scholarly journals The Quaternary Sedimentology and Stratigraphy of Small, Ice-Proximal, Subaqueous Grounding-Line Moraines in the Central Niagara Peninsula, Southern Ontario

2002 ◽  
Vol 55 (1) ◽  
pp. 75-86 ◽  
Author(s):  
John Menzies
Keyword(s):  
Lake Erie ◽  
Ice Sheet ◽  
Surface Expression ◽  
Aqueous Environment ◽  
Glacial Lakes ◽  
Southern Ontario ◽  
Short Period ◽  
Grounding Line ◽  
The Impact

abstract A series of small moraine ridges in the central Niagara Peninsula, southern Ontario, were investigated in order to understand the impact the retreating Lauren- tide Ice Sheet had on this area of Canada, in terms of the Quaternary sedimentology, stratigraphy and geomorphology. As the ice retreated from the Lake Erie Basin, the area was simultaneously inundated by a series of glacial lakes. The only surface expression of this retreat phase of the ice sheet are suites of small moraine ridges. The morphology, stratigraphy, and sedimentology of these ridges indicates that they were probably formed, over a short period of time, in an ice proximal sub- aqueous environment at the rapidly retreating grounding-line margin of the ice sheet. The sediments reveal a stratigraphy that indicates an association of grounded ice sheet and sub- aqueous marginal conditions.

scholarly journals Uncertainties in mass balance estimation of the Antarctic Ice Sheet using the input and output method

2021 ◽  
Author(s):  
Yijing Lin ◽  
Yan Liu ◽  
Zhitong Yu ◽  
Xiao Cheng ◽  
Qiang Shen ◽  
...  
Keyword(s):  
Mass Balance ◽  
Scale Effect ◽  
Ice Sheet ◽  
Ice Thickness ◽  
Clear Understanding ◽  
Antarctic Ice Sheet ◽  
Grounding Line ◽  
Ice Velocity ◽  
The Antarctic ◽  
The Impact

Abstract. The input-output method (IOM) is one of the most popular methods of estimating the ice sheet mass balance (MB), with a significant advantage in presenting the dynamics response of ice to climate change. Assessing the uncertainties of the MB estimation using the IOM is crucial to gaining a clear understanding of the Antarctic ice-sheet mass budget. Here, we introduce a framework for assessing the uncertainties in the MB estimation due to the methodological differences in the IOM, the impact of the parameterization and scale effect on the modeled surface mass balance (SMB, input), and the impact of the uncertainties of ice thickness, ice velocity, and grounding line data on ice discharge (D, output). For the assessment of the D’s uncertainty, we present D at a fine scale. Compared with the goal of determining the Antarctic MB within an uncertainty of 15 Gt yr−1, we found that the different strategies employed in the methods cause considerable uncertainties in the annual MB estimation. The uncertainty of the RACMO2.3 SMB caused by its parameterization can reach 20.4 Gt yr−1, while that due to the scale effect is up to 216.7 Gt yr−1. The observation precisions of the MEaSUREs InSAR-based velocity (1–17 m yr−1), the airborne radio-echo sounder thickness (±100 m), and the MEaSUREs InSAR-based grounding line (±100 m) contribute uncertainties of 17.1 Gt yr−1, 10.5 ± 2.7 Gt yr−1 and 8.0~27.8 Gt yr−1 to the D, respectively. However, the D’s uncertainty due to the remarkable ice thickness data gap, which is represented by the thickness difference between the BEDMAP2 and the BedMachine reaches 101.7 Gt yr−1, which indicates its dominant cause of the future D’s uncertainty. In addition, the interannual variability of D caused by the annual changes in the ice velocity and ice thickness are considerable compared with the target uncertainty of 15 Gt yr−1, which cannot be ignored in annual MB estimations.

scholarly journals Representation of basal melting at the grounding line in ice flow models

2018 ◽  
Vol 12 (10) ◽  
pp. 3085-3096 ◽  
Author(s):  
Hélène Seroussi ◽  
Mathieu Morlighem
Keyword(s):  
Finite Element ◽  
Ice Sheet ◽  
Ocean Model ◽  
Flow Models ◽  
Grounding Line ◽  
Ice Sheet Modeling ◽  
Mesh Resolution ◽  
Intercomparison Project ◽  
Basal Melting ◽  
The Impact

