Simulated decadal variations of surface and subsurface phytoplankton in the upstream Kuroshio Extension region

Abstract

Using outputs from an ecosystem model embedded in an eddy-resolving ocean general circulation model that can realistically simulate decadal modulations of the Kuroshio Extension (KE) between stable and unstable states, decadal variations of phytoplankton concentration in the upstream KE region are investigated. During stable states of the KE, surface phytoplankton concentrations are anomalously suppressed to the south of the KE front, while those to the north are anomalously enhanced. Although the surface phytoplankton concentration anomalies are prominent only during winter to spring, significant subsurface anomalies centered around 60 m depth persist even in summer and autumn. Anomalies persist throughout the year in phytoplankton biomass integrated over the upper 100 m despite the strong surface anomalies during the spring bloom season. An analysis of nitrogen concentration anomalies suggests that the vertical movement of the isopycnal surfaces, vertical mixing of nutrients, and meridional shifts in the KE jet contribute to the anomalous phytoplankton biomass.

Machine learning–based feature prediction of convergence zones in ocean front environments

“…This region stands out as a notable source of marine energy and exhibits extensive biogeochemical cycling, rendering it an area of great scientific interest. The KE area not only serves as a significant source of marine and airborne energy (Zhou and Cheng, 2022;Yu et al, 2023)but also facilitates rich biogeochemical cycling (Tozuka et al, 2022). Consequently, this subject has been a focus of intense research in recent years.…”

Skillful Multiyear Prediction of the Kuroshio and Gulf Stream Jets and Eddy Activity

“…Also, both large‐ and small‐scale oceanic features in the WBC regions are observed to exhibit temporal variations over a wide range of timescales (Frankignoul et al., 2001; Kelly et al., 2010; Kohyama et al., 2021; Kwon et al., 2010; Qiu, 2002; Taylor & Stephens, 1998; among others). Such anomalous changes in the WBC jets and associated modulations in mesoscale eddy fields induce significant sea surface temperature anomalies and thereby affect regional and large‐scale atmospheric circulation (Frankignoul et al., 2011; Joyce et al., 2009; Ma et al., 2015; Smirnov et al., 2015; Taguchi et al., 2012), marine ecosystems (Lin et al., 2014; Nye et al., 2011; Tozuka et al., 2022; Yatsu et al., 2013), and the occurrence of extreme events such as marine heat waves (Miyama et al., 2021). Thus, an accurate prediction of spatiotemporal variations in jets and eddies in WBC regions is of major importance for both scientific and socioeconomic reasons.…”

Role of Mixed Layer Depth in Kuroshio Extension Decadal Variability

“…Decadal variations in the North Pacific sea surface temperature (SST) have received much attention because of their impacts on global climate and marine ecosystems (Mantua et al., 1997; Miller et al., 2004; Newman et al., 2016; Tozuka et al., 2022). Strong decadal SST anomalies tend to be confined to the frontal region east of Japan associated with the Kuroshio Extension (KE) (Nakamura et al., 1997; Nonaka et al., 2006).…”