the S4 urrent meters were exluded from this data report beause the quality of the signals tended to degrade over time and were 3

17 inferior to those of the SEACA T sensors. Wind speed and diretion, barometri pressure, and air temperature were monitored hourly at Folly Beah (FBIS1), a nearby C-MAN (Coastal-Marine Automated Network) station whih was maintained by the National Oeani and Atmospheri Administration (NOAA). FBIS 1 is about 30 kilometers east-northeast of the North Edisto River study area. The meteorologial information obtained at this station should represent loal onditions. The wind speed and diretion files were onverted to x and y omponents. The orresponding surfae wind stress omponents were alulated by an iterative tehnique whih adjusted the wind speed to a 10-meter level and used a variable drag oeffiient depending on the magnitude of the wind speed. 2.2 Shipboard sampling Several hydrographi and larval abundane surveys were arried out on board the RN BLUE FIN of the Skidaway Institute of Oeanography, and the R/V ANITA of the South Carolina Marine Resoures Researh Institute for a 14-day period in May The BLUE FIN generally oupied offshore stations on the adjaent ontinental shelf (Fig. la) in an attempt to map the struture of the oastal frontal zone and the distribution of larval abundane perpendiular to the shore (stations Tl3 to Tl) and then parallel to the ebb tide delta (ar stations All to ). The timing of the offshore surveys was set to reah station A6 at the maximum flood tide whih best oinided with the nighttime surveys in the throat. The ANITA was stationed in the North Edisto throat and sampled during nighttime flood tides at three positions aross the throat designated "N" (north), "M" (middle) and 4

18 "S" (south). These station loations are depited as three short parallel lines near mooring Ml on Figure lb. The throat surveys were designed to measure oeanographi properties of temperature, salinity, density and larval abundane entering the inlet and asertain lateral variability in these parameters Hydrographi sampling Eah ship was equipped with an instrument alled a CTD whih reorded vertial profiles of ondutivity (C), temperature (T), and depth (D). All the vertial profiles (or asts) were taken with a Sea-Bird Eletronis, In. Model Sealogger CTD, exept those for Offshore Survey #5 whih were taken with an InterOean Systems, In. S4 CTD. Salinity and density were alulated from the ondutivity, tempera.ture and depth values using standard algorithms. An optional fluorometer was installed on eah unit and the CTD on the BLUE FIN also had an optial baksatter (OBS) sensor. The fluorometer was designed to measure hlorophyll a fluoresene (Fl) and the OBS sensor measured turbidity by deteting infrared radiation sattered from suspended matter. The OBS values were not alibrated with suspended sediment samples, so they represent relative turbidity only. All the sensors on the CTD were manufatured by Sea-Bird Eletronis, In. (SBE), exept the fluorometer, the Model OBS-3 sensor and the psia strain gauge pressure sensor whih were manufatured by SEA TECH In., D & A Instrument Company and Paine Corporation, respetively. The CfD unit was lowered through the water olumn and real-time data were displayed on a personal omputer. The SBE Sealogger CfD was set up to sample all the 5

19 above parameters (C, T, D, Fl, OBS and alulated salinity and density) at 1 Hz in realtime mode. Thus, the vertial struture of the water olumn ould immediately be asertained. The CfD ast information was also stored as a binary data file (with a sample rate of 4 Hz) on the personal omputer. Software provided by SBE allowed several ways to view the data, inluding graphial or tabular display of the variables. As part of the post-deployment proessing, data from eah CfD downast were averaged by depth into 1.0 meter bins. This allowed hundreds of data points to be summarized into relatively few values and still keep the vertial resolution of various features. The bin-averaged data were then grouped appropriately to reate ontour plots of seleted parameters, suh as temperature, sa?ffity and fluoresene. The station log (Table 2) indiates the timing and position for the 114 CID asts taken on the BLUE FIN and the 78 asts from the ANITA. A more graphial representation shows the relative shedules for the various offshore and throat surveys for eah vessel (Fig. 3). The throat and offshore surveys were intended to simultaneously sample the inlet and nearshore regions. However, sine the nighttime flood tide was about one hour later every day (2 semi-diurnal tidal yles - hours), the offshore surveys gradually progressed out of the nighttime hours and many offshore stations were sampled during the day. The original shedule was also disrupted by oasional bad weather whih preluded the BLUE FIN from going offshore. Additionally, we experiened mehanial problems with the ANITA for several days near the beginning of the study period and two throat surveys were onduted on the BLUE FIN. 6

20 There were a ouple of surveys labeled "lw" and "hw" (Fig. 3) whih represent hydrographi sampling only (no larval sampling) along offshore and estuarine transets entered in time at onseutive Low Water and High Water periods. They were designed to show how far water masses were translated during one-half of a semi-diurnal tidal yle and to see if onditions hanged during the neap to spring tidal yle. These surveys will be desribed in a later setion Continuous mapping of near-surfae oean properties An Oeanographi Data Interfae System (ODIS) aboard the BLUE FIN was designed to interfae with an assortment of instruments. A primary navigation interfae onsisted of a Global Positiqning System (GPS) and a fathometer. Near-surfae oean water was ontinuously pumped through a suite of sensors interfaed to ODIS that inluded temperature, ondutivity, and fluoresene sensors. The fluoresene output of a Turner Designs fluorometer was alibrated by periodially olleting subsamples downstream of the fluorometer and measuring their hlorophyll a (hl a) ontent in the lab. These alibrations are still underway. ODIS data were logged automatially onto disk during most of the BLUE FIN ruises at sampling intervals ranging from 2 min to 15 min Phytoplankton biomass sampling Vertial profiles of fluoresene representing phytoplankton biomass were measured aboard eah ship. The two Sea-Bird CfDs used aboard the BLUE FIN and ANITA were both equipped with SEA TECH in situ fluorometers. Prior to the spring ruises, both were alibrated against the same phytoplankton ultures. These tests showed that the fluoresene output of both instruments was linear over their maximum range. During the 7

21 ruises, natural plankton samples were olleted by buket immediately adjaent to the CI'D at the surfae during seleted vertial profiles. Subsamples were onentrated on filters, extrated later in aetone, and hi a was measured in the lab using a Turner Designs Fluorometer. These data were used to derive a alibration urve to onvert in situ fluoresene from ern vertial profiles into hi a (Fig. 4) Larval sampling Net tows in the offshore domain were taken at stations outside the oastal front, inside the oastal front and 3 ar stations (A9, A6, and A3); A6 was sampled near the time of maximum flood urrent. Tows in the inlet were done in the North Edisto throat (near Ml; see Fig. 1 b) and sampled during nighttime flood tide at three positions aross the throat designated "N" (north), "M" (middle) and "S" (south). This plan omplements the hydrographi sampling plan in the inlet desribed at the beginning of Setion 2.2. Inboard and outboard nets were set at surfae and bottom at eah station using 0.6m bongo nets (0.505 mesh) fitted with an opening and losing devie. Tow duration was approximately 5 minutes in the throat and 10 minutes offshore. 3.0 Results and Disussion Results from NED 1 are desribed by a series of tables and plots that ome from moored and shipboard instrumentation. The main fores that affet estuarine and oastal waters are bottom frition indued by tidal and wind-generated urrents and surfae wind stress. These fores affet the degree of stratifiation imposed by buoyany soures from freshwater disharges along the oast and surfae heating, as well as govern the strength 8

22 and diretion of urrents. The role of these interating fores will beome obvious in the results that follow. 3.1 Wind stress events The alongshelf omponent of wind stress is the prinipal foring for oastal urrents and wind-driven sea level flutuations. Figure 5 shows the rotated omponent and vetor plots of wind stress that have been subjeted to a 40-hour low-pass filter. (Filtered data sets are disussed in the next setion.) The wind stress diretion was predominantly upwelling-favorable (positive alongshelf; i.e., northeastward along the oast) with the exeption of two downwelling events (negative alongshelf). One downwelling event began on 20 May and lasted about 3 days; the other began late on 26 May and lasted for 2 days. When wind stress is upwelling-favorable (loal wind blowing from the southwest), water near the surfae is adveted offshore and replaed by deeper water from farther offshore. The oastal front is spread seaward and the strength of vertial stratifiation inreases.. When wind stress is downwelling-favorable (loal wind blowing from the northeast) water near the surfae is adveted shoreward, near bottom water is arried seaward, the front is strengthed lose to shore, and vertial stratifiation diminishes. The signifiane of the upwelling- and downwelling-favorable wind stress is evident in the offshore transet ontour plots of temperature, salinity, density and hlorophyll a desribed in a later setion. 3.2 Moored instrument statistis All moored instruments at Ml and M2 had a sample rate of six minutes, but for this analysis every tenth value was seleted to reate hourly reords. Then the hourly values 9

23 for both the oeanographi and meteorologial data were independently filtered with a 3-hour and 40-hour low-pass digital filter. The 3-hour filter (3hlp) removes the high frequeny noise from the reord and the 40-hour filter ( 40hlp) removes variations assoiated with phenomena with periodiities of less than 40 hours (i.e. mainly tides). The 3hlp values have a delta-t of 1 hour, while the 40hlp files have been deimated to have a delta-t of 6 hours. We determined the prinipal axes along whih urrent and wind vetors had their maximum variane. All 3hlp and 40hlp data had prinipal axes within degrees of the loal shoreline orientation of 50 degrees east of north. Thus, for simpliity, all urrent and wind stress vetors were rotated 50 degrees ounter-lokwise, so the prinipal axes would be losely parallel to the loal shoreline and isobaths. For this rotated oordinate system, positive x-omponents are direted offshore and positive y-omponents are alongshore toward the north. Three tables of statistis present first order properties for the filtered data sets (Tables 3, 4 and 5). Table 3 shows 3hlp and 40hlp statistis for the omplete data sets. The effet of the low-pass filter is most evident in the urrents where the 40hlp standard deviations are signifiantly smaller than the orresponding 3hlp values. Redutions in the other oean parameters are not so large. Hourly wind data are least affeted by the filters. Note that under the vetor rotations used, 3hlp urrents (whih ontain most of their variane in the semi-diurnal tide) mostly flutuate along the axis of the inlet and perpendiular to the shoreline (the x-axis). When the tidal varianes are exluded by the 40hlp filter, most of the variane in the inlet is still along the x-axis (the inlet's axis), while that of the oastal urrents offshore is more shore-parallel. 10

