In Situ Techniques for Measuring Carbonate Chemistry in Deep-Sea Pore Waters
In Situ Techniques for Measuring Carbonate Chemistry in Deep-Sea Pore Waters
Abstract:
An expanding human population directly influences increasing carbon dioxide emissions, which
is the principal contributor to anthropogenic climate change. These changes are now being felt in
environments as deep as the ocean's floor. Ocean acidification and warming are impacting the
carbonate chemistry of deep-sea sediments, and understanding the fluxes of dissolved inorganic
carbon (DIC) and alkalinity in and out of sediments, specifically via reactions that occur in pore
water, will help to show the role of sediments and their potential to mitigate rising pCO2. The
typical method of analyzing pore water, by collecting a sediment core and extracting pore water
once brought to the surface, has inherent artifacts associated with extreme pressure and
temperature changes while pore water is still interacting with sediment. To address this issue, we
have built a device to collect pore water in situ, where a more pristine sample can be obtained
and later tested for select carbonate chemistry parameters. This method allows for better-
preserved integrity of pore water constituents, as well as for in situ carbonate dissolution
experimentation. From the pore water, DIC and alkalinity data are modeled via diffusion-
advection-reaction equations and dissolution fluxes derived. δ13C is also measured to inform on
the source of DIC, whether organic or inorganic. In addition to extracting pore water, our device
is also equipped to perform a dissolution experiment in situ. This will show if carbonate grains
can dissolve in presumed pockets of undersaturation, even if the environment is primarily
supersaturated. This dissolution potential is critical to evaluating the natural capacity of minerals
at the seafloor to sequester anthropogenic CO2. Laboratory tests show this is possible, and we
will soon test this in the field. We will present data from the lab, as well as from field tests in the
San Pedro Basin off the coast of Los Angeles, that show the ability of our device to perform as
expected and the possibility of enhanced carbonate dissolution beyond what has previously been
predicted.
is the principal contributor to anthropogenic climate change. These changes are now being felt in
environments as deep as the ocean's floor. Ocean acidification and warming are impacting the
carbonate chemistry of deep-sea sediments, and understanding the fluxes of dissolved inorganic
carbon (DIC) and alkalinity in and out of sediments, specifically via reactions that occur in pore
water, will help to show the role of sediments and their potential to mitigate rising pCO2. The
typical method of analyzing pore water, by collecting a sediment core and extracting pore water
once brought to the surface, has inherent artifacts associated with extreme pressure and
temperature changes while pore water is still interacting with sediment. To address this issue, we
have built a device to collect pore water in situ, where a more pristine sample can be obtained
and later tested for select carbonate chemistry parameters. This method allows for better-
preserved integrity of pore water constituents, as well as for in situ carbonate dissolution
experimentation. From the pore water, DIC and alkalinity data are modeled via diffusion-
advection-reaction equations and dissolution fluxes derived. δ13C is also measured to inform on
the source of DIC, whether organic or inorganic. In addition to extracting pore water, our device
is also equipped to perform a dissolution experiment in situ. This will show if carbonate grains
can dissolve in presumed pockets of undersaturation, even if the environment is primarily
supersaturated. This dissolution potential is critical to evaluating the natural capacity of minerals
at the seafloor to sequester anthropogenic CO2. Laboratory tests show this is possible, and we
will soon test this in the field. We will present data from the lab, as well as from field tests in the
San Pedro Basin off the coast of Los Angeles, that show the ability of our device to perform as
expected and the possibility of enhanced carbonate dissolution beyond what has previously been
predicted.