Climate change and recent sedimentation in Nastapoka Sound, eastern coast of Hudson Bay

Abstract

In an attempt to determine to what extent the impact of recent climate changes that occurred east of Hudson Bay, including important reduction of areas in permafrost, had on the coastal marine environment, a series of shallow cores were extracted from the seabed off the mouth of the Sheldrake River, in Nastapoka Sound. A total of 25 cores were taken in April 2009 from the ice cover. A preliminary seafloor map was first done to help in the selection of the coring sites. Nastapoka Sound has a complex subaqueous relief, formed of asymmetric ridges and deep basins. After preliminary sedimentological analyses, six of the cores were selected for physical and chronological analyses (14 C, 210 Pb, and 137 Cs dating); among them, three were selected for elemental (C, N, OC/TN) and isotopic (␦ 13 C, ␦ 15 N) analyses to identify sedimentary organic matter sources. Sedimentation processes are complex and are primarily driven by bottom currents. This is confirmed by the absence of a clay fraction in several cores, some erosion surfaces in a few cores, and the presence of comet-like mark features on the seafloor. The highest sedimentation rates are found near the coast of the province of Quebec and Gillies Island and the lowest ones occur in the deep depocenters. Isotopic and elemental analyses reveal that Nastapoka Sound is an area of mixing between marine and terrestrial inputs and can be compared to an estuarine system similar to nearby Lac Guillaume-Delisle. Those conditions altogether make it difficult to extract a perfectly clear signal of climate change in the recent sediment record. However, the downcore application of a simple two end-member mixing model to measured ␦ 13 C values strongly suggests that the fraction of sedimentary organic matter from terrestrial sources increased by 30% since about the middle of the Little Ice Age. This trend accelerated at the end of the 20th century. Rapid permafrost decay in adjacent river catchments is likely one source for this terrestrial carbon. However, it cannot be distinguished from other potential sources that are also related to environmental changes such as increase in primary productivity both on land, where peatlands, shrubs, and forest are expanding, and at sea, where sea ice cover duration is diminishing. Résumé : Dans le but de déterminer l'étendue des impacts des changements climatiques récents qui ont eu lieu à l'est de la baie d'Hudson, incluant une réduction significative des secteurs de pergélisol, sur l'environnement marin côtier, une série de carottes peu profondes a été prélevée du lit marin à l'embouchure de la rivière Sheldrake, dans le détroit de Nastapoka. Un total de 25 carottes a été prélevé à partir de la couverture glaciaire en avril 2009. Une carte préliminaire du plancher océanique a été dressée afin d'aider à choisir les sites de prélèvement des carottes. Le détroit de Nastapoka a un relief subaquatique complexe, formé de crêtes asymétriques et de bassins profonds. Après des analyses sédimentologiques préliminaires, six carottes ont été choisies pou...

Coastal sedimentation across North America doubled in the 20th century despite river dams

“…3,4) and give credence to the patterns and trends extracted from the dataset. For example, the main sediment source for subpolar Nastapoka Sound in Hudson Bay is permafrost decay in adjacent river catchments 31 , for arid Corpus Christi Bay, TX it is fluvial sediment from the small (39,000 km 2 ) Nueces River drainage basin and erosion of underlying Pleistocene strata 32 , and for tropical Florida Bay, it is in-situ carbonate production 33 associated higher resolution exhibited some decadal variability, the most extreme being Florida Bay where sediment MAR increased disproportionately from 1950 to 1980 with a subsequent decrease due to changes in Everglades water management that increased freshwater delivery and reduced macroalgae productivity, the main source of carbonate sediment to the depocenter 33,34 . The sediment geochronologies show post 1950 median MAR and first-quartile values increased above the pre 1950 median MAR and third-quartile values at most of the sites.…”

“…The exception being the coastal depocenters of Louisiana where these sources promoted the MAR increase post 1950 despite the distinct reduction in Mississippi River flow and suspended-sediment flux to the margin 52 , which contributed to the loss of wetlands 53 . Rapid permafrost decay in river catchments from warming climate is a source of sediment to high latitude depocenters and contributed to the MAR increase in Nastapoka Sound 31 . This study falls short of identifying the relative additional contributions of specific downstream sediment sources to coastal depocenters; a necessary next step because each sediment source has a different implication for coastal-hazard mitigation, the carbon cycle, and the transport of contaminants attached to fine-grained particles.…”

Impact of permafrost thaw on the turbidity regime of a subarctic river: the Sheldrake River, Nunavik, Quebec

“…The released sediments are mobilized by soil erosion, in overland flow and in water courses; they feed sedimentation (Guo et al 2004;Goni et al 2005;Jolivel et al 2015) and get involved in biogeochemical processes (Emmerton et al 2008;Galand et al 2008;Vonk et al 2015) in lakes, deltas, and coastal seas.…”

“…These inputs can alter terrestrial and aquatic ecosystems and affect food webs as well as primary and secondary production (Kokelj et al 2002(Kokelj et al , 2009Bowden et al 2008;Mesquita et al 2010). Ultimately, a significant fraction of the organic carbon released by thermokarst may reach the marine environment (Jolivel et al 2015;Vonk et al 2015).…”