24 Statistis during neap and spring tide periods illustrate the effets of the larger spring tides on tidal urrents (Table 4). The x-axis tidal urrents inreased by and 11 perent in the inlet throat at mid-water and bottom, respetively. Similar inreases of 7 and 21 perent were measured in the oastal waters offshore. Subsurfae pressure flutuations (whih represent tidal height elevations) were 40%/30% higher at M2/Ml during spring tides than for neap tides. An upwelling and downwelling event was defined for May and May, respetively (Table 5). Both offshore urrent meters were loated below the pynoline for the upwelling event in a zone of onshore flow that sttengthed toward the bottom, a feature that has been seen off Georgia during upwelling (Blanton, 1986). Presumably, above the pynoline, a urrent meter would have measured an offshore omponent. The reversal of alongshelf urrents from an upwelling to a downwelling regime is apparent at the offshore station. The water olumn was well mixed during the downwelling event, and both meters measured an onshore flow that dereased with depth. Continuity demands that a ompensating offshore flow take plae somewhere, presumably either in a bottom boundary layer or at some other loation north or south of M2. The 40hlp urrents in the inlet are diffiult to interpret. If we had been able to loate Ml in mid-hannel, we would have expeted to measure influx of oean water during the downwelling event. The fat that sea level rose at the onset of downwelling (disussed later) suggests that was indeed the ase. Sine Ml was, in fat, loated off the main axis hannel on a ledge with omplex surrounding topography, the 40hlp d~ta probably are refleting a more omplex wind and pressure-generated irulation. Therefore, we will not disuss further the 40hlp urrent meter data from M 1. 11

25 3.3 Time series of winds, urrents, and water mass properties Plots of the 3hlp and 40hlp moored data display the rotated wind stress and urrent vetors, as well as temperature, salinity, rt and subsurfae pressure data (Figs. 6-11). The plots of 3hlp urrent meter data at Ml (Fig. 6) show strong tidal urrents along the axis of the inlet (x-omponent). Positive x-omponent urrents ebb toward the oean. Currents are only slightly diminished at the near-bottom meter. The flutuations in the ross-inlet (y) diretion are very small (note differenes in sale) when ompared to the axial flutuations. These omponents are diffiult to interpret beause a slight hange in the oordinate rotation would hange the algebrai sign of the ross-inlet omponent. Therefore, we plae no signifiane on the ross-axis omponents in the inlet until further analyses are ompleted. Offshore tidal urrents at mooring M2 are strongest in the ross-shelf (x) omponent (Fig. 7). They are also embedded in the alongshelf (y) omponent to a smaller degree, a harateristi that illustrates that tidal urrent vetors trae out an ellipse in oastal waters. Note the positive and negative trends in the alongshelf omponent that will be disussed for the 40hlp data. Temperature, salinity, and rt at mooring Ml in the inlet show the effets of the tidal urrent as it advets horizontal gradients of properties past the sensors (Fig. 8). The similarity in the top and bottom data indiates that the water olumn is essentially vertially homogeneous. The situation is different offshore. The dereased magnitude of the ross-shelf (xomponent) tidal urrents does not advet large flutuations in temperature, salinity and rt 12

26 by the sensors (Fig. 8). However, the presene of vertial gradients of these parameters is evident from the fat that the "TOP" and "BOT" are vertially stratified until 22 May, after whih they beome well mixed. This beomes learer in plots of the 40hlp data and in the hydrographi setion plots from the BLUE FIN that follow. The 40hlp data for wind stress and urrents off the oast at mooring M2 (Fig. 9) show the effets of wind on oastal urrents. The long episode of upwelling-favorable wind stress from 15 to 20 May was mathed by positive alongshelf (y-omponent) urrent, exept for a brief 18-hr interlude of weak downoast urrents beginning just before 16 May. There are short period flutuations in wind stress evident in the 3hlp data that are filtered out in the 40hlp data (ompare Fig. 6a to Fig. lla). These flutuations an reverse urrents if they last more than 6 hours and may aount for short-term reversals in the 40hlp urrent that do not math the 40hlp wind. Thus the 18-hr interlude of downoast ilrrents before positive alongshelf urrents set in may have been triggered by a strong onshore wind omponent (Fig. 6a) that was filtered out of the 40hlp wind data. When the wind stress reversed on 20 May, alongshelf urrents also reversed and remained so until upwelling-favorable winds resumed just before 24 May. In general, the 40hlp alongshelf (y-omponent) urrents at bottom are less than those measured about 6 m above bottom (Fig. 10). The opposite is true for the ross-shelf (x) omponents. During the first upwelling-favorable wind event, the near-bottom omponent is onshore at about 5 m/s as predited in the disussion under wind measurements. As the water mass setion plots will show, oastal waters at M2 were vertially stratified and the barolini pressure gradient assoiated with suh a regime predits onshore flow in a bottom layer at this time. 13

27 Note that during the downwelling event and the following upwelling one, offshore flow and subsequent onshore flow near bottom does not develop. Vertial stratifiation at M2 had disappeared by this time. The ross-shelf omponent 6 meters above bottom swings onshore during downwelling and offshore during upwelling. We interpret the onshore flow as a manifestation of the flow required to raise sea level at the oast, and the following offshore flow as a similar manifestation of the flow that lowers sea level during upwelling. The distribution of ross-shelf flow in the vertial is dependent upon vertial stratifiation whih governs the internal pressure gradient affeting suh flows. Our vertial resolution of urrents is not suffiient to offer more preise interpretation of rossshelf omponents, and expetations derived from stratified fluids do not neessarily follow from suh poorly resolved data. The evolution of temperature, salinity and density fields at Ml and M2 is easily seen in the 40hlp data (Fig. 11). At the offshore station, mid-water olumn and bottom temperatures rose during the upwelling event as northward urrents brought in warmer shelf waters from the south. Temperature in the inlet fell during the downwelling event and began inreasing again during the seond upwelling event. Atually, temperatures at Ml began falling about 1 day before the wind reversed. The 3hlp wind data, whih are more representative of the instantaneous winds (Fig. 6a), were the strongest during this event. Falling inlet temperatures at this time suggest that ooler water from offshore was brought into the inlet. Simultaneous temperatures at Ml and M2 showed an overall inrease in temperature, but a temperature gradient between inlet and oastal waters that diminished over time. Thermal stratifiation offshore had disappeared by 22 May. 14

28 Salinities in the inlet were 3 to 4 PSU fresher than those in oastal waters (Fig. llb). An early dip in inlet salinity oinided with a lull in wind stress. Salinities rose more or less steadily during the study, but the rate of inrease was greatest during the downwelling event Mterward, salinity was pratially steady. The salinity differene between inlet and oastal water dereased to about 2 PSU after 22 May. Subsurfae pressure (SSP) flutuations (Fig. lld) reflet the ombined effets of hanging sea level elevation and barometri pressure. SSP flutuations were haraterized by three rapid inreases in pressure followed by slower dereases. The abrupt inreases ourred near times of hange in wind stress, but SSP was generally higher during downwelling and lower during upwelling, indiating an influx of water into the inlet during downwelling periods. 3.4 Offshore hydrographi setions The following figures onsist of ross-shelf versus depth plots of salinity, hlorophyll a, temperature and O"t for eah of the offshore surveys. Tables of bin-averaged data from whih these plots are drawn are available from the authors upon request. We also used a flowthrough system that pumped water from 1.6m below the surfae along the ship trak and reorded salinity, temperature, and fluoresene. The flow-through system allowed us to tie in the near-surfae estuarine data to similar data offshore as well as help resolve sales of variation. We have divided this setion into surveys that were done under upwelling-favorable wind stress onditions and ompared them to those onduted during downwelling-favorable wind stress. 15

29 3.4.1 Offshore surveys OS1 through OS4 (14-22 May 1993) These surveys (Figs ) were done under upwelling-favorable winds that diminished at the time of OS3 and shifted to downwelling-favorable during OS4. During OS1 and OS2, the front (see the salinity plot) was spread seaward. It outropped near Tl3 during OS1 but had moved farther offshore during OS2. Vertial stratifiation was quite strong, and the two-layered nature of the oastal front is most apparent at this time. Note that the nose of the front (seen near T3 on OS 1) shows up as a high-salinity subsurfae zone at A6 along the ar. The offshore transet was always done near the time of low water, but the tide was flooding by the time the ship ruised along the ar. Thus, the nose of the front ontaining the 34-PSU isohaline was apparently adveted shoreward by the flooding tide so that it interseted the ar below the surfae during the first three surveys. Wind stress had diminished signifiantly during OS3. The higher salinity subsurfae water had progressed shoreward to station T3, and a strong oastal front appeared between T3 and T5. A shallow lens of low salinity water extended shoreward and shows up along the ar through A6. (The water mass struture along the ar must be interpreted with the flooding tide in mind.) Through the time of OS3, the shallow water along the ar was vertially stratified to varying degrees beause the oastal front was adveted over the ar during flood tide. Vertial mixing was not strong enough to destroy the front at this time. By the time of OS4, the haloline and pynoline depth inreased seaward of T5 whih reflets strong upwelling of deeper water from farther offshore. The water mass above the pynoline was relatively warm and fresh and may have been part of the oastal front at one time. We were unable to define the offshore extent of this warm and relatively low salinity path during OS4, whih extended out an additional 9 nautial miles 16

