Marine Isotope Stage 31 Anomalous Continental Scale Warmth

• An enigmatic interval of foraminiferal ooze and coccolith-bearing assemblages in the Weddell Sea and Prydz Bay cores together with a bioclastic limestone in the Ross Sea at — 1 Ma, imply a significant warming and change in ocean chemistry around the periphery of Antarctica.

• This event that occurs within the short normal polarity Jaramillo Subchron is correlated with warm Marine Isotope Stage 31 (Villa et al.. 2007; Scherer et al., 2008).

• The anomalous warming implies an increase of 4-6°C in SST, possible incursion of Subantarctic Surface Waters and depression of the lysocline - an event that is apparently unique in the last 3 Ma.

• The warming may occur during a unique configuration in orbital parameters that may have produced an extended interval (20 kyr) of unusually warm (e.g. Raymo et al., 2006; Scherer et al., 2008), or alternatively unusually long (Denton and Huybers, 2008) SH summers.

• Planned future recovery of a 1-1.5 Ma ice core from Antarctica should shed valuable light on the greenhouse gas and temperature conditions at this time.

11.6.4. Mid-Pleistocene Climate Transition and Antarctica G-l variability in the 100 Kyr Glacial World

• The change in frequency of the G-I climate cycle between 900-700 kyr, from the 40 kyr duration, that dominated much of the glacial Cenozoic (last ~35Ma), to ~ 100 kyr cycles remains one of the most poorly understood events in palaeoclimatology. Explanations have involved amplification of the weak orbital influence by non-linear feedbacks in the carbon cycle (Shackleton, 2000), the internal dynamics of large continental ice sheets (Clark and Pollard, 1998), precessional-forcing (Raymo, 1997) and obliquity-beat skipping (Huybers and Wunsch, 2005).

• Depositional characteristics of the Late Pleistocene AND-1B G-I sedimentary cycles such as: the predominance of subglacial diamictites, thin interglacial ice shelf mudstones and no evidence for meltwater suggests a further cooling and stabilisation of the margins of the Antarctic Ice Sheets after the B-M polarity transition ~ 800 kyr. A similar pattern occurs in ODP Site 1167 core from the Prydz Bay trough mouth fan which shows a significant reduction in sedimentation rate and change in sediment provenance attributed to a less erosive, dry-based ice sheet from ~ 1Ma (O'Brien et al., 2007).

• The calving line of the Ross Ice Shelf appears not to have retreated south of its present interglacial position during subsequent 'warmer-than-Holocene, super-interglacials' (e.g. Marine Isotope Stages 11, 9 and 5; e.g. Jouzel et al., 2007). This evidence is in contradiction to hypothesised Late Quaternary collapse of the WAIS (Scherer et al., 1998) and far-field evidence for sea-levels at +20 m above present assigned to Marine Isotope Stage 11 (Hearty et al., 1999).

• Ocean records (e.g. ODP 1123 and 1090) imply northward expansion of seasonal sea ice, intensified thermohaline circulation and northward displacement of wind-driven, gyral circulation and subantarctic water masses from ~ 700 kyr to present.

• The atmospheric temperature and greenhouse gas records from Antarctic ice cores show a pronounced 100 kyr periodicity that is coherent and in phase with marine temperature records (e.g. SSTs, Crundwell et al., 2008), but leads the deconvolved ice volume signal (e.g. 818O, Shackleton, 2000).

• The records of greenhouse gases from Dome C show very strong congruence with many features of the temperature record, and are consistent with CO2 in particular playing a significant role in temperature amplification, and also suggest that the Southern Ocean plays a leading role in controlling the atmospheric concentration of CO2 on G-I time scales.

• Most of the variation in total grounded ice volume in Antarctic glacial-cycle ice sheet models (e.g. Ritz et al., 2001; Huybrechts, 2002) is due to expansion and contraction of grounding lines across continental shelves, mostly in the WAIS Ross and Weddell sectors, but also to the west of the Antarctic Peninsula and other areas and is equivalent to ~ 15-20 m of sea level.

• The EAIS interior responds in the opposite sense, contracting slightly at Northern Hemispheric glacial maxima due to lower model snowfall rates (which are reduced as temperatures fall). Glacial surface elevations based on ice core temperature modelling (Parrenin et al., 2007b) suggest central EAIS plateau decreased by ~100-150m compared to the present, with minor volume changes equivalent to just a few metres of sea level.

• In contrast ice build up on coastal Antarctica was of the order of several hundred metres during the LGM (e.g. Law Dome, Delmotte et al., 1999). In situ accumulation, rather than flow, is indicated from the ice composition which precludes an interior Antarctic source.

• Higher dust flux to Antarctica during glacial maxima compared with warm periods is considered to have radiative affects over Antarctica and provide nutrients (e.g. Fe) to the Southern Ocean promoting higher algal productivity and atmospheric CO2 drawdown (Wolff et al., 2006).

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