Sequence of events during the last deglaciation in Southern Ocean sediments and Antarctic ice cores

Abstract

[1] The last glacial to interglacial transition was studied using down core records of stable isotopes in diatoms and foraminifera as well as surface water temperature, sea ice extent, and ice-rafted debris (IRD) concentrations from a piston core retrieved from the Atlantic sector of the Southern Ocean. Sea ice is the first variable to change during the last deglaciation, followed by nutrient proxies and sea surface temperature. This sequence of events is independent of the age model adopted for the core. The comparison of the marine records to Antarctic ice CO 2 variation depends on the age model as 14 C determinations cannot be obtained for the time interval of 29.5-14.5 ka. Assuming a constant sedimentation rate for this interval, our data suggest that sea ice and nutrient changes at about 19 ka B.P. lead the increase in atmospheric pCO 2 by approximately 2000 years. Our diatom-based sea ice record is in phase with the sodium record of the Vostok ice core, which is related to sea ice cover and similarly leads the increase in atmospheric CO 2 . If gas exchange played a major role in determining glacial to interglacial CO 2 variations, then a delay mechanism of a few thousand years is needed to explain the observed sequence of events. Otherwise, the main cause of atmospheric pCO 2 change must be sought elsewhere, rather than in the Southern Ocean.

Morphometric variability in the diatom Fragilariopsis kerguelensis: Implications for Southern Ocean paleoceanography

“…Meltwater peaks bracketing this time interval have also been recognized in the Atlantic Sector of the Southern Ocean [27] by δ 18 O diatom at 14 and 11 kyr BP in core TN057-13, sampled just south of the APF. These changes go in the opposite direction as what mentioned for the 14-15 ka interval, and thus result in a size (and, partly, relative abundance) reduction for F. kerguelensis.…”

“…A major meltwater event (dark gray), correlative to the ACR, and the F. kerguelensis shape shift interval (light gray) have been highlighted to facilitate comparison. Meltwater peaks at 14 and 11 kyr BP have also been recognized close to the APF in another core (TN057-13) from the Atlantic Sector of the Southern Ocean [27]. The age scale [17] is in calendar years, with an 800 year reservoir correction.…”

Diatom δ13C, δ15N, and C/N since the Last Glacial Maximum in the Southern Ocean: Potential impact of Species Composition

“…The LGM maximum in d 15 N has been ascribed to nitrate concentrations being drawn down to relatively low levels, because of biological utilization, and, likewise, the minimum in d 13 C has been related to the balance between CO 2 uptake and availability [François et al, 1992[François et al, , 1997Singer and Shemesh, 1995;De La Rocha et al, 1998;Rosenthal et al, 2000;Shemesh et al, 2002;Robinson et al, 2004Robinson et al, , 2005Crosta et al, 2005;Schneider-Mor et al, 2005]. Given the importance of understanding what is going on with the biological pump in the glacial Southern Ocean, and that nutrient utilization proxies based on diatom opal are the most direct way of assessing this, it is worth considering if there is an ecological component to the signal.…”

“…[28] Despite grave differences in cleaning and analytical methods employed in obtaining d 13 C and d 15 N from fossil diatoms in various studies [e.g., Crosta et al, , 2005Robinson et al, 2004Robinson et al, , 2005, most studies of diatom-bound organic matter in Southern Ocean sediments (from south of the present-day Antarctic Polar Front) report an increase in d 13 C [Shemesh et al, 1993De La Rocha et al, 1998;Rosenthal et al, 2000;Crosta et al, 2005;Schneider-Mor et al, 2005;Singer and Shemesh, 1995] and a decrease in d 15 N [François et al, 1992[François et al, , 1997Shemesh et al, 2002;Crosta et al, 2005;Robinson et al, 2005;Schneider-Mor et al, 2005] between LGM and the Holocene. The situation here is more complex.…”

Origin and significance of ice‐rafted detritus in the Atlantic sector of the Southern Ocean

“…[12] The published radiocarbon chronology for TN057-13PC4 [Shemesh et al, 2002] was adjusted in a similar manner and the oxygen isotope stratigraphy age model for ODP Site 1094 of Kanfoush et al [2000Kanfoush et al [ , 2002 was adopted. The chronologies of IO1176-83 and RC11-78 are based on Eucampia antarctica stratigraphy and are only used to ensure that the tephra samples were from the last glacial period [Smith et al, 1983;Burckle and Cooke, 1983].…”