Carbon cycling in the East Sea (Japan Sea): A review

Abstract

The East Sea (also known as the Japan Sea; hereafter, EJS) is a semi-enclosed marginal sea surrounded by the Korean Peninsula, Russia, and the Japanese Islands. The EJS is connected to the Pacific through shallow straits. Thus, the EJS has its own thermohaline circulation and the characteristic biogeochemistry. The deep overturning circulation plays a critical role in carbon cycling including absorption of atmospheric CO2 and its sequestration into the interior of the sea. The turnover time of the deep EJS (>1000 m) is ~ hundred years and probably varies depending on physical climate forcing. Thus, the effect of climate change on oceanic processes may be more easily detected in the EJS. In this paper, we summarize the current understanding of carbon cycling in the EJS. We focus especially on the Ulleung Basin in the southwestern EJS, from which more extensive data are available. Notable features of carbon cycling in the EJS include the following: primary productivity and the export/production ratio are higher than in the adjacent Pacific; the EJS is a net sink of atmospheric CO2 and anthropogenic CO2 content is ~1% of the dissolved inorganic carbon inventory; dissolved inorganic carbon in the sea interior is mostly supplied by organic matter decomposition rather than CaCO3 dissolution and thus, the deep waters are vulnerable to acidification; N:P molar ratio of the deep waters is ~13, lower than the Redfield ratio; concentration of dissolved organic carbon is significantly higher than in the oceans; and sediment resuspension and lateral transport is an important component of sinking particulate organic carbon (POC) flux. Another important feature is the temporal trends observed for the last few decades. For example, pH, calcium carbonate saturation status, and dissolved oxygen concentration in the sea interior have decreased, whereas dissolved inorganic carbon and likely, the inventory of anthropogenic CO2 have increased. These temporal trends have an implication on better understanding of the processes occurring more slowly in the oceans. Brief suggestions for future research that will improve our understanding of carbon cycling and its variability are provided at the end of the paper.

Transport of Aged Dissolved Organic Carbon via the Surface Current Revealed by Radiocarbon

“…The Δ 14 C values decreased from 500 to 1,000 m and were relatively constant below 1,000 m (mean −355 ± 13‰, n = 11) at all stations, showing no significant spatial variation. The lack of spatial variation is consistent with the rapid horizontal circulation in the deep layer, within a decade or less (note that horizontal circulation in the deep layer is much faster than the vertical turnover in the East Sea; M. Kim et al, 2022;Senjyu et al, 2005). The Δ 14 C values in the deep layer were significantly higher (by 19‰-177‰) than those of the open oceans (Figure 2b).…”

Low Sea Surface Salinity Event of the Japan Sea During the Last Glacial Maximum

“…The reemergence of microfossils in the marine sediment cores indicates that the benthic fauna have recovered with the oxygen supply from the upper water to the deep water (Itaki et al., 2004). In addition, the present‐day Japan Sea is a net sink for atmospheric CO 2 (M. Kim et al., 2022) and the hypoxic deep/bottom waters in the glacial period have been considered as a potential carbon source to the atmosphere (Dong et al., 2021; D. Li et al., 2019). With the re‐ventilation since the LGM, the changing role of the Japan Sea in the carbon cycle deserves further study.…”

A method for estimating particulate organic carbon at the sea surface based on geodetector and machine learning

“…POC accounts for approximately 10% of ocean organic carbon reservoirs (Jahnke and Richard, 1996;Loisel et al, 2002). Although POC accounts for a small proportion of the open ocean, it is an essential component of biological pumps with a high carbon turnover rate and significant carbon flux (Sarmiento, 2006;Kim et al, 2022;Lao et al, 2023a). Therefore, analyzing spatiotemporal variations in the stock and flux of POC in the ocean is of great significance for studying the marine carbon cycle.…”