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THE HOLOCENE THERMAL MAXIMUM ON NORTHEASTERN BAFFIN ISLAND

BRINER, JASON P  INSTAAR.
Miller, Gifford H  INSTAAR.
Francis, Donna R  University of Masssachusetts.
Axford, Yarrow L  INSTAAR.

New lake cores from the Clyde region, northeastern Baffin Island, provide continuous records of Holocene environmental conditions. A core from 6 m depth in lake CF3, which has a surface area of ~0.4 km2, a drainage basin of ~1 km2, and no significant inflow stream, has received the most attention. Macrofossil 14C ages from six depths provide a chronology from ~11.5 ka, the timing of regional deglaciation, through to the 20th century via an overlapped surface core. Magnetic susceptibility, sediment appearance, grain size, loss-on-ignition (LOI), and total carbon measurements from CF3 show a strong trend from early to late Holocene. We hope to show chironomid taxonomy-based summer temperature estimates from a dozen levels in the core.

Among all of our downcore data, LOI values have been obtained at the highest resolution (~60 yr.), and are supported by total carbon measurements from overlapping levels to represent fluctuations in organic carbon. Due to the simplicity of the hydrologic system, we interpret LOI as a proxy for lake productivity. LOI rises to intermediate values (~20%) at ~11.5 ka, and to their highest values of the Holocene (~35%) by ~10.4 ka. LOI values decrease significantly after ~9.5 ka, indicating a Holocene thermal maximum (HTM) between ~10.4 and ~9.5 ka. The decreasing LOI values through to the Little Ice Age (LIA) are punctuated by several millennial-scale variations. A surface core from the same site records a transition from LOI values of ~10% during the LIA to values of >20% in the most recent (20th century) sediments, the highest values in the last ~8 ka. The Holocene LOI pattern is repeated in several cores from the Clyde Region, and the surface core pattern is virtually identical to a 210Pb-dated surface core from a neighboring lake.

The LOI-defined HTM at Clyde is earlier than in adjacent Baffin Bay (Dyke et al., 1996), but is later than lake core estimates for the HTM from southern Baffin Island (e.g., Miller et al., 1999). These comparisons suggest that southern Baffin Island warmed before northern Baffin Island, even though both locations were deglaciated at roughly the same time. The CF3 LOI record is very similar to the Agassiz ice cap melt layer record (Fisher and Koerner 2003), and may indicate that warming at these sites leads the initial warming of Baffin Bay.

REFERENCES
Dyke, A. S., Dale, J. E., and McNeely, R. N., 1996, Marine molluscs as indicators of environmental change in glaciated North America and Greenland during the last 18,000 years: Géographie physique et Quaternaire, v. 36, p. 5-14.



Fisher, D. A., and Koerner, R. M., 2003, Holocene ice-core climate history - A multi-variable approach. In "Global Change in the Holocene." (R. Battarbee, and e. al, Eds.), pp. 281-293. Hodder Arnold, London.



Miller, G. H., Mode, W. N., Wolfe, A. P., Sauer, P. E., Bennike, O., Forman, S. L., Short, S. K., and Stafford, T. W. J., 1999, Stratified interglacial lacustrine sediments from Baffin Island, Arctic Canada: Chronology and paleoenvironmental implications: Quaternary Science Reviews, v. 18, p. 789-810.



Figure 1. North-south transect of continuous records of summer temperature proxies from the eastern Canadian Arctic. A) Melt record from Agassiz Ice Cap (Fisher and Koerner 2003) and July insolation at 70 °N. B) Changes in the number of thermophilous mollusk taxa present in Baffin Bay (Dyke et al.,1996). C, D, E) Loss-on-ignition profiles from Baffin lakes (Robinson: Miller et al., 1999). Lakes on southern Baffin Island reach maximum summer temperature indicators about 1000 years earlier than at higher latitudes, and peak sea-surface temperatures lag another thousand years behind the northern terrestrial sites.


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