| 摘要: |
| 在全球变暖背景下，持续减少的海冰正在通过降水和蒸发改变着北极水循环。降水同位素及其过量氘参数（d）作为水循环示踪剂对北极水文气候变化研究具有重要帮助，但由于观测资料匮乏，目前有关北极水循环的同位素示踪研究鲜有报道。本文以冬季海冰主要消融区——巴伦支—格陵兰海（BGS）为例，调查了BGS冬季降水d值与海冰和大气环流的关系。结果表明：BGS降水d值与海冰范围呈显著正相关，而与巴伦支—喀拉海（BKS）反气旋指数呈显著负相关。BGS降水d主要受海冰变化导致的局地蒸发控制，当海冰减少时，局地蒸发水汽增加，贡献了更多低d的降水。增强的BKS反气旋通过绝热下沉增温和向极的水热输送，加强了BGS海冰消融与局地蒸发，降低了降水d值；而较低纬地区输送水汽以高的d值为特征，其对BGS降水的直接贡献有限。该项研究从同位素的视角厘清了局地蒸发与较低纬地区水汽输送对北极降水的相对重要性，不仅有助于理解海冰减少对北极水循环的影响，也对北极古气候重建具有重要启示。 |
| 关键词: 北极海冰 降水过量氘 局地蒸发 大气环流 |
| DOI：10.7515/JEE232011 |
| CSTR：32259.14.JEE232011 |
| 分类号: |
| 基金项目:国家自然科学基金项目（42025602，41876039）；中央高校基本科研专项资金 |
| 英文基金项目:National Natural Science Foundation of China (42025602, 41876039); Fundamental Research Funds for the Central Universities |
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| Arctic winter sea ice loss and moisture dynamics revealed by precipitation deuterium excess |
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WEI Xin, DANG Shaohua, LIU Zhongfang
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State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China
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| Abstract: |
| Background, aim, and scope The persistent reduction in sea ice under global warming is altering the Arctic hydrological cycle, especially in the Barents and Greenland Sea (BGS) where the strongest winter sea ice loss coupled with warming has increased local evaporation and precipitation. However, the relative importance of local evaporation and moisture advection from lower latitudes in BGS precipitation is still debated. In this study, we take deuterium excess (d) in BGS precipitation as a clue to explore how sea ice loss affects Arctic atmospheric water cycle. Materials and methods Monthly sea ice concentration (SIC) and sea ice extent (SIE) are obtained from the National Snow & Ice Data Center (NSIDC). Monthly precipitation d, calculated from δ18O and δD, is obtained from Global Network of Isotopes in Precipitation (GNIP) dataset. Monthly data of geopotential height and meridional wind at 500 hPa is obtained from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 reanalysis dataset. Our analysis focuses on winter season (from December through February, DJF) during the period 1990—2020, when the GNIP stations in the BGS have the longest and continuous precipitation d records. Some statistical methods including linear regression, correlation and composite analyses are used in our analysis, and a two-sided Student’s t-test is used to check the statistical significance. Results We found that the BGS precipitation d values are strongly positively correlated with SIE, but negatively with the BKS anticyclonic index. Discussion Changes in the BGS precipitation d values are controlled by both local evaporation due to sea ice loss and enhanced poleward moisture transport. The BKS anticyclonic circulation which accelerates sea ice reduction through adiabatic warming by subsidence is the dominant driver of BGS winter sea ice loss, and enhances poleward heat and moisture transport. The precipitation d values result mainly from enhanced local evaporation due to sea ice loss, rather than the poleward moisture advection that is characterized by higher precipitation d values. Conclusions The BGS winter sea ice loss is mainly driven by the BKS anticyclonic circulation through adiabatic warming by subsidence and enhanced poleward heat and moisture transport. The enhanced local evaporation due to sea ice loss is the major contributor to BGS winter precipitation, resulting low precipitation d values, while external moisture that features higher d values contributes less to BGS precipitation. Recommendations and perspectives This study provides isotopic evidence that the ongoing sea ice reduction is altering the Arctic hydrological cycle through enhanced local evaporation and precipitation. The results presented here contribute to a better understanding of how Arctic precipitation isotopes change in response to sea ice loss, and may have some implications for the past Arctic hydroclimate studies. |
| Key words: Arctic sea ice precipitation deuterium excess local evaporation atmospheric circulation |
