Sea surface temperature in the Indian sector of the Southern Ocean over the Late Glacial and Holocene

Abstract

Centennial and millennial scale variability of Southern Ocean temperature is poorly known, due to both short 15 instrumental records and sparsely distributed high-resolution temperature reconstructions, with evidence for past temperature variability instead coming mainly from ice core records. Here we present a high-resolution (~60 year), diatom-based seasurface temperature (SST) reconstruction from the western Indian sector of the Southern Ocean that spans the interval 14.2 to 1.0 ka BP (calibrated kiloyears before present). During the late deglaciation, the new SST record shows cool temperatures at 14.2-12.9 ka BP and gradual warming between 12.9-11.6 ka BP in phase with atmospheric temperature evolution. This 20 supports that the temperature of the Southern Ocean during the deglaciation was 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 11.6-8.7 ka BP followed 25 by a slight cooling and greater variability from 8.7 to 1 ka BP, with a quasi-periodic variability of 200-260 years as identified by spectral analysis. We suggest that the increased variability during the mid to late Holocene may reflect the establishment of centennial variability in SST connected with changes in the high latitude atmospheric circulation and Southern Ocean convection, as identified in models.

Antarctic Polar Front migrations in the Kerguelen Plateau region, Southern Ocean, over the past 360 kyrs

“…To complement these results, the downcore scores of three PCs are 2021), we used the Imbrie and Kipp method (IKM) (Imbrie and Kipp, 1971) for sub-STrad calculation to enable a direct comparison of our results to previous SO studies (Abelmann et al, 1999;Cortese and Abelmann, 2002;Cortese et al, 2007;Panitz et al, 2015). However, MAT is the most commonly used statistical approach to quantitatively reconstruct SST from diatom assemblages (Crosta et al, 2004;Gersonde et al, 2005;Esper and Gersonde, 2014;Nair et al, 2019;Ghadi et al, 2020;Orme et al, 2020) and was recently used for radiolarian-based reconstructions (Hernández-Almeida et al, 2020). We therefore applied the same approach to radiolarian assemblages to ensure a more robust comparison of SSTdiat and sub-STrad in core MD11-3353.…”

Seasonally Resolved Holocene Sea Ice Variability Inferred From South Pole Ice Core Chemistry

“…Records from marine cores TPC286 (62° S) and TPC078 (56° S) are near the inferred sodium source region for the South Pole during the instrumental period (Figure ) and show reduced winter sea ice during the mid‐Holocene relative to the early and late Holocene (Collins et al., 2012, 2013). A mid‐Holocene sea ice reduction is not observed in marine records further to the north (Bianchi & Gersonde 2004; Divine et al., 2010; Nielsen et al., 2004; Xiao et al., 2016), from the southern Indian Ocean (Mashiotta et al., 1999; Orme et al., 2020), nor from the Antarctic Peninsula (Domack et al., 2001), further emphasizing the geographic specificity of the mid‐Holocene ss‐Na + anomaly. In contrast, a progressive sea ice increase and/or sea surface cooling is widely observed (Divine et al., 2010; Etourneau et al., 2013; Hodell et al., 2001; Xiao et al., 2016), consistent with the secular Antarctic‐wide Na + increase (PC1).…”