| 1. |
- Prakash, Abhay, et al.
(författare)
-
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
-
Ingår i: MethodsX. - : Elsevier BV. - 1258-780X .- 2215-0161. ; 9
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 2. |
- Prakash, Abhay, et al.
(författare)
-
Impact of the Nares Strait sea ice arches on the long-term stability of the Petermann Glacier Ice Shelf
- 2024
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- One of the last remaining Greenland Ice Sheet (GrIS) glaciers featuring a floating tongue – the Petermann Glacier Ice Shelf (PGIS) is seasonally shielded by the formation of sea ice arches in the Nares Strait. However, continued decline of the Arctic sea ice extent and thickness suggest that arch formation is likely to become anomalous, necessitating an investigation into the response of PGIS to a year round mobile and thin sea ice cover. We use a high-resolution 3-D ocean-sea ice-ice shelf setup featuring an improved sub-ice shelf bathymetry and a realistic PGIS geometry, to investigate in unprecedented detail, the implications of transitions in the Nares Strait sea ice regime; from Thick Landfast to Thick Mobile and Thin Mobile, on the PGIS basal melt. Across all three regimes, basal melting increases occur during summer, and under the deeper (> 250 m) regions of the ice shelf. Diagnosing this variability via melt rate drivers suggest that a higher thermal driving under the deeper regions causes higher melt rates, which, as a secondary effect, increases the friction velocity slightly downstream. The increased meltwater production and a stronger melt overturning in the PGIS cavity deliver more meltwater from depth to the shallower regions which lowers the thermal driving and basal melt in these regions; with the winter season showing a converse pattern. Modulations in surface forcing under a mobile and thin sea ice cover act to enhance the heat transport in the cavity, enhancing the thermal driving and friction velocity at the ice shelf base, and thereby, the basal melt. Thermodynamically, under mobile sea ice, wind upwelled Atlantic Water (AW) from the Nares Strait enter the cavity. Additionally, when sea ice thins, convective overturning drives further upwelling of AW in winter. Mechanically, wind driven inflow intensifies, and is most pronounced under a (negligibly thin) mobile summer sea ice cover; and where it acts in concert with the stronger melt overturning to enhance the friction velocity which predominantly drives the basal melt under the deeper regions. These results suggest that the projected continuation of the warming of the Arctic Ocean until the end of the 21st century and the decline in Arctic sea ice extent and thickness will amplify the basal melt, impacting the long term stability of the Petermann Glacier and its contribution to the future GrIS mass loss and sea level rise.
|
|
| 3. |
- Prakash, Abhay, et al.
(författare)
-
Petermann Glacier Ice Shelf after a future calving: Destabilized by intense channelized basal melting?
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The formation and subsequent propagation of a large crack across the Petermann Glacier Ice Shelf (PGIS) has been well tracked since 2016, and the implications of an imminent calving - comparable to previous large calving events in 2010 and 2012 - on the dynamics of Petermann Glacier (PG) have been widely investigated. However, the ocean’s response to change in PGIS geometry post-calving has not yet been quantified. Using a complex unstructured 3-D numerical regional ice shelf-ocean model setup, we show that following the loss of the outer (shallower) regions of PGIS, caused by a break-up of PGIS along the contemporary large crack, wind enhanced fjord-scale currents act in concert with subglacial discharge (Qsg) at the grounding line (GL) to strengthen the overturning circulation, thereby increasing the basal melt. Further, a transition towards a shear driven regime is seen as Qsg is raised above 100% of contemporary summer mean estimates; implying that melting occurs with no requirement of any increase in oceanic thermal forcing. In particular, we see up to threefold increase in melt in large sections under the deeper regions of PGIS base near the GL. The highly channelized nature of this melt amplification indicates that an idealised (smooth) representation of PGIS draft in numerical models may lead to inaccurate results. We posit that such enhanced channelized basal melting of the dynamically significant and resilient inner (deeper) region of PGIS could promote undercutting driven calving, with perturbed GL and inland stresses resulting in accelerated mass loss from PG.
|
|
| 4. |
- Prakash, Abhay, et al.
