Paleodrainage on the Chukchi shelf reveals sea level history and meltwater discharge

Abstract

CHIRP subbottom data collected across the Chukchi shelf, offshore NW Alaska, imaged numerous paleochannels and valleys that appear to have been downcut and incised during sea level falls associated with glacial intervals. In contrast, the two most recent incisions appear to have been formed during the period of sea level rise following the Last Glacial Maximum (LGM). The architecture and infill associated with these two incisions suggests that they were formed by an increase in discharge. These events appear to be unrelated to sea level fluctuations, but rather triggered by climatic variations during the most recent deglaciation (i.e. meltwater discharge). Radiocarbon dates from sediment cores within the southern incised valley suggest that the two episodes of meltwater discharge may correlate with Meltwater Pulse 1-A (~ 14,000 cal. yr BP) and evidence of iceberg scouring on outer Chukchi shelf (~ 12,000 to 13,000 cal. yr BP), respectively. Regional transgression across the interfluves on the middle Chukchi shelf appears to postdate the second meltwater discharge and may correlate with Meltwater Pulse 1-B (11,500 cal. yr BP). This evidence suggests that in glacially dominated landscapes, episodes of large discharge to the shelf might be out of phase with the sea level cycle. In addition, the presence of glacial meltwater drainage on the shelf implies a greater volume of continental glaciation during the LGM than previously recognized.