Seasonal and habitat-based variations in vertical export of biogenic sea-ice proxies in Hudson Bay

Despite their wide use in past sea-ice reconstructions, the seasonal, habitat and species-based sources of sedimentary sea-ice proxies are poorly understood. Here, we conduct direct observations of the community composition of diatoms, dinoflagellate cysts and highly branched isoprenoid lipids within the sea ice, water column, sediment traps and sediment surface in the Belcher Islands Archipelago, Hudson Bay throughout spring 2019. We find that Arctic diatom and dinoflagellate cysts species commonly used as sea-ice proxies appear to be only indirectly linked to sea-ice conditions, and that the sediment assemblages of these groups overrepresent summertime pelagic blooms. Species contributing to the diverse sea-ice diatom communities are rare in the sediment. Dinoflagellate cysts form a typical Arctic assemblage in the sediment, although they are virtually absent in the sea ice and water column in spring. We also find that certain highly branched isoprenoid lipids that were previously considered indicators of open water, can be produced in sea-ice. We conclude that contextual knowledge and a multiproxy approach are necessary in reconstruction, encouraging further studies on the sources and controls of sea-ice proxy production in different geographic areas

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

Sediment trap geochemistry from the Belcher islands archipelago, Hudson Bay, Canada

Data collected from sediment trap samples from the Belcher Islands Archipelago, south-eastern Hudson Bay, Canada between April and July 2019 using an automated Gurney Instruments Baker-style, cylindrical sediment trap (aperture 0.032 m2). The sediment trap was deployed at 40-m depth, 30-m above the seafloor and the rotation for the trap was set to 8-day intervals

Sea ice diatoms concentration from the Belcher islands archipelago, Hudson Bay, Canada

Data collected from modern sea ice samples from the Belcher Islands Archipelago, south-eastern Hudson Bay, Canada between April and May 2019 using a Kovacs Mark II core barrel with an internal diameter of 9 cm. Data includes diatom concentrations (valves/ml) from the bottom 5 cm of the sea-ice from each sampling day. Diatom quantification was done using a light microscope (Zeiss Axio Imager.A2 upright research microscope, University of Helsinki) with phase contrast optics at a x1000 magnification

Seasonal and habitat-based variations in vertical export of biogenic sea-ice proxies in Hudson Bay

Despite their wide use in past sea-ice reconstructions, the seasonal, habitat and species-based sources of sedimentary sea-ice proxies are poorly understood. Here, we conduct direct observations of the community composition of diatoms, dinoflagellate cysts and highly branched isoprenoid lipids within the sea ice, water column, sediment traps and sediment surface in the Belcher Islands Archipelago, Hudson Bay throughout spring 2019. We find that Arctic diatom and dinoflagellate cysts species commonly used as sea-ice proxies appear to be only indirectly linked to sea-ice conditions, and that the sediment assemblages of these groups overrepresent summertime pelagic blooms. Species contributing to the diverse sea-ice diatom communities are rare in the sediment. Dinoflagellate cysts form a typical Arctic assemblage in the sediment, although they are virtually absent in the sea ice and water column in spring. We also find that certain highly branched isoprenoid lipids that were previously considered indicators of open water, can be produced in sea-ice. We conclude that contextual knowledge and a multiproxy approach are necessary in reconstruction, encouraging further studies on the sources and controls of sea-ice proxy production in different geographic areas.Sedimentary assemblages of biogenic sea-ice proxies incorporate limited representation of the diverse sea-ice connected communities, according to direct springtime observations in the Belcher Islands Archipelago, Hudson Bay, Canada.Despite their wide use in past sea-ice reconstructions, the seasonal, habitat and species-based sources of sedimentary sea-ice proxies are poorly understood. Here, we conduct direct observations of the community composition of diatoms, dinoflagellate cysts and highly branched isoprenoid lipids within the sea ice, water column, sediment traps and sediment surface in the Belcher Islands Archipelago, Hudson Bay throughout spring 2019. We find that Arctic diatom and dinoflagellate cysts species commonly used as sea-ice proxies appear to be only indirectly linked to sea-ice conditions, and that the sediment assemblages of these groups overrepresent summertime pelagic blooms. Species contributing to the diverse sea-ice diatom communities are rare in the sediment. Dinoflagellate cysts form a typical Arctic assemblage in the sediment, although they are virtually absent in the sea ice and water column in spring. We also find that certain highly branched isoprenoid lipids that were previously considered indicators of open water, can be produced in sea-ice. We conclude that contextual knowledge and a multiproxy approach are necessary in reconstruction, encouraging further studies on the sources and controls of sea-ice proxy production in different geographic areas.Peer reviewe

Surface sediment highly branched isoprenoids (HBI) fluxes from the Belcher islands archipelago, Hudson Bay, Canada

Data collected from the top 0,5 cm surface sediment from the Belcher Islands Archipelago, south-eastern Hudson Bay, Canada on April 15th, 2019, using a Kajak-Brinkhurst gravity corer

Sea ice pigment concentrations from the Belcher islands archipelago, Hudson Bay, Canada

Data collected from modern sea ice samples from the Belcher Islands Archipelago, south-eastern Hudson Bay, Canada between April and May 2019 using a Kovacs Mark II core barrel with an internal diameter of 9 cm. Data includes pigment concentrations (nM/l) from the bottom 5 cm of the sea-ice from each sampling day

Under ice temperature and salinity from the Belcher islands archipelago, Hudson Bay, Canada

Data collected from modern sea ice samples from the Belcher Islands Archipelago, south-eastern Hudson Bay, Canada between April and May 2019 using a Kovacs Mark II core barrel with an internal diameter of 9 cm. Data includes under ice temperature (C) and salinity (psu) measurements from the bottom 5 cm of the sea-ice from each sampling day

Sediment trap diatoms as relative abundance from the Belcher islands archipelago, Hudson Bay, Canada

Data collected from sediment trap samples from the Belcher Islands Archipelago, south-eastern Hudson Bay, Canada between April and July 2019 using an automated Gurney Instruments Baker-style, cylindrical sediment trap (aperture 0.032 m2). The sediment trap was deployed at 40-m depth, 30-m above the seafloor and the rotation for the trap was set to 8-day intervals. Diatom and dinoflagellate cyst quantifications were done using a light microscope (Zeiss Axio Imager.A2 upright research microscope, University of Helsinki) with bright-field optics (dinoflagellate cysts) and phase contrast optics (diatoms) at a x600 (dinoflagellate cysts) and x1000 (diatoms) magnification