2016-2017 Science Planning Summaries
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2016-2017 USAP Field Season
Project Detail

Project Title

A field and laboratory examination of the diatom N and Si isotope proxies: Implications for assessing the Southern Ocean biological pump

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Event Number:

Program Manager:
Dr. Thomas Wilch

ASC POC/Implementer:
Chelsea Wegner / Adam Jenkins

Principal Investigator

Dr. Rebecca Robinson

University of Rhode Island
Graduate School of Oceanography
Narragansett, Rhode Island


Supporting Stations: RV/IB Nathaniel B. Palmer
Research Locations: Southern Ocean transect: 54-67S, 170W


Diatom nitrogen (N) and silicon (Si) isotopes are important paleoceanographic tools used to investigate the role of the Southern Ocean biological pump in regulating atmospheric CO2. Existing calibrations, including culture experiments, surface sediment data and downcore reconstructions, suggest that nutrient utilization is the primary driver of Southern Ocean N and Si. However, a strong species effect is implied by recent culture results. Moreover, field and laboratory studies present contradictory results on the relative importance of inter-specific variation and diagenetic alteration of nutrient isotope signals to isotope records. This project is a first-order test of N and Si diatom nutrient isotope paleo-proxies using field sampling of natural diatom assemblages and laboratory culturing of field-isolates. Researchers need natural samples to test the relationships between dissolved nitrate, organic matter, and diatom-bound N isotopes as well as silicic acid and diatom Si isotopes, and to verify culture observations. To that end, the science team will collect Southern Ocean water, biomass, live diatoms, and fossil diatoms to investigate species and assemblage related variability in diatom N and Si isotopes and their relationship to surface nutrient fields and early diagenesis.

Field Season Overview

Researchers will board the vessel at McMurdo Station and will sail to Lyttelton, New Zealand. They will sample at intervals of approximately 1 degree of latitude along 170°W between 54 and 66°S. The actual site locations will depend upon the availability of coring locations and sediments adequate for coring. They will sample the water column for dissolved phases using Niskin casts (12 depths/cast), for particulates using large volume McLane filtration pumps (4 depths/cast), and will sample the underlying sediments at each station using a Mega-Corer. They will also conduct several incubation experiments in the constant temperature cold room facilities on board.

Deploying Team Members

  • Mark Brzezinski (Co-PI)
  • Ivia Closset
  • Jessica Freedman
  • Marlo Garnsworthy
  • Diana Gutierrez Franco
  • Colin Jones
  • Janice Jones
  • Roger Kelly
  • Heather McNair
  • Rebecca Robinson (PI)