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Records of environmental changes during the Holocene from Isla de los Estados (54.4 degrees S), southeastern Tierra del Fuego
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2010 (English)In: Global and Planetary Change, ISSN 0921-8181, E-ISSN 1872-6364, Vol. 74Article in journal (Refereed) Published
Abstract [en]

Southernmost Patagonia, located at the relatively narrow passage between Antarctica and South America, is a highly sensitive region for recording meridional and zonal changes in the pattern of oceanic and atmospheric circulation. The island of Isla de los Estados, situated at 54.5 degrees S, 64 degrees W, east of Argentinean Tierra del Fuego, provides an exceptional possibility, to investigate terrestrial records of atmospheric conditions in an oceanic setting during the last deglaciation and the Holocene. Here we present geochemical and diatom analyses from 10600 to c. 1500 cal BP of one sequence (LGB) with peat, lake sediments and lagoon deposits at the northern coast of the island, and a lake sediment sequence (CAS) 3 km further inland. The data comprise TC, TN, loss on ignition analyses and continuous XRF scanning as well as age-depth modeling based on AMS-C-14 dating on both cores. Diatom analysis of the CAS record complements the geochemical proxies. During the Holocene, our two sites have been impacted by two different forcings: changes in the regional climate regime largely influenced by the varying strength and position of the Southern Hemisphere Westerlies (SHW), while relative sea-level changes affected the deposits of the coastal site. In concert with the onset of the Antarctic thermal optimum, our data suggest fairly warm conditions and the establishment of denser peat and forest vegetation on the island c. 10600 cal BP. Between 8500 and 4500 cal BP geochemistry and diatoms from the CAS record indicate stronger Westerlies at this latitude, which means higher wind speed or higher storm frequency and more precipitation, resulting in more pronounced surface run-off. After 4500 cal BP, the geochemical proxies and large changes in diatom assemblages indicate a decrease in precipitation, weaker winds and possibly cooler conditions, probably as an effect of weaker SHW and/or a latitudinal shift. The depositional environment of CAS changed from gyttja to peat around 1000 cal BP. At LGB, the onset of gyttja sedimentation around 7900 cal BP shows that the former wet land with peat accumulation had become a lake with a fairly rapid sedimentation. The chemical data from LGB imply a gradually increasing marine influence, probably as an effect of both rising sea level and increased impact of storms and maximum high tides. After a marine high-stand during the mid-Holocene, the LGB site returned into a peat bog again around 3400 cal BP. Our data suggest that since then relative sea level first dropped back below present sea level followed by a rise to present day sea level. (C) 2010 Elsevier B.V. All rights reserved.

Place, publisher, year, edition, pages
2010. Vol. 74
Keyword [en]
Holocene lake sediments peat diatom analysis XRF paleoclimate southern westerlies sea-level changes Tierra del Fuego sea-level changes dissolved organic-carbon south-america late pleistocene climatic changes quaternary lake deposition patagonia pacific Physical Geography Geology
Research subject
SWEDARP 2005/06, Isla de los Estados
Identifiers
URN: urn:nbn:se:polar:diva-1937DOI: 10.1016/j.gloplacha.2010.07.003OAI: oai:DiVA.org:polar-1937DiVA: diva2:810349
Note

ISI Document Delivery No.: 702QL Times Cited: 9 Cited Reference Count: 82 Unkel, Ingmar Fernandez, Marilen Bjorck, Svante Ljung, Karl Wohlfarth, Barbara German Research Council [Un261/2-1]; Swedish Research Council (VR) [621-2003-3611]; Kungliga Fysiografiska Sallskapet in Lund; Swedish Polar Secretariat; VR The position of Ingmar Unkel was funded by the German Research Council (DFG scholarship No. Un261/2-1). The research expedition to Isla de los Estados was carried out by Charlie Porter's ketch "Ocean Tramp" (Puerto Williams) and funded by a grant (621-2003-3611) to SB from the Swedish Research Council (VR) as part of his so-called Atlantis project. The field work at the two sites was carried out by SB, BW, KL and J. F. Ponce (Ushuaia). The analytical and logistic costs were funded both by the VR grant, by Kungliga Fysiografiska Sallskapet in Lund and the Swedish Polar Secretariat. Two anonymous reviewers gave valuable comments to improve our manuscript. To these persons and institutions we would like to express our sincere thanks. 9 Elsevier science bv Amsterdam Geography, Physical; Geosciences, Multidisciplinary

Available from: 2015-05-07 Created: 2015-05-06 Last updated: 2015-05-22

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