Eric A. Colhoun

Antarctic Glacial History Since the Last Glacial Maximum: An Overview of the Record on Land

This overview examines available circum-Antarctic glacial history archives on land, related to developments after the Last Glacial Maximum (LGM). It considers the glacial-stratigraphic and morphologic records and also biostratigraphical information from moss banks, lake sediments and penguin rookeries, with some reference to relevant glacial marine records. It is concluded that Holocene environmental development in Antarctica differed from that in the Northern Hemisphere. The initial deglaciation of the shelf areas surrounding Antarctica took place before 10 000 14 C yrs before present( BP ), and was controlled by rising global sea level. This was followed by the deglaciation of some presently ice-free inner shelf and land areas between 10 000 and 8000 yr BP . Continued deglaciation occurred gradually between 8000 yr BP and 5000 yr BP . Mid-Holocene glacial readvances are recorded from various sites around Antarctica. There are strong indications of a circum-Antarctic climate warmer than today 4700–2000 yr BP . The best dated records from the Antarctic Peninsula and coastal Victoria Land suggest climatic optimums there from 4000–3000 yr BP and 3600–2600 yr BP , respectively. Thereafter Neoglacial readvances are recorded. Relatively limited glacial expansions in Antarctica during the past few hundred years correlate with the Little Ice Age in the Northern Hemisphere.

Predictability of biomass burning in response to climate changes

Climate is an important control on biomass burning, but the sensitivity of fire to changes in temperature and moisture balance has not been quantified. We analyze sedimentary charcoal records to show that the changes in fire regime over the past 21,000 yrs are predictable from changes in regional climates. Analyses of paleo- fire data show that fire increases monotonically with changes in temperature and peaks at intermediate moisture levels, and that temperature is quantitatively the most important driver of changes in biomass burning over the past 21,000 yrs. Given that a similar relationship between climate drivers and fire emerges from analyses of the interannual variability in biomass burning shown by remote-sensing observations of month-by-month burnt area between 1996 and 2008, our results signal a serious cause for concern in the face of continuing global warming.

Circum-Antarctic Coastal Environmental Shifts During the Late Quaternary Reflected by Emerged Marine Deposits

This review assesses the circumpolar occurrence of emerged marine macrofossils and sediments from Antarctic coastal areas in relation to Late Quaternary climate changes. Radiocarbon ages of the macrofossils, which are interpreted in view of the complexities of the Antarctic marine radiocarbon reservoir and resolution of this dating technique, show a bimodal distribution. The data indicate that marine species inhabited coastal environments from at least 35 000 to 20 000 yr BP, during Marine Isotope Stage 3 when extensive iceberg calving created a ‘meltwater lid’ over the Southern Ocean. The general absence of these marine species from 20 000 to 8500 yr BP coincides with the subsequent advance of the Antarctic ice sheets during the Last Glacial Maximum. Synchronous re-appearance of the Antarctic marine fossils in emerged beaches around the continent, all of which have Holocene marine-limit elevations an order of magnitude lower than those in the Arctic, reflect minimal isostatic rebound as relative sea-level rise decelerated. Antarctic coastal marine habitat changes around the continent also coincided with increasing sea-ice extent and outlet glacial advances during the mid-Holocene. In view of the diverse environmental changes that occurred around the Earth during this period, it is suggested that Antarctic coastal areas were responding to a mid-Holocene climatic shift associated with the hydrological cycle. This synthesis of Late Quaternary emerged marine deposits demonstrates the application of evaluating circum-Antarctic phenomena from the glacial-terrestrial-marine transition zone.

Bunger Hills, East Antarctica: Ice free at the Last Glacial Maximum

Optically stimulated luminescence dating of glaciofluvial and glacial-lake shoreline sediments indicates that the Bunger Hills area, in coastal East Antarctica, was largely ice free by the Last Glacial Maximum (LGM). Deglaciation commenced as early as 30 ka, and the southern hills were completely exposed by 20 ka. The sediments do not record evidence of an LGM readvance. Previous reconstructions of LGM ice limits for the area are incompatible with this new evidence.

