CGRG Bibliography of Canadian Geomorphology
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Author : Bringue, M.; and Rochon, A.
Date : 2008.
Title : Reconstruction of Late Holocene sea surface parameters on the Mackenzie Slope (Beaufort Sea, Canadian Arctic): Preliminary results.
Publication : International Arctic Change 2008 Conference. December 9-12, 2008. Quebec City, Quebec.
Issue : Conference Programme and Abstracts
Page(s) : 189-190.
Abstract
This study aims at reconstructing past sea-surface parameters in the Beaufort Sea area (Western Canadian Arctic) on the base of sedimentary cores collected over the Mackenzie slope, and covering the last 4500 years. Piston, trigger and box cores were sampled at station 803 (70º38’N, 135º55’W) in 2004 aboard the CCGS Amundsen (CASES) at 218 m water depth. Sedimentation at this particular location is influenced by both the Beaufort gyre and the Mackenzie River, whose sedimentary discharge is by far the largest among all other Arctic rivers. Dinoflagellate cysts are used as proxies for paleoceanographic reconstructions. Past sea-surface temperature, salinity, sea-ice cover and productivity are estimated using transfer functions (modern analogue technique). Other palynomorphs such as freshwater algae (Halodinium, Pediastrum) and reworked material provide insight on the freshwater input (via the Mackenzie), and thus the hydroclimatic conditions over the late Holocene. Preliminary results from the upper 330 cm of the piston core are presented. According to the age model based on 4 AMS-14C datations along the core, this section represents the last 2600 calibrated years BP and the core was subsampled at a 10 cm interval. Dinocyst concentrations are relatively low throughout the section (from 198 to 1240 cysts/cm3). Dinocyst zone II (from 2600 to 1600 cal yr BP) is characterized by assemblages dominated by Operculodinium centrocarpum (~45% on average), accompanied by Islandinium minutum (~19%) and cysts of Pentapharsodinium dalei (~15%). Assemblages in dinocyst zone I (from 1600 cal yr BP to present) are dominated by I. minutum (~31% on average), with the accompanying taxa O. centrocarpum (~26%) and P. dalei (~20%). Changes in dinoflagellate cyst assemblages between zone I and zone II provide insights that are expressed quantitatively by transfer function analyses. In zone I, at the base of the core, summer sea-surface temperatures decrease up to 2°C below present value, as the duration of sea ice cover increases by 1 month a year (below actual value). The autotroph vs heterotroph (G:P) dinoflagellate ratio drops from 3,14 to 0,38, which suggests limited primary productivity due to increasing sea ice cover during this period. In zone II (from 1600 cal yr BP to present), summer sea-surface temperatures increase to reach modern value, and a decrease in duration of sea ice cover is observed. The G:P ratio increases up to 3,12 at the top of the core. These data are consistent with similar studies held in adjacent areas. It is also consistent with other studies describing the warming of Western Canadian Arctic, in comparison with a cooling Eastern Arctic. Spectral and wavelet analysis will also be run on the entire dataset in order to document hydroclimatic cycle(s) prevailing in the Beaufort Sea area, such as the Arctic Oscillation. These results will provide useful data on the evolution of sea surface conditions in the Western Canadian Arctic for the late Holocene as well as for the hydroclimatic variability (freshwater inputs). This will contribute to document the natural variability of Arctic’s climate, a key component in the understanding of earth’s warming climate.
Bibliography of Canadian Geomorphology