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

Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Quaternary Science Reviews 125 (2015): 144-159, doi:10.1016/j.quascirev.2015.08.010.A paleo-data compilation with 492 δ13C and δ18O observations provides the opportunity to better sample the Last Glacial Maximum (LGM) and infer its global properties, such as the mean δ13C of dissolved inorganic carbon. Here, the paleocompilation is used to reconstruct a steady-state water-mass distribution for the LGM, that in turn is used to map the data onto a 3D global grid. A global-mean marine δ13C 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 δ13C is estimated to be 0:14h±0:20h at the two standard error level, giving a glacial-to-modern change of 0:32h±0:20h. 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 0:1h, emphasizing that knowledge of the circulation is vital to accurately map δ13CDIC in three dimensions.GG is supported by NSF grants OIA-1124880 and OCE-1357121, the WHOI Ocean and Climate Change Institute, and The Joint Initiative Awards Fund from the Andrew W. Mellon Foundation

Benthic foraminiferal stable carbon isotope constraints on deglacial ocean circulation and carbon-cycle changes

How does deep-ocean circulation influence atmospheric CO2 across deglacial transitions? Although biogeochemical and physical processes complicate interpretation of foraminiferal stable carbon isotope data, these complications can be addressed with expanded data compilations, multiproxy approaches, and model-data assimilation efforts.Fil: Peterson, Carlye D.. University of California Riverside; Estados UnidosFil: Gebbie, G.. Woods Hole Oceanographic Institution; Estados UnidosFil: Lisiecki, L. E.. University of California Santa Barbara; Estados UnidosFil: Lynch Stieglitz, J.. School of Earth and Atmospheric Sciences; Estados UnidosFil: Oppo, D.. Woods Hole Oceanographic Institution; Estados UnidosFil: Muglia, Juan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Repschläger, Janne. Max Planck Institute for Chemistry; AlemaniaFil: Schmittner, A.. University of Oregon; Estados Unido

Orbital- to sub-orbital-scale cyclicity in seismic reflections and sediment character in early Pleistocene mudstone, Santa Barbara, California

High-resolution seismic reflection records from the Santa Barbara basin suggest that much of the early Pleistocene hemipelagic sedimentary sequence records climate variability on orbital to sub-orbital scales, much like strata of the last glacial cycle studied at ODP Site 893. This thesis develops and tests a new method to extract lithologic cyclicity from high-resolution marine seismic reflection data (towed chirp) collected on the R/V Melville in 2008 that penetrate 10's of meters below seafloor into a ∼1 km-long sequence of south-dipping seismic reflections. Spectral analysis of these data reveals orbital-scale cyclicity in Pleistocene sediments that shifts to higher frequencies at the location of an unconformity. This analysis suggests that acoustic impedance and physical properties of sediment are controlled by climatically-driven oscillations in lithologic composition and fabric during deposition. Furthermore, shifts in spectral character permit identification of unconformities and changes in sedimentation rate prior to physical sampling by core. Cyclostratigraphic analysis of sedimentary sequences usually requires measurement of geochemical proxies on sediment material recovered from coring or drilling efforts which can be expensive and time-consuming. Seismic reflection data are a remotely sensed record of acoustic impedance contrasts in sediments which vary with sediment density and velocity changes imparted by organic matter fluctuations which are controlled by climate oscillations. With sufficient resolution, this method could allow remote detection of sedimentary cycles imparted by climate forces without retrieving sediments. Paleoclimatologically significant, orbital-scale cycles have been detected in marine seismic reflection data from the outer California Continental Borderland basins (Janik et al., 2004), Mediterranean outflow contourites (Llave et al., 2006), and the Cape Basin off southwest Africa (Weigelt and Uenzelmann-Neben, 2007). In Santa Barbara basin, where sediment character is documented to be sensitive to climatic variation at a sub-millennial scale, strata older than 1 Ma have been uplifted to the surface. These Pleistocene-age sediments dip to the south at ∼30° allowing for short core recovery and acquisition of high-resolution seismic reflection data at a constant shallow depth. Due to consistently high sedimentation rates in the basin (0.1-1 m/kyr), high-resolution seismic data such as the towed chirp seismic reflection data acquired on the 2008 R/V Melville Cruise allows detection of cycles as fine as ∼4 kyrs. Mid-way through the seismic section, an abrupt shift in spectral character illuminates the location of an otherwise unnoticeable unconformity, and the magnitude of the shift to lower frequencies suggests a sedimentation rate increase of ∼0.06 m/kyr. This method can be used to help with coring expeditions, to identify uninterrupted sedimentary successions for cyclic analysis, and to locate discontinuities in the sedimentary record

