Thursday, September 9, 2010

Abrupt Cooling of Antarctica 3,000 B.C.

"[The] Antarctic may hold the future of archaeology." -- Norman Hammond, archaeologist, February 2008

Stager, J.C., Mayeswski, P.A., Abrupt Early to Mid-Holocene Climatic Transition Registered at the Equator and the Poles, Science, Volume 276, Number 5320, Pages 1834-1836, Jun 1997
Paleoclimatic records from equatorial East Africa, Antarctica, and Greenland reveal that atmospheric circulation changed abruptly at the early to mid-Holocene transition to full postglacial conditions. A climatic reorganization occurred at all three sites between 8200 and 7800 years ago that lasted 200 years or less and appears to have been related to abrupt transitions in both marine and terrestrial records around the world.
Masson, V., et al., Holocene Climate Variability in Antarctica Based on 11 Ice-Core Isotopic Records, Quaternary Research, Volume 54, Issue 3, Pages 348-358, Nov 2000
All the records confirm the widespread Antarctic early Holocene optimum between 11,500 and 9000 yr; in the Ross Sea sector, a secondary optimum is identified between 7000 and 5000 yr, whereas all eastern Antarctic sites show a late optimum between 6000 and 3000 yr.
Hodell, E.A., et. al, Abrupt Cooling of Antarctic Surface Waters and Sea Ice Expansion in the South Atlantic Sector of the Southern Ocean at 5000 cal yr B.P., Quaternary Research, Volume 56, Issue 2, Pages 191-198, Sep 2001
Antarctic surface waters were warm and ice free between 10,000 and 5000 cal yr B.P., as judged from ice-rafted debris and microfossils in a piston core at 53°S in the South Atlantic. This evidence shows that about 5000 cal yr B.P., sea surface temperatures cooled, sea ice advanced, and the delivery of ice-rafted detritus (IRD) to the subantarctic South Atlantic increased abruptly. These changes mark the end of the Hypsithermal and onset of Neoglacial conditions. They coincide with an early Neoglacial advance of mountain glaciers in South America and New Zealand between 5400 and 4900 cal yr B.P., rapid middle Holocene climate changes inferred from the Taylor Dome Ice Core (Antarctica), cooling and increased IRD in the North Atlantic, and the end of the African humid period. The near synchrony and abruptness of all these climate changes suggest links among the tropics and both poles that involved nonlinear response to gradual changes in Northern Hemisphere insolation. Sea ice expansion in the Southern Ocean may have provided positive feedback that hastened the end of the Hypsithermal and African humid periods in the middle Holocene.
Hjort, C., et al., Holocene and Pre-Holocene Temporary Disappearance of the George VI Ice Shelf, Antarctic Penninsula, Antarctic Science, Volume 13, Number 3, Pages 296-301, 2001
Barnacle Bathylasma corolliforme shells sampled from ice shelf moraines at Two Step Cliffs on Alexander Island have been dated to c. 5750-6000 14C yr BP (c. 6550-6850 cal yr BP)
Pudsey C.J., and Evans, J., First Survey of Antarctic Sub–Ice Shelf Sediments Reveals Mid-Holocene Ice Shelf Retreat, Geology, Volume 29, Number 9, Pages 787-790, Sep 2001
The retreat of five small Antarctic Peninsula ice shelves in the late 20th century has been related to regional (possibly anthropogenic) climate warming. We use the record of ice- rafted debris (IRD) in cores to show that the Prince Gustav Channel ice shelf also retreated in mid-Holocene time. Early and late Holocene-age sediments contain IRD derived entirely from local ice drainage basins, which fed the section of ice shelf covering each site. Core- top and mid-Holocene (5–2 ka) sediments include a wider variety of rock types, recording the drift of far-traveled icebergs, which implies seasonally open water at the sites. The period when the Prince Gustav ice shelf was absent corresponds to regional climate warming deduced from other paleoenvironmental records. We infer that the recent decay cannot be viewed as an unequivocal indicator of anthropogenic climate perturbation.
Perkins, S., Antarctic Sediments Muddy Climate Debate, Science News, Sep 8th 2001
Ocean-floor sediments drilled from Antarctic regions recently covered by ice shelves suggest that those shelves were only 2,000 years old.
Gore, D.B. et al., Bunger Hills, East Antarctica: Ice free at the Last Glacial Maximum, Geology, Volume 29, Number 12, Pages 1103-1106, Dec 2001
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.
Bentley, M.J., et al., Early Holocene Retreat of the George VI Ice Shelf, Antarctic Peninsula, Geology, Volume 33, Number 3, Pages 173-176, Mar 2005
The recent collapse of several Antarctic Peninsula ice shelves has been linked to rapid regional atmospheric warming during the twentieth century. New high-resolution lake sediment records of Holocene ice-shelf behavior show that the George VI Ice Shelf was absent beginning ca. 9595 calibrated (cal.) yr B.P., but reformed by ca. 7945 cal. yr B.P. This retreat immediately followed a period of maximum Holocene warmth that is recorded in some ice cores and occurred at the same time as an influx of warmer ocean water onto the Antarctic Peninsula shelf. The absence of the ice shelf suggests that early Holocene ocean-atmosphere variability in the Antarctic Peninsula was greater than that measured in recent decades.
Bentley, M.J., and Hodgson, D.A., Antarctic Ice Sheet and Climate History Since the Last Glacial Maximum, Pages, Volume 17, Number 1, Jan 2009
Results showed that there are two warm periods recorded in most of the proxy records - a period of early Holocene warmth, and a Mid-Holocene Hypsithermal (Fig. 3)
Bentley, M.J., et al., Mechanisms of Holocene Palaeoenvironmental Change in the Antarctic Peninsula Region, The Holocene, Volume 19, Number 1, Pages 51-69, 2009
Two warm events are well recorded in the Holocene palaeoclimate record, namely the early Holocene warm period, and the `Mid Holocene Hypsithermal' (MHH)
Sime, L.C., et al., Evidence For Warmer Interglacials in East Antarctic Ice Cores, Nature, Number 462, Pages 342-345, Nov 19th 2009
We conclude that previous temperature estimates from interglacial climates are likely to be too low.
Schiermeier, Q., Antarctic Temperature Spike Surprises Researchers, NatureNews, Nov 18 2009
Sime adds that scientists still know too little about what happened in Antarctica during warm climates similar to ours. "We'd be better off if we did."

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