Abstract
During a research expedition in Hudson Bay in June 2018, vast areas of thick (>10 m), deformed sediment-laden sea ice were encountered unexpectedly in southern Hudson Bay and presented difficult navigation conditions for the Canadian Coast Guard Ship Amundsen. An aerial survey of one of these floes revealed a maximum ridge height of 4.6 m and an average freeboard of 2.2 m, which corresponds to an estimated total thickness of 18 m, far greater than expected within a seasonal ice cover. Samples of the upper portion of the ice floe revealed that it was isothermal and fresh in areas with sediment present on the surface. Fine-grained sediment and larger rocks were visible on the ice surface, while a pronounced sediment band was observed in an ice core. Initial speculation was that this ice had formed in the highly dynamic Nelson River estuary from freshwater, but δ18O isotopic analysis revealed a marine origin. In southern Hudson Bay, significant tidal forcing promotes both sediment resuspension and new ice formation within a flaw lead, which we speculate promotes the formation of this sediment-laden sea ice. Historic satellite imagery shows that sediment-laden sea ice is typical of southern Hudson Bay, varying in areal extent from 47 to 118 km2 during June. Based on an average sediment particle concentration of 0.1 mg mL–1 in sea ice, an areal extent of 51,924 km2 in June 2018, and an estimated regional end-of-winter ice thickness of 1.5 m, we conservatively estimated that a total sediment load of 7.8 × 106 t, or 150 t km–2, was entrained within sea ice in southern Hudson Bay during winter 2018. As sediments can alter carbon concentrations and light transmission within sea ice, these first observations of this ice type in Hudson Bay imply biogeochemical impacts for the marine system.
Highlights
Hudson Bay is a large, shallow inland sea that is seasonally covered by a dynamic sea-ice cover
Extent and physical properties of sedimentladen sea ice Relative to the ice cover encountered by the Amundsen in other regions of Hudson Bay, the sediment-laden sea ice along the southern Hudson Bay coast was much thicker and nearly impassable even with the icebreaker
The ice core collected from an area with 1–2 cm of sediment at the surface was notably warmer and fresher than the ice cores collected where no sediment was present at the surface, which leads us to infer that increased absorption of solar radiation by dark sediments on the sea ice surface had enhanced surface melt and brine drainage
Summary
Hudson Bay is a large, shallow inland sea that is seasonally covered by a dynamic sea-ice cover. During the Canadian Coast Guard Ship (CCGS) Amundsen cruise in June 2018 as part of the Hudson Bay System (BaySys) study, vast areas of thick, heavily deformed, sediment-laden sea ice were encountered in southern Hudson Bay. the Amundsen is a capable Arctic class 3 icebreaker, we found ourselves having to back and ram, even in early summer conditions, due to the thickness and strength of this ice type. The Amundsen is a capable Arctic class 3 icebreaker, we found ourselves having to back and ram, even in early summer conditions, due to the thickness and strength of this ice type While these are the first in situ observations of sediment-laden sea ice in Hudson Bay, similar sediment-
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