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  • 1
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    The Cenozoic evolution of ocean circulation and water mass mixing in the SW Indian Ocean over the past 20 Million years? (2013)
    In:  EPIC311th International Congress on Palaeoceanography, Barcelona, Sitges, Spain, 2013-09-01-2013-09-06
    Details
    Publication Date: 2019-07-16
    Description: Seismic reflection data from the southern Mozambique Ridge, Southwestern Indian Ocean, show indications for a substantial modification in the oceanic circulation system during the Neogene. Major reorganisations in the Indian Ocean circulation system accompanying the closure of the Indonesian Gateway led to the onset of current controlled sedimentation in the vicinity of the Mozambique Ridge at ~14 million years ago. The modifications in water mass properties and pathways are documented in changes in reflection characteristics in the Mozambique Ridge area. The evidence from the seismic reflection data is compared to deep water Pb, Nd and Hf isotope time series of the past 20 million years obtained from three hydrogenetic ferromanganese crusts and one manganese nodule from the Mozambique Ridge in the SW Indian Ocean. The isotope systems enable tracing of the source provenances of deep water masses. The ferromanganese precipitates were recovered from 1850 m, 2780 m and 3790 m water depth and were dated by cosmogenic 10Be/9Be profiles. These precipitates serve as unique archives of the long term evolution of the mixing of ambient Indian Ocean water masses ultimately originating from the North Atlantic and the Southern Ocean at the respective depths over time. The evolution of the admixture of North Atlantic Deep Water at water depths greater than 2000 m is clearly mirrored by Nd and Hf isotopic compositions systematically about one ε unit lower than those of the overlying Antarctic Intermediate Water. This stratification has only existed since 9 million years ago suggesting that the general present day large scale circulation in the intermediate and deep southern Indian Ocean has only prevailed since then.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 2
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    GEOTRACES intercalibration of neodymium isotopes and rare earth element concentrations in seawater and suspended particles. Part 1: reproducibility of results for the international intercomparison (2012)
    In:  EPIC3Limnology and Oceanography: Methods, 10(4), pp. 234-251, ISSN: 15415856
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    Publication Date: 2018-03-12
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 3
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    Sources and input mechanisms of hafnium and neodymium in surface waters of the Atlantic sector of the Southern Ocean (2012)
    In:  EPIC3Geochimica et Cosmochimica Acta, 94, pp. 22-37, ISSN: 00167037
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    Publication Date: 2018-03-13
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 4
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    The hafnium and neodymium isotope composition of seawater in the Atlantic sector of the Southern Ocean (2012)
    In:  EPIC3Earth and Planetary Science Letters, 317-31, pp. 282-294, ISSN: 0012821X
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    Publication Date: 2018-03-13
    Repository Name: EPIC Alfred Wegener Institut
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  • 5
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    Geochemical proxies of North American freshwater routing during the Younger Dryas cold event (2007)
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © The Authors, 2006. This is the author's version of the work. It is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences 104 (2007): 6556-6561, doi:10.1073/pnas.0611313104.
    Description: The Younger Dryas cold interval represents a time when much of the Northern Hemisphere cooled from ~12.9 to 11.5 kiloyears before present. The cause of this event, which has long been viewed as the canonical example of abrupt climate change, was initially attributed to the routing of freshwater to the St. Lawrence River with an attendant reduction in Atlantic meridional overturning circulation. However, this mechanism has recently been questioned because current proxies and dating techniques have been unable to confirm that eastward routing with an increase in freshwater flux occurred during the Younger Dryas. Here we use new geochemical proxies (ΔMg/Ca, U/Ca & 87Sr/86Sr) measured in planktonic foraminifera at the mouth of the St. Lawrence Estuary as tracers of freshwater sources to further evaluate this question. Our proxies, combined with planktonic δ18Oseawater and δ13C, confirm that routing of runoff from western Canada to the St. Lawrence River occurred at the start of the Younger Dryas, with an attendant increase in freshwater flux of 0.06 ± 0.02 Sverdrup (1 Sverdrup (Sv) = 106 m3 s-1). This base discharge increase is sufficient to have reduced Atlantic meridional overturning circulation and caused the Younger Dryas cold interval. In addition, our data indicate subsequent fluctuations in the freshwater flux to the St. Lawrence River of ~0.06 to 0.12 Sv, thus explaining the variability in the overturning circulation and climate during the Younger Dryas.
    Description: This research was funded by the NSF Paleoclimate Program (P.U.C.) and the NSF (G.P.K.).
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
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  • 6
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    Eastern Pacific Warm Pool paleosalinity and climate variability : 0–30 kyr (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 21 (2006): PA3008, doi:10.1029/2005PA001208.
