Antarctic coastal polynyas are hotspots of biological production with intensive springtime phytoplankton blooms that strongly depend on meltwater-induced restratification in the upper part of the water column. However, the fundamental physics that determine spatial inhomogeneity of the spring restratification remain unclear. Here, we investigate how different meltwaters affect springtime restratification and thus phytoplankton bloom in Antarctic coastal polynyas. A high-resolution coupled ice-shelf/sea-ice/ocean model is used to simulate an idealized coastal polynya similar to the Terra Nova Bay Polynya, Ross Sea, Antarctica. To evaluate the contribution of various meltwater sources, we conduct sensitivity simulations altering physical factors such as alongshore winds, ice shelf basal melt, and surface freshwater runoff. Our findings indicate that sea ice meltwater from offshore is the primary buoyancy source of polynya near-surface restratification, particularly in the outer-polynya region where chlorophyll concentration tends to be high. Downwelling-favorable alongshore winds can direct offshore sea ice away and prevent sea ice meltwater from entering the polynya region. Although the ice shelf basal meltwater can ascend to the polynya surface, much of it is mixed vertically over the water column and confined horizontally to a narrow coastal region, and thus does not contribute significantly to the polynya near-surface restratification. Surface runoff from ice shelf surface melt could contribute greatly to the polynya near-surface restratification. Nearby ice tongues and headlands strongly influence the restratification through modifying polynya circulation and meltwater transport pathways. Results of this study can help explain observed spatiotemporal variability in restratification and associated biological productivity in Antarctic coastal polynyas.

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物理因素对南极滨海冰间湖上部水柱再层化的影响

南极沿海冰间湖是生物生产的热点，春季浮游植物大量繁殖，很大程度上依赖于融水引起的水柱上部的重新分层。然而，决定弹簧重分层空间不均匀性的基本物理原理仍不清楚。在这里，我们研究不同的融水如何影响春季再分层，从而影响南极沿海冰间湖中浮游植物的繁殖。使用高分辨率冰架/海冰/海洋耦合模型来模拟理想化的沿海冰间湖，类似于南极洲罗斯海的特拉诺瓦湾冰间湖。为了评估各种融水来源的贡献，我们进行了敏感性模拟，改变了沿岸风、冰架基底融化和地表淡水径流等物理因素。我们的研究结果表明，近海海冰融水是冰间湖近地表再分层的主要浮力来源，特别是在叶绿素浓度较高的冰间湖外区域。有利下降的沿岸风可以将近海海冰吹走，并防止海冰融水进入冰间湖地区。虽然冰架基底融水可以上升到冰间湖表面，但其中大部分在水柱上垂直混合并水平限制在狭窄的沿海地区，因此对冰间湖近地表重新分层没有显着贡献。冰架表面融化产生的地表径流可能极大地促进冰间湖近地表重新分层。附近的冰舌和岬角通过改变冰间湖循环和融水输送路径强烈影响再分层。这项研究的结果可以帮助解释观察到的南极沿海冰间湖重新分层的时空变化和相关的生物生产力。