Radium Isotopes Across the Arctic Ocean Show Time Scales of Water Mass Ventilation and Increasing Shelf Inputs
Radium Isotopes Across the Arctic Ocean Show Time Scales of Water Mass Ventilation and Increasing Shelf Inputs
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DOI：
10.1029/2018jc013888
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发表时间：
2018-07
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通讯作者：
M. M. Rutgers van der Loeff-M.;L. Kipp;M. Charette;W. Moore;Erin E. Black;I. Stimac;A. Charkin;D. Bauch;Ole Valk;M. Karcher;T. Krumpen;N. Casacuberta;W. Smethie;R. Rember
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作者：
M. M. Rutgers van der Loeff-M.;L. Kipp;M. Charette;W. Moore;Erin E. Black;I. Stimac;A. Charkin;D. Bauch;Ole Valk;M. Karcher;T. Krumpen;N. Casacuberta;W. Smethie;R. Rember
在GEOTRACES巡航PS94和HLY1502（2015）期间测量的地表水中228Ra的第一个完整跨北极剖面显示出与跨极漂移最大活动一致的分布。从2007年到2011年到2015年，北极中部的活动有所增加。228Ra输入的增加是由于更长无冰季节导致大陆架上更强的波浪作用。228Th/228Ra比值的降低可能是由于在大陆架上的清除使228Th耗尽的地表水更快地通过所致。在Amundsen盆地的中间水域（< 1500米）观测到的228Ra活动可以用大陆架水在大约15 - 18年的时间尺度上的通风来解释，这与基于SF6和129I/236U的估计非常吻合。在校正了由于228Ra和228Th衰变时间相似而产生的固有过剩后，混合层以下1500m深度的228Th过剩可以补充234和210Po作为出口生产的示踪剂。我们用Th/Ra剖面模型表明，1500米以下的228Th/228Ra比例不适合用于此目的，因为它是228Ra水平供应与228Th颗粒垂直通量之间的微妙平衡。226Ra在Makarov盆地深部的富集与Ba的富集无关，因此可以归因于底部沉积物中23030的衰变供应。我们估计马卡罗夫-加拿大盆地深处的通风时间为480年，与之前使用其他示踪剂的估计非常吻合。
The first full transarctic section of 228Ra in surface waters measured during GEOTRACES cruises PS94 and HLY1502 (2015) shows a consistent distribution with maximum activities in the Transpolar Drift. Activities in the central Arctic have increased from 2007 through 2011 to 2015. The increased 228Ra input is attributed to stronger wave action on shelves resulting from a longer ice‐free season. A concomitant decrease in the 228Th/228Ra ratio likely results from more rapid transit of surface waters depleted in 228Th by scavenging over the shelf. The 228Ra activities observed in intermediate waters (< 1500m) in the Amundsen Basin are explained by ventilation with shelf water on a time scale of about 15‐18 years, in good agreement with estimates based on SF6 and 129I/236U. The 228Th excess below the mixed layer up to 1500m depth can complement 234Th and 210Po as tracers of export production, after correction for the inherent excess resulting from the similarity of 228Ra and 228Th decay times. We show with a Th/Ra profile model that the 228Th/228Ra ratio below 1500m is inappropriate for this purpose because it is a delicate balance between horizontal supply of 228Ra and vertical flux of particulate 228Th. The accumulation of 226Ra in the deep Makarov Basin is not associated with an accumulation of Ba and can therefore be attributed to supply from decay of 230Th in the bottom sediment. We estimate a ventilation time of 480 years for the deep Makarov‐Canada Basin, in good agreement with previous estimates using other tracers.