    Description: Multi-proxy geologic records of δ18O and Mg/Ca in fossil foraminifera from sediments under the Eastern Pacific Warm Pool (EPWP) region west of Central America document variations in upper ocean temperature, pycnocline strength, and salinity (i.e., net precipitation) over the past 30 ky. Although evident in the paleotemperature record, there is no glacial-interglacial difference in paleosalinity, suggesting that tropical hydrologic changes do not respond passively to high-latitude ice sheets and oceans. Millennial variations in paleosalinity with amplitudes as high as ~4 PSU occur with a dominant period of ~3-5 ky during the glacial/deglacial interval and ~1.0-1.5 ky during the Holocene. The amplitude of the EPWP paleosalinity changes greatly exceeds that of published Caribbean and western tropical Pacific paleosalinity records. EPWP paleosalinity changes correspond to millennial-scale climate changes in the surface and deep Atlantic and the high northern latitudes, with generally higher (lower) paleosalinity during cold (warm) events. In addition to Intertropical Convergence Zone (ITCZ) dynamics, which play an important role in tropical hydrologic variability, changes in Atlantic-Pacific moisture transport, which is closely linked to ITCZ dynamics, may also contribute to hydrologic variations in the EPWP. Calculations of interbasin salinity average and interbasin salinity contrast between the EPWP and the Caribbean help differentiate long-term changes in mean ITCZ position and Atlantic-Pacific moisture transport, respectively.
    Description: Support for this research was provided by the U.S. National Science Foundation.
    Keywords: Water vapor ; Eastern tropical Pacific ; Paleoceanography
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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  • 7
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    Sediment and pore fluid chemistry for IODP Sites 311-U1325 and 311-U1329 (2012)
    PANGAEA
    In:  Supplement to: Kim, Ji-Hoon; Torres, Marta E; Haley, Brian A; Kastner, Miriam; Pohlman, John W; Riedel, Michael; Lee, Young-Joo (2012): The effect of diagenesis and fluid migration on rare earth element distribution in pore fluids of the northern Cascadia accretionary margin. Chemical Geology, 291, 152-165, https://doi.org/10.1016/j.chemgeo.2011.10.010
    Details
    Publication Date: 2023-04-27
    Description: Analytical challenges in obtaining high quality measurements of rare earth elements (REEs) from small pore fluid volumes have limited the application of REEs as deep fluid geochemical tracers. Using a recently developed analytical technique, we analyzed REEs from pore fluids collected from Sites U1325 and U1329, drilled on the northern Cascadia margin during the Integrated Ocean Drilling Program (IODP) Expedition 311, to investigate the REE behavior during diagenesis and their utility as tracers of deep fluid migration. These sites were selected because they represent contrasting settings on an accretionary margin: a ponded basin at the toe of the margin, and the landward Tofino Basin near the shelf's edge. REE concentrations of pore fluid in the methanogenic zone at Sites U1325 and U1329 correlate positively with concentrations of dissolved organic carbon (DOC) and alkalinity. Fractionations across the REE series are driven by preferential complexation of the heavy REEs. Simultaneous enrichment of diagenetic indicators (DOC and alkalinity) and of REEs (in particular the heavy elements Ho to Lu), suggests that the heavy REEs are released during particulate organic carbon (POC) degradation and are subsequently chelated by DOC. REE concentrations are greater at Site U1325, a site where shorter residence times of POC in sulfate-bearing redox zones may enhance REE burial efficiency within sulfidic and methanogenic sediment zones where REE release ensues. Cross-plots of La concentrations versus Cl, Li and Sr delineate a distinct field for the deep fluids (z 〉 75 mbsf) at Site U1329, and indicate the presence of a fluid not observed at the other sites drilled on the Cascadia margin. Changes in REE patterns, the presence of a positive Eu anomaly, and other available geochemical data for this site suggest a complex hydrology and possible interaction with the igneous Crescent Terrane, located east of the drilled transect.
    Keywords: 311-U1325; 311-U1329; Cascadia Margin Gas Hydrates; COMPCORE; Composite Core; Exp311; Integrated Ocean Drilling Program / International Ocean Discovery Program; IODP; Joides Resolution; North Pacific; off Vancouver Island
    Type: Dataset
    Format: application/zip, 2 datasets
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  • 8
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    Neodymium elemental and isotopic composition of Oregon, USA margin sediments
    PANGAEA
    In:  Supplement to: Abbott, April N; Haley, Brian A; McManus, James (2015): Bottoms up: Sedimentary control of the deep North Pacific Ocean's epsilon-Nd signature. Geology, 43(11), 1035-1035, https://doi.org/10.1130/G37114.1
    Details
    Publication Date: 2023-05-12
    Description: The ability to reconstruct past ocean currents is essential for determining ocean circulation's role in global heat transport and climate change. Our understanding of the relationship between circulation and climate in the past allows us to predict the impact of future climate-driven circulation changes. One proposed tracer of past ocean circulation is the neodymium isotope composition (epsilon-Nd) of ancient water masses. However, ambiguities in what governs the epsilon-Nd distribution in the modern ocean hamper interpretations of this tracer. Here we present epsilon-Nd values for marine pore fluids, sediments, and the overlying water column for three sites in the North Pacific. We find that ocean bottom water epsilon-Nd (epsilon-NdBW) in the northeast Pacific lies between the value expected for the water mass (-3.3) and the measured epsilon-Nd of sediment pore fluid (epsilon-NdPW; -1.8). Moreover, epsilon-NdPW resembles the epsilon-Nd of the sediment. Combined, these findings are consistent with recent assessments that sediment pore fluids may be a major source of rare earth elements to the ocean and suggest that the benthic flux of Nd from pore fluids exerts the primary control over the deep ocean distribution of epsilon-Nd.
