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Micropaleontological Records of the Last 1300 Years in the Beaufort Sea Shelf Highlight Exceptional Changes Over the Last Two Centuries

2022; RELX Group (Netherlands); Linguagem: Inglês

10.2139/ssrn.4314882

1556-5068

Jade Falardeau, Anne de Vernal, Marit‐Solveig Seidenkrantz, Michael Fritz, Thomas M. Cronin, Laura Gemery, André Rochon, Vladislav Carnero-Bravo, Claude Hillaire‐Marcel, Christof Pearce, Philippe Archambault,

Archaeology and ancient environmental studies

The Arctic Ocean nearshore areas are very variable as they are sensitive to wind and land-ocean interactions, thus making it difficult to evaluate the anthropogenic warming contribution to recent climate changes. A sediment record allowed us to reconstruct the impacts of climate and environmental changes over the last 1300 years in the southern Canadian Beaufort Sea, along the northern Yukon coast. Two sediment cores were collected in 2016 at the same site (PG2303; 69.513°N-138.895°W; water depth 32 m) in the Herschel Basin, where high sedimentation rates (0.1-0.5 cm a-1) permitted analyses at sub-centennial to decadal resolutions. Benthic foraminiferal, ostracod, and tintinnid content as well as the stable isotope composition of Elphidium clavatum and Cassidulina reniforme were used as paleoclimatic and ecological indicators, while radiometric analyses provided the age model. From 710 ± 160 to 1130 ± 150 CE, bottom waters in the basin reflected relatively saline and warm conditions typical of shelf-break waters. It is indicated by the dominance of C. reniforme in the foraminiferal assemblages and the alternated occurrence of the ostracods Kotoracythere arctoborealis-Normanicythere leioderma and the foraminifer Triloculina trihedra, which we associated to Pacific- and Atlantic-affiliated waters, respectively. From ~1130 to 1640 CE, restricted upwelling of shelf-break waters, limited sediment supply, and low abundances of microfossils suggest cold conditions and dense annual sea-ice cover until 1640 ± 60 CE. The occurrence of Tintinnopsis fimbriata and bacterial/complex organic carbon feeder foraminifera (Quinqueloculina stalkeri, Textularia earlandi and Stetsonia horvathi) together with depleted δ13C after ~1800 CE, suggest the increased influence of freshwaters rich in particulate-matter, which may relate to the Mackenzie River plume and/or permafrost degradation along the coast. Based on our records, the shift at ~1800 CE marks the onset of regional warming. There was an intensification of warming-related changes after ~1950 CE, likely in response to anthropogenic forcing.