Nutrient pumping/advection by propagating Rossby Waves in the Kuroshio Extension

Abstract

Ten years (1998–2007) of sea-level anomalies (SLA) from multiple satellite altimeters and chlorophyll -a concentration from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) were used to detect eddy pumping/advection of nutrients by the action of propagating Rossby waves in the Kuroshio Extension (KE) region near 35 oN after the seasonal SeaWiFS chlorophyll -a (Chl -a) concentrations cycles and annual changes of altimeter SLA were eliminated. Spatial structure of Chl -a anomalies to the seasonal cycle is examined in relation to altimeter eddy structure. Eddy propagation speeds and scales by the Rossby waves are also identified. Chl -a structure is evident during the spring bloom period with a scale around 460 km. Cold-core (cyclonic) rings correspond to areas of high Chl -a concentrations. Warm-core (anticyclonic) rings relate to areas of low Chl -a concentration. Chl -a anomalies and SLA have an overall modest negative correlation coefficient of r=−0.45, which may imply the co-existence of both eddy pumping and eddy advection mechanisms in the KE region. Swirl currents between eddies redistribute surface chlorophyll concentrations and can spatially bias maximum and minimum concentration levels off eddy center. The correlation coefficient has seasonal fluctuations. In the western KE region, it varies from high negative correlation ( r=−0.70) in April and September (eddy pumping dominant) to low negative correlation ( r=−0.33) in February and March (eddy advection dominant). In the eastern KE region, it varies from high negative correlation ( r=−0.67) in February to low negative correlation ( r=−0.42) in December. It is noted that the characteristic wavelengths of the SLA and Chl -a features, and the seasonality of the correlation between these two variables have not been previously documented.