Table of Contents

• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Related Publications
• Parameters
• Instruments
• Project Information
• Funding

Laboratory incubation experiments using the coccolithophore Emiliania huxleyi were conducted
in the presence of 234Th, 233Pa, 210Pb, 210Po, and 7Be to differentiate radionuclide uptake to the CaCO3
coccosphere from coccolithophore-associated biopolymers.

The seawater (< 1 kDa) was enriched with f/2 nutrients, trace metals and vitamins, and autoclaved in pre-combusted and seawater-preconditioned clear glassware. Then, ~50 Bq of each gamma emitting radionuclide, including 234Th, 233Pa, 210Pb and 7Be, was added. Since 210Po emits no gamma radiation, 210Po was added separately into the seawater. After checking the pH of each radiolabeled medium to be 8.0, 2 mL of laboratory axenic Emiliania huxleyi (CCMP 371) was added to 100 mL of media and incubated at a temperature of 19±1ºC with a light:dark cycle of 14 h:10 h under an irradiation condition of 100 µmol-quanta/m2/s.

Non-attached exopolymeric substances (NAEPS) and exopolymeric substances attached on the coccolithophore cellular surface (AEPS) were extracted followed the procedures described in Chuang et al. (2015) and Xu et al. (2011). In brief, laboratory cultures were centrifuged at 3000 ×g for 30 min, and then the supernatant for the NAEPS fraction was filtered, followed by the concentration and extensive desalting of supernatant against nanopure water (18.2 Ω) with 3 kDa Microsep centrifugal filter tubes (Milipore). For AEPS extraction, the resultant pellet from the centrifugation was resuspended by 50 mL 3% NaCl solution and stirred gently overnight at 4ºC. Lastly, the solution was centrifuged, and the supernatant containing the AEPS was then filtered before further desalting via the 3 kDa ultrafiltration centrifugation tubes. The pellet from the previous step was thus further digested in the 0.44 M HAc + 0.1 M NaCl solution at 4ºC for 8 h. After the digestion, the mixed solution was centrifuged and filtered, followed by ultrafiltration of the supernatant with 3 kDa Microsep centrifugal filter tubes. The retentate (> 3 kDa) was defined as coccosphere-associated biopolymers. The permeate (<3 kDa), defined as the fraction of digested biogenic calcite. Cells remaining from the last step was further heated in 20 mL of 1% SDS containing 10 mM Tris solution (pH 6.8) at 95 ºC for 1 h. The supernatant was also collected through centrifugation and filtration, followed by desalting and concentration with 3 kDa Microsep centrifugal filter tubes. Subsequently, the pellet was further digested by 0.04 M NH2OH HCl + 4.35 M HAc mixture at 96 ºC for 6 h, with occasional agitation to obtain the intracellular Fe-Mn associated metabolitic biopolymer. The sum of these two fractions represents the intracellular biopolymers after cell breakage.

Subsamples were taken from the concentrated biopolymers for the analysis of protein, total carbohydrate (TCHO) and uronic acid (URA), respectively. In brief, the protein abundance was measured through a modified Lowry protein assay, using bovine serum albumin (BSA) as the standard. For the concentrations of TCHO, samples were hydrolyzed by 0.09 M HCl (final concentration) at 150ºC for 1 h. After neutralization with NaOH solution, the hydrolysate was measured by the 2,4,6-tripyridyl-triazine (TPTZ) method (Hung et al., 2001), with glucose as the standard. URA concentrations were determined by the metahydroxyphenyl method using glucuronic acid as the standard (Hung and Santschi, 2001). 

All the solutions from the different extraction steps, including the >3 kDa biopolymer fractions and the permeate (< 3 kDa), were counted for the activity concentrations of 234Th, 233Pa, 210Pb and 7Be by a Canberra ultrahigh purity germanium well gamma detector. In addition, the 210Po activity in different separately incubated fractions was determined by Beckman Model 8100 Liquid Scintillation Counter.

BCO-DMO Processing Notes:
* added conventional header with dataset name, PI name, version date
* modified parameter names to conform with BCO-DMO naming conventions
* reorganized data from two tables into one table

NSF Award Abstract:

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) radionuclides are important proxies in oceanographic investigations, used for tracing particle and colloid cycling, estimating export fluxes of particulate organic carbon, tracing air-sea exchange, paleoproductivity, and/or ocean circulation in paleoceanographic 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. 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 nanoscale templates. These templates could serve as possible carriers for radionuclides and stable metals.

In this project, a research team at the Texas A & M University at Galveston hypothesize that radionuclide sorption is controlled by selective biopolymers that are associated with biogenic opal (diatoms), CaCO3 (coccolithophores) and the attached exopolymeric substances (EPS), rather than to pure mineral phase. To pursue this idea, the major objectives of their research will include separation, identification and molecular-level characterization of the individual biopolymers (e.g., polysaccharides, uronic acids, proteins, hydroquinones, hydroxamate siderophores, etc.) that are responsible for binding different radionuclides (Th, Pa, Pb, Po and Be) attached to cells or in the matrix of biogenic opal or CaCO3 as well as attached EPS mixture, in laboratory grown diatom and coccolithophore cultures. Laboratory-scale radiolabeling experiments will be conducted, and different separation techniques and characterization techniques will be applied.

Intellectual Merit : It is expected that this study 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). The proposed interdisciplinary research project will require instrumental approaches for molecular-level characterization of these radionuclides associated carrier molecules.

Broader Impacts: The results of this study will be relevant for understanding biologically mediated ocean scavenging of radionuclides by diatoms and coccoliths which is important for carbon cycling in the ocean, and will contribute to improved interpretation of data obtained by field studies especially through the GEOTRACES program. This new program will enhance training programs at TAMUG for postdocs, graduate and undergraduate students. Lastly, results will be integrated in college courses and out-reach activities at Texas A&M University, including NSF-REU, Sea Camp, Elder Hostel and exhibits at the local science fair and interaction with its after-school program engaging Grade 9-12 students from groups traditionally underrepresented.