Spatial variations in the Kuroshio nutrient transport from the East China Sea to south of Japan

Abstract

Abstract. Based on absolute geostrophic velocity, which was calculated using repeated hydrographic data of 39 cruises from 2000 to 2009 and nitrate concentrations measured in the same areas from 1964 to 2009, we obtained the temporally averaged nitrate flux (the product of velocity and nitrate concentration) and nitrate transport (integration of flux over one section) of four sections across the Kuroshio from the East China Sea (sections PN and TK) to an area south of Japan (sections ASUKA and 137E). In addition, we examined section OK east of the Ryukyu Islands in order to understand how the Ryukyu Current contributes to the

Seasonal and spatial contrast in the surface layer nutrient content around the Kuroshio along 138°E, observed between 2002 and 2013

“…9b). In the Kuroshio area, the vertical mixing is also developed in the upstream and the nutrient-rich surface water supplies to our investigated area by the horizontal advective transport from the upstream area (Guo et al 2013). Thus, it was suggested that the surface nutrient concentration is not always reflected in the nutrient conditions of the subsurface/intermediated water.…”

“…Thus, the horizontal advective transport was suggested to be the important factor of the nutrient concentrations, the same as for the Gulf Stream (Atkinson 1985;Lee et al 1991;Atkinson et al 1996). The horizontal advective transport from the Kuroshio area to the slope area could not be quantitatively evaluated because the nutrient concentrations were only obtained along the one latitudinal transect, and the current data were not analyzed in the present study, but Guo et al (2013) reported that the nutrient generally supplies from the slope area to the Kuroshio area along the 137°E transect. In addition, the T-S diagram in winter 2005 denotes that the Kuroshio water flows into the slope area (Fig.…”

“…Thus, it was suggested that the surface nutrient concentration is not always reflected in the nutrient conditions of the subsurface/intermediated water. Just as for the Kuroshio area, horizontal advection is important for the nutrient increase in the gyre area, because the nutrient is supplied by the Kuroshio recirculation (Guo et al 2013).…”

Biogeochemistry and ecosystems of continental margins in the western North Pacific Ocean and their interactions and responses to external forcing – an overview and synthesis

“…The mean nitrate transport of the Kuroshio along 137 • E, more downstream from the Tokara Strait, is significantly enhanced reaching an estimated value of ∼ 1000 kmol s −1 , which is comparable to the Gulf Stream transport (Pelegrí and Csanady, 1991;Pelegrí et al, 1996Pelegrí et al, , 2006Williams et al, 2011). Guo et al (2013) concludes that the Kuroshio recirculation has a significant contribution to the downstream increase of nitrate transport as occurred along the Gulf Stream (Williams et al, 2011). This is the first attempt to analyze nutrient and water mass transports in this region.…”

“…Based on the absolute geostrophic velocity, which was calculated from the repeated hydrographic data, and nitrate concentration measurements across five sections along the Kuroshio downstream during at least the last decade, Guo et al (2013) computed the nitrate transport by the Kuroshio Current from the ECS to south of Japan. Their estimated net nitrate transport crossing the PN line within the Okinawa Trough (Fig.…”