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  • 1
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    On the edge of death: Rates of decline and lower thresholds of biochemical condition in food-deprived fish larvae and juveniles (2011)
    Elsevier
    In:  Journal of Marine Systems, 93 (May). pp. 11-24.
    Details
    Publication Date: 2017-07-13
    Description: Gaining reliable estimates of how long fish early life stages can survive without feeding and how starvation rate and time until death are influenced by body size, temperature and species is critical to understanding processes controlling mortality in the sea. The present study is an across-species analysis of starvation-induced changes in biochemical condition in early life stages of nine marine and freshwater fishes. Data were compiled on changes in body size (dry weight, DW) and biochemical condition (standardized RNA–DNA ratio, sRD) throughout the course of starvation of yolk-sac and feeding larvae and juveniles in the laboratory. In all cases, the mean biochemical condition of groups decreased exponentially with starvation time, regardless of initial condition and endogenous yolk reserves. A starvation rate for individuals was estimated from discrete 75th percentiles of sampled populations versus time (degree-days, Dd). The 10th percentile of sRD successfully approximated the lowest, life-stage-specific biochemical condition (the edge of death). Temperature could explain 59% of the variability in time to death whereas DW had no effect. Species and life-stage-specific differences in starvation parameters suggest selective adaptation to food deprivation. Previously published, interspecific functions predicting the relationship between growth rate and sRD in feeding fish larvae do not apply to individuals experiencing prolonged food deprivation. Starvation rate, edge of death, and time to death are viable proxies for the physiological processes under food deprivation of individual fish pre-recruits in the laboratory and provide useful metrics for research on the role of starvation in the sea. Highlights ► Biochemical condition (RNA–DNA ratio) decreases exponentially during starvation. ► Starvation parameters of individuals can be derived from data collected on groups. ► Physiological rates of starvation compare well across a broad range of temperatures. ► Species and life stages specific starvation parameters indicate selective adaptation.
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  • 2
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    Linear-elastic crack models of jointing and faulting (1996)
    Elsevier
    In:  Professional Paper, Structural Geology and Personal Computers, New York, Elsevier, vol. 15, no. 16, pp. 359-388, (ISBN 1-86239-165-3, vi + 330 pp.)
    Details
    Publication Date: 1996
    Keywords: cracks and fractures (.NE. fracturing) ; Fracture ; Elasticity ; Rock mechanics ; Mathematica ; MATLAB ; MAPLE ; Modelling ; J ; w/out ; dot
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    BIBLIOGRAPHY SEISMOLOGY
  • 3
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    Fluid flow, methane fluxes, carbonate precipitation and biogeochemical turnover in gas hydrate-bearing sedimenta at Hydrate Ridge, Cascadia Margin: Numerical modeling and mass balances (2003)
    Elsevier
    In:  Geochimica et Cosmochimica Acta, 67 (18). pp. 3403-3421.
    Details
    Publication Date: 2017-09-08
    Description: A numerical model was applied to investigate and to quantify biogeochemical processes and methane turnover in gas hydrate-bearing surface sediments from a cold vent site situated at Hydrate Ridge, an accretionary structure located in the Cascadia Margin subduction zone. Steady state simulations were carried out to obtain a comprehensive overview on the activity in these sediments which are covered with bacterial mats and are affected by strong fluid flow from below. The model results underline the dominance of advective fluid flow that forces a large inflow of methane from below (869 mumol cm(-2) a(-1)) inducing high oxidation rates in the surface layers. Anaerobic methane oxidation is the major process, proceeding at a depth-integrated rate of 870 mumol cm(-2) a(-1). A significant fraction (14%) of bicarbonate produced by anaerobic methane oxidation is removed from the fluids by precipitation of authigenic aragonite and calcite. The total rate of carbonate precipitation (120 mumol cm(-2) a(-1)) allows for the build-up of a massive carbonate layer with a thickness of I m over a period of 20,000 years. Aragonite is the major carbonate mineral formed by anaerobic methane oxidation if the flow velocity of methane-charge fluids is high enough ( greater than or equal to10 cm a(-1)) to maintain super-saturation with respect to this highly soluble carbonate phase. It precipitates much faster within the studied surface sediments than previously observed in abiotic laboratory experiments, suggesting microbial catalysis. The investigated station is characterized by high carbon and oxygen turnover rates (approximate to1000 mumol cm(-2) a(-1)) that are well beyond the rates observed at other continental slope sites not affected by fluid venting. This underlines the strong impact of fluid venting on the benthic system, even though the flow velocity of 10 cm a(-1) derived by the model is relative low compared to fluid flow rates found at other cold vent sites. Non-steady state simulations using measured fluid flow velocities as forcing demonstrate a rapid respond of the sediments within a few days to changes in advective flow. Moreover, they reveal that efficient methane oxidation in these sediments prevents methane outflow into the bottom water over a wide range of fluid flow velocities (〈80 cm a(-1)). Only at flow rates exceeding approximately 100 cm a(-1), does dissolved methane break through the sediment surface to induce large fluxes of up to 5000 mumol CH4 cm(2) a(-1) into the overlying bottom water.
