@article{oai:nipr.repo.nii.ac.jp:00010176,
 author = {Wadhams, Peter and Toberg, Nick and Wadhams, Peter and Toberg, Nick},
 issue = {1},
 journal = {Polar science, Polar science},
 month = {Apr},
 note = {The advent of multibeam sonar permits us to obtain full three-dimensional maps of the underside of sea ice. In particular this enables us to distinguish the morphological characteristics of first-year (FY) and multi-year (MY) pressure ridges in a statistically valid way, whereas in the past only a small number of ridges could be mapped laboriously by drilling. In this study pressure ridge distributions from two parts of the Arctic Ocean are compared, in both the cases using mainly data collected by the submarine "Tireless" in March 2007 during two specific grid surveys, in the Beaufort Sea at about 75° N, 140° W (N of Prudhoe Bay), and north of Ellesmere Island at about 83° 20′ N, 64° W. In the Beaufort Sea the ice was mainly FY, and later melted or broke up as this area became ice-free during the subsequent summer. N of Ellesmere Island the ice was mainly MY. Ridge depth and spacing distributions were derived for each region using the boat's upward looking sonar, combined with distributions of shapes of the ridges encountered, using the Kongsberg EM3002 multibeam sonar. The differing shapes of FY and MY ridges are consistent with two later high-resolution multibeam studies of specific ridges by AUV. FY ridges are found to fit the normal triangular shape template in cross-section (with a range of slope angles averaging 27°) with a relatively constant along-crest depth, and often a structure of small ice blocks can be distinguished. MY ridges, however, are often split into a number of independent solid, smooth blocks of large size, giving an irregular ridge profile which may be seemingly without linearity.A:Our hypothesis for this difference is that during its long lifetime an MY ridge is subjected to several episodes of crack opening; new cracks in the Arctic pack often run in straight lines across the ridges and undeformed ice alike. Such a crack will open somewhat before refreezing, interpolating a stretch of thin ice into the structure, and breaking up the continuity and linearity of the ridge crest. Many such episodes over a number of years can cause the ridge to become simply a series of blocks. This has implications for ridge strength and for permeability to spilled oil. As the percentage of MY ice in the Arctic diminishes, Arctic ridging will be more and more dominated by FY ridges, and we discuss the implications of this change of character of the ice underside in the light of the statistics that we have generated for the two types of ridge., マルチビームソナー（多周波音響測深儀）の出現により水面下にある海氷の ３D形状を知ることができるようになった。著者らは2007年3月、Beaufort Sea (75°N, 140°W、Prudhoe湾北)及びEllesmere Island北(83°20'N, 64°W)での潜水艦 "Tireless"号を用いたgrid surveyによって得たデータを解析した。 Beaufort Seaの海氷は主として１年氷（FY）で、Ellesmere Island北の海氷は多年氷（MY）であった。 FY ridgeの断面は通常の三角形で傾斜角は平均で27°で、伸張方向の尾根の深さ(ridge crest)はほぼ一定であった。そして、しばしば小さな氷のブロックが認められた。一方MY ridgeは多数の独立する固い、大きくてなめらかなブロックに分裂していて、不規則な線型性のない形状をしている。 この違いは、crack opening（割れ目が開く）とそれがridgeを横切る走行方向、再凍結の際のcrestの連続性の破壊というepisode(事象)が多年にわたって起きた結果、見かけ上ridgeは単なるblockの連なりに変わって行くのだと解釈される。},
 pages = {71--77},
 title = {Changing characteristics of arctic pressure ridges},
 volume = {6},
 year = {2012}
}