<p><strong>Abstract.</strong> The East Sea (Japan Sea) has its own deep overturning circulation, but this operates over a much shorter timescale than that in the open ocean. This allows the East Sea to be used as a natural laboratory in which to investigate potential future changes in the oceanic system. Dissolved inorganic carbon (DIC) and total alkalinity (TA) were measured in 2014 and 2017 to investigate the characteristics and temporal variability of the carbonate system of the East Sea. When the East Sea was compared with a site in the South Atlantic that has similar apparent oxygen utilization (AOU) values, it was also found to have similar DIC content of the deep waters. However, the TA levels in the East Sea were much lower than those recorded in the South Atlantic. Consequently, the DIC&#8201;/&#8201;TA ratio of the deep waters of the East Sea was high and similar to that in the North Pacific, which leaves the deep waters of the East Sea vulnerable to acidification by CO<sub>2</sub> input. High export production of organic matter, together with low rates of CaCO<sub>3</sub> export, are responsible for this high DIC&#8201;/&#8201;TA ratio. In the Ulleung Basin, in the southwest of the East Sea, the DIC and AOU of the deep waters increased between 1999 and 2014. pH decrease of the deep waters and shoaling of the carbonate saturation horizons was faster than that recorded in the oceans. Both slowed deep-water ventilation, and the intrusion of anthropogenic CO<sub>2</sub> contributed to the acidification of the East Sea. However, a clear increase in DIC from the Japan Basin to the Ulleung Basin, accompanied by a commensurate increase in AOU, was observed in 2014, whereas the meridional gradient was absent in 1999. This observation appears to reflect recent changes in deep-water ventilation, such as the re-initiation of deep-water formation. The East Sea is extremely vulnerable to acidification and should be seen as a special case of ocean acidification rather than an example of how the oceans will respond to a slowdown in ventilation in the future.</p>
Experimental determinations of nitrogen cycling in deep-sea sediments are strongly underrepresented in the databases. To investigate the total N 2 production rates and relative contribution of denitrification and anaerobic ammonium oxidation (anammox) to benthic fixed-N removal processes, we conducted ). The contribution of anammox to the total N 2 production (ra) increased with increasing water depth from the shelf (ca. 17%) to the basin (ca. 56%). The enhanced ra in the center of the UB was associated with an increased availability of nitrite for anammox, which was likely a result of the competitive suppression of denitrification by manganese reduction under MnO 2 -rich conditions. Our results emphasize the importance of anammox as a sink for reactive nitrogen in deep-sea sediments and contribute toward a mechanistic understanding of the factors controlling benthic reactive nitrogen loss in the ocean.
The East Sea (also known as the Japan Sea; hereafter, EJS) has its own deep overturning circulation, that operates over a centurial timescale compared with a millennial timescale in the ocean. This allows the EJS to be used as a natural laboratory for investigating potential future changes in the oceanic system. Dissolved inorganic carbon (DIC), total alkalinity (TA), and pH were measured in 2019 in a wide area of the EJS to investigate the characteristics and changes of the carbonate system since the last extensive survey in 1999. In the layer below ∼1,000 m, DIC and apparent oxygen utilization (AOU) was uniform implying rapid horizontal mixing within a few years. Since 1999, DIC concentration increased by ∼11 μmol kg–1 in the layer deeper than 500 m. This increase accompanied a commensurate increase in AOU with the canonical ratio of 1.3, indicating that the accumulation of DIC was supplied from organic matter decomposition. This observation is consistent with a previous study suggesting that the slowed deep water ventilation was the cause of the increase in AOU and fast acidification. In the EJS, increase in DIC from the surface water to deep waters is much higher than that in TA, which is caused by high primary productivity and export production together with low rates of CaCO3 export. Thus, the DIC/TA ratio of deep waters, an indicator of vulnerability to acidification, is high. A recently reported change in deep water ventilation, namely, re-initiation of deep water formation reaching deeper depths to the Deep Water and the Bottom Water, implies that unexpected changes in the carbonate system may be detected in the future, which needs to be further monitored.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.