Chapter 11 Late Pliocene–Pleistocene Antarctic Climate Variability at Orbital and Suborbital Scale: Ice Sheet, Ocean and Atmospheric Interactions

摘要: Abstract Continental margin drill core and seismic data indicate that between 3.0 2.5 Ma, high-latitude climate cooling drove both the West East Antarctic Ice Sheets towards their present expanded cold polar state. margins developed permanent marine termini with ice shelves. Direct physical sedimentary records of Sheet variability (e.g. ice-rafted debris, proximal glacimarine cycles) more distal ocean sea-ice distribution diatom palaeoecology), thermohaline circulation sortable silt), temperatures δ 18 O), frontal dynamics surface palaeoecological assemblages sea-surface temperature (SST) reconstructions) all show a strong covariance 41 kyr cycle in Earth's obliquity 3 1 Ma. Glacial periods are characterised by northward expansion seasonal sea ice, SSTs up to 6°C colder than now, equatorward migration zones ∼5–10° latitude, intensification zonal westerly winds, invigorated Circumpolar Current) intensified abyssal currents. These processes lead O volume maximum 3–7 kyr, at which time were fully extended onto continental shelf. changes part controlled effect Northern Hemisphere glacio-eustasy on its margin, this mechanism accounts for much orbital last 2.6 myr. An enigmatic interval foraminiferal ooze coccolith-bearing sediments Weddell Sea Prydz Bay sediment cores, together bioclastic limestone Ross ∼1 Ma, imply significant warming change chemistry around periphery Antarctica. This event, occurs within short normal polarity Jaramillo Subchron is correlated warm Marine Isotope Stage 31. The anomalous implies an increase 4–6°C SST, possible incursion Subantarctic Surface Waters depression lysocline – event apparently unique 3 myr. geological record second step occurred Mid-Pleistocene Climate Transition ( ca . 900 ka). Glacial-interglacial cycles, spanning 1 myr, recovered cores from dominated coarse-grained, ice-proximal diamicts cold, subglacial affinity. Open-ocean pelagites hemipelagites rare atmospheric greenhouse gas pronounced amplitude 100 ka periodicity, coherent phase records, but lags signal. gases Dome C very congruence many features record, consistent CO 2 particular playing role amplification. also suggests Southern Ocean plays leading controlling concentration glacial-interglacial scales. Higher dust flux Antarctica during glacial maxima compared considered have radiative affects over providing nutrients Fe) promoting higher algal productivity drawdown. Most variation total grounded glacial-cycle sheet models due contraction grounding lines across shelves, mostly (WAIS) sectors, equivalent ∼15–20 m level. interior responds opposite sense, contracting slightly Hemispheric lower model snowfall rates. In general millennial-scale cycles occur high-resolution particularly methane records. However, they appear timing may differ counterparts (Dansgaard–Oeschger or D-O events). Although uncertainties age (methane) enclosing it makes evaluation precise inter-hemispheric, difficult, some be synchronous. pattern superimposed G-I prior 100 kyr cycle. Millennial-scale (A1–A7) well expressed silt southern mid-latitude ocean. One these events, Cold Reversal, ∼14.2–12.4 ka, associated abrupt ∼2°C Ocean, shelves modest winds deep inflow along eastern New Zealand through Pacific gateway.