Holocene climate change in the Bransfield Basin, Antarctic Peninsula: evidence from sediment and diatom analysis

AbstractWe present the first study from the Bransfield Basin that extends through the Holocene, recording the variable climate history back to the decoupling of the ice sheet from the continental shelf ~10 650 calendar years before present (cal yr bp). Detailed sediment analysis reveals three stratigraphic units in PC-61 concomitant with three sedimentary environments, similar to sedimentary facies reported elsewhere: 1) subglacial, 2) glacial proximal/sub-ice shelf, and 3) open marine. These interpretations are based on a variety of sedimentological criteria, supported by ten AMS radiocarbon dates and detailed diatom analysis. We note two significant volcanic ash layers (tephra) at 3870 and 5500 cal yr bp from nearby Deception Island. Based on diatom assemblage analysis, we identify five separate climate regimes, highlighting a significantly shorter Mid-Holocene Climatic Optimum than reported by other studies (6800–5900 cal yr bp). This period is marked by the highest Eucampia antarctica var. antarctica and Fragilariopsis curta abundance, total diatom abundance, sediment accumulation rates, and low magnetic susceptibility. We also identify a less pronounced Neoglacial period relative to other studies, which includes an increase of Cocconeis/Rhizosolenia spp. assemblage related to unstable surface water conditions. Such observations probably reflect important regional variations in atmospheric or ocean circulation patterns.

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Antarctic Climate History and Global Climate Changes

10.1093/oxfordhb/9780190699420.013.18 ◽

2017 ◽

Author(s):

Pontus Lurcock ◽

Fabio Florindo

Keyword(s):

Ocean Circulation ◽

Climate Changes ◽

Numerical Models ◽

Global Climate ◽

Sediment Cores ◽

Ice Sheets ◽

Global Ocean ◽

Climate History ◽

Global Climate Changes ◽

Planetary Albedo

Antarctic climate changes have been reconstructed from ice and sediment cores and numerical models (which also predict future changes). Major ice sheets first appeared 34 million years ago (Ma) and fluctuated throughout the Oligocene, with an overall cooling trend. Ice volume more than doubled at the Oligocene-Miocene boundary. Fluctuating Miocene temperatures peaked at 17–14 Ma, followed by dramatic cooling. Cooling continued through the Pliocene and Pleistocene, with another major glacial expansion at 3–2 Ma. Several interacting drivers control Antarctic climate. On timescales of 10,000–100,000 years, insolation varies with orbital cycles, causing periodic climate variations. Opening of Southern Ocean gateways produced a circumpolar current that thermally isolated Antarctica. Declining atmospheric CO2 triggered Cenozoic glaciation. Antarctic glaciations affect global climate by lowering sea level, intensifying atmospheric circulation, and increasing planetary albedo. Ice sheets interact with ocean water, forming water masses that play a key role in global ocean circulation.

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Pigment Preservation in Lake Sediments: A Comparison of Sedimentary Environments in Trout Lake, Wisconsin

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f91-061 ◽

1991 ◽

Vol 48 (3) ◽

pp. 472-486 ◽

Cited By ~ 39

Author(s):

James P. Hurley ◽

David E. Armstrong

Keyword(s):

