| The cross-dated subfossil and living trees at Nellie Juan Glacier were used to develop a tree-ring-width chronology spanning 1150 to the present. Correlation with monthly climate data at Seward, 67km to the southwest, showed that trees at Nellie Juan produce wide rings in warm and sunny summers and narrow rings in cool and cloudy summers. Thus, the dips in the green line (upper panel) are when summer temperatures were cooler than average and the rises are when summers were warmer. |
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| The lower panel shows the number of advancing glaciers (blue bars) and numbers of moraines formed (green bars) around Prince William Sound per 25 year interval. Times of ice advance are based on tree-ring dates of glacially buried forests whereas the moraine dates are from germination of trees on moraines and so record glacial retreat (i.e. the same type of data as used in this study at Nellie Juan). This record of glacial advance and retreat can be used to deliniate three distinct intervals of ice expansion around Prince William Sound, and we term these the early, middle and late phases of the Little Ice Age (LIA). Each phase of ice advance corresponds with cooler than average temperatures in the tree-ring record and ice retreat occurs when temperatures rise again. There are no moraines dating to the end of the early LIA because the middle and late LIA advances were larger and so destroyed the older moraines. |
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