Chapter 3 A History of Antarctic Cenozoic Glaciation – View from the Margin

摘要: Abstract The scale and antiquity of the Antarctic Ice Sheet was sensed from time earliest exploration a century ago. However, significant advances in scientific thinking, along with logistics technology for gathering data continent itself, were required before clear consistent framework ice-sheet history behaviour could develop this has emerged only last few years. main features present ice sheet established by over-snow traverses during following International Geophysical Year (1957–1958), but timing circumstances its origin remained uncertain. Geological records post-Jurassic largely buried under or sea floor around margin, though radiometric ages new K–Ar dating indicated glaciation likely older than Northern Hemisphere Quaternary Period. New post-World War II techniques offshore surveying marine geophysics ship-based drilling first applied to margin early 1970s, immediately productive. continental shelf found be underlain sedimentary basins promise history, 1973, cores Leg 28 Deep Sea Drilling Project (DSDP) Ross provided physical record extending back Oligocene times. DSDP 29 drilled Southern Ocean deep-sea whole Cenozoic Era, yielding set oxygen isotopic ratios (δ 18 O) benthic calcareous microfossils, estimates volume. These two-stage (cooling some at 34 Ma, persistent 14 Ma – time-scale Berggren et al., 1995). About same time, Dry Valleys (DVDP) launched recover onshore climate exploratory fast soon followed. Cores Program 1980s Prydz Bay Shelf Kerguelen Plateau 34 Ma. In period, deep continuous coring McMurdo Sound developed DVDP succeeded providing detail subsequent history. Core recovery ∼98% yielded lithological evidence level fluctuations implied isotope records. Further improved chronology 1990s confirming changes on Milankovitch frequencies 10–40 m equivalent. Micropalaeontological geochemical pointed slight cooling coastal cold temperate climate, beech forests interglacial Subsequent development modelling that most initiated consequence fall atmospheric CO 2 levels below critical threshold, allowing sheets form highly sensitive orbital forcing. This claim been supported recent work proxies indicators shift carbonate compensation depth sediments. Since measurements have increase volume persisted day. mid-1980s, diatoms glacial deposits Transantarctic Mountains suggested periods Pliocene times when seas invaded East interior, implying dynamic Sheets until Evidence continued mountains over 14 Ma, glaciological problems proposed over-riding scenario, lack signal loss possible alternative sources shifted weight favour east interior. outcrops core beneath shown globally warmer Pliocene, notably 3–5 Ma, several degrees warmer. Indeed, drill suggest Embayment perhaps also West interior periodically ice-free these Three decades ago, seen as long-standing feature Earth origins permanency assured mid-Miocene cooling. Research decade geological remote sensing, modelling, indicates is fact quite responsive global system, whether natural human-induced, different rates sectors. Recent developments both science outlined here provide opportunities projecting realistic scenarios future response human scales.