Abstract
AbstractTidewater glaciers in Greenland experienced widespread retreat during the last century. Information on their behaviour prior to this is often poorly constrained due to lack of observations, while determining the drivers prior to instrumental records is also problematic. Here we present a record of the dynamics of Kangiata Nunaata Sermia (KNS), southwest Greenland, from its Little Ice Age maximum (LIAmax) to 1859 – the period before continuous air temperature observations began at Nuuk in 1866. Using glacial geomorphology, historical accounts, photographs and GIS analyses, we provide evidence KNS was at its LIAmax by 1761, had retreated by ~5 km by 1808 and a further 7 km by 1859. This predates retreat at Jakobshavn Isbræ by 43–113 years, demonstrating the asynchroneity of tidewater glacier terminus response following the LIA. We use a one-dimensional flowband model to determine the relative sensitivity of KNS to atmospheric and oceanic climate forcing. Results demonstrate that terminus forcing rather than surface mass balance drove the retreat. Modelled glacier sensitivity to submarine melt rates is also insufficient to explain the retreat observed. However, moderate increases in crevasse water depth, driving an increase in calving, are capable of causing terminus retreat of the observed magnitude and timing.
Highlights
Tidewater glaciers (TWGs) exert a major control on the short- and long-term mass balance of the Greenland ice sheet (Van den Broeke and others, 2009; Alley and others, 2010; Bevan and others, 2012)
On the eastern fjord flank the moraine spans the forefield area of the land-terminating glacier Qamanarssup Sermia (QS), while the moraine on the western flank extends inland into the topographic depression opposite Akullerssuaq (Fig. 1)
The locations of modelled stable terminus positions driven by submarine melt (SM) and crevasse water depth (CWD) forcings are replicated between experiments (Fig. 6)
Summary
Tidewater glaciers (TWGs) exert a major control on the short- and long-term mass balance of the Greenland ice sheet (Van den Broeke and others, 2009; Alley and others, 2010; Bevan and others, 2012). TWG dynamics are poorly constrained by observations, placing limitations on the knowledge of their response to climate change. Multi-decadal records of terminus fluctuations are available for some TWGs back to the 1930s, and limited direct observations exist before this (Bjørk and others, 2012). There is limited potential to extend TWG records to their Little Ice Age maxima (LIAmax) due to the sparse and often indirect nature of observations (Weidick, 1959, 1968; Briner and others, 2010; Larsen and others, 2011). Characterization of TWG behaviour during the 18th and 19th centuries is problematic Where this is possible it provides insights into centennialtimescale TWG behaviour, and important context for contemporary observations and potential TWG response to future climate forcing
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