Hydrographic changes of the Southern Ocean (southeast Indian Sector) Over the last 230 kyr

Abstract

Hydrographical changes of the southern Indian Ocean over the last 230 kyr, is reconstructed using a 17‐m‐long sediment core (MD 88 770; 46°01′S 96°28′E, 3290m). The oxygen and carbon isotopic composition of planktonic (N. pachyderma sinistra and G. bulloides) and benthic (Cibicidoides wuellerstorfi, Epistominella exigua, and Melonis barleeanum) foraminifera have been analysed. Changes in sea surface temperatures (SST) are calculated using diatom and foraminiferal transfer functions. A new core top calibration for the Southern Ocean allows an extension of the method developed in the North Atlantic to estimate paleosalinities (Duplessy et al., 1991). The age scale is built using accelerator mass spectrometry (AMS) 14C dating of N. pachyderma s. for the last 35 kyr, and an astronomical age scale beyond. Changes in surface temperature and salinity clearly lead (by 3 to 7 kyr) deep water variations. Thus changes in deep water circulation are not the cause of the early response of the surface Southern Ocean to climatic changes. We suggest that the early warming and cooling of the Southern Ocean result from at least two processes acting in different orbital bands and latitudes: (1) seasonality modulated by obliquity affects the high‐latitude ocean surface albedo (sea ice coverage) and heat transfer to and from the atmosphere; (2) low‐latitude insolation modulated by precession influences directly the atmosphere dynamic and related precipitation/ evaporation changes, which may significantly change heat transfer to the high southern latitudes, through their control on latitudinal distribution of the major frontal zones and on the conditions of intermediate and deep water formation.

The last five glacial‐interglacial transitions: A high‐resolution 450,000‐year record from the subantarctic Atlantic

“…This is an indication of early warming of the surface ocean prior to glacial terminations at this subantarctic South Atlantic location, as SST rose substantially at subantarctic latitudes before any considerable continental ice volume change was recorded. The importance of the lead, and freshwater fluxes into the Southern Ocean, has already been stressed [Seidov et al, 2001], and a similar early response at terminations occurs in the California Current (East Pacific), at subtropical/subboreal latitudes [Herbert et al, 2001], at subantarctic latitudes [Charles et al, 1996;Labeyrie et al, 1996;Brathauer and Abelmann, 1999], in the eastern tropical Atlantic Ocean [Schneider et al, 1995], in the SW Africa upwelling system [Kim et al, 2002], and in the Polar and Antarctic Zone as well [Kunz-Pirrung et al, 2002;Gersonde, 2002, 2004]. In the California Current region SST increases several kyrs in advance of deglaciation at past glacial maxima [Herbert et al, 2001], suggesting that the surface ocean responded faster than continental ice sheets to an external climatic agent, for example, solar activity changes, sea-ice retreat, atmospheric CO 2 decrease [Shackleton, 2000].…”

The timing and cause of glacial advances in the southern mid-latitudes during the last glacial cycle based on a synthesis of exposure ages from Patagonia and New Zealand

“…Likewise, numerous SST reconstructions suggest that the decline towards peak glacial conditions had started by at least 30 ka in the south-eastern Pacific (Lamy et al, 2004;Kaiser et al, 2005;Lamy et al, 2007;Caniupán et al, 2011; Figure 8F and G), west of New Zealand and south of Australia (Pelejero et al, 2006;Barrows et al, 2007a;Calvo et al, 2007; Figure 8E), the Indian Ocean (Labeyrie et al, 1996), and the southeast Atlantic (Barker et al, 2009). A reconstruction from south of the Polar Front also shows a marked increase in Antarctic sea ice between ca.…”

Deep water variability on the southern Agulhas Plateau: Interhemispheric links over the past 170 ka

“…The few highresolution paleoceanographic records from the Southern Hemisphere oceans confirm this suggestion [Charles et al, 1996;Pahnke et al, 2003;Pahnke and Zahn, 2005], although such records are sparse and do not allow us to draw a conclusive picture for the wider Southern Hemisphere oceans. It has been suggested by early studies [Hays et al, 1976;Imbrie et al, 1989;Howard and Prell, 1992;Labeyrie et al, 1996] that on orbital timescales, Southern Ocean sea surface temperatures (SST) respond early to changes in the orbital parameters and might actually lead global ice volume [Charles et al, 1996]. The cause of such a lead is not well understood, as is the phasing of changes between the hemispheres on shorter suborbital timescales.…”