The relationship between pore water carbon isotopic composition and bottom water oxygen concentration

Abstract

We present pore water δ 13C profiles from the Western North Atlantic and the Eastern Pacific oceans, and interpret them using a stoichiometric model of the relationship between carbon isotopic composition and oxygen concentration. Pore water δ 13C at the depth in the sediments where oxygen approaches zero is largely determined by the oxygen concentration of the overlying bottom water, although sulfate reduction adds a significant amount of isotopically light carbon at some locations. The δ 13C difference between bottom water and pore water at O 2 = 0 (“Δδ 13C”) increases from 1 %. in sediments of three low bottom water oxygen basins in the Southern California Borderlands to 4%. in sediments underlying well oxygenated water in the Western North Atlantic. We suggest that the relationship between bottom water oxygen and Δδ 13C could form the basis for a new way to use the benthic foraminifera δ 13C record to estimate bottom water oxygen concentration. Paleo-oxygen values derived from a pair of benthic foraminifera species which record the bottom water/pore water ( O 2 = 0) δ 13C difference will be independent of the preformed δ 13C of the deep water mass.