Implications of a Carbonate Ion Effect on Shell Carbon and Oxygen Isotopes for Glacial Ocean Conditions
Implications of a Carbonate Ion Effect on Shell Carbon and Oxygen Isotopes for Glacial Ocean Conditions
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碳酸盐离子对冰川海洋条件下壳碳和氧同位素的影响
DOI：
10.1007/978-3-642-58646-0_21
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发表时间：
1999
影响因子：
1.2
通讯作者：
D. Archer
中科院分区：
文献类型：
--
作者：
D. Lea;J. Bijma;H. Spero;D. Archer
实验工作表明，浮游有孔虫贝壳的碳和氧同位素组成直接受到海水碳酸盐平衡状态的影响(Spero等人。1997年)。由于海面和大气的二氧化碳必须处于近似平衡状态，冰芯中记录的大气二氧化碳的冰川下降必然伴随着地表水碳酸盐离子浓度的增加。计算表明，冰川时期碳酸盐离子的增加可以解释大部分或全部观测到的浮游贝壳δ13C负移位。这一发现为在南大洋冰芯冰川部分观察到的浮游生物δ13C的大幅负摆动提供了新的解释。它还提出了陆地生物圈向海洋转移碳的另一种假说，该假说被普遍认为是对较低冰壳δ13C值的解释(Shackleton，1977)。我们的分析表明，贝壳同位素组成可以限制海洋碳酸盐离子变化的程度，潜在地缩小了对冰川二氧化碳下降的解释。对贝壳δ18O的碳酸盐离子效应的影响校正后，冰川热带海洋表面温度估计最多降低了1摄氏度，这使得氧同位素古温度更接近海洋SST的替代指标(例如珊瑚锶/钙)和那些陆地指标(例如雪线和冰芯δ18O)，这些指标表明在最后一次冰川高峰期有更强烈的热带冷却(Guilderson等人)。1994年；Thompson等人，1995年)。
Experimental work demonstrates that the carbon and oxygen isotopic composition of planktic foraminifera shells is directly influenced by the carbonate equilibrium state of seawater (Spero et al. 1997). Because the pCO2 of the sea surface and the atmosphere must be in approximate equilibrium, the glacial drop in atmospheric carbon dioxide recorded in ice cores must have been accompanied by an increase in surface water carbonate ion concentration. Calculations indicate that increased carbonate ion during glacial episodes can account for much or all of the observed negative δ13C shift in planktic shells. This discovery provides a novel explanation for the large, negative swings in planktic δ13C observed in the glacial sections of Southern Ocean cores. It also presents an alternative hypothesis to the terrestrial biosphere-to-ocean transfer of carbon that is generally accepted as an explanation for lower glacial shell δ13C values (Shackleton 1977). Our analysis suggests that shell isotopic composition can provide a constraint on the extent of oceanic carbonate ion changes, potentially narrowing explanations for the glacial pCO2 drawdown. Correcting for the influence of the carbonate ion effect on shell δ18O lowers glacial tropical sea surface temperature (SST) estimates by up to 1°C, which brings oxygen isotope paleotemperatures closer to those marine SST proxies (e.g. coral Sr/Ca) and those terrestrial indicators (e.g. snow-line and ice core δ18O) that suggest more intense tropical cooling at the last glacial maximum (Guilderson et al. 1994; Thompson etal.1995).