Description: The Arctic Oscillation (AO) is the dominant mode of variability of the mean sea level pressure (MSLP) in the Northern hemisphere. It is a result of an EOF-analysis for SLP3 anomalies during winter. Because of a decisive influence of the AO on atmospheric processes in the troposphere and stratosphere (Randall et al., 2007), it is of interest how the AO behaves during changing climatological conditions. Therefore three runs of the Kiel Climate Model (KCM) will be analyzed considering the AO: a control run with pre-industrial CO2-level, an A1B scenario and a scenario in which the CO2-level will change by one percent per year until a doubling of the pre-industrial CO2-level is reached ongoing with a stabilization period. Comparing the AO of the control run with the AO of the CO2-forced run the result reaches an equal anomaly in the Arctic centre. By contrast the variability in the western North Atlantic Ocean is sinking while it is clearly rising in the North Pacific Ocean. Additionally the second EOF indicates an increasing variability in the Pacific Ocean, while it is also presenting a higher degree regarding the overall variability. As a result of the temporal evolution of the AO, calculated for the control run, in the forced scenario there is a distinctive positive trend in the AO-Index. This implies a lower SLP than the average in the Arctic. In order to classify the results of the KCM, the AO of the A1B scenario in the period of 1950 to 1999 of the KCM is compared to results simulated by the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4) ensembles of 14 coupled atmosphere-ocean-models, the resulting Multi-Model and observed data with regard to Miller et al. (2006). The observed data indicate as well as the A1B scenario of the KCM and the Multi-Model a positive trend in the AO-Index but the magnitude is varying. The results of the spatial distribution of the variability are showing a strong dispersion in between the models. The variability in the North Pacific Ocean is overestimated in the KCM as it is in most of the other models as well. Furthermore the AO indicates, with regard to the other IPCC models, a high agreement with the observed data in the Arctic centre and the Atlantic area.

Description: Approximately half of the freshwater discharged from the Greenland and Antarctic Ice Sheets enters the ocean subsurface as a result of basal ice melt, or runoff draining via the grounding line of a deep ice shelf or marine-terminating glacier. Around Antarctica and parts of northern Greenland, this freshwater then experiences prolonged residence times in large cavities beneath floating ice tongues. Due to the inaccessibility of these cavities, it is unclear how they moderate the freshwater associated supply of nutrients such as iron (Fe) to the ocean. Here, we show that subglacial dissolved Fe export from Nioghalvfjerdsbrae (the ‘79°N Glacier’) is decoupled from particulate inputs including freshwater Fe supply, likely due to the prolonged ~162-day residence time of Atlantic water beneath Greenland’s largest floating ice-tongue. Our findings indicate that the overturning rate and particle-dissolved phase exchanges in ice cavities exert a dominant control on subglacial nutrient supply to shelf regions.

Description: Highlights • CH4 excess is detected in water masses interacting with sea ice. • CH4 excess in surface waters is sea ice-sourced. • The meltwater layer restricts the sea-to-air flux via increased stratification. • CH4 excess is redistributed in the marine environment. • In water masses transported to the shelf, CH4 oxidation acts as biological CH4 sink. Global warming has led to a sharp decrease in Arctic summer sea ice extent and a dramatic ice mass loss of the Greenland Ice Sheet over the past three decades. The Northeast Greenland continental shelf is a site of intense water mass transformation involving both sea ice processes and glacier dynamics. The Arctic shelf waters are considered to be a net source of atmospheric methane (CH4); however, the effect of glacier and sea ice melt on oceanic CH4 concentrations still needs to be investigated. To better understand the effect of meltwater on the CH4 budget of the ocean, our study constrains the CH4 pathways by following changes in water mass properties and infers potential CH4 sources and sinks. Based on measurements of concentration and carbon isotope delta (δ13C) of CH4, the water mass tracer δ18O(H2O) and physical properties of the water masses, we detected CH4 excess in surface waters, which we attribute to brine release during sea ice formation. We show that this CH4 excess is sustained throughout the melt season, due to a freshwater lid formed at the ocean surface. The meltwater hardly alters the CH4 excess, but enhances water stratification, which, in turn, restricts the sea-to-air flux. The CH4 excess is subject to mixing with surrounding shelf waters influenced by basal glacial meltwater discharge. We suggest that the CH4 excess of Northeast Greenland continental shelf waters is redistributed in the marine environment, while CH4 emission to the atmosphere is limited to regions not covered by sea ice.