Holocene alluvial chronology of One Tree Creek, Southern Alberta, Canada.

An alluvial chronology for the One Tree Creek basin, a southern tributary of the Red Deer River in southern Alberta, is reconstructed using terrace and palaeochannel remnants and associated radiocarbon dated bones. Prior to the development of One Tree Creek as a northeastward flowing tributary, the prairie surface was scoured by proglacial floodwaters decanting from Glacial Lake Bassano/Patricia in the west. Radiocarbon dates on bones from the bedload gravels in palaeochannels provide a morphochronology of Holocene stream incision. Tentative average incision rates for the middle and upper reaches are calculated at 0.34–0.38 cm a-1 since 2.8 ka BP and 0.80 – 1.60 cm and 0.81 – 0.96 cm a-1 for the two periods of 1870 to 1230 BP and 1230 BP to modern respectively. Terraces and palaeochannels dating to the period of highest incision (1870 BP to modern) include numerous reworked bones dating to earlier periods, indicating that fluvial downcutting triggered slope instability and terrace reworking. Although the lower bedrock reaches of the creek may have incised down to the present level of the Red Deer River during early postglacial time, the middle and upper reaches were rapidly incised into Quaternary sediments during the late Holocene when climatic conditions were more humid

A millennial-scale record of Arctic Ocean sea ice variability and the demise of the Ellesmere Island ice shelves

Sea-ice ice shelves, at the apex of North America (>80N), constitute the oldest sea ice in the Northern Hemisphere. We document the establishment and subsequent stability of the Ward Hunt Ice Shelf, and multiyear landfast sea ice in adjacent fiords, using 69 radiocarbon dates obtained on Holocene driftwood deposited prior to coastal blockage. These dates (47 of which are new) record a hiatus in driftwood deposition beginning 5500 cal yr BP, marking the inception of widespread multiyear landfast sea ice across northern Ellesmere Island. This chronology, together with historical observations of ice shelf breakup (1950 to present), provides the only millennial-scale record of Arctic Ocean sea ice variability to which the past three decades of satellite surveillance can be compared. Removal of the remaining ice shelves would be unprecedented in the last 5500 years. This highlights the impact of ongoing 20th and 21st century climate warming that continues to break up the remaining ice shelves and soon may cause historically ice-filled fiords nearby to open seasonally