30 from T13 (whih was usually our most offshore station loation). There was no evidene that the density gradient was beoming positive (whih it should as the outer shelf was approahed) at T22 indiating that the path size of the low density lens was greater than 6 nautial miles in the ross-shelf extent. During OS4, the 34-PSU isohaline had either upwelled or mixed to the surfae at 17 forming a relative high salinity zone with a weak oastal front (weakness indiated primarily by the rt gradient) situated between 17 and Tl. Winds had reversed to a downwelling-favorable diretion at the time of the T1 - T5 stations, and the water there had beome well mixed. Also, OS4 was onduted only one day before maximum spring tide Offshore surveys OS5 and OS6 (22-24 May 1993) These two surveys (Figs. 16 and 17) were ompleted during downwelling-favorable winds and oinidentally at the time of spring tide. Downwelling irulation and spring tide onditions provide the most effiient vertial mixing. Vertially stratified water previously appearing between 17 and TlO during upwelling-favorable winds was no longer present. Instead, the water here was vertially mixed to salinities greater than 34 PSU. The oastal front between T1 and T3 was still present for OS5 but water had mixed vertially by the time of OS6 and the front appeared to be destroyed. The water along the ar was essentially well mixed for both surveys, although there was some evidene of lower salinity water(< 33.6 PSU) being adveted by the flood tide from offshore. Data from OS6 suggest that some of the water mass struture in shallow water reflets alongshelf advetion. The oastal front between Tl and T3 was quite weak with salinities 17

31 between 33.8 and 34.0 PSU. We annot rule out the possibility of a stronger front being present loser to shore than Tl. Advetion of lower salinity water around the ar ould form weak stratifiation on the ar but leave water farther offshore unaffeted. OS6 was onduted as downwelling-favorable winds had diminished onsiderably before hanging to an upwelling-favorable mode. We presume that the low salinity lens observed during OS 1 through OS4 was adveted seaward during upwelling. During downwelling, the vertial gradient was destroyed in the relatively shallow water lose to the oast, but probably survived as a lens farther offshore (- TlO and T13). Upon relaxation of downwelling wind, the ross-shelf fores in this water mass struture are out of balane, and there is a tendeny for near-surfae water in the lens to be adveted onshore. This would explain the reappearane at Tl3 of the strongly stratified water, evident during OS Offshore surveys OS7 through OSlO (24-27 May 1993) These surveys (Figs ) were onduted during upwelling-favorable winds, but these had diminished by the time of OS 10 to the beginning of a downwelling episode that would last for two days (Fig. 5). Upwelling winds had blown for almost one day at the time of OS7. The low salinity lens offshore at Tl3 was still present but had weakened in vertial stratifiation. This feature remained in plae for OS8 and OS9, but was not present for OS 10. The water from T1 to TlO was essentially well-mixed during all these surveys, but there is a suggestion of more stratified onditions shoreward of Tl. For example, there was a weak oastal front between Tl and T7 during OS2 but stratifiation was muh stronger along the ar at A9, suggesting advetion of low salinity surfae water 18

32 into the area along the ar. Salinities along the ar had inreased slightly by the time of OSlO suggesting that the low salinity soure was pathy. A low salinity soure from along the oast is also suggested m one of the surveys in the inlet and will be desribed in Setion 3.5 of this report Offshore omparisons at neap and spring tide Neap and spring tides ourred on 15 May and 22 May, respetively. We onduted two quik hydrographi surveys along the "S" line of stations (Fig. 1a) on 15 May to define the hanges in oastal water masses between high and low water at neap tide. The setions (Fig. 22) showed the same high degree of vertial stratifiation as observed during OS1 and OS2 whih immediately preeded and followed the neap tide surveys. The low salinity lens was a relatively broad feature during slak low water extending from to S 10 (right panels on Fig. 22). At the end of flood tide, however, the vertial density gradient was onsiderably stronger beneath the lens whih was somewhat more ompat with a well-mixed surfae layer. Due to the horizontal nature of the isohalines and other properties, we were unable to estimate a horizontal tidal exursion for the neap tide survey. No omparable survey was done at spring tide, but the OS5 survey (Fig. 16) showed well-mixed onditions offshore of the oastal front whih was a relatively ompat feature lose to shore. This undoubtedly reflets the result of both the higher tidal urrent strengths at spring tide and the more effiient vertial mixing of oastal regions during downwelling onditions (Blanton and Atkinson, 1983; Blanton et al., 1989; Blanton et al., in press). In summary, neap tide and upwelling-favorable winds represented relatively weak 19

33 vertial mixing onditions that allowed oastal waters to be vertially stratified. Spring tide, on the other hand, ourred during downwelling onditions and was quite effetive in erasing vertial stratifiation exept near the oast. 3.5 Estuarine longitudinal setions A low water survey from the North Edisto inlet mouth to 13 nautial miles inland was onduted at neap tide on 15 May (Fig. 23). A similar high and low water survey was onduted at spring tide on 22 May (Fig. 24). The low water survey showed a weakly stratified (almost well-mixed) estuary with salinities of about 30 PSU at the mouth dereasing to about 23 PSU at the upstream survey limit. By the time of spring tide, low water salinities had inreased by 1 PSU throughout the inlet. The high water survey indiated the presene of relatively low salinity water that had intruded from offshore on the flood tide. This water was stratified and produed a. relative maxima in density slightly upriver in the region of maximum water depth. This is further evidene of a low salinity oastal soure near the inlet mouth (see Setion 3.4.3). The almost vertial nature of the isohalines allowed an estimate of the exursion of water from its high water to low water position (Fig. 24). Using the 31-PSU isohaline as an indiator, the tidal exursion through the inlet throat was approximately 5 nautial miles. The same exursion ourred for the 26 PSU isohaline farther inland. These distanes apply to spring tide, and they would presumably be somewhat smaller for neap tide. 20

34 3.6 Throat surveys South (S), Middle (M) and North (N) inlet stations (near M1 in Fig. la) were sampled as quikly as possible for eah of the 13 throat surveys. All CTD asts and plankton tows were taken only during nighttime flood onditions. The order of station seletion was random and if time permitted, the three stations were repeated. A preliminary look at the hydrographi data suggests slight variability of the water mass properties in the throat ross-setion. However, we need to examine the data more losely sine the asts were taken at different times relative to maximum flood, and tidal aliasing (espeially with suh strong tidal urrents) may onfound the relevant features. An additional CTD ast (without a plankton tow) was taken at the middle throat station at maximum flood tide whenever possible. A time series plot of these CfD measurements (Fig. ) displays the temporal variability in salinity, temperature and fluoresene in the water olumn. These data onfirm that salinities near the mouth were about 30 PSU on May (neap tide) and inreased from that time until 26 May to a level of about 32 PSU. The rate of inrease was greatest between 20 May and 22 May, whih oinided with downwelling winds and the onset of spring tidal onditions. It is likely that weakly stratified water present from May was erased by mixing from the faster spring tidal urrents on 22 May, but further analyses are needed to onfirm this Biology results Offshore surveys The spatial distribution of hlorophyll a (hi a) was quite similar throughout the study period, with variations apparently indued by the ombination of wind reversals and tidal 21

35 mixing. Generally, hl a was highest in the deeper samples at the ar stations, and dereased with distane offshore and at shallower depths (e.g., Fig. 17). Conentrations typially ranged from 4-5 ~gil nearshore to jlgll offshore. Under downwellingfavorable winds, hl a was vertially stratified only in the ar stations (Fig. 17). Under upwelling-favorable onditions, hl a was vertially stratified at offshore stations as well (Fig. 12). The highest hl a onentrations ourred in waters of intermediate salinities (33-34 PSU; Fig. 26a). Sine salinity was the major ontributor to water olumn stability, hl a fluoresene was also orrelated with intermediate values of rt ( ; Fig. 26b). Optial baksatter (OBS) measured by the CfD was highly orrelated with hl a fluoresene (Fig. 26) Estuarine longitudinal transets Three surveys downstream from NED6 to NED 1 were onduted, one during high water and two during low water (Figs. 23 and 24). The spatial distribution of hi a was similar in eah survey, with highest onentrations (4-5 jlgll) near the estuary mouth, and low onentrations (2-3 jlgll) at intermediate river stations. Upriver stations (NED 3-6) typially showed weak or little vertial stratifiation of hl a, whereas fluoresene inreased with depth at the downriver stations (NED 1-2). At a given station, hl a onentrations were greater at high water than low water Throat surveys. The middle throat station was sampled at the time of maximum flood tide oiniding with darkness. Chl a exhibited a pattern of inreasing onentration with depth (Fig. b ). Nearbottorn onentrations often saturated the sensor at 10 volts (- 5.6 ~gil) and are thus 22

36 minimum estimates of hl a. Beginning on 22 May, hl a inreased rapidly to saturated values throughout the water olumn. Surfae values gradually delined over the next 2-3 days. Patterns in the temporal and spatial distribution of salinity were similar to those of hl a (Fig. ), inreasing with depth and over time. As a result, salinity and hl a exhibited a highly signifiant positive orrelation (Fig. 27a). The most appropriate regression model to fit the data annot be determined beause of the samples whih saturated the fluorometer output, but it appears that approximately half of the variane in hl a distribution in spae and time an be explained by hanges in salinity. As observed in offshore waters, patterns in water olumn stability refleted hanges in salinity, so that hl a was also highly orrelated with rt ( Fig. 27b ). Chl a was again highly orrelated with optial baksatter (Fig. 27) Larval results Counting of postlarval samples has been finished for the middle and southern stations m the inlet (Fig. 28). The northern and offshore samples will be ounted during the seond year. Postlarval quantities of Penaeus were, in general, most abundant in surfae samples. The key result is that the two peaks on 22 May and 24 May and the two larger peaks on 27 May and 28 May ourred during downwelling onditions. Even the small peak on 15 May ourred during a brief downwelling-favorable wind event. There are some details in the abundane urve that raise questions. Note that abundanes of Penaeus began to inrease at the beginning of the downwelling event whih began on 20 May to a peak density on 22 May. There was a brief derease on 23 May 23

