scholarly journals ESD Ideas: Propagation of high-frequency forcing to ice age dynamics

2018 ◽  
Author(s):  
Mikhail Y. Verbitsky ◽  
Michel Crucifix ◽  
Dmitry M. Volobuev
Keyword(s):  
Conservation Laws ◽  
Time Scales ◽  
High Frequency ◽  
Ice Sheet ◽  
Ice Age ◽  
Age Dynamics ◽  
Linear Character ◽  
Astronomical Time ◽  
Continuous Background ◽  
Ice Sheet Dynamics

Abstract. The observational records display a continuous background of variability connecting centennial to 100-ka periods. Hence, the dynamics at the centennial, millennial, and astronomical time scales should not be treated apart. Here, we show that the non-linear character of ice sheet dynamics, which was derived naturally from the conservation laws, provides the scaling constraints to explain the structure of the observed spectrum of variability.

scholarly journals ESD Ideas: Propagation of high-frequency forcing to ice age dynamics

2019 ◽  
Vol 10 (2) ◽  
pp. 257-260 ◽  
Author(s):  
Mikhail Y. Verbitsky ◽  
Michel Crucifix ◽  
Dmitry M. Volobuev
Keyword(s):  
Conservation Laws ◽  
High Frequency ◽  
Ice Sheet ◽  
Ice Age ◽  
Ice Flow ◽  
Age Dynamics ◽  
Nonlinear Character ◽  
Continuous Background ◽  
Ice Sheet Dynamics ◽  
Flow Conservation

Abstract. Palaeoclimate records display a continuous background of variability connecting centennial to 100 kyr periods. Hence, the dynamics at the centennial, millennial, and astronomical timescales should not be treated separately. Here, we show that the nonlinear character of ice sheet dynamics, which was derived naturally from the ice-flow conservation laws, provides the scaling constraints to explain the structure of the observed spectrum of variability.

scholarly journals Mechanisms and time scales of glacial inception simulated with an Earth system model of intermediate complexity

2009 ◽  
Vol 5 (1) ◽  
pp. 595-633 ◽  
Author(s):  
R. Calov ◽  
A. Ganopolski ◽  
C. Kubatzki ◽  
M. Claussen
Keyword(s):  
Time Scales ◽  
Transient Response ◽  
Ice Sheet ◽  
Earth System Model ◽  
System Model ◽  
Boreal Summer ◽  
Earth System ◽  
Intermediate Complexity ◽  
Ice Sheet Dynamics ◽  
Inland Ice

Abstract. We investigate glacial inception and glacial thresholds in the climate-cryosphere system utilising the Earth system model of intermediate complexity CLIMBER-2, which includes modules for atmosphere, terrestrial vegetation, ocean and interactive ice sheets. The latter are described by the three-dimensional polythermal ice-sheet model SICOPOLIS. A bifurcation which represents glacial inception is analysed with two different model setups: one setup with dynamical ice-sheet model and another setup without it. The respective glacial thresholds differ in terms of maximum boreal summer insolation at 65° N (hereafter referred as Milankovich forcing (MF)). The glacial threshold of the configuration without ice-sheet dynamics corresponds to a much lower value of the MF compared to the full model. If MF attains values only slightly below the aforementioned threshold there is fast transient response. Depending on the value of MF relative to the glacial threshold, the transient response time of inland-ice volume in the model configuration with ice-sheet dynamics ranges from 10 000 to 100 000 years. We investigate implications of these time scales for past glacial inceptions and for the overdue Holocene glaciation hypothesis by Ruddiman (W. F. Ruddiman, Climatic Change 2003, Vol. 61, 261–293). We also have shown that the asynchronous coupling between climate and inland-ice components allows one sufficient realistic simulation of glacial inception and, at the same time, a considerable reduction of computational costs.

scholarly journals Fjord network in Namibia: A snapshot into the dynamics of the late Paleozoic glaciation

Geology ◽  
2021 ◽  
Author(s):  
Pierre Dietrich ◽  
Neil P. Griffis ◽  
Daniel P. Le Heron ◽  
Isabel P. Montañez ◽  
Christoph Kettler ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Ice Age ◽  
Late Paleozoic ◽  
Isostatic Adjustment ◽  
Climate Regulation ◽  
Continental Shelves ◽  
Glacial Dynamics ◽  
Ice Sheet Dynamics ◽  
Sedimentary Fill ◽  
Glacial Morphology

Fjords are glacially carved estuaries that profoundly influence ice-sheet stability by draining and ablating ice. Although abundant on modern high-latitude continental shelves, fjord-network morphologies have never been identified in Earth’s pre-Cenozoic glacial epochs, hindering our ability to constrain ancient ice-sheet dynamics. We show that U-shaped valleys in northwestern Namibia cut during the late Paleozoic ice age (LPIA, ca. 300 Ma), Earth’s penultimate icehouse, represent intact fjord-network morphologies. This preserved glacial morphology and its sedimentary fill permit a reconstruction of paleo-ice thicknesses, glacial dynamics, and resulting glacio-isostatic adjustment. Glaciation in this region was initially characterized by an acme phase, which saw an extensive ice sheet (1.7 km thick) covering the region, followed by a waning phase characterized by 100-m-thick, topographically constrained outlet glaciers that shrank, leading to glacial demise. Our findings demonstrate that both a large ice sheet and highland glaciers existed over northwestern Namibia at different times during the LPIA. The fjords likely played a pivotal role in glacier dynamics and climate regulation, serving as hotspots for organic carbon sequestration. Aside from the present-day arid climate, northwestern Namibia exhibits a geomorphology virtually unchanged since the LPIA, permitting unique insight into this icehouse.

