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Biogeosciences
202411202411
Orbital timescale CaCO3 burial and dissolution changes off the Chilean margin in the subantarctic Pacific over the past 140 kyr
Kasuya T, Okazaki Y, Iwasaki S, Nagashima K, Kimoto K, Frank F, Hagemann JR, Lembke-Jene L, Helge W. Arz HW, Murayama M, Lange CB, Harada NTakuto Kasuya, Yusuke Okazaki, Shinya Iwasaki, Kana Nagashima, Katsunori Kimoto, Frank Lamy, Julia R. Hagemann, Lester Lembke-Jene, Helge W. Arz, Masafumi Murayama, Carina B. Lange, Naomi Harada
Carbonate compensation, CaCO3 dissolution events, Southern Ocean, MIS 5, Last glacial cycle, XRF core scanning, Planktic foraminifera
Schematic diagram of deep water influences on the glacial/interglacial CaCO3 burial variations in the Southern Ocean. a Interglacials and b glacials. Arrows indicate deep waters and their color show the relative [CO32−] concentrations. Water masses abbreviations: LCDW, Lower Circumpolar Deep Water; NADW, North Atlantic Deep Water; PDW, Pacific Deep Water; and W-AABW, Weddell Sea-sourced Antarctic Bottom Water. Plotted symbols show the coring sites with orange of the Indo-Pacific-like and blue of the Atlantic-like pattern (details in Sect. 4.3 of the main text).
Calcium carbonate (CaCO3) dissolution at the Southern Ocean seafloor has hypothetically contributed to lowering the atmospheric carbon dioxide concentration by increasing ocean alkalinity during glacial periods. We present new CaCO3 burial and dissolution records from two sediment cores obtained off the Chilean margin in the subantarctic SE Pacific and covering the past 140 kyr since Marine Isotope Stage (MIS) 6. These records include CaCO3 contents and mass accumulation rates, and microfossil-based analysis results, including fragmentation ratios, sieve-based weights (SBWs), and ultrastructural observations of planktic foraminiferal tests. Our bulk CaCO3-based analyses and Globorotalia inflata SBWs revealed three major CaCO3 dissolution events during colder stages of MIS 5d and 5b and at the MIS 5/4 boundary that are traceable events in the eastern South Pacific along the Chilean margin and in the Drake Passage. Furthermore, CaCO3 burial exhibited pronounced glacial/interglacial fluctuations, with almost no burial during glacials (MIS 6, 4, 3, and 2) and recovery during interglacials (MIS 5e and 1) and early glacials (MIS 5d–a). This pattern agrees with previous observations over a wide area of the Southern Ocean, except in the deep Cape Basin > 4600 m in the South Atlantic Ocean. Considering that our sites were located upstream of the Drake Passage, the Circumpolar Deep Water, which was influenced by carbon-rich Pacific Deep Water, likely propagated from the subantarctic eastern Pacific to the South Atlantic at least at depths of ~ 3000 to ~ 4000 m and decreased CaCO3 burial during glacials. These findings supported the importance of carbonate compensation in the Southern Ocean for the carbon cycle on the glacial/interglacial timescale.
