scholarly journals Ice Induced Sea Level Change in the Late Neogene

2021 ◽  
Author(s):  
◽  
Gary Steven Wilson
Keyword(s):  
Sea Level ◽  
Ice Sheet ◽  
Level Fluctuation ◽  
Antarctic Ice Sheet ◽  
Continental Scale ◽  
Base Level ◽  
Late Neogene ◽  
Antarctic Continent ◽  
Sea Level Fluctuation ◽  
The Antarctic

<p>Two independent records of latest Neogene (2,0 - 6.0 Ma.) glacioeustasy are presented, one of Antarctic ice volume from East Antarctica and the other of eustatic sea level from the South Wanganui Basin, New Zealand. Glacial deposits in the Transantarctic Mountains (Sirius Group) and sediment at the Antarctic continental margin provide direct evidence of Antarctic ice sheet fluctuation. Evidence for deglaciation includes the occurrence of Pliocene marine diatoms in Sirius Group deposits, which are sourced from the East Antarctic interior. K/Ar and 39Ar/40Ar dating of a tuff in the CIROS-2 drill-core confirms their Pliocene age at high latitudes (78 [degrees] S) in Antarctica. Further evidence for Antarctic ice volume fluctuation is recorded by glaciomarine strata from the Ross Sea Sector cored by the CIROS-2 and DVDP-11 drill-holes. Magnetostratigraphy integrated with Beryllium-10, K/Ar and 39Ar/40Ar dating provides a high resolution ([plus or minus] 50 k.y.) chronology of events in these strata. In the Wanganui Basin, New Zealand, a 5 km thick succession of continental shelf sediments, now uplifted, records Late Neogene eustatic sea level fluctuation. In the Late Neogene, basin subsidence equalled sediment input allowing eustatic sea level fluctuation to produce a dynamic alternation of highstand, transgressive, and lowstand sediment wedges. This record of Late Neogene sea level variation is unequalled in its resolution and detail. Magnetostratigraphy provides a high resolution chronology for these sedimentary cycles as well as magnetic tie lines with the Antarctic margin record in McMurdo Sound. These two independent records of Late Neogene glacioeustasy are in good agreement and record the following history: The Late Miocene and Late Pliocene are times of low 'base level' glacioeustasy (here termed glacialism, rather than glacial), with growth of continental-scale ice sheets on the Antarctic continent causing a lowering of global sea level. The Early Pliocene was a time of high 'base level' glacioeustasy (here termed interglacialism, rather than interglacial), driven by collapsing of continental-scale ice sheets to local and subcontinental ice caps. The middle Pliocene is marked by a move into glacialism with an increasing 'base level' of glacioeustatic fluctuation. Higher-order glacial advances and associated eustatic sea-level lowering occurred at approximately 3.5 and 4.3 Ma., separating the Early Pliocene into 3 sea-level stages. Still higher-order glacioeustatic fluctuations are recognised in this study, with durations of 50 Ka. and 100 - 300 Ka.. The 100 - 300 Ka. duration cycles are prominent during interglacialisms, and the 50 Ka. duration cycles are prominent during glacialisms. These shorter duration fluctuations in glacioeustasy have already been recognised as glacial/deglacial cycles from detailed studies of the Quaternary. Four orders of sea-level fluctuation are recognised within the Late Neogene, these are of approximately 0.05 Ma., 0.1-0.3 Ma., 2 Ma., and 4 Ma. in duration. The 2 Ma. and 4 Ma. duration cycles are subdivisions of the third order cyclicity recognised by Vail et al. (1991) (referred to here as cyclicity orders 3a and 3b). The 0.1-0.3 Ma. duration cycles are a subset of the fourth order cyclicity recognised Vail et al. (1991), and the 0.05 Ma. Duration cycles are a subset of the 5 th order cyclicity recognised by Vail et al. (1991). 3a, 3b and 4 th order sea level fluctuations are driven by fluctuations in the volume of the Antarctic Ice Sheet. Fifth order sea level fluctuations are also suggested to be at least partially driven by fluctuations in the volume of the Antarctic Ice Sheet. Milankovitch cyclicities in glacioeustasy (<100 Ka., fifth order cyclicity) are prominent in the geologic record at times when there is large scale glaciation (glacialism) of the Antarctic Continent (e.g. for the Pleistocene). Conversely, at times when the Antarctic continent is in a deglaciated state (deglacialism) fourth order cyclicity is more prominent, with Milankovitch cyclicities present at a parasequence level.</p>

