Earth Institute Research Projects

Ocean Acidification - Category 1: Calibration and Application of the Boron Isotope Seawater-pH Indicator in Deep-water Corals

Lead PI: Dr. Baerbel Hoenisch

Unit Affiliation: Geochemistry, Lamont-Doherty Earth Observatory (LDEO)

September 2010 - August 2016
Global ; Atlantic Ocean ; Pacific Ocean
Project Type: Research

DESCRIPTION: This project funded the validation of boron isotopes, trace metal composition and stable isotopes in deep-sea corals from museum collections, and their application to quantify ocean acidification in recent history.

OUTCOMES: GRA Jesse Farmer calibrated modern specimens for the boron isotope/pH proxy and found that surface skeleton samples broadly correlate with pH as expected from the theoretical basis of the boron isotope proxy. However, intra-skeletal B isotope variability is larger than can be explained by seawater-pH variations alone, hinting at significant vital effects that preclude direct reconstruction of anthropogenic ocean acidification. Complementary carbon and oxygen isotopes are correlated, which supports the presence of kinetic/pH vital effects, which may be the cause of the observed boron isotope variability. Although the main goal of quantifying anthropogenic ocean acidification was not achieved with these corals, the B isotope results provide a new and important dataset for refining the interpretation of the boron isotope pH proxy in corals.


National Science Foundation (NSF)




Jesse Farmer


Bristol University



*Farmer, J.R., B. Hönisch, L.F. Robinson, T.M. Hill, “Investigating the effects of seawater-pH and biomineralization on the boron isotopic composition of deep-sea bamboo corals”, Geochimica et Cosmochimica Acta 155, p. 86-106,

*Farmer, J.R., L.F. Robinson, B. Hönisch, “Growth rate determinations from radiocarbon in bamboo corals (genus Keratoisis)”, Deep Sea Research I, Oceanographic Research Papers 105, 26-40.

*Farmer, J.R., B. Hönisch, J. Uchikawa, “Single laboratory comparison of MC-ICP-MS and N-TIMS boron isotope analyses in marine carbonates”, Chemical Geology 447, P. 173-182,

*Flöter, S., J. Fietzke, J.R. Farmer, M. Gutjahr, B. Hönisch, G. Nehrke, A. Eisenhauer, “Ontogenetic micro-structural constraints towards the potential of bamboo coral Mg/Ca and Ba/Ca to record ambient water temperature and dissolved [Si] and [Ba]”, Geochimica et Cosmochimica Acta 248, p. 43-60,


boron paleopH coral climate change calcium (ca) ocean acidification ph deep sea corals ocean and climate physics carbon dioxide


Modeling and Adapting to Future Climate