Deep-water carbonate concentrations in the southwest Pacific

We have compiled carbonate chemistry and sedimentary CaCO3% data for the deep-waters (> 1500 m 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 ([CO32-]), and the associated calcite saturation horizon (CSH, where Omega(calcite)=1). The Tasman Basin and the southeast (SE) New Zealand region have the deepest CSH at similar to 3100 m, primarily influenced by middle and lower Circumpolar Deep Waters (m or ICPDW), while to the northeast of New Zealand the CSH is similar to 2800 m, 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 4600 m to the SE New Zealand, but only similar to 4000 m 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 (Delta Z(CSH-CCD)), however, varies considerably in this region and globally. The global Delta Z(CSH)-(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 (Omega(calcite) = 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 3100-3500 m, 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 [CO32-] and dissolution of sedimentary CaCO3 resulting from increasing anthropogenic CO2. (C) 2010 Elsevier Ltd. All rights reserved.