Estimation of stratospheric input to the Arctic troposphere: 7Be and 10Be in aerosols at Alert, Canada

Concentrations of 7Be and 210Pb in 2 years of weekly high-volume aerosol samples collected at Alert, Northwest Territories, Canada, showed pronounced seasonal variations. We observed a broad winter peak in 210Pb concentration and a spring peak in 7Be. These peaks were similar in magnitude and duration to previously reported results for a number of stations in the Arctic Basin. Beryllium 10 concentrations (determined only during the first year of this study) were well correlated with those of 7Be; the atom ratio 10Be/7Be was nearly constant at 2.2 throughout the year. This relatively high value of 10Be/7Be indicates that the stratosphere must constitute an important source of both Be isotopes in the Arctic troposphere throughout the year. A simple mixing model based on the small seasonal variations of 10Be/7Be indicates an approximately twofold increase of stratospheric influence in the free troposphere in late summer. The spring maxima in concentrations of both Be isotopes at the surface apparently reflect vertical mixing in rather than stratospheric injections into the troposphere. We have merged the results of the Be-based mixing model with weekly O3 soundings to assess Arctic stratospheric impact on the surface O3 budget at Alert. The resulting estimates indicate that stratospheric inputs can account for a maximum of 10-15% of the 03 at the surface in spring and for less during the rest of the year. These estimates are most uncertain during the winter. The combination of Be isotopic measurements and O3 vertical profiles could allow quantification of the contributions of O3 from the Arctic stratosphere and lower latitude regions to the O3 budget in the Arctic troposphere. Although at present the lack of a quantitative understanding of the temporal variation of O3 lifetime in the Arctic troposphere precludes making definitive calculations, qualitative examples of the power of this approach are given

Marine-derived C-14 calibration and activity record for the past 50,000 years updated from the Cariaco Basin

Author Posting. © Elsevier B.V., 2006. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Quaternary Science Reviews 25 (2006): 3216-3227, doi:10.1016/j.quascirev.2006.03.014.An expanded Cariaco Basin 14C chronology is tied to 230Th-dated Hulu Cave speleothem records in order to provide detailed marine-based 14C calibration for the past 50,000 years. The revised, high resolution Cariaco 14C calibration record agrees well with data from 230Th-dated fossil corals back to 33 ka, with continued agreement despite increased scatter back to 50 ka, suggesting that the record provides accurate calibration back to the limits of radiocarbon dating. The calibration data document highly elevated Δ14C during the Glacial period. Carbon cycle box model simulations show that the majority of observed Δ14C change can be explained by increased 14C production. However, from 45 to 15 ka, Δ14C remains anomalously high, indicating that the distribution of radiocarbon between surface and deep ocean reservoirs was different than it is today. Additional observations of the magnitude, spatial extent and timing of deep ocean Δ14C shifts are critical for a complete understanding of observed Glacial Δ14C variability

Cariaco Basin calibration update; revisions to calendar and 14C chronologies for core PL07-58PC

Author Posting. © Arizona Board of Regents on behalf of the University of Arizona, 2004. This article is posted here by permission of Dept. of Geosciences, University of Arizona for personal use, not for redistribution. The definitive version was published in Radiocarbon 46 (2004): 1161-1187.This paper describes the methods used to develop the Cariaco Basin PL07-58PC marine radiocarbon calibration data set. Background measurements are provided for the period when Cariaco samples were run, as well as revisions leading to the most recent version of the floating varve chronology. The floating Cariaco chronology has been anchored to an updated and expanded Preboreal pine tree-ring data set, with better estimates of uncertainty in the wiggle-match. Pending any further changes to the dendrochronology, these results represent the final Cariaco 58PC calibration data set.This work was supported by LLNL (97-ERI-009), DOE (W-7405-Eng-48), and NSF (ATM- 9709563)

Interactive comment on ″Comment on : ″Possible source of ancient carbon in phytolith concentrates from harvested grasses″ by G.M. Santos et al. (2012)″ by L.A. Sullivan and J.F. Parr

International audienc

Extreme lowering of deglacial seawater radiocarbon recorded by both epifaunal and infaunal benthic foraminifera in a wood-dated sediment core

For over a decade, oceanographers have debated the interpretation and reliability of sediment microfossil records indicating extremely low seawater radiocarbon (14C) during the last deglaciation – observations that suggest a major disruption in marine carbon cycling coincident with rising atmospheric CO2 concentrations. Possible flaws in these records include poor age model controls, utilization of mixed infaunal foraminifera species, and bioturbation. We have addressed these concerns using a glacial–interglacial record of epifaunal benthic foraminifera 14C on an ideal sedimentary age model (wood calibrated to atmosphere 14C). Our results affirm – with important caveats – the fidelity of these microfossil archives and confirm previous observations of highly depleted seawater 14C at intermediate depths in the deglacial northeast Pacific.</p

Radiocarbon dating organic residues at the microgram level

Relation between submilligram sample size and {sup 14}C activity for sample blanks (wood from Pliocene sediments) and a contemporary standard (oxalic acid) for catalytically reduced graphitic carbon was examined down to 20 micrograms. Mean age of the 1 mg wood sample blanks is now about 51.3 ka (0.168 pMC) while the mean for 20 microgram sample blanks is about 42.9 ka. So far, the lowest value for a 1-mg wood sample blank is about 60.5 ka (0.056 pMC). We have determined a mean {sup 14}C age of about 9.4 ka from a suite of 7 organic extracts from hair, bone, and matting from a mummified human skeleton from Spirit Cave, Nevada. These data indicate that the Spirit Cave human is the third, oldest directly-dated, human skeleton currently known from North America

