Manifestation and consequences of warming and altered heat fluxes over the Bering and Chukchi Sea continental shelves
Manifestation and consequences of warming and altered heat fluxes over the Bering and Chukchi Sea continental shelves
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DOI：
10.1016/j.dsr2.2020.104781
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发表时间：
2020-07-01
影响因子：
3
通讯作者：
Weingartner, T. J.
中科院分区：
文献类型：
--
作者：
Danielson, S. L.;Ahkinga, O.;Weingartner, T. J.
温度和盐度水文剖面气候学组装，数据质量评价，并进行分析，以评估白令海和楚科奇海大陆架的变化，在季节性的世纪之久的时间尺度。气候学为描述两个大陆架上水团的空间分布和时间演变提供了信息，并量化了热量和淡水的大小和吞吐量的变化。对于楚科奇大陆架，对其1922-2018年记录期间的综合大陆架热含量进行线性趋势分析，发现夏季和秋季变暖1.4摄氏度（0.14 +/- 0.07摄氏度十年（-1））;在1990-2018年期间，变暖率增加了两倍，达到0.43 +/- 0.35摄氏度十年（-1）。相比之下，白令大陆架主要的十年尺度变化排除了在1966-2018年记录期间检测水柱变暖趋势的可能性，但海表温度数据显示，在同一时间范围内，气温显著上升了0.22 +/- 0.10摄氏度。欧洲中期天气预报中心（ECMWF）ERAS再分析计算的1979-2018年的热通量在整个大陆架的白令表面热通量中没有显示出创纪录的长度趋势，但楚科奇大陆架冷却季节（6月至3月）有更大的表面热损失趋势，其变暖季节（4月至9月）有更大的热增益趋势。在2014-2018年的五年中，北方白令海和楚科奇海的冬季和春季海冰覆盖率前所未有地低，这些变化与春季表面覆盖率降低、春季太阳辐射吸收增加以及夏季和秋季水柱热含量急剧升高相吻合。因此，温暖的海洋需要额外的时间来冷却到秋季的冰点。秋季和冬季海洋到大气的热通量非常大，并与增强的南风和升高的表面空气温度相关，这反过来又促进了更低的海冰产量，范围和浓度异常。海冰融化的可能减少与2014-2018年白令东南大陆架和沿着大陆坡的正盐度异常有关。2014-2018年期间，白令大陆架中部和北方的负盐度异常可能与1）盐度长期下降，2）冰融化增加和3）盐水产量下降的组合有关。我们假设，自2000年以来，白令海峡和白令大陆架的淡水化与阿拉斯加湾流域的净冰川消融有关。我们发现，白令和楚科奇大陆架的热机在2014-2018年间加速，表面热通量交换增加，海洋热平流增加。在此期间，楚科奇大陆架相对于气候学向北极海盆和/或海冰融化额外输送了5-9 x 10（19）J yr（-1）（50-90 EJ yr（-1））。类似数量的多余热量（60 EJ yr（-1））被输送到大气中，这表明楚科奇海对北极放大作用做出了巨大贡献。一个概念模型，总结了这些太平洋北极变化的控制反馈回路涉及热含量，海冰，淡水分布，地表热通量，平流通量。
A temperature and salinity hydrographic profile climatology is assembled, evaluated for data quality, and analyzed to assess changes of the Bering and Chukchi Sea continental shelves over seasonal to century-long time scales. The climatology informs description of the spatial distribution and temporal evolution of water masses over the two shelves, and quantification of changes in the magnitude and throughput of heat and fresh water. For the Chukchi Shelf, linear trend analysis of the integrated shelf heat content over its 1922-2018 period of record finds a significant summer and fall warming of 1.4 degrees C (0.14 +/- 0.07 degrees C decade(-1)); over 1990-2018 the warming rate tripled to 0.43 +/- 0.35 degrees C decade(-1). In contrast, the Bering Shelf's predominantly decadal-scale variability precludes detection of a water column warming trend over its 1966-2018 period of record, but sea surface temperature data show a significant warming of 0.22 +/- 0.10 degrees C decade(-1)) over the same time frame. Heat fluxes over 1979-2018 computed by the European Centre for Medium-Range Weather Forecast (ECMWF) ERAS reanalysis exhibit no record-length trend in the shelf-wide Bering surface heat fluxes, but the Chukchi Shelf cooling season (October-March) has a trend toward greater surface heat losses and its warming season (April-September) has a trend toward greater heat gains. The 2014-2018 half-decade exhibited unprecedented low winter and spring sea-ice cover in the Northern Bering and Chukchi seas, changes that coincided with reduced springtime surface albedo, increased spring absorption of solar radiation, and anomalously elevated water column heat content in summer and fall. Consequently, the warm ocean required additional time to cool to the freezing point in fall. Fall and winter ocean-to-atmosphere heat fluxes were anomalously large and associated with enhanced southerly winds and elevated surface air temperatures, which in turn promoted still lower sea-ice production, extent, and concentration anomalies. Likely reductions in sea-ice melt were associated with positive salinity anomalies on the Southeast Bering Shelf and along the continental slope over 2014-2018. Negative salinity anomalies during 2014-2018 on the central and northern Bering Shelf may be related to a combination of 1) long-term declines in salinity, 2) an increase of ice melt, and 3) a decline of brine production. We hypothesize that freshening on the Bering Shelf and in Bering Strait since 2000 are linked to net glacial ablation in the Gulf of Alaska watershed. We show that the heat engines of both the Bering and Chukchi shelves accelerated over 2014-2018, with increased surface heat flux exchanges and increased oceanic heat advection. During this time, the Chukchi Shelf delivered an additional 5-9 x 10(19) J yr(-1) (50-90 EJ yr(-1)) into the Arctic basin and/or sea-ice melt, relative to the climatology. A similar amount of excess heat (60 EJ yr(-1)) was delivered to the atmosphere, showing that the Chukchi Sea makes an out-sized contribution to Arctic amplification. A conceptual model that summarizes the controlling feedback loop for these Pacific Arctic changes relates heat content, sea ice, freshwater distributions, surface heat fluxes, and advective fluxes.