Abstract. While a lot of attention has been given to the numerical implementation of grounding lines and basal friction in the grounding zone, little has been done about the impact of the numerical treatment of ocean-induced basal melting in this region. Several strategies are currently being employed in the ice sheet modeling community, and the resulting grounding line dynamics may differ strongly, which ultimately adds significant uncertainty to the projected contribution of marine ice sheets to sea level rise. We investigate here several implementations of basal melt parameterization on partially floating elements in a finite-element framework, based on the Marine Ice Sheet–Ocean Model Intercomparison Project (MISOMIP) setup: (1) melt applied only to entirely floating elements, (2) melt applied over all elements that are crossed by the grounding line, and (3) melt integrated partially over the floating portion of a finite element using two different sub-element integration methods. All methods converge towards the same state when the mesh resolution is fine enough. However, (2) and (3) will systematically overestimate the rate of grounding line retreat in coarser resolutions, while (1) converges faster to the solution in most cases. The differences between sub-element parameterizations are exacerbated for experiments with high melting rates in the vicinity of the grounding line and for a Weertman sliding law. As most real-world simulations use horizontal mesh resolutions of several hundreds of meters at best, and high melt rates are generally present close to the grounding lines, we recommend not using (3) to avoid overestimating the rate of grounding line retreat and to carefully assess the impact of mesh resolution and sub-element melt parameterizations on all simulation results.

scholarly journals Erosion of Grooves by Subglacial Melt-Water Streams

1979 ◽  
Vol 23 (89) ◽  
pp. 424-425 ◽  
Author(s):  
I. M. Whillans
Keyword(s):  
Chemical Equilibrium ◽  
Lake Erie ◽  
Water Flux ◽  
Ice Sheet ◽  
Potential Gradient ◽  
Laurentide Ice Sheet ◽  
Southern Ontario ◽  
Water Flows ◽  
Melt Water ◽  
Course Changes

AbstractThe shape of the former Laurentide ice sheet in what is now northern Ohio and southern Ontario is calculated and the subglacial hydrological potential field computed. Subglacial water flow is found to be concentrated over high points in the bed, such as what is now Kelleys Island in Lake Erie. Some 1010 litres of subglacial melt water per year passed over Kelleys Island.It is argued that the “glacial” grooves on Kelleys Island are subglacial melt-water channels. Assuming that the subglacial melt water attained saturation with respect to CaCO3, in passing over the limestone of Kelleys Island, the material formerly occupying the grooves could have been dissolved in 102 years. This is a much shorter time than glacier occupancy and the assumption of chemical equilibrium is not critical.The features on Kelleys Island are fluted valleys about 6 m across and each flute is about 0.1 m in width. Each flute represents a subglacial channel but only one or two of these channels operated at any one time. Blockages, perhaps caused by basal debris, caused the rivers to make minor course changes and in many instances it is possible to determine the order of channel occupancy. The channels were striated after abandonment by water when moving basal debris or debris-laden ice occupied the channels. From the Gauckler-Manning formula and the potential gradient obtained from the ice-sheet model the river velocity is calculated to be about 4 m s–1, in rough agreement with the water flux calculated earlier.The grooves support the concept that subglacial water flows in “Nye” channels, and raise the suggestion that subglacial erosion by solution is of widespread importance.

Uncertainties in Mass Balance Estimation of the Antarctic Ice Sheet Using Input-output Method

2021 ◽  
Author(s):  
Yijing Lin ◽  
Yan Liu
Keyword(s):  
Mass Balance ◽  
Ice Sheet ◽  
Data Uncertainty ◽  
Ice Thickness ◽  
Input Output ◽  
Ice Dynamics ◽  
Grounding Line ◽  
Ice Velocity ◽  
The Antarctic ◽  
The Impact

