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ASLO/TOS Ocean Research Conference 2004, Feb. 15-20, 2004, Honolulu, Hawaii1/24 Some Peculiarities of Case 1 Waters Optical Properties in the Northwestern.

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Presentation on theme: "ASLO/TOS Ocean Research Conference 2004, Feb. 15-20, 2004, Honolulu, Hawaii1/24 Some Peculiarities of Case 1 Waters Optical Properties in the Northwestern."— Presentation transcript:

1 ASLO/TOS Ocean Research Conference 2004, Feb , 2004, Honolulu, Hawaii1/24 Some Peculiarities of Case 1 Waters Optical Properties in the Northwestern Mediterranean Sea (“BOUSSOLE” site, 43°22 ’N; 7°54 ’E) David ANTOINE André MOREL, Hervé CLAUSTRE Laboratoire d’Océanographie de Villefranche, Villefranche sur mer, France

2 ASLO/TOS Ocean Research Conference 2004, Feb , 2004, Honolulu, Hawaii2/24 The “problem” we aim at Bricaud et al. (1998)Morel and Maritorena (2001) Natural variability of Case 1 waters optical properties is known Can we explain this variability in terms of the AOPs versus IOPs relationships ?

3 ASLO/TOS Ocean Research Conference 2004, Feb , 2004, Honolulu, Hawaii3/24 Our approach to understand the natural variability of the AOPs and IOPs Combination of - A time series with ~monthly resolution (ship operations) - A high-frequency (i.e., 15 min.) permanent sampling near the surface with a new type of optical mooring - Collection of a full set of IOPs, needed to understand the AOPs and their “anomalies” with respect to standard, global, models (--> closure)

4 ASLO/TOS Ocean Research Conference 2004, Feb , 2004, Honolulu, Hawaii4/24 The site where we collect data : “BOUSSOLE” site & program “Buoy for the acquisition of a long-term (bio)optical series” Monthly cruises (started July 2001) + a new type of optical buoy (since Sept. 2003) Marine optics, Bio-optics, Ocean color calibration / validation program (MERIS, SeaWiFS, POLDER)

5 ASLO/TOS Ocean Research Conference 2004, Feb , 2004, Honolulu, Hawaii5/24 Site characteristics (oligotrophic to eutrophic) Winter, maximum of the water mixing Chl up to ~2-3 mg m -3 mixed layer down to 200 meters Spring, establishment of the deep chlorophyll maximum around 50 meters Chl ~ 0.3 mg m -3 Summer, maximum of the stratification. DCM is maximum, with surface Chl ~ 0.05 mg m -3 (up to 1 in the DCM) Fall, erosion of the thermocline, the DCM progressively disappears Chl ~ 0.5 mg m -3

6 ASLO/TOS Ocean Research Conference 2004, Feb , 2004, Honolulu, Hawaii6/24 SeaWiFS chlorophyll FebMarch AprMayJune JulSept Oct Nov Dec SeaWiFS/SIMBIOS diagnostic data sets ( )

7 ASLO/TOS Ocean Research Conference 2004, Feb , 2004, Honolulu, Hawaii7/24 “Anomalies” we already know in situ Tchla Regional algorithm (Bricaud et al., 2001) SeaWiFS OC4v4, rep. #4 Chlorophyll time series at the DYFAMED site Start of the optics time series

8 ASLO/TOS Ocean Research Conference 2004, Feb , 2004, Honolulu, Hawaii8/24 SeaWiFS OC4v4, rep. #4 Regional algorithm (Bricaud et al., 2001) May 1999 SeaWiFS composite

9 ASLO/TOS Ocean Research Conference 2004, Feb , 2004, Honolulu, Hawaii9/24 Already identified anomalous Blue-to-green ratios Claustre et al., 2002 (Geophys. Res. Letters) (PROSOPE cruise) And others : (Gitelson et al., 1996 D’Ortenzio et al., 2001, 2002 Corsini et al., 2002) Possible cause : deposition of small dust particles coming from Sahara, reinforcing absorption in the blue and scattering in the green Morel & Maritorena (2001).

