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Multi-decadal trends in Antarctic sea-ice extent driven by ENSO–SAM over the last 2,000 years

Nature Geoscience volume 14, pages 156–160 (2021)Cite this article

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Abstract

Antarctic sea ice has paradoxically become more extensive over the past four decades despite a warming climate. The regional expression of this trend has been linked to changes in vertical redistribution of ocean heat and large-scale wind-field shifts. However, the short length of modern observations has hindered attempts to attribute this trend to anthropogenic forcing or natural variability. Here, we present two new decadal-resolution records of sea ice and sea surface temperatures that document pervasive regional climate heterogeneity in Indian Antarctic sea-ice cover over the last 2,000 years. Data assimilation of our marine records in a climate model suggests that the reconstructed dichotomous regional conditions were driven by the multi-decadal variability of the El Niño Southern Oscillation and Southern Annular Mode (SAM). For example, during an El Niño/SAM– combination, the northward sea-ice transport was reduced while heat advection from the subtropics to the Southern Ocean increased, which resulted in reduced sea-ice extent in the Indian sector as sea ice was compacted along the Antarctic coast. Our results therefore indicate that natural variability is large in the Southern Ocean and suggest that it has played a crucial role in the recent sea-ice trends and their decadal variability in this region.

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Fig. 1: Location of studied marine cores and modern SO hydrographic features.
Fig. 2: Intercomparison of sea-ice and climate records over the last 2,000 years.
Fig. 3: Mean environmental conditions for the SST+/SIC+ composite and the SST+/SIC– composite based on offline DA using the CESM1-CAM5 model outputs.

Data availability

Diatom-based sea surface temperature data from core COR1GC can be found at https://doi.org/10.1594/PANGAEA.913621. Diatom and highly branched isoprenoid data from IODP Hole U1357B are available at https://doi.org/10.1594/PANGAEA.924721 and https://doi.org/10.1594/PANGAEA.924723, respectively.

Code availability

The results of the Last Millennium Ensemble performed with the CESM1 model are available at https://www.earthsystemgrid.org/dataset/ucar.cgd.ccsm4.CESM_CAM5_LME.html.

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Acknowledgements

This research was funded by the ERC StG ICEPROXY project (203441), the ANR CLIMICE project, FP7 Past4Future project (243908), the RCN OCTEL project (248776/E10), the Belgian Research Action through Interdisciplinary Networks Mass2Ant project (BR/165/A2/Mass2Ant), the JSPS KAKENHI (grants 23244102 and 17H06318), the Royal Society Te Apārangi Marsden Fund (MFP-VUW1808) and the MBIE NZ Antarctic Science Platform (ANTA1801). It also benefited from the ESF PolarClimate HOLOCLIP project. D.S. benefited from the Blue-Action project (European Union’s Horizon 2020 Research and Innovation Program, grant number: 727852) and the French LEFE-IMAGO programme. Hole U1357B samples and data were provided by the International Ocean Discovery Program (IODP).

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  1. Arto Miettinen

    Present address: Ecosystems and Environment Research Programme, University of Helsinki, Helsinki, Finland

Authors and Affiliations

  1. Université de Bordeaux, CNRS, EPHE, UMR 5805 EPOC, Pessac, France

    Xavier Crosta, Johan Etourneau, Philippine Campagne & Didier Swingedouw

  2. EPHE-PSL Research University, Paris, France

    Johan Etourneau

  3. ICARUS, Department of Geography, Maynooth University, Maynooth, Ireland

    Lisa C. Orme

  4. Earth and Life Institute (ELI), Université catholique de Louvain (UCL), Louvain-La-Neuve, Belgium

    Quentin Dalaiden & Hugues Goosse

  5. LOCEAN, UMR CNRS/UPCM/IRD/MNHN 7159, Université Pierre et Marie Curie, Paris, France

    Guillaume Massé

  6. Norwegian Polar Institute, Tromsø, Norway

    Arto Miettinen

  7. Antarctic Research Centre, Victoria University of Wellington, Wellington, New Zealand

    Robert M. McKay

  8. School of Earth, Energy, and Environmental Sciences, Stanford University, Stanford, CA, USA

    Robert B. Dunbar

  9. Andaluz Institute of Earth Sciences, CSIC-University of Granada, Granada, Spain

    Carlota Escutia

  10. Center for Advanced Marine Core Research, Kochi University, Nankoku, Japan

    Minoru Ikehara

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Contributions

X.C. designed and coordinated the study and led the writing. J.E. performed the HBI analysis on IODP Hole U1357B. P.C. and L.C.O. performed the diatom analyses on IODP Hole U1357B and COR1GC cores, respectively. Q.D., H.G. and D.S. performed the data assimilation experiments. G.M., X.C. and A.M. coordinated the projects that funded the analyses. C.E., R.M.M. and R.B.D. performed the stratigraphic analysis of IODP Hole U1357B. M.I. gave access to COR1GC sediments and helped develop its age model. All authors commented on the manuscript and contributed to the writing.

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Correspondence to Xavier Crosta.

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Extended data

Extended Data Fig. 1 Scaling diatom relative abundances to sea-ice presence.

a, Raw relative abundances of the Open Water Diatom (OWD) group in core DTCI2010 off Adélie Land (black line)15 and resampled relative abundances of the OWD group at a 1 year resolution (red line). b, Resampled relative abundance of the OWD group at a 1 year resolution (red line) compared to the length of the yearly sea-ice free season off Adélie Land between 1979 and 2010 (blue line)15. Grey shaded boxes represent the upper and lower end members used to scale the relative abundances of the OWD group to the yearly open water length. c, The mean upper and lower end members used to calculate the equation to scale the OWD group relative abundances to the length of the open season.

Extended Data Fig. 2 Sea-ice duration off Adélie Land over the last 2000 years.

Length of the sea-ice free season (orange line) calculated by applying the equation presented in Extended Data Fig. 1c to the relative abundances of the OWD group in IODP Hole U1357B and length of the sea-ice duration calculated (blue line) by subtracting the ice-free values from 365 days.

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Supplementary Information, Figs. 1–4 and Tables 1–3.

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Crosta, X., Etourneau, J., Orme, L.C. et al. Multi-decadal trends in Antarctic sea-ice extent driven by ENSO–SAM over the last 2,000 years. Nat. Geosci. 14, 156–160 (2021). https://doi.org/10.1038/s41561-021-00697-1

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