scholarly journals Ice Induced Sea Level Change in the Late Neogene

2021 ◽  
Author(s):  
◽  
Gary Steven Wilson
Keyword(s):  
Sea Level ◽  
Ice Sheet ◽  
Level Fluctuation ◽  
Antarctic Ice Sheet ◽  
Continental Scale ◽  
Base Level ◽  
Late Neogene ◽  
Antarctic Continent ◽  
Sea Level Fluctuation ◽  
The Antarctic

<p>Two independent records of latest Neogene (2,0 - 6.0 Ma.) glacioeustasy are presented, one of Antarctic ice volume from East Antarctica and the other of eustatic sea level from the South Wanganui Basin, New Zealand. Glacial deposits in the Transantarctic Mountains (Sirius Group) and sediment at the Antarctic continental margin provide direct evidence of Antarctic ice sheet fluctuation. Evidence for deglaciation includes the occurrence of Pliocene marine diatoms in Sirius Group deposits, which are sourced from the East Antarctic interior. K/Ar and 39Ar/40Ar dating of a tuff in the CIROS-2 drill-core confirms their Pliocene age at high latitudes (78 [degrees] S) in Antarctica. Further evidence for Antarctic ice volume fluctuation is recorded by glaciomarine strata from the Ross Sea Sector cored by the CIROS-2 and DVDP-11 drill-holes. Magnetostratigraphy integrated with Beryllium-10, K/Ar and 39Ar/40Ar dating provides a high resolution ([plus or minus] 50 k.y.) chronology of events in these strata. In the Wanganui Basin, New Zealand, a 5 km thick succession of continental shelf sediments, now uplifted, records Late Neogene eustatic sea level fluctuation. In the Late Neogene, basin subsidence equalled sediment input allowing eustatic sea level fluctuation to produce a dynamic alternation of highstand, transgressive, and lowstand sediment wedges. This record of Late Neogene sea level variation is unequalled in its resolution and detail. Magnetostratigraphy provides a high resolution chronology for these sedimentary cycles as well as magnetic tie lines with the Antarctic margin record in McMurdo Sound. These two independent records of Late Neogene glacioeustasy are in good agreement and record the following history: The Late Miocene and Late Pliocene are times of low 'base level' glacioeustasy (here termed glacialism, rather than glacial), with growth of continental-scale ice sheets on the Antarctic continent causing a lowering of global sea level. The Early Pliocene was a time of high 'base level' glacioeustasy (here termed interglacialism, rather than interglacial), driven by collapsing of continental-scale ice sheets to local and subcontinental ice caps. The middle Pliocene is marked by a move into glacialism with an increasing 'base level' of glacioeustatic fluctuation. Higher-order glacial advances and associated eustatic sea-level lowering occurred at approximately 3.5 and 4.3 Ma., separating the Early Pliocene into 3 sea-level stages. Still higher-order glacioeustatic fluctuations are recognised in this study, with durations of 50 Ka. and 100 - 300 Ka.. The 100 - 300 Ka. duration cycles are prominent during interglacialisms, and the 50 Ka. duration cycles are prominent during glacialisms. These shorter duration fluctuations in glacioeustasy have already been recognised as glacial/deglacial cycles from detailed studies of the Quaternary. Four orders of sea-level fluctuation are recognised within the Late Neogene, these are of approximately 0.05 Ma., 0.1-0.3 Ma., 2 Ma., and 4 Ma. in duration. The 2 Ma. and 4 Ma. duration cycles are subdivisions of the third order cyclicity recognised by Vail et al. (1991) (referred to here as cyclicity orders 3a and 3b). The 0.1-0.3 Ma. duration cycles are a subset of the fourth order cyclicity recognised Vail et al. (1991), and the 0.05 Ma. Duration cycles are a subset of the 5 th order cyclicity recognised by Vail et al. (1991). 3a, 3b and 4 th order sea level fluctuations are driven by fluctuations in the volume of the Antarctic Ice Sheet. Fifth order sea level fluctuations are also suggested to be at least partially driven by fluctuations in the volume of the Antarctic Ice Sheet. Milankovitch cyclicities in glacioeustasy (<100 Ka., fifth order cyclicity) are prominent in the geologic record at times when there is large scale glaciation (glacialism) of the Antarctic Continent (e.g. for the Pleistocene). Conversely, at times when the Antarctic continent is in a deglaciated state (deglacialism) fourth order cyclicity is more prominent, with Milankovitch cyclicities present at a parasequence level.</p>

