Evolution of palaeo-sea-surface conditions and sediment dynamics over the last 2700 years on the Mackenzie Slope, Beaufort Sea (Canadian Arctic)

摘要

A box core and a trigger weight core were recovered from the Mackenzie Slope (Canadian Beaufort Sea) and combined into a composite sequence (AMD0214-03BC/TWC: 03CS) to investigate dinocyst assemblages and the mineralogical and geochemical compositions. This allowed the estimation of sea-surface conditions and documentation of changes in detrital inputs related to Late Holocene ocean-climate variability over the last 2700 years. The trends of detrital proxies and freshwater palynomorphs were similar to the reconstructed changes in large-scale ocean-atmosphere climate modes, such as the Pacific Decadal Oscillation (PDO) and Arctic Oscillation (AO). The palynological data reveal four distinct time intervals. The first period from 700 to 0 BCE was characterized by high surface and benthic productivities. This and the high freshwater palynomorph flux recorded in this period imply considerable freshwater input from the Mackenzie River with northern Mackenzie Basin sediment sources and enhanced transport of nutrient-rich Pacific water along the Mackenzie Slope. From 0 to 1500 CE, the weather conditions were possibly drier, with a decrease in the Mackenzie River discharge and nutrient supply. Milder sea-surface conditions associated with the Medieval Warm Period (800-1525 CE) likely promoted more prolonged seasonal sea-ice melting. The period from 1500 to 1900 CE featured increasing fresh water and a mixed provenance of detrital particles (with most particles originating from the northern Mackenzie Basin and a minor contribution from the southern basin). Colder conditions associated with the Little Ice Age period (1525-1865 CE) likely promoted longer sea-ice durations on the Mackenzie Slope. The final period, from 1900 CE to the present, has been dominated by taphonomic processes rather than climatic variations. Overall, this study provides a better understanding of the evolution of land-ocean interactions on the Mackenzie Slope.