HR: 14:30h
AN: C13C-04    [Abstracts]
TI: Palaeoecological Quantitative Estimates of the Extent and Timing of the Holocene Thermal Maximum in Iceland
AU: * Caseldine, C
EM: C.J.Caseldine@ex.ac.uk
AF: Department of Geography University of Exeter, Amory Building Rennes Drive, Exeter, EX44RJ United Kingdom
AU: Langdon, P
EM: P.G.Langdon@ex.ac.uk
AF: Department of Geography University of Exeter, Amory Building Rennes Drive, Exeter, EX44RJ United Kingdom
AU: Holmes, N
EM: N.Holmes@ex.ac.uk
AF: Department of Geography University of Exeter, Amory Building Rennes Drive, Exeter, EX44RJ United Kingdom
AB: The magnitude and timing of Holocene maximum warmth in the Arctic and Sub-Arctic has been the subject of considerable recent interest, particularly in the context of future climate change (Kaufman et al., 2004). For Iceland, lying at a crucial location in the North Atlantic close to significant atmospheric and oceanic boundaries, data predominantly derive from glacial and palaeoecological evidence, but current understanding is relatively limited. Reconstruction of former glacial histories often reveals an apparent absence of glacial advances between the Preboreal and ca. 7000 cal. BP, but the exact extent of glaciation during this period is not known. If, as seems possible, ice caps such as Langjokull disappeared at this time (Geirsdottir et al., 2002) then it is possible to produce modelled estimates of summer temperature. Such models do however, of necessity, assume constant precipitation (usually as today) for which there is no empirical evidence, hence any temperature reconstructions have wide error margins. Palaeoecological data has so far relied on pollen and macrofossil evidence with peak summer warmth being inferred from expanding woodland and high tree lines formed by Betula pubescens ssp. tortuosa, the only woodland-forming tree in Iceland. July temperatures (or summer tri-/tetratherms) can be estimated by comparison with Fennoscandian studies, but the validity of this approach is open to question due to the lack of analogous `natural' tree lines in Iceland and questions over the comparability of the birch species between the two areas. Using this approach, July temperatures of 13C at sea level would be assumed for Trollaskagi in Northern Iceland between 7600 cal. BP and 6700 cal BP, compared to a figure of just below 11C for the period 1931-1990. Recent studies in both Trollaskagi and NW Iceland have compared pollen analyses with a July temperature reconstruction based on the analysis of sub-fossil chironomids from the same lake sediments. July temperatures have been derived using both an extensive Norwegian transfer function and a more limited Icelandic training set. Use of the Icelandic data suggest optimal temperatures only 1C above current levels around 8000 cal. BP, a time when birch woodland was well developed in Trollaskagi, but when woodland had still not fully developed in the more isolated NW peninsula. Use of the Norwegian training set reconstructs slightly higher temperatures. On the present available data it is assumed that optimal summer warmth did not occur in Iceland until 8000 cal. BP at the earliest, possible lasting until 6700 cal. BP. The amount of warming is as yet difficult to estimate but for July was at least 1C, possibly up to 2-3C higher than the 1931-1990 average. Comparison with data from elsewhere in adjacent Arctic regions, Greenland and Eastern Arctic Canada show peak warmth to be later in Iceland, and probably less pronounced. References Caseldine et al. (2003) ` Efstadalsvatn - a multi-proxy study of a Holocene lacustrine sequence', Journal of Paleolimnology, 30, 55-73. Geirsdottir et al. (2002) `How warm was the Early Holocene?' Abstract, ARCSS Workshop, Seattle. Kaufman, D.S. et al. (2004) `Holocene thermal maximum in the western Arctic (0-180W). Quaternary Science Reviews 23, 529-560.
DE: 9315 Arctic region
DE: 3344 Paleoclimatology
DE: 1823 Frozen ground
DE: 1824 Geomorphology (1625)
DE: 0315 Biosphere/atmosphere interactions
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting