Sedimentary records of climatically controlled river and sediment discharge in Hudson Bay and Labrador since 10,000 YR BP

Hülse, Peter (2012) Sedimentary records of climatically controlled river and sediment discharge in Hudson Bay and Labrador since 10,000 YR BP. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

In order to evaluate possible effects of climate change on freshwater discharge in northeastern Canada, and to place recently observed changes in freshwater discharge in an appropriate temporal and global framework of change, the sedime ntary record offshore the Great Whale River (GWR) in Hudson Bay and in Nachvak and Saglek Fjords, Labrador, were analyzed in terms of climatic and river discharge proxies. Results of AMS¹⁴C mass accumulation rates at the GWR suggest that a warming climate may lead to increasing water and sediment discharge. An inferred offshore shift in sediment deposition during the past ~150 yr (determined from ²¹⁰Pb and ¹³⁷Cs sediment radiochemistry) was re lated to a more energetic marine environment as a result of decreased sea-ice coverage and may already be a signal of global warming. Additionally, a fluctuati on in the magnetic susceptibility (MS) record of 195-263 years is inferred to be a signal of te rrestrial minerogenic input related to variability in the hydrologic cycle. Overall , consistent TOC, TN, C/N, and δ¹³C values suggest that no major changes in paleoenvironme ntal processes controlling carbon and nitrogen burial conditions occurred during the past ~2000 yr. The sediment cores from Nachvak and Saglek Fjords date to ~9,800 yr BC and ~5,400 yr BC, respectively. Ice-rafted debris contents implies a continuous net decrease in sea-ice cover until the end of the Holocene Thermal Maximum (-2,000 yr BC). After 2000 yr BC, sea-ice cover increased again during the Neoglacial cooling. This trend is accompanied by increasing productivity (determined from TOC, TN, TOC, and δ¹³C). These trends are likely related to orbitally-forced Milankovitch-scale variations in insolation. Relatively low sedimentation during the Temperate Period, which was of supposedly high meltwater discharge, is inferred to the presence of glacial lakes, trapping sediment and re routing freshwater discharge. Higher frequency variability in the MS record appears to be related to a solar forced ~1000 yr cyclicity and in Nachvak Fjord rates of input of terrestrial minerogenic matter appear to increase during warmer intervals relative to colder periods. This is interpreted as a sign of increased precipitation and river discharge during warm periods (the same trend like at the Great Whale River). Similar cyclicity is apparent in Saglek Fjord. Dating uncertainties, however, preclude precise correlations between the fjords or Labrador, and Hudson Bay. In Saglek Fjord, however, an increase in sediment accumulation rate (SAR) was recorded during the Little Ice Age (LIA) (the opposite trend to that of the Great Whale River). More detailed dating would Improve the understanding of the ancient climate-river discharge interactions of NE Canada.

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