Holocene Southern Ocean surface temperature variability west of the Antarctic Peninsula

Abstract

The disintegration of ice shelves, reduced sea-ice and glacier extent, and shifting ecological zones observed around Antarctica highlight the impact of recent atmospheric and oceanic warming on the cryosphere. Observations and models suggest that oceanic and atmospheric temperature variations at Antarctica's margins affect global cryosphere stability, ocean circulation, sea levels and carbon cycling. In particular, recent climate changes on the Antarctic Peninsula have been dramatic, yet the Holocene climate variability of this region is largely unknown, limiting our ability to evaluate ongoing changes within the context of historical variability and underlying forcing mechanisms. Here we show that surface ocean temperatures at the continental margin of the western Antarctic Peninsula cooled by 3-4 °C over the past 12,000 years, tracking the Holocene decline of local (65° S) spring insolation. Our results, based on TEX(86) sea surface temperature (SST) proxy evidence from a marine sediment core, indicate the importance of regional summer duration as a driver of Antarctic seasonal sea-ice fluctuations. On millennial timescales, abrupt SST fluctuations of 2-4 °C coincide with globally recognized climate variability. Similarities between our SSTs, Southern Hemisphere westerly wind reconstructions and El Niño/Southern Oscillation variability indicate that present climate teleconnections between the tropical Pacific Ocean and the western Antarctic Peninsula strengthened late in the Holocene epoch. We conclude that during the Holocene, Southern Ocean temperatures at the western Antarctic Peninsula margin were tied to changes in the position of the westerlies, which have a critical role in global carbon cycling.

Glacial discharge along the west Antarctic Peninsula during the Holocene

“…Further, from modern observations on the WAP, the dominant seasonal shift in surface water δ 18 O occurs with the summer glacial discharge to the coastal ocean and not the spring sea ice-derived snow melt 28 , hence, we are confident that glacial discharge is the dominant driver of our δ 18 O diatom record. Modern ice-free seasonal sea surface temperature (SST) variations along the WAP shelf of 2°C only account for up to 0.4‰ of the δ 18 O diatom variability and, correcting for Holocene changes 3 , we show that SST has little impact on δ 18 O diatom ( Supplementary Fig. S3).…”

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].…”

Confounding effects of oxygen and temperature on the TEX 86 signature of marine Thaumarchaeota

“…That is, disagreement with other proxy records, unreasonably large swings in TEX 86 over short time periods, or warm biases in semienclosed basins (Mediterranean and Red Sea) have been attributed to changes in circulation, seasonal timing of production, selective export to sediments, or to autochthonous archaeal populations having slightly different temperature responses (20,(23)(24)(25). Large Significance Ammonia-oxidizing archaea (AOA) are among the most abundant microorganisms in the ocean.…”

“…For example, inferred Cretaceous SSTs are higher than physically plausible for the ocean (29). Thus, considerable efforts have been made to develop and apply new TEX 86 equations suitable for high-temperature environments (TEX H 86 ), low-temperature environments (TEX L 86 ), local systems (TEX 86 ′), the marine water column, and mesocosms (24,(30)(31)(32)(33).…”