Accumulation Rate ◽

Sediment Cores ◽

Sediment Accumulation ◽

Sediment Surface ◽

Water Interface ◽

Sedimentary Pigments ◽

Sedimentary Environments ◽

Trout Lake ◽

Secondary Carotenoids ◽

Β Carotene

Fluxes and concentrations of a phorbins and major algal carotenoids were quantified in sediment trap material and sediment cores from two basins of Trout Lake, Wisconsin (TrDH and TrAB). The basins were chosen to contrast the influence of oxygen content at the sediment–water interface (TrDH, oxic and TrAB, reducing), sediment accumulation rate, and focusing. Pigment diagenesis occurred in both basins, but transformations and destruction were more extensive in TrDH. Although untransformed chlorophyll a was the major phorbin deposited at the sediment surface of both basins (51–64 mol%), pigment destruction, coupled with transition to pheophytin, accounted for substantial losses, especially in oxic TrDH sediments. Fucoxanthin, peridinin, and diadinoxanthin, despite representing > 70% of the deposited carotenoid flux, were substantially degraded or transformed in both basins. However, preservation was relatively high for secondary carotenoids, such as diatoxanthin and β-carotene, and for a major cryptomonad pigment, alloxanthin. Residual profiles in sediments show that pigment sedimentation from the epilimnion and accumulation in the permanent sediments are not directly related and that diagenesis must be considered in interpreting sedimentary pigments.

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Modelling the ocean circulation and the basal melting in the Prydz Bay-Amery Ice Shelf system

10.5194/egusphere-egu21-6425 ◽

2021 ◽

Author(s):

Jing Jin ◽

Antony J. Payne ◽

William Seviour ◽

Christopher Bull

Keyword(s):

Heat Transport ◽

Ocean Circulation ◽

Water Masses ◽

Prydz Bay ◽

Effect Of Temperature ◽

Oceanic Circulation ◽

Ice Shelf ◽

Thermodynamic Structure ◽

Amery Ice Shelf ◽

Basal Melting

The basal melting of the Amery Ice Shelf (AIS) in East Antarctica and its connections with the oceanic circulation are investigated by a regional ocean model. The simulated estimations of net melt rate over AIS from 1976 to 2005 vary from 1 to 2 m/yr depending primarily due to inflow of modified Circumpolar Deep Water (mCDW). Prydz Bay Eastern Costal Current (PBECC) and the eastern branch of Prydz Bay Gyre (PBG) are identified as two main mCDW intrusion pathways. The oceanic heat transport from both PBECC and PBG has significant seasonal variability, which is associated with the Antarctic Slope Current. The onshore heat transport has a long-lasting effect on basal melting. The basal melting is primarily driven by the inflowing water masses though a positive feedback mechanism. The intruding warm water masses destabilize the thermodynamic structure in the sub-ice shelf cavity therefore enhancing the overturning circulations, leading to further melting due to increasing heat transport. However, the inflowing saltier water masses due to sea-ice formation could offset the effect of temperature through stratifying the thermodynamic structure, then suppressing the overturning circulation and reducing the basal melting.

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Lake-level variability in Salar de Coipasa, Bolivia during the past ∼40,000 yr

Quaternary Research ◽

10.1017/qua.2018.108 ◽

2018 ◽

Vol 91 (2) ◽

pp. 881-891 ◽

Cited By ~ 4

Author(s):

J. Andrew Nunnery ◽

Sherilyn C. Fritz ◽

Paul A. Baker ◽

Wout Salenbien

Keyword(s):

Lake Level ◽

Sediment Accumulation ◽

Geochemical Data ◽

South American ◽

Climate History ◽

Oxygen Isotope Stage ◽

The Past ◽

History Of ◽

Diatom Stratigraphy ◽

The Last Glacial

AbstractVarious paleoclimatic records have been used to reconstruct the hydrologic history of the Altiplano, relating this history to past variability of the South American summer monsoon. Prior studies of the southern Altiplano, the location of the world’s largest salt flat, the Salar de Uyuni, and its neighbor, the Salar de Coipasa, generally agree in their reconstructions of the climate history of the past ∼24 ka. Some studies, however, have highly divergent climatic records and interpretations of earlier periods. In this study, lake-level variation was reconstructed from a ∼14-m-long sediment core from the Salar de Coipasa. These sediments span the last ∼40 ka. Lacustrine sediment accumulation was apparently continuous in the basin from ∼40 to 6 ka, with dry or very shallow conditions afterward. The fossil diatom stratigraphy and geochemical data (δ13C, δ15N, %Ca, C/N) indicate fluctuations in lake level from shallow to moderately deep, with the deepest conditions correlative with the Heinrich-1 and Younger Dryas events. The stratigraphy shows a continuous lake of variable depth and salinity during the last glacial maximum and latter stages of Marine Oxygen Isotope Stage 3 and is consistent with environmental inferences and the original chronology of a drill core from Salar de Uyuni.