37 then another peak on 24 May when upwelling-favorable winds ourred. These questions have prompted us to sample more frequently when the wind shifts from upwellingfavorable to downwelling-favorable so that temporal variability is better resolved. 4.0 Summary The upwelling/downwelling yles observed during NED 1 learly affet the oeanography of oastal waters [ompare Fig. 12 (upwelling) with Fig. 17 (downwelling)]. Coastal urrents were northward at M2 during upwelling and hanged to southward during downwelling. Sea level as represented by subsurfae pressure dereased/inreased in the inlet and offshore during upwelling/downwelling. Salinity at the inlet throat rose most rapidly during the downwelling event of May. Coupling of oastal waters with those of an estuarine nursery was optimized during the downwelling events whih transported oeani water into the estuary and raised sea level. 4.1 Preliminary interpretation We have two sets of setions done within one day of eah other in whih we an ompare the hydrographi and hi a distributions in both the estuary and aross the shelf (Fig. 29). The low water neap tide survey on 15 May (Fig. 29a) shows an essentially well-mixed estuary in the lower reahes between stations NEDl and NED3. One the inlet delta is rossed, stratified water harateristi of upwelling onditions is enountered offshore. Note the strong derease in hi a away from the bottom and offshore. This gradient is also refleted in the inlet with high values of hi a along the bottom adjoining the oean and in the inlet basin as a whole, whih has hi a values only slightly below 3 J.lg/1. 24

38 The next simultaneous survey was done at spring tide low water on 22 May during downwelling onditions. Salinity and hi a onentrations in the estuary (Fig. 29b) were similar with maximum hi a along the inlet bottom next to the ebb delta. A similar maximum ourred on the shelf at the bottom adjaent to the delta. Salinity on the shelf was vertially uniform, onsistent with high vertial mixing (downwelling winds plus spring tides). There was a 2-PSU salinity differene aross the inlet delta. Low salinity stratified water along the ar showed up several times in our surveys (e.g., Fig. 20). A stratified low salinity soure also showed up at HIGH water at the oean end of the estuary (Fig. 24), a feature that ould only have ome from the shelf. The origin of the low salinity soure is quite speulative at this time. We have data from the ODIS flow-through system as a means to extrapolate CTD surfae salinities between Ml in the inlet to A6 along the ar. (Cross-alibration between CTDs and the flow-through sensor has not been ompleted.) Five high water traverses aross the ebb-tide delta (Fig. 30) show that lowest salinities along this trak ourred near Deveaux Banks between 2 and 3 nautial miles seaward of Ml. The low salinity water was relatively warm. We speulate that it represents low salinity water adveted along the oast into the region of the inlet delta. Note the wide range of salinities observed at A6 (Fig. 30). These orrelate with upwelling/downwelling onditions that have adveted low/high salinity water into the ar from other soures. In summary, the lowest salinity water along the ar was often relatively warm (as in OS7 through OSlO), onsistent with heating in shallow water. More observations of tidal and wind-generated urrents on the ebb tide delta and along the ar are required before we an understand their temporal and spatial variability. Sine this water mass may provide a

39 food soure for the larvae, it is important to understand its origin. 4.2 Conluding remarks The primary food for early planktoni stages of shrimp larvae is phytoplankton. As the larvae age and inrease in size, their diet also inludes protozoan and metazoan mirozooplankton (Dobkin, 1961; Cook and Murphy, 1969; Christmas and Etzold, 1977). Sine spatial and temporal patterns in the distribution of herbivorous mirozooplankton in oastal waters are related to those of their prey (Verity et al., 1993), phytoplankton biomass (hl a) represents either a diret food soure.for shrimp larvae or a traer of that food soure. Thus, the distribution of hl a relative to more onservative properties (salinity, temperature, density) provides an indiator of water masses or hydrographi regions whih may be nutritionally benefiial to shrimp larvae during their transport from offshore spawning sites to estuarine nursery grounds. The key to understanding the proesses influening the mesosale distribution of plankton during May is to resolve the apparent paradox in the relationship between salinity and hi a in the mouth of the estuary, and that observed seaward. Chi a peaked at intermediate salinities in oastal waters but was positively orrelated with salinity in the estuary (Fig. 29). The deline in hi a in waters of 34 PSU or greater is due to inreasing nutrient limitation of phytoplankton growth with distane offshore (Verity et al., 1993; Yoder et al., 1993). The deline in hi a in oastal waters of <33.5 PSU (Fig. 26a) is similar to that whih ourred in estuarine waters of <33.5 PSU (Fig. 27a). Sine the soure of new nutrients for phytoplankton growth is freshwater, one would expet a negative orrelation between salinity and hi a, as observed farther upstream in the North 26

40 Edisto river transets (Figs. 23 and 24) and nearby waters (Verity et al. 1993), but ontrary to that observed at the middle throat station over time (Fig. ). The positive orrelation reflets higher hi a in deeper waters, whih are also more saline. Sine fresher water at the surfae should ontain more nutrients and also provide more light for algal photosynthesis, the inrease in hi a with depth is provoative. This inrease with depth was also observed at ar stations (Figs ; 17-21) as well as in the estuary. Explanations for this near-bottom hi a maximum inlude enhaned prodution at depth, sinking of phytoplankton from surfae waters, and epibenthi soures. Several observations are instrutive in this regard. First, the North Edisto estuary is tidally dominated, with tidal urrent veloities often exeeding 100 m/s (2 knots) and oasionally exeeding 150 rn/s (3 knots) on the spring tide ebb. Seond, a region of enhaned hi a onentrations oinides with the mouth of the estuary, whih is shallow (Fig. 29) and thus suseptible to wind- and tide-indued souring of surfae sediments. Third, the temporal peak in hi a near station Ml oinides with the time of spring tides, whih flood larger areas of the marshes and inrease the amount of bottom material pumped or soured out. Fourth, the elevated hi a in nearbottom waters ours in both stratified and non-stratified (i.e., vertially mixed) waters (e.g., Fig. 29). If the subsurfae maximum in hi a was due to enhaned prodution at depth or settling from above, then mixing suffiient to produe homogeneous salinity distributions should result in homogeneous phytoplankton distributions. However, if the soure of hl a is epibenthi phytoplankton, then a near-bottom peak should expand upwards from the bottom as observed in the inlet throat (Fig. ). The inrease in water olumn hi a would be further stimulated by addition of previously sessile algae flushed from the marshes by high water. 27

41 Thus, we hypothesize that hydrography and meteorology ombine to regulate the temporal and spatial distribution of phytoplankton in the North Edisto estuary and adjaent oastal waters. In tum, these distributions may affet how larvae are distributed in oastal waters. A tidal exursion of approximately 5 nautial miles has impliations for future sampling plans. A partile loated on the ar at the beginning of flood tide would be adveted aross the delta and into the inlet throat, a situation that was not expeted at the beginning of the study. Thus, larvae sampled on the ar may show up in samples taken in the throat allowing us to better link data found along the ar to data in the inlet. This motivates us to devote some of our future sampling efforts to the delta itself, although suh efforts will be somewhat restrited due to shoals and other hazards. Preliminary Penaeid abundane data in the inlet throat suggest that ingress inreases during downwelling events, whih is onsistent with one of the hypotheses we advaned at the beginning of this study. However, some ritial questions arise. In the first of two large ingress events on 22 May and 24 May (Fig. 28), downwelling winds had diminished on the 23rd. So why did abundanes peak again on 24 May when upwelling onditions had begun? While downwelling onditions push oastal water into the inlet and arry any larvae present at _the mouth into the inlet, there are other plausible mehanisms that ould arry larvae in oastal waters to the inlet during the onset of upwelling. Sine bottom water is arried shoreward as downwelling relaxes and upwelling begins, larvae near bottom ould be adveted toward the inlet during the initial stages of upwelling. Clearly more information is required to understand how larvae "pool" in oastal waters in the viinity of the inlet, and how flutuating oeanographi onditions optimize the ommuniation of oastal waters with inlet waters. This requires a better determination 28

42 of temporal flutuations in irulation and larval abundanes at the onset and through a downwelling event before mehanisms operating on the sale of an upwelling/downwelling yle an be understood and put in proper ontext with larval ingress. 5.0 Referenes Blanton, J Coastal frontal zones as barriers to offshore fluxes of ontaminants. Rapp. P. -v. Reun. Cons. int. Explor. Mer 186: Blanton, J. 0. and L. P. Atkinson Transport and fate of river disharge on the ontinental shelf of the southeastern United States. J. Geophys. Res., 88(C8): Blanton, J. 0., L.-Y. Oey, J. Amft, and T. N. Lee Advetion of momentum and buoyany in a oastal frontal zone. J. Phys. Oeanogr. 19: Blanton, J. 0., F. Werner, C. Kim, L. Atkinson, T. Lee and D. Savidge. Transport and fate of low-density water in a oastal frontal zone. Cont. Shelf Res: in press. Christmas, J. Y. and D. J. Etzold The shrimp fishery of the Gulf of Mexio United States; a regional management plan. Gulf Coast Res. Lab. Teh. Rep. Ser. No pp. Cook, H. L. and M.A. Murphy The ulture of larval penaeid shrimp. Trans. Am. Fish. So. 98(4): Dobkin, S Early developmental stages of pink shrimp, Penaeus duorarum, from Florida waters. U.S. Fish Wildl. Serv. Fish. Bull. 190(61):

