Oxygen isotope ratios in the shell of <i>Mytilus edulis</i>: archives of glacier meltwater in Greenland?

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 (δ 18 O w ) 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 (δ 18 O c ) values are in equilibrium with ambient water and generally reflect meltwater conditions. Subsequently we investigated if this species recorded the full range of δ 18 O w values occurring during the years 2007 to 2010. Results show that δ 18 O w values were not recorded at very low salinities (< ∼ 19), because the mussels appear to cease growing. This implies that M. edulis δ 18 O c 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 midregion 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.

Population structure of Mytilus edulis in the intertidal zone in a sub-Arctic fjord, SW Greenland

“…Recent shell growth was seen as a narrow band at the shell edge. This result agrees with a recent study of oxygen isotope ratios in the shell of Mytilus edulis in the Godthåbsfjord, indicating that growth checks are formed during winter growth cessation (Versteegh et al 2012).…”

“…In terms of salinity, the glacier-fjord-ocean transect provides a clear gradient. A recent study reported summer minimum values as low as <10 psu in surface waters in the inner part of Godthåbsfjord during peak melt water runoff and suggested that M. edulis ceased growing at salinities <19 psu (Versteegh et al 2012). However, our data did not reveal any trends in the overall growth patterns that could be related to inhibition by the low salinity in the inner part of the fjord.…”

“…There is a range overlap between M. edulis and the very similar congener M. trossulus throughout the North Atlantic. However, genetic studies of blue mussels in Greenland waters have not identified any species other than M. edulis (Wanamaker et al 2007, Versteegh et al 2012.…”

Local Coastal Water Masses Control Heat Levels in a West Greenland Tidewater Outlet Glacier Fjord

“…The presence of marine-terminating glaciers was found to explain sustained high productivity in fjords in Greenland (Meire et al, 2017). Interpretation of paleo-climatic proxies from fjords in Greenland (e.g., Versteegh et al, 2012) similarly depends on a knowledge of spatial gradients toward the open ocean. Thus, the exchange between the fjord and the open ocean and the link between this exchange and the fjord's seasonal circulation system is important for understanding physical conditions, biogeochemical cycling, and ecosystem dynamics inside fjords around Greenland.…”

CO&lt;sub&gt;2&lt;/sub&gt; and CH&lt;sub&gt;4&lt;/sub&gt; in sea ice from a subarctic fjord under influence of riverine input

“…Analysis was performed on a Picarro Isotopic Water Analyzer, L2120-I (Picarro, Sunnyvale, USA) equipped with a PAL auto sampler (Leap Technologies, Carrboro, USA). Details of the method can be found in Versteegh et al (2012). Results are expressed in standard δ 18 O notation using the Vienna Standard Mean Ocean Water (VSMOW) standard as a reference.…”