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  • 4
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    The role of sediment recycling in EM-1 inferred from Os, Pb, Hf, Nd, Sr isotope and trace element systematics of the Pitcairn hotspot (2002)
    Elsevier
    In:  Earth and Planetary Science Letters, 196 (3-4). pp. 197-212.
    Details
    Publication Date: 2016-11-15
    Description: We present comprehensive radiogenic isotope (Os, Pb, Hf, Nd, Sr) and trace element data on basaltic lavas from Pitcairn Island and the Pitcairn seamounts and examine the origin of the enriched mantle isotopic signature (EM-1) found in these lavas. The 187Os/188Os ratios of the lavas range from 0.131 to 0.254, while those of the high-Os concentration samples (〉50 pg/g) lie between 0.131 and 0.148. All 187Os/188Os ratios are higher than the bulk silicate Earth reference value of 0.127. Since ancient subcontinental lithospheric mantle (SCLM) is expected to have a 187Os/188Os ratio less than 0.127, it appears that recycled SCLM plays no role in the Pitcairn source. Variations in 187Os/188Os ratios appear to be unconnected with those of 206Pb/204Pb ratios in Pitcairn lavas, suggesting that Pb and Os isotopic variations are controlled by different factors. Modeling shows that variations in Pb isotopic compositions may mainly reflect the proportion of recycled sediment in the source, while those of 187Os/188Os ratios may reflect the proportion of peridotite mantle versus recycled oceanic crust. The occurrence of negative Nb anomalies in some of the lavas, a correlation between Nb anomaly and 87Sr/86Sr ratios (0.7036–0.7051), and extremely unradiogenic and strongly correlated Nd and Hf isotopic compositions (ϵNd of −5.9 to +1.1 and ϵHf of −5.3 to +2.2) together suggest that the Pitcairn mantle source contains a recycled continental crustal component. The slope of the ϵHf vs. ϵNd correlation is shallower for Pitcairn Island than for the Pitcairn seamounts or the global OIB array, and may be due to a variable ratio of recycled mud to sand in the Pitcairn source. A trace element mixing model also indicates the presence of small amounts of recycled pelagic and terrigenous sediment and permits variable amounts of depleted components such as recycled MORB, gabbro and depleted mantle. The 206Pb/204Pb ratios of the Pitcairn lavas vary between 17.47 and 18.10 and are very unradiogenic compared to those of other ocean island basalts. By contrast, 208Pb/204Pb ratios are high and relatively homogeneous at values of ∼39.0. This observation along with the measured Th/U ratios of the lavas, which range up to 14.1, indicate a long-term history of U loss in the Pitcairn source. In 207Pb/204Pb–206Pb/204Pb space, the data form a linear array that can be interpreted in terms of mixing between a minor recycled sediment end member and more depleted material. Lead isotopic compositions suitable for the recycled end member were investigated using a three-stage evolution model by Monte Carlo methods and suggest ages between 0.7 and 1.9 Ga for the recycled sediment. The relationships between measured Th/U and radiogenic 208Pb*/206Pb* ratios suggest that the isotopic arrays displayed by the lavas were produced by mixing, probably occurring during magma genesis.
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  • 5
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    (U-Th)/He Dating of Uplift-Induced Cooling in a Complex Terrestrial Impact Structure: The Manicouagan Example (2014)
    Elsevier
    In:  Chemical Geology, 377 . pp. 56-71.
