Variability in the Distribution of Fast Ice and the Sub-ice Platelet Layer Near McMurdo Ice Shelf
Variability in the Distribution of Fast Ice and the Sub-ice Platelet Layer Near McMurdo Ice Shelf
复制标题
DOI：
10.1029/2019jc015678
复制
发表时间：
2020-03-01
影响因子：
3.6
通讯作者：
Leonard, G. H.
中科院分区：
文献类型：
--
作者：
Brett, G. M.;Irvin, A.;Leonard, G. H.
麦克默多海峡过冷冰架水流出量的变化反映在下面的固定冰和亚冰片层的厚度和分布上。在2011年、2013年、2016年和2017年春末，对麦克默多海峡冰架影响的快冰和冰下血小板层的分布和厚度进行了地基电磁感应和钻孔调查。在2011年和2017年，分别观察到了高达7.5和6米的较厚的冰下血小板层。2011年和2017年冬季的快速结冰受到强烈南风事件发生率较高以及罗斯海Polynya活动的影响。相比之下，2016年的风力条件较低，导致海冰基本上未受干扰地增长，并导致快速冰覆盖范围非常广泛。在2016年，观测到了一个更薄的冰下血小板层，厚度可达4米。2011年和2017年，在罗斯海和麦克默多-罗斯冰架空腔之间的水团交换区域检测到大量和可变的冰下血小板层，这在2013年和2016年没有观察到。我们假设，更高频率的强南风事件，由此产生的冰间湖活动，和高盐度陆架水生产在冬季加速流通，并增加融化在近端浅麦克默多冰架和更深的罗斯冰架地区的联合腔。海洋驱动的冰架底部融化形成冷的和新鲜的冰架水（ISW），它可以结晶成片状冰。冰架附近的海冰增长是由于上层海洋被ISW冷却和稳定，或通过冻结成海冰的血小板冰。一个松散的血小板冰称为亚冰血小板层（SPL）可以形成下面。为了研究ISW影响的变化，我们测量了南极罗斯海麦克默多冰架附近的海冰和SPL厚度，并进行了钻孔和地球物理调查。在冬季海冰形成时，海上强风发生率较高的年份，观察到较厚的SPL。强风将海冰吹向近海，形成了被称为冰穴的开放水域。冰穴内密集地产生新冰，废弃的盐形成一个非常密集的咸水团，称为高盐度陆架水，它可以循环进入冰架空腔，并驱动底部融化和深层ISW形成。我们假设，海上强风的发生率越高，会导致更多的冰间湖活动，高盐度陆架水的产生，和ISW形成流出到麦克默多声音产生较厚的SPL。关键点冰架影响海冰和冰下血小板层进行了评估与电磁感应和钻孔厚度调查。冰片层在冬季随着偏南风事件和冰间湖活动的增加而变厚。冬季麦克默多海峡的水外流和冰下片层厚度与冰间湖驱动的HSSW环流有关
Variability in the volume of supercooled Ice Shelf Water outflow in McMurdo Sound is reflected in the thickness and distribution of fast ice and the sub-ice platelet layer beneath. Ground-based electromagnetic induction and drill hole surveys of the distribution and thickness of ice shelf-influenced fast ice and the sub-ice platelet layer in McMurdo Sound were carried out in late spring of 2011, 2013, 2016, and 2017. In 2011 and 2017, thicker sub-ice platelet layers of up to 7.5 and 6 m were observed, respectively. Fast ice formation throughout the winters of 2011 and 2017 was influenced by a higher occurrence of strong southerly wind events and resultant activity of the Ross Sea Polynya. In contrast, lower wind conditions in 2016 led to largely undisturbed sea ice growth and anomalously extensive fast ice coverage. A thinner sub-ice platelet layer of up to 4 m was observed in 2016. In 2011 and 2017, substantial and variable sub-ice platelet layers were detected in a region of exchange of water masses between the Ross Sea and the McMurdo-Ross ice shelf cavity, which were not observed in 2013 and 2016. We hypothesize that a higher frequency of strong southerly wind events, resultant polynya activity, and High Salinity Shelf Water production over winter accelerates circulation and increases melting in the proximal shallow McMurdo Ice Shelf and the deeper Ross Ice Shelf regions of the conjoined cavity. The outflow of supercooled Ice Shelf Water and sub-ice platelet layer formation in McMurdo Sound are consequently promoted.Plain Language Summary Ocean-driven basal melting of ice shelves forms cold and fresh Ice Shelf Water (ISW) which can crystallize into platelet ice. Sea ice growth near an ice shelf is enhanced as the upper ocean is cooled and stabilized by ISW or by freezing of platelet ice into the sea ice. An unconsolidated mass of platelet ice called a sub-ice platelet layer (SPL) can form beneath. To investigate variability in the influence of ISW, we measured sea ice and SPL thicknesses near McMurdo Ice Shelf in the Ross Sea, Antarctica with drill hole and geophysical surveys. Thicker SPLs were observed in years subject to a higher occurrence of strong offshore winds over winter as the sea ice was forming. Strong winds blow sea ice offshore and form regions of open water called polynyas. New ice is produced intensively within polynyas and the rejected salts form a very dense and saline water mass called High Salinity Shelf Water which can circulate into ice shelf cavities and drive basal melting and ISW formation at depth. We hypothesize that a higher occurrence of strong offshore winds results in more polynya activity, High Salinity Shelf Water production, and ISW formation which outflows into McMurdo Sound producing thicker SPLs.Key PointsIce shelf-influenced sea ice and the sub-ice platelet layer were assessed with electromagnetic induction and drill hole thickness surveys The sub-ice platelet layer was thicker in years with more strong southerly wind events and polynya activity over winter Ice Shelf Water outflow and sub-ice platelet layer thickness in McMurdo Sound are connected to polynya-driven HSSW circulation over winter