Southern Ocean carbonate dissolution paced by Antarctic Ice-Sheet expansion in the early Miocene

Abstract The preservation of calcium carbonate deposits on the seafloor is one of the factors that regulates Earth's carbon cycle over longer timescales. Fluctuations in the carbonate compensation depth (CCD), the depth below which calcium carbonate is completely dissolved, can therefore significantly alter the ocean's capacity to sequester or release atmospheric carbon. High-latitude deep oceans are particularly important to the carbon cycle given their large capacity to store carbon dioxide. Here we present carbonate content results from an abyssal Subantarctic record (Site U1514) that spans the early Miocene and the onset of the Miocene Climatic Optimum. We show that carbonate preservation was highly variable from 19.9 to 17 Ma, with multiple episodes of total carbonate dissolution. Carbonate preservation then improved gradually after 17 Ma following the onset of the Miocene Climatic Optimum. Episodes of carbonate dissolution occurred preferentially at long eccentricity minima while periods of long eccentricity maxima improved carbonate preservation. These patterns of carbonate accumulation are in opposite phase to lower latitude Atlantic and Pacific records, which suggests that different mechanisms of carbonate accumulation/preservation were in place in high and low-latitude oceans. Comparison of Site U1514 with Antarctic records indicates an influence of ice sheet oscillations on carbonate preservation at the Subantarctic seafloor. We propose that carbonate dissolution occurred via the northward expansion of southern-derived undersaturated waters during periods of Antarctic ice sheet expansion. These findings indicate that the Subantarctic Southern Ocean was highly sensitive to Antarctic ice sheet fluctuations during the early Miocene, consistent with observations from Antarctica that show intensified polar amplification under a warmer climate.