scholarly journals Late Neogene Sirius Group strata in Reedy Valley, Antarctica: a multiple-resolution record of climate, ice-sheet and sea-level events

1998 ◽  
Vol 44 (148) ◽  
pp. 437-447 ◽  
Author(s):  
Gary S. Wilson ◽  
David M. Harwood ◽  
Rosemary A. Askin ◽  
Richard H. Levy
Keyword(s):  
Sea Level ◽  
Ice Sheet ◽  
Glacier Area ◽  
Antarctic Ice Sheet ◽  
Western Margin ◽  
Type Section ◽  
Late Neogene ◽  
Formation Type ◽  
Spur Formation ◽  
The Antarctic

AbstractLate Neogene Sirius Group strata from Tillite Spur and Quartz Hills in the Reedy Glacier area, Antarctica, demonstrate the variability in Sirius Group facies and contrasts Sirius Group strata deposited at high and low paleo-elevation, respectively. The Tillite Spur and Quartz Hills Formations (Pliocene) are formally defined here.The Tillite Spur Formation type section crops out on the edge of the Wisconsin Plateau overlooking Tillite Spur. It comprises 32m of alternating coarse gray conglomerate and muddy olive-brown diamictites. The Quartz Hills Formation type section crops out above the western margin of Reedy Glacier in a pre-existing cirque towards the southern end of the Quartz Hills. It comprises c.100m of alternating massive diamictites and rhythmically interbedded sandstone and laminated mudstones which were deposited close to sea level and subsequently rapidly uplifted (&gt;500 m Myr−1) to their present elevation at c. 1500 m. Three orders of paleoclimatic variability are recorded in the Sirius Group strata from Reedy Valley: (1) recycled marine microfloras in glacial diamictites indicate intervals of marine incursion into the Antarctic cratonic interior co-occurring with reductions in the East Antarctic ice sheet; (2) an advancing and retreating paleo-Reedy Glacier deposited a glacial/interglacial sequence alternating on a 10-100 kyr scale; 3) Centimeter and millimeter stratification in strata of the Quartz Hills Formation record annual kyr scale variability.

scholarly journals Late Neogene Sirius Group strata in Reedy Valley, Antarctica: a multiple-resolution record of climate, ice-sheet and sea-level events

1998 ◽  
Vol 44 (148) ◽  
pp. 437-447 ◽  
Author(s):  
Gary S. Wilson ◽  
David M. Harwood ◽  
Rosemary A. Askin ◽  
Richard H. Levy
Keyword(s):  
Sea Level ◽  
Ice Sheet ◽  
Glacier Area ◽  
Antarctic Ice Sheet ◽  
Western Margin ◽  
Type Section ◽  
Late Neogene ◽  
Formation Type ◽  
Spur Formation ◽  
The Antarctic

