講演情報
[18p-D62-17]Vertical distributions of 129I and insight of current in the Southern Canada Basin
〇(M1)Xinru Xu1, Yuanzhi Qi1, Takeyasu Yamagata1, Hiroyuki Matsuzaki1, Yuichiro Kumamoto2 (1.Univ. of Tokyo, 2.JAMSTEC)
キーワード：
Marine radioactivity、129I、Arctic Ocean
The Sellafield facility in the UK and the La Hague facility in France are the predominant contributors to 129I discharges into the ocean. 129I subsequently travels through the North Atlantic Ocean to the Arctic Ocean, eventually reaching the Canadian Basin. 129I has been widely utilized in studies of ocean currents and water mass origins, providing significant insights into current systems.
This study investigated two depth profiles at stations St.14 (72.4°N, 155.4°W) and St.32 (74.0°N, 162.0°W) in the region. Vertically, the 129I/127I ratio initially decreased from the surface layer to a minimum value of 2×10–10, then increased to a maximum value of 138×10–10 (Figure 1). It remained relatively stable within a depth range to 1000 m, before gradually decreasing with further depth (Figure 1). Based on these ratio data, the water source composition is categorized into a freshwater mixed layer (0–20 m), Pacific-origin water (20–100 m), Atlantic-origin water (200–1000 m), and bottom aged water mass (near the seabed). Vertical mixing occurs between these water masses. Further analysis of the Atlantic-origin water layer revealed a distinct peak in the 129I/127I ratio at approximately 250 m (Figure 2). Previous studies have identified two primary currents from the Atlantic Ocean: the Fram Strait Branch Water (FSBW), with a core at around 400 m, and the Barents Sea Branch Water (BSBW), with a core at about 800 m. However, this observed peak at 250 m is not attributable to either FSBW or BSBW and exhibits a higher signal than both. This suggests the possibility of an unknown 129I source in the Arctic or an unrecognized Atlantic Ocean current carrying a high 129I signal.
This study investigated two depth profiles at stations St.14 (72.4°N, 155.4°W) and St.32 (74.0°N, 162.0°W) in the region. Vertically, the 129I/127I ratio initially decreased from the surface layer to a minimum value of 2×10–10, then increased to a maximum value of 138×10–10 (Figure 1). It remained relatively stable within a depth range to 1000 m, before gradually decreasing with further depth (Figure 1). Based on these ratio data, the water source composition is categorized into a freshwater mixed layer (0–20 m), Pacific-origin water (20–100 m), Atlantic-origin water (200–1000 m), and bottom aged water mass (near the seabed). Vertical mixing occurs between these water masses. Further analysis of the Atlantic-origin water layer revealed a distinct peak in the 129I/127I ratio at approximately 250 m (Figure 2). Previous studies have identified two primary currents from the Atlantic Ocean: the Fram Strait Branch Water (FSBW), with a core at around 400 m, and the Barents Sea Branch Water (BSBW), with a core at about 800 m. However, this observed peak at 250 m is not attributable to either FSBW or BSBW and exhibits a higher signal than both. This suggests the possibility of an unknown 129I source in the Arctic or an unrecognized Atlantic Ocean current carrying a high 129I signal.
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