CHLOROPHYLL A AND NUTRIENTS FLUXES AND TRANSPORTS IN THE SOUTH PORTUGUESE COAST

Transcription

1 CHLOROPHYLL A AND NUTRIENTS FLUXES AND TRANSPORTS IN THE SOUTH PORTUGUESE COAST Sara Cardeira, Alexandra Cravo and Paulo Relvas CIMA, FCT, University of Algarve, Campus de Gambelas, Faro, PORTUGAL cardeira_sara@hotmail.com

2 INTRODUCTION SPC is well characterised from the physical oceanographic point of view but the chemical consequences of the occurring processes are not deeply described. Fluxes and transports of nutrients and chlorophyll a were never described before Physical Oceanographic Processes Surface and subsurface: - coastal upwelling, coastal countercurrents with influence of rivers discharge coastal and bottom topography Bottom- Mediterreanean water (> 5 m)

3 COASTAL UPWELLING Recurrent in Cape of São Vicente, more frequent in the western part of the SPC, till CSM May to October, during favorable winds N/NW COUNTERCCURENTS Currents of opposite direction to usual circulation SPC: favorable winds East, South or West wind relaxation Current direction: EAST WEST (Saltier and warmer water) INFLUENCE OF RIVERS IN THE SPC GUADIANA (~14 m 3 /s) ARADE <2 x (~1,5 m 3 /s)

4 OBJECTIVES: Chemical characterization of the SPC in the late upwelling season (October 26), describing: - water masses (from surface down to 7 m) and - dominant oceanographic processes, mainly regarding the fluxes and transports of nutrients and chlorophyll a.

5 MATERIAL AND METHODS Oceanographic Survey CIMA-26 (financed( by FCT- Portugal) 1-5 October 26, on board of N. R.P. D. Carlos I vessel, IH P Q G CSV CSM # stations: 9 (5-7 m) Stations spacing: 2.5 nm (~4 km) # Meridional Transects : 5 (from 1 ) Total study area: ~6 km 2

6 DATA ACQUISITION SST SATELLITE IMAGE (26 SEP - 5 OCT): CERSAT Data Center- IFREMER spatial resolution: 4 km; daily, with average 12 hours WIND (26 SEP - 5 OCT): SeaWinds MicroWaves Sensor, QuikScat satellite (POET) spatial resolution:,25º; time resolution: 1 day CTD: CTD Idronaut OS 316 CURRENT VELOCITY: Vessel mounted ADCP RDI 15 khz CHLOROPHYLL a: Spectrofluorometric method (Yentsch and Menzel, 1963) NUTRIENTS: Spectrophotometric methods (adapted from Grasshof et al., 1983)

7 RESULTS AND DISCUSSION 14 NITRATE -2µM µM Mixture Layer ML SAW 4-1µM µM PHOSPHATE -.1µM.1-.3µM Mixture Layer ML 37 SAW.2-.4µM µM Mixed Layer 21 SAW (Surface Atlantic Water) µM SAW 3µM µM 3-5µM NACW NACW SAW ML layer Misture NACW 37 MW SAW ML Misture layer MW 1 MW 36.5 Salinity 36 5 Mixture ML Layer SiO44-(µM) T (ºC) Mediterranean Water (> 4 m) 37 SILICATE 1-3.5µM ML layer Misture.1. MW NACW (North Atlantic Central Water) µM NACW SAW PO43-(µM) T (ºC) MW MW µM NACW NACW 1 NO3-(µM) T (ºC) As already identified by other authors Salinity 37

8 Rivers Discharge ~insignificant, after a period of dry and hot summer: S > 35,9; Coastal stations - 5 km from the coast WIND REGIME CSV CSM GUADIA NA By that time and previously to the cruise the wind regime despite weak ( 8 m/s) was mainly westerlies, favourable to upwelling N and NW winds, during 2 preceding weeks, max in Guadiana Transect. Favorable to Coastal Upwelling Wind relaxation in 1ST October QuickScat Wind vectors for the study area, from 25th September to 5 th October 26. Source:Ifremer

9 SURFACE SEAWATER TEMPERATURE (SST) 26 SET SET SET 26 Temperature near coast, particularly at Portimão Coastal stations: Colder Water Upwelling Oceanic stations: Warmer water, water recirculation to Gulf of Cádiz NO CCC!!! 29 SET 26 3 SET 26 1 OUT 26 5 Outubro 26 SST S P G Portimão a ) source: CERSAT Data Center IFREMER.

10 Upwelling more intense: - CSV and P sections, max chl a concentration. -Chla in the coastal zone:.3 and 3 mg m -3. Chlorophyll a concentration (mg m -3 ) imagery from 22 nd to 29 th Septembre (left) and 3 th Septembre to 7 th Octobre 26. Source: OceanColor, Nasa.

