Abstract
Sixteen years of satellite observational data in the Northwestern Pacific Ocean are used to describe the variability in the sea surface temperature (SST) gradient and its impact on chlorophyll-a concentrations (Chl-a). Spatially, a meridional dependence is identified in which the SST gradient increases to the north in association with elevated Chl-a. Temporally, the seasonal variability shows a large SST gradient and high Chl-a in winter and spring, while the SST gradient and Chl-a are much lower in summer. The seasonal variability in Chl-a leads the variability in the SST gradient by one month. A significant correlation between the SST gradient and Chl-a in the anomalous field is obtained only in the western section of the Kuroshio extension (KE) and the highest correlation is identified without any lags. An index for the section is defined as the proportion of the number of times that the SST gradient magnitude is anomalously large in each year, and the index is highly related to the stability of the KE and has a prominent influence on Chl-a in the region. An anomalously large positive (negative) SST gradient magnitude occurs when the KE is unstable (stable) and the corresponding Chl-a is high (low).
Highlights
In the northwestern Pacific Ocean, there are two major currents, the Kuroshio current and the Oyashio current, which flow from the southwest and northeast, respectively [1].These currents are crucial for the meridional transport of water and heat in the region and play an important role in global circulation [2]
The current study focuses on the Kuroshio extension (KE) region, in the northwestern Pacific Ocean at mid-latitudes, where the upper ocean is characterized as highly dynamic with prominent variability
As a typical mid-latitude area, the seasonal cycle dominates the entire region, which is revealed by the distinctive seasonal pattern in Chl-a
Summary
In the northwestern Pacific Ocean, there are two major currents, the Kuroshio current and the Oyashio current, which flow from the southwest and northeast, respectively [1].These currents are crucial for the meridional transport of water and heat in the region and play an important role in global circulation [2]. As one of the major western boundary currents in the world, the Kuroshio current is characterized by warm temperatures and high salinities [4]. It can extend more than 1000 m in depth and transport substantial quantities of water, i.e., 42 Sv excluding the local recirculation, and energy into the midlatitude region [5]. The annually averaged transport of the Oyashio current is 31 Sv, with a larger value during winter [7] Both currents converge east of Japan, and the confluence flows eastward, where it is subsequently referred to as the Kuroshio extension (KE) [8].
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