Pre-Industrial Climate Change in the Mackenzie Trough Area, Beaufort Sea, Canada
Abstract
Two short sediment cores were collected along a nearshore-offshore transect in the Mackenzie Trough (Canadian Beaufort Sea) in order to reconstruct the evolution of sea surface parameters (temperature, salinity, sea ice cover) during the industrial and pre-industrial periods, and assess the impact of anthropogenic activities. Dinoflagellate cysts (dinocysts) and freshwater palynomorphs were used as proxy indicators of sea surface conditions and freshwater input, respectively. The cores were dated using measurements and range from approximately 1550 A.D. to the modern period, providing a multi-annual to decadal-scale resolution for our reconstructions. Sedimentation rates are maximum at the offshore site (2.3 mm/yr) and lower at the nearshore site (0.7 mm/yr). This is due to the energy at the river mouth, which induces a bypass of the proximal trench and shelf areas, allowing sediment deposition further offshore. In both cores we observe the passage from a heterotrophic to an autotrophic regime over the last 450 years, which we associate with increased nutrient input and/or increased open water conditions throughout the study area. The Little Ice Age period (LIA; 1550 to 1850 A.D.) is marked by low, but increasing, dinocyst fluxes (enhanced productivity) and low sea surface temperature in surface waters. Freshwater palynomorhs reach their maximum abundance toward the end of the LIA, and start decreasing toward modern times. This is accompanied by a reduction of salinity suggesting decreased freshwater inflow from the Mackenzie River. The industrial period (1850 A.D. and onward) is marked by a decrease of dinocyst fluxes by a factor of 2.5. These data suggest that the observed decrease in surface productivity in the Beaufort Sea may be related to the apparent reduction in the rate of summer sea surface temperature increase that occurred at the onset of the industrial period (increase rate of 1.2°C/century during the LIA and increase rate of 0.33°C/century during the industrial period). However, there is no clear link between anthropogenic activities and the warming trend observed with the reconstructed sea surface parameters.
- Publication:
-
AGU Spring Meeting Abstracts
- Pub Date:
- May 2009
- Bibcode:
- 2009AGUSMPP71A..03R
- Keywords:
-
- 4900 PALEOCEANOGRAPHY (0473;
- 3344)