Global Ice-Sheet System Interlocked by Sea Level

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.

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Modelling the Antarctic and Northern Hemisphere ice-sheet changes with global climate through the Glacial cycle

Annals of Glaciology ◽

10.3189/1998aog27-1-153-160 ◽

1998 ◽

Vol 27 ◽

pp. 153-160 ◽

Cited By ~ 29

Author(s):

W. F. Budd ◽

B. Coutts ◽

Roland C. Warner

Keyword(s):

Sea Level ◽

Northern Hemisphere ◽

Global Climate ◽

Past History ◽

Ice Sheets ◽

Ice Sheet ◽

Ice Age ◽

Antarctic Region ◽

Ice Shelves ◽

The Antarctic

The future behaviour of the Antarctic ice sheet depends to some extent on its current state of balance and its past history. The past history is primarily influenced by global climate changes, with some small amount of local feedback, and by sea-level changes generated primarily by the Northern Hemisphere ice-sheet changes, again with a small amount of feedback from the Antarctic ice sheet. An ice-sheet model which includes ice shelves has been used to model the Antarctic region and the whole Northern Hemisphere high-latitude region through the last ice-age cycle. For the climate forcing, the results from the global energy-balance model of Budd and Rayner (1990) are used. These are based on the Earth's orbital radiation changes with ice-sheet albedo feedback. Additional sensitivity studies are carried out for the amplitudes of the derived temperature changes and for changes in precipitation over the ice-sheets. For the Antarctic snow-accumulation changes, the results from the Voslok ice core are used with proportional changes over the rest of the ice sheet. For the sea-level variations, the results generated by the Northern Hemisphere ice-sheet changes provide the primary forcing, but account is also taken of the feedback effects from bed response under changing ice and ocean loading and from the Antarctic changes. The results of the modelling provide a wide range of features for comparison with observations, such as the margins of maximum ice extent. For the Northern Hemisphere the results indicate that the peak mean temperature shift required for the ice-edge region is about -12°C, whereas outside the ice-sheet region this change is smaller but over the ice sheets it is larger. For the Antarctic region during the ice age the interior region decreases in thickness, due to lower accumulation, while the grounding-edge region expands and thickens due to the sea-level lowering. As a result, the derived present state of balance shows a positive region over most of inland East Antarctica, whereas coastal regions tend to be nearer to balance, with some slightly negative regions around some of the large ice shelves and coastal ice streams which are still adjusting slowly to the post-ice-age changes of sea level and accumulation rates.

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Is the basin-wide warming in the North Atlantic Ocean related to atmospheric carbon dioxide and global warming?

Geophysical Research Letters ◽

10.1029/2010gl042743 ◽

2010 ◽

Vol 37 (8) ◽

Cited By ~ 15

Author(s):

Chunzai Wang ◽

Shenfu Dong

Keyword(s):

Carbon Dioxide ◽

Global Warming ◽

Atlantic Ocean ◽

North Atlantic ◽

Atmospheric Carbon Dioxide ◽

North Atlantic Ocean ◽

The North ◽

The North Atlantic ◽

Atmospheric Carbon

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The water column distribution of carbonate system variables at the ESTOC site from 1995 to 2004

Biogeosciences Discussions ◽

10.5194/bgd-7-1995-2010 ◽

2010 ◽

Vol 7 (2) ◽

pp. 1995-2032 ◽

Cited By ~ 1

Author(s):

M. González-Dávila ◽

J. M. Santana-Casiano ◽

M. J. Rueda ◽

O. Llinás

Keyword(s):

Carbon Dioxide ◽

Time Series ◽

North Atlantic ◽

Atmospheric Carbon Dioxide ◽

Inorganic Carbon ◽

Total Alkalinity ◽

Carbonate System ◽

Anthropogenic Co2 ◽

Atmospheric Carbon ◽

System Variables

Abstract. The accelerated rate of increase in the atmospheric carbon dioxide (CO2) and the substantial fraction of anthropogenic CO2 emissions absorbed by the oceans are affecting the anthropocenic properties of seawater. Long-term time series are a powerful tool for investigating any change in ocean bio-geochemistry and its effects on the carbon cycle. We have evaluated the ESTOC (European Station for Time series in the Ocean at the Canary islands) observations of measured pH (total scale at 25 °C) and total alkalinity plus computed total dissolved inorganic carbon CO2 concentration (CT) from 1995 to 2004 for surface and deep waters, by following all changes in response to increasing atmospheric carbon dioxide. The experimental values for the partial surface pressure of CO2 from 1995 to 2008 were also taken into consideration. The data were treated to better understand the fundamental processes controlling vertical distributions in the Eastern North Atlantic Ocean and the accumulation of anthropogenic CO2, CANT. CT at constant salinity, NCT, increased at a rate of 1 μmol kg−1 yr−1 in the first 200 m, linked to an fCO2 increase of 1.7±0.7 μatm yr−1 in both the atmosphere and the ocean. Consequently, the ESTOC site has also become more acidic, −0.0018±0.0003 units yr−1 over the first 100 m, whereas the carbonate ion concentrations and CaCO3 saturation states have also decreased over time. The rate of change is to be observed over the first 1000 m, where at 300, 600, and 1000 m the NCT increases at a rate of 0.69, 0.61 and 0.48 μmol kg−1 yr−1, respectively. The vertical distribution of the carbonate system variables are affected by the water mass structure and, to a different extent, controlled by the production/decomposition of organic matter, the formation/dissolution of carbonates, and differences in their respective pre-formed values. At 3000 m, 30% of the inorganic carbon production is related to the dissolution of calcium carbonate, with a total of 35% at the bottom. The total column inventory of anthropogenic CO2 for the decade was 66±3 mol m−2. A model fitting indicated that the column inventory of CANT increased from 61.7 mol m−2 in the year 1994 to 70.2 mol m−2 in 2004. The ESTOC site is presented by way of a reference site to follow CANT changes in the North Atlantic Sub-tropical gyre.

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