Carbonate deposition and benthicδ13C in the subarctic Pacific: implications for changes of the oceanic carbonate system during the past 750,000 years

• Published in: Earth and Planetary Science Letters
• Main Authors: Zahn, Rainer, Rushdi, Ahmed, Pisias, Nicklas G., Bornhold, Brian D., Blaise, Bertrand, Karlin, Robert
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 1991
• Subjects: Pacific; North Atlantic; Subarctic
• Online Access: https://oceanrep.geomar.de/id/eprint/33465/; https://oceanrep.geomar.de/id/eprint/33465/1/Zahn1.pdf; https://doi.org/10.1016/0012-821X(91)90154-A

Carbonate deposition at two core sites in the subarctic Pacific (48°N, 133°W; 2.9 km and 3.7 km water depth) follows the standard Pacific carbonate cycles, with glacial values being increased over interglacial values. Benthicδ13C follows the global trend; that is, glacial values are more negative than interglacial values. Comparison with the benthicδ13C record of North Atlantic DSDP Site 552 (56°N, 23°W; 2.3 km water depth) shows the North Pacific records to be nearly in phase with and continuously more negative relative to the North Atlantic record. This suggests that concentrations of∑CO2(org) were permanently higher in the North Pacific than in the North Atlantic during the past 750,000 years conceivably supporting the hypothesis that there was no deep-water forming in the late Pleistocene North Pacific. Whereas one would expect that the North Pacific deep waters were continuously more corrosive to carbonates than deep waters in the North Atlantic, carbonate deposition at the deep North Pacific core sites is enhanced during glacial periods, and occasionally higher than at shallow North Atlantic Site 552 even though Site 552 was probably above lysocline-depth during most of the late Pleistocene. This apparent paradox can be resolved only by invoking an increase in alkalinity in the glacial North Pacific which would have increased the degree of carbonate ion saturation and thereby improved the state of carbonate preservation.