Temporal changes in total and size-fractioned chlorophyll-a in surface waters of three provinces in the Atlantic Ocean (September to November) between 2003 and 2010

Racault, Marie-Fanny LP/0000-0002-7584-2515; Martinez-Vicente, Victor/0000-0003-3492-583X; Agirbas, Ertugrul/0000-0001-7987-9668; Airs, Ruth/0000-0003-0861-742X; Brewin, Robert/0000-0001-5134-8291; Llewellyn, Carole/0000-0003-1545-5190WOS: 000361862600006Phytoplankton total chlorophyll concentration (TCHLa) and phytoplankton size structure are two important ecological indicators in biological oceanography. Using high performance liquid chromatography (HPLC) pigment data, collected from surface waters along the Atlantic Meridional Transect (AMT), we examine temporal changes in TCHLa and phytoplankton size class (PSC: micro-, nano- and pico-phytoplankton) between 2003 and 2010 (September to November cruises only), in three ecological provinces of the Atlantic Ocean. the HPLC data indicate no significant change in TCHLa in northern and equatorial provinces, and an increase in the southern province. These changes were not significantly different to changes in TCHLa derived using satellite ocean-colour data over the same study period. Despite no change in AMT TCHLa in northern and equatorial provinces, significant differences in PSC were observed, related to changes in key diagnostic pigments (fucoxanthin, peridinin, 19'-hexanoyloxyfucoxanthin and zeaxanthin), with an increase in small cells (nano- and picophytoplankton) and a decrease in larger cells (micro-phytoplankton). When fitting a three-component model of phytoplankton size structure - designed to quantify the relationship between PSC and TCHLa to each AMT cruise, model parameters varied over the study period. Changes in the relationship between PSC and TCHLa have wide implications in ecology and marine biogeochemistry, and provide key information for the development and use of empirical ocean-colour algorithms. Results illustrate the importance of maintaining a time-series of in-situ observations in remote regions of the ocean, such as that acquired in the AMT programme. (C) 2015 Elsevier B.V. All rights reserved.British Oceanographic Data Centre (BODC) [NER/0/5/2001/00680]; Natural Environment Research CouncilNERC Natural Environment Research Council; National Oceanography Centre, Southampton; Natural Environment Research CouncilNERC Natural Environment Research Council [pml010009, nceo020006, pml010007, pml010008] Funding Source: researchfishData was used from the Atlantic Meridional Transect (AMT) Consortium (NER/0/5/2001/00680), provided by the British Oceanographic Data Centre (BODC) and supported by the Natural Environment Research Council National Capability funding to Plymouth Marine Laboratory and the National Oceanography Centre, Southampton. We sincerely thank officers and crew of the RRS James Clark Ross, RRS James Cook and RRS Discovery, for their help during the AMT cruises and all those involved in pigment data collection and analysis. We also thank Alex J. Poulton for comments on the manuscript. This is contribution number 272 of the AMT programme