BERING GLACIER RETREAT PHASE: DISCOVERIES OF OVERRUN FIORDS AND FORESTS

The post-surge retreat of Bering Glacier, Alaska has created a dynamic landscape of reticulated and fluted surfaces covered with subtidal invertebrates and previously overrun forests. Subfossil forests are being exposed that contain large upright trees over 1 m in diameter. These exhibit trunks splintered by ice that overrode up to 2 m above their bases. Numerous trees remain rooted in a surface covered with 0.5 m thick peat that also exhibits perfectly preserved spruce cones and needles. Mapping of the standing trees indicates spacing and sizes similar to modern spruce-hemlock forests near the current ice margin. Radiocarbon dating indicates the forest existed as early as 200 BC and was overrun by 800 AD. The newly deglaciated surfaces are covered by small invertebrate shells melting out of the ice. Over 400 specimens have been recovered that include 57 genera: 29 gastropods, 16 pelecypods, 4 arthropods, 3 bryozoans, 1 echinoderm, 1 polychaete worm, 1 sponge and 1 chiton plate. The assemblage is consistent with those currently found in shallow marine waters on an unconsolidated substrate, and indicate a ice-free coastline below/behind the modern piedmont terminus of Bering Glacier. Radiocarbon dating of these shells suggest that Bering Glacier occupied a retracted position from ca. 8-10 K with a proglacial shoreline/fiord environment conducive to the development of this subtidal community.