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  • 1
    Electronic Resource
    Electronic Resource
    He, Pb, Sr and Nd isotope constraints on magma genesis and mantle heterogeneity beneath young Pacific seamounts (1988)
    Springer
    Contributions to mineralogy and petrology 99 (1988), S. 446-463 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Pb, Sr and Nd isotope variations are correlated in diverse lavas erupted at small seamounts near the East Pacific Rise. Tholeiites are isotopically indistinguishable from MORB (206Pb/204Pb=18.1–18.5; 87Sr/86Sr=0.7023–0.7028; 143Nd/144Nd=0.51326-0.51308); associated alkali basalts always show more radiogenic Pb and Sr signatures (206Pb/204Pb=18.8–19.2; 87Sr/86Sr=0.7029–0.7031) and less radiogenic Nd (143Nd/144Nd=0.51289–0.51301). The isotopic variability covers ∼80% of the variability for Pacific MORB, due to the presence of small-scale heterogeneity in the underlying mantle. Isotope compositions also correlate with trace element ratios such as La/Sm. Tholeiites at these seamounts have 3He/4He between 7.8–8.7 R A(R A= atmospheric ratio), also indistinguishable from MORB. He trapped in vesicles of alkali basalts, released by crushing in vacuo, has low 3He/4He (1.2–2.6 R)Ain conjunction with low helium concentrations ([He]〈5×10−8 ccSTP/g). In many cases post-eruptive radiogenic ingrowth has produced He isotope disequilibrium between vesicles and glass in the alkali basalts; subatmospheric 3He/4He ratios characterize the He dissolved in the glass which is released by melting the crushed powders. The narrow range of 3He/4He in the vesicles of the alkali basalts suggests that low 3He/4He is a source characteristic, but given their low [He] and high (U + Th), pre-eruptive radiogenic ingrowth cannot be excluded as a cause for low inherited 3He/4He ratios. Pb, Sr and Nd isotope compositions in lavas erupted at Shimada Seamount, an isolated volcano on 20 m.y. old seafloor at 17°N, are distinctly different from other seamounts in the East Pacific (206Pb/204Pb=18.8–19.0, 87Sr/ 86Sr≅0.7048 and 143Nd/144Nd≅0.51266). Relatively high 207Pb/204Pb (15.6–15.7) indicates ancient (〉2 Ga) isolation of the source from the depleted upper mantle, similar to Dupal components which are more prevalent in the southern hemisphere mantle. 3He/4He at Shimada Seamount is between 3.9–4.8 R A. Because the helium concentrations range up to 1.5×10−6, the low 3He/4He can not be due to radiogenic accumulation of 4He in the magma for reasonable volcanic evolution times. The low 3He/4He may be due to the presence of “enriched” domains within the lithosphere with high (U + Th)/He ratios, possibly formed during its accretion near the ridge. Alternatively, the low 3He/4He may be an inherent characteristic of an enriched component in the mantle beneath the East Pacific. Collectively, the He-Pb-Sr-Nd isotope systematics at East Pacific seamounts suggest that the range of isotope compositions present in the mantle is more readily sampled by seamount and island volcanism than by axial volcanism. Beneath thicker lithosphere away from the ridge axis, smaller degrees of melting in the source regions are less efficient in averaging the chemical characteristics of small-scale heterogeneities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00371936
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  • 2
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    Growth and composition of high-Mg calcite in the skeleton of a Bermudian gorgonian (Plexaurella dichotoma) : potential for paleothermometry (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: 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 Geochemistry Geophysics Geosystems 6 (2005): Q08010, doi:10.1029/2005GC000911.
