Collaborative Research: The Cold Late Oligocene Arctic Ocean and its Unique Biota

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This is a collaborative proposal from Principal Investigators at the California Academy of Sciences and Florida Atlantic University. This study is an integrated assessment of mollusks, microfossils, and oxygen isotopes which will be used to document the presently unknown late Oligocene marine paleoclimate of the Arctic Ocean. Fossils will first be collected from the Nuwok Member of the Sagavanirktok Formation, in northeastern Alaska, the only upper Oligocene marine sediments known to crop out in the Arctic Ocean region. After fieldwork, the Principal Investigators will undertake taxonomic and oxygen isotopic analyses to generate information that will form the basis for their conclusions. Based on a pilot study of oxygen isotopes derived from mollusk shells, the first hypothesis to be tested is that the Arctic Ocean was almost as cold in the late Oligocene as it is today, that it was colder than contemporaneous mid- and low-latitude seas, but that it was not as cold as Antarctica. If true, this would be the first evidence of hemispheric climatic asymmetry during the Earth's Oligocene transition from a Greenhouse to an Icehouse world. Pilot d18O values from Nuwok mollusks imply greater seasonality than occurs in the adjacent Arctic Ocean today. A second hypothesis is that Nuwok late Oligocene mollusks and ostracodes are the earliest manifestation of the modern Arctic Ocean biota. The globally unique presence of what appear to be entirely extant genera in the late Oligocene Nuwok biota, and the equally unique absence of Eocene holdover mollusks in such an Oligocene fauna, make a compelling case for this idea. The Nuwok biota provides a unique opportunity to place the Arctic within the context of global patterns of Cenozoic marine evolution and diversification during a time of rapid global climate change. A third hypothesis is that late Oligocene Nuwok mollusks and ostracodes evolved very little, based on their uncanny resemblance to extant Arctic Ocean species. This will be addressed in comparative taxonomic analysis of fossil and modern arctic and North Atlantic faunas.The intellectual merit of the proposed activity: This study will be the first to document the presently unknown late Oligocene paleoclimate and seasonal temperature fluctuations of the Arctic Ocean, based on oxygen isotope analysis of mollusk shells. Knowledge of Oligocene global cooling has dramatically increased in recent decades, mainly due to oxygen isotope studies of microfossils in deep-sea cores, but no such work has been done on Arctic Ocean marine faunas. This proposed study, using coordinated isotopic and paleontological analyses, will be the first to place the Arctic Ocean's late Oligocene paleoclimate into a global context, and allow factoring this paleoclimate into global climate models during the transition from a Greenhouse to an Icehouse world.The broader impacts resulting from the proposed activity: The climate history of the Arctic Ocean is one of the last unsolved epics of Earth history. Documenting its late Oligocene (26-27 million years ago) paleoclimate, including seasonal extremes, during initiation of the modern Icehouse world will uniquely add to overall understanding of global climate history. This study will provide the first insights from the Arctic Ocean realm during the dramatic transition from a Greenhouse to an Ice House world, and will have implications for many paleoclimate-related fields of marine and continental geoscience. These new data from one of the world's most sensitive, but least known, environments will be useful in considering the scale, rate, and potential effects of global climate change.