TOWARDS UNDERSTANDING BIOGEOCHEMICAL CYCLING OF MERCURY IN GLACIAL ENVIRONMENTS: A CASE STUDY, MATANUSKA GLACIER, ALASKA

Mercury (Hg II) and especially methylmercury (MeHg) is increasing in a number of marine species in the Arctic while atmospheric elemental mercury (Hg⁰) levels show only little signs of change suggesting that other processes than atmospheric deposition leads to release of mercury into the Arctic environment. Glacier have accumulated atmospheric derived gaseous pollutants over time making them to a potential source for mercury. This paper presents first results towards a better understanding of mercury deposition, export and biogeochemical cycling in a glacier system.

The easily accessible Matanuska Glacier in the Chugach Mountains in south central Alaska, about 138 km north of Anchorage was choosen for a case study. It is a large valley glacier that flows north about 45 km from the Ted Stevens Ice Field to its terminus, ranging in width from approximately 3 km near the equilibrium line to about 5 km at the head of the Matanuska Valley. The glacier features overdeepenings creating supercooled, subglacial water which discharges from vents at the terminus. This meltwater is routed through subglacial cavities within distributed and channelized drainage systems and can be easily sampled at the ice margin throughout the year.

We sampled the supraglacial and subglacial meltwater from June to August in 2013 and 2014. Snow samples were collected in spring 2014. Basal ice samples were collected at the terminus in summer 2013 and November 2014. All samples were analyzed for cation, anion and mercury, and some selected samples were analyzed for monomethylmercury (MeHg). Suspended sediment was sampled by filtering between 10 to 20L water for further microbiological investigations. Our initial results reveal elevated concentrations of mercury in the subglacial meltwater in vents. MeHg values in all waters are either below or close to the limit of detection of about 0.02 ppt. Highest vales of Hg (II) and MeHg were measured in basal ice followed by that in snow samples. These limited results show no apparent seasonal trend or relationship to the water source.