<p>Input-Output method (IOM) is a common method for estimating ice sheet mass balance, which shows ice dynamics in mass loss to analyze the response of ice sheet to climate change. However, compared with the altimetry method and the gravity method, the mass balance estimation using IOM has relatively large uncertainty. Assessing the impact of the uncertainties of each component in IOM on the mass balance estimation is conducive to effectively lowering uncertainty in the Antarctic mass budget estimate but of which there has been little quantitative analysis. We assess the uncertainty in the mass balance due to methodological differences in IOM, compare the differences of surface mass balance (SMB, input) in diverse versions and at different spatial scales, and evaluate the uncertainty in ice discharge (FG, output) due to data uncertainty in ice thickness, ice velocity and grounding line. Results showed that the SMBs at different scales are more divergent than that in different versions, resulting in a variation of 216.7 Gt yr<sup>-1</sup> in Antarctica, of which the Antarctic peninsula accounts for 55.1%, followed by East Antarctica. The largest variation in FG due to uncertainty in the location of the grounding line is observed, where a 1 km retreat and a 1 km advance of the Antarctic grounding line would respectively result in FG reductions of 82.8 Gt yr<sup>-1</sup> and 272.7 Gt yr<sup>-1</sup>, which are significant in all regions, with the FG corresponding to a 1 km retreat of grounding line in the islands being closer to the multi-year average SMB of the islands. The difference in Antarctic FG due to different ice thickness products is 124.4 Gt yr<sup>-1</sup>, consistent with the trend in the thickness of ice shelves, and that due to different ice velocity products is only 18.7 Gt yr<sup>-1</sup>. Within the same margin of error, systematic errors in ice thickness and ice velocity result in an order of magnitude higher difference of FG than random errors.</p>

scholarly journals Erosion of Grooves by Subglacial Melt-Water Streams

1979 ◽  
Vol 23 (89) ◽  
pp. 424-425 ◽  
Author(s):  
I. M. Whillans
Keyword(s):  
Chemical Equilibrium ◽  
Lake Erie ◽  
Water Flux ◽  
Ice Sheet ◽  
Potential Gradient ◽  
Laurentide Ice Sheet ◽  
Southern Ontario ◽  
Water Flows ◽  
Melt Water ◽  
Course Changes

Abstract The shape of the former Laurentide ice sheet in what is now northern Ohio and southern Ontario is calculated and the subglacial hydrological potential field computed. Subglacial water flow is found to be concentrated over high points in the bed, such as what is now Kelleys Island in Lake Erie. Some 1010 litres of subglacial melt water per year passed over Kelleys Island. It is argued that the “glacial” grooves on Kelleys Island are subglacial melt-water channels. Assuming that the subglacial melt water attained saturation with respect to CaCO3, in passing over the limestone of Kelleys Island, the material formerly occupying the grooves could have been dissolved in 102 years. This is a much shorter time than glacier occupancy and the assumption of chemical equilibrium is not critical. The features on Kelleys Island are fluted valleys about 6 m across and each flute is about 0.1 m in width. Each flute represents a subglacial channel but only one or two of these channels operated at any one time. Blockages, perhaps caused by basal debris, caused the rivers to make minor course changes and in many instances it is possible to determine the order of channel occupancy. The channels were striated after abandonment by water when moving basal debris or debris-laden ice occupied the channels. From the Gauckler-Manning formula and the potential gradient obtained from the ice-sheet model the river velocity is calculated to be about 4 m s–1, in rough agreement with the water flux calculated earlier. The grooves support the concept that subglacial water flows in “Nye” channels, and raise the suggestion that subglacial erosion by solution is of widespread importance.

scholarly journals Ocean melting of the Zachariae Isstrøm and Nioghalvfjerdsfjorden glaciers, northeast Greenland

2020 ◽  
Vol 118 (2) ◽  
pp. e2015483118
Author(s):  
Lu An ◽  
Eric Rignot ◽  
Michael Wood ◽  
Josh K. Willis ◽  
Jérémie Mouginot ◽  
...  
Keyword(s):  
Gravity Data ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Ocean Model ◽  
Airborne Gravity ◽  
Intermediate Water ◽  
Grounding Line ◽  
Independent Observations ◽  
Global Sea Level ◽  
The Impact

