|
Seabed gouging by ice is a process that occurs when floating ice features (typically icebergs and sea ice ridges) drift into shallower areas and their keel comes into contact with the seabed.〔King 2011〕〔Palmer & Been 2011〕〔Barrette 2011〕 As they keep drifting, they produce long, narrow furrows most often called ''gouges'', or ''scours''.〔Wadhams 2000, p. 72〕〔Weeks 2010, Ch. 13〕〔Other less frequently used synonyms include ''ploughs'' and ''scores''〕 This phenomenon is common in offshore environments where ice is known to exist. Although it also occurs in rivers and lakes,〔Noble and Comfort 1982〕〔Grass 1984〕 it appears to be better documented from oceans and sea expanses.〔Palmer & Been 2011〕〔Wadhams 2000, p. 72〕〔Weeks 2010, Ch. 13〕 Seabed scours produced via this mechanism should not be confused with strudel scours. These result from spring run-off water flowing onto the surface of a given sea ice expanse, which eventually drains away through cracks, seal breathing holes, etc. The resulting turbulence is strong enough to carve a depression into the seabed. Seabed scouring by ice should also be distinguished from another scouring mechanism: the erosion of the sediments around a structure due to water currents, a well known issue in ocean engineering and river hydraulics〔See Annandale 2006, for instance〕 – see bridge scour. ==Historical perspective and relevance== It appears Charles Darwin speculated in 1855 about the possibility that icebergs could gouge the seabed as they drifted across isobaths.〔Weeks 2010, p. 391〕 Some discussion on the involvement of sea ice was brought up in the 1920s, but overall this phenomenon remained poorly studied by the scientific community up to the 1970s.〔Weeks 2010, p. 391: Until then, “...whatever was occurring between the () and the seafloor was not causing sufficient trouble to have arrived on anyone’s list of problems that needed to be investigated."〕 At that time, ship-borne sidescan sonar surveys in the Canadian Beaufort Sea began to gather actual evidence of this mechanism. Seabed gouges were subsequently observed further north, in the Canadian Arctic Archipelago, and in the Russian Arctic as well.〔 Throughout that decade, seabed gouging by ice was investigated extensively. What sparked the sudden interest for this phenomenon was the discovery of oil near Alaska’s northern coastlines, and two related factors:〔 1) the prospect that oilfields could abound in these waters, and 2) a consideration that submarine pipelines would be involved in future production developments, as this appeared to be the most practical approach to bring this resource to the shore. Since then, means of protecting these structures against ice action became an important concern.〔Pilkington and Marcellus 1981〕〔Woodworth-Lynas et al. 1985〕〔Woodworth-Lynas et al. 1996〕〔Clark et al. 1987〕 An oil spill in this environment would be problematic in terms of detection and clean-up.〔McHale et al. 2000〕 Scientists in fields of research other than offshore engineering have also addressed seabed gouging. For instance, biologists have linked regions of the seabed reshaped by seabed gouging by ice to the formation of black pools, seabed depressions filled with anoxic high-salinity water which are death traps for small marine organisms.〔 Kvitek et al. 1998〕 However, much of it appears to have been documented from an offshore engineering perspective, for the purpose of oil exploration.〔Weeks 2010, p. 403〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Seabed gouging by ice」の詳細全文を読む スポンサード リンク
|