Diatoms are microscopic, single-celled phytoplankton, that secrete walls of silica, called frustules, on an organic template. The frustules of growing diatoms and their organic template record the environmental conditions in which they grow. Once frustules sink and become sediment, paleoceanographers are able to use their chemical and isotopic composition to study past nutrient utilization (15N/14N ratio) and productivity (13C/12C ratio), as well as determine the radiocarbon age of sedimentary frustules. Currently, sedimentary frustules are physically isolated and chemically cleaned prior to the analysis of the elemental and isotopic composition of bulk organic matter associated with the frustules. Unfortunately, the records that have been through these prevailing methods have lead to ambiguous reconstructions of past oceanographic environments.
For this reason, researchers at the University of Washington and Oregon State University will develop several new, more reliable methods for analyzing the molecular and isotopic signatures of organic matter associated with diatom frustules. Specifically, the team of scientists will characterize the organic matter in diatoms frustules from cultures, plankton tows and sediments by using liquid chromatography coupled to mass spectrometry. The influence of frustule-cleaning and partial dissolution on frustule-bound organic compounds and the absolute relative abundance of biomarkers in frustules under iron limited and iron replete conditions will also be examined. In addition, the team of researchers will also purify individual frustule-bound biomarkers. By improving the methods for analyzing the molecular and isotopic signature of organic matter associated with diatom frustules, the dating of diatom-rich samples of Holocene age will be more accurate, the core integrity will be properly assessed, and the methods for measuring 13C/12C, 15N/14N and C/N ratios in diatom frustules will be improved.
As regards broader impacts, the work will not only open up entirely new avenues in paleoceanography, but also lead to a better understanding of past climate conditions and the ocean's biogeochemical cycles response to future anthropogenic impacts. The project will also provide for the support and training of one female graduate student and one or two undergraduate students.