43 Verity, P. G., J. A. Yoder, S. S. Bishop, J. R. Nelson, D. B. Craven, J. 0. Blanton, C. Y. Robertson, and C. R. Tronzo Composition, produtivity and nutrient hemistry of a oastal oean planktoni food web. Cont. Shelf Res. 13: Yoder, J. A., P. G. Verity, S. S. Bishop, and F. E. Hoge Phytoplankton hi a, primary prodution, and nutrient distributions aross a oastal frontal zone off Georgia, USA. Cont. Shelf Res. 13: Aknowledgments We wish to express our appreiation to the several individuals without whose help this projet would not have been possible. First, our thanks go to Marsha Ward who partiipated in the ruises and Lane Mitham of Skidaway Institute who developed muh of the instrumentation and software used in the ODIS system aboard the BLUE FIN. Next, we thank Charlie Barans, Betty Wenner, Brue Stender and David Knott of the South Carolina Marine Resoures Researh Institute, our sientifi partners in this projet. We also appreiate the able support of Captain Jay Fripp and rew Raymond Sweatte and Chris Knight of the RN BLUE FIN, and Captain Paul Tuker of the RN ANITA. This work was sponsored by joint grants from the Georgia Sea Grant Program (Grant No. RJEA-15) to the Skidaway Institute of Oeanography and the South Carolina Sea Grant Consortium (Grant No ) to the SC Marine Resoure Researh Institute. 30

44 Table 1. Moored instrumentation used during NED1 in May ********************************************************************************************************* INSTRU. WATER PARAMETERS DEPLOYMENT LATITUDE LONGITUDE STATION DEPTH DEPTH INSTRUMENT MEASURED DATES (deg N) (deg W) (m) (m) (1993) ******************************************* **** ***************************************************** *** ** M SEACAT 295 C,T 05/13-05/ M S4 706 C,T,V 05/13-05/ M S C,T,V 05/13-05/ M SEACAT 849 C,P,T 05/13-05/ w... M SEACAT 327 C, T 05/15-05/ M ** S4 908 ** C,T,V 05/15-05/ M S4 909 C,T,V 05/15-05/ M SEACAT 848 C,P,T 05/15-05/ FBIS land C-MAN A,B,W 05/13-05/ ********************************************************************************************************* Instrument: Parameters: SEACAT serial# S4 serialtl Weather Stations: Sea-Bird Eletronis SEACAT data logger InterOean Systems S4 urrent meter FBIS1 Folly Beah (C - MAN) C- MAN Coastal - Marine Automated Network (NOAA) A B p T v w air temperature baromet-ri pressure ondutivity subsurfae pressure water temperature urrent veloity wind vel oity *********************************************************************************************************** ** S4-908 had a data gap from 22 May 1993 at 1754 GMT to 23 May 1993 at 0006 GMT; it was filled in with information from S4-909

45 Table 2a. R/V BLUE FIN station log for NED1. ====================================================z======= ========== Cruise Cast I Sta Offshore Transet survey 11: + + Bl Bl T13 TlO T7 T5 T3 T1 A9 A6 A3 Date rnm dd yy 05/15/93 05/15/93 05/15/93 05/15/93 05/15/93 05/15/93 05/15/93 05/15/93 05/15/93 (os1) Offshore Low Water Neap Tide Survey: Time (GMT) (lw) Water Depth (m) Latitude (N) deg min Longitude (W) deg min Throat Survey 13: Bl Bl Bl Bl Bl Throat Survey 14 : Bl Bl N M s M s N M M N s M N s (ts3) (ts4) 05 / 17/93 05/17/ /93 05/17/93 05/17/93 05/17/93 05/17/93 05/18/93 05/18/93 05/18/93 05/18/93 05/18/93 05/18/ Bl S3 S5 S7 SlO 05/15/93 05/15/93 05/15/93 05/15/93 05/15/93 Offshore High Wa ter Neap Tide survey : SlO S7 S5 S3 Al 05/15/93 05/15/93 05 / 15/93 05/15/93 05/15/ (hw) ======== ====================== ====================== ======== ====== ==== Offshore Transet Survey 1 2 : Bl Bl Tl3 TlO T7 T5 T3 T1 A9 A6 A3 05/16/93 05/16/93 05/16/93 05/16/93 05/16/93 05/16/93 05/16/93 05/16/93 05/16/93 (os2) Offshore Transet Survey 13: (os3 ) Bl B1 B Tl3 TlO T7 TS T3 T1 A9 A6 A3 05/20/93 05/20/93 05/20/93 05/20/93 05/20/93 05/20/93 05/20/93 05/20/93 05/20/ =========== == ========================================== === ============= Offshore Transet Survey 14 : + Bl Bl Bl S10 T22 T19 T16 TlO T7 T5 T3 Tl A6 05/21 / /21 /93 05/21 /93 05/21/93 05/21/93 05/21/93 05/2 1 /93 05/21/93 05/21/93 05/21/93 05/21/93 (os4) ==== =========== == ===== === ==== ===== ============================= ==== ====

46 Table 2a (ontinued) === === =============3=== =============================================== u.l u.l === =========== === ============================ == =========== = == === ~= Offshore Transet survey IS : (oss) 062 Tl3 05/22/ T10 05/22/ T7 05/22/ T5 05/22/ T3 05/22/ T1 05/22/ A9 05/22/ A6 05/22/ A3 05/22/ ======= -========================== ===================== == ======= === Offshore Transet Survey I 6: (os6) 071 T13 05/23/ T10 05/23/ T7 05/23/ TS 05/23/ Bl 075 T3 05/23/ Bl 076 Tl 05/23/ A9 05/23/ A6 05/23/ A3 05/23/ z::z&:z z zz::::::::::::::::::z::::z == = ======================= = =s z==== Offshore Transet survey 17: (os7) Bl 080 T13 05/2 4/ Bl 0 TlO 05/24/ Bl 08 2 T7 05/24/ TS 05/24/ T3 05/2 4/ A9 05/24/ A6 05/2 4/ AJ 05/24/ ============ =========== ============ ===== ======================= === ===== Offshore Transet survey 1 8 : (os8) 088 Tl3 05// T10 05// T7 05// Bl 091 T5 05/2 5/ T3 05// Tl 05// A9 05// A6 05// Offshore Transet Survey 19: (os9) 096 T13 05// TlO 05// Bl 098 T7 05// Bl 100 T5 05// TJ 05// T1 05// A9 05/26/ A6 05/26/ Bl 105 A3 05/26/ =============== === ===================================================== Offshore Transet Survey (oslo) Bl 106 T13 05/26/ TlO 05/26/ Bl 108 T7 05/26/ T5 05/26/ Bl 110 T3 05!26/ Bl 111 T1 05/27/ Bl 112 A9 05/27/ Bl 113 A6 05/27/ Bl 114 AJ 05/27/ ruise: Station : plankton net tows were taken at this station ; R/ V BLUE FIN (May 93 ruise) S south side of hannel (near Edisto Island) M ; middle of hannel (in throat) N ; north side of hannel (near Privateer Point) Tt S l AI offshore transe t station (North) offshore transet station (South) offshore ar station

47 Table 2b. R/V ANITA station log for NED1. Throat Survey 15 : (tss) Cruise Cast I Sta Date mm dd yy Time (GMT) Water Depth (m) Latitude (N) deg min Longitude (W) deg min M s N M 05/20/93 05/20/93 05/20/93 05/20/ Throat Survey 16: (ts6) Throat Survey 11: N M s s (ts1) 05/14/93 05/14/93 05/14/93 05/14/ M N s M 05/21/93 05/21/93 05/21/93 05/21/ Throat Survey 17: (ts7) Throat Survey 12: M N s M s M N (ts2) 05/15/93 05/15/93 05/15/93 05/15/93 05/15/93 05/15/93 OS /15/ M s N M 05/22/93 05/22/93 05/22/93 05/22/ Inshore High Water Spring Tide Survey: (hw) Inshore Low Water Neap Tide survey : NED1 NED2 NED3 NED4 NEDS NED6 05/15/93 05/15/93 05/15/93 05/15/93 05/15/93 05/15/93 (lw) NED1 NED2 NED3 NED4 NEDS NED6 05/22/93 05/22/93 05/22/93 05/22/93 05/22/93 05/22/93 Inshore Low Water Spring Tide Survey: (lw) =~====== == ======================= =z ==== == ======================== = = == = = CTD time-series: N M s M M M N M s (tdts) 05 / 19/93 05/19/93 05/19/93 05/19/93 05/19/93 05/19/93 05/19/93 05/19/93 05/19/ Throat Survey 18: NED1 NED2 NED3 NED4 NEDS NED6 M M N s (ts8) 05 / 22/93 05/2 2 /93 05/22/93 05/22/93 05/2 2 /93 05/22/93 05 / 22/93 05/23/93 05/23/93 05/23/ )

48 Table 2b (ontinued) Cruise: ~ R/V ANITA (May 93 ruise) Throat Survey 19: (ts9) Al 055 M 05/24/ Al 056 M 05/24/ s 05/24/ N 05/24/ Station' S south side of hannel (near Edisto Island) M middle of hannel (in throat) N north side of hannel (near Privateer Point) NEDI estuarine station in North Edisto River Throat Survey 110: (tslo) Al 059 M 05// Al 060 M NO CTD CAST Al 061 s 05// Al 062 N 05// Throat Survey Ill: (ts11) Al 063 M 05/26/ v.> 064 s 05/26/ Ul Al 065 M 05/2 6/ Al 066 N 05/26/ === =z======:=====================s ==================================== Throat Survey 112: (ts12) Al 067 M 05/27/ Al 068 N 05/27/ s 05/27/ Al 070 N 05/27/ Al 071 M 05/27/ Al 072 s 05/27/ ) ===========================z=========================================== Throat Survey 113: (ts13) + Al 073 N 05/28/ Al 074 M 05/28/ Al 075 s 05/28/ Al 076 M 05/28/ Al 077 s 05/28/ Al 078 N 05/28/ plankton net tows were taken at this station

