Shelf-basin exchange times of Arctic surface waters estimated from 228Th/228Ra disequilibrium
Shelf-basin exchange times of Arctic surface waters estimated from 228Th/228Ra disequilibrium
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DOI：
10.1029/2011jc007478
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发表时间：
2012-03
影响因子：
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通讯作者：
M. Loeff;P. Cai;I. Stimac;D. Bauch;C. Hanfland;Tobias Roeske;S. B. Moran
中科院分区：
文献类型：
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作者：
M. Loeff;P. Cai;I. Stimac;D. Bauch;C. Hanfland;Tobias Roeske;S. B. Moran
经极漂移强烈富集在宽广的北极大陆架上积累的228Ra，并伴随着随后的快速近海运输。我们提出了北极中部和喀拉海和拉普捷夫海极地探险的新数据。由于226Ra在太平洋水域的活度比大西洋水域高30%，因此我们在用226Ra正态化228Ra时对太平洋混合物中的226Ra进行了校正。228Ra衰变作为年龄标记的使用主要取决于源活动在空间和时间上的恒定性，这一条件尚未得到充分的测试。228Ra在穿越中央盆地的过程中会衰减，228Th的向内生长可以提供另一种年龄标志。中部盆地228Th/228Ra活度比值高（AR = 0.8 ~ 1.0）与基于水平涡动扩散的混合模式不相容。平流模式预测228Th增长到平衡AR，其值取决于清除制度。罗蒙诺索夫海岭（Lomonosov Ridge）上空的低AR （AR = 0.5）可能是由于快速运输（没有清除的最低年龄为1.1年）或清除增强所致。悬浮颗粒物负荷（来自波束传输和颗粒234）和总234耗竭数据表明，尽管北极中部的清除量极低，但在罗蒙诺索夫海岭的清除量增加，使3年的年龄更有可能。228Ra衰变和228Th长入的综合资料证实了欧亚盆地东部地表水存在一个停留时间至少为3年的再循环环流。
The transpolar drift is strongly enriched in 228Ra accumulated on the wide Arctic shelves with subsequent rapid offshore transport. We present new data of Polarstern expeditions to the central Arctic and to the Kara and Laptev seas. Because 226Ra activities in Pacific waters are 30% higher than in Atlantic waters, we correct 226Ra for the Pacific admixture when normalizing 228Ra with 226Ra. The use of 228Ra decay as age marker critically depends on the constancy in space and time of the source activity, a condition that has not yet adequately been tested. While 228Ra decays during transit over the central basin, ingrowth of 228Th could provide an alternative age marker. The high 228Th/228Ra activity ratio (AR = 0.8–1.0) in the central basins is incompatible with a mixing model based on horizontal eddy diffusion. An advective model predicts that 228Th grows to an equilibrium AR, the value of which depends on the scavenging regime. The low AR over the Lomonosov Ridge (AR = 0.5) can be due to either rapid transport (minimum age without scavenging 1.1 year) or enhanced scavenging. Suspended particulate matter load (derived from beam transmission and particulate 234Th) and total 234Th depletion data show that scavenging, although extremely low in the central Arctic, is enhanced over the Lomonosov Ridge, making an age of 3 years more likely. The combined data of 228Ra decay and 228Th ingrowth confirm the existence of a recirculating gyre in the surface water of the eastern Eurasian Basin with a river water residence time of at least 3 years.