Matthew McCarthy 

Marine Organic Geochemistry, Biogeochemical Cycles

        My research is a sub-discipline of chemical oceanography, focused on the cycling and transformations of organic matter in the sea. The biochemical and isotopic composition of non-living organic matter in the environment carries a detailed molecular history of its origins and of the transformation processes it has undergone.  We thus use organic molecules as tracers to understand biogeochemical cycles in the ocean.  Whereas much organic geochemistry has traditionally focused on paleoenvironmental processes and long-term abiotic transformations of organic matter, my interests instead are focused on using biologically produced molecules to understand modern, active oceanic biogeochemical cycles. My main research interests thus tend to sit at the interface between biological and geochemical cycles. 

This type of research deals with questions like:

•  What classes of organisms are most important in producing active reservoirs of carbon and nitrogen in the sea?

•  Which biomolecule classes, such as proteins and carbohydrates, are most abundant in a given environment?  What can these patterns of abundance tell us about that environment, and how are these molecules cycled or preserved?

•  What can specific molecules tell us about biological sources, passage through trophic levels, age, and the ultimate origins of elemental building blocks for a specific biogeochemical system?

Tools  

       In practical terms, my lab measures specific organic molecules- or the stable and radio-isotopic signatures of those molecules- and uses presence, abundance, and isotopic ratios to target specific questions. One focus continues to be exploring new molecular-level approaches to trace C and N flows in the ocean. Some ongoing projects include:

•  Developing protocols to make very low level molecular-level radiocarbon (14C) measurements on individual amino acids (in conjunction with Laurence Livermore National Labs) 

• Exploring enantiomeric (D/L) measurements ratios of amino acids as tracers for bacterial types, and influence of prokaryotic-sourced molecules in oceanic cycles 

•  Investigating the uses of stable isotopic fingerprints of the full range of protein amino acids as tracers of major metabolic origin of dissolved organic nitrogen preserved in detrital material.

Applications

       Current field research areas include dissolved nitrogen and carbon (DOM) in both blue water oceanic and coastal-upwelling systems, as well as sub-seafloor crustal fluid systems. Other interests include exploring cell wall novel biomarkers for bacterial or algal groups.