Abstract
Abstract. Melting of the Greenland Ice Sheet (GrIS) is accelerating and will contribute significantly to global sea level rise during the 21st century. Instrumental data on GrIS melting only cover the last few decades, and proxy data extending our knowledge into the past are vital for validating models predicting the influence of ongoing climate change. We investigated a potential meltwater proxy in Godthåbsfjord (West Greenland), where glacier meltwater causes seasonal excursions with lower oxygen isotope water (δ18Ow) values and salinity. The blue mussel (Mytilus edulis) potentially records these variations, because it precipitates its shell calcite in oxygen isotopic equilibrium with ambient seawater. As M. edulis shells are known to occur in raised shorelines and archaeological shell middens from previous Holocene warm periods, this species may be ideal in reconstructing past meltwater dynamics. We investigate its potential as a palaeo-meltwater proxy. First, we confirmed that M. edulis shell calcite oxygen isotope (δ18Oc) values are in equilibrium with ambient water and generally reflect meltwater conditions. Subsequently we investigated if this species recorded the full range of δ18Ow values occurring during the years 2007 to 2010. Results show that δ18Ow values were not recorded at very low salinities (< ~ 19), because the mussels appear to cease growing. This implies that Mytilus edulis δ18Oc values are suitable in reconstructing past meltwater amounts in most cases, but care has to be taken that shells are collected not too close to a glacier, but rather in the mid-region or mouth of the fjord. The focus of future research will expand on the geographical and temporal range of the shell measurements by sampling mussels in other fjords in Greenland along a south–north gradient, and by sampling shells from raised shorelines and archaeological shell middens from prehistoric settlements in Greenland.
Highlights
The Greenland Ice Sheet (GrIS) is the world’s second largest ice mass
Minimum δ18Ow values show a similar behaviour with −9.1 and −9.8 ‰, for GF3 and GF5 respectively, and a very low −18.6 ‰ at GF10 (Fig. 2a–c)
Lighter growth lines than the annual ones can be seen in several specimens (Godthabsfjord archipelago 1a & 1b, Ice Fjord south 4b, Ice Fjord north 3b, Kapisillit 13a; Fig. 4a, b, f, h and i). These lighter lines apparently correspond with troughs in the δ18Oc records, and are probably caused by an additional cessation of growth during maximum meltwater input
Summary
The Greenland Ice Sheet (GrIS) is the world’s second largest ice mass. The natural variability in GrIS mass balance over time is reconstructed by means of modelling studies, using instrumental data (covering the most recent decades) and proxy data (Alley et al, 2010; Israelson et al, 1994). Uncertainties in model projections are still considerable (Applegate et al, 2012; IPCC, 2007). In order to reduce these uncertainties and validate models, it is vital to collect proxy data on past ice sheet behaviour, such as surface mass balance and runoff (Alley et al, 2010; Applegate et al, 2012; Hanna et al, 2011).
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