New paper finds Antarctic sea ice has markedly increased over past 7000 years

A forthcoming paper in Climate of the Past finds the annual sea ice duration around the west Antarctic Peninsula has markedly increased over the past 7,000 years. The authors attribute the changes to "decreasing mean annual and spring [solar] insolation despite an increasing summer insolation" and to ENSO variability changes. In addition, the authors find the temperature of the Antarctic Peninsula has dropped ~2C over the past 9000 years.

Second graph from top shows decrease in temperature over past 9000 years. Third graph from top shows the proxy for sea-ice and shows a marked increase over the past 7000 years.

  

Clim. Past Discuss., 9, 1-41, 2013
www.clim-past-discuss.net/9/1/2013/
doi:10.5194/cpd-9-1-2013
Holocene climate variations in the western Antarctic Peninsula: evidence for sea ice extent predominantly controlled by insolation and ENSO variability changes

J. Etourneau^1,*, L. G. Collins¹, V. Willmott², J. H. Kim², L. Barbara³, A. Leventer⁴, S. Schouten², J. S. Sinninghe Damsté², A. Bianchini⁴, V. Klein¹, X. Crosta³, and G. Massé<sup>1

1</sup>Laboratoire d'Océanographie et du Climat: Expérimentations et Approches Numériques, UMR7159, CNRS/UPMC/IRD/MNHN, 4 Place Jussieu, 75252 Paris, France
²Royal Netherlands Institute for Sea Research, Department of marine Biogeochemistry and toxicology, 1790 Den Burg, Texel, The Netherlands
³EPOC, UMR5805, CNRS, Université Bordeaux 1, Avenue des Facultés, 33405 Talence, France
⁴Colgate University, Department of Geology, 13 Oak Drive, 13346 Hamilton, USA
^*current address: Institute of Biogeosciences, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka, 237-0061, Japan
Abstract. The West Antarctic ice sheet is particularly sensitive to global warming and its evolution and impact on global climate over the next few decades remains difficult to predict. In this context, investigating past sea ice conditions around Antarctica is of primary importance. Here, we document changes in sea ice presence, upper water column temperatures (0–200 m) and primary productivity over the last 9000 yr BP (before present) in the western Antarctic Peninsula (WAP) margin from a sedimentary core collected in the Palmer Deep basin. Employing a multi-proxy approach, we derived new Holocene records of sea ice conditions and upper water column temperatures, based on the combination of two biomarkers proxies (highly branched isoprenoid (HBI) alkenes for sea ice and TEX^L₈₆for temperature) and micropaleontological data (diatom assemblages). The early Holocene (9000–7000 yr BP) was characterized by a cooling phase with a short sea ice season. During the mid-Holocene (~ 7000–3000 yr BP), local climate evolved towards slightly colder conditions and a prominent extension of the sea ice season occurred, promoting a favorable environment for intensive diatom growth. The late Holocene (the last ~ 3000 yr) was characterized by more variable temperatures and increased sea ice presence, accompanied by reduced local primary productivity likely in response to a shorter growing season compared to the early or mid-Holocene. The stepwise increase in annual sea ice duration over the last 7000 yr might have been influenced by decreasing mean annual and spring insolation despite an increasing summer insolation. We postulate that in addition to precessional changes in insolation, seasonal variability, via changes in the strength of the circumpolar Westerlies and upwelling activity, was further amplified by the increasing frequency/amplitude of El Niño-Southern Oscillation (ENSO). However, between 4000 and 2100 yr BP, the lack of correlation between ENSO and climate variability in the WAP suggests that other climatic factors might have been more important in controlling WAP climate at this time.

 Discussion Paper (PDF, 2529 KB)   Interactive Discussion (Open, 0 Comments)  Manuscript under review for CP