Geology topics

H. Kassens

Publications and source records attributed to H. Kassens.

3 recordsLinked to original sources

USGS2000

Coastal erosion vs riverline sediment discharge in the Arctic shelfx seas

This article presents a comparison of sediment input by rivers and by coastal erosion into both the Laptev Sea and the Canadian Beaufort Sea (CBS). New data on coastal erosion in the Laptev Sea, which are based on field measurements and remote sensing information and existing data on coastal erosion in the CBS as well as riverine sediment discharge into both the Laptev Sea and the CBS are included. Strong regional differences in the percentages of coastal ero- sion and riverine sediment supply are observed. The CBS is dominated by the riverine sediment discharge (64.45x106 t a-1) mainly of the Mackenzie River. which is the largest single source of sediments in the Arctic. Riverine sediment discharge into the Laptev Sea amounts to 24.10x106 t a-1, more than 70% of which are related to the Lena River. In comparison with the CBS. the Laptev Sea coast on average delivers approximately twice as much sediment mass per kilometer, a result of higher erosion rates due to higher cliffs and seasonal ice melting. In the Laptev Sea sediment input by coastal erosion (58.4x106 t a-1) is therefore more important than in the CBS and the ratio between riverine and coastal sediment input amounts to 0.4. Coastal erosion supplying 5.6x106 t a-1 is less significant for the sediment budget of the CBS where riverine sediment discharge exceeds coastal sediment input by a factor of ca. 10.

International Journal of Earth Sciences↗

USGS1997

Sea-ice processes in the Laptev Sea and their importance for sediment export

Based on remote-sensing data and an expedition during August-September 1993, the importance of the Laptev Sea as a source area for sediment-laden sea ice was studied. Ice-core analysis demonstrated the importance of dynamic ice-growth mechanisms as compared to the multi-year cover of the Arctic Basin. Ice-rafted sediment (IRS) was mostly associated with congealed frazil ice, although evidence for other entrainment mechanisms (anchor ice, entrainment into freshwater ice) was also found. Concentrations of suspended particulate matter (SPM) in patches of dirty ice averaged at 156 g m-3 (standard deviation ?? = 140 g m-3), with a background concentration of 5 g m-3. The potential for sediment entrainment over the broad, shallow Laptev Sea shelf during fall freeze-up was studied through analysis of remote-sensing data and weather-station records for the period 1979-1994. Freeze-up commences on 26 September (?? = 7 d) and is completed after 19 days (?? = 6 d). Meteorological conditions as well as ice extent prior to and during freeze-up vary considerably, the open-water area ranging between 107 x 103 and 447 x 103 km2. Ice motion and transport of IRS were derived from satellite imagery and drifting buoys for the period during and after the expedition (mean ice velocities of 0.04 and 0.05 m s-1, respectively). With a best-estimate sediment load of 16 t km-2 (ranging between 9 and 46 t km-2), sediment export from the eastern Laptev Sea amounts to 4 x 10-6 t yr-1, with extremes of 2 x 10-6 and 11 x 106 t yr-1. Implications for the sediment budget of the Laptev shelf, in particular with respect to riverine input of SPM, which may be of the same order of magnitude, are discussed.

Continental Shelf Research↗

USGS1994

Sediments in Arctic sea ice: Implications for entrainment, transport and release

Despite the Arctic sea ice cover's recognized sensitivity to environmental change, the role of sediment inclusions in lowering ice albedo and affecting ice ablation is poorly understood. Sea ice sediment inclusions were studied in the central Arctic Ocean during the Arctic 91 expedition and in the Laptev Sea (East Siberian Arctic Region Expedition 1992). Results from these investigations are here combined with previous studies performed in major areas of ice ablation and the southern central Arctic Ocean. This study documents the regional distribution and composition of particle-laden ice, investigates and evaluates processes by which sediment is incorporated into the ice cover, and identifies transport paths and probable depositional centers for the released sediment. In April 1992, sea ice in the Laptev Sea was relatively clean. The sediment occasionally observed was distributed diffusely over the entire ice column, forming turbid ice. Observations indicate that frazil and anchor ice formation occurring in a large coastal polynya provide a main mechanism for sediment entrainment. In the central Arctic Ocean sediments are concentrated in layers within or at the surface of ice floes due to melting and refreezing processes. The surface sediment accumulation in central Arctic multi-year sea ice exceeds by far the amounts observed in first-year ice from the Laptev Sea in April 1992. Sea ice sediments are generally fine grained, although coarse sediments and stones up to 5 cm in diameter are observed. Component analysis indicates that quartz and clay minerals are the main terrigenous sediment particles. The biogenous components, namely shells of pelecypods and benthic foraminiferal tests, point to a shallow, benthic, marine source area. Apparently, sediment inclusions were resuspended from shelf areas before and incorporated into the sea ice by suspension freezing. Clay mineralogy of ice-rafted sediments provides information on potential source areas. A smectite maximum in sea ice sediment samples repeatedly occurred between 81°N and 83°N along the Arctic 91 transect, indicating a rather stable and narrow smectite rich ice drift stream of the Transpolar Drift. The smectite concentrations are comparable to those found in both Laptev Sea shelf sediments and anchor ice sediments, pointing to this sea as a potential source area for sea ice sediments. In the central Arctic Ocean sea ice clay mineralogy is significantly different from deep-sea clay mineral distribution patterns. The contribution of sea ice sediments to the deep sea is apparently diluted by sedimentary material provided by other transport mechanisms.

Marine Geology↗