Anthropogenic carbon dioxide emissions do not only warm our planet but
also acidify our oceans. It is currently unclear to which degree Earth's
climate and marine life will be impacted by these changes but
information from Earth history, particularly the geochemical signals of
past environmental changes stored in the fossil remains of marine
organisms, can help us predict possible future changes. This book aims
to be a primer for scientists who seek to apply boron proxies in marine
carbonates to estimate past seawater carbonate chemistry and atmospheric
pCO2.
Boron proxies (δ11B and B/Ca) were introduced nearly three
decades ago, with subsequent strides being made in understanding their
mechanistic functioning. This text reviews current knowledge about the
aqueous systematics, the inorganic and biological controls on boron
isotope fractionation and incorporation into marine carbonates, as well
as the analytical techniques for measurement of boron proxies.
Laboratory and field calibrations of the boron proxies are summarized,
and similarities between modern calibrations are explored to suggest
estimates for proxy sensitivities in marine calcifiers that are now
extinct. Example applications illustrate the potential for
reconstructing paleo-atmospheric pCO2 from boron isotopes.
Also explored are the sensitivity of paleo-ocean acidity and
pCO2 reconstructions to boron isotope proxy systematics that
are currently less well understood, including the elemental and boron
isotopic composition of seawater through time, seawater alkalinity,
temperature and salinity, and their collective impact on the uncertainty
of paleo-reconstructions.
The B/Ca proxy is based on the same mechanistic principles as the boron
isotope proxy, but empirical calibrations suggest seawater pH is not the
only controlling factor. B/Ca therefore has the potential to provide a
second carbonate parameter that could be paired with δ11B to
fully constrain the ocean carbonate system, but the associated
uncertainties are large. This text reviews and examines what is
currently known about the B/Ca proxy systematics. As more scientists
embark on characterizing past ocean acidity and atmospheric
pCO2, Boron in Paleoceanography and Paleoclimatology provides
a resource to introduce geoscientists to the opportunities and
complications of boron proxies, including potential avenues to further
refine them.