Regional to global assessments of phytoplankton dynamics from the SeaWiFS mission

To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by Elsevier and can be found at: http://www.elsevier.com/.Photosynthetic production of organic matter by microscopic oceanic phytoplankton fuels ocean ecosystems\ud and contributes roughly half of the Earth's net primary production. For 13 years, the Sea-viewing Wide\ud Field-of-view Sensor (SeaWiFS) mission provided the first consistent, synoptic observations of global ocean\ud ecosystems. Changes in the surface chlorophyll concentration, the primary biological property retrieved\ud from SeaWiFS, have traditionally been used as a metric for phytoplankton abundance and its distribution\ud largely reflects patterns in vertical nutrient transport. On regional to global scales, chlorophyll concentrations covary\ud with sea surface temperature (SST) because SST changes reflect light and nutrient conditions. However, the\ud oceanmay be too complex to be well characterized using a single index such as the chlorophyll concentration. A\ud semi-analytical bio-optical algorithm is used to help interpret regional to global SeaWiFS chlorophyll observations\ud from using three independent, well-validated ocean color data products; the chlorophyll a concentration,\ud absorption by CDM and particulate backscattering. First, we show that observed long-term, global-scale trends\ud in standard chlorophyll retrievals are likely compromised by coincident changes in CDM. Second, we partition\ud the chlorophyll signal into a component due to phytoplankton biomass changes and a component caused by\ud physiological adjustments in intracellular chlorophyll concentrations to changes in mixed layer light levels.\ud We show that biomass changes dominate chlorophyll signals for the high latitude seas and where persistent\ud vertical upwelling is known to occur, while physiological processes dominate chlorophyll variability over\ud much of the tropical and subtropical oceans. The SeaWiFS data set demonstrates complexity in the interpretation\ud of changes in regional to global phytoplankton distributions and illustrates limitations for the assessment of\ud phytoplankton dynamics using chlorophyll retrievals alone