Zachariae Isstrøm (ZI) and Nioghalvfjerdsfjorden (79N) are marine-terminating glaciers in northeast Greenland that hold an ice volume equivalent to a 1.1-m global sea level rise. ZI lost its floating ice shelf, sped up, retreated at 650 m/y, and experienced a 5-gigaton/y mass loss. Glacier 79N has been more stable despite its exposure to the same climate forcing. We analyze the impact of ocean thermal forcing on the glaciers. A three-dimensional inversion of airborne gravity data reveals an 800-m-deep, broad channel that allows subsurface, warm, Atlantic Intermediate Water (AIW) (+1.25○C) to reach the front of ZI via two sills at 350-m depth. Subsurface ocean temperature in that channel has warmed by 1.3±0.5○C since 1979. Using an ocean model, we calculate a rate of ice removal at the grounding line by the ocean that increased from 108 m/y to 185 m/y in 1979–2019. Observed ice thinning caused a retreat of its flotation line to increase from 105 m/y to 217 m/y, for a combined grounding line retreat of 13 km in 41 y that matches independent observations within 14%. In contrast, the limited access of AIW to 79N via a narrower passage yields lower grounded ice removal (53 m/y to 99 m/y) and thinning-induced retreat (27 m/y to 50 m/y) for a combined retreat of 4.4 km, also within 12% of observations. Ocean-induced removal of ice at the grounding line, modulated by bathymetric barriers, is therefore a main driver of ice sheet retreat, but it is not incorporated in most ice sheet models.

The impact of internal variability in ocean-induced melting on Totten Glacier

2020 ◽  
Author(s):  
Felicity McCormack ◽  
Mathieu Morlighem ◽  
David Gwyther ◽  
Jason Roberts ◽  
Tyler Pelle
Keyword(s):  
Mass Flux ◽  
Ice Sheet ◽  
Internal Variability ◽  
East Antarctica ◽  
Ocean Temperature ◽  
Ice Shelf ◽  
Bed Topography ◽  
Grounding Line ◽  
The Mean ◽  
The Impact

<p>The Totten Glacier, located in the Aurora Subglacial Basin of East Antarctica, drains a catchment containing approximately 3.5 m of global sea level rise equivalent ice mass. The This glacier has been losing mass over recent decades, and modelling studies indicate that it is the most vulnerable glacier in East Antarctica to warming oceans and atmosphere over the coming century. Satellite altimetry shows high internal variability in ocean-forced melting of the Totten Ice Shelf; however, the extent to which this variability signal impacts the upstream ice sheet dynamics, and therefore its mass balance, is unknown. Here we use the Ice Sheet System Model (ISSM) combined with a plume and basal melting parameterisation called PICOP to investigate the impact of variability in ocean temperature on the evolution of Totten Glacier. We find that the southernmost portion of the Totten Glacier grounding line - from which the majority of the catchment’s ice is channeled - is stable within only a limited range of background ocean temperatures close to present-day values. In the stable simulations, the magnitude of the ice mass flux depends on the extent to which the ice shelf is pinned on a bed topography rumple located approximately 10 km downstream of its grounding line, but the period of the mass flux is decadal to multi-decadal in each simulation, irrespective of the magnitude of the variability in ocean forcing. We further find that the impact of variability in ocean melt rates decreases as the mean background ocean temperature increases, suggesting that the mean state may have a relatively more important role in the evolution of the Totten Glacier than variability in ocean forcing. Our results have implications for detection and attribution of climate change and internal climate variability in modeling studies, and may inform fieldwork campaigns mapping bed topography in the Aurora Subglacial Basin.</p>

The Impact of Iroquoian Populations on the Northern Distribution of Pawpaws in the Northeast

1998 ◽  
Vol 18 (4) ◽  
pp. 327-342 ◽  
Author(s):  
Craig Keener ◽  
Erica Kuhns
Keyword(s):  
New York ◽  
Lake Erie ◽  
Great Lakes Region ◽  
Southern Ontario ◽  
Tropical Tree Species ◽  
Far North ◽  
Asimina Triloba ◽  
The North ◽  
Northern Distribution ◽  
The Impact

