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  • 1
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    A simulation of small to giant Antarctic iceberg evolution: Differential impact on climatology estimates (2017)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2022-03-08
    Description: We present a simulation of Antarctic iceberg drift and melting that includes small, medium‐sized, and giant tabular icebergs with a realistic size distribution. For the first time, an iceberg model is initialized with a set of nearly 7000 observed iceberg positions and sizes around Antarctica. The study highlights the necessity to account for larger and giant icebergs in order to obtain accurate melt climatologies. We simulate drift and lateral melt using iceberg‐draft averaged ocean currents, temperature, and salinity. A new basal melting scheme, originally applied in ice shelf melting studies, uses in situ temperature, salinity, and relative velocities at an iceberg's bottom. Climatology estimates of Antarctic iceberg melting based on simulations of small (≤2.2 km), “small‐to‐medium‐sized" (≤10 km), and small‐to‐giant icebergs (including icebergs 〉10 km) exhibit differential characteristics: successive inclusion of larger icebergs leads to a reduced seasonality of the iceberg meltwater flux and a shift of the mass input to the area north of 58°S, while less meltwater is released into the coastal areas. This suggests that estimates of meltwater input solely based on the simulation of small icebergs introduce a systematic meridional bias; they underestimate the northward mass transport and are, thus, closer to the rather crude treatment of iceberg melting as coastal runoff in models without an interactive iceberg model. Future ocean simulations will benefit from the improved meridional distribution of iceberg melt, especially in climate change scenarios where the impact of iceberg melt is likely to increase due to increased calving from the Antarctic ice sheet.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Reducing the uncertainty in projections of future ice-shelf basal melting (2014)
    International Glaciological Society
    In:  EPIC3International Symposium on Contribution of Glaciers and Ice Sheets to Sea Level Change, Chamonix, France, 2014-05-26-2014-05-30International Glaciological Society
    Details
    Publication Date: 2014-07-04
    Description: Simulations of ice-shelf basal melting in future climate scenarios from the IPCC’s Fourth Assessment Report (AR4) have revealed a large uncertainty and the potential of a rapidly increasing basal mass loss particularly for the large cold-water ice shelves in the Ross and Weddell Seas. The large spread in model results was traced back to uncertainties in the freshwater budget on the continental shelf, which is governed by sea-ice formation. Differences in sea-ice formation, in turn, follow the regional differences between the atmospheric heat fluxes imprinted by the climate models. A more recent suite of BRIOS and FESOM model experiments was performed with output from two members of the newer generation of climate models engaged in the IPCC’s Fifth Assessment Report (AR5). Comparing simulations forced with output from the AR5/CMIP5 models HadGem2 and MPI-ESM, we find that uncertainties arising from inter-model differences in high latitudes have reduced considerably. Projected heat fluxes and thus sea-ice formation over the Southern Ocean continental shelves have converged to an ensemble with a much smaller spread than between the AR4 experiments. For most of the ten larger ice shelves in Antarctica, a gradual (but accelerating) increase of basal melt rates during the 21st century is a robust feature throughout the various realizations. Both with HadGem2 and with MPI-ESM forcing, basal melt rates for the Filchner–Ronne Ice Shelf in FESOM increase by a factor of two by the end of the 21st century in the RCP85 scenario. For the smaller, warm-water ice shelves, inter-model differences in ice-shelf basal mass loss projections are still slightly larger than differences between the scenarios RCP45 and RCP85; compared with AR4 projections, however, the model-dependent spread has been strongly reduced.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
    Format: application/pdf
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  • 3
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    A simulation of small to giant Antarctic iceberg evolution: Differential impact on climatology estimates (2017)
    Wiley
    In:  EPIC3Journal of Geophysical Research: Oceans, Wiley, ISSN: 21699275
    Details
    Publication Date: 2017-05-04
    Description: We present a simulation of Antarctic iceberg drift and melting that includes small, medium-sized, and giant tabular icebergs with a realistic size distribution. For the first time, an iceberg model is initialized with a set of nearly 7000 observed iceberg positions and sizes around Antarctica. The study highlights the necessity to account for larger and giant icebergs in order to obtain accurate melt climatologies. We simulate drift and lateral melt using iceberg-draft averaged ocean currents, temperature, and salinity. A new basal melting scheme, originally applied in ice shelf melting studies, uses in situ temperature, salinity, and relative velocities at an iceberg's bottom. Climatology estimates of Antarctic iceberg melting based on simulations of small (≤ 2.2 km), 'small-to-medium'-sized (≤ 10 km), and small-to-giant icebergs (including icebergs 〉 10 km) exhibit differential characteristics: successive inclusion of larger icebergs leads to a reduced seasonality of the iceberg meltwater flux and a shift of the mass input to the area north of 58 °S, while less meltwater is released into the coastal areas. This suggests that estimates of meltwater input solely based on the simulation of small icebergs introduce a systematic meridional bias; they underestimate the northward mass transport and are, thus, closer to the rather crude treatment of iceberg melting as coastal runoff in models without an interactive iceberg model. Future ocean simulations will benefit from the improved meridional distribution of iceberg melt, especially in climate change scenarios where the impact of iceberg melt is likely to increase due to increased calving from the Antarctic ice sheet.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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    PAPER (OA)
