Southern Weddell Sea surface freshwater flux modulated by icescape and atmospheric forcing

IF 4.1 3区 地球科学 Q2 METEOROLOGY & ATMOSPHERIC SCIENCES Ocean Science Pub Date : 2023-12-14 DOI:10.5194/os-19-1791-2023
L. Stulic, R. Timmermann, S. Paul, Rolf Zentek, G. Heinemann, T. Kanzow
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引用次数: 2

Abstract

Abstract. Sea ice formation dominates surface salt forcing in the southern Weddell Sea. Brine rejected in the process of sea ice production results in the production of High Salinity Shelf Water (HSSW) that feeds the global overturning circulation and fuels the basal melt of the adjacent ice shelf. The strongest sea ice production rates are found in coastal polynyas, where steady offshore winds promote divergent ice movement during the freezing season. We used the Finite Element Sea ice–ice shelf–Ocean Model (FESOM) forced by output from the regional atmospheric model COSMO-CLM (CCLM) with 14 km horizontal resolution to investigate the role of polynyas for the surface freshwater flux of the southern Weddell Sea (2002–2017). The presence of stationary icescape features (i.e., fast-ice areas and grounded icebergs) can influence the formation of polynyas and, therefore, impact sea ice production. The representation of the icescape in our model is included by prescribing the position, shape and temporal evolution of a largely immobile ice mélange formed between the Filchner–Ronne Ice Shelf (FRIS) and a major grounded iceberg based on satellite data. We find that 70 % of the ice produced on the continental shelf of the southern Weddell Sea is exported from the region. While coastal polynyas cover 2 % of the continental shelf area, sea ice production within the coastal polynyas accounts for 17 % of the overall annual sea ice production (1509 km3). The largest contributions come from the Ronne Ice Shelf and Brunt Ice Shelf polynyas and polynyas associated with the ice mélange. Furthermore, we investigate the sensitivity of the polynya-based ice production to the (i) representation of the icescape and (ii) regional atmospheric forcing. Although large-scale atmospheric fields determine the sea ice production outside polynyas, both the treatment of the icescape and the regional atmospheric forcing are important for the regional patterns of sea ice production in polynyas. The representation of the ice mélange is crucial for the simulation of polynyas westward/eastward of it, which are otherwise suppressed/overestimated. Compared to using ERA-Interim reanalysis as an atmospheric forcing data set, using CCLM output reduces polynya-based ice production over the eastern continental shelf due to weaker offshore winds, yielding a more realistic polynya representation. Our results show that the location and not just the strength of the sea ice production in polynyas is a relevant parameter in setting the properties of the HSSW produced on the continental shelf, which in turn affects the basal melting of the Filchner–Ronne Ice Shelf.
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南威德尔海表层淡水通量受冰景和大气胁迫的影响
摘要海冰的形成主导了威德尔海南部的表层盐强迫。海冰形成过程中排出的盐水会产生高盐度大陆架水(HSSW),为全球翻转环流提供养分,并促进邻近冰架的基底融化。海冰生成率最高的地方是沿岸多冰带,那里稳定的离岸风在冰冻季节会促进冰的发散运动。我们利用有限元海冰-冰架-海洋模型(FESOM),并以 14 千米水平分辨率的区域大气模型 COSMO-CLM 的输出结果为强迫,研究了多冰带对威德尔海南部海面淡水通量的作用(2002-2017 年)。静止冰景特征(即快冰区和接地冰山)的存在会影响多冰带的形成,从而影响海冰的生成。在我们的模型中,冰景的表现形式包括根据卫星数据,规定菲尔希纳-罗纳冰架(FRIS)和一座主要接地冰山之间形成的基本不动的冰混杂区的位置、形状和时间演变。我们发现,威德尔海南部大陆架上生成的冰有 70%是从该地区出口的。虽然沿岸多冰带占大陆架面积的 2%,但沿岸多冰带的海冰产量占整个海冰年产量(1509 立方公里)的 17%。最大的贡献来自龙恩冰架和布伦特冰架多冰带以及与冰混杂带有关的多冰带。此外,我们还研究了基于多冰盖的冰产量对(i)冰景表示和(ii)区域大气强迫的敏感性。虽然大尺度大气场决定了多冰带以外的海冰产量,但冰景处理和区域大气强迫对多冰带海冰产量的区域模式都很重要。冰混杂区的表示对于模拟冰混杂区以西/以东的多冰带至关重要,否则多冰带就会被抑制/高估。与使用ERA-Interim再分析数据集作为大气强迫数据集相比,使用CCLM输出的数据集可减少东部大陆架上由于离岸风减弱而产生的多冰带冰量,从而获得更真实的多冰带表示。我们的研究结果表明,在确定大陆架上产生的 HSSW 的属性时,多雨带海冰生成的位置而不仅仅是强度是一个相关参数,而 HSSW 的属性反过来又会影响 Filchner-Ronne 冰架的基底融化。
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来源期刊
Ocean Science
Ocean Science 地学-海洋学
CiteScore
5.90
自引率
6.20%
发文量
78
审稿时长
6-12 weeks
期刊介绍: Ocean Science (OS) is a not-for-profit international open-access scientific journal dedicated to the publication and discussion of research articles, short communications, and review papers on all aspects of ocean science: experimental, theoretical, and laboratory. The primary objective is to publish a very high-quality scientific journal with free Internet-based access for researchers and other interested people throughout the world. Electronic submission of articles is used to keep publication costs to a minimum. The costs will be covered by a moderate per-page charge paid by the authors. The peer-review process also makes use of the Internet. It includes an 8-week online discussion period with the original submitted manuscript and all comments. If accepted, the final revised paper will be published online. Ocean Science covers the following fields: ocean physics (i.e. ocean structure, circulation, tides, and internal waves); ocean chemistry; biological oceanography; air–sea interactions; ocean models – physical, chemical, biological, and biochemical; coastal and shelf edge processes; paleooceanography.
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