Global Ice-Sheet System Interlocked by Sea Level

1986 ◽  
Vol 26 (1) ◽  
pp. 3-26 ◽  
Author(s):  
George H. Denton ◽  
Terence J. Hughes ◽  
Wibjörn Karlén
Keyword(s):  
Carbon Dioxide ◽  
Sea Level ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
North Atlantic ◽  
High Frequency ◽  
Atmospheric Carbon Dioxide ◽  
Ice Sheet ◽  
Ice Age ◽  
Atmospheric Carbon

Denton and Hughes (1983, Quaternary Research 20, 125–144) postulated that sea level linked a global ice-sheet system with both terrestrial and grounded marine components during late Quaternary ice ages. Summer temperature changes near Northern Hemisphere melting margins initiated sea-level fluctuations that controlled marine components in both polar hemispheres. It was further proposed that variations of this ice-sheet system amplified and transmitted Milankovitch summer half-year insolation changes between 45 and 75°N into global climatic changes. New tests of this hypothesis implicate sea level as a major control of the areal extent of grounded portions of the Antarctic Ice Sheet, thus fitting the concept of a globally interlocked ice-sheet system. But recent atmospheric modeling results (Manabe and Broccoli, 1985, Journal of Geophysical Research 90, 2167–2190) suggest that factors other than areal changes of the grounded Antarctic Ice Sheet strongly influenced Southern Hemisphere climate and terminated the last ice age simultaneously in both polar hemispheres. Atmospheric carbon dioxide linked to high-latitude oceans is the most likely candidate (Shackleton and Pisias, 1985, Atmospheric carbon dioxide, orbital forcing, and climate. In “The Carbon Cycle and Atmospheric CO2: Natural Variations Archean to Present” (E. T. Sundquest and W. S. Broecker, Eds.), pp. 303–318. Geophysical Monograph 32, American Geophysical Union, Washington, D.C.), but another potential influence was high-frequency climatic oscillations (2500 yr). It is postulated that variations in atmospheric carbon dioxide acted through an Antarctic ice shelf linked to the grounded ice sheet to produce and terminate Southern Hemisphere ice-age climate. It is further postulated that Milankovitch summer insolation combined with a warm high-frequency oscillation caused marked recession of Northern Hemisphere ice-sheet melting margins and the North Atlantic polar front about 14,000 14C yr B.P. This permitted renewed formation of North Atlantic Deep Water, which could well have controlled atmospheric carbon dioxide (W. S. Broecker, D. M. Peteet, and D. Rind, 1985, Nature (London) 315, 21–26). Combined melting and consequent sea-level rise from the three warming factors initiated irreversible collapse of the interlocked global ice-sheet system, which was at its largest but most vulnerable configuration.

scholarly journals An ice-sampling programme in the Thule area, North Greenland

1987 ◽  
Vol 135 ◽  
pp. 81-84
Author(s):  
N Reeh ◽  
H.H Thomsen
Keyword(s):  
Great Britain ◽  
Ice Sheet ◽  
Ice Age ◽  
Geological Museum ◽  
Climatic History ◽  
Last Ice Age ◽  
Sampling Programme ◽  
Ice Sheet Dynamics ◽  
Area North ◽  
North Greenland

A glaciological programme was carried out as part of the NORDQUA 86 expedition to the Thule area, Nbrth Greenland, from 7 to 24 August 1986. The expedition included researchers from the five Nordic countries and Great Britain and was organised by the Geological Museum, Copenhagen (Funder, in press). The expedition had a Quaternary geological programme, as well as a glaciological programme dealing with the climatic history and ice-sheet dynamics before and during the last Ice Age in the area.

scholarly journals Causes of ice age intensification across the Mid-Pleistocene Transition

2017 ◽  
Vol 114 (50) ◽  
pp. 13114-13119 ◽  
Author(s):  
Thomas B. Chalk ◽  
Mathis P. Hain ◽  
Gavin L. Foster ◽  
Eelco J. Rohling ◽  
Philip F. Sexton ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Southern Ocean ◽  
Phase Locking ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Age ◽  
Climate Forcing ◽  
Testing Hypotheses ◽  
Ice Sheet Dynamics ◽  
The Relationship

During the Mid-Pleistocene Transition (MPT; 1,200–800 kya), Earth’s orbitally paced ice age cycles intensified, lengthened from ∼40,000 (∼40 ky) to ∼100 ky, and became distinctly asymmetrical. Testing hypotheses that implicate changing atmospheric CO2 levels as a driver of the MPT has proven difficult with available observations. Here, we use orbitally resolved, boron isotope CO2 data to show that the glacial to interglacial CO2 difference increased from ∼43 to ∼75 μatm across the MPT, mainly because of lower glacial CO2 levels. Through carbon cycle modeling, we attribute this decline primarily to the initiation of substantive dust-borne iron fertilization of the Southern Ocean during peak glacial stages. We also observe a twofold steepening of the relationship between sea level and CO2-related climate forcing that is suggestive of a change in the dynamics that govern ice sheet stability, such as that expected from the removal of subglacial regolith or interhemispheric ice sheet phase-locking. We argue that neither ice sheet dynamics nor CO2 change in isolation can explain the MPT. Instead, we infer that the MPT was initiated by a change in ice sheet dynamics and that longer and deeper post-MPT ice ages were sustained by carbon cycle feedbacks related to dust fertilization of the Southern Ocean as a consequence of larger ice sheets.

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