Mark A. Altabet and Roger Francois; University of Massachusetts, Dartmouth and Woods Hole Oceanographic Institute

"Nitrogen and Carbon Isotope PaleoProxy Verification and Calibration in the Southern Ocean"

Our project focuses on both water column and sea floor properties and processes that influence sedimentary ¹⁵N/¹⁴N (¹⁵N) and organic ¹³C/¹²C (¹³C_org) in the Southern Ocean and impact on their use as paleoproxies of surface water nutrient utilization and [CO_2aq], respectively. Isotopic measurements will be made on samples collected seasonally across the large surface gradient in these properties that occurs between the subtropical convergence and the Ross Sea. Surface water NO₃, DIC, and POM will be collected at 1 to 2E lat. resolution along the cruise track using the ship's clean seawater intake system. At each mooring site, vertical profiles of in the upper water column will also be obtained. We plan to obtain from the sediment trap and coring programs sinking POM samples on a time-series basis, sea surface 'fluff', and coretop material. Our cruise participation will focus on the first Palmer site survey (Austral winter), the Palmer mooring deployment cruise (Austral spring), the Thompson APFZ spring survey cruise, the Thompson summer survey cruise, and the Thompson mooring recovery cruise (Austral fall). In addition to the trap and coring projects, we anticipate interactions with groups involved in nutrients, CO₂, radiochemical measures of particle flux, DOM, and phytoplankton productivity (carbon and nitrogen) and growth rate.