Nature2014-06-18 6:28 PM

海平面和海洋温度记录相一致 Sea-level and deep-sea-temperature variability over the past 5.3 million years


关于过去海平面变化以及海洋温度相关变化的大部分记录,都依赖于深海海洋微生物中所记录的氧同位素的变化。遗憾的是,这些信号受到了其他因素的影响,使得我们难以获取与气候相关的明确信号。现在,Eelco Rohling及同事提出了用来估计过去530万年海平面和深海温度变化的一个新方法。基于来自东地中海的氧同位素变化的这一记录避免了深海方法所存在的问题,与关于过去160万年的一个独立记录基本上对应。正如所预料的,温度和海平面大体上是相互关联的,但也显示出有趣的时间不连续性,因为在上新世-更新世冰期开始时,海平面的一次大幅度下降滞后于一次温度骤降数十万年时间。


Ice volume (and hence sea level) and deep-sea temperature are key measures of global climate change. Sea level has been documented using several independent methods over the past 0.5 million years (Myr). Older periods, however, lack such independent validation; all existing records are related to deep-sea oxygen isotope (δ18O) data that are influenced by processes unrelated to sea level. For deep-sea temperature, only one continuous high-resolution (Mg/Ca-based) record exists, with related sea-level estimates, spanning the past 1.5 Myr. Here we present a novel sea-level reconstruction, with associated estimates of deep-sea temperature, which independently validates the previous 0–1.5 Myr reconstruction and extends it back to 5.3 Myr ago. We find that deep-sea temperature and sea level generally decreased through time, but distinctly out of synchrony, which is remarkable given the importance of ice-albedo feedbacks on the radiative forcing of climate. In particular, we observe a large temporal offset during the onset of Plio-Pleistocene ice ages, between a marked cooling step at 2.73 Myr ago and the first major glaciation at 2.15 Myr ago. Last, we tentatively infer that ice sheets may have grown largest during glacials with more modest reductions in deep-sea temperature.






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