I urval från Stockholms universitets publikationsdatabas

• Ryder Glacier in northwest Greenland is shielded from warm Atlantic water by a bathymetric sill

  2020. Martin Jakobsson (et al.). Communications earth & environment 1 (1)

  Artikel

  The processes controlling advance and retreat of outlet glaciers in fjords draining the Greenland Ice Sheet remain poorly known, undermining assessments of their dynamics and associated sea-level rise in a warming climate. Mass loss of the Greenland Ice Sheet has increased six-fold over the last four decades, with discharge and melt from outlet glaciers comprising key components of this loss. Here we acquired oceanographic data and multibeam bathymetry in the previously uncharted Sherard Osborn Fjord in northwest Greenland where Ryder Glacier drains into the Arctic Ocean. Our data show that warmer subsurface water of Atlantic origin enters the fjord, but Ryder Glacier's floating tongue at its present location is partly protected from the inflow by a bathymetric sill located in the innermost fjord. This reduces under-ice melting of the glacier, providing insight into Ryder Glacier's dynamics and its vulnerability to inflow of Atlantic warmer water. A bathymetric sill in Sherard Osborn Fjord, northwest Greenland shields Ryder Glacier from melting by warm Atlantic water found at the bottom of the fjord, according to high-resolution bathymetric mapping and oceanographic data.

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• Calving at Ryder Glacier, Northern Greenland

  2021. Felicity A. Holmes (et al.). Journal of Geophysical Research - Earth Surface 126 (4)

  Artikel

  Recent evidence has shown increasing mass loss from the Greenland ice sheet, with a general trend of accelerated mass losses extending northwards. However, different glaciers have been shown to respond differently to similar external forcings, constituting a problem for extrapolating and upscaling data. Specifically, whilst some outlet glaciers have accelerated, thinned, and retreated in response to atmospheric and oceanic warming, the behavior of other marine terminating glaciers appears to be less sensitive to climate forcing. Ryder glacier, for which only a few studies have been conducted, is located in North Greenland and terminates with a floating ice tongue in Sherard Osborn Fjord. The persistence or disintegration of floating ice tongues has impacts on glacier dynamics and stability, with ramifications beyond, including sea level rise. This study focuses on understanding the controls on calving and frontal ablation of the Ryder glacier through the use of time-lapse imagery and satellite data. The results suggest that Ryder glacier has behaved independently of climate forcing during recent decades, with fjord geometry exerting a first order control on its calving.

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• A nested high-resolution unstructured grid 3-D ocean-sea ice-ice shelf setup for numerical investigations of the Petermann ice shelf and fjord

  2022. Abhay Prakash (et al.). MethodsX 9

  Artikel

  Three-dimensional numerical simulation of circulation in fjords hosting marine-terminating ice shelves is challenging because of the complexity of processes involved in such environments. This often requires a comprehensive model setup. The following elements are needed: bathymetry (usually unknown beneath the glacier tongue), ice shelf draft (impacting water column thickness), oceanographic state (including tidal elevation, salinity, temperature and velocity of the water masses), sea ice and atmospheric forcing. Moreover, a high spatial resolution is needed, at least locally, which may be augmented with a coarser and computationally cheaper (nested) model that provides sufficiently realistic conditions at the boundaries. Here, we describe procedures to systematically create such a setup that uses the Finite Volume Community Ocean Model (FVCOM) for the Petermann Fjord, Northwest Greenland. The first simulations are validated against temperature and salinity observations from the Petermann Fjord in September 2019. We provide

  •Complete bathymetry, ice-draft and water column thickness datasets of the Petermann Fjord, with an improved representation of the topography underneath the glacier tongue.

  •Boundary conditions for ocean, atmosphere and sea ice derived from a suite of high-resolution regional models that can be used to initialize and run the regional ocean model with realistic geophysical settings.

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• Petermann Glacier Ice Shelf in a warming world: Insights from 3-D numerical modelling of ice shelf-ocean interactions at Petermann Fjord, Northwest Greenland

  2023. Abhay Prakash.

  Avhandling (Dok)

  The Greenland Ice Sheet (GrIS) is currently the largest contributor to global mean sea level rise, and contemporary mass loss rates are likely lower bounds for the rates to be observed in decades to come. At present, marine outlet glaciers along the northern GrIS margin, with an ice volume estimated at 400 cm mean global sea level rise equivalent, are still largely buttressed by ice shelves. However, thinning and retreat of these ice shelves, combined with perturbations of the outlet glacier’s grounding line (GL) can lead to a loss of backstress and accelerated mass loss via dynamic ice discharge, and likely render the latter the major contributor (as opposed to surface mass balance) to GrIS mass loss towards the end of the century.

  Here, the focus is on processes that drive basal melting of the Petermann Glacier Ice Shelf (PGIS), northwest Greenland, because contemporary knowledge regarding the full spectrum of mechanisms that dictate basal melting, and how they respond to a warming climate, is incomplete. This often results in poorly constrained oceanic boundary conditions, and consequently, afflicts estimates of GrIS’s contribution to future sea level rise with uncertainty.

  To address these questions, a non-idealized, nested, three-dimensional ocean-sea ice-ice shelf setup centered on PGIS and Petermann Fjord (PF) was created, based on the Finite Volume Community Ocean Model. With the setup developed and a “standard run” validated against observations from the fjord, the following scientific questions were investigated: How are basal melt rates at PGIS affected by 1. the presence, and likely future absence, of sea ice arches in Nares Strait? 2. subglacial discharge (Q_sg), through increased surface runoff from the GrIS and entering PF across the GL? 3. changes in the PGIS cavity geometry in a post future-calving scenario?

  Our results indicate that climate warming driven transition towards a mobile and thin sea ice cover from a landfast and thick one could result in up to twofold increase in melt. In such a scenario, wind and convectively upwelled warm Atlantic Water enter the PGIS cavity. Further, in summer, under the deeper regions of PGIS, more efficient melting occurs in a more turbulent cavity, without any noticeable increase in thermal driving. We find that the presence of Q_sg at the GL, and its subsequent increase in a warming atmosphere, increases melt by more than threefold. Melting also shows strong sensitivity to how Q_sg is routed across the GL. Importantly, we uncover that if Q_sg increases beyond 100% of present summer mean estimates, PGIS cavity enters a shear-controlled regime. Here, enhanced turbulent heat delivered by the vertical shear of the Qsg intensified current is sufficient to drive substantial increase in melt, even if there is no further increase in ocean heat forcing. Following the loss of the outer regions of PGIS post-calving, we find that wind enhanced fjord-scale currents act in concert with the Q_sg at the GL to strengthen the overturning circulation, thereby increasing the basal melt. In particular, we see up to threefold increase in melt in large sections of the basal channels under the deeper PGIS draft near the GL. These results suggest that intensified basal melting of PGIS in a warming climate; in particular, of its dynamically significant and resilient deeper regions, could accelerate mass loss from Petermann Glacier, with major implications for GrIS’s contribution to future sea level rise.

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