This project by investigators from the University of Washington, and in collaboration with various colleagues, will continue to examine whether the organic molecules or classes of organic compounds found in the organic matrix of diatom frustules are useful biomarkers for the oceanographic conditions under which the organisms grew in the surface ocean. These biomarkers are useful as diatoms are responsible for a substantial fraction of global primary productivity and are globally distributed, ensuring their widespread applicability. Frustules are composed primarily of silica, but there are organic compounds entrapped in the siliceous matrix during biomineralization. This organic template is mostly unexploited in paleoceanographic and related studies, but recent work has suggested that these compounds are potential useful biomarkers. Additionally, it is possible that the isotopic signature of carbon and nitrogen in the organic molecules may provide additional information and insight into ocean conditions during growth.
Therefore, this project will investigate the organic compound composition and employ molecular isotope analyses of organic compounds in diatom frustules to fully capture the potential of diatom frustules as recorders of the changes in ecosystems, biogeochemical cycles and climate. The project will involve mainly controlled laboratory culture studies, but will also examine field populations and surface sediment samples, to examine the factors that influence the organic template of frustules, and specifically the molecular and isotopic composition of mycosporine-like amino acids, long chain polyamines and chitin extracted from these frustules. The project will also examine whether species composition influences the isotopic signature. The results could provide suitable biomarkers reflective of different important oceanographic conditions, such as past nutrient utilization, and environmental stress (UV and nutrient).
The project will provide new methods to examine ocean-climate feedbacks that will help clarify the response of oceans to major regime shifts. The project will support a post-doctoral investigator and a graduate student, and will involve continued international collaboration with Russia scientists. The investigators will also interact and be involved with the University of Washington's Center for Ocean Sciences Education Excellence (COSEE) and work on outreach activities for K-12 students.
Diatoms are single celled algae responsible for 20% of global photosynthesis. Their productivity helps drive the marine food web and exerts a major control on the composition of earth’s atmosphere. Diatoms form an ornate shell called a frustule that is made of glass (silicon dioxide). When a diatom dies, its frustule can sink to the seafloor and be preserved as marine sediment for millions of years. In some locations, diatom frustules are a major component of marine sediments. Both the silicon dioxide and its associated organic carbon in marine sedimentary deposits are of interest to investigators studying the history of the oceans, such as the availability of nutrients in the past and the extent of sea ice at high latitudes. However, there are many challenges associated with extracting environmental records from deposits of diatom frustules. This project aimed to address some of these challenges by refining our understanding of the organic carbon present in diatom frustules. Diatom frustules are deposited on an organic template that catalyzes the precipitation of silicon dioxide with in the diatom cell. A major component of the organic template is a complex mixture of long chain polyamines. However other minor components have also been observed in frustules including natural sunscreen compounds called mycosporine-like amino acids. Here we developed new methods to determine the composition of the organic template in diatoms and applied this method to ditaom cultures and to environmental samples ranging in age from living plankton to 120 million year old sedimentary deposits. The extremely long-term preservation of the organic template is likely a result of physical protection of the organic carbon by the frustule. Trends in the composition of these compounds were observed between species, sample types and locations. We also determined the radiocarbon age of these compounds in marine sediments in order to refine our understanding of the age of marine sedimentary deposits so that we are able to better know the timing of events in the past. The Broader Impacts of this project were the training of one graduate student, one postdoctoral fellow and several undergraduates. This project fostered international relations through a collaboration with Russian and German scientists at the Alfred Wagener Institute for Polar Marine Research and the Limnological Institute, Irkutsk, Siberia, respectively. Both institutions were visited by project scientists. Each participant also undertook outreach activities through Sound Citizen, The Seattle Aquarium, COMPASS, UW Advance, SACNAS, the Comer Foundation and the eScience Institute. This award resulted in six publication and numerous presentations at national meetings and invited talks.
