2016-2017 USAP Field Season
Water mass structure and bottom water formation in the ice-age Southern Ocean
Dr. Robert Frederick Anderson
Supporting Stations: RV/IB Nathaniel B. Palmer
The objective of this project is to collect sediment cores from the Southwest Pacific sector of the Southern Ocean in order to measure radiocarbon ages in contemporary benthic and planktonic foraminifera. These measurements will establish glacial-to-Holocene changes in the age structure of the water column in a critical region for the ventilation of the deep Pacific Ocean. Core samples will include both Jumbo Piston Cores that reach about 20 meters in depth to capture the Last Glacial Maximum, and gravity cores that reach approximately three meters in depth. The radiocarbon ages of the foraminifera collected from these cores will be interpreted to discriminate between two proposed mechanisms of ice-age deepwater formation: (1) Coastal processes around Antarctica; and (2) Open-ocean deepwater polynyas. This work will advance interpretations of the ice-age carbon cycle and provide a benchmark for the development of models used to simulate ice-age climate. The science team will also collect water samples to measure the flux of dissolved thorium (Thorium-232), which will be used to develop a tracer for the supply of essential nutrient metals to the ocean by dust. Collecting dissolved thorium samples will complement related work funded by the NSF in the tropical Pacific (Award #1233688) and in the subtropical Pacific (Award #1555726), enabling the comparison of fluxes of dissolved metals from dust across diverse regions of extremely low dust flux to the ocean.
Field Season Overview
Team members with this project will sail from McMurdo Station and will share ship time with another science project, Robinson (G-152-N). The team will collect six gravity cores (three meters) and two piston cores (15-20 meters) from five different sites along the cruise transect, at depths ranging from 3000-4000 m. All of these coring locations are approximately co-located with the Robinson sampling locations. The cruise transect will run approximately along the 170°W longitude line between 54°S and 66°S at each degree of latitude. The science team will revisit two sites along this transect that were previously cored on the Joint Global Ocean Flux Study (JGOFS) cruise (NBP98-02), and will collect two gravity cores per site. They will also collect two additional gravity cores at one or two sites between 63°S and 61°S, and two piston cores at 61°S. One memeber of the science team will be highly trained in core collection; additional coring support will come from ASC Marine Technicians. The science team will provide a gravity corer from Lamont-Doherty Earth Observatory (LDEO) and will use the USAP Jumbo Piston corer. Cores will be stored in the walk-in cooler for the duration of the cruise and then transferred to a USAP-provided refrigerated van for shipping back to the Lamont-Doherty Core Repository.
Deploying Team Members