49 Table 3. First order statistis for parameters measured during NED1. The station loation and depth above bottom are designated for eah sensor. All parameters with x- andy-omponents have been rotated SO degrees ounter-lokwise. Series with a length of 15. days begin 13 May 1993 at 18 GMT and end 29 May 1993 at 00 GMT; series with a length of days begin 15 May 1993 at 00 GMT and end 26 May 1993 at 18 GMT. (a) 3hlp data; (b) 40hlp data. Parameter Min Max Mean Stan. Dev. Length (days ) (a) 3-HOUR LOW-PASS (3hlp) DATA FBIS1 x-omp wind stress (Pa 10) FBIS1 y-omp wind s tress (Pa * 10 ) FBIS1 barometri pressure (mb ) FBIS1 air temperature (deg C) M1 8. 0m temperature (deg C) M1 8. 0m salinity (PSU) M1 8. 0m sigma-t (kg/ma3) M1 6.5m x - omp urrent (m/ s) M1 6.5m y-omp urrent (m/ s ) M1 2. 5m x-omp urrent (m/ s ) M1 2.5m y-omp urrent (m/ s ) M1 1. 0m temperature (deg C) M1 1.0m salinity (PSU) M1 1. 0m sigma- t (kg/ ma3) M1 1. 0m pressure (dbar ) M2?.Om temperature (deg C) M2?. Om salinity (PSU) M2?. Om sigma-t (kg/ma3) M2 6.0m x-omp urrent (m/s ) M2 6.0m y-omp urrent (m/ s l M2 2. Sm x-omp urrent (m/s l M2 2. 5m y-omp urrent (m/ s ) M2 1.0m temperature (deg C) M2 1.0m salinity (PSU) M2 1.0m sigma-t (kg/rna)) M2 1.0m pressure (dbar) (b ) 40-HOUR LOW-PASS (40hlp) DATA FBIS1 x-omp wind stress (Pa 10) FBIS1 y-omp wind stress (Pa 10) FBIS1 barometri pressure (mb ) FBIS1 air temperature (deg C) M1 8.0m temperature (deg C) M1 8.0m salinity (PSU) M1 8.0m sigma-t (kg/ma3) M1 6.5m x-omp urrent (m/s) M1 6. 5m y-omp urrent (m/s) M1 2.5m x-omp urrent (m/ s ) M1 2.5m y-omp urrent (m/s) M1 1.0m 849 temperature (deg C) M1 1.0m salinity (PSU ) M1 1.0m sigma-t (kg/ma3) M1 1.0m pressure (dbarl M2?.Om temperature (deg C) M2 7.0m sali nity (PSU) M2 7.0m s i gma- t (kg/ma3) M2 6.0m x - omp urrent (m/s) M2 6.0m y-omp urrent (m/sl M2 2. 5m x-omp urrent (m/s) M2 2. 5m y- omp urrent (m/s) M2 1.0m temperature (deg C) M2 1.0m salinity (PSU) M2 1.0m s i gma-t (kg/ma3) M2 1.0m pressure (dbarl

50 Table 4. First order statistis using 3hlp data for parameters measured for 2 tidal yles eah during the neap and spring tide of NED1. The station loation and depth above bottom are designated for eah sensor. All parameters with x- andy-omponents have been rotated SO degrees ounter-lokwise. (a) Neap tide data begin 15 May 1993 at 09 GMT and end 16 May 1993 at 09 GMT; (b) spring tide data begin 22 May 1993 at 14 GMT and end 23 May 1993 at 14 GMT. Parameter Min Max Mean Stan. Dev. Length (hours ) (a) NEAP TIDE DATA FBIS1 x-omp wind stress (Pa 10) FBIS1 y-omp wind stress (Pa 10) FBIS1 barometri pressure (mb) FBIS1 air temperature (deg C) M1 8.0m temperature (deg C) M1 8.0m salinity (PSU) M1 8.0m sigma-t (kg/ma3) M1 6.Sm x-omp urrent (m/s) Ml 6.Sm y-omp urrent (m/s ) Ml 2.5m x-omp urrent (m/s) Ml 2.Sm y-omp urrent (m/s) M1 1.0m temperature (deg C) M1 1.0m salinity (PSU) M1 1.0m sigma-t (kg/ma3) M1 1.0m pressure (dbar) M2 7.0m temperature (deg C) M2 7.0m salinity (PSU) M2?.Om sigma-t (kg/ma3) M2 6.0m x-omp urrent (m/s) M2 6.0m y-omp urrent (m/s ) M2 2.5m x-omp urrent (m/s ) M2 2.Sm y-omp urrent (m/s) M2 1.0m temperature (deg C) M2 1.0m salinity (PSU) M2 1.0m sigma-t (kg/ma3) M2 1.0m pressure (dbar) (b) SPRING TIDE DATA FBIS1 x-omp wind stress (Pa 10) FBISl y-omp wind stress (Pa 10) FBIS1 barometri pressure (mb) FBIS1 air temperature (deg C) M1 8.0m temperature (deg C) M1 8.0m salinity (PSU) M1 8.0m sigma-t (kg/ma3) M1 6.5m x-omp urrent (m/s) M1 6.Sm y-omp urrent (m/s) M1 2.Sm x-omp urrent (m/s) M1 2.Sm y-omp urrent (m/s) M1 1.0m temperature (deg C) M1 1.0m salinity (PSU) M1 1.0m sigma-t (kg/ma3) Ml 1.0m pressure (dbar) M2?.Om temperature (deg C) M2?.Om salinity (PSU) M2 7.0m sigma- t (kg/ma3) M2 6.0m x-omp urrent (m/s) M2 6.0m y-omp urrent (m/s) M2 2.Sm x-omp urrent (m/s) M2 2.Sm y-omp urrent (m/s) M2 1.0m temperature (deg C) M2 1.0m salinity (PSU) M2 1.0m sigma-t (kg/ma3) M2 1.0m pressure (dbarl

51 Table 5. First order statistis using 40hlp data for parameters measured for two events (one upwe lling and one downwelling) during NED1. The station loation and depth above bottom are designated for eah sensor. All parameters with x - and y-omponents have been rotated 50 degrees ounter-lokwise. (a) The upwelling event begins 16 May 1993 at 12 GMT and ends 19 May 1993 at 12 GMT; (b) the downwelling event begins 21 May 1993 at 00 GMT and ends 23 May 1993 at 00 GMT. Parameter Min Max Mean Stan. Dev. Length (days) (a) UPWELLING EVENT FBIS1 x-omp wind stress (Pa 10) FBIS1 y-omp wind stress (Pa 10) FBIS1 barometri pressure (mb) FBIS1 air temperature (deg C) M1 8.0m t emperature (deg C) M1 8.0m salinity (PSU) M1 8.0m sigma-t (kg/ma3) M1 6.5m x-omp urrent (m/s) M1 6.5m y-omp urrent (m/s) M1 2. 5m x-omp urrent (m/s) M1 2.Sm y-omp urrent (m/s ) M1 1.0m temperature (deg C) M1 1.0m salinity (PSU) M1 1.0m sigma-t (kg/ma3) M1 1.0m pressure (dbar) M2 7.0m temperature (deg C) M2 7.0m salinity (PSU) M2 7.0m sigma-t (kg/ma3) M2 6.0m x-omp urrent (m/s ) M2 6.0m y-omp urrent (m/ s ) M2 2. 5m x-omp urrent (m/s) M2 2.5m y-omp urrent (m/s) M2 1.0m temperature (deg C) M2 1.0m salinity (PSU) M2 1.0m sigma-t (kg/ma3) M2 1.0m pressure (dbar) (b) DOWNWELLING EVENT FBIS1 x-omp wind stress (Pa 10) FBIS1 y-omp wind stress (Pa 10) FBIS1 barometri pressure (mb ) FBIS1 air temperature (deg C) M1 8.0m temperature (deg C) M1 8.0m salinity (PSU) M1 8.0m s igma-t (kg/ma3) M1 6.5m urrent (m/s) M1 6.5m y-omp urrent (m/s ) M1 2.5m x-omp urrent (m/s) M1 2.5m y-omp urrent (m/s) M1 1.0m temperature (deg C) M1 1.0m salinity (PSU) M1 1.0m sigma-t (kg/ma3) M1 1.0m pressure (dbar) so M2 7.0m temperature (deg C) M2 7.0m salinity (PSU) M2 7.0m sigma-t (kg/ma3) M2 6.0m x-omp urrent (m/s) M2 6.0m y-omp urrent (m/s) M2 2.5m x-omp urrent (m/s ) M2 2.5m y-omp urrent (m/s) M2 1.0m temperature (deg C) p M2 1.0m salinity (PSU) 40hlp M2 1.0m sigma-t (kg/ma3) M2 l.om pressure (dbar)

52 : 4m,' _. 6m en Bm T ' ' - Bm <- ~ \,) 0 1.,.) :: -..:: < ' :::: ---- ' ~ --- am ' M2 15 T6 n TB T9 T10 30' T12 T ' Figure la 39

53 4m ', m ' ' 2m -,'\, / ' ' ~ ' - ~,~~- ~-- i :t, _ -' -.. :,', 0 ',,,': (,'-, ::,:,: \. \ ',\... _;,,':,'... ~... ;----,',' ~ ~ t" -- '. '; ';,:: m,,)(' -~', : - -_- -:: ;'O ~ \>, I "",'' Bm ' 80 15' 80 10' Figure lb 40

