A record of Neogene seawater δ11B reconstructed from paired δ11B analyses on benthic and planktic Foraminifera

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doi: 10.5194/cp-13-149-2017
Author(s): Greenop, Rosanna; Hain, Mathis P.; Sosdian, Sindia M.; Oliver, Kevin I. C.; Goodwin, Philip; Chalk, Thomas B.; Lear, Caroline H.; Wilson, Paul A.; Foster, Gavin L.
Author Affiliation(s): Primary:
University of Southampton, National Oceanography Centre Southampton, Southampton, United Kingdom
Other:
Cardiff University, United Kingdom
Volume Title: Climate of the Past
Source: Climate of the Past, 13(2), p.149-170. Publisher: Copernicus, Katlenburg-Lindau, International. ISSN: 1814-9324
Note: In English. 113 refs.; illus., incl. 3 tables
Summary: The boron isotope composition (δ11B) of foraminiferal calcite reflects the pH and the boron isotope composition of the seawater the foraminifer grew in. For pH reconstructions, the δ11B of seawater must therefore be known, but information on this parameter is limited. Here we reconstruct Neogene seawater δ11B based on the δ11B difference between paired measurements of planktic and benthic foraminifera and an estimate of the coeval water column pH gradient from their δ13C values. Carbon cycle model simulations underscore that the ΔpH-Δδ13C relationship is relatively insensitive to ocean and carbon cycle changes, validating our approach. Our reconstructions suggest that δ11Bsw was ∼ 37.5 ppm during the early and middle Miocene (roughly 23-12 Ma) and rapidly increased during the late Miocene (between 12 and 5 Ma) towards the modern value of 39.61 ppm. 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 14 Ma.
Year of Publication: 2017
Research Program: ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 12 Stratigraphy, Historical Geology and Paleoecology; Air-sea interface; Alkali metals; Alkaline earth metals; Atlantic Ocean; B-11/B-10; Benthic taxa; Boron; Bottom water; C-13/C-12; CYCLOPS model; Ca-44/Ca-40; Calcite; Calcium; Carbon; Carbon cycle; Carbon dioxide; Carbonates; Caribbean Sea; Ceara Rise; Cenozoic; Chemical composition; Colombian Basin; Controls; Data processing; Depth; Equatorial Atlantic; Foraminifera; Geochemical cycle; Indian Ocean; Indicators; Invertebrata; Isotope fractionation; Isotope ratios; Isotopes; Leg 121; Leg 122; Leg 154; Leg 165; Li-7/Li-6; Lithium; Magnesium; Metals; Mg-26/Mg-24; Microfossils; Miocene; Monte Carlo analysis; Neogene; Ninetyeast Ridge; North Atlantic; ODP Site 758; ODP Site 761; ODP Site 926; ODP Site 999; Ocean Drilling Program; PH; Planktonic taxa; Pleistocene; Pliocene; Protista; Quaternary; Reconstruction; Sea surface water; Sea water; Secondary minerals; Sensitivity analysis; Spatial variations; Stable isotopes; Statistical analysis; Stream transport; Tertiary; Transport; Uncertainty; Weathering; Wombat Plateau
Coordinates: N052302 N052303 E0902141 E0902140
N124437 N124437 W0784422 W0784422
N034309 N034309 W0425430 W0425430
S164414 S164413 E1153206 E1153206
Record ID: 2017027692
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Copernicus Gesellschaft, Katlenburg-Lindau, Germany