National Science Foundation – Chemical Oceanography, “Biopolymers produced by diatoms and coccolithophores as carriers for selected natural radionuclides (of Th, Pa, Pb, Po, Be) in the ocean”, Peter H. Santschi, PI, Quigg, A., Schwehr, K.A., and Xu, C., co-PIs, Feb. 1, 2014 – Jan. 31, 2017 ($506,849).

Involvement of particle-reactive radionuclides in organic carbon cycling in the Ocean.

Particle-associated natural radioisotopes are transported to the ocean floor mostly via silica and carbonate ballasted particles, allowing their use as tracers for particle transport. Th(IV), Pa (IV,V), Po(IV), Pb(II) and Be(II) radioisotopes are important proxies in oceanographic investigations, used for tracing particle and colloid cycling, estimating export fluxes of POC, tracing air-sea exchange, paleoproductivity, and/or ocean circulation in paleo-oceanographic studies. Even though tracer approaches are considered routine, there are cases where data interpretation or validity has become controversial, largely due to uncertainties about inorganic proxies and organic carrier molecules. Our recent studies showed that cleaned diatom frustules and pure silica particles, sorb natural radionuclides to a much lower extent (by 1-2 orders of magnitude) than whole diatom cells (with or without shells). Phytoplankton that build siliceous or calcareous shells, such as the diatoms and coccolithophores, are assembled via bio-mineralization processes using biopolymers as nano-scale templates. These templates could serve as possible carriers for radionuclides and stable metals. Isoelectric-focusing experiments using radionuclide-labeled exopolymeric substances (EPS) from the Phaeodactylum tricornutum diatom showed that a variety of individual biopolymers were indeed responsible for radionuclide binding. Thus, we propose here to identify the individual biopolymeric carrier molecules that strongly bind specific radionuclides.

The intellectual merit of the proposed research will help elucidate the molecular basis of the templated growth of diatoms and coccoliths, EPS and their role in scavenging natural radionuclides in the ocean, and help resolve debates on the oceanographic tracer applications of different natural radioisotopes (230,234Th, 231Pa, 210Po, 210Pb and 7,10Be). Our proposed interdisciplinary research project will require instrumental approaches for molecular-level characterization of these radionuclides associated carrier molecules.

Publications

• Chuang, C.-Y., Santschi, P.H., Ho, Y.-F., Chen Xu, C., Jiang, Y., Quigg, A., Guo, L.D., Hatcher, P.G., Ayranov, M., Schumann, D. 2015. Molecular level characterization of diatom associated biopolymers that bind 234Th, 233Pa, 210Pb, and 7Be in seawater: a case study with Phaeodactylum tricornutum. J. Geophys. Res. Biogeosci., 120, 9, 1858-1869.
• Yang, W.F., Guo, L.D., Chuang, C.-Y., Santschi, P.H.,, Schumann, D., Ayranov, M. 2015. Influence of macromolecular organic matter on the adsorption of 210Pb, 210Po and 7Be on nanoparticles in seawater. Earth and Planetary Science Letters 423, 193–201.
• Chuang, C.-Y., Santschi, P.H., Ho, Y.-F., Conte, M.H., Guo, L.D., Schumann, D., Ayranov, M. 2013. Biopolymers as major carrier phases and redox regulators of Th, Pa, Pb, Po, and Be in settling particles from the Atlantic Ocean. Marine Chemistry, 157, 131–143.
• Chuang, C.-Y., Santschi, P.H., Jiang, Y., Ho, Y.-F., Quigg, A., Guo, L.D.,, Ayranov, M., Schumann, D. 2014. Important role of diatoms in the scavenging of particle reactive radionuclides, Thorium, Protactinium, Lead, Polonium and Beryllium, in the ocean: a case study with Phaeodactylum tricornutum. Limnol. Oceanogr., 59(4), 1256–1266.
• Chuang, C.-Y., Santschi, P.H., Wen, L.S., Xu, C., Zhang, S., Ho, Y.-F., Schwehr, K.A., Jiang, Y., Ho, Y.F., Schwehr, K.A., Quigg, A., Hung, C.-C., Guo, L.D.,, Ayranov, M., Schumann, D. 2015. Strongly radionuclide (Th, Pa, Pb, Po and Be) binding moieties in marine colloidal organic matter. Marine Chemistry, 173, 320–329.

Dr. Peter H.Santschi
Professor
Department of Marine Sciences
1001 Texas Clipper Rd
Bld# 3029, Office 346
Galveston, TX, 77554 USA

E-mail: santschi@tamug.edu
Phone: (409) 740-4476
Fax: (409) 740-4786