Deep-water carbonate concentrations in the southwest Pacific

We have compiled carbonate chemistry and sedimentary CaCO₃% data for the deep-waters (>1500m water depth) of the southwest (SW) Pacific region. The complex topography in the SW Pacific influences the deep-water circulation and affects the carbonate ion concentration [Formula: see text] , and the associated calcite saturation horizon (CSH, where Ωcₐₗcᵢₜₑ=1). The Tasman Basin and the southeast (SE) New Zealand region have the deepest CSH at ∼3100m, primarily influenced by middle and lower Circumpolar Deep Waters (m or lCPDW), while to the northeast of New Zealand the CSH is ∼2800m, due to the corrosive influence of the old North Pacific deep waters (NPDW) on the upper CPDW (uCPDW). The carbonate compensation depth (CCD; defined by a sedimentary CaCO₃ content of <20%), also varies between the basins in the SW Pacific. The CCD is ∼4600m to the SE New Zealand, but only ∼4000m to the NE New Zealand. The CaCO₃ content of the sediment, however, can be influenced by a number of different factors other than dissolution; therefore, we suggest using the water chemistry to estimate the CCD. The depth difference between the CSH and CCD (ΔZCSH₋CCD), however, varies considerably in this region and globally. The global ΔZCSH₋CCD appears to expand with increase in age of the deep-water, resulting from a shoaling of the CSH. In contrast the depth of the chemical lysocline (Ωcₐₗcᵢₜₑ=0.8) is less variable globally and is relatively similar, or close, to the CCD determined from the sedimentary CaCO₃%. Geochemical definitions of the CCD, however, cannot be used to determine changes in the paleo-CCD. For the given range of factors that influence the sedimentary CaCO₃%, an independent dissolution proxy, such as the foraminifera fragmentation % (>40%=foraminiferal lysocline) is required to define a depth where significant CaCO₃ dissolution has occurred back through time. The current foraminiferal lysocline for the SW Pacific region ranges from 3100–3500m, which is predictably just slightly deeper than the CSH. This compilation of sediment and water chemistry data provides a CaCO₃ dataset for the present SW Pacific for comparison with glacial/interglacial CaCO₃ variations in deep-water sediment cores, and to monitor future changes in [ [Formula: see text] ] and dissolution of sedimentary CaCO₃ resulting from increasing anthropogenic CO₂.