Intellectual Merit:  Portions of most small ice caps in low-relief Arctic landscapes remained largely cold-based since their inception during the Holocene. As a result, cold-based portions preserve in situ tundra plants that were killed as ice expanded across vegetated landscapes. As summers warmed in recent decades, ice caps in the Eastern Canadian Arctic have receded rapidly, exposing entombed plants. The radiocarbon ages of these ice-entombed plants define times when ice caps expanded in the past.  In a previous study many of the plant ages coincided with episodes of explosive volcanism, which subsequent climate modeling suggested triggered cold episodes, including the Little Ice Age, the coldest centuries of the past 8000 years in the Northern Hemisphere.  Ice recession since the initial plant collections has  been 150 to 200 meters.  We revisited the two main ice complexes and re-collected plants at the current ice margin to test whether we could reproduce those results.  59 new radiocarbon dates on ice-edge plants confirmed our former results, and showed that more ages of early Common Era ice expansion are now being exposed as ice recedes farther to its point of origin.

Broader Impacts: Although maximum ice dimensions can be often reconstructed from moraines and moraine ages may be dated by various means, but the timing of onset of ice expansion has largely vexed the paleo-community.  Lake sediment records sometimes provide ancillary evidence, but direct dating has eluded the community.  Ice-advance-killed tundra plants preserved beneath cold-based ice provides the most secure evidence of past ice advance, providing the paleo-community with secure evidence on decadal to century time scales of past ice expansion, to compare with model simulations and other proxy climate evidence.  Ice-entombed plants, and the evidence they provide is also easily communicated to a broader audience.  These data not only provide timing of past ice expansion, they also place contemporary warming in a millennial perspective, as plant preservation requires continuous ice-cover, and their current exposure is, in most instances, the first time summer temperatures have been consistently warm enough to melt the ice since their date of plant death.  Our results indicate that summers are currently warmer than any century average  on millennia.  They also support our earlier interpretation of explosive volcanism as a trigger for widespread climate change, when sufficient positive feedbacks are triggered to perpetuate the summer cooling. This provides easily understood mechanisms for climate change and positive feedback to an interested public.

Last Modified: 06/07/2021
Modified by: Gifford H Miller