Meltwater Intrusions Reveal Mechanisms for Rapid Submarine Melt at a Tidewater Glacier

Jackson, R. H.; Nash, Jonathan D.; Kienholz, Christian; Sutherland, David A.; Amundson, J. M.; Motyka, R. J.; Winters, Dylan S.; Skyllingstad, Eric D.; Pettit, E. C.

doi:10.1029/2019gl085335

Cited by 63 publications

(186 citation statements)

References 48 publications

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“…2b). Studies that have assessed subglacial runoff from fjord observations find agreement between their oceanographic estimates and the method de-scribed here (Jackson and Straneo, 2016;Mankoff et al, 2016;Jackson et al, 2017).…”

Section: Hydrological Drainage Basinsmentioning

confidence: 55%

Twenty-first century ocean forcing of the Greenland ice sheet for modelling of sea level contribution

et al. 2020

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Abstract. Changes in ocean temperature and salinity are expected to be an important determinant of the Greenland ice sheet's future sea level contribution. Yet, simulating the impact of these changes in continental-scale ice sheet models remains challenging due to the small scale of key physics, such as fjord circulation and plume dynamics, and poor understanding of critical processes, such as calving and submarine melting. Here we present the ocean forcing strategy for Greenland ice sheet models taking part in the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6), the primary community effort to provide 21st century sea level projections for the Intergovernmental Panel on Climate Change Sixth Assessment Report. Beginning from global atmosphere–ocean general circulation models, we describe two complementary approaches to provide ocean boundary conditions for Greenland ice sheet models, termed the “retreat” and “submarine melt” implementations. The retreat implementation parameterises glacier retreat as a function of projected subglacial discharge and ocean thermal forcing, is designed to be implementable by all ice sheet models and results in retreat of around 1 and 15 km by 2100 in RCP2.6 and 8.5 scenarios, respectively. The submarine melt implementation provides estimated submarine melting only, leaving the ice sheet model to solve for the resulting calving and glacier retreat and suggests submarine melt rates will change little under RCP2.6 but will approximately triple by 2100 under RCP8.5. Both implementations have necessarily made use of simplifying assumptions and poorly constrained parameterisations and, as such, further research on submarine melting, calving and fjord–shelf exchange should remain a priority. Nevertheless, the presented framework will allow an ensemble of Greenland ice sheet models to be systematically and consistently forced by the ocean for the first time and should result in a significant improvement in projections of the Greenland ice sheet's contribution to future sea level change.

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Section: Hydrological Drainage Basinsmentioning

confidence: 55%

Twenty-first century ocean forcing of the Greenland ice sheet for modelling of sea level contribution

et al. 2020

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“…Simulations with these runoff values were repeated using two subglacial drainage configurations that are broadly representative of 'channelised' and 'distributed' subglacial drainage (Methods). Our primary simulations used melt rate parameter values commonly used in the literature 8 (Methods; Supplementary Table 1); however, recent observations 45,46 suggest that these 'standard' values may underestimate glacier submarine melt rates. We therefore repeated each simulation using the 'adjusted' parameter values ( Supplementary Table 1) suggested by Jackson et al 45 .…”

mentioning

confidence: 99%

Iceberg melting substantially modifies oceanic heat flux towards a major Greenlandic tidewater glacier

et al. 2020

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Fjord dynamics influence oceanic heat flux to the Greenland ice sheet. Submarine iceberg melting releases large volumes of freshwater within Greenland’s fjords, yet its impact on fjord dynamics remains unclear. We modify an ocean model to simulate submarine iceberg melting in Sermilik Fjord, east Greenland. Here we find that submarine iceberg melting cools and freshens the fjord by up to ~5 °C and 0.7 psu in the upper 100-200 m. The release of freshwater from icebergs drives an overturning circulation, resulting in a ~10% increase in net up-fjord heat flux. In addition, we find that submarine iceberg melting accounts for over 95% of heat used for ice melt in Sermilik Fjord. Our results highlight the substantial impact that icebergs have on the dynamics of a major Greenlandic fjord, demonstrating the importance of including related processes in studies that seek to quantify interactions between the ice sheet and the ocean.

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“…At the glacier face, the basal melt rate may be underestimated by the ICEPLUME model (Holland & Jenkins, 1999;Sutherland et al, 2019). Recent data from LeConte Glacier, Alaska, for example, suggest that modeled basal melt rates could be 100× lower than reality (Jackson et al, 2019). Our model also does not include icebergs and iceberg melting, which can drive localized nutrient upwelling and dilute phytoplankton (Schwarz & Schodlok, 2009;Vernet et al, 2011).…”

Section: 1029/2020jc016185mentioning

confidence: 95%

Meltwater‐Enhanced Nutrient Export From Greenland's Glacial Fjords: A Sensitivity Analysis

et al. 2020

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As mass loss from the Greenland Ice Sheet accelerates, this modeling study considers how meltwater inputs to the ocean can impact marine ecosystems using a simplified fjord scenario. At marine‐terminating glaciers in Greenland fjords, meltwater can be delivered far below the sea surface, both as subglacial runoff (from atmosphere‐driven surface melt) and as basal melt (from ocean heat). Such delivery can result in buoyancy‐driven upwelling and the upward entrainment of nutrient‐rich deep water, which can support phytoplankton growth in fjord surface waters. For this study, we use an idealized fjord‐scale model to investigate which properties of glaciers and fjords govern the transport of buoyantly upwelled nutrients from fjords. We model the influence of fjord geometry, hydrology, wind, tides, and phytoplankton growth within the fjord on meltwater‐driven nutrient export to the ocean. We use the Regional Ocean Modeling System (ROMS) coupled to a buoyant plume model and a biogeochemical model to simulate physical and biogeochemical processes within an idealized tidewater glacial fjord. Results show that meltwater‐driven nutrient export increases with larger subglacial discharge rates and deeper grounding lines, features that are both likely to change with continued ice sheet melting. Nutrient export decreases with longer residence times, allowing greater biological drawdown. While the absence of a coastal current in the model setup prevents the downstream advection of exported nutrients, results suggest that shelf‐forced flows could influence nutrient residence time within fjords. This simplified model highlights key uncertainties requiring further observation to understand ecological impacts of Greenland mass loss.

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Meltwater Intrusions Reveal Mechanisms for Rapid Submarine Melt at a Tidewater Glacier

Cited by 63 publications

References 48 publications

Twenty-first century ocean forcing of the Greenland ice sheet for modelling of sea level contribution

Twenty-first century ocean forcing of the Greenland ice sheet for modelling of sea level contribution

Iceberg melting substantially modifies oceanic heat flux towards a major Greenlandic tidewater glacier

Meltwater‐Enhanced Nutrient Export From Greenland's Glacial Fjords: A Sensitivity Analysis

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