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Rutgers van der Loeff, Michiel; Kipp, Lauren; Charette, Matthew A.; Moore, Willard S.; Black, Erin; Stimac, Ingrid; Charkin, Alexander; Bauch, Dorothea; Valk, Ole; Karcher, Michael; Krumpen, Thomas; Casacuberta, Núria; Smethie, William; Rember, Robert

Radium Isotopes Across the Arctic Ocean Show Time Scales of Water Mass Ventilation and Increasing Shelf Inputs

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  • Media type: E-Article
  • Title: Radium Isotopes Across the Arctic Ocean Show Time Scales of Water Mass Ventilation and Increasing Shelf Inputs
  • Contributor: Rutgers van der Loeff, Michiel; Kipp, Lauren; Charette, Matthew A.; Moore, Willard S.; Black, Erin; Stimac, Ingrid; Charkin, Alexander; Bauch, Dorothea; Valk, Ole; Karcher, Michael; Krumpen, Thomas; Casacuberta, Núria; Smethie, William; Rember, Robert
  • imprint: American Geophysical Union (AGU), 2018
  • Published in: Journal of Geophysical Research: Oceans
  • Language: English
  • DOI: 10.1029/2018jc013888
  • ISSN: 2169-9275; 2169-9291
  • Origination:
  • Footnote:
  • Description: <jats:title>Abstract</jats:title><jats:p>The first full transarctic section of <jats:sup>228</jats:sup>Ra 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 <jats:sup>228</jats:sup>Ra input is attributed to stronger wave action on shelves resulting from a longer ice‐free season. A concomitant decrease in the <jats:sup>228</jats:sup>Th/<jats:sup>228</jats:sup>Ra ratio likely results from more rapid transit of surface waters depleted in <jats:sup>228</jats:sup>Th by scavenging over the shelf. The <jats:sup>228</jats:sup>Ra activities observed in intermediate waters (&lt;1,500 m) 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 SF<jats:sub>6</jats:sub> and <jats:sup>129</jats:sup>I/<jats:sup>236</jats:sup>U. The <jats:sup>228</jats:sup>Th excess below the mixed layer up to 1,500 m depth can complement <jats:sup>234</jats:sup>Th and <jats:sup>210</jats:sup>Po as tracers of export production, after correction for the inherent excess resulting from the similarity of <jats:sup>228</jats:sup>Ra and <jats:sup>228</jats:sup>Th decay times. We show with a Th/Ra profile model that the <jats:sup>228</jats:sup>Th/<jats:sup>228</jats:sup>Ra ratio below 1,500 m is inappropriate for this purpose because it is a delicate balance between horizontal supply of <jats:sup>228</jats:sup>Ra and vertical flux of particulate <jats:sup>228</jats:sup>Th. The accumulation of <jats:sup>226</jats:sup>Ra in the deep Makarov Basin is not associated with an accumulation of Ba and can therefore be attributed to supply from decay of <jats:sup>230</jats:sup>Th 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.</jats:p>
  • Access State: Open Access