CGRG Bibliography of Canadian Geomorphology
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Author : Frechette, B.; Richard, P. J.H.; Wolfe, A.P.; and Miller, G.
Date : 1998
Title : Over 50,000 years of environmental change recorded in the sediments of Fog Lake, Baffin Island, Nunavut, Canada: palynological evidence.
Publication : 28th Arctic Workshop, March 12 - 14, 1998. Institute of Arctic and Alpine Research University of Colorado, Boulder, CO USA
Issue :
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Abstract
Fog Lake (northern Cumberland Peninsula, Baffin Island) is located above moraines of the last glacial cycle. Sediments from Fog Lake offer the first repository of terrestrial paleoenvironmental information pertaining to the stability of climate in the Eastern Canadian Arctic during the last glacial maximum (LGM) and preceding interglacial conditions. Four cores recovered from the central deep (9.5 m) record the following sequence of stratigraphic units: (1) basal diamicton; (2) laminated silts; (3) compact de-watered gyttja; (4) stratified minerogenic sediment (laminated silt); and (5) Holocene gyttja. Core 96FOG-05 (total length: 137 cm) is constrained by 16 AMS radiocarbon dates on mosses and humic acid extracts. Both materials yield non-finite dates for the lowest organic horizons (Unit 3). Humic acids from Unit 4 have dates in the 14-16 ka BP range. Pollen analysis was undertaken on 71 samples from 96FOG-05 in order to document vegetational history in terms of both composition and stability of local plant communities, as well as variability of atmospheric delivery mechanisms responsible for distantly-derived (exotic, boreal) pollen types. Pollen and spore concentrations in the basal diamicton (Unit 1) are similar to those of the mid Holocene (Unit 5). Concentrations are outstandingly high (>10,000 grains cm-3) throughout pre-Holocene sediments (Units 2, 3 and 4), and consistently lower (mean of 5,000 grains cm-3) in Holocene sediments (Unit 5). To account for these unexpected trends, we suggest that Fog Lake captured pollen through two distinct mechanisms that regulated the efficiency of pollen recruitment to the basin during the period represented by pre-Holocene sediments (Units 3 and 4). The different modus operandi (open and closed) are inferred from the pollen and spore concentration data. For example, we show that pollen and spore concentrations exploded (e.g. 70,000-95,000 grains cm-3) during transitions from the closed to the open state. Contrasting pollen assemblages are illustrated objectively by cluster analysis and Principal Components Analysis (PCA). Between-group tests reveal the significance of the various zones and sub-zones proposed for the pollen diagram. Equatorial diameter measurements of Betula pollen grains (typically 100 measured per sample) provide important clues concerning exotic (tree, large diameters) and regional (shrub, <25 µm) provenances. Pollen and spores from the basal diamicton (Unit 1) are secondary inheritances from a previous non-glacial interval. Units 2 and 3 represent the last interglacial (sensu lato), with indications of a climate as warm or warmer than any time during the Holocene, manifested by a progression from herb- to shrub-dominated pollen assemblages. A sequence of Salix - Cyperaceae - Betula - Alnus is fully expressed. Pollen and spore assemblages from Unit 4, dated to the LGM, are remarkably uniform, with Betula being by far the most abundant taxon. Since the pollen assemblages from pre-Holocene Units 2 and 3 differ markedly in floristic terms, we reject the hypothesis of pollen reworking to account for high pollen concentrations in sediments of apparent LGM age. Changes in the efficiencies of long-distance atmospheric transport mechanisms are more likely involved. The Holocene record (Unit 5) contains most of the salient palynostratigraphic features recognized from the Baffinland region: successive increases of Cyperaceae, Alnus and Ericaceae. Fog Lake appears to have experienced events of massive pollen input during the Wisconsinan: both exotic and local types are well-represented, indicating that moderately dense stands of vegetation were locally present at the time. Several pollen types, typically under-represented in Holocene sediments from this region, have rich expressions in the pre-Holocene sediments of Fog Lake (Salix herbacea-type, Oxyria digyna-type, for instance). These trends have been corroborated by analyses of pre-Holocene sediments from additional sites on both northern and southern Cumberland Peninsula, indicating that they are regionally consistent and not basin-specific. Our results imply that either our AMS 14C ages in the 14-35 ka BP range must be reconsidered, or that conventional wisdom surrounding issues of Arctic biotic refugia and Wisonsinan paleo-circulation needs serious reconsideration.
Bibliography of Canadian Geomorphology