Phvtoplankton (Coccolithophores) 

 June 1979 



Frontal boundaries between water masses with distinct hydrographic 

 properties and plankton communities (Pingree el ai, 1982) are seen on 

 CZCS images on 19 June (76-1) as regions with relatively high diffuse 

 attenuation coefficients (upper image) and pigment values (lower image). 

 The shelf break frontal system (SBF. 77-1), which follows the 200-m 

 isobath, represents the eastern extent of surface mesoscale eddies 

 characteristic of the deep waters of the Bay of Biscay. On the shelf between 

 southwestern England and northwestern France, the tidal front (TF) 

 marks the transition from seasonally stratified and relatively warm water 

 in the Celtic Sea to tidally mi.xed water in the English Channel. The 

 coccolithophore populations appear on the Channel 3 image (77-2, 

 Subsurface Radiance) as areas of high reflectance in outer shelf waters. 



The coccolithophores give maximum reflectance in Channel 1 (blue) 

 and. relative to clear offshore and turbid coastal waters, significant 

 reflectance in Channel 4 (red; Holligan et ai. 1983). The latter property 

 affects the atmospheric corrections so that appropriate adjustments 

 should be made for water-leaving radiance by correlation with Channels 

 1-3. or the Channel 4 radiance values for pixels adjacent to the bloom 

 used. These channels are in reference to Level 1 images, which are not 

 shown in this publication. 



The influence of coccolith reflectance on the chlorophyll algorithm is 

 more difficult to define, as no correlation between coccolith density and 

 pigment concentration is expected for the scene as a whole. This problem 

 is illustrated by the comparison between the Channel 3 image (77-2) and 

 either the diffuse attenuation coefficient or pigment image (76-1). In the 

 coastal, tidally mixed water, for which the levels of suspended material 

 and chlorophyll can be considered proportional, the spatial patterns of 

 high reflectance are positively correlated. By contrast, no such 

 relationship holds for the coccolithophore water. 



The maximum chlorophyll a levels observed in the coccolithophore 

 blooms are generally 2-3 mg m"' compared to values of up to 5 mg m' 

 associated with persistent diatom populations at the shelf break. A more 

 important parameter to derive from the CZCS imagery, however, is 

 coccolith abundance as a measure of calcite-carbon that will be lost to the 

 bottom sediments. The reflectance signal is generated both by living cells 

 and detached coccoliths. and preliminary calibration values suggest that 

 typical maximum reflectance values correspond to about 1 gm m*^ CaCO^ 

 in the surface water. 



References 



Holligan. P. M.. M. Viollier, D. S. Harbour. P. Camus, and M. Champagne-Philippe, 



1983; Satellite and ship studies of coccolithophore production along a continental shelf 



edge. Nature. 304. 3.19-342. 

 Pingree, R. D.. G. T. Mardell. P. M. Holligan. D. K.. Griffiths, and J. Smithers, 1982: Celtic 



Sea and Armorican current structure and the vertical distribution of temperature and 



chlorophyll- Commenlal Shelf Research. 1.99-116. 



76 



NIMBUS T CZCS 



ORBIT 03Z93 19JUN79 120132 TO 120332 GMT GAIN 1-4=1 THRESHOLD OFF TILT ANGLE 16-0 

 GRID CENTER DATA: 120232 GMT 'f6-30N 012-56N SUN EL 65 AZ 153 ROLL 0.1 PITCH 0.0 YAW -0-1 



DIFFUSE hTTEH^TIOII CCCFFICIENT 



algorithms: 01 00 00 00 

 970 SCAN LINES PROCESSED 



• 19 ■■i^ 



02 01 00 00 



SCAN LINES MISSING 



83 1-28 2.11 3.46 5-69 9-35 11-98 iS-iS 



CIP VER CRT NO DPS VER SPEC- # FRAME^* 

 V801005 ZE09301- V820401 FT32040 ZG009.0: 



76- 



Nimbus-7. Orbit 3293. 19 June 1979. CZCS Diffuse Attenuation Coefficient (upper) and Pigment (lower! Images. 



