The Surface of the Ice-Age EarthQuantitative geologic evidence is used to reconstruct boundary conditions for the

climate 18,000 years ago.

CLIMAP Project Members, 1973(Climate: Long-range Investigation, Mapping, and Prediction)

Presented by Greg HammondDecember 2, 2009

CLIMAP

Objective: to study the history of global climate, beginning with a model of February 18,000 ka (August was modeled in 1981) and establish boundary conditions for:

– Continent geography– Ice and land albedo– Extent and elevation of permanent ice– Sea-Surface temperature patterns

Boundary ConditionsGeography

85 m sea level drop estimated from dated submerged terraces and on undated wave-cut notches at similar depths.Small errors in sea level not considered significant with a model grid with 250-500 km spacing.

Land Albedo

Pollen, snow line, and sedimentary records used to determine paleo-ground cover.Modern analogous ground albedo used for model.

Ice Sheets

Ice sheet extent determined by a survey of literature supplemented with field work

CLIMAP Ice Extent and Vegetation Distribution

Snow/Ice Desert Loess Grassland Vegetated Water

Boundary ConditionsSea-Surface Temperature

•Analysis of assemblages of foraminifera, coccoliths, and radiolara can be related to temperature based on modern analogues. Coccoliths preferred because they live in the euphotic zone, and thus most directly reflect surface temperature.

•Oxygen-18 isotope data used to correlate carbonate remains with ice volume.

•Carbon-14 dating applicable for some cases as dating control.

•Ice sheet extent also based on biological records. Clays deposited by basal melting of ice sheets inhibit diatom growth, making an absence of diatoms an indicator of extent.

Sea-Surface Temperature: Difference between CLIMAP and modern values

CLIMAP Model of Sea-Surface Temperature, 18,000 ka

Results

•The southern hemisphere was dominated by sea ice, the northern by a land-dominated combination.•Changes in sea-surface temperature distribution may have reduced and/or relocated currents.

•Ice insulation may have inhibited thermohaline currents.

•Altered currents may have thermally isolated certain areas.

•Increased permanent snow/ice cover and less dense vegetation increased global albedo.

Atmospheric Response to Modified CLIMAP Ocean Boundary Conditions

during the Last Glacial Maximum

Toracina, E, et al, 2002

Problems with the original CLIMAP model

•CLIMAP suggests possible warming in the tropics. No other study has replicated this and instead suggest cooling of 1-8°C.

•Overall average global sea-surface temperature modeled 1-2°C warmer than recent studies.

•Not all northern seas would be ice bound—seasonal melting is likely. This would change circulation patterns.

•Estimated sea-level drop too small.