Impacts of variability in fjord circulation on glacier dynamics in Cumberland Bay, South Georgia &#160;
Authors: Zanker Joanna , Young Emma , Haigh Ivan , Brickle Paul 
Published: March 2022

&lt;p&gt;&lt;span xml:lang=&quot;EN-GB&quot; data-contrast=&quot;none&quot;&gt;&lt;span&gt;South Georgia is a mountainous and heavily glaciated sub-&lt;/span&gt;&lt;span&gt;Antarctic island&lt;/span&gt;&lt;span&gt; in the Southern Ocean&lt;/span&gt;&lt;span&gt;, lying in the path of the Antarctic Circumpolar Current&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;Cumberland Bay is the largest fjord on the island, split into two arms, Cumberland East and West Bay, with a large marine-terminating glacier at the head of each arm. Water circulation in such fjords&lt;/span&gt;&lt;span&gt;, and associated transport and exchange of heat,&lt;/span&gt;&lt;span&gt; directly governs the stability of glaciers at the ice-ocean interface&lt;/span&gt;&lt;span&gt; and the&lt;/span&gt; &lt;span&gt;subsequent&lt;/span&gt;&lt;span&gt; glacier&lt;/span&gt;&lt;span&gt; dynamics&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;Over the past century there has been a markedly different behaviour in the retreat rate of &lt;/span&gt;&lt;span&gt;Nordenskj&lt;/span&gt;&lt;span&gt;&amp;#246;&lt;/span&gt;&lt;span&gt;ld&lt;/span&gt;&lt;span&gt; glacier in East Bay, compared &lt;/span&gt;&lt;span&gt;with &lt;/span&gt;&lt;span&gt;that of Neumayer glacier in West Bay&lt;/span&gt;&lt;span&gt;. Fjord circulation patterns are complex with influencing factors including winds, &lt;/span&gt;&lt;span&gt;meltwater runoff&lt;/span&gt;&lt;span&gt;, bathymetry and coastal current systems. Precise understanding of the variability in ocean circulation and exchange in Cumberland Bay cannot be understood from limited observational data alone. &lt;/span&gt;&lt;span&gt;Here, we&lt;/span&gt;&lt;span&gt; use observations together with a new high-resolution numerical mode&lt;/span&gt;&lt;span&gt;l built using the NEMO4 framework&lt;/span&gt;&lt;span&gt; to determine &lt;/span&gt;&lt;span&gt;the &lt;/span&gt;&lt;span&gt;dominant physical drivers of variability. &lt;/span&gt;&lt;span&gt;Nordenskj&lt;/span&gt;&lt;span&gt;&amp;#246;&lt;/span&gt;&lt;span&gt;ld&lt;/span&gt;&lt;span&gt; and Neumayer glaciers are represented as a vertical wall with a theoretical annual cycle of freshwater &lt;/span&gt;&lt;span&gt;discharge&lt;/span&gt;&lt;span&gt; injected at the depth of neutral buoyancy. &lt;/span&gt;&lt;span&gt;The model &lt;/span&gt;&lt;span&gt;is&lt;/span&gt;&lt;span&gt; used to investigate how &lt;/span&gt;&lt;span&gt;variability in &lt;/span&gt;&lt;span&gt;the circulation regime &lt;/span&gt;&lt;span&gt;couples with the associated&lt;/span&gt; &lt;span&gt;heat transport within the two fjord arms, and to el&lt;/span&gt;&lt;span&gt;ucidate &lt;/span&gt;&lt;span&gt;the role of such variability on&lt;/span&gt; &lt;span&gt;glaci&lt;/span&gt;&lt;span&gt;er dynamics&lt;/span&gt;&lt;span&gt; and rate of retreat. &lt;/span&gt;&lt;span&gt;The sensitivity of the&lt;/span&gt; &lt;span&gt;system&lt;/span&gt;&lt;span&gt; to&lt;/span&gt;&lt;span&gt; sill depth, fjord geometry and wind direction will be &lt;/span&gt;&lt;span&gt;demonstrated&lt;/span&gt; &lt;span&gt;through a series of model experiments&lt;/span&gt;&lt;span&gt;, gaining a&lt;/span&gt;&lt;span&gt; stronger&lt;/span&gt;&lt;span&gt; understand&lt;/span&gt;&lt;span&gt;ing&lt;/span&gt; &lt;span&gt;of the key&lt;/span&gt; &lt;span&gt;drive&lt;/span&gt;&lt;span&gt;r&lt;/span&gt;&lt;span&gt;s&lt;/span&gt; &lt;span&gt;of &lt;/span&gt;&lt;span&gt;the different retreat rates of these glaciers.&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;/p&gt;