Holocene climate variations in the western Antarctic Peninsula: evidence for sea ice extent predominantly controlled by changes in insolation and ENSO variability

Abstract

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, based on the combination of two biomarkers proxies (highly branched isoprenoid (HBI) alkenes for sea ice and TEX86L for temperature) and micropaleontological data (diatom assemblages), we derived new Holocene records of sea ice conditions and upper water column temperatures. The early Holocene (9000–7000 yr BP) was characterized by a cooling phase with a short sea ice season. During the mid-Holocene (~7000–3800 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 ~2100 yr) was characterized by warmer 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 gradual increase in annual sea ice duration over the last 7000 yr might have been influenced by decreasing mean annual and spring insolation, despite 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 the El Niño–Southern Oscillation (ENSO). However, between 3800 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.

Centennial‐Scale SE Pacific Sea Surface Temperature Variability Over the Past 2,300 Years

“…This is in accordance with two records displaying increased sea ice in the western Ross Sea at a similar timing (between 1,250 and 650 cal yr BP) to the cooling (Figure 5g; Mezgec et al, 2017). Late Holocene sea-ice increases are also observed to the west of the Ross Sea (Denis et al, 2010), to the west of the West Antarctic Peninsula (Etourneau et al, 2013), and in the Eastern Ross Sea (Mayewski et al, 2013). Associated ice-albedo and ice-insulation feedbacks (Renssen et al, 2005;Varma et al, 2012) may have contributed to the rapidity of the cooling and sea-ice expansion.…”

Southern Ocean deep convection as a driver of Antarctic warming events

“…Heat release from changes in SO overturning is invoked in multiple hypotheses seeking to explain Antarctic climate variations, ranging from centennial-scale variability in SSTs on the western margin of the Antarctic Peninsula [Etourneau et al, 2013;Shevenell et al, 2011] to millennial-scale variability in Antarctic temperatures during the glacial EPICA 2006, Anderson, 2009Menviel et al, 2015]. Previous studies have primarily considered the response of SO overturning to externally-imposed or remotely-triggered forcings, such as wind stress [Anderson et al, 2009;Lee et al, 2011], changes in deep water production in the North Atlantic [Broecker et al, 1998;Menviel et al, 2015], locally applied meltwater (or salinity) fluxes Menviel et al, 2015] and atmospheric temperature changes [Watson and Garabato, 2006].…”

Climate variability and spatiotemporal dynamics of five Southern Ocean krill species

“…One persistent and relatively predictable climate cycle influencing the Antarctic Peninsula is the Antarctic Dipole of which the $3-7 year El Niño-Southern Oscillation (ENSO) cycle has been apparent throughout the Holocene and as far back as the Eocene, 50 million years ago (Ivany et al, 2011;Shevenell et al, 2011;Mulvaney et al, 2012;Etourneau et al, 2013). It is quite likely that the lower frequency decadal-and multidecadal-scale variations of the other dominant Southern Ocean climate mode, the Southern Annular Mode (SAM), have modulated ENSO during at least the Holocene, the combined impacts of which would drive climate ''regime shifts'' (Alley et al, 2003;McGlone et al, 2010;Yuan and Yonekura, 2011).…”