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

Abstract

Eocene Thermal Maximum 2 (ETM2 or Hl; ∼53.7 Ma) represents a short-lived warming episode, associated with the injection of a large mass of 13C-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, ∼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 (∼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 ∼96% of the total flux), associated with rapid depletions in bulk carbonate carbon (up to ∼l-1.5%o) and oxygen (up to ∼0.7-1.5%o) isotope values. H2 shows a ∼0.7%o negative carbon isotope excursion, with a coeval decrease in δ18O of ∼0.5%o and ∼80% of carbonate dissolution. During ETM2, the lysocline recovered within ∼30 ka. We attribute this rapid recovery to terrestrial CaCu3 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 δ13C 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. Copyright 2009 by the American Geophysical Union.