from a decade of CCD temperature data

Transcription

1 (Some of) What we have learned from a decade of CCD temperature data Craig Gelpi and Karen Norris Long Beach Aquarium of the Pacific August 15, 2008

2 Introduction Catalina Conservancy Divers collected temperature data in Southern California Bight for over a decade. Unique, long-term data set provides insight into Bight and Island water dynamics.

3 Temperature and Currents Temperature is a tracer of water movement Temperature gradient required Temperature changes measure integrated effects Example: measuring water speeds of 1 mm/s directly is economically hopeless. But 1 mm/s advection of a 1 o C/10 m gradient can be easily measured in 3 hours.

4 Talk Goals Report what has been established with CCD data. Temperature description - annual and tidal Significant understanding of annual dynamics Global context What can we learn about much larger issues with the CCD data? Local context New questions to be answered

5 Experiment: instruments and sites

6 Thermograph and housing top view Accuracy: 0.3 o C Response Time: 5 minutes Image: Derek Smith

7 Thermograph housing side view Image: Derek Smith

8 Submarine Measurements Image: Derek Smith Image:

9 Catalina Thermograph Sites Array of bottom-mounted thermographs Marine life census areas Open-ocean locations Depths of Site Location Instruments (m) 1 WIES 5, 9, 18, 30 2 Pumpernickel 12 3 Italian Gardens 12 4 Casino Point 12 5 East End 5, 9, 18 6 Little Harbor 5, 9, 18 7 Cactus Bay 5, 9,

10 Thermograph Sites Southern California Bight

11 Experiment results: temperature data

12 Short-term Variations Sample 200-Hour Time Series Cyclic fluctuations that increase in amplitude with depth. 6 o Cat 30 m smaller modulations at 5 m Major fluctuations have a period of about 12 hours.

13 Spectrograms LA Harbor mean sea level 30-m temperature

14 Lunar tide not in buoy data Solar Lunar

15 Deep thermograph data exhibits lunar and solar tides Solar Lunar

16 Catalina Island Temperatures Temporally smoothed and averaged over sites

17 Catalina Island Temperatures average intra-annual variation

18 California Diving News Article How to Accurately Predict Water Temperature at Depth On Your Next Catalina Dive In preparation for a dive, there are a number of things I d like to know: surf, visibility, and temperature at depth. I can find surf information online, while visibility and temperature are presently not available. However, recent data released by the Catalina Conservancy Divers (CCD) indicate that there may be some hope to determine the temperature. February 2003, Vol. 20, No 2

19 Temperature Description Island waters rife with internal waves and internal tides. Modulations, phases and apparent propagation measured. Annual variation quantified Complex behavior with depth noted (first annual variation plots published). Described in Sixth California Island Symposium

20 Data analysis (the fun stuff)

21 Seasonal Temperature Change Annual variation appears to the unconstrained eye as a diffusion phenomena. Nobody believed that. Vertical diffusion is extremely important in the ocean. Biological activities Climate processes

22 Vertical Eddy Diffusion Parcels of water mix and diffuse. Effective diffusion rate is much larger than molecular rate; higher rate is termed eddy diffusion. Nutrients, heat, salinity diffuse at same rate. Opposite gradients Eddy diffusion is mitigated by density gradients and enhanced by wind, waves and tidal action.

23 Biology and Mixing ocean surface phytoplankton diffusion bacteria sinking of organic matter

24 Energy input and heating Solar radiation Absorption Diffusion Advection

25 Major Issue Are the temporal and depth temperature dynamics produced by Horizontal Advection Or Vertical Diffusion? Answer requires Meteorological analysis Horizontal array of measurements

26 Physical Conditions in SCB relative to Northern California Orientation of coast is different Transverse mountain ranges modify winds Eddying California Current branch Little upwelling Large North-South temperature gradient Southern California Bight is the transition region between the warmer southern waters and the northern upwelling waters 85% of California marine fishes found in Bight

27 X Southern California Bight simplified currents X X X X - Buoy

28 Average wind direction and speed is constant in inner Bight N Bight winds Upwelling winds

29 Sea Surface Temperature Upwelling off California Variable upwelling winds in NoCal, steady state in SoCal

30 SST in SCB

31 Monterey Bay CalCOFI station Pier NOAA buoy Pt. Conception Santa Catalina Line 90 Horizontal Array Latitude N. Channel Islands San Clemente Oceanside Pier Scripps Pier CalCOFI stations, NOAA buoys and piers. Data collection since 1949 Longitude

32 Horizontal Array Thermograph Stations: CINP and CCD San Miguel Santa Cruz FH Anacapa Latitude Santa Rosa GI FH GI W CalCOFI station Thermograph NOAA buoy Fry s Harbor Gull Island WIES Santa Barbara Santa Catalina W San Clemente Longitude

33 Ancillary Data Reduction For each site fit the annual sinusoid and extract: Amplitude of the annual temperature signal Phase (day of maximum temperature) Mean temperature phase All as a function of depth mean Amp. Construct 3-D maps Jan Jul Dec