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Viscosity and elasticity: a model intercomparison of ice-shelf bending in an Antarctic grounding zone

Journal of Glaciology ◽

10.1017/jog.2017.15 ◽

2017 ◽

Vol 63 (240) ◽

pp. 573-580 ◽

Cited By ~ 7

Author(s):

CHRISTIAN T. WILD ◽

OLIVER J. MARSH ◽

WOLFGANG RACK

Keyword(s):

Young’S Modulus ◽

Ocean Circulation ◽

Young's Modulus ◽

Viscoelastic Model ◽

Ice Sheet ◽

Global Ocean ◽

Elastic Model ◽

Ice Shelf ◽

Bending Stresses ◽

Global Ocean Circulation

ABSTRACTGrounding zones are vital to ice-sheet mass balance and its coupling to the global ocean circulation. Processes here determine the mass discharge from the grounded ice sheet, to the floating ice shelves. The response of this transition zone to tidal forcing has been described by both elastic and viscoelastic models. Here we examine the validity of these models for grounding zone flexure over tidal timescales using field data from the Southern McMurdo Ice Shelf (78° 15′S, 167° 7′E). Observations of tidal movement were carried out by simultaneous tiltmeter and GPS measurements along a profile across the grounding zone. Finite-element simulations covering a 64 d period reveal that the viscoelastic model fits best the observations using a Young's modulus of 1.6 GPa and a viscosity of 1013.7 Pa s (≈ 50.1 TPa s). We conclude that the elastic model is only well-constrained for tidal displacements >35% of the spring-tidal amplitude using a Young's modulus of 1.62 ± 0.69 GPa, but that a viscoelastic model is necessary to adequately capture tidal bending at amplitudes below this threshold. In grounding zones where bending stresses are greater than at the Southern McMurdo Ice Shelf or ice viscosity is lower, the threshold would be even higher.

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Ice-shelf basal channels in a coupled ice/ocean model

Journal of Glaciology ◽

10.3189/2012jog12j003 ◽

2012 ◽

Vol 58 (212) ◽

pp. 1227-1244 ◽

Cited By ~ 56

Author(s):

Carl V. Gladish ◽

David M. Holland ◽

Paul R. Holland ◽

Stephen F. Price

Keyword(s):

Ocean Circulation ◽

Coupled System ◽

Ocean Model ◽

Subsurface Water ◽

Ice Thickness ◽

Ice Shelf ◽

First Approximation ◽

Grounding Line ◽

History Of ◽

Basal Melting

AbstractA numerical model for an interacting ice shelf and ocean is presented in which the ice- shelf base exhibits a channelized morphology similar to that observed beneath Petermann Gletscher’s (Greenland) floating ice shelf. Channels are initiated by irregularities in the ice along the grounding line and then enlarged by ocean melting. To a first approximation, spatially variable basal melting seaward of the grounding line acts as a steel-rule die or a stencil, imparting a channelized form to the ice base as it passes by. Ocean circulation in the region of high melt is inertial in the along-channel direction and geostrophically balanced in the transverse direction. Melt rates depend on the wavelength of imposed variations in ice thickness where it enters the shelf, with shorter wavelengths reducing overall melting. Petermann Gletscher’s narrow basal channels may therefore act to preserve the ice shelf against excessive melting. Overall melting in the model increases for a warming of the subsurface water. The same sensitivity holds for very slight cooling, but for cooling of a few tenths of a degree a reorganization of the spatial pattern of melting leads, surprisingly, to catastrophic thinning of the ice shelf 12 km from the grounding line. Subglacial discharge of fresh water along the grounding line increases overall melting. The eventual steady state depends on when discharge is initiated in the transient history of the ice, showing that multiple steady states of the coupled system exist in general.

