IS GREENLAND ICE CAP MELTWATER RUNOFF RECORDED IN GROWTH INCREMENT CHEMISTRY OF THE BAY MUSSEL (MYTILUS TROSSULUS)?

The Greenland ice cap (GrIC) is the world second largest ice mass. Current global warming causes accelerated melting, resulting in increased runoff since the early 1990s. Complete loss of the GrIC will result in a global sea level rise of ~7 m. Therefore it is crucial to gain insight in the dynamics of the GrIC through time. Instrumental data for Greenland cover the last few decades. Modeling studies investigate the natural variability in ice cap mass balance before that time, and under the influence of future global warming. Proxy data are crucial for the validation of these models. Since glacial meltwater has very low oxygen isotope (d¹⁸O) values of -30 to -20 ‰, we expect variations in meltwater runoff to be distinguishable in d¹⁸O values of coastal water.

Blue mussels of the genus Mytilus have been demonstrated to be faithful recorders of environmental variability (e.g. temperature, salinity) in the chemical composition of their shell. Although most work has been done on Mytilus edulis, this is also true for M. trossulus, the abundant species around Greenland. M. trossulus reaches an age of >20 years and as such can record possible decadal scale runoff variability.

We aim to evaluate the utility of M. trossulus shell chemistry as a proxy for past Greenland meltwater runoff. Research questions are: Do the apparently annual ridges on the shell correspond to yearly growth cycles? Can we distinguish between years of low and high meltwater runoff based on d¹⁸O records of the shells? Can we distinguish between shells of low runoff and high runoff time intervals? What can d¹³C and trace element records from these shells tell us about past environmental variability?

We present stable isotope and trace element records of a set of M. trossulus shells from Disko Bay (West-Greenland) covering the period 1996-2008. We compare these seasonal records with instrumental data and modeled runoff for the same time period. We also compare these with similar records from a specimen covering the years 1921-1933, representing the pre-global warming period.

Mytilus shells are readily found in Greenland archaeological finds from different settlement periods. The developed proxy can give insight in the climatic circumstances accompanying the rise and demise of Greenland cultures, such as the Norse settlement period during the Medieval Warm Period.