Collaborative Research: Bringing the Late Pleistocene into Focus: Better Estimates of Ages and Ocean Circulation Through Data-Model Comparison

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Measurements of past climate changes are crucial for understanding the causes, amplitudes, and rates of natural climate variability. Ocean sediments contain abundant microfossils that are an important archive of past climate information with near-global coverage. To place an ocean sediment sample into context, researchers need two kinds of information: (1) an interpretation of the climate represented by that sample and (2) the age of the sample. Age information is crucial for reconstructing the rate and sequence of climate changes globally. Some sediments are well-dated using radiocarbon. However, the ages of many samples can only be estimated indirectly, resulting in age uncertainties as large as 4,000 years. This research project aims to improve these indirect age estimates using statistical analysis of the available radiocarbon-dated samples. Improvements in indirect age estimates will be used to increase the accuracy of global datasets of climate changes for the past 150,000 years.More specifically, the aim of this project is to improve indirect age estimates derived from the stratigraphic alignment of benthic delta18O (a proxy for global ice volume and deep ocean temperature). A major source of uncertainty in these ages derives from differences of up to 4,000 years in the timing of benthic delta18O change observed at a few core sites with very accurate radiocarbon models. However, little is known about how the timing of benthic delta18O signals differs at other locations. The research approach for this project incorporates ocean circulation models, paleoclimate data (benthic delta18O and 14C from ~100 globally distributed sediment cores), and statistical inference. Phase one of the project is to characterize benthic delta18O age differences (delta18O lags) globally using radiocarbon data from ~100 sediment cores in conjunction with results from ocean circulation models. Phase two is to apply the results from phase one to develop improved methods for delta18O alignment. Phase three is to generate a new database of improved delta18O age models. Thus, the final products of the project will be (1) probabilistic stacks (averages) describing regional and global patterns of benthic delta18O variability, (2) probabilistic algorithms for multiproxy core alignments and for generating Bayesian inferences of delta18O lags, (3) a database of age models for ~300 cores with benthic delta18O data, and (4) estimates of ocean circulation changes based on comparing benthic del18O data with different circulation model scenarios.This project has broader impacts for climate change research and education. Accurate paleoclimate age estimates are crucial for creating data compilations that are used to test the effectiveness of climate models and improve confidence in their ability to simulate potential future climate changes. The spatial coverage of paleoclimate data compilations is often increased by including data with indirect age estimates that have large uncertainties. By improving age estimates for benthic delta18O alignments and quantifying alignment age uncertainties, this project will allow for more informed selection of which data to include in compilations and overall better accuracy. Data-model comparison performed as part of this project will also better constrain ocean circulation changes, which could help describe the causal chain of events for past climate changes and may identify isolated reservoirs of carbon sequestered in the ocean during glaciations. This project will also provide interdisciplinary training in earth science and mathematics to two graduate students. Research methods and findings will be incorporated into undergraduate and graduate classes through the development and dissemination of interactive computer lab activities.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.