Neogene ice volume and ocean temperatures: Insights from infaunal foraminiferal Mg/Ca paleothermometry
Neogene ice volume and ocean temperatures: Insights from infaunal foraminiferal Mg/Ca paleothermometry
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DOI：
10.1002/2015pa002833
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发表时间：
2015-11
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影响因子：
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通讯作者：
C. Lear;H. Coxall;G. Foster;D. Lunt;E. Mawbey;Y. Rosenthal;S. Sosdian;E. Thomas;P. Wilson
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文献类型：
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作者：
C. Lear;H. Coxall;G. Foster;D. Lunt;E. Mawbey;Y. Rosenthal;S. Sosdian;E. Thomas;P. Wilson
南极大陆规模的冰川作用通常被认为是在始新世-渐新世过渡开始的，但其随后的演变受到很大的限制。我们重建底层水温和全球冰量的变化从0到17？妈妈吸毒？~（18）O与底栖有孔虫的Mg/Ca记录相结合，O.从大洋钻探计划（ODP）806站点（赤道太平洋; ~2500？m）。考虑到岩心顶部校准的不确定性和对海水Mg/Ca（Mg/Ca）SW的敏感性，我们产生了一系列Mg/Ca-温度-Mg/Casw校准。我们最喜欢的指数温度校准是Mg/Ca？=？0.66？±？0.08× Mg/Ca ~（3+）= 0.27 ±0.06 × e（0.114±0.02 × BWT）。(1.21?±？0.04？+？0.12？±？0.004 × BWT（底层水温））×（Mg/Casw？0.003±0.02）（规定误差为2？s.e.）。通过比较O.从大洋钻探计划（ODP）690号站点（威德尔海）到？18 O温度，计算假设无冰条件下，在这个高峰期温暖的新生代。该程序表明Mg/Casw对Mg分配系数（DMg）的影响可以忽略不计。应用新的方程的网站806记录导致的建议，全球冰量大于今天后，中中新世气候转变（~14？Ma）。ODP站点806底部沃茨冷却和清新的太平洋纬向海面温度梯度增加，气候冷却通过上新世，之前的上新世-更新世冰期的北方半球。这些记录表明，深水温度和全球冰量脱钩，表明南极冰盖演变中阈值的重要性。
Antarctic continental-scale glaciation is generally assumed to have initiated at the Eocene-Oligocene Transition, yet its subsequent evolution is poorly constrained. We reconstruct changes in bottom water temperature and global ice volume from 0 to 17?Ma using ?18O in conjunction with Mg/Ca records of the infaunal benthic foraminifer, O. umbonatus from Ocean Drilling Program (ODP) Site 806 (equatorial Pacific; ~2500?m). Considering uncertainties in core top calibrations and sensitivity to seawater Mg/Ca (Mg/Ca)sw, we produce a range of Mg/Ca-temperature-Mg/Casw calibrations. Our favored exponential temperature calibration is Mg/Ca?=?0.66?±?0.08 × Mg/Casw0.27±0.06 × e(0.114±0.02 × BWT) and our favored linear temperature calibration is Mg/Ca?=?(1.21?±?0.04?+?0.12?±?0.004 × BWT (bottom water temperature)) × (Mg/Casw?0.003±0.02) (stated errors are 2?s.e.). The equations are obtained by comparing O. umbonatus Mg/Ca for a Paleocene-Eocene section from Ocean Drilling Program (ODP) Site 690 (Weddell Sea) to ?18O temperatures, calculated assuming ice-free conditions during this peak warmth period of the Cenozoic. This procedure suggests negligible effect of Mg/Casw on the Mg distribution coefficient (DMg). Application of the new equations to the Site 806 record leads to the suggestion that global ice volume was greater than today after the Middle Miocene Climate Transition (~14?Ma). ODP Site 806 bottom waters cooled and freshened as the Pacific zonal sea surface temperature gradient increased, and climate cooled through the Pliocene, prior to the Plio-Pleistocene glaciation of the Northern Hemisphere. The records indicate a decoupling of deep water temperatures and global ice volume, demonstrating the importance of thresholds in the evolution of the Antarctic ice sheet.