北冰洋海冰重建方法研究进展

REVIEW OF SEA-ICE RECONSTRUCTION APPROACH IN THE ARCTIC OCEAN

近几十年来,伴随着全球变暖和大气中CO2的增加,北极海冰的范围和厚度都显著衰减。数值模拟预测在未来20~50年,北冰洋中心海盆在夏季将可能成为无冰区。研究北冰洋海冰历史演变的沉积记录可以更清楚地了解现代海冰减少的控制机制并对预测未来变化趋势提供依据。文章回顾了北冰洋古海冰的重建方法,主要包括指标重建和数值模拟。用于重建古海冰的传统指标有IRD(Ice-Rafted Debris,冰筏碎屑)、微体生物化石以及地球化学指标等,北冰洋IRD和微体生物化石的记录表明北冰洋的海冰出现于大约47.5 Ma,永久性海冰出现于大约14 Ma,是北冰洋古海冰研究的重要发现。但是传统指标是间接指示海冰的变化且不能量化海冰,限制了北冰洋海冰历史演变的研究。近十几年来,海冰的直接指标IP25(Ice Proxy with 25 carbon atoms)的发展,是北极海冰历史演变研究从定性到定量的里程碑,通过与海冰数值模拟结合,首次验证了氧同位素6期北冰洋在陆架边缘存在冰间湖(Polynya)。近年来,最新的气候模式结果显示中全新世北极海冰变化可以影响中低纬度及北半球气候。未来研究中,北冰洋多指标沉积记录与数值模拟研究结合,可以使我们更清楚地了解海冰变化的控制机制及其对全球气候变化的驱动。

In recent decades,with the global warming and the increase of atmospheric CO2 concentrations,the extent and thickness of the Arctic sea ice have been greatly reduced.The numerical simulation predicted that in the next 20~50 years,the central Arctic basin may become an ice-free area in summer.The sedimentary records of sea-ice variability in the Arctic Ocean can provide us a clear understanding of the controlling mechanism of modern sea ice decrease and provide an insight for predicting the future sea-ice change.This paper reviewed the approaches of Arctic sea-ice reconstruction,including proxies and modeling.Traditional proxies of paleo-sea ice include IceRafted Detritus(IRD),paleo-microfossils,and geochemical indicators.The sedimentary records of IRD and paleomicrofossils suggested that the onset of sea ice in the Arctic was ca.47.5 Ma and the onset of permanent sea ice was ca.14 Ma.However,these proxies have limitations to reconstruct paleo-sea ice because they are indirect proxies and cannot quantify sea-ice concentrations.In the past ten years,the development of IP25(Ice Proxy with 25 carbon atoms,biomarkers),a direct proxy of sea ice,is a milestone in the study of sea-ice reconstruction from qualitative evaluation to quantitative estimates.The combination of IP25 records and numerical simulation indicate the occurrence of polynya along the Arctic continental margins during Marine Isotope Stage 6.In recent years,new climate model showed that northern hemisphere temperature during the mid-Holocene was driven by the Arctic seaice variability.In future studies,with the combination of multi-proxy approach and the numerical simulation,we can better understand the controlling mechanism of sea-ice change and its driving to the global climate change.