Spatial variations of 226Ra, 228Ra, and 228Th activities in seawater from the eastern East China Sea

Changes in East Asian summer monsoon precipitation during the Holocene deduced from a freshwater flux reconstruction of the Changjiang (Yangtze River) based on the oxygen isotope mass balance in the northern East China Sea

“…A core material of KY07-04-01 (31 • 38.35 N, 128 • 56.64 E; 758 m water depth), which was retrieved from the Danjo Basin, at the northern edge of the Okinawa Trough (Kubota et al, 2010) was used for Mg / Ca and δ 18 O analyses of planktic foraminifer. It is confirmed that CDW can reach to the core site across the shelf break during summer based on 226 Ra and 228 Ra measurement (Inoue et al, 2012). Inoue et al (2012) also calculated the relative contribution of the Changjiang freshwater in this area as approximately 2-3 % in July and October using salinity and 228 Ra concentration data from 2008 to 2010.…”

228Ra/226Ra ratio and 7Be concentration in the Sea of Japan as indicators for water transport: comparison with migration pattern of Fukushima Dai-ichi NPP-derived 134Cs and 137Cs

“…Negative anomalies of 228 Ra/ 226 Ra ratios on the eastern-side of Tsushima Island (1.0 at OS11-A6) and Iki Island (0.8 at OS11-A2) are considered to reflect primarily reverse stream from the Sea of Japan to the Tsushima Strait (Takikawa et al, 2005). This indicates that the mixing ratio of the 228 Ra-rich ECS continental shelf water was lower than that of the 228 Ra-poor Kuroshio water on the Japanese Archipelago side of the Sea of Japan (Inoue et al, 2012a). The 134 Cs concentrations of surface waters were below the detectable limit (<0.1 mBq/L) along the entire transect, reflecting little contamination by the FDNPP-derived radiocesium in waters from the ECS (Inoue et al, 2012c).…”

“…At the Japanese Archipelago side of the Sea of Japan, 228 Ra/ 226 Ra ratios in surface water are useful for investigating mass water movement for several reasons. 1) The 228 Ra/ 226 Ra ratios of the Kuroshio water (w0.2) and the ECS continental shelf water (w3.5), the two dominant sources of the TWC in the Sea of Japan, are markedly different (Nozaki et al, 1989;Inoue et al, 2012a). 2) In the Tsushima Strait, the 228 Ra/ 226 Ra ratios in surface water exhibit large seasonal changes (w0.5e3), reflecting the mixing ratio of the two currents (Inoue et al, 2010).…”

Millennial-scale variability of East Asian summer monsoon inferred from sea surface salinity in the northern East China Sea (ECS) and its impact on the Japan Sea during Marine Isotope Stage (MIS) 3

“…The lower SSS during the summer suggests that river discharge due to the EASM dominates the seasonal changes in the Kuroshio (Sun et al 2005); otherwise, the strengthened Kuroshio results in increased SSS during summer, when its volume transport is the largest (Ichikawa and Beardsley 1993;Andres et al 2008). It was demonstrated that the CDW reaches the easternmost part of the northern ECS across the shelf break during summer, based on 226 Ra and 228 Ra measurements of surface waters (Inoue et al 2012). Inoue et al (2012) calculated the relative contribution of the Changjiang freshwater in this area as approximately 2-3% in July and October, based on mass balance calculation of the SSS and 228 Ra concentration of surface water samples collected between 2008 and 2010.…”

“…It was demonstrated that the CDW reaches the easternmost part of the northern ECS across the shelf break during summer, based on 226 Ra and 228 Ra measurements of surface waters (Inoue et al 2012). Inoue et al (2012) calculated the relative contribution of the Changjiang freshwater in this area as approximately 2-3% in July and October, based on mass balance calculation of the SSS and 228 Ra concentration of surface water samples collected between 2008 and 2010. Instrumental SSS data around the core site shows a negative correlation with the Changjiang River discharge during the wet season for the past 50 years (Kubota et al 2015), confirming that the studied site is an appropriate location to reconstruct SSS.…”