Late Pleistocene vegetation and climate history of Lake Selina, western Tasmania

Analysis of pollen, NRM intensity of sediments, and dating of a 397 cm core from Lake Selina in western Tasmania provides a detailed record of vegetation and climate changes for the Last Interglacial–Last Glacial cycle. The vegetation record shows that cool temperate rainforest was present during Isotope Substage 5e and during the Holocene. Wet montane forest and subalpine shrublands dominated the early Last Glacial interstades; subalpine–alpine heathlands and herbfield the stadials. Stages 4–2 mainly had grassland, herbland and heath vegetation. There is close correlation between phases of maximum magnetic intensity in the sediments with pollen zones indicating presence of herbaceous vegetation. This suggests erosion of the catchment was greater in the absence of forest or woodland. Climate may have been slightly cooler than present during Substage 5e but the evidence is not definitive. Climate was colder at all times during the Last Glacial Stage until after ca. 14 kyr BP. Maximum temperature depression from present during Stage 2 was >3.5°C at Lake Selina, but probably as much as 6.5°C in the West Coast Range. Holocene climate was cool and wet. Comparison of the Lake Selina record, with others in western Tasmania and Victoria, indicate that variations in vegetation during the Last Interglacial–Last Glacial cycle were primarily responses to temperature changes in western Tasmania, and to precipitation changes, particularly summer drought, in western Victoria.

Late cainozoic glaciation in western tasmania, Australia

Abstract Four major Quaternary glaciations, with associated interglaciations and interstadials, have been identified in Tasmania, for which some chronological cotrol is given by radiocarbon and amino-acid assays, pollen analysis and relative weathering characteristics. The glaciations are known as the Margaret, Henty, Moore and Linda. The Margaret Glaciations has two clear stadial intervals (Isotope Stages 4 and 2), separated by the Tullabardine Interstadial dated at ca. 50-25 ka BP. An interglaciation corresponding to Isotope Stage 5 (Pieman Interglaciation) is characterised by sediments containing a pollen assemblage of a temperate rain forest. Weathered glacial deposits lying beneath the Pieman sediments are inferred to be those of the Penultimate Glaciation; three stadial moraines are identified. A preceding interglaciation (Langdon) contains wood that yielded an amino-acid ratio equivalent to the age of marine Isotope Stage 7. The following Moore Glaciation had three stadial intervals, two of which are separated by a clear interstadial (Baxter) with organic sediments that have amino-acid ‘ages’ equivalent to Isotope Stage 10; the non-glacial sediments have a DRM of normal polarity and are inferred to be of Mid-Quaternary age. The oldest interglaciation (Regency) is identified from organic-rich sediments (pollen assemblage of a temperate rain forest) overlying intensely weathered glacial deposits that have a DRM with reversed polarity (i.e. > 730 ka). The Linda Glaciation is the most extensive of all in Tasmania; although dating is uncertain, it has been assigned tentatively to the Early Quaternary.

Late‐glacial and Holocene record of vegetation and climate from Cynthia Bay, Lake St Clair, Tasmania

A Late-glacial–Holocene pollen record was obtained from a 3.96 m sediment core taken from Lake St Clair, central Tasmania. Modern vegetation and pollen analyses formed the basis for interpretation of the vegetation and climate history. Following deglaciation and before ca. 18450 yr BP Podocarpus lawrencei coniferous heath and Astelia–Plantago wet alpine herbfield became established at Lake St Clair. A distinct Poaceae-Plantago peak occurs between 18450 and 11210 yr BP and a mean annual temperature depression from ca. 6.2°C to 3°C below present is inferred for this period. The marked reduction in Podocarpus and strong increase of Poaceae suggests reduced precipitation levels during the period of widespread deglaciation (ca. 18.5–11 kyr BP). The local Late Pleistocene–Holocene non-forest to forest biostratigraphical boundary is dated at 11.2 kyr BP. It is characterised by expansion of the subalpine taxa Athrotaxis/Diselma with Nothofagus gunnii, and by the establishment of Nothofagus cunninghamii with Eucalyptus spp. A ‘Phyllocladus bulge’ prior to the expansion of Nothofagus cunninghamii, reported at other Tasmanian sites, is not present at Lake St Clair. Nothofagus cunninghamii cool temperate rainforest peaked at 7800 yr BP, probably under wetter climatic conditions than present. The maximum development of rainforest in the early–middle Holocene may indicate that the temperature was slightly warmer than present, but the evidence is not definitive. The expansion of Eucalyptus spp. and Poaceae after 6000 yr BP may be partly a disclimax effect as a result of Aboriginal burning, but appears also to reflect reduced precipitation. The changes in vegetation and inferred climate can be explained by major changes in synoptic patterns of southern Australia and the adjacent southwest Pacific. Copyright

