Sources and Accumulation of Sediment and Particulate Organic Carbon in a Sub-Arctic Fjard-Estuary: 210Pb, 137Cs, and δ13C records from Lake Melville, Labrador

The sources and distribution of sediment and particulate organic carbon (OC) to Lake Melville, Labrador, were characterized to better understand impacts from climate and hydrological changes to the system. Mass accumulation rates (MARs) across the Lake Melville System (LMS) were established from 15 sediment cores collected in 2013 and 2014 by fitting excess 210Pb (210Pbex) profiles to a two-layer advection–diffusion model. MARs, validated using 137Cs, varied between 0.04 and 0.41 g cm−2 a−1, and overall decreased with increasing distance from the Churchill River, which drains into Goose Bay, a western extension of Lake Melville. The Churchill River is the greatest source of sediment to the system, but surprisingly, MARs were greatest in western Lake Melville rather than Goose Bay, reflecting the contribution of fine material carried eastward in the Churchill River plume and inputs from nearby tributaries. A comparison of 137Cs and 210Pbex inventories to expected atmospheric fallout (1.5 and 23.6 disintegrations per minute (dpm) cm−2, respectively) in sediment across the LMS suggests particles are largely sourced from the watershed. In eastern Lake Melville, elevated 210Pbex inventories and marine OC point to particle scavenging of dissolved 210Pb from inflowing marine water. A transient tracer mixing model was used to determine the depth in each core where >90% of sediment was deposited before and after hydroelectric development at Churchill Falls (1970) and applied to down-core profiles of OC and organic carbon isotopes (δ13Corg). We observed a significant increase of terrestrial OC to Lake Melville post 1970, which we interpret as change from climate or hydrology of the Churchill River.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Sedimentary records of contaminant inputs in Frobisher Bay, Nunavut

Contaminants, such as polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), heavy metals, and per and polyfluoroalkyl substances (PFASs), primarily reach the Arctic through long-range atmospheric and oceanic transport. However, local sources within the Arctic also contribute to the levels observed in the environment, including legacy sources and new sources that arise from activities associated with increasing commercial and industrial development. The City of Iqaluit in Frobisher Bay, Nunavut (Canada), has seen rapid population growth and associated development during recent decades yet remains a site of interest for ocean protection, where Inuit continue to harvest country food. In the present study, seven dated marine sediment cores collected in Koojesse Inlet near Iqaluit, and from sites in inner and outer Frobisher Bay, respectively, were analyzed for total mercury (THg), major and trace elements, PAHs, PCBs, and PFASs. The sedimentary record in Koojesse Inlet shows a period of Aroclor 1260-like PCB input concurrent with military site presence in the 1950–60s, followed by decades of input of pyrogenic PAHs, averaging about ten times background levels. Near-surface sediments in Koojesse Inlet also show evidence of transient local-source inputs of THg and PFASs, and recycling or continued slow release of PCBs from legacy land-based sources. Differences in PFAS congener composition clearly distinguish the local sources from long-range transport. Outside Koojesse Inlet but still in inner Frobisher Bay, 9.2 km from Iqaluit, sediments showed evidence of both local source (PCB) and long-range transport. In outer Frobisher Bay, an up-core increase in THg and PFASs in sediments may be explained by ongoing inputs of these contaminants from long-range transport. The context for ocean protection and country food harvesting in this region of the Arctic clearly involves both local sources and long-range transport, with past human activities leaving a long legacy insofar as levels of persistent organic pollutants are concerned

On the Intermittent Formation of an Ice Bridge (Nunniq) across Roes Welcome Sound, Northwestern Hudson Bay and Its Use to Local Inuit Hunters

Ice bridges are unique features that form when sea ice consolidates and remains immobilized within channels. They form in many locations throughout the Arctic and are typically noted for the polynyas that form on their lee side. However, ice bridges also provide a temporary platform that may be used by both humans and wildlife to cross otherwise impassable channels. For generations, Inuit in Coral Harbour, Nunavut, have used an ice bridge to cross Roes Welcome Sound and expand their hunting territory, though they report that the bridge only forms approximately every four years. Of interest both to Inuit and the scientific community is why the bridge forms so intermittently, by what mechanisms, and whether the frequency will change with ongoing warming and sea ice loss. Using satellite imagery, we determined that the bridge formed during 14 of the past 50 years (1971 – 2020). Generally, the bridge forms between January and March during a cold period that coincides with neap tide and after surface winds have rotated from the prevailing northerly (along-channel) winds to west-northwesterly (across-channel) winds. This rotation compresses the existing ice pack against Southampton Island, where it remains stationary because of the calm along-channel winds and low tidal range and coalesces under cold air temperatures. Breakup occurs between mid-June and early July after the onset of melt. Overall, the bridge forms when a specific set of conditions occur simultaneously; however, a warming climate, specifically a reduction in very cold days and a shorter ice season may affect the frequency of bridge formation, thereby limiting Inuit travel.Les ponts de glace sont des caractéristiques uniques qui se forment lorsque la glace de mer se consolide et reste immobilisée dans les chenaux. Ils se forment en maint endroit de l’Arctique et se démarquent généralement par les polynies qui se créent de leur côté sous le vent. Cependant, les ponts de glace font aussi office de plateforme temporaire dont peuvent se servir tant les humains que la faune pour traverser des chenaux qui seraient autrement impraticables. Depuis des générations, les Inuits de Coral Harbour, au Nunavut, empruntent un pont de glace pour traverser le détroit de Roes Welcome et agrandir leur territoire de chasse, même si selon eux, ce pont ne se forme qu’aux quatre ans environ. Les Inuits et les scientifiques se demandent pourquoi le pont se forme de manière si intermittente, grâce à quels mécanismes ils apparaissent, et si la fréquence de formation des ponts va changer en raison du réchauffement continu et de la perte de glace de mer. À l’aide d’imagerie satellitaire, nous avons déterminé qu’un pont s’est formé durant 14 des 50 dernières années (1971–2020). De manière générale, le pont apparaît entre janvier et mars pendant une période froide qui coïncide avec la marée de morte-eau, après la rotation des vents de surface, qui passent des vents dominants du nord (longeant le chenal) aux vents de l’ouest-nord-ouest (traversant le chenal). Cette rotation a pour effet de comprimer la banquise actuelle contre l’île Southampton, où elle demeure stationnaire en raison des vents calmes longeant le chenal et de la faible amplitude de la marée, et où elle coalesce sous les froides températures de l’air. La dislocation se produit entre la mi-juin et le début de juillet, après le début de la fonte des glaces. Dans l’ensemble, le pont se forme lorsque certaines conditions se manifestent simultanément. Toutefois, le réchauffement climatique, plus précisément en ce qui a trait à la réduction du nombre de journées très froides et au raccourcissement de la saison des glaces, pourrait avoir un effet sur la fréquence de la formation du pont, ce qui limiterait les déplacements des Inuits