Temporal variability in phytoplankton pigments, picoplankton and coccolithophores along a transect through the North Atlantic and tropical southwestern Pacific

Abstract

International audienceBiogeochemical processes in the sea are triggered in various ways by chlorophyll-containing phytoplankton groups. While the variability of chlorophyll concentration at sea has been observed from satellites for several years, these groups are known only from cruises which are limited in space and time. The Geochemistry, Phytoplankton and Color of the Ocean programme (GeP&CO) was set up to describe and understand the variability of phytoplankton composition on large spatial scales under a multi-year sampling strategy. It was based on sea-surface sampling along the route of the merchant ship Contship London which travelled four times a year from Le Havre (France) to Noumea (New Caledonia) via New York, Panama and Auckland. Observations included the measurement of photosynthetic pigments, counts of picoplanktonic cells by flow cytometry (Prochlorococcus, Synechococcus, and picoeucaryotes) and counting and identification of coccolithophores. The results confirmed that tropical areas have low seasonal variability and are characterized by relatively high divinyl-chlorophyll a and zeaxanthin concentration and that the variability is strongest at high latitudes-where the phytoplankton biomass and population structure are found to have large seasonal cycles. Thus, the spring bloom in the North Atlantic and an austral winter bloom north of New Zealand are marked by chlorophyll concentrations which are often higher than 0.5 mu g l(-1) and by high concentration of fucoxanthin (a pigment used as an indicator for diatoms), while summer populations are dominated by Prochlorococcus sp. and have low chlorophyll concentrations. Apart from this yearly bloom at temperate latitudes, fucoxanthin is scarce, except in the equatorial upwelling zone in the eastern Pacific Ocean, where it is found in moderate amounts. In this region, relatively high chlorophyll concentrations extend generally as far as 14 degrees S and do not respond to the seasonal strengthening of the equatorial upwelling during the austral winter. Prochlorococcus, which is known to dominate in oligotrophic tropical seas and to disappear in cold conditions, in fact has its minimum during the spring bloom in the North Atlantic, rather than during the winter. Coccolithophores are ubiquitous, showing a succession of species ill response to oceanic conditions and provinces. 19'Hexanoyloxyfucoxanthin, the pigment generally considered as all indicator of coccolithophores, is relatively abundant at all times and in all regions, but its abundance is generally not tightly correlated with that of coccolithophores. The regional differences revealed by these results are in overall agreement with Longhurst's division of the ocean into ecological provinces. (c) 2006 Elsevier Ltd. All rights reserved

Phytoplankton community dynamics during late spring coccolithophore blooms at the continental margin of the Celtic Sea (North East Atlantic, 2006–2008)

“…This is further corroborated by the presence of surface diatom-dominated blooms at stations where drawdown of alkalinity had occurred and PIC had accumulated below the pycnocline, reminiscent of prior coccolithophorid calcification (Table SP5) (Suykens et al, 2010). Furthermore, our findings confirm previous reports (Barlow et al, 1993(Barlow et al, , 2002Gibb et al, 2001;Joint et al, 2001;Lampert et al, 2002;Dandonneau et al, 2006;Leblanc et al, 2009) which show that the late spring blooms in the NE Atlantic are composed of mixed assemblages, dominated by diatoms and coccolithophores, but also with important contributions of prasinophytes and dinoflagellates.…”

Predominance of heavily calcified coccolithophores at low CaCO 3 saturation during winter in the Bay of Biscay

“…The evidence for the phenomenon is based on direct sampling of surface waters and uses a straightforward technique (visual examination of SEM images; 3,500 cells were examined in the Bay of Biscay and 8,900 cells were examined in total). Our findings agree with other data: (i) the same pattern recurred along our transect in 2009-2010 (SI Appendix, Tables S12-S21); (ii) summer dominance of type A morphotypes was also seen during crossings in 2006 (SI Appendix, Table S22) and 2007 (SI Appendix, Table S23) (winters were not sampled in these years); (iii) the same trend in morphotypes was seen in the more abundant detached coccoliths (SI Appendix, section 1 and Table S24); and (v) a similar morphotype seasonality was seen in less-frequently collected data from farther west in the Atlantic (21). Horizontal advection of a patch of water cannot explain a seasonal shift occurring all along the transect (deep water and shelf) and in multiple years.…”

Spatial variability of phytoplankton pigment distributions in the Subtropical South Pacific Ocean: comparison between in situ and predicted data

“…Within the following discussion, several areas, characterized by atypical pigment distributions and associations, will be depicted. (Claustre and Marty, 1995;Bidigare and Ondrusek, 1996;Mackey et al, 1996;Dandonneau et al, 2006). In these strongly illuminated waters, cyanobacteria essentially dominate the phytoplankton populations.…”