Pleistocene climate in Alaska from stable isotopes in an ice wedge

The CRREL permafrost tunnel offers a unique opportunity to sample ice wedges in a climate-controlled environment, penetrating frozen silts which host massive ground ice that may record Dansgaard-Oeschger (D-O) and Heinrich Events. Ice wedges in the tunnel have been dated to approximately 36-22 ka (Hamilton et al., 1988), allowing the paleoclimate of the region to be reconstructed during MIS 3, when D-O and Heinrich events were documented in various other records. These climate cycles are rapid climate oscillations that have been recognized in records from the Arctic and subarctic, and suggest that climate can rapidly shift by 10°C over millennial scale times. I hypothesize that climate in the interior of Alaska varied with Heinrich events during MIS 3, and that these events were recorded as stable isotope variations in local permafrost ground ice. To test this hypothesis, I sampled aQ LFH ZHGJH LQ WKH SHUPDIURVW WXQQHO IRU 􏰁182􏰂 􏰁' DQG 14C to obtain a detailed climate record from central Alaska. 􏰁18O values from within the wedge display a gradual decrease of 5.95‰ from the center toward the left edge, interpreted to reflect decreasing temperature, and is the same magnitude of decrease seen during the transition from the warm D-O interstadial 5 to the cold of Heinrich Event 3 in the NGRIP record in Greenland. Radiocarbon dates from within the wedge range from 28 – 37 cal kyr BP, and are interpreted here not to be the same age as the ice, but rather represent warm periods when sediment aggraded prior to ice wedge growth. These results suggest that D-O and Heinrich events impacted Late Pleistocene climate and ground ice in central Alaska.