Collaborative Research: Understanding the Southern Ocean's Contribution to Cenozoic Deep-Water Circulation

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Ocean circulation plays an important role in the transport of heat around the planet and the cycling of carbon and nutrients in the ocean, directly affecting life and climate. This project aims to better understand the histories of two of the largest and most important sets of deep ocean currents. Ocean water masses that originate from both the Southern Ocean and North Atlantic Ocean intersect the continental margin of Argentina and records of how the circulation of these waters changed over time are preserved by the marine sediments that accumulate along this margin. An integrated program of seismic imaging, seafloor sediment sampling, and seawater property measurements will be used to investigate the southern Argentine margin and its sedimentary records of past ocean circulation. Seismic techniques will be used to image the surface of the seafloor and the underlying sediments down to 1 km. This imaging will enable better understanding of the large-scale oceanographic/geological processes that affected the margin over the Cenozoic (the past 65 million years). Sediment cores along with ocean water property data will be collected from a range of water depths to reconstruct the temporal evolution of the compositions and geometries of the water masses during the late Pleistocene. The seismic survey will also provide the requisite information to locate sites for future scientific drilling programs. The project includes student training, public education through museum exhibits, and at-sea activities potentially including a teacher-at-sea. The field component will provide opportunities to train graduate students in professionally relevant data acquisition and interpretation techniques.The Southern Ocean is the engine for today's deep- to intermediate-water circulation, supplying about half of the energy for deep ocean mixing; yet, most understanding of late Pleistocene thermohaline circulation changes derives from the North Atlantic. Understanding of the role of Southern Ocean water masses is limited by a paucity of deep-sea sedimentary records of these water masses. Sediments deposited along the continental slope of the Argentine margin offer a unique opportunity to reconstruct comprehensive histories of Southern Ocean sourced intermediate and deep waters close to their origin, and to better understand their fundamental connections to global ocean circulation and climate during the late Pleistocene. During a 43-day oceanographic cruise to the margin, the research team will collect seismic data (multibeam-mapping, high-resolution subbottom profiling, and multichannel seismic surveying) and sediment cores (multicores and piston cores) from water depths of ~500 to ~5000 meters, a range that spans the depths where all major intermediate and deep waters in the South Atlantic occur today. Ship- and shore-based analyses of a broad suite of physical and geochemical proxies will allow the researchers to reconstruct the temporal evolution of the compositions and geometries of the water masses during the late Pleistocene. The seismic and sediment data combined will enable better understanding of the nature of the sediments that comprise the southern Argentine margin and the oceanographic/geological processes that influenced the margin during both the late Pleistocene and the Cenozoic. The latter will provide a broad regional and temporal context to better understand the interaction between sediments and bottom currents that can be further exploited with scientific ocean drilling; moreover, the multichannel seismic data will be used to situate proposed drilling sites.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.