    Description: We used Secondary Ion Mass Spectrometry (SIMS) ion microprobe to analyze magnesium-to-calcium (Mg/Ca) and strontium-to-calcium (Sr/Ca) ratios of high-Mg calcite loculi within the skeleton of a shallow water gorgonian, Plexaurella dichotoma, from Bermuda. A cross-section of the gorgonian skeleton reveals loculi embedded within proteinaceous gorgonin arranged in concentric rings about the axial core. Viewed in cross-section, the loculi are fan-shaped, 10-140 μm in diameter, and composed of bundles of needle-shaped crystals that appear to radiate out from a calcification center. Discrete sample spots, each 20 μm diameter, were sputtered from successive loculi along a sample track 3 mm long. Over this distance, twenty-five bands of high-low density gorgonin couplets were encountered, estimated to represent the period 1963 to 1988. Mg/Ca ratios show an overall, positive correlation with annual sea surface temperatures (SSTs) that is strongest in the autumn months (October- December). High-resolution analyses along the growth axes of individual loculi reveal low variability and no trend, consistent with our interpretation of seasonal growth of these calcite inclusions. The sensitivity of Mg/Ca to interannual changes in average autumn temperatures is 0.47 mmol/mol per ºC. Conversely, interannual variability in calcite Sr/Ca does not follow the interannual variability in SST and may be influenced primarily by growth rate.
    Description: This study was supported by an Independent Study Award from the Woods Hole Oceanographic Institution No. 270051.81; NERC grant GR3/12800; a WHOI Ocean Life Institute grant to ALC; Bermuda Government, in support of the Benthic Ecology Research Programme at BBSR to SRS. Support for the WHOI Northeast National Ion Microprobe Facility was provided by NSF EAR-9628749.
    Keywords: Gorgonian ; Octocoral ; Mg/Ca ; Sr/Ca ; Sea surface temperature ; Biomineralization ; Growth bands ; SIMS ion microprobe ; Bermuda
    Repository Name: Woods Hole Open Access Server
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  • 3
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    Evidence for an extensive hydrothermal plume in the Tonga-Fiji region of the South Pacific (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 5 (2004): Q01003, doi:10.1029/2003GC000607.
    Description: Several hydrographic stations in the vicinity of the Samoa Islands have 3He/4He above the regional background in the depth range of 1500–1800 m, indicating injection of mantle helium from a local hydrothermal source. The highest δ(3He) = 43.4% was detected at 1726-m depth at 15.0°S, 173.1°W in the bathymetric gap between the Samoa Islands and the northern end of the Tonga-Kermadec Arc. The δ(3He) profile at this station decreases to δ(3He) = 26% at 2500-m depth. The relatively shallow depth of the maximum hydrothermal signal suggests a source different from the conventional Pacific basin helium plume centered at 2500 m that is carried westward from the East Pacific Rise. Stations to the west of this locality show a progressive decrease in the maximum δ(3He) values in the depth range of 1480–1790 m out to 169°E. Stations east of the Tonga-Fiji region show lower 3He values (〈26%) at 1700 m and the profiles are dominated by a deeper maximum at 2500 m, presumably the distal traces of hydrothermal input from East Pacific Rise. This pattern in the 3He distribution suggests that the 1700-m deep helium plume is carried in a northwesterly direction some 2000 km from its source near the northern end of the Tonga-Kermadec Arc. At this time very little is known about the source of this hydrothermal plume or the details of its areal extent. Numerous seamounts and rift zones in the region are possible hydrothermal sources for the plume. The summit crater of Vailulu'u, a young seamount at the eastern end of the Samoa chain, was recently discovered to be hydrothermally active at ∼600 m depth [Hart et al., 2000]. However this shallow hydrothermal field on Vailulu'u is an unlikely source for the deeper 1700-m signal. The most likely source would appear to be the extensional zones of the northern Lau Basin system, such as the Mangatolo Triple Junction. Just as the helium plume emanating from Lo'ihi has helped our understanding of the circulation near the Hawaiian Islands [Lupton, 1996], this helium plume in the Tonga-Fiji region has great potential for delineating circulation in this area of the south Pacific.
    Description: This work was supported by the NOAA Vents Program and by Grants OCE91-05884, OCE92-96237, OCE92-96169, and OCE98-20132 of the Ocean Sciences Division of the National Science Foundation.
    Repository Name: Woods Hole Open Access Server
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  • 4
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    The subtropical nutrient spiral (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2003. 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 17 (2003): 1110, doi:10.1029/2003GB002085.
