Sea ice scouring on the inner shelf of the southeastern Canadian Beaufort Sea

Arnaud Hequette; Marc Desrosiers; Peter W. Barnes

doi:10.1016/0025-3227(95)00095-g

Home/Archive/USGS

USGS · 70245171

Sea ice scouring on the inner shelf of the southeastern Canadian Beaufort Sea

Arnaud Hequette·Marc Desrosiers·Peter W. Barnes

View original source ↗Export metadata ↓

Abstract

About 2200 ice scours were observed and analyzed over a distance of approximately 500 km on the inner shelf of the southeastern Canadian Beaufort Sea. Ice scours were divided into two types based on their morphology: multiple scours consisting of a series of parallel scours and ridges, and single scours. Single scours are the dominant type representing more than 85% of the total observations. The mean scour depth and width are 0.3 m and 11 m respectively, but scour depths of more than 2 m and a scour width up to 345 m were documented. The magnitude of ice scouring processes increases with water depth. In water depths less than 10 m, less than 25% of the seafloor surface is reworked by ice scours. This percentage increases significantly seaward of the 10 m isobath, being more than 75% in water depths in excess of 12 m. A break in the seabed slope at about 10 to 12 m water depth marks a boundary between a nearshore zone moderately influenced by ice processes and an outer zone affected by intense ice scouring. This morphological boundary could be due to intense erosion by the keels of pressure ice ridges at the inner edge of a zone of grounded ice ridges. Most of the observed ice scours appear to be reworked, especially in water depths of less than 10 m, and represent small-scale sediment sinks. Inshore of the 10 m isobath, scour reworking is believed to be mainly due to frequent bottom disturbance by wave orbital currents and mean near-bottom flows during the open water season. Scour orientations show that the dominant motion of ice during scouring events is east or west, which is subparallel to the bathymetric contours and coastline. Scour terminal push mounds, however, suggest a dominant east to southeast movement that may contribute to onshore sediment transport during ice push events.

Explore related subjects

Marine Geology Article

Source-reported bounding extent: 68.08659955534648° to 71.98916841649827° latitude; -141.03647929645314° to -125.84605634257517° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

Arnaud Hequette, Marc Desrosiers, Peter W. Barnes. 1995. Sea ice scouring on the inner shelf of the southeastern Canadian Beaufort Sea. https://doi.org/10.1016/0025-3227(95)00095-g

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related USGS reports

USGS2025

Submarine canyon sediment transport and accumulation during sea level highstand: Interactive seasonal regimes in the head of Astoria Canyon, WA

The majority of submarine canyons on Earth today do not directly intersect littoral or fluvial sediment sources, yet these systems are rarely studied. The shelf-incised head of Astoria Canyon receives sediment from the nearby Columbia River and is subject to energetic forcing from shelf and slope processes, making it an ideal site to evaluate the modern activity of canyons in high-stand sea level conditions. This study uses in-situ data from Astoria Canyon to identify the active sediment transport processes and patterns of accumulation in temperate canyon systems that are decoupled from their sediment sources during sea level highstand. Hydrodynamic data from a benthic tripod deployment in the head of Astoria Canyon shows that sediment resuspension and transport during summer is driven by internal tides and plume-associated nonlinear internal waves. Observations of shoreward-directed currents and low shear stresses (<0.14 Pa) along with sediment trap data suggest that seasonal loading of the canyon head occurs during summer. Nearby long-term wave data show that winter storm significant wave height often exceeds 10 m, driving shear stress capable of resuspending all grain sizes present within the canyon head. Swell events are generally concurrent with downwelling flows, providing a mechanism for episodic downcanyon sediment flux. Century-scale accumulation rates evaluated from sediment cores show slow accumulation in the upper canyon head, but rates progressively increase with depth to at least 300 m. The depositional environment in Astoria Canyon continues to respond to fluvial and oceanic forcing over an annual cycle. This study indicates that canyon heads can continue to function as sites of sediment winnowing and bottom boundary layer export even with a detached, shelf-depth canyon head.

