An official website of the United States government
Abstract Parameterization of submarine melting represents a large source of uncertainty in modeling ice sheet response to climate change. Here we present in situ observations of melt at near‐vertical ice faces using a novel instrument platform mounted rigidly to icebergs. We investigate boundary layer dynamics controlling melt across 31 measurement periods that span a range of momentum and thermal forcing (1–12 cm/s flows and 3–10 K). While melt generally scales with velocity and temperature, we find substantially enhanced melt linked with unsteady forcing. Several implementations of the three‐equation melt parameterization show melt can be predicted within a factor of 2 if the model is evaluated with peak near‐boundary velocities and flows are quasi‐steady. However, if flows are unsteady or the model is evaluated with low‐resolution velocities, melt is underpredicted by 2– We conclude that understanding the detailed character of near‐boundary flows is critical for submarine melt predictions.
more »
« less
Localized velocity, temperature, salinity, and backscatter data from melting icebergs near Xeitl Sít' (LeConte Glacier, Southeast Alaska), 2023
Parameterization of submarine melt at near-vertical ice faces is a significant source of uncertainty in predicting ice mass loss and freshwater input into the ocean. Direct observations in this environment have historically been hindered by the dangers posed by actively calving glacier termini and potentially unstable icebergs. Aimed at filling this gap, this dataset contains observations from robotically-deployed Meltstakes at the near-vertical sides of icebergs in Xeitl Geeyí (LeConte Bay, Alaska). Measured quantities are ocean temperature, ocean salinity, ocean velocity, and backscatter data used to track the retreat (melt) of the ice-ocean interface. The observations are separated into 31 discrete segments (lasting 13-71 minutes) under which ocean forcing is relatively stationary and a reliable melt rate can be determined from the backscatter data. These sets of observations enable a direct comparison between small-scale oceanic forcing (~1 meter) and localized submarine melt rate across a wide parameter space (3-10°Celsius and 1-12 centimeters per second (cm/s) flows). Additionally, the observations allow testing of ice-ocean melt rate parameterizations. For more information about the Meltstake platform, see: Nash, J.D., Weiss, K., Wengrove, M.E., Osman, N., Pettit, E.C., Zhao, K., Jackson, R.H., Nahorniak, J., Jensen, K., Tindal, E., Skyllingstad, E., Cohen, N., and Sutherland, D (2024) Turbulent Dynamics of Buoyant Melt Plumes Adjacent Near-Vertical Glacier Ice. Geophysical Research Letters, 51, e2024GL108790. https://doi.org/10.1029/ 2024GL108790
more »
« less
- Award ID(s):
- 2023674
- PAR ID:
- 10660297
- Publisher / Repository:
- NSF Arctic Data Center
- Date Published:
- Subject(s) / Keyword(s):
- iceberg boundary layer submarine melt ice-ocean interactions
- Format(s):
- Medium: X Other: text/xml
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Submarine melting at Greenland's marine terminating glaciers is a crucial, yet poorly constrained process in the coupled ice‐ocean system. Application of Antarctic melt rate representations, derived for floating glacier tongues, to non‐floating marine terminating glaciers commonly found in Greenland, results in a dramatic underestimation of submarine melting. Here, we revisit the physical theory underlying melt rate parameterizations and leverage recently published observational data to derive a novel melt rate parameterization. This is the first parameterization that (a) consistently comprises both convective‐ and shear‐dominated melt regimes, (b) includes coefficients quantitatively constrained using observational data, and (c) is applicable to any vertical glacier front. We show that, compared to the current state‐of‐the‐art approach, the scheme provides an improved fit to observed melt rates on the scale of the terminating front, offering an opportunity to incorporate this critical missing forcing into ocean circulation models.more » « less
-
