Journal of Geophysical Research: Oceans
The Kuroshio current separates from the Japanese coast to become the eastward flowing Kuroshio Extension (KE) characterized by a strong latitudinal density front, high levels of mesoscale (eddy) energy, and high chlorophyll a (Chl). While satellite measurements of Chl show evidence of the impact of mesoscale eddies on the standing stock of phytoplankton, there have been very limited synoptic, spatially resolved in situ estimates of productivity in this region. Here, we present underway measurements of oxygen/argon supersaturation (ΔO2/Ar), a tracer of net biological productivity, for the KE made in spring, summer, and early autumn. We find large seasonal differences in the relationships between ΔO2/Ar, Chl, and sea level anomaly (SLA), a proxy for local thermocline depth deviations driven by mesoscale eddies derived from satellite observations. We show that the KE is a pronounced hotspot of high ΔO2/Ar in spring, but corresponding surface Chl values are low and have no correlation with ΔO2/Ar. In summer, there is a hotspot of productivity associated with the Oyashio front, where ΔO2/Ar and Chl are strongly positively correlated. In autumn, ΔO2/Ar and Chl are consistently low throughout the region and also positively correlated. By combining our analysis of the in situ ΔO2/Ar data with complementary Argo, BGC-Argo, repeat hydrography, and SLA observations, we infer the combination of physical and biological controls that drive the observed distributions of ΔO2/Ar and Chl. We find that the KE and Oyashio currents both act to supply nutrients laterally, fueling regions of high productivity in spring and summer, respectively.
Original Publication Citation
Clayton, S., Palevsky, H. I., Thompson, L., & Quay, P.D. (2021). Synoptic mesoscale to basin scale variability in biological productivity and chlorophyll in the Kuroshio Extension region. Journal of Geophysical Research: Oceans, 126, e2021JC017782. https://doi.org/10.1029/2021JC017782
Clayton, Sophie; Palevsky, Hilary I.; Thompson, LuAnne; and Quay, Paul D., "Synoptic Mesoscale to Basin Scale Variability in Biological Productivity and Chlorophyll in the Kuroshio Extension Region" (2021). OES Faculty Publications. 420.
Sea Level Anomaly (SLA) data files
mdt_cnes_cls2013_global.nc (24328 kB)
Mean Dynamic Topography (MDT) data file
MLD_datafiles.zip (172 kB)
MILAGPV mixed layer depth (MLD) data files
JMA_cruises.zip (1573 kB)
Nitrate data from JMA cruises
Kuro_ARGO_nitrate.zip (830 kB)
Biogeochemical ARGO float data files