11 Flow field ADCP velocity vectors of the upper layer (1-25m) revealing the eastward alongshore flow associated with the upwelling G,CSM and CSV (max.)

12 Levels < 2 m (upwelling and aquisition of ADCP flow) Alongshore Flow (max:.35 m/s) Chl a (µg/l) Transect G Transect G Guadiana Transect G outflow Max chl a (2 µg/l), low flow, upwelling NO 3 - PO 4 3- SiO 4 4- (µm) Transect G Transect G Transect G

13 Fluxes (mmol/m 2 s) Guadiana Transect Chla (mg/m 2 s) Transect G NO 3 - Transect G PO 4 3- SiO 4 4- Transect G Transect G

14 Flow(max:.3 m/s) Chl a (µg/l) CSM Transect -1 Transect CSM -1 Transect CSM RF Max chl a (~.4 µg/l), low flow, upwelling NO 3 - PO 4 3- SiO 4 4- (µm) Transect CSM Transect CSM Transect CSM

15 Fluxes (mmol/m 2 s) CSM Transect Chla (mg/m 2 s) Transect CSM NO 3 - Transect CSM PO 4 3- SiO 4 4- Transect CSM Transect CSM

16 Flow(max:.25 m/s) Chl a (µg/l) Q Transect Transect - Q Transect - Q Max chl a (~.8 µg/l), low flow, -19 NO 3 - Transect - Q -19 PO 4 3- SiO 4 4- Transect - Q upwelling Transect - Q (µm)

17 Fluxes (mmol/m 2 s) Chla (mg/m 2 s) Transect - Q NO 3 - Transect - Q Q Transect PO 4 3- SiO 4 4- Transect - Q Transect - Q

18 Flow(max: m/s) Chl a (µg/l) P Transect Transect P Transect P Max chl a (3 µg/l), min flow, Chl a plumealongthesection upwelling NO 3 - Transect P PO 4 3- SiO 4 4- Transect P Transect P (µm)

19 Fluxes (mmol/m 2 s) P Transect Chla (mg/m 2 s) Transect P NO 3 - Transect P PO 3-4 SiO 4-4 Transect P Transect P

20 Flow(max: m/s) Chl a (µg/l) CSV Transect N -1 Transect CSV -1 Transect CSV Max chl a (~1 µg/l), low flow, upwelling NO 3 - PO 4 3- SiO 4 4- (µm) Transect CSV Transect CSV Transect CSV

21 Fluxes (mmol/m 2 s) Chla (mg/m 2 s) NO 3 - CSV Transect Transect CSV Transect CSV PO 4 3- SiO 4 4- Transect CSV Transect CSV

22 Table 1 Net Eastward chlorophyll a (g/s) and nutrients (mol/s) transport below 3 and between 3-1 m. CSV P Q CSM G <3m 3-1 m <3m 3-1 m <3m 3-1 m <3m 3-1 m <3m 3-1 m Chl a NO PO SiO Nutrients and Chl a fluxes were maximal where the current flow was highest, particularly in the cape regions (CSV, CSM) and in G Section. G=4.5 ton/day chl a!!! P section Lower flow and max Chl a (upwelling and relaxation) Min transports, along with consumption due to stratification ( upwelling shadow ) CSM < 3 m Max transports due to higher velocity and low chl a (instability to phytoplankton growth) freshly upwelled waters

23 Chl a in the study area Chl a (µg/l) - 5 dbar 37.2 V.R.S.A LAT (N) Sagres Faro LONG (W) 37.2 Chl a (ug/l) - 2 dbar V.R.S.A LAT (N) Sagres 3.1 Fa ro LONG (W) Amount of Chl a in the study area ~12 tons in a period of weak upwelling!!! Rough estimate (6 km 2 x 75m x.3 mg/m 3 )

24 CONCLUSIONS In this period of late upwelling season the major oceanographic processes derived from the physical forcing of wind, favorable to upwelling, despite of weak intensity Upwelling was observed till Guadiana Section, further eastward than CSM. In P Section intensification of upwelling; absolute max of chl a, relatively high to the period of year (3 mg/m 3 ), retention bay with a large slope By this time of the year rivers discharge show to be not important in the study area. Despite NW wind relaxation CCC was not evident The current flow is a key parameter affecting the magnitude of both chlorophyll a and nutrients fluxes and transports, even when these are present in low concentrations, as found at the surface levels. Transports were mainly alongshore and eastward. The amount of Chl a present in the study area is significant regarding the relaxed upwelling conditions, expected to be much higher in periods of intense upwelling!!!.

25 ACKNOWLEDGEMENTS We acknowledge to CIMA To Joaquim Luís for running MIRONE suite of MatLab (w3.ualg.pt/~jluis/mirone/ )