AbstractLate Neogene Sirius Group strata from Tillite Spur and Quartz Hills in the Reedy Glacier area, Antarctica, demonstrate the variability in Sirius Group facies and contrasts Sirius Group strata deposited at high and low paleo-elevation, respectively. The Tillite Spur and Quartz Hills Formations (Pliocene) are formally defined here.The Tillite Spur Formation type section crops out on the edge of the Wisconsin Plateau overlooking Tillite Spur. It comprises 32m of alternating coarse gray conglomerate and muddy olive-brown diamictites. The Quartz Hills Formation type section crops out above the western margin of Reedy Glacier in a pre-existing cirque towards the southern end of the Quartz Hills. It comprises c.100m of alternating massive diamictites and rhythmically interbedded sandstone and laminated mudstones which were deposited close to sea level and subsequently rapidly uplifted (>500 m Myr−1) to their present elevation at c. 1500 m. Three orders of paleoclimatic variability are recorded in the Sirius Group strata from Reedy Valley: (1) recycled marine microfloras in glacial diamictites indicate intervals of marine incursion into the Antarctic cratonic interior co-occurring with reductions in the East Antarctic ice sheet; (2) an advancing and retreating paleo-Reedy Glacier deposited a glacial/interglacial sequence alternating on a 10-100 kyr scale; 3) Centimeter and millimeter stratification in strata of the Quartz Hills Formation record annual kyr scale variability.

scholarly journals Holocene thinning history of David Glacier, Antarctica

2021 ◽  
Author(s):  
◽  
James Stutz II
Keyword(s):  
Sea Level ◽  
Ross Sea ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Antarctic Ice Sheet ◽  
Continental Scale ◽  
Grounding Line ◽  
The Antarctic ◽  
Exposure Ages ◽  
East Antarctic Ice Sheet

<p>The Antarctic Ice Sheet is a significant component of the Earth System, modulating Earth‘s sea level and climate. Present day and projected ice mass losses from Antarctica are of paramount concern to human populations in low-lying communities around the world. Ocean freshening from future ice discharge events also has the potential to destabilise global climate patterns. Over 40 years of satellite observations have tracked changes in ice mass, extent and thickness in Antarctica. However, ice sheets respond on timescales that range from annual to millennial, and a geologic perspective is needed to fully understand ice sheet response on timescales longer than a few decades. This research seeks to provide an improved understanding of Antarcticas future by constraining its past. I focus on one of the largest outlet glaciers in Antarctica, the David Glacier/Drygalski Ice Tongue system which drains the East Antarctic Ice Sheet, dissects the Transantarctic Mountains and discharges into the Ross Sea. I seek to answer two questions; (1) what is the timing and nature of David Glacier thinning since the Last Glacial Maximum approximately 20,000 years ago, and (2) what physical processes were responsible for the observed thinning? I answer these questions by mapping the terrestrial and marine geomorphology along the former margins and seaward extension of David Glacier, and by using surface exposure dating of bedrock and glacial erratics to constrain the timing of glacier thinning. I then use a numerical flowline model to identify the processes that drove glacier thinning and retreat. Surface exposure ages from bedrock and glacial erratics at field sites both upstream and downstream of the modern grounding line reveal that David Glacier thinned for two millennia during the mid-Holocene. Near the coast, this thinning occurred at ∼6.5 kya at a rapid rate of up to 2 m/yr. Upstream from the grounding line, the thinning was more gradual but occurred simultaneously with thinning downstream. The timing of glacial thinning at David Glacier correlates with thinning events at other glaciers in the region and is consistent with offshore marine geological records. To identify the mechanisms responsible for the observed thinning of David Glacier, I conduct numerical model sensitivity experiments along a 1,600 km flowline, extending from the ice sheet interior to the continental shelf edge in the western Ross Sea. Offshore, the glacier flowline follows the Drygalski Trough, where it crosses numerous grounding zone wedges of various sizes. The flowline and prescribed ice shelf width is guided by the orientation and distribution of mega-scale glacial lineations as well as overall sea floor bathymetry. I explore the response of a stable, expanded David Glacier to the effects of increasing sub-ice shelf melt rates, and decreasing lateral buttressing which may have occurred as grounded ice in the Ross Sea migrated southward of the David Glacier. These forcings were also combined to explore potential feedbacks associated with Marine Ice Sheet Instability. This modelling demonstrates that David Glacier likely underwent rapid thinning over a period of ∼500 years as the grounding line retreated to a prominent sill at the mouth of David Fjord. After a period of ∼ 5 ka of stability, a second period of grounding line retreat in the model leads to the glacier reaching its modern configuration. This simulated two-phase grounding line retreat compares well with onshore geologically constrained thinning events at two sites (Mt. Kring and Hughes Bluff), both in terms of timing and rates of past glacier thinning. This retreat pattern can be forced by either increased ice shelf melting or reduced buttressing, but when combined, lower melt rates and less lateral buttressing is required to match onshore geologic constraints. Together, the findings in this thesis provide new data to constrain the past behaviour of a significant portion of the East Antarctic Ice Sheet and critical insights into the mechanisms that control ice sheet thinning and retreat. Incorporation of these constraints and improved understanding of the underlying mechanisms driving glacier thinning and grounding line retreat will ultimately improve continental scale ice sheet models which are used to project the future behaviour of the Antarctic Ice Sheet and its influence on global sea level.</p>

