Global-mean marine δ13C and its uncertainty in a glacial state estimate

Abstract

A paleo-data compilation with 492 δ 13 C and δ 18 O observations provides the opportunity to better sample the Last Glacial Maximum (LGM) and infer its global properties, such as the mean δ 13 C of dissolved inorganic carbon. Here, the paleocompilation is used to reconstruct a steady-state water-mass distribution for theLGM, that in turn is used to map the data onto a 3D global grid. A global-mean marine δ 13 C value and a self-consistent uncertainty estimate are derived using the framework of state estimation (i.e., combining a numerical model and observations). The LGM global-mean δ 13 C is estimated to be 0.14 ± 0.20 at the two standard error level, giving a glacial-to-modern change of 0.32 ± 0.20 .The magnitude of the error bar is attributed to the uncertain glacial ocean circulation and the lack of observational constraints in the Pacific, Indian, and Southern Oceans. Observations in the Indian and Pacific Oceans generally have 10 times the weight of an Atlantic point in the computation of the global mean. To halve the error bar, roughly four times more observations are needed, although strategic sampling may reduce this number. If dynamical constraints can be used to better characterize the LGM circulation, the error bar can also be reduced to 0.05 to Preprint submitted to Quaternary Science Reviews August 5, 2015 0.1 , emphasizing that knowledge of the circulation is vital to accurately map δ 13 C DIC in three dimensions.

Carbon isotope evidence for a northern source of deep water in the glacial western North Atlantic

“…We interpret C isotopes in benthic foraminifera as quasi-conservative tracers for paleocirculation (5), although the data could reflect, in part, remineralization of biogenic C (13). The most recent analysis by Gebbie et al (14) indicates that remineralization is less significant than previously thought, in essential agreement with Marchal and Curry (15), who estimated that organic matter remineralization makes little contribution today to the δ 13 C of ΣCO 2 in the deep (>1 km) Atlantic. From Carolina Slope sites (1 km to 2 km water depth), δ 13 C steadily decreased down Blake Ridge to 4.2 km (Fig.…”

“…Ventilation estimates based on the difference in conventional 14 C age between pairs of planktonic and benthic foraminifera (or bivalves) ( 14 C B-P ) during the LGM are consistent with the δ 13 C data (Fig. 3B).…”

“…2B). Chronology of 17GGC is based on 11 accelerator mass spectrometer (AMS) 14 C dates on the planktonic foraminifer Globorotalia inflata (Dataset S2), and linear interpolation assuming zero age at the core top. Ages are calibrated years before present, with only the standard 400-y reservoir correction [CALIB calibration program 6.1 (3)].…”

“…If this new source of bottom water resulted from brine rejection and not heat loss to the atmosphere, there may not have been the same climate impact as modern NADW production. The new deep northern component is indicated by the reversal in C isotope trends to higher δ 13 C and lower 14 C B-P below 4.2 km in the western North Atlantic and more vigorous flow (23). Thus, in this view, water of southern source was sandwiched between glacial North Atlantic intermediate water and the new dense bottom water.…”

Deglacial carbon cycle changes observed in a compilation of 127 benthic <i>δ</i><sup>13</sup>C time series (20–6 ka)

“…Additionally, the Cibicides species C. kullenbergi and C. mundulus, often measured in deep South Atlantic cores, appear to record more depleted δ 13 C values than C. wuellerstorfi (Gottschalk et al, 2016). Mean δ 13 C has been estimated for the Last Glacial Maximum (LGM, 20 ka) and Late Holocene (6-0 ka) using global compilations of Cibicides wuellerstorfi δ 13 C records (e.g., Shackleton, 1977;Duplessy et al, 1988;Curry et al, 1988;Boyle, 1992;Matsumoto and Lynch-Stieglitz, 1999;Curry and Oppo, 2005;Herguera et al, 2010;Oliver et al, 2010;Hesse et al, 2011;Peterson et al, 2014;Gebbie et al, 2015). These time slice studies include as many as 500 core sites, but generally undersample portions of the ocean with poor carbonate preservation, low primary productivity, and low sedimentation rates (i.e., the Southern Ocean south of 55 • S, the Indian Ocean, and the Pacific Ocean).…”