In this paper, we investigate the seasonal and spatial variability of stratification on the Siberian shelves with a case study from the Laptev Sea based on shipboard hydrographic measurements, year-round oceanographic mooring records from 2013 to 2014 and chemical tracer-based water mass analyses. In summer 2013, weak onshore-directed winds caused spreading of riverine waters throughout much of the eastern and central shelf. In contrast, strong southerly winds in summer 2014 diverted much of the freshwater to the northeast, which resulted in 50% less river water and significantly weaker stratification on the central shelf compared with the previous year. Our year-long records additionally emphasize the regional differences in water column structure and stratification, where the northwest location was well-mixed for 6 months and the central and northeast locations remained stratified into spring due to the lower initial surface salinities of the river-influenced water. A 26 year record of ocean reanalysis highlights the region’s interannual variability of stratification and its dependence on winds and sea ice. Prior the mid-2000s, river runoff to the perennially ice-covered central Laptev Sea shelf experienced little surface forcing and river water was maintained on the shelf. The transition toward less summer sea ice after the mid-2000s increased the ROFI’s (region of freshwater influence) exposure to summer winds. This greatly enhanced the variability in mixed layer depth, resulting in several years with well-mixed water columns as opposed to the often year-round shallow mixed layers before. The extent of the Lena River plume is critical for the region since it modulates nutrient fluxes and primary production, and further controls intermediate heat storage induced by lateral density gradients, which has implications for autumnal freeze-up and the eastern Arctic sea ice volume. MAIN POINTS 1. CTD surveys and moorings highlight the regional and temporal variations in water column stratification on the Laptev Sea shelf. 2. Summer winds increasingly control the extent of the region of freshwater influence under decreasing sea ice. 3. Further reductions in sea ice increases surface warming, heat storage, and the interannual variability in mixed layer depth.

中文翻译：

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受淡水影响的拉普捷夫海区分层变化的研究

在本文中，我们通过基于船载水文测量、2013 年至 2014 年全年海洋系泊记录和基于化学示踪剂的水团分析的拉普捷夫海案例研究，研究了西伯利亚大陆架分层的季节性和空间变异性。2013 年夏季，微弱的陆上导向风导致河流水域在东部和中部大陆架的大部分地区蔓延。相比之下，2014 年夏季的强南风将大部分淡水转移到东北部，导致河水减少了 50%，中央陆架的分层与上一年相比明显减弱。我们长达一年的记录还强调了水体结构和分层的区域差异，由于受河流影响的水的初始表面盐度较低，西北地区混合了 6 个月，中部和东北地区仍然分层进入春季。26 年的海洋再分析记录突出了该地区分层的年际变化及其对风和海冰的依赖。在 2000 年代中期之前，流向常年被冰覆盖的中央拉普捷夫海架的河流径流几乎没有受到表面强迫，并且河水保持在大陆架上。2000 年代中期之后向夏季海冰减少的过渡增加了 ROFI（淡水影响区域）对夏季风的暴露。这极大地增加了混合层深度的可变性，导致几年内水柱混合良好，而不是以前常年常年的浅混合层。勒拿河羽流的范围对该地区至关重要，因为它调节养分通量和初级生产，并进一步控制由横向密度梯度引起的中间蓄热，这对秋季冻结和北极东部海冰量有影响。主要观点 1. CTD 调查和系泊突出了拉普捷夫海架上水体分层的区域和时间变化。2. 在海冰减少的情况下，夏季风越来越多地控制着淡水影响区域的范围。3. 海冰的进一步减少增加了地表变暖、热量储存和混合层深度的年际变化。并进一步控制由横向密度梯度引起的中间蓄热，这对秋季冻结和北极东部海冰体积有影响。主要观点 1. CTD 调查和系泊突出了拉普捷夫海架上水体分层的区域和时间变化。2. 在海冰减少的情况下，夏季风越来越多地控制着淡水影响区域的范围。3. 海冰的进一步减少增加了地表变暖、热量储存和混合层深度的年际变化。并进一步控制由横向密度梯度引起的中间蓄热，这对秋季冻结和北极东部海冰体积有影响。主要观点 1. CTD 调查和系泊突出了拉普捷夫海架上水体分层的区域和时间变化。2. 在海冰减少的情况下，夏季风越来越多地控制着淡水影响区域的范围。3. 海冰的进一步减少增加了地表变暖、热量储存和混合层深度的年际变化。在海冰减少的情况下，夏季风越来越多地控制着淡水影响区域的范围。3. 海冰进一步减少会增加地表变暖、热量储存和混合层深度的年际变化。在海冰减少的情况下，夏季风越来越多地控制着淡水影响区域的范围。3. 海冰的进一步减少增加了地表变暖、热量储存和混合层深度的年际变化。