Table of Contents

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

Radiocarbon dates on calcite and organic material (gorgonin) in bamboo coral skeletons

Related References:
Farmer, J.R., Hönisch, B., Robinson, L.F. and Hill, T.M. (2015) Effects of seawater-pH and biomineralization on the boron isotopic composition of deep-sea bamboo corals. In revision, Geochim. Cosmochim. Acta.

Sherwood, O.A., Edinger, E.N., Guilderson, T.P., Ghaleb, B., Risk, M.J. and Scott, D.B. (2008). Late Holocene radiocarbon variability in Northwest Atlantic slope waters. Earth Planet. Sci. Lett. 275, 146-153, doi:10.1016/j.epsl.2008.08.019.

Sampling and Analytical Methodology:
All radiocarbon dates were obtained at the National Ocean Sciences Accelerator Mass Spectrometry facility (NOSAMS). Prior to sample submission, 3 to 5 mg of powdered calcite was cleaned of organic material following the oxidative procedure given in Farmer et al. (2015). Clean calcite powders were submitted to NOSAMS and leached with 200 µL of 0.1N HCl under sonication immediately prior to hydrolysis to remove any adsorbed modern CO₂. Approximately 10-20% of the sample mass was removed by the HCl leach. Gorgonin samples were prepared following Sherwood et al. (2008): decalcified nodes were separated with tweezers and a scalpel into individual gorgonin units, comprising 3 to >10 gorgonin layers where distinguishable. Approximately 2 to 3 mg of gorgonin was subsampled from larger units, soaked in 5% HCl for 48 hours to remove any residual carbonate, rinsed in deionized water and dried prior to submission to NOSAMS.

Full methodology, equations, and discussion of instrumental precision are available from the NOSAMS website: http://www.whoi.edu/nosams/

Data Processing:
Fraction Modern (Fm) = ((¹⁴C /¹²C_sample - ¹⁴C /¹²C_blank)/( ¹⁴C /¹²C_reference - ¹⁴C /¹²C_blank))* ((1-25/1000)/(1+δ¹³C/1000))^2;

The reference is 95% of the radiocarbon concentration of NBS Oxalic Acid I (in 1950 AD) normalized to δ¹³C_VPDB=-19‰.

Conventional ¹⁴C age (in ¹⁴C years before 1950) = -8033*ln(Fm)

δ¹³C (‰) = (((¹³C/¹²C_sample)/( ¹³C/¹²C_standard))-1)*1000; The standard is Vienna Pee Dee Belemnite (VPDB)

BCO-DMO Processing Notes
 - Generated from original file: "DATASET-14C.xlsx" contributed by Jesse Farmer
 - Parameter names edited to conform to BCO-DMO naming convention found at Choosing Parameter Name
 - Lat/Lon sampling locations added from locations dataset to allow plotting in MapServer
 - "nd" (no data) added to blank cells

Description from NSF award abstract:
Anthropogenic CO2 enters the ocean in the high latitudes, from where it spreads into the deep ocean interior. Because carbonate ion saturation at greater water depth is generally reduced in the deep ocean, deep-sea corals may be particularly vulnerable to ocean acidification. Efforts are needed to determine the effects of changing seawater chemistry on these ecosystems, and in particular reconstructions of past pH-variations experienced by these corals may help to implement long-term management plans for deep-sea coral reefs. This project will provide new insight into the effect of changing seawater carbonate chemistry and anthropogenic ocean acidification on deep-sea coral reefs. The researchers will calibrate the boron isotope and B/Ca paleo-pH proxies in several species of modern and cultured deep-sea corals. The resulting proxy calibrations will be used to interpret the boron isotope composition of live collected and fossil deep-sea corals with regard to past ocean pH changes. Live collected corals from the North Atlantic and Southern Ocean will provide ultra-high resolution temporal records of anthropogenic CO2 invasion at intermediate depths. Radiometrically dated corals from the same locations will be used to document pH changes in the deep ocean over the last deglaciation. Comparison of paleo-pH with already established changes in coral species composition will allow interpretation of coral sensitivity to ocean acidification. The project will also improve paleo-pH reconstructions by cross- calibrating the principal techniques of boron isotope analysis.

Related Reference:
Hoenisch_ocean_acidification_2010