The North American pawpaw ( Asimina triloba) is found in Michigan, southern Ontario, Ohio, and New York. It is the only indigenous tropical tree species found as far north as the Great Lakes region. The purpose of this article is to ascertain whether or not Iroquoian populations were directly responsible for the northernmost distribution of pawpaw trees. Pawpaw populations located in southern Ontario and in isolated pockets in New York are conspicuous because of their extreme northern location and their isolation from pawpaw populations to the south. Ethnohistoric and archaeological information is analyzed in an attempt to discover how coincidental it is that these isolated pawpaw populations correspond with the former habitation areas of several Iroquoian speaking groups. It is argued that trade and warfare between Iroquoian groups located in southern Ontario, New York, and the southern Lake Erie area were responsible for the spread of pawpaws from the Ohio and Michigan regions northward and eastward.

scholarly journals Sensitivity of the Weddell Sea sector ice streams to sub-shelf melting and surface accumulation

2014 ◽  
Vol 8 (6) ◽  
pp. 2119-2134 ◽  
Author(s):  
A. P. Wright ◽  
A. M. Le Brocq ◽  
S. L. Cornford ◽  
R. G. Bingham ◽  
H. F. J. Corr ◽  
...  
Keyword(s):  
Adaptive Mesh Refinement ◽  
Reference Model ◽  
Ice Sheet ◽  
Deep Ocean ◽  
Weddell Sea ◽  
Ice Shelf ◽  
Ice Streams ◽  
Deep Ocean Water ◽  
Grounding Line ◽  
The Impact

Abstract. A recent ocean modelling study indicates that possible changes in circulation may bring warm deep-ocean water into direct contact with the grounding lines of the Filchner–Ronne ice streams, suggesting the potential for future ice losses from this sector equivalent to ~0.3 m of sea-level rise. Significant advancements have been made in our knowledge of both the basal topography and ice velocity in the Weddell Sea sector, and the ability to accurately model marine ice sheet dynamics, thus enabling an assessment to be made of the relative sensitivities of the diverse collection of ice streams feeding the Filchner–Ronne Ice Shelf. Here we use the BISICLES ice sheet model, which employs adaptive-mesh refinement to resolve grounding line dynamics, to carry out such an assessment. The impact of realistic perturbations to the surface and sub-shelf mass balance forcing fields from our 2000-year "reference" model run indicate that both the Institute and Möller ice streams are highly sensitive to changes in basal melting either near to their respective grounding lines, or in the region of the ice rises within the Filchner–Ronne Ice Shelf. These same perturbations have little impact, however, on the Rutford, Carlson or Foundation ice streams, while the Evans Ice Stream is found to enter a phase of unstable retreat only after melt at its grounding line has increased by 50% of likely present-day values.

scholarly journals Representation of basal melting at the grounding line in ice flow models

2018 ◽  
Author(s):  
Hélène Seroussi ◽  
Mathieu Morlighem
Keyword(s):  
Finite Element ◽  
Ice Sheet ◽  
Ocean Model ◽  
Flow Models ◽  
Grounding Line ◽  
Ice Sheet Modeling ◽  
Mesh Resolution ◽  
Intercomparison Project ◽  
Basal Melting ◽  
The Impact

Abstract. While a lot of attention has been given to the numerical implementation of grounding lines and basal friction in the grounding zone, little has been done about the impact of the numerical treatment of ocean-induced basal melting in this region. Several strategies are currently being employed in the ice sheet modeling community, and the resulting grounding line dynamics may differ strongly, which ultimately add significant uncertainty to the projected contribution of marine ice sheets to sea level rise. We investigate here several implementations of basal melt parameterization on partially floating elements in a finite element framework, based on the Marine Ice Sheet-Ocean Model Intercomparison Project (MISOMIP) setup: (1) melt applied only to entirely floating elements, (2) melt applied over the entire elements that are crossed by the grounding line, and (3) melt integrated partially over the floating portion of a finite element using two different sub-element integration methods. All methods converge towards the same state when the mesh resolution is fine enough. However, (2) and (3) will systematically overestimate the rate of grounding line retreat in coarser resolutions, while (1) converges faster to the solution in most cases. The differences between sub-element parameterizations are exacerbated for experiments with large melting rates in the vicinity of the grounding line and for a Weertman sliding law. As most real-world simulations use horizontal mesh resolutions of several hundreds of meters at best, and large melt rates are generally present close to the grounding lines, we recommend using (1) to avoid overestimating the rate of grounding line retreat.

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