Improving the representation of ice-sheet mass changes in the global inversion for sea-level contributions
Authors: Willen Matthias O. , Uebbing Bernd , Horwath Martin , Kusche Jürgen , Rietbroek Roelof , Strößenreuther Undine , Schröder Ludwig 
Published: March 2020

&lt;p&gt;&lt;span&gt;G&lt;/span&gt;&lt;span&gt;lobal-mean sea level rises (GMSLR) by 3.1-3.5 mm a&lt;sup&gt;-1 &lt;/sup&gt;&lt;/span&gt;&lt;span&gt;(1993-2017)&lt;/span&gt;&lt;span&gt; and &lt;/span&gt;&lt;span&gt;of which&lt;/span&gt;&lt;span&gt; about 50 % can be attributed to changes in global-mean ocean mass due to hydrological variations, m&lt;/span&gt;&lt;span&gt;ass changes&lt;/span&gt;&lt;span&gt; of land glaciers, &lt;/span&gt;&lt;span&gt;and&lt;/span&gt; &lt;span&gt;mass &lt;/span&gt;&lt;span&gt;c&lt;/span&gt;&lt;span&gt;hanges&lt;/span&gt;&lt;span&gt; of the major ice sheets in Greenland and Antarctica. The i&lt;/span&gt;&lt;span&gt;ce-sheet contributions&lt;/span&gt;&lt;span&gt; account for more than &lt;/span&gt;&lt;span&gt;the&lt;/span&gt;&lt;span&gt; half of the contemporary ocean mass change &lt;/span&gt;&lt;span&gt;and can be&lt;/span&gt;&lt;span&gt; observed w&lt;/span&gt;&lt;span&gt;ith&lt;/span&gt;&lt;span&gt; time-variable gravi&lt;/span&gt;&lt;span&gt;metry&lt;/span&gt;&lt;span&gt; by the Gravity Recovery and Climate Experiment (GRACE) and its follow-on mission (GRACE-FO). In addition, geometric surface changes due to &lt;/span&gt;&lt;span&gt;the volume change of&lt;/span&gt;&lt;span&gt; ice sheets is also observed b&lt;/span&gt;&lt;span&gt;y polar &lt;/span&gt;&lt;span&gt;altimetry &lt;/span&gt;&lt;span&gt;missions&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;Of particular importance here is the signal of glacial isostatic adjustment (GIA) which is superimposed with i&lt;/span&gt;&lt;span&gt;ce mass change&lt;/span&gt;&lt;span&gt;.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;Conventionally, the g&lt;/span&gt;&lt;span&gt;ravimetry&lt;/span&gt;&lt;span&gt; and ice-altimetry observations are processed independently. For ocean applications, a global fingerprint inversion (Rietbroek et al., 2016) allows to estimate individual mass and steric contributors to the sea-level budget by combi&lt;/span&gt;&lt;span&gt;ni&lt;/span&gt;&lt;span&gt;ng GRACE and ocean-altimetry data in a joint approach. To improve the estimates of the ice-sheet contributions to GMSLR, we present first results from additionally incorporating independent ice-altimetry data over Greenland and Antarctica into the fingerprint inversion. We examine the sensitivity of the sea-level contributions to the additional ice-altimetry data &lt;/span&gt;&lt;span&gt;(from &lt;/span&gt;&lt;span&gt;ERS-2, Envisat, ICESat, CryoSat-2 &lt;/span&gt;&lt;span&gt;missions)&lt;/span&gt;&lt;span&gt; and provide validation against independent estimates. &lt;/span&gt;&lt;span&gt;I&lt;/span&gt;&lt;span&gt;n our standard runs&lt;/span&gt;&lt;span&gt;, &lt;/span&gt;&lt;span&gt;GIA is &lt;/span&gt;&lt;span&gt;accounted for &lt;/span&gt;&lt;span&gt;a&lt;/span&gt;&lt;span&gt;s an a-priori correction during the inversion.&lt;/span&gt;&lt;span&gt; H&lt;/span&gt;&lt;span&gt;owever,&lt;/span&gt;&lt;span&gt; we demonstrate the potential and limitations of a regional inverse approach i&lt;/span&gt;&lt;span&gt;n which&lt;/span&gt;&lt;span&gt; GIA is separated from ice mass change &lt;/span&gt;&lt;span&gt;over Antarctica&lt;/span&gt;&lt;span&gt; using GRACE and ice altimetry. In our future work, we a&lt;/span&gt;&lt;span&gt;im to &lt;/span&gt;&lt;span&gt;parametrise&lt;/span&gt;&lt;span&gt; and&lt;/span&gt;&lt;span&gt; co-&lt;/span&gt;&lt;span&gt;estimate GIA &lt;/span&gt;&lt;span&gt;with&lt;/span&gt;&lt;span&gt;in the global inversion framework.&lt;/span&gt;&lt;/p&gt;