C13C-01 INVITED 13:40h
Postglacial Development of the Circumpolar Peatland Complex and Its Potential Impact on Atmospheric Methane Concentrations
The development of extensive peatlands in the circumpolar subarctic and arctic zones produced immense alterations in edaphic conditions, hydrology, vegetation, animal forage and habitat conditions, human land-use potential, carbon storage and land-atmosphere fluxes of CO2 and CH4. There has been much speculation regarding the impact that circumpolar peatland development may have played on Holocene atmospheric CH4 concentrations as recorded in ice-core records from Greenland and Antarctica. A recently acquired network of 226 basal dates from the western Siberian Lowlands has been combined with over 1300 similar dates from peatlands throughout the circumpolar region to provide continental and hemispheric scale reconstructions of northern peatland development. The data suggest there was only very limited peatland development, even in unglaciated regions, prior to 12,000 Cal yr BP. Euarasian peatlands experienced a sharp rise in development between 12,000 and 10,000 Cal yr BP. This corresponds with a period of high atmospheric concentrations of CH4. Although North American peatlands also expanded during this period, the tempo of development in North America also strongly reflected the more gradual retreat of the Laurentide Ice Sheet and the associated exposure of land surfaces for peatland expansion. Following 8000 to 6000 Cal yr BP there was a general decrease in the rate of peatland development.
C13C-02 14:00h
Late-Quaternary Climate Change Within the Beringian Buckle: Multidisciplinary Results From St. Michael Island
Zagoskin Lake is a 19 m deep maar beyond the limits of late Cenozoic glaciation that contains a 30,000 14C yr B.P. record of climate change. We quantitatively reconstructed the summer thermal regime using midge, diatom, and pollen data. Preliminary inferred mean July air temperatures based on the diatom and midge data show similar trends with LGM temperatures surprisingly similar to modern ones. In addition, both reach maximum values from about 11,000 to 9500 14C yr B.P. coincident with a peak of poplar pollen - a tree that does not occur on the island today. In contrast, the pollen-based reconstructions indicate a cold LGM relative to modern temperatures, a small peak in temperatures coincident with the poplar pollen peak, and then sustained high levels for most of the Holocene. Potential problems and how these differing records may be reconciled will be discussed.
C13C-03 14:15h
Late Quaternary Environment Of Central Yakutia, East Siberia
A Russian-German joint project, investigating the late Quaternary development of periglacial and glacial landscapes, lacustrine systems, as well as permafrost complexes and ground ice features in central Yakutia, is currently in progress. Field work was carried out in 2002 and 2003 along the Tumara and Djanushka rivers in the Verkhoyansk Mountains and its foreland, and in 2004 in the alass region northeast of Yakutsk. Geomorphological and sedimentological findings, satellite-image evaluation, and first dating results by optical-stimulated luminescence give evidence of multiple glacial advances in the foreland of the Verkhoyansk Mountains that were not in phase with variations in global ice volume. The last episode with extended piedmont glaciers entering the Verkhoyansk foreland took place around 32 ka BP. No major glacier advances are evident for the global last glacial maximum, because dry conditions apparently prevented sufficient snow and ice accumulation, as suggested by the deposition of extended loess-like sediments at that time. Stable-isotope records of ice wedges, as indicators of palaeo winter temperatures, together with pollen records from Lake Satagay give evidence of an early Holocene climate optimum between approximately 8.0 and 6.0 ka BP, followed by climate deterioration during the late Holocene. Variations in the concentration and composition of organic matter in the Lake Satagay sediment record, moreover, reveal pronounced fluctuations of lake-level status, attributed to short-term climate oscillations at centennial time scales that caused cyclic changes in aridity.
C13C-04 14:30h
Palaeoecological Quantitative Estimates of the Extent and Timing of the Holocene Thermal Maximum in Iceland
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.
C13C-05 14:45h
An annually resolved 2500 yr long record of rain events in a polar desert
Varved sediments of Sawtooth lake, Nunavut Canada contain a ~2500 years long record of past environments. Sediment accumulation is mainly due to spring snowmelt that forms silty laminations grading into clay. However, coarser non-erosive sand beds frequently interrupt this regular sedimentation. Field observation and evidences from the analysis of the sediment, mainly from thin-sections, point out that these coarse beds are due to summer rain events. Results from the analysis of the occurrence of these events are presented. We investigate both short (interannual) and long (centennial) scale variability. We also investigate the possibility of geomorphic influences on the delivery of sediment to the lake basin. Our preliminary data reveal that the so-called medieval period might have been characterized by rainy summers in this part of the Arctic.
C13C-06 15:00h
Cirque Glacier Activity in Arctic Norway During the Last Deglaciation
Numerous cirques of the Lofoten-Vester$\aa$len archipelago in northern Norway have distinct moraine sequences that previously have been assigned to the Younger Dryas-Allerod (11 600 to 13 400 cal yrs BP) era, constraining the regional distribution of the equilibrium-line altitude (ELA) of both cirque glaciers and larger ice masses. In this study, we present evidence from a once glacier-fed lake on southern Andoya that contest this view. Detailed analyses of radiocarbon dated lacustrine sediments including rock magnetic parameters, grain size, organic matter, dry bulk density and visual interpretation suggest that there were no glacier in the low-lying cirque during Younger Dryas-Allerod. The initiation of the glacial retreat commenced with the onset of the Bolling warming (14 760 cal yrs BP) and was completed by the arrival of Allerod Interstade (13 400 cal yrs BP). The reconstructed glacier stages constrained by the attributes of the glaciolacustrine sediments and the moraine chronology of the investigated cirque suggest advances during a cool period from about 14 700 to 17 500 cal yrs BP coinciding with Heinrich event 1 (H1), and a somewhat larger advance between ca 19 100 and 21 050 cal yrs BP.
C13C-07 15:15h
Sediments from the North Siberian Margin as Archive of Paleoenvironmental Change
Empirical data as well as modelling experiments show that the stability of the Arctic cryosphere is today under threat due to global warming. Along the circum-arctic ocean periphery this cryosphere is comprised of terrestrial permafrost. However, during Quaternary times this frozen landscape was repeatedly changed due to global sea-level fluctuations which particularly affected the wide and shallow Siberian shelves. As western part of the Beringian landmass the entire Laptev Sea shelf was subaerially exposed in last glacial times. During postglacial sea-level rise the landscape gradually changed from a terrestrial permafrost landscape into a marine environment. Various geochemical, micropaleontological, palynological, and sedimentological data obtained from sediment cores reveal the strong influence of this tranformation process on the shelf environment. So far, sediment material older than early Holocene could not be obtained from the shelf by conventional means. A scientific drilling campaign was therefore conducted to the outer Laptev Sea shelf with the goal to recover sediments that would allow an environmental study of this area on time scales beyond the Holocene. Previous site investigations by acoustic profiling and a gravity core suggested a Holocene sediment package of about 10 m thickness. The cores recovered during the drilling campaign from below this depth level reveal various types of ice-bearing, frozen sediments which contain a rich terrestrial plant flora as well as beetle fauna, both suggesting a late glacial age in accordance with the other obtained dates. Further micropaleontological and isotopic analyses corroborate a strong influence of a terrestrial-fuvial environment during this time of permafrost formation, and that at present frozen sediments are being preserved on these shelves below a soft sediment cover of Holocene age.