Time Series of Bio-Optical Properties in a Subtropical Gyre: Implications for the Evaluation of Interannual Trends of Biogeochemical Properties
NAVAL RESEARCH LAB STENNIS SPACE CENTER MS OCEANOGRAPHY DIV
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With a validated Quasi-Analytical Algorithm, an 11 year 1998-2008 monthly time series of the primary optical properties of waters in the center of the South Pacific gyre was developed from Sea-viewing Wide Field-of-view Sensor SeaWiFS and Moderate Resolution Imaging Spectroradiometer MODIS. Also derived are chlorophyll a Chi a concentrations with the operational empirical algorithms for SeaWiFS and MODIS. The optical properties include the absorption coefficient at 443 nm of phytoplankton aph and that of the combination of detritus and gelbstoff adg. From these time series, we further derived their annual background summer low and seasonal intensity the difference between winter high and summer low. These time series show that 1 the optical properties have different seasonal and interannual variations, indicating different dynamics of these properties in the subtropical gyre 2 there is a decreasing trend r-squared 0.24 of the background apn in the 1998-2008 period and an increasing trend of the aph seasonal intensity r-squared 0.11 for this period, and both trends are not statistically significant 3 the aph time series agrees with the Chi a time series at the seasonal scale, but differs with respect to interannual variations and 4 different interannual trends could be inferred with different time frames. These results emphasize that it is difficult to draw unequivocal conclusions about long-term trends of biogeochemical properties in the oceans with the current relatively short bio-optical records. To clarify and predict such trends, it is critical to get a full account of the forces that are responsible for the seasonal and interannual variations of these properties.
- Physical and Dynamic Oceanography
- Optical Detection and Detectors
- Atomic and Molecular Physics and Spectroscopy