Virginia Institute of Marine Science
Nearly half of the earth's photosynthetically fixed carbon derives from the oceans. To determine global and region specific rates, we rely on models that estimate marine net primary productivity (NPP) thus it is essential that these models are evaluated to determine their accuracy. Here we assessed the skill of 21 ocean color models by comparing their estimates of depth-integrated NPP to 1156 in situ C-14 measurements encompassing ten marine regions including the Sargasso Sea, pelagic North Atlantic, coastal Northeast Atlantic, Black Sea, Mediterranean Sea, Arabian Sea, subtropical North Pacific, Ross Sea, West Antarctic Peninsula, and the Antarctic Polar Frontal Zone. Average model skill, as determined by root-mean square difference calculations, was lowest in the Black and Mediterranean Seas, highest in the pelagic North Atlantic and the Antarctic Polar Frontal Zone, and intermediate in the other six regions. The maximum fraction of model skill that may be attributable to uncertainties in both the input variables and in situ NPP measurements was nearly 72%. On average, the simplest depth/wavelength integrated models performed no worse than the more complex depth/wavelength resolved models. Ocean color models were not highly challenged in extreme conditions of surface chlorophyll-a and sea surface temperature, nor in high-nitrate low-chlorophyll waters. Water column depth was the primary influence on ocean color model performance such that average skill was significantly higher at depths greater than 250 m, suggesting that ocean color models are more challenged in Case-2 waters (coastal) than in Case-1 (pelagic) waters. Given that in situ chlorophyll-a data was used as input data, algorithm improvement is required to eliminate the poor performance of ocean color NPP models in Case-2 waters that are close to coastlines. Finally, ocean color chlorophyll-a algorithms are challenged by optically complex Case-2 waters, thus using satellite-derived chlorophyll-a to estimate NPP in coastal areas would likely further reduce the skill of ocean color models.
SATELLITE CHLOROPHYLL; SKILL ASSESSMENT; PACIFIC-OCEAN; NORTH PACIFIC; PHOTOSYNTHESIS; TEMPERATURE; VARIABILITY; SIMULATION; RATES; SEA
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This research was supported by a grant from the National Aeronautics and Space Agency Ocean Biology and Biogeochemistry program (NNG06GA03G), as well as by numerous other grants to the various participating investigators. We thank Michael Dinniman, Birol Kara, and Scott Doney for providing MLD data for WAP, the Black Sea, and BATS/NEA, respectively. We also thank Marta Estrada and Zosim Finenko for providing data from the Mediterranean and Black Seas, respectively. We are grateful to the various sampling programs (Tables 1 and S1) for allowing public access to their datasets. We are also grateful for the hard work of the many scientists who helped acquire the in situ data used in this study. This is VIMS contribution # 3132.
Saba, V. S.; Friedrichs, Marjorie A.M.; and Smith, Walker O. Jr., An evaluation of ocean color model estimates of marine primary productivity in coastal and pelagic regions across the globe (2011). BIOGEOSCIENCES, 8(2), 489-503.