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    Format: application/zip, 2 datasets
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  • 9
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    Elemental and neodymium isotopic composition of sediments from the Oregon, USA margin
    PANGAEA
    In:  Supplement to: Abbott, April N; Haley, Brian A; McManus, James (2016): The impact of sedimentary coatings on the diagenetic Nd flux. Earth and Planetary Science Letters, 449, 217-227, https://doi.org/10.1016/j.epsl.2016.06.001
    Details
    Publication Date: 2023-05-12
    Description: Because ocean circulation impacts global heat transport, understanding the relationship between deep ocean circulation and climate is important for predicting the ocean's role in climate change. A common approach to reconstruct ocean circulation patterns employs the neodymium isotope compositions of authigenic phases recovered from marine sediments. In this approach, mild chemical extractions of these phases is thought to yield information regarding the epsilon-Nd of the bottom waters that are in contact with the underlying sediment package. However, recent pore fluid studies present evidence for neodymium cycling within the upper portions of the marine sediment package that drives a significant benthic flux of neodymium to the ocean. This internal sedimentary cycling has the potential to obfuscate any relationship between the neodymium signature recovered from the authigenic coating and the overlying neodymium signature of the seawater. For this manuscript, we present sedimentary leach results from three sites on the Oregon margin in the northeast Pacific Ocean. Our goal is to examine the potential mechanisms controlling the exchange of Nd between the sedimentary package and the overlying water column, as well as the relationship between the epsilon-Nd composition of authigenic sedimentary coatings and that of the pore fluid. In our comparison of the neodymium concentrations and isotope compositions from the total sediment, sediment leachates, and pore fluid we find that the leachable components account for about half of the total solid-phase Nd, therefore representing a significant reservoir of reactive Nd within the sediment package. Based on these and other data, we propose that sediment diagenesis determines the epsilon-Nd of the pore fluid, which in turn controls the epsilon-Nd of the bottom water. Consistent with this notion, despite having 1 to 2 orders of magnitude greater Nd concentration than the bottom water, the pore fluid is still 〈0.001% of the total Nd reservoir in the upper sediment column. Therefore, the pore fluid reservoir is too small to maintain a unique signature, and instead must be controlled by the larger reservoir of Nd in the reactive coatings. In addition, to achieve mass balance, we find it necessary to invoke a cryptic radiogenic (epsilon-Nd of +10) trace mineral source of neodymium within the upper sediment column at our sites. When present, this cryptic trace metal results in more radiogenic pore fluid.
    Type: Dataset
    Format: application/zip, 7 datasets
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  • 10
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    Pore water rare earth element concentrations from the Oregon, USA margin
    PANGAEA
    In:  Supplement to: Abbott, April N; Haley, Brian A; McManus, James; Reimers, Clare (2015): The sedimentary flux of dissolved rare earth elements to the ocean. Geochimica et Cosmochimica Acta, 154, 186-200, https://doi.org/10.1016/j.gca.2015.01.010
    Details
    Publication Date: 2023-05-12
    Description: We determined pore fluid rare earth element (REE) concentrations in near-surface sediments retrieved from the continental margin off Oregon and California (USA). These sites represent shelf-to-slope settings, which lie above, within, and below the oxygen minimum zone of the Northeast Pacific. The sediments are characterized by varying degrees of net iron reduction, with pore fluids from the shelf sites being generally ferruginous, and the slope sediments having less-pronounced iron reduction zones that originate deeper in the sediment package. REE concentrations show maxima in shallow (upper 2-10 cm) subsurface pore fluids across all sites with concentrations that rise more than two orders of magnitude higher than seawater. These pore fluid enrichments highlight the importance of a sedimentary source of REEs to the ocean's water column. Here we use our measurements to estimate the diffusive flux of Nd out of ocean sediments resulting in a global flux between 18 and 110 × 10**6 mol Nd/yr. While we do assume that our pore fluid profiles as well as the very limited data previously published are representative of a wide array of ocean environments, this calculated flux can account for the modeled missing Nd source flux (76 × 10**6 mol Nd/yr) in global budgets (Arsouze et al., 2009). Pore fluid normalized REE patterns show distinct variation in the middle REE and heavy REE enrichments with sediment depth and amongst sites. These patterns show that the heavy REE enrichment of pore fluids at our deep slope site (3000 m water depth) is closest to the heavy REE enrichment of seawater. This observation supports the view that REE cycling within the upper ten centimeters of deep-sea marine sediments, as opposed to shallower continental shelf and slope sediments, plays a significant role in controlling the integrated global REE flux from the pore fluids and consequently the broad-scale REE pattern in seawater.
    Type: Dataset
    Format: application/zip, 3 datasets
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