Large mercury release from the Greenland Ice Sheet invalidated.

The major input of mercury (Hg) to the Arctic is normally ascribed to long-range transport of anthropogenic Hg emissions. Recently, alarming concentrations of Hg in meltwater from the Greenland Ice Sheet (GrIS) were reported with bedrock as the proposed source. Reported Hg concentrations were 100 to 1000 times higher than in known freshwater systems of Greenland, calling for independent validation of the extraordinary concentrations and conclusions. Here, we present measurements of Hg at 21 glacial outlets in West Greenland showing that extreme Hg concentrations cannot be reproduced. In contrast, we find that meltwater from below the GrIS is very low in Hg, has minor implications for the global Hg budget, and pose only a very limited risk for local communities and the natural environment of Greenland.

PAHs in high Arctic copepods Calanus hyperboreus following exposure of residues from in situ burning of oil spill.

In situ burning of marine oil spills reduces the total amount of oil in the environment, but a negative side effect may be the generation of environmentally hazardous polycyclic aromatic hydrocarbons (PAHs) that may pose a risk for bioaccumulation, particularly in organisms having a high lipid content. In this study uptake of PAHs from oil and burn residue were examined in the high arctic copepod Calanus hyperboreus. A major part of the low ring number petrogenic PAHs in the oil was removed during burning and relative higher concentrations of pyrogenic high ring number PAHs was found in the burn residue. This suggests that burning markedly reduces the general PAH exposure load. Furthermore, the pyrogenic PAHs generated during the burn were not bioconcentrated to quantifiable levels in the copepods. We conclude that in situ burning can mitigate the potential risk of PAH uptake for copepods and other pelagic organisms in the marine environment as the pyrogenic PAHs only pose low risk for uptake from the water by the copepods and other pelagic organisms.

First observation of direct methane emission to the atmosphere from the subglacial domain of the Greenland Ice Sheet.

During a 2016 field expedition to the West Greenland Ice Sheet, a striking observation of significantly elevated CH4 concentrations of up to 15 times the background atmospheric concentration were measured directly in the air expelled with meltwater at a subglacial discharge point from the Greenland Ice Sheet. The range of hourly subglacial CH4 flux rate through the discharge point was estimated to be 3.1 to 134 g CH4 hr-1. These measurements are the first observations of direct emissions of CH4 from the subglacial environment under the Greenlandic Ice Sheet to the atmosphere and indicate a novel emission pathway of CH4 that is currently a non-quantified component of the Arctic CH4 budget.

Microbial oxidation of pyrite coupled to nitrate reduction in anoxic groundwater sediment.

Although many areas in Denmark are intensively agricultured, the discharge of nitrate from groundwater aquifers to surface water is often lower than expected. In this study it is experimentally demonstrated that anoxic nitrate reduction in sandy sediment containing pyrite is a microbially mediated denitrification process with pyrite as the primary electron donor. The process demonstrates a temperature dependency (Q10) of 1.8 and could be completely inhibited by addition of a bactericide (NaN3). Experimentally determined denitrification rates show that more than 50% of the observed nitrate reduction can be ascribed to pyrite oxidation. The apparent zero-order denitrification rate in anoxic pyrite containing sediment at groundwater temperature has been determined to be 2-3 micromol NO3- kg(-1) day(-1). The in situ groundwater chemistry at the boundary between the redoxcline and the anoxic zone reveals that between 65 and 80% of nitrate reduction in the lower part of the redoxcline is due to anoxic oxidation of pyrite by nitrate with resulting release of sulfate. It is concluded that microbes can control groundwater nitrate concentrations by denitrification using primarily pyrite as electron donor at the oxic-anoxic boundary in sandy aquifers thus determining the position and downward progression of the redox boundary between nitrate-containing and nitrate-free groundwater.