54 NORTH EDISTO MOORINGS M 1: MWL M 2: MWL ~ 12 ~ 10 Q) E BUOY SEACAT 295 S4 706 BUOY SEACAT 327 S S41530 S4 909 SEACAT 849 SEACAT 848 0~ L ~ Figure 2 41

55 Oo o O o 00 0 OOo Oo O oo O o o o# o o o o o 00 o o o o O 0 0 oo o o oo _. u. dark:... ~.... ; North Edisto Predited Currents and Sample Times... :.. :.. : m w 13 BLU.E FIN : ANITA: 0 ~ 1 I: ': 0 ~ 2 ;~ :+-+. C>p 07-0 (H) :o---o ts1 ts2 lw :tdts Days in May 1993 (EDT) _. u. North Edisto Predited Currents and Sample Times (/) -0.::.:. -2 m w os4. os5 os6 : : i--+ : ()-() ()-() ()-() ()-() : ts7 hw lw ts8 : o-o: ts9 : os7 : i---t : os8 os9 : : : o-o: oo : tsfo tsf1 Q--9 tsf2 ~ tsf Days in May 1993 (EDT)

56 ,.::- 5 I = =-a4 6 ~ ~ A Anita NED 1.. (..)... (.) a... ~3 ~2 1 5,.. -4 I ::::n =- ";'3. (..)... (.) a... ~2 >< LL.I1 2 B Blue Fin NED CTD Fluoresene (volts) o~~~~~~--~--~--~--~~--~--~ CTD Fluoresene (volts) Figure 4 43

57 FBIS1 WIND STRESS (40hlp) ~ ~---. Along:shelf a o Oo o o o 0 oo oo o oo o o oo o o oo,o ooo o oo o ooo o o o o o o 0 o o + o oo o O O O+O oo o o o 0 o o o o O ooo o o oo.. o ooo o oo o ooo o o Oo o; oo oo O o o ooo o o Oo o,.., o o o o oo o o o o o o o o o : Cros$-shelf : : : : : L..... L., J omponents rotated -50 degrees --L.. J 0.- b ro a... -o.s.....j....l L.l L L, L Days in May 1993 (GMT)

58 FBIS1 WIND STRESS (3hlp) 1~--~------~ ~------~ _ : ::::y-omp a I \ : f I ''V', : I J-"' "''"\t \J 1 : ': 1 '/:. 11' 'u..../... ~ :...:....; :... ~...: : ---- ~ x-omp : : : : : -1L---~------~ ~------~ ~------~ ~------~--~ 1 00 f k.. ~ M1!!.! ~!. t~.. A.. A.. A.. k.. {\'.. ~.. ~~.. II ~.. : X-COMP CURRENT (3hlp) II! fl tl.. ".. :. ".. II...,..!! ~... r-....,.... :.,... ~... \.... n. ll : \,.... ~ b E Of >- I y u~.. \J.. V.V.I1Y \J.. IJ.V.v. u.. ~.. ~... ~.. ~.. v.u.. ~.. Y.. ~.. V. t. tj.. ~... ~. \.. ~- i (rot -50) i i i i i i i _ = S4 706 (TOP) = S (BOT) M1 Y-COMP CURRENT (3hlp) (/) -- E 0 0,, -50 (rot -50) Days in May 1993 (GMT)

59 FBIS1 WIND STRESS (3hlp) 1~-~----~------~ ~------~ , _ : =y-omp 0..- a <U 0.. I \ : 1 I. \ 1: "./ \. ; ; ;....; : ;...; : ---- ~ x-omp : : : : : -1L L L ~ ~ L------~ ~------~--~ M2 X-COMP CURRENT (3hlp) so~--~------~------~ ~------~ (f) b "E o.. _:_--.\--J.-\--J.-:tr-J-,l-l-*-+-.l-+~~4-l=-\--/-;~++-Ht-TH--Hr-HH-++++-H-hf-\-H-+-+-I-----l 0 (rot -50) -SOL---~----_: L ~_: ~ L------~L ~ L--~ _ = S4 908 (TOP) ---- = S4 909 (BOT) M2 Y-COMP CURRENT (3hlp) 50~--~------~------~ ~------~------~ ~------~---, (f) "E o._: --\..IJ--\.~...-JJ-++~-L~----"J---J.JL...l"'-~+++-..:~.,...--~+-~-+J-\-;:}-1r+-M--+I--.JJL-\JL ~ 0 (rot -50} -SOL- L _L J L _L J ~------~--~ Days in May 1993 (GMT}

60 'Tj... OQ I= '"1 (t) ~ ~ 0"..._, 26 TEMPERATURE.. : : a b : : H... :..... <..... < : :,.,. : : f.: ~.,._.r.,..... : : : 1.1 : I :. I._,. ~ ' : : 21.. l f. It'\. I \J-.J : j..:.;_.. ;. :t: ~..... ~.-. '~:,...,.,_ : ;......, ~~: ~, )'-\}~......,... :..:, i..,: :\.,.,.....:.: :..... : :.. '\.. \. \. '" I \. '... I',...,..../ ~.. I... :.:~ --~ v:'.: 'I... : :... ~... :t:j. i"' :. :,... :. \... 20~~~ ~----~--~------~ L J L ~-- J --- = SEACAT 295 (M1 TOP) = SEACAT 849 (M1 BOT) 3 HLP -.- = SEACAT 327 (M2 TOP)... = SEACAT 848 (M2 BOT) SALINITY ~ ,, ,~ , ,, ! , , f ; ; ; ::.. : '....; ; ;..... : : : : : " ' I.... 1, r 1.r 1,... : : : : 34 r ; ' : f / r, ": ~ :.;. ; ~ 1 fi:'\:\/.'.../".~./.. j.....":(..-,_i.. -:--. T.~.-~ ~ ~ ~: :~ :- T ~ : :.... y ~... : ~ A l f\.. A. 0.."..(\.. \,:.. ~~-:-: :.-:-. -:.-:-.. -:-.. : -..:.. (\-.... n J'. I~ (',... (\ 'l\'..... A. ' ' \ ',.. f ". ft.... f\./"\ A~ /\ A ~ ~ A n r\ AA r > ~ I ,..:.. h,.. #,..... )" : i.. :..... : : ~ A : I : : :.. I I... ~ 30r-... : : ;.. <....'..... ~... > V... :...,......, f N..... v ~. :... ~I :. : ;... :.:... T... 1 ~ :.... : V. 1 1 I : l1 I : I I II : j tl I j J j j j j j Days in May 1993 (GMT) ' : '... - i 28

61 .. l.i SIGMA-T , ~ : :.,..-y.... )n..,.,.... : : :.. I.... ' i;. I. l \ '.A. ' '., : '"'.. : <., ;._.., : '...,, -~- -:1.... rt. / :.....,..., ;..;......_, :..: :... -: :... - : I,.''.: (,._1\\ft!\ ~ : \1.1 \' :. / : : - '-:,,_ ~... ; :.; ~ - iiil : : \" : : : 23 r- -: -: ili i : : A. i\ x 1\. :..... : :... - r2-.a haa~;~[a:fl A A._li _Af\AAAAA[.....:: 21 _.....,( -nr - ~..... r... ~.... J'.... ~ -...: : : :.... : : I : : : (..... : I ~ ~ -~-... ~ -~ r J ~ :.. -~... : - 19r... )... V,.... ~. J....'J ) ~... '..:....: : : ~ : I I II : V t I : ~ I J : J : : : : i i i i i i i i 18~--~ L------~--~----~ L------~ ~ L--~ --- = SEACAT 295 (M1 TOP) 3 HLP -.- = SEACAT 327 (M2 TOP)... _:: SEACAT 849 (M1 BOT) DEMEANED PRESSURE... :: SEACAT 848 (M2 BOT) ~! ~ ~! ~! ~ ~! ~ ~ mean = : : n.. : 1- ~ : ~ ~ ;., :... : A :- ~.. n.. 0.5r-... 'f ~.. ~.. fi....a.... :.. A. ---, ~~ -~- n.. h II... ~ A ~ A fl: A ~. : A n 11 : ~ ~..... A... A... :... A d ~ t-t-t-t-t--t-t--t-t-t-t-+-t-+-+-t--t-f-hrt t-t--r-:1-t lrt-t-+-t-+-h-t-l-t--i-f-+-t-+-l-+f-+-+-+l " : v \1 v \J : v v :. v :. v : ' : u :v v : u.. y : : : : : : : : :... - :. 848 mean = :. :. :. :.,_i._i.., Days in May 1993 (GMT) _1.. 1.i

62 Wind Stress and Current Vetors (40hlp) FBIS1 wind stress (rot-50) 0..- a.. u []_ -0.5'------' ' L..,.,l ---L.., (/) 20 b 'E o I I u M2 TOP (rot-50),j/11\\\\\\\\\,,/ I < \ ' I / //II I I I I I I I I -20'------'------' ~---~---~----~--~-- 20 M2 BOT (rot-50) (/) 'E o u >J '\1//11' '''"'''' -2o~~---~---~--~~--~---~---~---~ Days in May 1993 (GMT)

63 0,... a.. m a... FBIS1 WIND STRESS (40hlp) : : _ : = y-omp : (rot -50) :... :_.,.. ~...-..,..--- ;..... '"" :". :--- = x-omp : : : , 0 ~ 0 0 VI 0 b M2 X-COMP CURRENT (40hlp) 20 ~--~------~------~------~------~------~------~------~---.!!! I!!!! 10 f : :. : : (rot -50) : : : : : (/) : : : : : : : 0 : :... : : 0 0 : ' 0. :' ' - "E o-., /-- 0 : /.," ~:... : : - : : - : : : / : - : : : ~ > < < >......: : : o; ~-- ~ ~~ ~i ~j ~j j~------~~ ~1 -J _ = S4 908 (TOP) --- = S4 909 (BOT) M2 Y-COMP CURRENT (40hlp) ~------~------~------~------~--~ : : ~-- :: : ~ 0 0. : : : (rot -50) : : : : : ~--~------~------~------~------~------~------~------~--~ Days in May 1993 (GMT).

