Intellectual merit: Instrumental records show that the Earth has warmed ca. 0.7 degreesC over the past century, with the most dramatic increase in the decades since the 1960s. The Arctic has experienced a similar pattern, but the magnitude is greater, with average annual temperature increases of 2 to 5 degreesC across portions of the Arctic since the1960s. The short time span of direct observations makes it difficult to evaluate the roles of natural climate variability and greenhouse gas forcing in explaining these observations, but the pattern of change is consistent with Global Climate Model (GCM) simulations of the consequences of increased greenhouse gases. The Principal Investigators will provide a Holocene context for 20th century Arctic warming. How unusual is the rate and magnitude of this warming? When was the Arctic last as warm as it is now? Is this degree of warmth within the range of natural variability or is it unprecedented? The Arctic instrumental record is limited in time and space, so natural archives of proxy climate data must be exploited to address these questions. Extensive, thin, cold-based ice caps mantling the north-central plateau of Baffin Island, Canada, have receded by 97% in area since their Little Ice Age (LIA) maxima. One ice cap studied in the 1960s and early 1980s has now completely melted; many others are predicted to vanish in the next five to ten years, and all are expected to be gone before 2050. This research will identify three ways that these ice caps can contribute to the Arctic warming debate: 1) Aerial rates of ice-cap retreat over the past 50 years will be defined from air photo and satellite imagery, from which their final disappearance can be predicted; 2) Plant remains preserved beneath extant plateau ice caps will be collected by boring through the ice along transects from the ice margin to the ice divide. Radiocarbon ages of the entombed vegetation define the last time the Arctic was warm enough to completely melt these ice caps, 3) In situ 14C produced in quartz collected along transects from the current ice margins to beyond the edge of the LIA margin will define exposure histories across the plateau. The duration of surface exposure defines what proportion of the Holocene the plateaus have been ice-free since regional deglaciation, providing a longer-term perspective on current warming.
Broader impacts: Why is the Arctic warming, and how much warmer it may become are questions of immense societal importance. Defining how unusual is the present warmth, and quantifying the rates of ice-cap melt, will help focus the debate over greenhouse gases and the potential consequences of global warming. Research activities under this award will be made accessible to indigenous peoples by translating the goals and eventual results into Inuktitut, making posters that describe the research, and by offering public lectures in Iqaluit, the capital of Nunavut, and at Clyde River, the INSTAAR field base. This research program will train a PhD student, and provides opportunities for undergraduates to become involved with research, building on successful traditions from previous years. This projectl is a direct consequence of incorporating research into undergraduate teaching. While updating a lecture on Arctic warming for a freshman class in 2003, Miller discovered that the ice cap he studied in the1980s was unexpectedly gone, and following that lead, led to this proposal.
Version:1.0 StartHTML:0000000180 EndHTML:0000006482 StartFragment:0000002952 EndFragment:0000006446 SourceURL:file://localhost/Users/gmiller/Desktop/PublicReport.0454662.doc @font-face { font-family: "Times New Roman"; }p.MsoNormal, li.MsoNormal, div.MsoNormal { margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: "Times New Roman"; }table.MsoNormalTable { font-size: 10pt; font-family: "Times New Roman"; }div.Section1 { page: Section1; }ol { margin-bottom: 0in; }ul { margin-bottom: 0in; } The goal of this award was to capitalize on an unusual characteristic of thin ice caps in the Eastern Canadian Arctic that rest on relatively flat terrain. These ice caps do not erode at their bed, and consequently, vegetation that was present when the ice caps formed is preserved intact and in its original growth position. Collecting these vegetation samples exposed in the year of collection provides material for radiocarbon dating. These dates provide two fundamental pieces of information important to understand the global climate system in general, and Arctic climate specifically. 1. The radiocarbon date defines the last time the climate was warm enough that the collection site was not covered by permanent snow or ice. This provides a millennial perspective on 20th Century warming, and whether the warmth of the past century is unusual or not in a time scale much longer than can be provided by the instrumental record 2. The radiocarbon date also defines when the collection site became covered with permanent snow and/or ice that did not melt again until the year of collection; in this case between 2005 and 2010, the collection years supported by this award. Our results show two fundamental conclusions. Some of the in situ vegetation samples collected adjacent to receding ice margins are more than 2000 years old, indicating that warmth of the past century exceeds any century in more than 20 centuries. And this is despite the fact that Earth’s orbital irregularities have been reducing the solar energy reaching the Arctic in summer throughout this interval. A paper describing these conclusions appeared in Geophysical Research Letters in 2008 (Anderson et al.). The second conclusion is that ice cap expansion occurred suddenly at all elevations several times in the past millennium. This suggests that cooling into the Little Ice Age was not gradual, but that significant summer cooling occurred abruptly in the past, and this abrupt cooling was maintained until the past century. We have suggested that the abrupt cooling was do to explosive tropical volcanism, and climate modeling suggests that the cooling was sustained by powerful sea ice-ocean feedbacks. A paper describing these results is currently in review.
