Abstract
To improve knowledge of marine-terminating glaciers in western Greenland, marine sediment cores from the Ata Sund fjord system, hosting two outlet glaciers, Eqip Sermia and Kangilerngata Sermia, were investigated. The main objective was to reconstruct glacial activity and paleoceanographic conditions during the past 600 years. Ice-rafted debris (IRD) was quantified by wet-sieving sediment samples and by using a computed tomography scan. Variability in relative bottom water temperatures in the fjord was reconstructed using foraminiferal analysis. On the basis of this, three periods of distinct glacial regimes were identified: Period 1 (1380–1810 CE), which covers the culmination of the Little Ice Age (LIA) and is interpreted as having advanced glaciers with high IRD content. Period 2 (1810–1920 CE), the end of the LIA, which was characterised by a lowering of the glaciers’ calving flux in response to climate cooling. During Period 3 (1920–2014 CE), both glaciers retreated substantially to their present-day extent. The bottom water temperature started to decrease just before Period 2 and remained relatively low until just before the end of Period 3. This is interpreted as a local response to increased glacial meltwater input. Our study was compared with a study in Disko Bay, nearby Jakobshavn Glacier and the result shows that both of these Greenlandic marine-terminating glaciers are responding to large-scale climate change. However, the specific imprint on the glaciers and the different fjord waters in front of them result in contrasting glacial responses and sediment archives in their respective fjords.
Highlights
Meltwater from Greenland’s outlet glaciers contributes to global sea level rise (Church et al, 2011; IPCC, 2013), and the increased freshwater input to the North Atlantic may affect circulation in the sub-polar gyre (Bamber et al, 2012; Fichefet et al, 2003)
We suggest that the observed reduction in Ice-rafted debris (IRD) at this stage indicates that the marine-terminating glaciers experienced a reduced calving rate due to a retreat of Warm Polar Water (WPW), resulting in colder bottom water temperatures and potentially a colder surface layer from meltwater
The records are based on grain-size variability and IRD fluxes from two sediment cores as well as from foraminiferal assemblage variations from one sediment core
Summary
Meltwater from Greenland’s outlet glaciers contributes to global sea level rise (Church et al, 2011; IPCC, 2013), and the increased freshwater input to the North Atlantic may affect circulation in the sub-polar gyre (Bamber et al, 2012; Fichefet et al, 2003). Models of future sea level rise require a detailed understanding of the causes behind the retreat of marine-terminating glaciers in Greenland, as well as their links with climate change (Straneo et al, 2013). It has been shown that the warming of the ocean around Greenland is playing an important role in the current destabilisation of marine-terminating glaciers (Straneo and Heimbach, 2013; Vieli and Nick, 2011). Ocean waters can cause submarine melting at the glacier front, which may affect grounding-line stability as well as calving activity (Rignot et al, 2010). The dynamic behaviour of an outlet glacier front and how it responds to climate change are strongly influenced by its bed slope and the fjord’s topography – as, for example, given by grounding thresholds and overdeepenings (Meier and Post, 1987; Vieli et al, 2001)
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