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Multi-scale seasonal variability in Net Community Production and Chlorophyll in the Kuroshio Extension
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  • Sophie Clayton,
  • Hilary Ilana Palevsky,
  • LuAnne Thompson,
  • Paul D. Quay
Sophie Clayton
Old Dominion University

Corresponding Author:[email protected]

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Hilary Ilana Palevsky
Boston College, Department of Earth and Environmental Sciences
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LuAnne Thompson
University of Washington
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Paul D. Quay
University of Washington
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The Kuroshio current separates from the Japanese coast to become the Kuroshio Extension (KE) characterized by a strong latitudinal density front, high levels of mesoscale (eddy) energy, and high chlorophyll (CHL). Recent work has also shown that the KE carries subsurface nutrients into the region horizontally. While satellite measurements of CHL show evidence of the impact of eddies on the standing stock of phytoplankton, there have been very limited in situ estimates of productivity over synoptic scales in this region. Here, we present highly spatially resolved estimates of net community production (NCP) for the KE region derived from underway O2/Ar measurements made in spring, summer, and early autumn. We find large seasonal differences in the relationships between NCP, CHL, and sea level anomaly (SLA, a proxy for local thermocline depth deviations driven by mesoscale eddies). The KE front is a pronounced hotspot of NCP in spring when NCP is almost completely decorrelated with CHL. Conversely, we find that NCP and CHL are strongly correlated in summer away from the front. We explore the mechanistic underpinnings of the relationship between NCP and CHL and suggest that the KE nutrient stream as well as vertical motions associated with mesoscale eddies might be a key factor in supporting an NCP hotspot that is seasonally decoupled from CHL at the KE front. Our observations also highlight seasonal and regional (de)coupling between NCP and CHL which may impact the accuracy of CHL-based estimates of productivity.