    Description: We present an extended series of observations and more comprehensive analysis of a tracer-based measure of new production in the Sargasso Sea near Bermuda using the 3He flux gauge technique. The estimated annually averaged nitrate flux of 0.84 ± 0.26 mol m−2 yr−1 constitutes only that nitrate physically transported to the euphotic zone, not nitrogen from biological sources (e.g., nitrogen fixation or zooplankton migration). We show that the flux estimate is quantitatively consistent with other observations, including decade timescale evolution of the 3H + 3He inventory in the main thermocline and export production estimates. However, we argue that the flux cannot be supplied in the long term by local diapycnal or isopycnal processes. These considerations lead us to propose a three-dimensional pathway whereby nutrients remineralized within the main thermocline are returned to the seasonally accessible layers within the subtropical gyre. We describe this mechanism, which we call “the nutrient spiral,” as a sequence of steps where (1) nutrient-rich thermocline waters are entrained into the Gulf Stream, (2) enhanced diapycnal mixing moves nutrients upward onto lighter densities, (3) detrainment and enhanced isopycnal mixing injects these waters into the seasonally accessible layer of the gyre recirculation region, and (4) the nutrients become available to biota via eddy heaving and wintertime convection. The spiral is closed when nutrients are utilized, exported, and then remineralized within the thermocline. We present evidence regarding the characteristics of the spiral and discuss some implications of its operation within the biogeochemical cycle of the subtropical ocean.
    Description: This work was supported by grants from the National Science Foundation (OCE-0221247) and NSF/ONR NOPP (N000140210370).
    Keywords: Nutrients ; Productivity ; Tritium ; Helium-3
    Repository Name: Woods Hole Open Access Server
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  • 5
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    A new automated method for measuring noble gases and their isotopic ratios in water samples (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 10 (2009): Q05008, doi:10.1029/2009GC002429.
    Description: A method is presented for precisely measuring all five noble gases and their isotopic ratios in water samples using multiple programmed multistage cryogenic traps in conjunction with quadrupole mass spectrometry and magnetic sector mass spectrometry. Multiple automated cryogenic traps, including a two-stage cryotrap used for removal of water vapor, an activated charcoal cryotrap used for helium separation, and a stainless steel cryotrap used for neon, argon, krypton, and xenon separation, allow reproducible gas purification and separation. The precision of this method for gas standards is ±0.10% for He, ±0.14% for Ne, ±0.10% for Ar, ±0.14% for Kr, and ±0.17% for Xe. The precision of the isotopic ratios of the noble gases in gas standards are ±1.9‰ for 20Ne/22Ne, ±2.0‰ for 84Kr/86Kr, ±2.5‰ for 84Kr/82Kr, ±0.9‰ for 132Xe/129Xe, and ±1.3‰ for 132Xe/136Xe. The precision of this method for water samples, determined by measurement of duplicate pairs, is ±1% for He, ±0.9% for Ne, ±0.3% for Ar, ±0.3% for Kr, and ±0.2% for Xe. An attached magnetic sector mass spectrometer measures 3He/4He with precisions of ±0.1% for air standards and ±0.14% for water samples.
    Description: We are grateful for support by the National Science Foundation Chemical Oceanography program (OCE-0221247), by the Department of Defense (graduate fellowship to RHRS), and by the Woods Hole Oceanographic Institution (postdoctoral fellowship for B.B.).
    Keywords: Noble gas ; Oceanography ; Mass spectrometry ; Seawater ; Isotope ; Cryogenic
    Repository Name: Woods Hole Open Access Server
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  • 6
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    Noble gas constraints on air-sea gas exchange and bubble fluxes (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 114 (2009): C11020, doi:10.1029/2009JC005396.
