West Greenland ice sheet retreat history reveals elevatedprecipitation during the Holocene thermal maximum

Abstract. We investigate changing precipitation patterns in the Kangerlussuaq region of west central Greenland during the Holocene thermal maximum, using a new chronology of ice sheet terminus position through the Holocene and a novel inverse modeling approach based on the unscented transform (UT). The UT is applied to estimate changes in annual precipitation in order to reduce the misfit between modeled and observed terminus positions. We demonstrate the effectiveness of the UT for time-dependent data assimilation, highlighting its low computational cost and trivial parallel implementation. Our results indicate that Holocene warming coincided with elevated precipitation, without which modeled retreat in the Kangerlussuaq region is more rapid than suggested by observations. Less conclusive is if high temperatures during the HTM were specifically associated with a transient increase in precipitation, as the results depend on the assumed temperature history. The importance of precipitation in controlling ice sheet extent during the Holocene underscores the importance of Arctic sea ice loss and changing precipitation patterns on the future stability of the GrIS.