scholarly journals Holocene thinning history of David Glacier, Antarctica

2021 ◽  
Author(s):  
◽  
James Stutz II
Keyword(s):  
Sea Level ◽  
Ross Sea ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Antarctic Ice Sheet ◽  
Continental Scale ◽  
Grounding Line ◽  
The Antarctic ◽  
Exposure Ages ◽  
East Antarctic Ice Sheet

<p>The Antarctic Ice Sheet is a significant component of the Earth System, modulating Earth‘s sea level and climate. Present day and projected ice mass losses from Antarctica are of paramount concern to human populations in low-lying communities around the world. Ocean freshening from future ice discharge events also has the potential to destabilise global climate patterns. Over 40 years of satellite observations have tracked changes in ice mass, extent and thickness in Antarctica. However, ice sheets respond on timescales that range from annual to millennial, and a geologic perspective is needed to fully understand ice sheet response on timescales longer than a few decades. This research seeks to provide an improved understanding of Antarcticas future by constraining its past. I focus on one of the largest outlet glaciers in Antarctica, the David Glacier/Drygalski Ice Tongue system which drains the East Antarctic Ice Sheet, dissects the Transantarctic Mountains and discharges into the Ross Sea. I seek to answer two questions; (1) what is the timing and nature of David Glacier thinning since the Last Glacial Maximum approximately 20,000 years ago, and (2) what physical processes were responsible for the observed thinning? I answer these questions by mapping the terrestrial and marine geomorphology along the former margins and seaward extension of David Glacier, and by using surface exposure dating of bedrock and glacial erratics to constrain the timing of glacier thinning. I then use a numerical flowline model to identify the processes that drove glacier thinning and retreat. Surface exposure ages from bedrock and glacial erratics at field sites both upstream and downstream of the modern grounding line reveal that David Glacier thinned for two millennia during the mid-Holocene. Near the coast, this thinning occurred at ∼6.5 kya at a rapid rate of up to 2 m/yr. Upstream from the grounding line, the thinning was more gradual but occurred simultaneously with thinning downstream. The timing of glacial thinning at David Glacier correlates with thinning events at other glaciers in the region and is consistent with offshore marine geological records. To identify the mechanisms responsible for the observed thinning of David Glacier, I conduct numerical model sensitivity experiments along a 1,600 km flowline, extending from the ice sheet interior to the continental shelf edge in the western Ross Sea. Offshore, the glacier flowline follows the Drygalski Trough, where it crosses numerous grounding zone wedges of various sizes. The flowline and prescribed ice shelf width is guided by the orientation and distribution of mega-scale glacial lineations as well as overall sea floor bathymetry. I explore the response of a stable, expanded David Glacier to the effects of increasing sub-ice shelf melt rates, and decreasing lateral buttressing which may have occurred as grounded ice in the Ross Sea migrated southward of the David Glacier. These forcings were also combined to explore potential feedbacks associated with Marine Ice Sheet Instability. This modelling demonstrates that David Glacier likely underwent rapid thinning over a period of ∼500 years as the grounding line retreated to a prominent sill at the mouth of David Fjord. After a period of ∼ 5 ka of stability, a second period of grounding line retreat in the model leads to the glacier reaching its modern configuration. This simulated two-phase grounding line retreat compares well with onshore geologically constrained thinning events at two sites (Mt. Kring and Hughes Bluff), both in terms of timing and rates of past glacier thinning. This retreat pattern can be forced by either increased ice shelf melting or reduced buttressing, but when combined, lower melt rates and less lateral buttressing is required to match onshore geologic constraints. Together, the findings in this thesis provide new data to constrain the past behaviour of a significant portion of the East Antarctic Ice Sheet and critical insights into the mechanisms that control ice sheet thinning and retreat. Incorporation of these constraints and improved understanding of the underlying mechanisms driving glacier thinning and grounding line retreat will ultimately improve continental scale ice sheet models which are used to project the future behaviour of the Antarctic Ice Sheet and its influence on global sea level.</p>

