Terrestrial carbon storage is dramatically decreased during glacial periods due to cold temperatures, increased aridity, and the presence of large ice sheets on land. Most of the carbon released by the terrestrial biosphere is stored in the ocean, where the light isotopic signature of terrestrial carbon is observed as a 0.32-0.7‰ depletion in benthic foraminiferal δ 13 C. The wide range in estimated δ 13 C change results from the use of different subsets of benthic δ 13 C data and different methods of weighting the mean δ 13 C by volume. We present a more precise estimate of glacial-interglacial δ 13 C change of marine dissolved inorganic carbon using benthic Cibicidoides spp. δ 13 C records from 480 core sites (more than 3 times as many sites as previous studies). We divide the ocean into eight regions to generate linear regressions of regional δ 13 C versus depth for the Late Holocene (0-6 ka) and Last Glacial Maximum (19-23 ka) and estimate a mean δ 13 C decrease of 0.38 ± 0.08‰ (2σ) for 0.5-5 km. Estimating large uncertainty ranges for δ 13 C change in the top 0.5 km, below 5 km, and in the Southern Ocean, we calculate a whole-ocean change of 0.34 ± 0.19‰. This implies a terrestrial carbon change that is consistent with recent vegetation model estimates of 330-694 Gt C. Additionally, we find that a well-constrained surface ocean δ 13 C change is essential for narrowing the uncertainty range of estimated whole-ocean δ 13 C change.

Although detailed age models exist for some marine sediment records of the last glacial cycle (0–150 ka), age models for many cores rely on the stratigraphic correlation of benthic δ18O, which measures ice volume and deep ocean temperature change. The large amount of data available for the last glacial cycle offers the opportunity to improve upon previous benthic δ18O compilations, such as the “LR04” global stack. Not only are the age constraints for the LR04 stack now outdated but a single global alignment target neglects regional differences of several thousand years in the timing of benthic δ18O change during glacial terminations. Here we present regional stacks that characterize mean benthic δ18O change for 8 ocean regions and a volume‐weighted global stack of data from 263 cores. Age models for these stacks are based on radiocarbon data from 0 to 40 ka, correlation to a layer‐counted Greenland ice core from 40 to 56 ka, and correlation to radiometrically dated speleothems from 56 to 150 ka. The regional δ18O stacks offer better stratigraphic alignment targets than the LR04 global stack and, furthermore, suggest that the LR04 stack is biased 1–2 kyr too young throughout the Pleistocene. Finally, we compare global and regional benthic δ18O responses with sea level estimates for the last glacial cycle.

[1] Constraints on the timing of Atlantic meridional overturning circulation (AMOC) changes during the last deglaciation are fundamental to understanding the climate's rapid response to insolation forcing. However, uncertainty about high-latitude North Atlantic (HLNA) radiocarbon reservoir ages has previously precluded robust age model development for this critical region. HLNA reservoir ages also serve as a proxy for AMOC strength. We present regionally averaged HLNA reservoir ages for 0 to 41 thousand years before the present (kyr BP) based on over 500 radiocarbon dates from 33 North Atlantic cores. An early deglacial increase to >1000 14 C yr reservoir ages between 18.5 and 16.5 kyr BP suggests reduced AMOC before peak Heinrich Stadial 1 (HS1) ice-rafted debris (IRD). A rapid decrease in reservoir ages coincident with the IRD maximum at 16 kyr BP indicates strong stratification of the upper water column caused by massive freshwater release.Citation: Stern, J. V., and L. E. Lisiecki (2013), North Atlantic circulation and reservoir age changes over the past 41,000 years, Geophys. Res. Lett., 40,[3693][3694][3695][3696][3697]

Benthic δ 18 O changes are often assumed to be globally synchronous, but studies comparing 2-9 radiocarbon-dated records over the most recent deglaciation (Termination 1) have proposed differences in the timing of benthic δ 18 O change between the Atlantic and Pacific, intermediate and deep, and North and South Atlantic. Because of the relatively small number of records used in these previous studies, it has remained unclear whether these differences are local or regional in scale. Here we present seven regional benthic δ 18 O stacks for 0-40 kyr B.P. that include 252 records with independent regional age models constrained by 852 planktonic foraminiferal 14 C dates from 61 of these cores. We find a 4000 year difference between the earliest termination onset in the intermediate South Atlantic demonstrates that intermediate-depth benthic δ 18 O change was not globally synchronous. These regional stacks provide better age models than a global stack across Termination 1 and potentially important constraints on deglacial ocean circulation changes.

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