Deglacial carbon cycle is observed in a compilation of 127 benthic delta C-13 time series (20-6 ka)

Abstract. We present a compilation of 127 time series δ13C records from Cibicides wuellerstorfi spanning the last deglaciation (20–6 ka) which is well-suited for reconstructing large-scale carbon cycle changes, especially for comparison with isotope-enabled carbon cycle models. The age models for the δ13C records are derived from regional planktic radiocarbon compilations (Stern and Lisiecki, 2014). The δ13C records were stacked in nine different regions and then combined using volume-weighted averages to create intermediate, deep, and global δ13C stacks. These benthic δ13C stacks are used to reconstruct changes in the size of the terrestrial biosphere and deep ocean carbon storage. The timing of change in global mean δ13C is interpreted to indicate terrestrial biosphere expansion from 19–6 ka. The δ13C gradient between the intermediate and deep ocean, which we interpret as a proxy for deep ocean carbon storage, matches the pattern of atmospheric CO2 change observed in ice core records. The presence of signals associated with the terrestrial biosphere and atmospheric CO2 indicates that the compiled δ13C records have sufficient spatial coverage and time resolution to accurately reconstruct large-scale carbon cycle changes during the glacial termination

Deglacial carbon cycle changes observed in a compilation of 127 benthic δ13C time series (20–6 ka)

We present a compilation of 127 time series δ13C records from Cibicides wuellerstorfi spanning the last deglaciation (20–6 ka) which is well-suited for reconstructing large-scale carbon cycle changes, especially for comparison with isotope-enabled carbon cycle models. The age models for the δ13C records are derived from regional planktic radiocarbon compilations (Stern and Lisiecki, 2014). The δ13C records were stacked in nine different regions and then combined using volume-weighted averages to create intermediate, deep, and global δ13C stacks. These benthic δ13C stacks are used to reconstruct changes in the size of the terrestrial biosphere and deep ocean carbon storage. The timing of change in global mean δ13C is interpreted to indicate terrestrial biosphere expansion from 19–6 ka. The δ13C gradient between the intermediate and deep ocean, which we interpret as a proxy for deep ocean carbon storage, matches the pattern of atmospheric CO2 change observed in ice core records. The presence of signals associated with the terrestrial biosphere and atmospheric CO2 indicates that the compiled δ13C records have sufficient spatial coverage and time resolution to accurately reconstruct large-scale carbon cycle changes during the glacial termination

Deglacial carbon cycle changes observed in a compilation of 127 benthic δ¹³C time series (20-6 ka)

We present a compilation of 127 time series δ¹³C records from Cibicides wuellerstorfi spanning the last deglaciation (20-6 ka) which is well-suited for reconstructing large-scale carbon cycle changes, especially for comparison with isotope-enabled carbon cycle models. The age models for the δ¹³C records are derived from regional planktic radiocarbon compilations (Stern and Lisiecki, 2014). The δ¹³C records were stacked in nine different regions and then combined using volume-weighted averages to create intermediate, deep, and global δ¹³C stacks. These benthic δ¹³C stacks are used to reconstruct changes in the size of the terrestrial biosphere and deep ocean carbon storage. The timing of change in global mean δ¹³C is interpreted to indicate terrestrial biosphere expansion from 19-6 ka. The δ¹³C gradient between the intermediate and deep ocean, which we interpret as a proxy for deep ocean carbon storage, matches the pattern of atmospheric CO₂ change observed in ice core records. The presence of signals associated with the terrestrial biosphere and atmospheric CO₂ indicates that the compiled δ¹³C records have sufficient spatial coverage and time resolution to accurately reconstruct large-scale carbon cycle changes during the glacial termination