Ice volume

Fig. 18-21 The last 250 000 years of environmental history, recorded in the central Antarctic ice sheet. Bottom three panels are data from the Vostok ice core (Lorius et al., 1990 Jouzel et at., 1993). Top panel is marine data representing global ice volume (Shackle-ton el al., 1990).

Fig. 18-22 The last 50 000 years of environmental history, recorded in central Greenland (GISP2 and GRIP ice cores), plus the CO2 record from Vostok, Antarctica, and global ice volume measured as sea level depression. (From top to bottom, references are Shackleton, 1987 Cuffey et ai, 1995 and Grootes et al, 1993 Cuffey and Clow, 1997 Chapellaz et al, 1990 Brook et al., 1996 Mayewski et al., 1997 Saltzman et al., 1997.)...

Lorius et al. (1990) performed a simple multivariate analysis in which they correlate the temperature changes of the past 160 kyr (as recorded in the Vostok SD record) with changes in five forcings atmospheric CO2 plus CH4, ice volume, aerosol loading (dust and sepa-... 

In the previous studies it was considered that the climate change has been reflected by the changes in ocean circulation pattern, ice volume, albedo, and weathering. Many... 

Fig. 4.3. (A) Composite multispecies benthic foraminiferal Mg/Ca records from three deep-sea sites DSDP Site 573, ODP Site 926, and ODP Site 689. (B) Species-adjusted Mg/Ca data. Error bars represent standard deviations of the means where more than one species was present in a sample. The smoothed curve through the data represents a 15% weighted average. (C) Mg temperature record obtained by applying a Mg calibration to the record in (B). Broken line indicates temperatures calculated from the record assuming an ice-free world. Blue areas indicate periods of substantial ice-sheet growth determined from the S 0 record in conjunction with the Mg temperature. (D) Cenozoic composite benthic foraminiferal S 0 record based on Atlantic cores and normalized to Cibicidoides spp. Vertical dashed line indicates probable existence of ice sheets as estimated by (2). 3w, seawater S 0. (E) Estimated variation in 8 0 composition of seawater, a measure of global ice volume, calculated by substituting Mg temperatures and benthic 8 0 data into the 8 0 paleotemperature equation (Lear et al., 2000).

Fig. 4.14. Tracing climate change in the Miocene. Shown here are records of ice volume and temperature (based on foraminiferal S 0) and relative organic carbon burial (based on foraminiferal S C), compared with the CO2 estimates of Pagani et al. (1999), and tectonic events that may have affected ocean heat transport. Trends in CO2 are consistent with organic carbon burial and CO2 drawdown during the Monterey Excursion, but cannot explain the Miocene Climatic Optimum (MCO) or expansion of the East Antarctic Ice Sheet (EAIS).

Lear, C.H., Elderfield, H. and Wilson, P.A. (2000) Cenozoic deep-sea temperatures and global ice volumes from Mg/Ca in benthic foraminiferal calcite. Science, 287, 269-272. 

Milankovitch cycles Changes in global ice volume that reach maxima every 23,000, 41,000, and 100,000 years. They are thought to be related to changes in astronomical alignments that have similar periods. 

It is expected that the temperature of deep-water masses is more or less constant, as long as ice caps exist at the poles. Thus, the oxygen isotope composition of benthic organisms should preferentially reflect the change in the isotopic composition of the water (ice-volume effect), while the 5 0-values of planktonic foraminifera are affected by both temperature and isotopic water composition. 

Sowers et al. (1993) and Bender et al. (1994) showed that it is possible to con-strnct an oxygen isotope cnrve similar to that derived from deep-sea foraminifera from molecnlar O2 trapped in ice. These anthors argued that 5 0(atm) can serve as a proxy for ice volume jnst as 5 0-valnes in foraminifera. The isotope signal of atmospheric oxygen can be converted from sea water via photosynthetic marine organisms according to the following scheme... 

Variations in the benthic foraminifera record after 33 Ma indicate fluctuations in global ice volume in addition to temperature changes. Since then the majority of the 5 0 variations can be attributed to fluctuations in the global ice volume. Thus, Tiedemann et al. (1994) demonstrated the presence of at least 45 glacial-interglacial cycles over the last 2.5 Ma. 

A 17 Ma trend toward cooler conditions followed, as expressed by a 3%c rise in 5 0, which can be attributed to a 7°C decline in deep-sea temperatures. All subsequent changes reflect a combined effect of ice-volume and temperature. 

Sowers T, Bender M, Raynaud D, Korotkevich YS, Orchardo J (1991) The 6 0 of atmospheric O2 from air inclusions in the Vostok ice core timing of CO2 and ice volume changes during the Penultimate degladation. Paleoceanography 6 679-696... 

Mountain glacier decrease 1961-1997 3.7 x 103 km3 decrease in mountain glacier ice volume 1.1 x 1021 J... 

Decrease in Arctic perennial sea ice volume 1950s-1990s 40% decrease in sea ice thickness Thickness of the melted sea ice 1.5 m 2.4 x 1019 J... 

Prentice M.L. and Matthews R.K. (1988) Cenozoic ice-volume history Development of a composite oxygen isotope record. Geology 16,963-966. 

Radiometric evidence for glacial and interglacial events generally corroborate the racemization dates in Table V. Oxygen isotope data (53) suggest a low ice volume (i.e., sea level maximum) at 100,000 years as well as at 120,000 years. Locality 14 may represent the 100,000-year event. Localities 1 and 130 yielded racemization dates of 180,000-... 

In spite of their limitations, the °Th and Pa methods have made an important contribution to the establishment of the Late Pleistocene chronology of deep-sea sediments. They provided the timescale upon which the deep-sea 5 0 record of global ice volume could be correlated with solar insolation, thus providing strong support for the astronomical theory of climate change (Broecker and Van Donk, 1970). 

Broecker W. S. and Van Donk J. (1970) Insolation changes, ice volumes, and the record in deep-sea cores. Rev. Geophys. Space Phys. 8, 169—198. 

Although sea level is closely related to continental ice volume, it is also a function of other variables, most notably isostatic effects (see Clark et al. (1978) and review of Peltier (1998) and references therein). Sea-level change can be divided into a eustatic component, which depends... 

A completely different strategy involves recon-stmction of past ocean 0/ 0 ratios as a proxy for past ice volume. Glacial ice has a lower 180/I60 ratio than seawater. Therefore, when ice volume is high, seawater has relatively high 180/I60 ratio. When ice volume is low, seawater has relatively low 0/ 0 ratio. If the average 180/I60 ratio of glacial ice is constant with time,... 

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