    Description: Air-sea gas exchange is an important part of the biogeochemical cycles of many climatically and biologically relevant gases including CO2, O2, dimethyl sulfide and CH4. Here we use a three year observational time series of five noble gases (He, Ne, Ar, Kr, and Xe) at the Bermuda Atlantic Time series Study (BATS) site in tandem with a one-dimensional upper ocean model to develop an improved parameterization for air-sea gas exchange that explicitly includes separate components for diffusive gas exchange and bubble processes. Based on seasonal timescale noble gas data, this parameterization, which has a 1σ uncertainty of ±14% for diffusive gas exchange and ±29% for bubble fluxes, is more tightly constrained than previous parameterizations. Although the magnitude of diffusive gas exchange is within errors of that of Wanninkhof (1992), a commonly used parameterization, we find that bubble-mediated exchange, which is not explicitly included by Wanninkhof (1992) or many other formulations, is significant even for soluble gases. If one uses observed saturation anomalies of Ar (a gas with similar characteristics to O2) and a parameterization of gas exchange to calculate gas exchange fluxes, then the calculated fluxes differ by ∼240% if the parameterization presented here is used compared to using the Wanninkhof (1992) parameterization. If instead one includes the gas exchange parameterization in a model, then the calculated fluxes differ by ∼35% between using this parameterization and that of Wanninkhof (1992). These differences suggest that the bubble component should be explicitly included in a range of marine biogeochemical calculations that incorporate air-sea gas fluxes.
    Description: Funding from the National Science Foundation Chemical Oceanography program (OCE-0221247 and OCE-0623034).
    Keywords: Air-sea gas exchange ; Noble gas ; Bubbles
    Repository Name: Woods Hole Open Access Server
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  • 7
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    Mantle 3He distribution and deep circulation in the Indian Ocean (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 109 (2004): C06012, doi:10.1029/2003JC002028.
    Description: The World Ocean Circulation Experiment Indian Ocean helium isotope data are mapped and features of intermediate and deep circulation are inferred and discussed. The 3He added to the deep Indian Ocean originates from (1) a strong source on the mid-ocean ridge at about 19°S/65°E, (2) a source located in the Gulf of Aden in the northwestern Indian Ocean, (3) sources located in the convergent margins in the northeastern Indian Ocean, and (4) water imported from the Indonesian Seas. The main circulation features inferred from the 3He distribution include (1) deep (2000–3000 m) eastward flow in the central Indian Ocean, which overflows into the West Australian Basin through saddles in the Ninetyeast Ridge, (2) a deep (2000–3000 m) southwestward flow in the western Indian Ocean, and (3) influx of Banda Sea Intermediate Waters associated with the deep core (1000–1500 m) of the through flow from the Pacific Ocean. The large-scale 3He distribution is consonant with the known pathways of deep and bottom water circulation in the Indian Ocean.
    Description: National Science Foundation support is acknowledged for the UM part of the work through grants OCE-9820131 and OCE-998150. Support for the LDEO portion of the work was obtained from the National Science Foundation through awards OCE 94-13162 and OCE 98-20130.
    Keywords: Indian Ocean ; Tracers ; Deep circulation
    Repository Name: Woods Hole Open Access Server
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  • 8
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    Deposition and recirculation of tritium in the North Pacific Ocean (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 109 (2004): C06009, doi:10.1029/2003JC002150.
    Description: Tritium data, primarily from the GEOSECS and WOCE cruises of the 1970s and 1990s, are used to estimate the time-evolving 3H inventory of the North Pacific basin. In the years between the two surveys, there have been changes both laterally and vertically in the distribution of 3H in the North Pacific that reflect the mean circulation and exchanges of the basin. We develop a simple multibox model of the shallow circulation of the North Pacific to explore the long-term redistribution and changes in 3H inventories within the basin. To do this, we derived a new estimate of the delivery of bomb 3H to the North Pacific by precipitation for the period 1960–1997 and include other minor sources such as rivers. Vapor deposition dominates over direct precipitation of tritium to the basin, while inputs from continental runoff and the inflow from the south contribute over an order of magnitude less. The model predicted tritium budget of 25.1 ± 3.3 kg compares well with the estimated WOCE inventory of 23.4 ± 2.0 kg. We explore in detail the sensitivity of the budget calculations to model circulation and assumptions, as well as uncertainties in observations. We find that the ratio of tritium in vapor to that in precipitation is the most sensitive variable in the model budget, and the basin tritium inventory is consistent with a vapor-to-precipitation ratio of 0.67 (range 0.60–0.74), predictably somewhat less than the isotopic equilibrium value of 0.89. An inverse calculation shows that despite uncertainties in the tritium source function, the data also help constrain aspects of the basin circulation, including the Indonesian Throughflow.