Limited contribution of ancient methane to surface waters of the U.S. Beaufort Sea shelf

© The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Science Advances 4 (2018): eaao4842, doi:10.1126/sciadv.aao4842.In response to warming climate, methane can be released to Arctic Ocean sediment and waters from thawing subsea permafrost and decomposing methane hydrates. However, it is unknown whether methane derived from this sediment storehouse of frozen ancient carbon reaches the atmosphere. We quantified the fraction of methane derived from ancient sources in shelf waters of the U.S. Beaufort Sea, a region that has both permafrost and methane hydrates and is experiencing significant warming. Although the radiocarbon-methane analyses indicate that ancient carbon is being mobilized and emitted as methane into shelf bottom waters, surprisingly, we find that methane in surface waters is principally derived from modern-aged carbon. We report that at and beyond approximately the 30-m isobath, ancient sources that dominate in deep waters contribute, at most, 10 ± 3% of the surface water methane. These results suggest that even if there is a heightened liberation of ancient carbon–sourced methane as climate change proceeds, oceanic oxidation and dispersion processes can strongly limit its emission to the atmosphere.The National Science Foundation (PLR-1417149; awarded to J.D.K.) primarily supported this work with additional support provided by the U.S. Department of Energy (DE-FE0028980; awarded to J.D.K.). Atmospheric 14C-CH4 measurements were funded by NASA via the Jet Propulsion Laboratory (Earth Ventures project “Carbon in Arctic Reservoirs Vulnerability Experiment”) to the University of Colorado under contract 1424124. K.M.S. acknowledges support from the University of Minnesota Grant-in-Aid program

The Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory

CAMS operates an HVEC FN tandem accelerator for use in both basic research and technology development. The accelerator is operated under a distributed computer control system with sophisticated auto-scaling, beam flat-topping, archiving, and recall capabilities, which makes possible rapid and precise switching between experimental configurations daily. Using the spectrometer, the AMS group can routinely measure the isotopes {sup 3}H, {sup 9}Be, {sup 10}Be, {sup 14}C, {sup 26}Al, {sup 36}Cl, {sup 41}Ca, and {sup 129}I at abundances as low as 1 part in 10{sup 16}

Blank assessment for ultra-small radiocarbon samples : chemical extraction and separation versus AMS

Author Posting. © Arizona Board of Regents on behalf of the University of Arizona, 2010. This article is posted here by permission of Dept. of Geosciences, University of Arizona for personal use, not for redistribution. The definitive version was published in Radiocarbon 52 (2010): 1322-1335.The Keck Carbon Cycle AMS facility at the University of California, Irvine (KCCAMS/UCI) has developed protocols for analyzing radiocarbon in samples as small as ~0.001 mg of carbon (C). Mass-balance background corrections for modern and 14C-dead carbon contamination (MC and DC, respectively) can be assessed by measuring 14C-free and modern standards, respectively, using the same sample processing techniques that are applied to unknown samples. This approach can be validated by measuring secondary standards of similar size and 14C composition to the unknown samples. Ordinary sample processing (such as ABA or leaching pretreatment, combustion/graphitization, and handling) introduces MC contamination of ~0.6 ± 0.3 μg C, while DC is ~0.3 ± 0.15 μg C. Today, the laboratory routinely analyzes graphite samples as small as 0.015 mg C for external submissions and ≅0.001 mg C for internal research activities with a precision of ~1% for ~0.010 mg C. However, when analyzing ultra-small samples isolated by a series of complex chemical and chromatographic methods (such as individual compounds), integrated procedural blanks may be far larger and more variable than those associated with combustion/graphitization alone. In some instances, the mass ratio of these blanks to the compounds of interest may be so high that the reported 14C results are meaningless. Thus, the abundance and variability of both MC and DC contamination encountered during ultra-small sample analysis must be carefully and thoroughly evaluated. Four case studies are presented to illustrate how extraction chemistry blanks are determined

Punctuated Shutdown of Atlantic Meridional Overturning Circulation during Greenland Stadial 1.

The Greenland Stadial 1 (GS-1; ~12.9 to 11.65 kyr cal BP) was a period of North Atlantic cooling, thought to have been initiated by North America fresh water runoff that caused a sustained reduction of North Atlantic Meridional Overturning Circulation (AMOC), resulting in an antiphase temperature response between the hemispheres (the 'bipolar seesaw'). Here we exploit sub-fossil New Zealand kauri trees to report the first securely dated, decadally-resolved atmospheric radiocarbon ((14)C) record spanning GS-1. By precisely aligning Southern and Northern Hemisphere tree-ring (14)C records with marine (14)C sequences we document two relatively short periods of AMOC collapse during the stadial, at ~12,920-12,640 cal BP and 12,050-11,900 cal BP. In addition, our data show that the interhemispheric atmospheric (14)C offset was close to zero prior to GS-1, before reaching 'near-modern' values at ~12,660 cal BP, consistent with synchronous recovery of overturning in both hemispheres and increased Southern Ocean ventilation. Hence, sustained North Atlantic cooling across GS-1 was not driven by a prolonged AMOC reduction but probably due to an equatorward migration of the Polar Front, reducing the advection of southwesterly air masses to high latitudes. Our findings suggest opposing hemispheric temperature trends were driven by atmospheric teleconnections, rather than AMOC changes