Abstract
Abstract. Centennial- and millennial-scale variability of Southern Ocean temperature over the Holocene is poorly known, due to both short instrumental records and sparsely distributed high-resolution temperature reconstructions, with evidence for past temperature variations in the region coming mainly from ice core records. Here we present a high-resolution (∼60 year), diatom-based sea surface temperature (SST) reconstruction from the western Indian sector of the Southern Ocean that spans the interval 14.2 to 1.0 ka (calibrated kiloyears before present). During the late deglaciation, the new SST record shows cool temperatures at 14.2–12.9 ka and gradual warming between 12.9 and 11.6 ka in phase with atmospheric temperature evolution. This supports the evolution of the Southern Ocean SST during the deglaciation being linked with a complex combination of processes and drivers associated with reorganisations of atmospheric and oceanic circulation patterns. Specifically, we suggest that Southern Ocean surface warming coincided, within the dating uncertainties, with the reconstructed slowdown of the Atlantic Meridional Overturning Circulation (AMOC), rising atmospheric CO2 levels, changes in the southern westerly winds and enhanced upwelling. During the Holocene the record shows warm and stable temperatures from 11.6 to 8.7 ka followed by a slight cooling and greater variability from 8.7 to 1 ka, with a quasi-periodic variability of 200–260 years identified by spectral analysis. We suggest that the increased variability during the mid- to late Holocene reflects the establishment of centennial variability in SST connected with changes in the high-latitude atmospheric circulation and Southern Ocean convection.
Highlights
Research into the sequence of events associated with the deglacial period has highlighted that there were contrasting patterns of millennial-scale warming and cooling between the southern and northern high latitudes, considered to have resulted from global-scale processes, namely fluctuations in the strength of the Atlantic Meridional Overturning Circulation (AMOC) and latitudinal shifts in the major atmospheric circulation cells
The diatom assemblage of COR1GC is dominated by pelagic open-ocean taxa, Fragilariopsis kerguelensis and Thalassiosira lentiginosa (Zielinski and Gersonde, 1997; Crosta et al, 2005), with accompanying species typical of the Polar Front Zone (PFZ) and Permanent Open Ocean Zone (POOZ) (Fig. 3)
POOZ species abundances were lower at 14.2–9.5 ka, after which point they gradually increased in proportion over the Holocene
Summary
Research into the sequence of events associated with the deglacial period has highlighted that there were contrasting patterns of millennial-scale warming and cooling between the southern and northern high latitudes, considered to have resulted from global-scale processes, namely fluctuations in the strength of the Atlantic Meridional Overturning Circulation (AMOC) and latitudinal shifts in the major atmospheric circulation cells. During the Younger Dryas (12.9–11.7 ka; Rasmussen et al, 2014) a prolonged weakening of the AMOC reduced the northward heat transport in the Atlantic allowing heat to accumulate in the Southern Ocean causing a “bipolar seesaw” characterised by opposite ocean temperature anomalies between the two hemispheres (Denton et al, 2010, and references therein) These temperature changes caused a rapid alteration of the atmospheric circulation, with a southward shift of the Intertropical Convergence Zone (ITCZ) and southern westerly winds (SWWs). The increased upwelling in the Southern Ocean enhanced CO2 outgassing and warming globally Despite many of these processes occurring within the Southern Ocean the strongest evidence for the patterns and magnitude of southern high-latitude warming during the Younger Dryas comes from Antarctic ice cores Acquiring high-resolution proxy records of past sea surface temperature (SST) is important for establishing the spatio-temporal patterns of warming in the Southern Ocean and their link with Antarctic temperature variability
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