Washington↗

USGS2025

Tracking diagenetic alteration of magnetic susceptibility in thrust ridge and slope basin sediments of the Cascadia margin (ODP Sites 1249 and 1252; IODP Site U1325)

We investigated sediment core records from the Cascadia Margin (Ocean Drilling Program Sites 1249 and 1252 at Hydrate Ridge; Integrated Ocean Drilling Program Site U1325 offshore Vancouver Island) using a Zr/Rb heavy mineral proxy from X-ray fluorescence (XRF) core scanning to identify intervals of primary detrital magnetic susceptibility (κ) and predict intervals where diagenesis caused magnetite dissolution by hydrogen sulfide. We also measured total sulfur (TS) content, grain size distributions, total organic carbon (TOC) content, and the magnetic mineral assemblage to further constrain the role of diagenesis on κ. Understanding how κ can be used to better characterize the varied effects of detrital and diagenetic signals in marine settings is important for understanding biogeochemical cycling and records of paleoenvironmental change. The upper 100 m of slope basin Site 1252 contains multiple intervals (> 90 m total) of decreased κ correlated with elevated TS content, consistent with dissolution of magnetite and precipitation of pyrite, iron monosulfides, and/or elemental sulfur. Similarly at the other slope basin site, Site U1325, κ is lower and TS is elevated in the interval between 24 and 51 mbsf, due to sulfide formation. At both slope basin sites, these low κ intervals correspond with high TOC, suggesting the possibility that organoclastic sulfate reduction (OSR) is likely a major driver of diagenetic alteration of κ at these sites. High TS:TOC ratios at Site U1325 suggests anaerobic oxidation of methane (AOM) during sulfate-methane transition zone (SMTZ) migration may have contributed to alteration of κ. In contrast, within the upper 90 m of Site 1249, a methane seep site at the summit of Hydrate Ridge, κ is almost entirely altered by diagenetic processes, with much of the low κ explained by a high degree of iron sulfide formation, while some intervals are affected by precipitation of magnetic iron sulfides that maintain or even increase κ. The presence of abundant methane seepage and gas hydrate as well as chemosynthetic seafloor fauna at this site, suggests that sulfide is released to the water column and AOM, rather than OSR, drives diagenetic alteration of κ at this site. Overall, the slope basin sites show episodic variation of κ that is influenced by TOC content, likely driven by changes in marine primary productivity and sedimentation rate, while the seep site shows consistently altered κ with lower TS content and no correlation with TOC. Methane seep environments likely experience loss of hydrogen sulfide to the water column and oxidation of hydrogen sulfide by seafloor seep fauna, which limits the amount of solid phase sulfur (pyrite, iron monosulfides, elemental sulfur) that can be precipitated within the sediments. In contrast, the migration of a buried SMTZ at slope basin sites results in enhanced sulfur precipitation within the sediments. This integrated magnetic and geochemical approach reveals the diagenetic production pathway and residence time of sulfide with the sediment column ultimately controls the style and degree of diagenetic loss of κ in marine sediments. This approach works best in environments with unaltered reference intervals/sites, consistent magnetic mineralogy, and clay-to-silt grain sizes.

Cascadia margin, Pacific Ocean↗

USGS2024

Methane seeps on the U.S. Atlantic margin: An updated inventory and interpretative framework

Since the discovery of >570 methane flares on the northern U.S. Atlantic margin between Cape Hatteras and Georges Bank in the last decade, the acquisition of thousands of kilometers of additional water column imaging data has provided greater coverage at water depths between the outer continental shelf and the lower continental slope. The additional high-resolution data reveal >1400 gas flares, but the removal of probable duplicates from the combined database of new flares and those recognized in 2014 yields ∼1139 unique sites. Most of these sites occur in clusters of 5 or more seeps, leaving about 275 unique locations (including 47 clusters) for seepage along the margin. As a function of depth, seep distribution is heavily skewed toward the upper continental slope at water depths shallower than 400 m on the southern New England margin and ∼ 550 m in the Mid-Atlantic Bight, with additional seeps clustered at ∼1100 m and just deeper than ∼1400 m in both sectors. Despite little ongoing tectonic deformation or active faulting on this passive margin, a variety of processes driven from below the seafloor (e.g., migration of fluids along faults or through permeable strata, seepage above diapirs or other pre-existing structures) and from above (e.g., erosion, sapping, unroofing) contribute to the development of seeps in different settings along the margin. In addition, the prevalence of seeps on promontories overlooking shelf-breaking canyons may be directly related to the three-dimensional nature of the hydrate stability zone in these locations. As a function of depth, the parts of the slope at the contemporary landward limit of gas hydrate stability are devoid of seeps, and the upper slope zones with the most concentrated seepage were not within the gas hydrate stability zone even during the Last Glacial Maximum. Thus, if the large number of upper slope seeps is at least partially sourced in gas hydrate degradation, the gas emitted at these seeps must have migrated there from greater depths on the continental slope.

Marine Geology↗