Radiocarbon in dissolved organic matter in the central North Pacific Ocean

The origin of dissolved organic carbon (DOC) in the ocean has been long debated. Whereas Mantoura and Woodward1have used the conservative nature of DOC in a British estuary to conclude that ≥50% of DOC in the oceans could be river-derived, recent lignin results in the equatorial Pacific2have indicated that ≤10% of the DOC is potentially of terrestrial origin. In addition, the δ13C signature (relative to the PDB standard) of DOC ranges from -20 to -24‰ (refs 3,4), indicating that the primary source of DOC is from marine-derived organic carbon. Here we present the first detailed profile of radiocarbon measured in DOC and dissolved inorganic carbon (DIC) in the oligotrophic gyre of the central North Pacific. δ14C (per mil deviation from the activity of 19th-century wood) of DOC ranged from -150‰ (1,310 yr BP) in surface waters to -540‰ (6,240 yr BP) at 5,710 m, 40 m off the bottom, where these 'apparent ages' or 'residence times' are mean values for the combined constituents of the DOC. The surprising similarity in the shapes of the profiles of δ14C in the DOC and DIC pools suggests that similar processes are controlling the radiocarbon distribution in each of the two reservoirs and that bomb-produced radiocarbon has penetrated the DOC + DIC pools to a depth of ~900 m. The depletion of the δ14CDOCvalues by 300‰ with respect to the δ14CDICvalues suggests that a certain fraction of the DOC is recycled within the ocean on longer time-scales than DIC. © 1987 Nature Publishing Group

Two centuries of limited variability in subtropical North Atlantic thermocline ventilation

© The Author(s), 2012. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nature Communications 3 (2012): 803, doi:10.1038/ncomms1811.Ventilation and mixing of oceanic gyres is important to ocean-atmosphere heat and gas transfer, and to mid-latitude nutrient supply. The rates of mode water formation are believed to impact climate and carbon exchange between the surface and mid-depth water over decadal periods. Here, a record of 14C/12C (1780–1940), which is a proxy for vertical ocean mixing, from an annually banded coral from Bermuda, shows limited inter-annual variability and a substantial Suess Effect (the decrease in 14C/12C since 1900). The Sargasso Sea mixing rates between the surface and thermocline varied minimally over the past two centuries, despite changes to mean-hemispheric climate, including the Little Ice Age and variability in the North Atlantic Oscillation. This result indicates that regional formation rates of sub-tropical mode water are stable over decades, and that anthropogenic carbon absorbed by the ocean does not return to the surface at a variable rate.Funding provided by NSF’s Chemical Oceanography Program OCE - 0526463 and 0961980 and the Stephen Hui Trust Fund

Low reservoir ages for the surface ocean from mid-Holocene Florida corals

Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 23 (2008): PA2209, doi:10.1029/2007PA001527.The 14C reservoir age of the surface ocean was determined for two Holocene periods (4908–4955 and 3008–3066 calendar (cal) B.P.) using U/Th-dated corals from Biscayne National Park, Florida, United States. We found that the average reservoir ages for these two time periods (294 ± 33 and 291 ± 27 years, respectively) were lower than the average value between A.D. 1600 and 1900 (390 ± 60 years) from corals. It appears that the surface ocean was closer to isotopic equilibrium with CO2 in the atmosphere during these two time periods than it was during recent times. Seasonal δ 18O measurements from the younger coral are similar to modern values, suggesting that mixing with open ocean waters was indeed occurring during this coral's lifetime. Likely explanations for the lower reservoir age include increased stratification of the surface ocean or increased Δ14C values of subsurface waters that mix into the surface. Our results imply that a more correct reservoir age correction for radiocarbon measurements of marine samples in this location from the time periods ∼3040 and ∼4930 cal years B.P. is ∼292 ± 30 years, less than the canonical value of 404 ± 20 years.NSF Chemical Oceanography program provided monetary support under grants OCE-9711326, OCE-0137207, and OCE-0551940 (to ERMD)

Variability of Monthly Radiocarbon During the 1760S in Corals from the Galapagos Islands

From the 18th International Radiocarbon Conference held in Wellington, New Zealand, September 1-5, 2003.Radiocarbon (∆14C) measurements of monthly samples from a Galapagos surface coral are among the first data sets from the new Keck Carbon Cycle Accelerator Mass Spectrometry laboratory at the University of California, Irvine. An average ∆14C value of -62 is obtained for 144 measurements of samples from monthly coral bands that lived from about AD 1760-1771 (+/6 yr). High ∆14C values were found during January through March, when upwelling was weak or absent at the Galapagos Islands. Low ∆14C values were obtained mid-year during strong upwelling. The average seasonal variability of ∆14C was 15-25 ppm, which is greater than that at other tropical and subtropical locations in the Pacific Ocean because of intense seasonal upwelling at this site. Periods of sustained high ∆14C values were found during 1762-1763 and 1766. A spectral analysis revealed that the spectral density for the ∆14C data displays most of its variance at the 5-yr cycle, which is reflective of El Niño periodicity during the 20th century.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Dissolved organic radiocarbon in the central Pacific Ocean

© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Druffel, E. R. M., Griffin, S., Wang, N., Garcia, N. G., McNichol, A. P., Key, R. M., & Walker, B. D. Dissolved organic radiocarbon in the central Pacific Ocean. Geophysical Research Letters, 46(10), (2019):5396-5403, doi:10.1029/2019GL083149.We report marine dissolved organic carbon (DOC) concentrations, and DOC ∆14C and δ13C values in seawater collected from the central Pacific. Surface ∆14C values are low in equatorial and polar regions where upwelling occurs and high in subtropical regions dominated by downwelling. A core feature of these data is that 14C aging of DOC (682 ± 86 14C years) and dissolved inorganic carbon (643 ± 40 14C years) in Antarctic Bottom Water between 54.0°S and 53.5°N are similar. These estimates of aging are minimum values due to mixing with deep waters. We also observe minimum ∆14C values (−550‰ to −570‰) between the depths of 2,000 and 3,500 m in the North Pacific, though the source of the low values cannot be determined at this time.We thank Jennifer Walker, Xiaomei Xu, and Dachun Zhang for their help with the stable carbon isotope measurements; John Southon and staff of the Keck Carbon Cycle AMS Laboratory for their assistance and advice; the support of chief scientists Samantha Siedlecki, Molly Baringer, Alison Macdonald, and Sabine Mecking; the guidance of Jim Swift and Dennis Hansell for shared ship time; and Sarah Bercovici for collecting water on the GoA cruise. We appreciate the comments of Christian Lewis and Niels Hauksson on this manuscript. This work was supported by NSF (OCE‐141458941 to E. R. M. D. and OCE‐0824864, OCE‐1558654, and Cooperative Agreement OCE1239667 to R. M. K. and A. P. M.), the Fred Kavli Foundation, the Keck Carbon Cycle AMS Laboratory, and the NSF/NOAA‐funded GO‐SHIP Program. This research was undertaken, in part, thanks to funding from the Canada Research Chairs program (to B. D. W.) and an American Chemical Society Petroleum Research Fund New Directions grant (55430‐ND2 to E. R. M. D. and B. D. W.). Data from the P16N cruises are available in Table S2 in the Supporting Information and at the Repeat Hydrography Data Center at the CCHDO website (http://cdiac.esd.ornl.gov/oceans/index.html) using the expo codes 3RO20150329, 3RO20150410, and 3RO20150525. There are no real or perceived financial conflicts of interests for any author.2019-11-0

Photochemical reactivity of ancient marine dissolved organic carbon

Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 39 (2012): L18602, doi:10.1029/2012GL052974.Marine dissolved organic carbon (DOC) is the largest reservoir of reduced carbon in seawater and persists up to 4,000–6,000 conventional radiocarbon (14C) years on average. Photochemical degradation has been suggested as a geochemical sink for these long-lived molecules, yet there have been no studies relating photochemical lability to the 14C-ages of surface DOC. We observed apparent second order (2°) kinetics with respect to DOC and a strong trend from Δ14C-enriched to depleted values during exhaustive photomineralization of surface marine DOC with high energy UV light. Geochemically, these results suggest that surface DOC is an isotopically-heterogeneous mixture of molecules for which photochemical lability and 14C ages are correlated. Photochemical mineralization may therefore be an important control on the persistence of 14C-depleted DOC in the ocean.This study was supported under NSF grant OCE-0961980 to E. R. M. Druffel.2013-03-2

Radiocarbon distributions in Southern Ocean dissolved and particulate organic matter

Dissolved organic carbon (DOC) is the largest actively exchanging pool of organic carbon in the ocean, yet its sources and sinks are not well constrained. The average C-14 ages of DOC in the deep N. Atlantic and N. Pacific Oceans are 4,000 [Bauer et al., 1992; Druffel et al., 1992] and 6,000 years [Williams and Druffel, 1987], respectively, and represent the beginning and end of the deep ocean conveyor [Broecker, 1991]. Here we report that the deep Southern Ocean DOC has a C-14 age (5,600 y) much closer to that of the deep N. Pacific, but its concentration in seawater (41 +/- 2 mu M) is nearly equal to that of the deep N. Atlantic. The radiocarbon and concentration data indicate that most, but not all, deep DOC is transported conservatively with the ocean\u27s conveyor. A younger (post-bomb) source of DOC to the N. Atlantic is the most likely explanation for the large age difference we observe between deep DOC in the Atlantic and Southern Oceans. Other possibilities are a source of older DOC or a smaller microbial sink in the S. Ocean, or perhaps a possible slowdown of S. Ocean deep water formation during the past century [Broecker et at, 1999]

Transport of organic carbon from the California coast to the slope region : a study of Δ14C and δ13C signatures of organic compound classes

Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 19 (2005): GB2018, doi:10.1029/2004GB002422.Surface sediments along a transect from an abyssal site in the northeastern Pacific (Station M, 34°50′N, 123°00′W) to a small mountainous river on the California coast (Santa Clara River) were studied to investigate the sources and cycling of organic matter on the continental margin. Sediment samples were separated into organic compound fractions (extractable lipids, amino acids (THAA), carbohydrates (TCHO), and the acid-insoluble fraction), and their carbon isotope ratios were measured. The Δ14C values of all the THAA and TCHO fractions were greater than −100‰, indicating relatively modern organic carbon (OC) source(s), and rapid cycling of these fractions. In contrast, the Δ14C values of extractable lipids and the acid-insoluble fraction were distinctly lower than those of the THAA and TCHO fractions. The Δ14C values of source OC to the sediments were estimated using a simple mixed layer model. These values were lower than the Δ14C signatures of pre-industrial plankton suggesting input of both old OC and contemporary plankton to the margin sediments. The source of old OC at the 2000-m site was likely from laterally transported coastal sediment. The estimated low Δ14C value of the transported OC suggests that old lipids and acid-insoluble material were selectively transported to the 2000-m site. The contribution of riverine POC to the margin sediments were estimated from Δ14C and δ13C values and indicate that relict OC exported by rivers was an important source of old lipids and acid-insoluble material to sedimentary OC on the shelf.This research was supported by NSF OCE Chemical Oceanography Program and ACS Petroleum Research Fund (to E. R. M. D.), the UCOP Marine Science Fellowship Program (to J. H.), and the Dreyfus Foundation for an Environmental Science Postdoctoral Fellowship grant (to T. K.)