Terrestrial and Marine Organic Matter Accumulation in Hudson Bay: A High-Resolution Record of Climate/Watershed Processes over the Late Holocene

Tuesday, 16 December 2014
Yvan Alleau1, Miguel A Goni1, Lauren Kolcynski1, Guillaume St-Onge2, Patrick Lajeunesse3 and Torsten Haberzettl4, (1)Oregon State University, Corvallis, OR, United States, (2)University of Quebec at Rimouski UQAR, Rimouski, QC, Canada, (3)Universite Laval, Quebec, QC, Canada, (4)Friedrich Schiller University of Jena, Jena, Germany
A high-resolution record of organic matter accumulation in sediments from a combined gravity-piston core was collected from a site located at a water depth of 104 m inside Nastapoka Sound in the south-eastern region of Hudson Bay. The drainage basins in this region of Hudson Bay coincide roughly with the present-day tree line location and are within the forest-tundra transition zone. CAT- Scan and multi-sensor core logger data revealed relatively uniform sediments throughout the core. 14C-based geochronology indicates that the combined record extends to ~3200 cal BP and that accumulation rates were relatively constant (0.1-0.2 cm/y). Organic carbon, inorganic carbon and nitrogen contents display down-core variability consistent with changes in organic matter inputs but overall relatively stable depositional conditions over the last 3,000 years. Compositionally, we measured steady increases in the carbon:nitrogen ratios and lignin phenol content of sedimentary organic matter from 3200 cal BP to present consistent with enhanced inputs of vascular plant-derived organic matter. Lignin compositions (i.e. S/V and C/V phenol ratios) throughout the core are consistent with contributions from a mixture of conifer and angiosperm non-woody plant sources. Steady decreases in both S/V and C/V phenol ratios since 3200 cal BP to the present indicate enhanced contributions from conifer-dominated vegetation and are consistent with a steady expansion of boreal forests (white and black spruce) over shrub -dominated tundra (dwaf birch, willows, sedges) in this southern Arctic region over the late Holocene. No clear trends in the ratio of combustion products over lignin products are evident, suggesting a low fire frequency in the area during the covered time span of the record.