Glacial climates in the Antarctic region during the late Paleogene: Evidence from northwest Tasmania, Australia

Published data suggest that ice buildup commenced in Antarctica during the late middle Eocene. This predates by 30 m.y. the earliest evidence of Cenozoic glaciation on other fragments of Gondwana, although several of these were at high latitudes during the Paleogene. We provide new evidence for local glacier development during the late Paleogene in Tasmania, then a mountainous peninsula at about lat 55°-63°S projecting into the circum-Antarctic ocean. The date of glaciation is not precisely known, but an earliest Oligocene age is indicated. We suggest that episode may correlate with abrupt cooling of the sea surface surrounding Antarctica during the earliest Oligocene (36 Ma).

Pleistocene glaciation of the King Valley, Western Tasmania, Australia

Abstract Analysis of the geomorphology, geology, and palynology of deposits in the King Valley permits the identification of four glaciations and two interglaciations and has led to a revision of the Pleistocene stratigraphy of the West Coast Range. The oldest late-Cenozoic deposits in the valley appear to predate glaciation, contain extinct pollen types, and are probably of late-Tertiary age. Overlying deposits of the Linda Glaciation show intense chemical weathering and have a reversed detrital remanent magnetization indicating deposition before 730,000 yr B.P. The highly weathered tills are conformably overlain by organic deposits of the Regency Interglaciation which show a transition from montane scrub rainforest to lowland temperate rainforest. Deposits formed during the later Moore Glaciation record advances of the King Glacier and glaciers from the West Coast Range. A pollen-bearing fluvial deposit records an interstade during this glaciation. On the basis of weathering rinds, amino acid dating, and palaeomagnetism the deposits are estimated to have formed between 730,000 and 390,000 yr B.P. The Moore Glaciation deposits are overlain by sediments of the Henty Glaciation which are believed to predate 130,000 yr B.P. These deposits record multiple advances of the King Glacier and the development of a large lake during an interstade. Deposits of the subsequent Pieman Interglaciation consist of organic fine sands and silts that record a lowland scrub rainforest. Deposits of the last (Margaret) glaciation are restricted to small areas in the northern part of the valley. Although the most recent ice advance culminated after 19,000 yr B.P., evidence of older deposits of the Margaret Glaciation suggests that an early last-glaciation ice advance may have occurred. When combined with earlier studies, the recent work in the King Valley has provided one of the more complete records of Pleistocene glaciation in the Southern Hemisphere. Comparison of the deposits with the record of glaciation in southern South America and Westland, New Zealand, suggests some similarities exist between pre-last-glaciation events and indicates that glacial events in Southern Hemisphere middle latitude areas were synchronous during the last glaciation.

Application of Iversen's glacial-interglacial cycle to interpretation of the late last glacial and holocene vegetation history of western Tasmania

Abstract The Iversen glacial-interglacial cycle of vegetation change is modified and applied to glacial, Lateglacial and Holocene age pollen records from western Tasmania. Cryocratic conditions occurred at high altitude (ca. 500 m+) during glacial and Lateglacial time. Transition from cold humid to cool humid climate occurred on the lowlands by 13 ka BP and in the mountains by 10 ka BP. There is regional parallelism of vegetation development from grassland-herbland-sedgeland through alpine-subalpine scrub and woodland to temperate rainforest dominated by Nothofagus cunninghamii . However, radiocarbon dating shows that changes in the vegetation succession and Nothofagus rainforest maximum were non-synchronous. Although climate change from glacial to interglacial conditions directed the general succession, variations in dates for similar vegetation changes show that biological and physical variables were important for local vegetation development. Some sites show late Holocene vegetation changes that could be interpreted as revertance. Aboriginal fire and lake infilling were probably responsible. There is no evidence for an Allerod-type warm phase between 13 and 11 ka BP or a Younger Dryas-type cold phase between 11 and 10 ka BP. The climate was cool temperate between 13 and 0 ka BP, and neither temperature nor precipitation change was sufficient to cause vegetation change of regional significance.