Continental weathering fluxes during the last glacial/interglacial cycle: insights from the marine sedimentary Pb isotope record at Orphan Knoll, NW Atlantic

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• 作者：Kirsty C. Crocket^a ; ^{k.crocket@imperial.ac.uk} ; Derek Vance^b ; ^{d.vance@bristol.ac.uk} ; Gavin L. Foster^b ; ¹ ; ^{gavin.foster@noc.soton.ac.uk} ; David A. Richards^a ; ^{david.richards@bristol.ac.uk} ; Martyn Tranter^c ; ^{m.tranter@bristol.ac.uk}
• 关键词：Pb isotopes ; Laurentide ice sheet (LIS) ; Last glacial maximum ; Glacial/interglacial cycles ; Chemical weathering ; Authigenic and pre-formed FeMn oxyhydroxides
• 刊名：Quaternary Science Reviews
• 出版年：2012
• 期刊代码：78_02773791
• 类别：ear
• 出版时间：30 March, 2012
• 卷：38
• 期：Complete
• 页码：89-99
• 文件大小：1221 K

摘要

Regional weathering intensity must have changed dramatically at high latitudes during the Quaternary as a consequence of repeated continental glaciation. Investigation of these glacial/interglacial changes at high temporal resolution is possible with the recent development of Pb isotopes in FeMn oxyhydroxide phases as a proxy for region-specific weathering intensity, where increases in the radiogenic component are thought to correspond to increased continental weathering fluxes. Here we present a Pb isotope record sourced from the FeMn oxyhydroxide fraction in marine sediments from IODP Sites U1302/3 on Orphan Knoll (鈭?500聽mbsl, NW Atlantic), spanning the last 37聽ka. Located at the eastern edge of the Laurentide Ice Sheet (LIS), Site U1302/3 is well-placed to monitor changes in weathering intensity associated with LIS glacial history. Overall, the data show a close correspondence to local surface water 未¹⁸O, with least radiogenic values during times of heavy 未¹⁸O (glacial maximum) and most radiogenic values during times of light 未¹⁸O (Holocene). This supports the prediction that weathering intensity in glaciated regions of the North Atlantic correlates with the exposure age of glacial debris. Superimposed on these background trends are extreme radiogenic excursions (e.g. variation in ²⁰⁶Pb/²⁰⁴Pb from 鈭?9.2-21.0) contemporaneous with Heinrich events and the Younger Dryas. These data are substantially more radiogenic than existing records from the NW Atlantic, and most likely represent episodes of exceptionally high inputs of pre-formed FeMn oxyhydroxides during drainage of the LIS. Due to its extreme isotope composition, at least in the NW Atlantic region, Pb would appear to be a good proxy for the fluxes of weathered continental material and perhaps, by inference, nutrients to the surface ocean.