Ocean Deoxygenation Conference | Kiel 2018

Intermediate waters (500 - 2000 m) from the equatorial- to North Pacific are currently hypoxic (oxygen concentrations below 120 µmol/kg), while deeper waters are well oxygenated. For the last ice-age, proxy records suggest that this trend was reversed, with well-oxygenated Pacific intermediate waters, and lower oxygenated deeper waters associated with an increased deep carbon reservoir. Here we assess changes in bottom water oxygen concentrations at an intermediate water depth from the eastern equatorial Pacific (site ODP 1242, 1360 m depth) over the last 140,000 years, to test whether intermediate water oxygen concentrations increased during glacial intervals (e.g. Marine Isotope Stages 2 and 4). We use the carbon isotope gradient between bottom water (recorded by epifaunal benthic foraminifera Cibicidoides wuellerstorfi) and pore water at the anoxic boundary (recorded by infaunal Globobulimina spp.) as a quantitatively proxy to reconstruct intermediate water oxygen concentrations at this site, following the approach of Hoogakker et al. (2015).