This award supports a project to develop both a record of past local temperature change at the WAIS Divide site, and past mean ocean temperature using solubility effects on atmospheric krypton and xenon. The two sets of products share some of the same measurements, because the local temperature is necessary to make corrections to krypton and xenon, and thus synergistically support each other. Further scientific synergy is obtained by the fact that the mean ocean temperature is constrained to vary rather slowly, on a 1000-yr timescale, due to the mixing time of the deep ocean. Thus rapid changes are not expected, and can be used to flag methodological problems if they appear in the krypton and xenon records. The mean ocean temperature record produced will have a temporal resolution of 500 years, and will cover the entire 3400 m length of the core. This record will be used to test hypotheses regarding the cause of atmospheric carbon dioxide (CO2) variations, including the notion that deep ocean stratification via a cold salty stagnant layer caused atmospheric CO2 drawdown during the last glacial period. The local surface temperature record that results will synergistically combine with independent borehole thermometry and water isotope records to produce a uniquely precise and accurate temperature history for Antarctica, on a par with the Greenland temperature histories. This history will be used to test hypotheses that the ?bipolar seesaw? is forced from the North Atlantic Ocean, which makes a specific prediction that the timing of Antarctic cooling should slightly lag abrupt Greenland warming. The WAIS Divide ice core is expected to be the premier atmospheric gas record of the past 100,000 years for the foreseeable future, and as such, making this set of high precision noble gas measurements adds value to the other gas records because they all share a common timescale and affect each other in terms of physical processes such as gravitational fractionation. Broader impact of the proposed work: The clarification of timing of atmospheric CO2 and Antarctic surface temperature, along with deep ocean temperature, will aid in efforts to understand the feedbacks among CO2, temperature, and ocean circulation. These feedbacks bear on the future response of the Earth System to anthropogenic forcing. A deeper understanding of the mechanism of deglaciation, and the role of atmospheric CO2, will go a long way towards clarifying a topic that has become quite confused in the public mind in the public debate over climate change. Elucidating the role of the bipolar seesaw in ending glaciations and triggering CO2 increases may also provide an important warning that this represents a potential positive feedback, not currently considered by IPCC. Education of one graduate student, and training of one technician, will add to the nation?s human resource base. Outreach activities will be enhanced and will to continue to entrain young people in discovery, and excitement will enhance the training of the next generation of scientists and educators.
Our goals for this project were to reconstruct the past history of average ocean temperature, using trapped air bubbles from the recently collected West Antarctic Ice Sheet Divide (WAIS Divide) ice core, and to place some constraints of the temperature of the ice core site. The idea of the method is that krypton and xenon are soluble gases, whose atmospheric concentrations rise when the ocean warms due to the fact that warm water holds less gas than cold water. The main project outcomes include the finding that the last glacial maximum (about 24,000 to 19,000 years ago) had a mean ocean temperature about 2.5 degrees C (4.5 ?F) colder than present, and that most of the warming occurred between 18,000 years ago and 16,000 years ago. This latter finding was a surprise, since much of the world was still partially in an ice age at 16,000 years ago. The answer to the puzzle may lie in the fact that most of the deep ocean is known to acquire its temperature in the coastal ocean around Antarctica, and that area is thought to have undergone strong warming during this 2000 year period. Broader impacts of the work include the contribution this finding may make in improving predictions of warming during the century to come. Our findings underscore the reality that the deep ocean may continue warming even as much of the surface air temperature remains constant without an upwards trend, a situation that is reminiscent of the past 15 years. Other broad impacts include the education of two graduate students, and cultivation of several undergraduates. Training of one technician also added to the Nation's skilled workforce.
