Synoptic relationships quantified between surface Chlorophyll-a and diagnostic pigments specific to phytoplankton functional types.

Error-quantified, synoptic-scale relationships between chlorophyll-a (Chla) and phytoplankton pigment groups at the sea surface are presented. A total of nine pigment groups were considered to represent nine phytoplankton functional types (PFTs) including microplankton, nanoplankton, picoplankton, diatoms, dinoflagellates, green algae, picoeukaryotes, prokaryotes and Prochlorococcus sp. The observed relationships between Chla and pigment groups were well-defined at the global scale to show that Chla can be used as an index of not only phytoplankton abundance but also community structure; large (micro) phytoplankton monotonically increase as Chla increases, whereas the small (pico) phytoplankton community generally decreases. Within these relationships, we also found non-monotonic variations with Chla for certain pico-plankton (picoeukaryotes, Prokaryotes and Prochlorococcus sp.) and for Green Algae and nano-sized phytoplankton. The relationships were quantified with a least-square fitting approach in order to estimate the PFTs from Chla alone. The esti15 mated uncertainty of the relationships quantified depends on both phytoplankton types and Chla concentration. Maximum uncertainty over all groups (34.7% Chla) was found from diatom at approximately Chla=1.07mgm-³. However, the mean uncertainty of the relationships over all groups was 5.8 [% Chla] over the entire Chla range observed (0.02<Chla<6.84mgm-³). The relationships were applied to SeaWiFS satellite Chla data from 1998 to 2009 to show the global climatological fields of the surface distribution of PFTs. Results show that microplankton are present in the mid and high latitudes, constituting ∼ 9.0 [% Chla] of the phytoplankton community at the global surface, in which diatoms explain ∼ 6.0 [% Chla]. Nanoplankton are ubiquious throught much of the global surface oceans except subtropical gyres, acting as a background population, constituting ∼ 44.2 [% Chla]. Picoplankton are mostly limited in subtropical gyres, constituting ∼ 46.8 [% Chla] globally, in which prokaryotes are the major species explaining 32.3 [% Chla] (prochlorococcus sp. explaining 21.5 [% Chla]), while pico-eukaryotes are notably abundant in the Southern Pacific explaining ∼ 14.5 [% Chla]. These results may be used to constrain or validate global marine ecosystem models. [ABSTRACT FROM AUTHOR]