Estimating Spring Terminus Submarine Melt Rates at a Greenlandic Tidewater Glacier Using Satellite Imagery

Oceanic forcing of the Greenland Ice Sheet is believed to promote widespread thinning at tidewater glaciers, with submarine melting proposed as a potential trigger of increased glacier calving, retreat, and subsequent acceleration. The precise mechanism(s) driving glacier instability, however, remain poorly understood, and while increasing evidence points to the importance of submarine melting, estimates of melt rates are uncertain. Here we estimate submarine melt rate by examining freeboard changes in the seasonal ice tongue of Kangiata Nunaata Sermia (KNS) at the head of Kangersuneq Fjord (KF), southwest Greenland. We calculate melt rates for March and May 2013 by differencing along-fjord surface elevation, derived from high-resolution TanDEM-X digital elevation models (DEMs), in combination with ice velocities derived from offset tracking applied to TerraSAR-X imagery. Estimated steady state melt rates reach up to 1.4 ± 0.5 m d−1 near the glacier grounding line, with mean values of up to 0.8 ± 0.3 and 0.7 ± 0.3 m d−1 for the eastern and western parts of the ice tongue, respectively. Melt rates decrease with distance from the ice front and vary across the fjord. This methodology reveals spatio-temporal variations in submarine melt rates (SMRs) at tidewater glaciers which develop floating termini, and can be used to improve our understanding of ice-ocean interactions and submarine melting in glacial fjords

The sensitivity of primary productivity in Disko Bay, a coastal Arctic ecosystem, to changes in freshwater discharge and sea ice cover

The Greenland ice sheet is melting, and the rate of ice loss has increased 6-fold since the 1980s. At the same time, the Arctic sea ice extent is decreasing. Meltwater runoff and sea ice reduction both influence light and nutrient availability in the coastal ocean, with implications for the timing, distribution, and magnitude of phytoplankton production. However, the integrated effect of both glacial and sea ice melt is highly variable in time and space, making it challenging to quantify. In this study, we evaluate the relative importance of these processes for the primary productivity of Disko Bay, west Greenland, one of the most important areas for biodiversity and fisheries around Greenland. We use a high-resolution 3D coupled hydrodynamic–biogeochemical model for 2004–2018 validated against in situ observations and remote sensing products. The model-estimated net primary production (NPP) varied between 90–147 gC m−2 yr−1 during 2004–2018, a period with variable freshwater discharges and sea ice cover. NPP correlated negatively with sea ice cover and positively with freshwater discharge. Freshwater discharge had a strong local effect within ∼ 25 km of the source-sustaining productive hot spots during summer. When considering the annual NPP at bay scale, sea ice cover was the most important controlling factor. In scenarios with no sea ice in spring, the model predicted a ∼ 30 % increase in annual production compared to a situation with high sea ice cover. Our study indicates that decreasing ice cover and more freshwater discharge can work synergistically and will likely increase primary productivity of the coastal ocean around Greenland.publishedVersio

The Day after Tomorrow - uniformitaristernes mareridt?

Dmi.dk har smugkigget på The Day after Tomorrow. Filmen er sprængfyldt med vilde, visuelle vejrfænomener; som vi i denne artikel sætter under meteorologisk lup. Hvad er fup,  og hvad er fakta

Analysing Spatial Distribution in Cattle within a Virtual Fence System

The interest in virtual fencing, as opposed to traditional physical barriers, has increased since it makesit easier to move the boundaries of animal enclosures for agricultural and rewilding purposes. Despite this, theimplementation of virtual fence systems, such as the Nofence© system, requires large financial investments. Thenecessity of individual collars also makes it more difficult to implement this system on a larger scale. If a herd ofcattle tend to maintain cohesive social groups around dominant individuals, it might be possible to use fewercollars thereby making the system more cost efficient. This study investigates the pattern in spatial distributionin a herd of 17 Angus cows on Fanø in Denmark with GPS locations, using a Nofence© system. The aim of thispaper is to determine how individuals position themselves in a herd, spatially, and identify a pattern in ranks. Themethod used in this study examines the distances between an individual to the rest of the herd mates using nearestneighbour and distribution plots. Contrary to the expectations, this study did not show a distinct pattern in herddistribution. While some tendencies in spatial distribution patterns were observed, only a low concordance couldbe found (W = 0.15, p = 3.02e−16). Therefore, interactions among individuals should be considered in futurestudies, rather than only investigating the herd as one unit. A cumulative curves of the ranks estimated over theentire periods allowed however a rough estimation of the hierarchy and allowed the identification of the highestranked cows. Therefore it might be possible to use fewer collars if the high ranked cows are discovered, but theestimation of the hierarchy will require a period of observation overall several days as the hierarchical positionsare fluctuating too much from days to days. Therefore the cumulative rank curves seems to be a valid solution.<br/

Greenland Ice Sheet late-season melt: investigating multi-scale drivers of K-transect events

One consequence of recent Arctic warming is an increased occurrence and longer seasonality of above-freezing air temperature episodes.There is significant disagreement in the literature concerning potential physical connectivity between high-latitude open water duration proximate to the Greenland Ice Sheet (GrIS) and unseasonal (i.e. late summer and autumn) GrIS melt events. Here, a new date of sea ice advance (DOA) product is used to determine the occurrence of Baffin Bay sea ice growth along Greenland’s west coast for the 2011–2015 period. For the unseasonal melt period preceding the DOA, northwest Atlantic Ocean and atmospheric conditions are analyzed and linked to unseasonal melt events observed at a series of on-ice automatic weather stations (AWS) along the K-transect in southwest Greenland. Mesoscale and synoptic influences on the above and below freezing surface air temperature events are assessed through analyses of AWS wind, pressure, and humidity observations. These surface observations are further compared against Modèle Atmosphérique Régional (MAR), Regional Atmospheric Climate Model (RACMO2), and ERA-Interim reanalysis fields to understand the airmass origins and (thermo)dynamic drivers of the melt events. Results suggest that the K-transect late season, ablation zone melt events are strongly affected by ridging atmospheric circulation patterns that transport warm, moist air from the sub-polar North Atlantic toward west Greenland. While thermal conduction and advection off south Baffin Bayopen waters impact coastal air temperatures, consistent with previous studies, marine air incursions from Baffin Bay onto the ice sheet are obstructed by barrier flows and the pressure gradient-driven katabatic regime along the western GrIS margin