  • 4
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    Basal Melt and Freezing Rates From First Noble Gas Samples Beneath an Ice Shelf (2018)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 45(16), pp. 8455-8461, ISSN: 00948276
    Details
    Publication Date: 2018-09-27
    Description: A climatically-induced acceleration in ocean-driven melting of Antarctic ice shelves would have consequences for both the discharge of continental ice into the ocean and thus global sea level, and for the formation of Antarctic Bottom Water and the oceanic meridional overturning circulation. Using a novel gas-tight in-situ water sampler, noble gas samples have been collected from six locations beneath the Filchner Ice Shelf, the first such samples from beneath an Antarctic Ice shelf. Helium and neon are uniquely suited as tracers of glacial meltwater in the ocean. Basal meltwater fractions range from 3.6% near the ice shelf base to 0.5% near the sea floor, with distinct regional differences. We estimate an average basal melt rate for the Filchner-Ronne Ice Shelf of 177 ± 95 Gt/year, independently confirming previous results. We calculate that up to 2.7% of the meltwater has been refrozen, and we identify a local source of crustal helium.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 5
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    Enhanced cross-shelf exchange by tides in the western Ross Sea (2013)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 40(21), pp. 5735-5739, ISSN: 0094-8276
    Details
    Publication Date: 2019-07-16
    Description: The western Ross Sea is one of the key sites for cross-shelf water exchange around Antarctica. The mech- anism through which tides affect the cross-shelf exchange in the northwestern Ross Sea is investigated using numeri- cal simulations. Tides are found to increase the high-salinity shelf water (HSSW) outflow through the impact on the warm water intrusion of open ocean origin. The residual tidal currents are onshore along the Modified Circumpolar Deep Water pathway and therefore enhance its intrusion. Lighter ambient water adjacent to the HSSW increases the cross-flow density gradient, thus strengthening the HSSW export. At the same time, the onshore residual current and increased dilution of the HSSW have the potential to reduce the export rate. Owing to the existence of opposite tidal effects, the strongest HSSW export happens at the inter- mediate tidal forcing strength. The amplification of tides on cross-shelf exchange indicates that the relevant dynam- ical processes should be simulated or parameterized in climate models in order to adequately predict the ocean.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 6
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    Quantification of ice-shelf basal melting using a global finite-element sea ice--ice shelf--ocean model (2011)
    International Glaciological Society
    In:  EPIC3IGS-International Symposium on "Interactions of Ice Sheets and Glaciers with the Ocean", La Jolla, CA, USA, 2011-06-05-2011-06-10Proceedings of Glaciology 59, International Glaciological Society
    Details
    Publication Date: 2019-07-16
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 7
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    Exceptionally warm and prolonged flow of warm deep water toward the Filchner-Ronne Ice Shelf in 2017 (2020)
    Wiley
    Details
    Publication Date: 2022-10-26
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Ryan, S., Hellmer, H. H., Janout, M., Darelius, E., Vignes, L., & Schroeder, M. Exceptionally warm and prolonged flow of warm deep water toward the Filchner-Ronne Ice Shelf in 2017. Geophysical Research Letters, 47(13),(2020): e2020GL088119, doi:10.1029/2020GL088119.
    Description: The Filchner‐Ronne Ice Shelf, fringing the southern Weddell Sea, is Antarctica's second largest ice shelf. At present, basal melt rates are low due to active dense water formation; however, model projections suggest a drastic increase in the future due to enhanced inflow of open‐ocean warm water. Mooring observations from 2014 to 2016 along the eastern flank of the Filchner Trough (76°S) revealed a distinct seasonal cycle with inflow if Warm Deep Water during summer and autumn. Here we present extended time series showing an exceptionally warm and long inflow in 2017, with maximum temperatures exceeding 0.5°C. Warm temperatures persisted throughout winter, associated with a fresh anomaly, which lead to a change in stratification over the shelf, favoring an earlier inflow in the following summer. We suggest that the fresh anomaly developed upstream after anomalous summer sea ice melting and contributed to a shoaling of the shelf break thermocline.
    Description: The authors would like to express their gratitude to the officers and crews of RV Polarstern (cruises PS92 [Grant AWI_PS82_02], PS96 [Grant AWI_PS96_01], and PS111 [Grant AWI_PS111_01]), RRS Ernest Shackleton (Cruise ES060), and RSS James Clark Ross (Cruise JR16004) for their efficient assistance. E. D. received funding from the project TOBACO (267660), POLARPROG, Norges Forskningsrd.
    Keywords: Ocean-ice shelf interaction ; Weddell Sea ; Warm inflow ; Antarctic Slope Front ; Filchner-Ronne Ice Shelf
    Repository Name: Woods Hole Open Access Server
    Type: Article
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