    Details
    Publication Date: 2020-10-21
    Description: Highlights: • The central uplift of the Manicouagan impact structure has been dated by (U–Th)/He • A (U–Th)/He central age (207.1 ± 6.4 Ma, 2 standard error, n = 40) has been determined • This age reflects the rapid uplift, cooling and closure of He in ~ 1 Gyr-old titanites • This correlates with the previously determined U–Pb impact-melt age of 214 ± 1 Ma • Our new approach enables dating complex impact structures that lack impact melt rocks Abstract Forty titanite grain fragments from 9 central uplift samples of metamorphosed anorthosite from the Manicouagan impact structure were dated by the (U–Th)/He technique. A (U–Th)/He central age of 207.1 ± 6.4 Ma (2 standard error (SE), n = 40) has been determined. With 4 outlier ages removed the central age is refined to 208.9 ± 5.1 Ma (2 SE). Both of these ages are within error of the previously determined U–Pb zircon age of 214 ± 1 Ma (2σ) derived from the impact melt. Manicouagan's central uplift formed due to rapid elevation from ~ 7–10 km depth as part of the modification stage of the impact process, which has facilitated the dating of its emplacement due to resulting rapid exhumation and cooling and closure of the (U–Th)/He system in titanite. Correlation with the previous U–Pb zircon 214 ± 1 Ma impact melt crystallization age indicates that the (U–Th)/He titanite dating technique offers a new approach to dating complex impact structures in the absence of viable melt sheets, or other melt products. The youngest ca. 195 Ma (U–Th)/He dates preserved in some titanite fragments are synchronous with Early Jurassic, rift-induced lithospheric thinning and associated igneous activity that defines the Central Atlantic Magmatic Province (CAMP). The (U–Th)/He titanite data from Manicouagan indicate that the influence of this regional event may extend west of the previously proposed limit of CAMP activity.
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  • 6
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    Freshening of the Marmara Sea prior to its post-glacial reconnection to the Mediterranean Sea (2015)
    Elsevier
    In:  Earth and Planetary Science Letters, 413 . pp. 176-185.
    Details
    Publication Date: 2017-12-19
    Description: During the last glaciation the Marmara Sea was isolated from the Mediterranean Sea because global sea level was below the depth of the Dardanelles sill. Prior to the postglacial reconnection to the Mediterranean Sea (~14.7 cal kyr BP), the surface waters of the Marmara Sea were brackish (Marmara Lake). Freshening of a previously saline Marmara Sea could have happened via spill-out of brackish to fresh water from the surface water of the Black Sea through the Bosphorus Strait. This hypothesis has not been tested against alternative possibilities (salt flushing by river run-off and precipitation). Here we use the dissolved Cl- and stable isotope composition (δO18 and δD) of Marmara Sea sediment pore water to estimate the salinity and stable isotope composition of Marmara Lake bottom water and to evaluate possible freshening scenarios. We use a transport model to simulate pore water Cl-, δO18 and δD in Marmara Sea sediments in the past 130 kyr, which includes the last interglacial (130-75 cal kyr BP), the last glacial (75-14 cal kyr BP) and the current postglacial period. Our results show that the bottom waters of the Marmara Lake were brackish (~4‰ salinity) and isotopically depleted (δO18~-10.2‰ and δD~-70‰, respectively) compared to modern seawater. Their salinity and stable isotope ratios show that they are a mixture of Mediterranean waters and Danube-like waters implying that the freshening took place via spill-out of freshwater through the Bosphorus. Our modelling approach indicates that the transit of fresh water from glacial Eurasia to the Mediterranean via the Marmara Sea started at least 50 cal kyr BP, was continuous throughout most of the last glaciation and persisted up to the post glacial reconnection to the Mediterranean through the Dardanelles sill (14.7 cal kyr BP). These results are consistent with previously published micropaleontological and geochemical investigations of sediment cores that indicate lacustrine conditions in the Marmara Sea from about 75 to 14.7 cal kyr BP.
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  • 7
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    An assessment of the Arctic Ocean in a suite of interannual CORE-II simulations. Part I: Sea ice and solid freshwater (2016)
    Elsevier
    In:  Ocean Modelling, 99 . pp. 110-132.