{"Abstract":["These data include processed multibeam sonar and drone-derived three-dimensional point clouds of icebergs surveyed between 2022 and 2023 in Xeitl Geeyí’ (LeConte Bay), Southeast Alaska. Thirteen grounded icebergs were mapped using Norbit iWBMS and Winghead i77h/i80s sonars, and one recently capsized floating iceberg was mapped using a DJI Air 2S drone. The datasets were collected to quantify submarine iceberg morphology and surface roughness as part of a broader effort to improve understanding of ice–ocean interactions at near-vertical ice-ocean boundaries. The methods and analyses are described in Cohen et al. (submitted in 2025), "Characterizing submarine ice roughness at icebergs from a temperate tidewater glacier", under review in the Journal of Glaciology. All data are georeferenced to World Geodetic System 1984 (WGS 84) and Universal Transverse Mercator Zone 8 N (meters in easting/northing)."]}more » « less
-
Melting glaciers are projected to produce several centimeters of sea level rise over the next few decades. Despite this threat, the fundamental fluid dynamics which drive melt at tidewater glaciers remain poorly characterized. This is primarily attributed to challenges associated with measuring the temperature and velocity of ocean water at the submerged cliffs of actively calving glaciers. To this end, we have developed a robotically-deployed instrument that can be bolted to a glacier's face. This instrument is capable of measuring temperature and velocity of ocean waters within a few centimeters of the ice, representing the first measurements of their kind. Our observations demonstrate the ways in which meltwater at ice boundaries can accelerate melt. Meltwaters tend to be less salty (and hence lighter) than the nearby ocean waters (which are salty, warm and heavy), so the meltwater rises along the ice face, creating an energetic, near boundary flow. The data here are used in Nash et al., 2024 to demonstrate that buoyant melt plumes are as important as large-scale currents in providing energy to the ice to fuel melt. We anticipate these data will help our community create more accurate models of ice melt needed to predict the advance or retreat of marine ice cliffs of Greenland, Alaska and Antarctica. Three distinct flow regimes are included in this dataset, corresponding to the following cases: Case 1A: Quasi-steady buoyant plume. Case 1B: Strongly-undulating buoyant plume. Case 2: Strong crossflow. Each of these are described in more detail in the following manuscript: Nash, J.D., Weiss, K., Wengrove, M.E., Osman, N., Pettit, E.C., Zhao, K., Jackson, R.H., Nahorniak, J., Jensen, K., Tindal, E., Skyllingstad, E., Cohen, N., and Sutherland, D (2024) Turbulent Dynamics of Buoyant Melt Plumes Adjacent Near-Vertical Glacier Ice. Geophysical Research Letters, in press. https://doi.org/10.22541/au.170869824.49695931/v1more » « less
-
Abstract. The role of icebergs in narrow fjords hosting marine-terminating glaciers in Greenland is poorly understood, even though iceberg melt results in asubstantial freshwater flux that can exceed the subglacial discharge. Furthermore, the melting of deep-keeled icebergs modifies the verticalstratification of the fjord and, as such, can impact ice–ocean exchanges at the glacier front. We model an idealised representation of thehigh-silled Ilulissat Icefjord in West Greenland with the MITgcm ocean circulation model, using the IceBerg package to study the effect of submarineiceberg melt on fjord water properties over a runoff season, and compare our results with available observations from 2014. We find the subglacialdischarge plume to be the primary driver of the seasonality of circulation, glacier melt and iceberg melt. Furthermore, we find that melting oficebergs modifies the fjord in three main ways: first, icebergs cool and freshen the water column over their vertical extent; second, iceberg-melt-induced changes to fjord stratification cause the neutral buoyancy depth of the plume and the export of glacially modified waters to be deeper;third, icebergs modify the deep basin, below their vertical extent, by driving mixing of the glacially modified waters with the deep-basin watersand by modifying the incoming ambient waters. Through the combination of cooling and causing the subglacial-discharge-driven plume to equilibratedeeper, icebergs suppress glacier melting in the upper layer, resulting in undercutting of the glacier front. Finally, we postulate that the impactof submarine iceberg melt on the neutral buoyancy depth of the plume is a key mechanism linking the presence of an iceberg mélange with theglacier front, without needing to invoke mechanical effects.more » « less