64 'Tj... ()Q ~ (t) ~ ~ 0"' "-" ,;_-.-.., ; TEMPERATURE : ~.... : : :''....,..... : ~ : ~ ' ' ~.. ~ : a : : : :- : : ;... ~ - : :. -. ' : : : : : ~~-~~:~:.or. - - ~ ~ ''"' : : : :.,... :. --:--~ : : : : :.,.: :. 21 \...._ : - ~ -.. ~ : ~ ~ ~-. :-~.--. ~ > -. ~. --. ~>:.t. ~---~ - ;/... r r ; : : : : : : ~-~------~ ~ ~------~ ~ ~------~--~ --- = SEACAT 295 (M1 TOP) 40 HLP -.- = SEACAT 327 (M2 TOP) = SEACAT 849 (M1 BOT) SALINITY... = SEACA T 848 (M2 BOT) ~ b : ':' : ~ : : : : : : '-- - _.. _ :..... : 0 :~ /~~ \._ ~ : ~- -.. :.. -._: : : :..:. ~ - ~ -.-~;.:..:.: ~...:..., : ~ : : : : : : : :. ~ ~~ / : : ;..; : : :. ~ , : ~ ~ -~ :-; t"". ~.... : : ~ : ~ :. 0 0 ~ ~--~------~ ~ ~------~ ~ ~------~--~ Days in May 1993 (GMT).

65 ... 'T.I OQ s:: '"'t (1) n ~ U\ N SIGMA-T... )... : ~ -.:. J _. ~ : ~. 0 ;; : : =.=)~ <. ~ ~-:, <: -~ --- ~.-. -: ;,~-,-~..:. - -'- -:- ~:l :.:., :.... ~ ~: ~ :. ~ ~ :.:.. :..... ; " ' ~ : : :......:... / ~.....:.....: :......: : : :::--= ~- : :---: -- _. --:". ~ - -:.. ~. --:-- -: ~ - ~ - 7"':.-:-. :--: - ~-. : : : ~--~ L------~ ~------~------~~------~------~--~ ---= SEACAT 295 (M1 TOP) 40 HLP -.-= SEACAT 327 (M2 TOP) = SEACAT 849 (M1 BOT) DEMEANED PRESSURE... = SEACAT 848 (M2 BOT} 0. 3~--~ , ~------~ , , d 2 " : :... : :... :..... : ; ; ;....: : :.,._....; : ~ : : ~... ~...,, :... ~ ~ ~-.... ~ ~ : 84~ mean.. = : : : : : : : : : :..... : : :. 848 mean = :. :. :..: : Days in May 1993 (GMT)

66 NED1 Offshore Survey Number May 1993 A3 A6 A9 T1 T3 T5 T7 T10 T13-2 E -4 -= Cis G) E :;;4 - ~ <1 e2 :;;4 - ~6 8 0~ ~ ~ ~-----~~-----~-----~ ~-----~ E :;;4-1" Figure 12 53

67 NED1 Offshore Survey Number May 1993 A6 A9 T1 T13.. 'E.6 Q) 'E.G Q) 'E.6 Q) 0.. 'E.6 Q) Figure 13 54

68 NED1 Offshore Survey Number 3 20 May 1993 ' A3 A6 A9 T1 T3 TS n T10 T13 "E2---f;;~~~..: 4. ~ ~----~------~--~--~----~----~----~ - e-z = Q. 4 g Q 6 8 0~------~-----L------~--~--~----L-----~----~ e-z - = 4 Q. CD Q 6 8 Figure 14 55

69 NED1 Offshore Survey Number May e a ::;; 10 i T1 T3 T5 T7 T10 T16 T19 T22 T1 T3 T5 T7 T10 T16 T19 T E8 - = 1:1. 10 ~ ' S1o 1:1. ~

70 NED1 Offshore Survey Number 5 22 May A3 A6 A9 T1 T3 T5 _2 ~ E CL CD 6 Cl / 8 T7 T10 T13 10 A3 A6 A9 T1 T3 T5 0 2 )..4 > ~6 / <21.5 Cl 8 10 T7 T10 T13 ) >21.5 Figure 16 57

71 NED1 Offshore Survey Number 6 23 May 1993 A3 A6 -. a. 6 CD >34.4. a. 6 CD Q \ 'C.6 CD 8 0~------~----~----~----~--~--~~----~----~ 10 >23.5 ""' ' _ Figure 17 58

72 NED1 Offshore Survey Number 7 24 May 1993 A3 A6 A9 T3 TS T7 T10 T13 ~,. -/ :: / /.. 4 / I. I I, =. 6 II) 8 10 \,/ ',. I I I I I I I I I I I =. 6 II) 0~------~----~~ ~--~----~----~------~ C.6 II) 8 22:-\ <22 <22 > ~------~------L ~--~----~----~------~ - 2 / 'C.6 G) 8 10 >23.5 Figure 18 59

73 NED1 Offshore Survey Number 8 May 1993 A6 A9 T1 T3 T5 n 110 T 'E. 6 u 8 o-r l---l , E u ~22 ~ "' 22.5 <22 \ I 'E. 6 u 8 10 \ 23.5 "-.. Figure 19 60

74 NED1 Offshore Surv May ey Number 9 A3..:. 6 Q)..: 'C.6 Q) ~ : -Cl. CD >23.5 Figure 20 61

75 0 2 - E Q,) 8 10 NED1 Offshore Survey Number May 1993 A3 A6 A9 T1 T3 T5 n no T13 ( Q,) 8 10 \ e4 =. 6 Q,) ~------~----~--~--~----~----~----~ - e4 = 6. Q,) / 23.5~ 10 Figure 21 62

76 Offshore Survey - 15 May RN Blue Fin High Water- Neap Tide =... Ci.4 =! Distane offshore (nautial miles) Distane offshore (nautial miles) Figure 22 63

77 North Edisto Estuarine Survey - 15 May RN Anita Low Water- Neap Tide E :5. 8 Q) 12 N \ 30 \ NED 2 3 N 4 N 5 N \\ ~. 26) \ e :5 8. Q) Distane from mouth (nautial miles) Figure 23 64

78 North Edisto Estuarine Survey - 22 May RN Anita High Water - Spring Tide Low Water - Spring Tide NED E -.= a u Cl NED E E -.= a ~ 1 2 NED Figure Distan~e from mouth (nautial miles) Distane from mouth (nautial miles)

79 Time versus Depth Plots during Maximum Flood Current in Throat of North Edisto Inlet Salinity (psu) May ~--~~~~~--~~~~--~~~~~~ - = 12 -e 8 a. Q) Chlorophyll (IJg 1-1) - e - = 12 a. Q) Temperature ( C) May e 8. a 12 Q) \ 23 <23 t 20 Lt (kg m 3) May a 12 Q) I 20.5~ Figure 66

80 ,.. -I = :::s. - o.: (.l -,.. I :::s. -= o.: (.l 8 7- A , B I 32 I Salinity (psu) I,;. :-' J.-~..,... ~.!..: ;. i ::.... >., J ' ~... :... -~.... 'j.' : ~ ;... ~... =. :~-~;.. ~1 :.~:.. -;.. :"':.;.... : "\ :"' \. I 35.~~~ : : ' L ;~?;.~~J,:.', :; ~,: :. ': :1l.:-~.r -. ':...!".,.<CI!" I I I I , ~ Cl) CCI ::.. : I 10-..: 1. :. I.. "li.... :,,:~ --,~. ": ~.!.:..,, :.:.... '-...:JI-~"~..-~ ~-... ~ i...!i.., = ~».a~~=4 ;;to',;~.-(...: :;;-....,.»~..!'... ~... 0~--~-~~~--~~~--~~~--r~~--T~~~ Chi a (pg r 1 ) Figure 26 67

81 Salinity (psu) Lt Cl) 40-.:. CIQ "'...,.: i. ~= = ;... :"-.:. "\. $._. v., '.":;.. ~ ""<( I 3 I 4 I 5 6 Chi a (IJO r 1 ) Figure 27 68

82 - ~ Density (No./1 OOm3) ~... en 0 N en ()I) 0 N N 00 0\ Ill 1.0 -<tl 5/14 5/15 5/16 5/17 ""C 5/18 CD :::J Q) 5/19 CD :::J a: ro 5/20 - ""C -I =r 0.., en 5/ !!a. Q).., -I 5/22 < Ill Q) :::J (J) <tl )> 5/23 u (J) CT :::J 5/24 0. Q) :::J 5/ () CD 5/26 5/27 5/28..-=-..:::-.-- ro~ 0 ::: 0 3

83 IT,!... E1 (t) North Edisto Low Water Neap Tide Survey - 15 May 1993 Estuary - AN Anita Offshore - AN Blue Fin -~ NED At S3 S5 S7 S10 Pl 0 0~----~----~----~------~ ~._ 0"" - e - =a Cl. Cl) 4 4 -e -. Cia Cl) I ~ l e e -. :5 a Cl. g. a Cl) 3 /

84 4 I T5 n T10 T E I.. Ci.8 Cl) 12 -.),_ '"' 4 4 E 4 - E = -. 8 Cl) =. 8 Cl) \

85 Course from M1 to A :J ~ /. /, ;.: "". ;, :-: : ;!' I ' :..: :..; ;_ :..: :..: ;...." :...> 26 32~---4~ Distane (n. mi.) Course from M1 to A6 - () C> a> a>... ~ ~ 23 2'5- -.'"':. :-: a> ~ E : - ~ _ a> : ':' Distane (n. mi.) Figure 30 72

86