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Foraminiferal radiocarbon record of northeast Pacific decadal subsurface variability
Author(s) -
Roach Lydia D.,
Charles Christopher D.,
Field David B.,
Guilderson Thomas P.
Publication year - 2013
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/jgrc.20274
Subject(s) - benthic zone , radiocarbon dating , geology , oceanography , foraminifera , total organic carbon , upwelling , dissolved organic carbon , sediment , sedimentary rock , carbon fibers , paleontology , chemistry , environmental chemistry , materials science , composite number , composite material
The decadal dynamics of the subsurface North Pacific Ocean are largely inaccessible beyond sparse instrumental observations spanning the last 20 years. Here we present a ∼200 year long record of benthic foraminiferal radiocarbon (Δ 14 C), extracted at biennial resolution from the annually laminated sediments at the Santa Barbara Basin (SBB) depocenter (∼600 m). The close match between core top benthic foraminiferal Δ 14 C values and the Δ 14 C of seawater dissolved inorganic carbon (DIC) suggests that benthic foraminifera faithfully capture the bottom water radiocarbon concentrations, as opposed to that of the deeper (>0.5 cm) sediment porewater zone. The full time series of benthic foraminiferal Δ 14 C displays significant variability on decadal timescales, with excursions on the order of 40‰. These excursions are overprinted by a unidirectional trend over the late 20th century that likely reflects the sedimentary incorporation of bomb radiocarbon (via remineralized particulate organic carbon). We isolate this trend by means of a one‐dimensional oxidation model, which considers the possible contribution of remineralized particles to the total ambient carbon pool. This oxidation model also considers the possible influence of carbon with a variety of sources (ages). Though variable oxidation of preaged carbon could exert a strong influence on benthic foraminiferal radiocarbon variability, the totality of evidence points to the vertical density structure along the Southern California Margin (SCM) as the primary driver of the SBB benthic foraminiferal Δ 14 C record. For example, intervals characterized by significantly lower Δ 14 C values correspond to periods of enhanced upwelling and subsurface equatorward flow along the SCM.