Reconstruction of changes in sea-ice, water temperature and Greenland Ice Sheet runoff into Disko Bay, Greenland (RECONNECT)

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Global warming will lead to major Arctic changes in years to come, with increasing climatic, biological, and social impacts - also reaching regions outside the Arctic. Greenland is particularly vulnerable to ongoing anthropogenic climate change and a warming "hotspot". Observational data document recent rapid mass loss of many of the Greenland ice sheet (GIS) glaciers, accelerated decline in Arctic sea-ice and substantial oceanic freshening trends. Mass loss of the GIS represents a major contributor to global sea level rise, but uncertainties in future projections are large. Thus, it is crucial to understand internal processes and ocean-ice-atmosphere interactions driving variability in Arctic temperatures, sea-ice characteristics and freshwater flux from the GIS, in order to better assess the influence of anthropogenic contributions. Available observational records from high latitudes are sparse and short, thus large uncertainties remain, making predictions difficult. Models require high-resolution data of past variability to resolve how fast the GIS reacts to warming. Past climate can be reconstructed from so-called proxy archives. In high latitudes, however, most proxy time series utilised to date come from indirect land-based archives, while marine archives generally do not exceed century- or decadal-scale resolution. Hence, the exploration of new high-resolution marine archives is a top priority. This proposal focuses on calcified coralline algal buildups growing attached to the seafloor, that have recently emerged as novel subannual resolution climate recorders. By targeting long-lived individuals from Disko Bay, West-Greenland, I address this data gap. My study sites are located close to Jakobshavn Glacier, one of the largest glaciers in Greenland and the single largest source of mass loss from the GIS over the last 20 years. Estimates of melt variability and glacier runoff remain uncertain before the satellite era and long-term decadal- to multidecadal variability and mechanisms are not well understood. The main goals of this project are: (1) to develop the first annually-resolved multicentury-length proxy reconstructions of past seawater temperature, seasonal duration of sea-ice, and freshwater flux to Disko Bay, Greenland, by means of sclerochronological and geochemical analysis of long-lived algal skeletons, (2) to establish baseline data of pre-industrial natural low-frequency arctic climate and ocean variability, and (3) to reconstruct decadal- to multidecadal-scale variability in Jakobshavn Glacier runoff, providing a long-term perspective on linkages to oceanic and atmospheric processes. These new long-term annual-resolution records are highly needed and represent a major milestone for improving predictions of future cryospheric change and underlying steering mechanisms which have regional and global implications.