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An improved bathymetry compilation for the Bellingshausen Sea, Antarctica, to inform ice-sheet and ocean models

The Cryosphere Discussions ◽

10.5194/tcd-4-2079-2010 ◽

2010 ◽

Vol 4 (4) ◽

pp. 2079-2101 ◽

Cited By ~ 3

Author(s):

A. G. C. Graham ◽

F. O. Nitsche ◽

R. D. Larter

Keyword(s):

Ocean Circulation ◽

Ice Sheet ◽

West Antarctica ◽

Ice Shelf ◽

Ice Streams ◽

Ice Shelves ◽

Sea Floor ◽

Bellingshausen Sea ◽

Warm Deep Water ◽

Basal Melting

Abstract. The southern Bellingshausen Sea (SBS) is a rapidly-changing part of West Antarctica, where oceanic and atmospheric warming has led to the recent basal melting and break-up of the Wilkins ice shelf, the dynamic thinning of fringing glaciers, and sea-ice reduction. Accurate sea-floor morphology is vital for understanding the continued effects of each process upon changes within Antarctica's ice sheets. Here we present a new bathymetric grid for the SBS compiled from shipborne echo-sounder, spot-sounding and sub-ice measurements. The 1-km grid is the most detailed compilation for the SBS to-date, revealing large cross-shelf troughs, shallow banks, and deep inner-shelf basins that continue inland of coastal ice shelves. The troughs now serve as pathways which allow warm deep water to access the ice fronts in the SBS. Our dataset highlights areas still lacking bathymetric constraint, as well as regions for further investigation, including the likely routes of palaeo-ice streams. The new compilation is a major improvement upon previous grids and will be a key dataset for incorporating into simulations of ocean circulation, ice-sheet change and history. It will also serve forecasts of ice stability and future sea-level contributions from ice loss in West Antarctica, required for the next IPCC assessment report in 2013.

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Representation of basal melting in idealised coupled ice sheet ocean models

10.5194/egusphere-egu21-10448 ◽

2021 ◽

Author(s):

Chen Zhao ◽

Rupert Gladstone ◽

Ben Galton-Fenzi ◽

David Gwyther

Keyword(s):

Ocean Circulation ◽

Critical Role ◽

Ice Sheet ◽

Ocean Model ◽

Periodic Pattern ◽

Regional Ocean Modeling System ◽

Ice Shelf ◽

Grounding Line ◽

Ocean Models ◽

Basal Melting

The ocean-driven basal melting has important implications for the stability of ice shelves in Antarctic, which largely affects the ice sheet mass balance, ocean circulation, and subsequently global sea level rise. Due to the limited observations in the ice shelf cavities, the couple ice sheet ocean models have been playing a critical role in examining the processes governing basal melting. In this study we use the Framework for Ice Sheet-Ocean Coupling (FISOC) to couple the Elmer/Ice full-stokes ice sheet model and the Regional Ocean Modeling System (ROMS) ocean model to model ice shelf/ocean interactions for an idealised three-dimensional domain. Experiments followed the coupled ice sheet&#8211;ocean experiments under the first phase of the Marine Ice Sheet&#8211;Ocean Model Intercomparison Project (MISOMIP1). A periodic pattern in the simulated mean basal melting rates is found to be highly consistent with the maximum barotropic stream function and also the grounding line retreat row by row, &#160;which is likely to be related with the gyre break down near the grounding line caused by some non-physical instability events from the ocean bottom. Sensitivity tests are carried out, showing that this periodic pattern is not sensitive to the choice of couple time intervals and horizontal eddy viscosities but sensitive to vertical resolution in the ocean model, the chosen critical water column thickness in the wet-dry scheme, and the tracer properties for the nudging dry cells at the ice-ocean interface boundary. Further simulations are necessary to better explain the mechanism involved in the couple ice-ocean system, which is very significant for its application on the realistic ice-ocean systems in polar regions.