(författare)
-
Uncovering how a warmer atmosphere will control the basal melting of Petermann Glacier Ice Shelf
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Long-term stability of the Petermann Glacier Ice Shelf (PGIS), which buttresses 4% of the total Greenland Ice Sheet (GrIS) discharge, will significantly impact GrIS’s contribution to future sea level rise. Basal melting of PGIS has been widely attributed to increased ocean warming, however, the role of a warmer atmosphere and the mechanisms that will dictate the basal melt have not been properly quantified. Here, we use a state-of-the-art 3-D numerical regional model setup centered at the Petermann Fjord to investigate how a warmer atmosphere, via enhanced subglacial discharge (Qsg), will control PGIS basal melt. Our results show that area averaged summer mean PGIS basal melt increases by more than threefold under a future warmer atmosphere as compared to winter (no Qsg), and is sensitive to how Qsg is routed across the grounding line. We show that if Qsg 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. Given the recent estimates of Qsg and its expected future increase, we posit that a large part of the contemporary summer melt is being driven by this regime; and which will likely control the entirety of future summer melt.
|
|
| 5. |
- Rabe, Benjamin, et al.
(författare)
-
Polar Fresh Water in a Changing Global Climate Linking Arctic and Southern Ocean Processes
- 2023
-
Ingår i: Bulletin of the American Meteorological Society. - 0003-0007 .- 1520-0477. ; 104:5
-
Tidskriftsartikel (refereegranskat)abstract
- NORP-SORP Workshop on Polar Fresh Water: Sources, Pathways and Impacts of Freshwater in Northern and Southern Polar Oceans and Seas (SPICE-UP) What: Up to 60 participants at a time and more than twice as many registrants in total from 20 nations and across experience levels met to discuss the current status of research on freshwater in both polar regions, future directions, and synergies between the Arctic and Southern Ocean research communities When: 19–21 September 2022 Where: Online
|
|
| 6. |
- Silvano, Alessandro, et al.
(författare)
-
Observing Antarctic Bottom Water in the Southern Ocean
- 2023
-
Ingår i: Frontiers in Marine Science. - 2296-7745. ; 10
-
Forskningsöversikt (refereegranskat)abstract
- Dense, cold waters formed on Antarctic continental shelves descend along the Antarctic continental margin, where they mix with other Southern Ocean waters to form Antarctic Bottom Water (AABW). AABW then spreads into the deepest parts of all major ocean basins, isolating heat and carbon from the atmosphere for centuries. Despite AABW's key role in regulating Earth's climate on long time scales and in recording Southern Ocean conditions, AABW remains poorly observed. This lack of observational data is mostly due to two factors. First, AABW originates on the Antarctic continental shelf and slope where in situ measurements are limited and ocean observations by satellites are hampered by persistent sea ice cover and long periods of darkness in winter. Second, north of the Antarctic continental slope, AABW is found below approximately 2 km depth, where in situ observations are also scarce and satellites cannot provide direct measurements. Here, we review progress made during the past decades in observing AABW. We describe 1) long-term monitoring obtained by moorings, by ship-based surveys, and beneath ice shelves through bore holes; 2) the recent development of autonomous observing tools in coastal Antarctic and deep ocean systems; and 3) alternative approaches including data assimilation models and satellite-derived proxies. The variety of approaches is beginning to transform our understanding of AABW, including its formation processes, temporal variability, and contribution to the lower limb of the global ocean meridional overturning circulation. In particular, these observations highlight the key role played by winds, sea ice, and the Antarctic Ice Sheet in AABW-related processes. We conclude by discussing future avenues for observing and understanding AABW, impressing the need for a sustained and coordinated observing system.
|
|
