Science2014-06-13 5:47 PM

大西洋中的一个暖和的但不稳定的间冰期 Rapid Reductions in North Atlantic Deep Water During the Peak of the Last Interglacial Period

论文摘要 

据一项新的研究披露,经历了某些温暖的间冰期时期的大西洋并非如研究人员过去认为的那样稳定。研究人员说,事实上,北大西洋深层海水——这是与大西洋深层通气的主要水体——的产生在大约12万8000年至11万6000年间有着很大的变化,当时地球的气候相对温暖。这些发现提示,全球变暖会导致对区域气候、海平面及大气二氧化碳浓度所产生的某些意想不到的效应。Eirik Galaasen及其同事利用来自北欧海底的且得到了良好保存的沉积岩芯来检测随着时间的推移在那个区域中的海水碳同位素组成。研究人员在某次间冰期间发现了若干与北大西洋深层水循环有关的长达一个世纪的异常现象。他们说,这一变动是突然开始的并与冰盖融化以及淡水加入北大西洋有关。这些异常没有像它们在寒冷的冰川期间那样显著,但它们是在大西洋与当今许多气候模型所预测的海洋,即一个较暖且含盐量略少的大西洋类似的时候发生的。这些发现提示,大西洋中存在着一个关键性的稳定阈值,它仍然可以在暖和的间冰期时被触发。

Abstract 

Deep ocean circulation has been considered relatively stable during interglacial periods, yet little is known about its behavior on submillennial time scales. Using a subcentennially resolved epibenthic foraminiferal δ13C record, we show that the influence of North Atlantic Deep Water (NADW) was strong at the onset of the last interglacial period and was then interrupted by several prominent centennial-scale reductions. These NADW transients occurred during periods of increased ice rafting and southward expansions of polar water influence, suggesting that a buoyancy threshold for convective instability was triggered by freshwater and circum-Arctic cryosphere changes. The deep Atlantic chemical changes were similar in magnitude to those associated with glaciations, implying that the canonical view of a relatively stable interglacial circulation may not hold for conditions warmer and fresher than at present.

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