15:45 〜 16:00
[MIS12-06] The Last 5,000 years BP paleoceanographic changes off Wakasa Bay (Japan Sea) as inferred by radiolarian assemblages
キーワード：Japan Sea、Holocene、Tsugaru Current、Winter Monsoon
The Japan Sea is a semi-enclosed marginal sea located in the mid-latitudes of the northwestern Pacific. It is isolated from the intermediate and deep waters of the North Pacific by straits with depths of less than 130 m. The only current flowing into the Japan Sea is the Tsushima Warm Current, which transports heat, freshwater, and nutrients from the East China Sea, influenced by the East Asian summer monsoon, and controls the marine environment and ecosystem of the Japan Sea. In contrast, during the East Asian winter monsoon, cooling of surface waters occurs in the northern part of the Japan Sea, leading to the formation of deep waters and the supply of dissolved oxygen to the intermediate and deep waters of the Japan Sea. This intermediate and deep water, known as Japan Sea Proper Water, has high dissolved oxygen concentrations, high biodiversity, and very low water temperatures, and its residence time is about 100 years.
The surface water temperature increase rate in the Japan Sea over the past 100 years due to the influence of global warming is approximately +1.80℃, which is about three times faster than the global average of +0.56℃ (IPCC, 2018, etc.). In particular, the winter surface water temperature increase rate is +2.45℃, indicating the most vulnerable impact of global warming. When winter cooling of surface waters weakens, there is concern that the supply of dissolved oxygen to the intermediate and deep waters may cease due to weakened ventilation, potentially leading to mass extinction of deep-sea ecosystems, including deep-sea organisms and benthic fauna.
The objective of this study is to analyze environmental changes over the past 5,000 years in the Japan Sea, distinguishing between anthropogenic and natural factors and providing valuable insights. We conducted successful piston coring during the KR15-10 WB6_PL cruise at various sites in Wakasa Bay of the Japan Sea. Specifically, we focused on analyzing the KR15-10 WB6_PL core at 2 cm intervals (approximately every 80 years) to assess variations in the Tsushima Warm Current and winter monsoon over the past 5,000 years. While the sampling resolution may be somewhat crude, it enables a comparison of paleoceanographic changes since Japan's industrial revolution with those prior to it, allowing us to gain a better understanding of how society may have impacted regional oceanography and marine biota. To achieve this, we propose to analyze changes in radiolarian species assemblages, as they have proven to be a suitable proxy for paleoceanographic studies in the Japan Sea.
The surface water temperature increase rate in the Japan Sea over the past 100 years due to the influence of global warming is approximately +1.80℃, which is about three times faster than the global average of +0.56℃ (IPCC, 2018, etc.). In particular, the winter surface water temperature increase rate is +2.45℃, indicating the most vulnerable impact of global warming. When winter cooling of surface waters weakens, there is concern that the supply of dissolved oxygen to the intermediate and deep waters may cease due to weakened ventilation, potentially leading to mass extinction of deep-sea ecosystems, including deep-sea organisms and benthic fauna.
The objective of this study is to analyze environmental changes over the past 5,000 years in the Japan Sea, distinguishing between anthropogenic and natural factors and providing valuable insights. We conducted successful piston coring during the KR15-10 WB6_PL cruise at various sites in Wakasa Bay of the Japan Sea. Specifically, we focused on analyzing the KR15-10 WB6_PL core at 2 cm intervals (approximately every 80 years) to assess variations in the Tsushima Warm Current and winter monsoon over the past 5,000 years. While the sampling resolution may be somewhat crude, it enables a comparison of paleoceanographic changes since Japan's industrial revolution with those prior to it, allowing us to gain a better understanding of how society may have impacted regional oceanography and marine biota. To achieve this, we propose to analyze changes in radiolarian species assemblages, as they have proven to be a suitable proxy for paleoceanographic studies in the Japan Sea.