Patterns and magnitude of deep sea carbonate dissolution during Eocene Thermal Maximum 2 and H2, Walvis Ridge, southeastern Atlantic Ocean

Eocene Thermal Maximum 2 (ETM2 or H1; similar to 53.7 Ma) represents a short-lived warming episode, associated with the injection of a large mass of C-13-depleted carbon into the ocean-atmosphere system. The mass of injected carbon, the extent of deep sea dissolution, and the amount of warming during ETM2 appear to be approximately half of those documented for the Paleocene-Eocene thermal maximum (PETM, similar to 55.5 Ma), but the pattern of lysocline migration during ETM2 has not yet been documented sufficiently to decipher potential differences in carbon sources and sequestration mechanisms. We present high-resolution carbonate dissolution and bulk stable isotope records across ETM2 and the successive H2 event (similar to 53.6 Ma) on a common age model for four sites along the Walvis Ridge depth transect (1500 to 3600 m paleowater depth) to assess lysocline evolution. The onset of ETM2 is characterized by multiple, depth-dependent transitions of carbonate dissolution (up to similar to 96% of the total flux), associated with rapid depletions in bulk carbonate carbon (up to similar to 1-1.5%) and oxygen (up to similar to 0.7-1.5%) isotope values. H2 shows a similar to 0.7% negative carbon isotope excursion, with a coeval decrease in delta O-18 of similar to 0.5% and similar to 80% of carbonate dissolution. During ETM2, the lysocline recovered within similar to 30 ka. We attribute this rapid recovery to terrestrial CaCO3 neutralization through enhanced chemical weathering of carbonates in soils and rocks. According to theory, carbonate dissolution was lower after recovery than prior to ETM2, indicating carbonate ion oversaturation and a deeper position of the lysocline. Spectral analysis indicates that the changes in carbonate dissolution and delta C-13 values were precession paced, implying that weathering feedbacks and short-term perturbations in the carbon cycle were important in determining early Eocene background and hyperthermal ocean [CO32-] conditions.