34 SCB Mean Temperature 36 o N Depth = 0 m o N Depth = 30 m o N o N o N o N o N o N o N 36 o N 34 o N 32 o N 30 o N 28 o N o W122 o W120 o W 118 o W116 o W 124 o W122 o W120 o W 118 o W116 o W Depth = 10 m Depth = 50 m o N o N o N o N o N 28 o N o W122 o W120 o W 118 o W116 o W 124 o W122 o W120 o W 118 o W116 o W 10

35 Annual Amplitude in Bight 36 o N 1.25 Depth = 0 m o N Depth = 30 m o N o N o N 30 o N o N 30 o N o N 36 o N 28 o N o W 122 o W 120 o W 118 o W 116 o W 124 o W122 o W 120 o W 118 o W116 o W Depth = 10 m o N 0.25 Depth = 50 m o N 32 o N o N o N o N 28 o N o N o N 124 o W 122 o W 120 o W 118 o W 116 o W 124 o W122 o W 120 o W 118 o W116 o W

36 Phase Maps Depth = 0 m Depth = 30 m 36 o N o N o N o N o N o N o N o N o N o N 124 o W 122 o W 120 o W 118 o W116 o W 124 o W 122 o W 120 o W 118 o W116 o W Depth = 10 m Depth = 50 m o N o N o N o N o N o N o N 28 o N o N o N 124 o W 122 o W 120 o W 118 o W116 o W 124 o W 122 o W 120 o W 118 o W116 o W

37 Phase Gradient, days/meter Inner Bight is unique

38 CalCOFI Salinity Data No Advection 36 o N Mean Salinity Depth = 0 m o N 0.10 Amplitude Depth = 0 m o N 32 o N o N 32 o N o N o N o N 124 o W 122 o W 120 o W 118 o W 116 o W o N 124 o W 122 o W 120 o W 118 o W116 o W 0 36 o N 34 o N Fitting Uncertainty Depth = 0 m o N 34 o N Fitting Uncertainty in Phase Depth = 0 m o N o N o N o N o N 124 o W 122 o W 120 o W 118 o W 116 o W 0 28 o N 124 o W 122 o W 120 o W 118 o W116 o W 0

39 Temperature Model No Advection One-dimensional eddy diffusion Energy into sea determined by NCEP data Energy quickly absorbed in the upper water layers.

40 Catalina Data and Model

41 Conclusions Annual temperature variations in the inner SCB indicate Little advection but significant vertical eddy diffusion Vertical diffusion coefficient is 1.3 x 10-4 m 2 s -1 Horizontal eddy field deduced Anomalous warming is produced by upwelling interrupting annual temperature increase

42 What do the conclusions mean? Upper-ocean water residence time is longer (much longer) than expected The inner Bight does not flush as quickly as previously thought Pollution remains longer Possible to compute nutrient availability to upper-ocean marine life

43 Novelty Ocean mixing is very difficult to measure Deposit tracer material and follow it (difficult) Dye tracers and lidars (new) Expensive procedures First time temperature dynamics used in open ocean to measure mixing* Very good measurement Strong signal not subject to distortion by episodic events *Journal of Geophysical Research, Vol., 113, C04034, doi: /2006jc003820, 2008

44 Global Context General Ocean Mixing The ocean significantly affects climate Transports heat from tropics to poles Responsible for ½ of total energy transport Thermohaline circulations Mixing required to upwell cold water is same as measured with CCD data

45 Conveyor Belt Model Thermohaline circulation

46 Global Context Pedagogy on General Ocean Mixing Arctic Surface flow Antarctic mixing downwelling North

47 Diffusion values in ocean 30 m 10-4 m 2 s -1 measured with CCD data depth ~70 m 10-5 m 2 s -1 measured with injected tracers >1000 m 10-4 m 2 s -1 required to close circulation

48 Bight/Ocean Mixing Mixing values in the Bight are similar quantitatively to what is required in the abyss. Mixing is not understood in either location. Insight into Bight near-surface mixing should produce better understanding of how ocean affects climate.

49 Mixing Laboratory We haven t contributed to the mixing solution, but We found a natural laboratory to study the problem. Easily accessible Long-term data sets exist

50 Next questions in Physical Oceanography What is the relation between the internal waves and the tide? Has the amount of mixing varied over time? What is the fate of the energy transported downward into the basins? What produces the mixing in the Bight? Is it related to deep ocean mixing? Do the Northern Channel Islands form a border to the area of mixing? What are the variations at intermediate frequencies (weeks)?

51 Next questions in Marine Biology How do the internal waves interact with marine life? Is the mixing consistent with nutrient supply? Do fish assemblages correlate with mixing regions? Is there an island mass effect? What are the effects of Santa Ana winds, coastally trapped waves, other phenomena on nutrients?

52 But about the mixing solution Internal waves are rife on the island