Antarctic ice sheet response to upper-bound scenarios

2021 ◽  
Author(s):  
Sainan Sun ◽  
Frank Pattyn
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Upper Bound ◽  
Ice Sheet ◽  
Climate Forcing ◽  
Ice Shelf ◽  
Antarctic Ice Sheet ◽  
Ice Shelves ◽  
Basal Sliding ◽  
The Antarctic

&lt;p&gt;Mass loss of the Antarctic ice sheet contributes the largest uncertainty of future sea-level rise projections. Ice-sheet model predictions are limited by uncertainties in climate forcing and poor understanding of processes such as ice viscosity. The Antarctic BUttressing Model Intercomparison Project (ABUMIP) has investigated the 'end-member' scenario, i.e., a total and sustained removal of buttressing from all Antarctic ice shelves, which can be regarded as the upper-bound physical possible, but implausible contribution of sea-level rise due to ice-shelf loss. In this study, we add successive layers of &amp;#8216;realism&amp;#8217; to the ABUMIP scenario by considering sustained regional ice-shelf collapse and by introducing ice-shelf regrowth after collapse with the inclusion of ice-sheet and ice-shelf damage (Sun et al., 2017). Ice shelf regrowth has the ability to stabilize grounding lines, while ice shelf damage may reinforce ice loss. In combination with uncertainties from basal sliding and ice rheology, a more realistic physical upperbound to ice loss is sought. Results are compared in the light of other proposed mechanisms, such as MICI due to ice cliff collapse.&lt;/p&gt;

scholarly journals Antarctic Ice-Sheet Volume at 18000 Years B.P. and Holocene Sea-Level Changes at the West Antarctic Margin

1979 ◽  
Vol 24 (90) ◽  
pp. 213-230 ◽  
Author(s):  
Craig S. Lingle ◽  
James A. Clark
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Sea Level Changes ◽  
Ice Shelf ◽  
Relative Sea Level ◽  
Antarctic Ice Sheet ◽  
West Antarctic Ice Sheet ◽  
West Antarctic ◽  
The Antarctic

AbstractThe Antarctic ice sheet has been reconstructed at 18000 years b.p. by Hughes and others (in press) using an ice-flow model. The volume of the portion of this reconstruction which contributed to a rise of post-glacial eustatic sea-level has been calculated and found to be (9.8±1.5) × 106 km3. This volume is equivalent to 25±4 m of eustatic sea-level rise, defined as the volume of water added to the ocean divided by ocean area. The total volume of the reconstructed Antarctic ice sheet was found to be (37±6) × 106 km3. If the results of Hughes and others are correct, Antarctica was the second largest contributor to post-glacial eustatic sea-level rise after the Laurentide ice sheet. The Farrell and Clark (1976) model for computation of the relative sea-level changes caused by changes in ice and water loading on a visco-elastic Earth has been applied to the ice-sheet reconstruction, and the results have been combined with the changes in relative sea-level caused by Northern Hemisphere deglaciation as previously calculated by Clark and others (1978). Three families of curves have been compiled, showing calculated relative sea-level change at different times near the margin of the possibly unstable West Antarctic ice sheet in the Ross Sea, Pine Island Bay, and the Weddell Sea. The curves suggest that the West Antarctic ice sheet remained grounded to the edge of the continental shelf until c. 13000 years b.p., when the rate of sea-level rise due to northern ice disintegration became sufficient to dominate emergence near the margin predicted otherwise to have been caused by shrinkage of the Antarctic ice mass. In addition, the curves suggest that falling relative sea-levels played a significant role in slowing and, perhaps, reversing retreat when grounding lines approached their present positions in the Ross and Weddell Seas. A predicted fall of relative sea-level beneath the central Ross Ice Shelf of as much as 23 m during the past 2000 years is found to be compatible with recent field evidence that the ice shelf is thickening in the south-east quadrant.