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Constraining ice shelf basalt melting rates from isochrone data

10.5194/egusphere-egu21-3053 ◽

2021 ◽

Author(s):

Vjeran Visnjevic ◽

Reinhard Drews ◽

Clemens Schannwell ◽

Inka Koch

Keyword(s):

Ocean Circulation ◽

Radar Data ◽

Ice Shelf ◽

Ice Dynamics ◽

Ice Flow ◽

Ice Shelves ◽

Inverse Approach ◽

History Of ◽

Forward And Inverse Modeling ◽

Basal Melting

Ice shelves buttress ice flow from the continent towards the ocean, and their disintegration results in increased ice discharge.&#160; Ice-shelf evolution and integrity is influenced by surface accumulation, basal melting, and ice dynamics. We find signals of all of these processes imprinted in the ice-shelf stratigraphy that can be mapped using isochrones imaged with radar.Our aim is to develop an inverse approach to infer ice shelf basal melt rates using radar isochrones as observational constraints. Here, we investigate the influence of basalt melt rates on the shape of isochrones using combined insights from both forward and inverse modeling. We use the 3D full Stokes model Elmer/Ice in our forward simulations, aiming to reproduce isochrone patterns observed in our data. Moreover we develop an inverse approach based on the shallow shelf approximating, aiming to constrain basal melt rates using isochronal radar data and surface velocities. Insights obtained from our simulations can also guide the collection of new radar data (e.g., profile lines along vs. across-flow) in a way that ambiguities in interpreting the ice-shelf stratigraphy can be minimized. Eventually, combining these approaches will enable us to better constrain the magnitude and history of basal melting, which will give valuable input for ocean circulation and sea level rise projections.

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Sources and transport of glacial meltwater in the Bellingshausen Sea, Antarctica

10.5194/egusphere-egu21-2746 ◽

2021 ◽

Author(s):

Peter Sheehan ◽

Karen Heywood ◽

Andrew Thompson ◽

Mar Flexas

Keyword(s):

Ocean Circulation ◽

World Ocean ◽

Cyclonic Circulation ◽

Shelf Break ◽

Multiple Sources ◽

Ice Shelf ◽

Transport Pathways ◽

Ice Shelves ◽

Bellingshausen Sea ◽

The Impact

Quantifying meltwater content and describing transport pathways is important for understanding the impact of a warming, melting Antarctica on ocean circulation. Meltwater fluxes can affect density-driven, on-shelf flows around the continent, and the formation of the dense water masses that ventilate abyssal regions of the world ocean. We present observations collected from two ocean gliders that were deployed in the Bellingshausen Sea for a period of 10 weeks between January and March of 2020.&#160; Using multiple high-resolution sections, we quantify both the distribution of meltwater concentrations and lateral meltwater fluxes within the Belgica Trough in the Bellingshausen Sea. We observe a cyclonic circulation in the trough, in agreement with previous studies. A meltwater flux of 0.46 mSv is observed flowing northwards in the&#160; western limb of the cyclonic circulation. A newly identified meltwater re-circulation (0.88 mSv) is observed flowing back towards the ice front (i.e. southwards) with the eastern limb of the cyclonic circulation. In addition, 1.16 mSv of meltwater is observed flowing northeastward, parallel to the shelf break, with the northern limb of the cyclonic circulation. Peak meltwater is concentrated into two layers associated with different density surfaces: one approximately 150 m deep (27.4 kg m-3) and one approximately 200 m deep (27.6 kg m-3}). The deeper of these layers is characterised by an elevated optical backscatter, which indicates a more turbid water mass. The shallower layer is less turbid, and is more prominent closer to the shelf break and in the eastern part of the Belgica Trough. We hypothesise that the deeper, turbid meltwater layer originates locally from the Venables Ice Shelf, whereas the shallower, less turbid meltwater layer, comprises meltwater from ice shelves in the eastern Bellingshausen Sea. The broad distribution of meltwater from multiple sources suggests the potential for remote interactions and feedbacks between the various ice shelves that abut the Bellingshausen Sea.

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