Funded Research - Project Profile: Close, NSF-OCE 1830016

Project Title: Isotopic Indicators for Mechanisms of Organic Matter Degradation in the Northeast Pacific

Project Lead: Hilary G. Close, RSMAS, University of Miami



The biological pump is largely responsible for the vertical transport of organic carbon from the surface to the ocean interior. However, only a small fraction of organic material produced in surface waters is sequestered in the deep ocean. The rest is consumed, or respired, by bacteria and larger organisms. The overarching goal of this project is to characterize the relative influences of bacteria versus larger organisms on the degradation of organic material with depth. Guided by recent results from the subtropical Pacific, the investigators will use measurements of stable isotopes of carbon and nitrogen in different amino acids (compound-specific isotopic analysis of amino acids, known as AA-CSIA), along with measurements of the abundances of different forms of amino acids, and other parameters derived from these analyses to identify how the partitioning and flux of large and small particles are affected by different degradation processes. By improving the interpretive power of the AA-CSIA technique the investigators propose to determine: 1) the relative importance of microbial and zooplankton consumption on the efficiency of the biological carbon pump in the subarctic northeast Pacific, and 2) how much microbially-altered small particles fuel the metabolisms of mid-water zooplankton. This work capitalizes on an existing, comprehensive field program (NASA EXPORTS) specifically focused on building a predictive framework relating surface ocean properties to the vertical flux of organic carbon. The tremendous amount of data to be collected on all aspects of the biological pump as part of the EXPORTS program will aid the development and interpretation of the investigators' amino acid isotopic tool. Results will be broadly communicated via production and distribution of several episodes of Voice of the Sea, a local television program that will air in Hawaii and across many Pacific islands. Episodes also will be posted online with Spanish subtitles and publicized through social media to the south Florida community.

Keywords: biological pump, particulate organic matter, amino acids, compound-specific isotopic analysis (CSIA), zooplankton, microbes

Project Lead(s):

  • Hilary G. Close, University of Miami, RSMAS, Department of Ocean Sciences


  • Brian N. Popp, University of Hawaii at Manoa, SOEST, Department of Earth Sciences

  • Kanesa Duncan Seraphin, University of Hawaii at Manoa, Hawaii Sea Grant Center for Marine Science Education


  • TBD


  • TBD


  • Tamara Allen, University of Hawaii at Manoa, SOEST, Department of Earth Sciences


  • Ken Buesseler, WHOI

  • Claudia Benitez-Nelson, South Carolina

  • Meg Estapa, Skidmore

  • Phoebe Lam & Jong-Mi Lee, UC Santa Cruz

  • Deborah Steinberg, VIMS


  • Albert Ortiz, University of Miami, RSMAS, Department of Ocean Sciences)

  • Natalie Wallsgrove, University of Hawaii at Manoa, SOEST, Department of Earth Sciences