Oxygen isotopic composition of interstitial waters from Leg 154: determination of the temperature and isotopic composition of the glacial ocean

Abstract

Oxygen isotope measurements of interstitial waters from Ocean Drilling Program Leg 154, sampled at high resolution from Sites 925 and 929, are used to reconstruct the oxygen isotopic composition of deep water during the last glacial maximum (LGM). The data from both sites show an increase with depth, predicted by modeling the diffusion of water through the sediment, although only data from Hole 925E are appropriate for calculating the composition of seawater during the LGM. Using a numerical model to simulate diffusion of water in the sediments, we obtained a glacial-interglacial change in the d 18 O of seawater at Site 925 of 0.8 ± 0.1ä. This implies that the bottom water at Site 925 cooled by approximately 4ûC during the LGM. Although these data from a single site do not represent a global average, we suggest that the substantial cooling of deep water at Site 925 is consistent with a global average change in the d 18 O of seawater of 1.0ä. This value is within the limits imposed by the freezing point of seawater and is more consistent with estimates of the d 18 O of continental ice during the glacial maximum. In addition, a lower contribution from ice volume to the change in d 18 O of planktonic foraminifers allows for 1û-2û additional cooling in the tropics during the LGM, partially reconciling the foraminiferal oxygen isotope record of tropical sea surface temperatures with estimates from Barbados corals and terrestrial climate proxies.

Stable isotope evidence for moisture sources in the asian summer monsoon under present and past climate regimes

“…These lower isotope compositions are governed by prevailing air circulation regimes, resulting in a much greater influx of isotopically-depleted moisture transported over continental land mass, rather than by differences in temperature or amount of precipitation compared to monsoon and tropical precipitation to the west or the east. After corrections for known changes in the isotopic composition of the oceans, measured isotopic composition of glacial period groundwaters reveal that the basic structure of air circulation and moisture LGM ocean water (with an unknown d 2 H) is also shown based on the data of Schrag et al [1997] and Fairbanks [1989]. The slope and intercept of the regression line are nearly the same as the global meteoric water line, indicating that the groundwater archive is an excellent proxy for the isotopic composition of paleoprecipitation.…”

“…δ 2 H versus δ 18 O values of groundwater from coastal aquifers in the CMT and OMT The isotopic composition of present‐day and LGM ocean water (with an unknown δ 2 H) is also shown based on the data of Schrag et al [1997] and Fairbanks [1989]. The slope and intercept of the regression line are nearly the same as the global meteoric water line, indicating that the groundwater archive is an excellent proxy for the isotopic composition of paleo‐precipitation.…”

“…Figure 4 shows oxygen isotope values in dated groundwater from the Asian monsoon region. Also shown is the enrichment in ocean δ 18 O values (by a maximum of 1.2‰) due to ice‐volume effect during the glacial period [ Schrag et al , 1997].…”

Antarctic glacial history from numerical models and continental margin sediments

“…It is generally considered that by far the greater part of these effects is the result of growth and decay of vast Northern Hemisphere ice sheets (e.g. Broecker and Peng, 1982;Schrag et al, 1997), and that the past 3 million years have seen these effects grow, from an initial isotopic signal amplitude of 0.4 to 0.6 ppm and sea-level change of perhaps 25 m, with a dominant period close to 40,000 years. It seems likely that change in volume of the Antarctic ice sheet itself was the major cause of these lower-amplitude and shorter-period changes before 3 million years, but the relative importance of ice volume and ocean temperature contributions to the isotopic variation is unknown.…”