An important aspect of studies targeting inorganic and organic proxies of particle flux to the open ocean has been to trace aluminosilicate inputs to constrain sources of atmospheric dust and fluvial material, both of which are critical for understanding biogeochemical cycling and climate variability in space and time. Quantifying detrital material in particles and sediments is essential to determine dust and fluvial fluxes, so as to account for compositional dilution (i.e., normalization to 100% as a closed array) that affects measured composition. Accounting for the inorganic aluminosilicate material is vital in order to "remove" the terrigenous component from the total flux.
Along with the aluminum and the isotope Th232, the element titanium (Ti) is commonly used towards these ends, but the assumption that these species are truly only contained in the refractory aluminosilicate phase(s) needs to be considered more carefully. There are less than five published profiles of Ti in the open ocean, and greater coverage is needed to fully understand the complex biogeochemistry of this important element. Without such an understanding, the use of Ti as a tracer will not be to its fullest potential. Pioneering work in the early 1990s laid the groundwork for a resin-based pre-concentration procedure followed by quantification by ICP-MS analysis.
With funding through this EAGER award, researchers at Boston University will (a) develop a methodology to quantify dissolved Ti in open ocean seawater, and (b) apply this methodology to a suite of previously gathered samples to test whether the GEOTRACES rosette sampling system, small parts of which are constructed of Ti-bearing materials, can be used to gather seawater samples that are uncontaminated with respect to Ti. The new analytical procedure is based on a new resin, NOBIAS CHELATE-PA1. This EDTA-based resin is tailored specifically for GEOTRACES research, and has been shown to result in excellent pre-concentration, followed by ICP-MS analysis, for a suite of other low-concentration elements. This study will be the first to solely focus on Ti. In consultation with collaborators at GSO-URI, MIT, and UC Santa Cruz, the Boston University team have developed an analytical research plan comprising the study of coastal seawater samples, Standard Reference Materials, calibration samples (e.g., SAFe), non-GEOTRACES samples gathered with established clean sampling techniques, and GEOTRACES materials. This strategy will allow the team to achieve the dual goals of establishing the new technique and testing the suitability of the GEOTRACES rosette for Ti.
Broader Impacts: The proposed research is expected to have several significant Broader Impacts. First, the research has clear benefit to society in that the ability to eventually understand the geochemical cycling of Ti will significantly improve our ability to trace dust and fluvial fluxes -- both of which will assist in the study of climate change over multiple temporal and spatial scales. The project also will enhance infrastructure for research and education, by establishing collaborations between multiple institutions (Boston University, University of Rhode Island, Massachusetts Institute of Technology, UC-Santa Cruz). This proposal also speaks to the development of next-generation instrumentation and analytical methodologies. Finally, the lead investigator has a long record of incorporating his research results into learning and education at the undergraduate and graduate level, and this project is well-suited to continuing such activities.
This project was funded to develop a challenging analytical methodology to quantify the abundances of titanium (Ti) dissolved in seawater and to generate preliminary results on samples to demonstrate the feasibility of the method. Prior to this research, there have been only a few (less than five) published profiles of dissolved Ti in the open ocean, and only two were using a high precision mass spectrometric method. Our research is to develop a newly improved technique using isotope dilution mass spectrometry to enable the near-routine measurement of Ti as part of the US GEOTRACES program. We were successful in our pursuit. Drawing heavily upon expertise in the GEOTRACES community, we have demonstrated the ability to gather clean samples. We have shown that we can construct the clean laboratory apparatus necessary to preconcentrate the Ti so that it is enriched in the analyte solution to the degree necessary to be quantified. We have developed the isotope dilution spike and calibrated it. The very large number of individual steps in the process have been codified, and we are in the process of writing a methodology paper. We have generated some preliminary results from the GEOTRACES Intercalibration and SAFe references that agree with the few published analyses of Ti that exist. Our results even at this early stage are either at or better than other techniques. We are starting to generate data from open ocean samples, and are very near being in ‘routine’ mode. Consistent with the goals of the EAGER program, this support was entirely crucial for us to get the laboratory built, technicians trained, data reduction spreadsheets developed, and to be ready for hoped for inclusion in future GEOTRACES programs in the Pacific and other oceans. We are active participants in the GEOTRACES community, via our presence in workshops and various discussions, and feel that the potential addition of Ti to the suite of trace elements that can be accurately quantified in the open ocean will be a valuable asset to the US and international communities. None of this would have been possible with the EAGER program support.
