Present and Past Glaciation Threshold in the Cascade Range, Washington, U.S.A.: Topographic and Climatic Controls, and Paleoclimatic Implications
Present and Past Glaciation Threshold in the Cascade Range, Washington, U.S.A.: Topographic and Climatic Controls, and Paleoclimatic Implications
复制标题
美国华盛顿州喀斯喀特山脉当前和过去的冰川阈值：地形和气候控制以及古气候影响
DOI：
10.3189/s0022143000021559
复制
发表时间：
1977
影响因子：
3.4
通讯作者：
S. C. Porter
中科院分区：
文献类型：
--
作者：
S. C. Porter
描述华盛顿冰川作用界限的等冰川隆起大致平行于喀斯喀特山脉的山脊，并围绕奥林匹克山脉的西、南翼弯曲。在这两个高地的冰川阈值上升内陆（东）的平均梯度为10-12米/公里。然而，由于冰川作用阈值表面有五个向东的槽，与山脉波峰沿着的地形凹陷相吻合，显然是由于潮湿的海洋空气向东渗透，因此小瀑布的坡度变化更大（7-25米/公里）。平均累积季节降水量与北喀斯喀特山脉冰川阈值的高度密切相关（r2 = 0.86），但冰川阈值与7月冻结等温线的高度的相关性要弱得多（r2 = 0.40）。多元回归分析表明，90.4%的方差是由累积季节降水量和估计的年平均温度在冰川阈值的高度影响独立的气候变量。北喀斯喀特山脉南部最后一次（弗雷泽）冰川作用最大冰推进期间的冰川作用阈值（c。18 000-22 000年B. P.）比现在低900 ± 100 m。冰川作用阈值降低了这么多，很可能是由于累积季节降水量与目前值相比变化不超过30%，消融季节平均温度降低了5-5 ± 1.5摄氏度。
Abstract Isoglacihypses depicting the configuration of the glaciation threshold (= “glaciation limit”) in Washington broadly parallel the crest of the Cascade Range and curve around the west and south flanks of the Olympic Mountains. In both uplands the glaciation threshold rises inland (eastward) with a mean gradient of 10-12 m/km. However, the gradient in the Cascades is more variable (7-25 m/km) due to five east-trending troughs in the glaciation threshold surface that coincide with topographic depressions along the range crest and that apparently result from greater eastward penetration of moist maritime air. Mean accumulation-season precipitation correlates strongly (r2 = 0.86) with altitude of the glaciation threshold in the North Cascade Range, but the correlation of glaciation threshold with altitude of the July freezing isotherm, determined from the calculated July lapse rate within the mountains, is much weaker (r2 = 0.40). Multiple regression analysis relating independent climatic variables that affect the height of the glaciation threshold indicates that 90.4% of variance is explained by accumulation-season precipitation and estimated mean annual temperature at the glaciation threshold. The glaciation threshold during the greatest ice advance of the last (Fraser) glaciation in the southern North Cascade Range (c. 18 000-22 000 years B.P.) was 900 ± 100 m below that of the present. Depression of the glaciation threshold by this amount most likely resulted from a change in accumulation-season precipitation of no more than 30% from present values and a decrease in mean ablation-season temperature of 5-5 ± 1.5 deg.