Bio-Physical Coupling in the Atlantic Three-year (2003-2005) project funded through NASA to study bio-physical coupling in the Atlantic. This project will determine the relationship between thermocline depth, sea surface height, nutrient availability, and phytoplankton blooms, and their annual to interannual scale variability, using a combination of satelite data and modeling techniques. Preliminary results show good temporal and spatial patterns of chlorophyll or phytoplankton variability in a numerical model as compared to remotely sensed observations, as seen in the figure to the right. The sea surface height variability is less well simulated, and may require more realistic model forcing. This work is in collaboration with Victoria Coles (UMCES).

EOF modes showing the seasonal spatial components for chlorophyll (top panels) and SSH (middle panels) and their principal components (bottom panels) for the satellite data (left) and for the numerical model results (right). To avoid interannual variability, the analysis was done on the climatological monthly averages of the satellite chlorophyll and SSH data, and model results using only climatological forcing.

Pacific Subtropical Blooms SeaWiFS recorded large chlorophyll blooms in the oligotrophic North Pacific Subtropical Gyre (NPSG) near 30°N in the late summer of 1997, 1999, and 2000, as seen in the figure on the left (updated figures available on my bloom page). These blooms are distinct from the surface seasonal cycle in both timing and amplitude, and they are not associated with either SSH or SST anomalies that would be indicative of changes in subsurface structure. It is hypothesized that the chlorophyll blooms are fueled by nitrogen fixation or by biologically mediated vertical fluxes of nitrogen. GRL, 30(18), 1942, doi:10.1029/2003GL017770, 2003 and paper accepted to JMS in Oct. 2005.

Global Bio-Physical coupling SSH and chlorophyll should be predominately negatively correlated because a smaller SSH implies a shallower thermocline which will increase the availability of nutrients for biological production. The global distribution of this correlation, shown to the right, was examined, with emphasis on explaining the dynamics where they appear uncoupled. The strongest absolute correlations are in the Indian and Pacific basins. Positive correlations are seen in the polar region (poleward of 40°) due to light limitations driving the ecosystem rather than nutrient limitation. GRL, 29, 10.1029/2001GL014063, 2002.

Pacific ENSO Bio-Physical coupling The impact of the 1997/1998 ENSO event on SSH and chlorophyll distributions was examined using EOF (empirical orthogonal function) analysis. The dominant chlorophyll response to the ENSO is an off-equatorial chlorophyll increase during the La Niña that extends between 2-18° latitude from the eastern Pacific to the dateline, shown to the left. The chlorophyll mode is tightly correlated to the SSH, suggesting that the chlorophyll increase is a result of the shoaling thermocline, which increases the surface nutrient supply. The better known equatorial decrease in chlorophyll during El Niño is seen in a separate EOF mode which is not correlated temporally with ENSO. Using ADCP data from the TAO/TRITON array, we showed that the cessation of the El Niño equatorial chlorophyll minimum is tied to the recommencement of the iron-rich Equatorial UnderCurrent which occurs several months prior to the termination of the El Niño. JGR, 106, 31,175-31,188, 2001.