Fluctuations of a Greenlandic tidewater glacier driven by changes in atmospheric forcing: observations and modelling of Kangiata Nunaata Sermia, 1859–present

J M Lea,F M Nick,A Weidick,B R Rea,D W F Mair,M Morlighem,D Van As,P W Nienow

doi:10.5194/tc-8-2031-2014

Abstract

Abstract. Many tidewater glaciers in Greenland are known to have undergone significant retreat during the last century following their Little Ice Age maxima. Where it is possible to reconstruct glacier change over this period, they provide excellent records for comparison to climate records, as well as calibration/validation for numerical models. These glacier change records therefore allow for tests of numerical models that seek to simulate tidewater glacier behaviour over multi-decadal to centennial timescales. Here we present a detailed record of behaviour from Kangiata Nunaata Sermia (KNS), SW Greenland, between 1859 and 2012, and compare it against available oceanographic and atmospheric temperature data between 1871 and 2012. We also use these records to evaluate the ability of a well-established one-dimensional flow-band model to replicate behaviour for the observation period. The record of terminus change demonstrates that KNS has advanced/retreated in phase with atmosphere and ocean climate anomalies averaged over multi-annual to decadal timescales. Results from an ensemble of model runs demonstrate that observed dynamics can be replicated. Model runs that provide a reasonable match to observations always require a significant atmospheric forcing component, but do not necessarily require an oceanic forcing component. Although the importance of oceanic forcing cannot be discounted, these results demonstrate that changes in atmospheric forcing are likely to be a primary driver of the terminus fluctuations of KNS from 1859 to 2012. We propose that the detail and length of the record presented makes KNS an ideal site for model validation exercises investigating links between climate, calving rates, and tidewater glacier dynamics.

Highlights

Calving from tidewater glaciers (TWGs) presently accounts for up to 50 % of the mass loss from the Greenland Ice Sheet (Van den Broeke et al, 2009)
The importance of oceanic forcing cannot be discounted, these results demonstrate that changes in atmospheric forcing are likely to be a primary driver of the terminus fluctuations of Kangiata Nunaata Sermia (KNS) from 1859 to 2012
We propose that the detail and length of the record presented makes KNS an ideal site for model validation exercises investigating links between climate, calving rates, and tidewater glacier dynamics

Summary

Introduction

Calving from tidewater glaciers (TWGs) presently accounts for up to 50 % of the mass loss from the Greenland Ice Sheet (Van den Broeke et al, 2009). Determining controls on tidewater glacier dynamics over decadal to centennial timescales is crucial to understanding their contribution to sea level in a warming climate (Alley et al, 2010; Vieli and Nick, 2011). The ability to achieve this in Greenland has been restricted in part by the relative lack of TWG terminus observations prior to the satellite age, as well as evidence of terminus locations being spread across a disparate array of sources. The synthesis of these sources has previously allowed for multi-decadal to centennial records of TWG glacier behaviour to be reconstructed Lea et al.: Observations and modelling of Kangiata Nunaata Sermia, 1859–present

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