Ice-sheet surges and the geological record

1969 ◽  
Vol 6 (4) ◽  
pp. 903-910 ◽  
Author(s):  
John T. Hollin
Keyword(s):  
United States ◽  
Sea Level ◽  
Ice Sheet ◽  
The United States ◽  
Tectonic Activity ◽  
Ice Ages ◽  
Antarctic Ice Sheet ◽  
Geological Record ◽  
Glacial Time ◽  
The Antarctic

If they had occurred, ice-sheet surges would have caused sea-level rises of up to 50 m from Gondwanaland and say 20 m from Antarctica. The rises would have taken 100 years or much less, and the sub sequent falls would have taken 50 000 years or so, as the ice built up again. Such rises may explain the extensive (hundreds of miles ?) and sharp (submergence time 4 years ?) coal – marine shale contacts in the Carboniferous cyclothems. The chief rival explanation for these contacts is sudden subsidence. Tests should show (1) if such contacts are better correlated with periods of glaciation or with areas of tectonic activity, (2) how extensive the contacts really are, (3) if there is any evidence of erosion during sea-level falls, (4) if the amplitudes and periods of the cycles fit surges or subsidence, (5) how fast the submergences were, and (6) if any coolings began at the contacts. Wilson suggests that in the Pleistocene the surge coolings were sufficient to trigger the northern ice ages. If so, interglacial pollen profiles should show rapid but temporary marine transgressions beginning at the break of climate. Evidence suggesting such transgressions occurs in England and the United States, but is still insufficient to disprove explanations such as local downwarping. There is no evidence yet for surges in Wisconsin or Post-glacial time. There is some evidence that the Antarctic Ice Sheet is currently building up, but this could be a response to a Post-glacial accumulation increase rather than the prelude to a surge.

scholarly journals Nonlinear response of the Antarctic Ice Sheet to late Quaternary sea level and climate forcing

2019 ◽  
Vol 13 (10) ◽  
pp. 2615-2631 ◽  
Author(s):  
Michelle Tigchelaar ◽  
Axel Timmermann ◽  
Tobias Friedrich ◽  
Malte Heinemann ◽  
David Pollard
Keyword(s):  
Sea Level ◽  
Late Quaternary ◽  
Ice Sheet ◽  
Volume Changes ◽  
Antarctic Ice Sheet ◽  
Glacial Ice ◽  
Ice Volume ◽  
Global Sea Level ◽  
The Individual ◽  
The Antarctic

Abstract. Antarctic ice volume has varied substantially during the late Quaternary, with reconstructions suggesting a glacial ice sheet extending to the continental shelf break and interglacial sea level highstands of several meters. Throughout this period, changes in the Antarctic Ice Sheet were driven by changes in atmospheric and oceanic conditions and global sea level; yet, so far modeling studies have not addressed which of these environmental forcings dominate and how they interact in the dynamical ice sheet response. Here, we force an Antarctic Ice Sheet model with global sea level reconstructions and transient, spatially explicit boundary conditions from a 408 ka climate model simulation, not only in concert with each other but, for the first time, also separately. We find that together these forcings drive glacial–interglacial ice volume changes of 12–14 ms.l.e., in line with reconstructions and previous modeling studies. None of the individual drivers – atmospheric temperature and precipitation, ocean temperatures, or sea level – single-handedly explains the full ice sheet response. In fact, the sum of the individual ice volume changes amounts to less than half of the full ice volume response, indicating the existence of strong nonlinearities and forcing synergy. Both sea level and atmospheric forcing are necessary to create full glacial ice sheet growth, whereas the contribution of ocean melt changes is found to be more a function of ice sheet geometry than climatic change. Our results highlight the importance of accurately representing the relative timing of forcings of past ice sheet simulations and underscore the need for developing coupled climate–ice sheet modeling frameworks that properly capture key feedbacks.

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