%0 Journal Article %T A record of Neogene seawater 汛¹¹B reconstructed from paired 汛¹¹B analyses on benthic and planktic foraminifera %A Chalk %A Thomas B. %A Foster %A Gavin L. %A Goodwin %A Philip %A Greenop %A Rosanna %A Hain %A Mathis P. %A Lear %A Caroline H. %A Oliver %A Kevin I. C. %A Sosdian %A Sindia M. %A Wilson %A Paul A. %J - %D 2017 %R https://doi.org/10.5194/cp-13-149-2017 %X

Abstract. The boron isotope composition (汛¹¹B) of foraminiferal calcite reflects the pH and the boron isotope composition of the seawater the foraminifer grew in. For pH reconstructions, the 汛¹¹B of seawater must therefore be known, but information on this parameter is limited. Here we reconstruct Neogene seawater 汛¹¹B based on the 汛¹¹B difference between paired measurements of planktic and benthic foraminifera and an estimate of the coeval water column pH gradient from their 汛¹³C values. Carbon cycle model simulations underscore that the 忖pH每忖汛¹³C relationship is relatively insensitive to ocean and carbon cycle changes, validating our approach. Our reconstructions suggest that 汛¹¹B_sw was ˋ‵ˋˋ37.5ˋ㏑ during the early and middle Miocene (roughly 23每12ˋMa) and rapidly increased during the late Miocene (between 12 and 5 Ma) towards the modern value of 39.61ˋ㏑. Strikingly, this pattern is similar to the evolution of the seawater isotope composition of Mg, Li and Ca, suggesting a common forcing mechanism. Based on the observed direction of change, we hypothesize that an increase in secondary mineral formation during continental weathering affected the isotope composition of riverine input to the ocean since 14ˋMa.