ADVANCE OF NELLIE JUAN GLACIER

Tree-ring cross-dating was used to date the subfossil trees. This method entails matching the sequence of wide and narrow tree-rings between living and subfossil trees, and provides exact calander dates for germination and death if the innermost rings and bark of the subfossil tree are preserved.

Each green bar represents the lifespan of a cross-dated subfossil tree from the main sample gully and adjacent fan delta. The last years of growth are strongly clustered between 1592 and 1596, suggesting that this was the interval when Nellie Juan Glacier advanced over this area. The apparent earlier kill dates in the lower panel are all from rotted or abraded trees where the outermost rings have been lost. Germination dates show that forest was established in this area by the 1060s.

A further 14 subfossil trees from around the lagoon shore were successfully cross-dated. The numbers along the lagoon shore are the last years of growth for the logs found in each area, and these show a distinct spatial pattern; progressively later kill dates are farther down-fjord from the present ice margin and farther back from the lagoon shore. This is consistent with Nellie Juan Glacier advancing in the 16th and 17th centuries and expanding laterally as the terminus reached closer to Derickson Bay. Ice-scarred trees growing at the terminal moraine indicate that the ice margin reached its maximum stand (shown by the red dashed line) by 1842 and stayed at this extended position until at least 1880. Trees began to germinate on the terminal moraine by 1893, indicating that ice recession was underway by this time.

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