Surface phytoplankton pigment distributions in the Atlantic Ocean: an assessment of basin scale variability between 50 degrees N and 50 degrees S

We present an overview of the spatial distributions of phytoplankton pigmen ts along transects between the UK and the Falkland Islands. These studies, undertaken as a component of the UK Atlantic Meridional Transect (AMT) prog ramme, provided the first post-launch validation data for the NASA SeaWiFS satellite. Pigment data are used to characterise basin-scale variations in phytoplankton biomass and community composition over 100 degrees of latitud e, and to compliment the definition of hydrographic oceanic provinces. A su mmary of the key pigment characteristics of each province is presented. Concentrations of total chlorophyll a (totCHLa = chlorophyll a, CHLa + divi nyl CHLa, dvCHLa) were greatest in high latitude temperate waters (>37 degr ees N and >35 degrees S), and in the Canary Current Upwelling system. In th ese regions, the total carotenoid (totCAR) budget was dominated by photosyn thetic carotenoids (PSCs). High accessory pigment diversity was observed of which fucoxanthin (FUC), 19'-hexanoyloxyfucoxanthin (HEX), and diadinoxant hin (DIAD) were most abundant, indicating proliferation of large eukaryotes and nanoflagellates. In contrast, tropical and sub-tropical waters exhibit ed concentrations of totCHLa below 500 ng 1(-1), with the North Atlantic Su b-tropical East gyre (NASE, 26.7-35 degrees N), South Equatorial Current (S eqC, 7-14.6 degrees S) and South Atlantic tropical Gyre (SATG, 14.6-26 degr ees S) characterised by totCHLa of <100 ng(-1). These waters exhibited rela tively limited pigment diversity, and the totCAR budget was dominated by ph otoprotecting pigments (PPCs) of which zeaxanthin (ZEA), a marker of prokar yotes (cyanobacteria and prochlorophytes), was most abundant. DVCHLa, a mar ker of prochlorophytes was detected in waters at temperatures >15 degrees C , and between the extremes of 48 degrees N and 42 degrees S. DvCHLa account ed for up to two-thirds of totCHLa in oligotrophic provinces demonstrating the importance of prochlorophytes to oceanic biomass. Overall, HEX was the dominant PSC, contributing up to 75% of totCAR. HEX al ways represented >2% of totCAR and was the only truly ubiquitous carotenoid . Since HEX is a chemotaxonomic marker of prymnesiophytes, this observation reflects the truly cosmopolitan distribution of this algal class. ZEA was found to be the most abundant PPC contributing more than one third of the t otal carotenoid budget in each transect. Greatest seasonality was observed in highly productive waters at high latit udes and in shallow continental shelf waters and attributed to proliferatio n of large eukaryotes during spring. Concentrations of the prokaryote pigme nts (ZEA + dvCHLa) also exbibited some seasonality, with elevated concentra tions throughout most of the transect during Northern Hemisphere spring. (C ) 2000 Elsevier Science Ltd. All rights reserved.