Benthic marine calcifiers coexist with CaCO3-undersaturated seawater worldwide

• Published in: Global Biogeochemical Cycles
• Main Authors: Lebrato, M., Andersson, A.J., Ries, J.B., Aronson, R.B., Lamare, L.B., Koeve, W., Oschlies, A., Iglesias-Rodriguez, M.D., Thatje, S., Amsler, M., Vos, S., Jones, D.O.B., Ruhl, H.A., Gates, A.R., McClintock, J.B.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2016
• Subjects: Ocean acidification
• Online Access: http://nora.nerc.ac.uk/id/eprint/513700/; https://nora.nerc.ac.uk/id/eprint/513700/7/Lebrato_et_al-2016-Global_Biogeochemical_Cycles.pdf; https://doi.org/10.1002/2015GB005260

Ocean acidification and decreasing seawater saturation state with respect to calcium carbonate (CaCO3) minerals have raised concerns about the consequences to marine organisms, especially those building structures made of CaCO3. A large proportion of benthic marine calcifiers incorporate Mg2+ into their calcareous structures (i.e., Mg-calcite) which, in general, reduces mineral stability. The vulnerability of some marine calcifiers to ocean acidification is related to the solubility of their calcareous structures, but not all marine organisms conform to this because of sophisticated biological and physiological mechanisms to construct and maintain CaCO3 structures. Few studies have considered seawater saturation state with respect to species-specific mineralogy in evaluating the effect of ocean acidification on marine organisms. Here, a global dataset of skeletal mol % MgCO3 of benthic calcifiers and in situ environmental conditions (temperature, salinity, pressure, and [CO32-]) spanning a depth range of 0 m (subtidal/neritic) to 5500 m (abyssal) was assembled to calculate in situ seawater saturation states with respect to species-specific Mg-calcite mineral compositions (?Mg-x). Up to 20% of all studied calcifiers at depths <1200 m and approximately 90% of calcifiers at depths >1200 m currently experience seawater mineral undersaturation with respect to their skeletal mineral phase (?Mg-x<1). We conclude that as a result of predicted anthropogenic ocean acidification over the next 150 years, the predicted decrease in seawater mineral saturation, will expose approximately 50% (<1200 m) and 100% (>1200 m) of all studied calcifying species to seawater undersaturation. These observations underscore concerns over the ability of marine benthic calcifiers to continue to construct and maintain their calcareous structures under these conditions. We advocate that ocean acidification tipping points can only be understood by assessing species-specific responses, and because of different seawater ?Mg-x ...