Modulation of decadal oscillation on surface chlorophyll in the Kuroshio Extension

Abstract

[1] In the study, the responses of chlorophyll to decadal oscillations of Kuroshio Extension (KE) between two dynamical states are investigated using satellite data. Associated with the KE stable and unstable states, the surface chlorophyll south of 35 N also undergoes two different contrast patterns: low (high) chlorophyll ( 12% relative to multiyear mean) corresponding to strengthened (weakened) KE jet, i.e., stable (unstable) KE. Two distinct seesaw patterns exist on the north and south side of 35 N for both chlorophyll and sea level anomaly and on the east and west side of 153 E for both chlorophyll and eddy kinetic energy. Similarly, the magnitude of spring bloom was also modulated by decadal variations of KE. The spring bloom was suppressed (enhanced)

Mixed‐layer carbon cycling at the Kuroshio Extension Observatory

“…During negative PDO phases, the KE jet is weakened and located south of its mean position. This destabilizes the southern recirculation gyre and leads to higher eddy activity that is associated with elevated surface chlorophyll concentrations as a result of enhanced nutrient supply [ Lin et al ., ]. Over the course of our study period the KE jet was in an unstable state from 2007 to 2009 and was in a stable state from 2010 to 2014 [ Oka et al ., ]; therefore, we might anticipate elevated biological activity, and NCP, before 2010.…”

“…Unstable states are associated with southward migration of the KE jet that results in a reduced southern recirculation gyre, higher eddy activity, negative sea surface height (SSH) anomalies, and smaller mode water formation volumes [ Oka et al ., ]. Divergent surface flow associated with this eddy activity gives rise to elevated surface chlorophyll concentrations and net primary production thought to be fueled by enhanced nutrient supply [ Lin et al ., ]. In the stable state, the KE jet is located farther north and the recirculation gyre is more pronounced, as evidenced by positive sea surface height (SSH) anomalies.…”

“…In the stable state, the KE jet is located farther north and the recirculation gyre is more pronounced, as evidenced by positive sea surface height (SSH) anomalies. Larger volumes of mode water formation have been observed during these stable periods [ Oka et al ., ] when convergence depresses the nutricline and surface chlorophyll concentrations are lower [ Lin et al ., ].…”

Physical oceanographic conditions around the S1 mooring site

“…In surface chlorophyll a (Fig. 10b), there was a variability possibly associated with a decadal-scale change (e.g., Lin et al 2014;Kouketsu et al 2015). The chlorophyll a anomaly tended to be negative (positive) when the KE was stable (unstable) in 2002-2005 (2006-2009).…”

Juvenile recruitment in loggerhead sea turtles linked to decadal changes in ocean circulation

“…As a result, a few years after the start of a positive PDO phase, the KEC tends to be weaker, less stable and located a few degrees south from its average position, with the reverse observed a few years after the start of a negative PDO phase (Qiu, ; Qiu & Chen, ; Taguchi et al ., ). The TZCF also responds to the PDO and tends to have a more southerly position (by about 1°) during a positive PDO phase in the central Pacific and a few years after the start of that phase in the KEC region (Chai et al ., ; Bograd et al ., ; Lin et al ., ). The decadal variability of KEC and TZCF is, however, not entirely dictated by the PDO as they are also influenced by secondary climate modes (such as the North Pacific Gyre Oscillation) as well as by the internal variability of the KEC itself (Di Lorenzo et al ., , ; Ceballos et al ., ; Qiu & Chen, ; Lin et al ., ; Pierini, ; Qiu et al ., ).…”