Feldman G. C.

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Feldman
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G. C.
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  • Article
    Satellite-detected fluorescence reveals global physiology of ocean phytoplankton
    (Copernicus Publications on behalf of the European Geosciences Union, 2009-05-08) Behrenfeld, Michael J. ; Westberry, Toby K. ; Boss, Emmanuel S. ; O'Malley, Robert T. ; Siegel, David A. ; Wiggert, Jerry D. ; Franz, Bryan A. ; McClain, Charles R. ; Feldman, G. C. ; Doney, Scott C. ; Moore, J. Keith ; Dall'Olmo, Giorgio ; Milligan, A. J. ; Lima, Ivan D. ; Mahowald, Natalie M.
    Phytoplankton photosynthesis links global ocean biology and climate-driven fluctuations in the physical environment. These interactions are largely expressed through changes in phytoplankton physiology, but physiological status has proven extremely challenging to characterize globally. Phytoplankton fluorescence does provide a rich source of physiological information long exploited in laboratory and field studies, and is now observed from space. Here we evaluate the physiological underpinnings of global variations in satellite-based phytoplankton chlorophyll fluorescence. The three dominant factors influencing fluorescence distributions are chlorophyll concentration, pigment packaging effects on light absorption, and light-dependent energy-quenching processes. After accounting for these three factors, resultant global distributions of quenching-corrected fluorescence quantum yields reveal a striking consistency with anticipated patterns of iron availability. High fluorescence quantum yields are typically found in low iron waters, while low quantum yields dominate regions where other environmental factors are most limiting to phytoplankton growth. Specific properties of photosynthetic membranes are discussed that provide a mechanistic view linking iron stress to satellite-detected fluorescence. Our results present satellite-based fluorescence as a valuable tool for evaluating nutrient stress predictions in ocean ecosystem models and give the first synoptic observational evidence that iron plays an important role in seasonal phytoplankton dynamics of the Indian Ocean. Satellite fluorescence may also provide a path for monitoring climate-phytoplankton physiology interactions and improving descriptions of phytoplankton light use efficiencies in ocean productivity models.
  • Article
    Regional to global assessments of phytoplankton dynamics from the SeaWiFS mission
    (Elsevier, 2013-04-20) Siegel, David A. ; Behrenfeld, Michael J. ; Maritorena, S. ; McClain, Charles R. ; Antoine, David ; Bailey, S. W. ; Bontempi, P. S. ; Boss, Emmanuel S. ; Dierssen, Heidi M. ; Doney, Scott C. ; Eplee, R. E. ; Evans, R. H. ; Feldman, G. C. ; Fields, Erik ; Franz, Bryan A. ; Kuring, N. A. ; Mengelt, C. ; Nelson, Norman B. ; Patt, F. S. ; Robinson, W. D. ; Sarmiento, Jorge L. ; Swan, C. M. ; Werdell, P. J. ; Westberry, Toby K. ; Wilding, J. G. ; Yoder, James A.
    Photosynthetic production of organic matter by microscopic oceanic phytoplankton fuels ocean ecosystems and contributes roughly half of the Earth's net primary production. For 13 years, the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) mission provided the first consistent, synoptic observations of global ocean ecosystems. Changes in the surface chlorophyll concentration, the primary biological property retrieved from SeaWiFS, have traditionally been used as a metric for phytoplankton abundance and its distribution largely reflects patterns in vertical nutrient transport. On regional to global scales, chlorophyll concentrations covary with sea surface temperature (SST) because SST changes reflect light and nutrient conditions. However, the ocean may be too complex to be well characterized using a single index such as the chlorophyll concentration. A semi-analytical bio-optical algorithm is used to help interpret regional to global SeaWiFS chlorophyll observations from using three independent, well-validated ocean color data products; the chlorophyll a concentration, absorption by CDM and particulate backscattering. First, we show that observed long-term, global-scale trends in standard chlorophyll retrievals are likely compromised by coincident changes in CDM. Second, we partition the chlorophyll signal into a component due to phytoplankton biomass changes and a component caused by physiological adjustments in intracellular chlorophyll concentrations to changes in mixed layer light levels. We show that biomass changes dominate chlorophyll signals for the high latitude seas and where persistent vertical upwelling is known to occur, while physiological processes dominate chlorophyll variability over much of the tropical and subtropical oceans. The SeaWiFS data set demonstrates complexity in the interpretation of changes in regional to global phytoplankton distributions and illustrates limitations for the assessment of phytoplankton dynamics using chlorophyll retrievals alone.