10 ASLO/TOS Ocean Research Conference 2004, Feb , 2004, Honolulu, Hawaii10/24 Which AOPs/IOPs we are looking at “Blue-to-green reflectance ratios” R( 1 )/R( 2 ) Irradiance reflectances at the “0-” level, and normalized for a sun at zenith : R( ) = E u ( 1 )/E d ( 2 ) Diffuse attenuation coefficients for the downwelling irradiance : K d ( ) = -d[ln(E d ( )] / dZ AOPs (using a Satlantic 13-wavelengths “SPMR” radiometer) IOPs (Wetlabs’ AC9 & particulate absorption on filtered samples) Total absorption, scattering, attenuation Particulate absorption (total, phytoplankton, detritus)

11 ASLO/TOS Ocean Research Conference 2004, Feb , 2004, Honolulu, Hawaii11/24 Time series of the blue-to-green ratio R(443)/R(560) Model Data in situ Chl “reconstructed” Chl

12 ASLO/TOS Ocean Research Conference 2004, Feb , 2004, Honolulu, Hawaii12/24 Time series of the blue-to-green ratio R(490)/R(560)

13 ASLO/TOS Ocean Research Conference 2004, Feb , 2004, Honolulu, Hawaii13/24 Time series of the blue-to-green ratio R(510)/R(560)

14 ASLO/TOS Ocean Research Conference 2004, Feb , 2004, Honolulu, Hawaii14/24 Time series of the K d ’s 443 nm 490 nm 412 nm

15 ASLO/TOS Ocean Research Conference 2004, Feb , 2004, Honolulu, Hawaii15/24 Time series of the K d ’s (continued) 510 nm560 nm 670 nm

16 ASLO/TOS Ocean Research Conference 2004, Feb , 2004, Honolulu, Hawaii16/24 Time series of the reflectances 443 nm 490 nm 412 nm

17 ASLO/TOS Ocean Research Conference 2004, Feb , 2004, Honolulu, Hawaii17/24 Time series of the reflectances (cont’d) 560 nm510 nm 670 nm

18 ASLO/TOS Ocean Research Conference 2004, Feb , 2004, Honolulu, Hawaii18/24 Time series of particulate absorption coefficients Summer : absorption by detritus is at least equal to, and actually greater than, phytoplankton absorption Winter : phytoplankton absorption dominates Year 2003 only

19 ASLO/TOS Ocean Research Conference 2004, Feb , 2004, Honolulu, Hawaii19/24 Particulate absorption spectra a p is decomposed into a  and a d following Bricaud and Stramski, 1990 apap aa adad February July May March

20 ASLO/TOS Ocean Research Conference 2004, Feb , 2004, Honolulu, Hawaii20/24 Spectra of the total (minus water) absorption and scattering coefficient April JulyMay February c( ) b( ) a( )

21 ASLO/TOS Ocean Research Conference 2004, Feb , 2004, Honolulu, Hawaii21/24 Particulate scattering coefficient at 550 nm as a function of Chl from AC9 measurements (+/- a factor of 2) « Fresh bloom » ? A lot of detritus in summer Loisel & Morel (1998)

22 ASLO/TOS Ocean Research Conference 2004, Feb , 2004, Honolulu, Hawaii22/24 In short... - “Lower-than-expected” reflectances in the blue are due to high absorption : several causes are possibly intermingled, such as Saharan dust, detritus, CDOM... - “Greater-than-expected” reflectances in the green : Saharan dust, detritus, others (coccolithophorids) ? The “summer anomaly” The “winter anomaly” - “Greater-than-expected” reflectances in the blue might be due to a lower absorption : “fresh phytoplankton bloom” with a lower proportion of detritus - “Lower-than-expected” reflectances in the green : could be due to large proportion of big cells - It is not a permanent feature

23 ASLO/TOS Ocean Research Conference 2004, Feb , 2004, Honolulu, Hawaii23/24 General conclusions, perspectives - The preliminary analysis of the AOPs and IOPs time series has confirmed some trends already observed in the Med. Sea (although not permanent), and revealed others - Understanding of the causes requires further analysis of the data, and may require as well some additional parameters (in particular CDOM absorption, backscattering coefficient, AOPs in the UV), as well as inversion of the AOPs into IOPs (e.g., Loisel and Stramski 2001) - Exploitation of the buoy time series (AOPs, c(660), b b (443 & 550)) should help in this respect - Anomalies in the AOPs can be explained in terms of the IOPs, yet fundamental causes remain to be ascertained. - Any index in the reflectance spectra that may help in a better interpretation of the remotely-sensed observations ?

24 ASLO/TOS Ocean Research Conference 2004, Feb , 2004, Honolulu, Hawaii24/24 Acknowledgements Alec SCOTT, Chief engineer for the project, monthly cruises, AOPs collection, data processing Bernard GENTILI, Data processing codes Davy MERIEN Joséphine RAS, HPLC and a p measurements Dominique TAILLIEZ, CTD + IOPs, monthly cruises R/V Téthys-II Captains & crews Thank you for your attention


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