    Description: Support for this work was provided by UK Natural Environment Research Council grant GR3/12800, and by the U.S. National Science Foundation grant OCE26080500.
    Keywords: Transient tracer ; Ocean circulation ; Ventilation
    Repository Name: Woods Hole Open Access Server
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  • 9
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    C-14 Blank Corrections for 25-100 mu G samples at the National Ocean Sciences AMS Laboratory (2020)
    Cambridge University Press
    Details
    Publication Date: 2022-10-26
    Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Roberts, Mark L., Elder, Kathryn L., Jenkins, William J., Gagnon, Alan R., Xu, Li, Hlavenka, Joshua D., & Longworth, Brett E. C-14 Blank Corrections for 25-100 mu G samples at the National Ocean Sciences AMS Laboratory. Radiocarbon, 61(5), (2019): 1403-1411, Doi: 10.1017/RDC.2019.74.
    Description: Replicate radiocarbon (14C) measurements of organic and inorganic control samples, with known Fraction Modern values in the range Fm = 0–1.5 and mass range 6 μg–2 mg carbon, are used to determine both the mass and radiocarbon content of the blank carbon introduced during sample processing and measurement in our laboratory. These data are used to model, separately for organic and inorganic samples, the blank contribution and subsequently “blank correct” measured unknowns in the mass range 25–100 μg. Data, formulas, and an assessment of the precision and accuracy of the blank correction are presented.
    Description: This work is supported by a Cooperative Agreement (OCE-1755125) with the U.S. National Science Foundation.
    Keywords: AMS ; AMS dating ; Blank corrections
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  • 10
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    A comprehensive global oceanic dataset of helium isotope and tritium measurements. (2019)
    Copernicus Publications
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    Publication Date: 2022-05-26
    Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Jenkins, W. J., Doney, S. C., Fendrock, M., Fine, R., Gamo, T., Jean-Baptiste, P., Key, R., Klein, B., Lupton, J. E., Newton, R., Rhein, M., Roether, W., Sano, Y., Schlitzer, R., Schlosser, P., & Swift, J. A comprehensive global oceanic dataset of helium isotope and tritium measurements. Earth System Science Data, 11(2), (2019):441-454, doi:10.5194/essd-11-441-2019.
    Description: Tritium and helium isotope data provide key information on ocean circulation, ventilation, and mixing, as well as the rates of biogeochemical processes and deep-ocean hydrothermal processes. We present here global oceanic datasets of tritium and helium isotope measurements made by numerous researchers and laboratories over a period exceeding 60 years. The dataset's DOI is https://doi.org/10.25921/c1sn-9631, and the data are available at https://www.nodc.noaa.gov/ocads/data/0176626.xml (last access: 15 March 2019) or alternately http://odv.awi.de/data/ocean/jenkins-tritium-helium-data-compilation/ (last access: 13 March 2019) and includes approximately 60 000 valid tritium measurements, 63 000 valid helium isotope determinations, 57 000 dissolved helium concentrations, and 34 000 dissolved neon concentrations. Some quality control has been applied in that questionable data have been flagged and clearly compromised data excluded entirely. Appropriate metadata have been included, including geographic location, date, and sample depth. When available, we include water temperature, salinity, and dissolved oxygen. Data quality flags and data originator information (including methodology) are also included. This paper provides an introduction to the dataset along with some discussion of its broader qualities and graphics.
    Description: This synthesis work was funded under the auspices of a U.S. National Science Foundation grant number OCE-1434000. Financial support for the actual measurements came from a wide variety of different research grants from many agencies in many countries, far too numerous to list here. William J. Jenkins is grateful to a number of US funding sources, most notably the National Science Foundation, NOAA, DOE, and ONR.
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