    Details
    Publication Date: 2020-11-04
    Description: Highlights: • Arctic sea ice extent and solid freshwater in 14 CORE-II models are inter-compared. • The models better represent the variability than the mean state. • The September ice extent trend is reasonably represented by the model ensemble mean. • The descending trend of ice thickness is underestimated compared to observations. • The models underestimate the reduction in solid freshwater content in recent years. Abstract: The Arctic Ocean simulated in fourteen global ocean-sea ice models in the framework of the Coordinated Ocean-ice Reference Experiments, phase II (CORE II) is analyzed. The focus is on the Arctic sea ice extent, the solid freshwater (FW) sources and solid freshwater content (FWC). Available observations are used for model evaluation. The variability of sea ice extent and solid FW budget is more consistently reproduced than their mean state in the models. The descending trend of September sea ice extent is well simulated in terms of the model ensemble mean. Models overestimating sea ice thickness tend to underestimate the descending trend of September sea ice extent. The models underestimate the observed sea ice thinning trend by a factor of two. When averaged on decadal time scales, the variation of Arctic solid FWC is contributed by those of both sea ice production and sea ice transport, which are out of phase in time. The solid FWC decreased in the recent decades, caused mainly by the reduction in sea ice thickness. The models did not simulate the acceleration of sea ice thickness decline, leading to an underestimation of solid FWC trend after 2000. The common model behavior, including the tendency to underestimate the trend of sea ice thickness and March sea ice extent, remains to be improved.
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  • 8
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    An assessment of the Arctic Ocean in a suite of interannual CORE-II simulations. Part II: Liquid freshwater (2016)
    Elsevier
    In:  Ocean Modelling, 99 . pp. 86-109.
    Details
    Publication Date: 2020-11-04
    Description: Highlights: • Arctic liquid freshwater budget simulated in 14 CORE-II models is studied. • The models better represent the temporal variability than the mean state. • Multi-model mean (MMM) FW fluxes compare well with observations. • MMM FWC shows an upward trend in the recent years, with an underestimated rate. • FW flux interannual variability is more consistent where volume flux determines it. Abstract: The Arctic Ocean simulated in 14 global ocean-sea ice models in the framework of the Coordinated Ocean-ice Reference Experiments, phase II (CORE-II) is analyzed in this study. The focus is on the Arctic liquid freshwater (FW) sources and freshwater content (FWC). The models agree on the interannual variability of liquid FW transport at the gateways where the ocean volume transport determines the FW transport variability. The variation of liquid FWC is induced by both the surface FW flux (associated with sea ice production) and lateral liquid FW transport, which are in phase when averaged on decadal time scales. The liquid FWC shows an increase starting from the mid-1990s, caused by the reduction of both sea ice formation and liquid FW export, with the former being more significant in most of the models. The mean state of the FW budget is less consistently simulated than the temporal variability. The model ensemble means of liquid FW transport through the Arctic gateways compare well with observations. On average, the models have too high mean FWC, weaker upward trends of FWC in the recent decade than the observation, and low consistency in the temporal variation of FWC spatial distribution, which needs to be further explored for the purpose of model development.
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  • 9
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    Dissolution kinetics of biogenic silica in the water column (2002)
    Elsevier
    In:  Geochimica et Cosmochimica Acta, 66 (3). pp. 439-455.
    Details
    Publication Date: 2019-07-02
    Description: Stirred flow-through experiments were conducted for the first time with planktonic biogenic silica (BSi). We investigated the dissolution kinetics of uncleaned and chemically cleaned BSi collected in ocean surface water, sediment traps, and sediments from the Norwegian Sea, the Southern Ocean, and the Arabian Sea. The solubility at 2°C is rather constant (1000 to 1200 μM). The dissolution rates are, however, highly variable, declining with water depth, and phytoplankton reactivity is two to three orders of magnitude higher than pure siliceous oozes. The reactivity decrease correlates well with an increase in the integrated peak intensity ratios of Si-O-Si/Si-OH measured by Fourier transform infrared (FTIR) spectroscopy. The removal of organic or inorganic coatings enhance the reactivity by at least an order of magnitude. Atomic Al/Si ratios of 0.03 to 0.08 in sedimentary diatom frustules decrease significantly to 0.02 as a result of removal of inorganic coatings and detritals present. Near equilibrium, the dissolution rates exhibit a linear dependence on the degree of undersaturation. At higher degrees of undersaturation—that is, at low concentrations of dissolved silica—the dissolution rates of uncleaned samples define a nonlinear trend. The nonlinear kinetics imply that the dissolution of natural BSi is strongly accelerated in silica-depleted surface waters. The FTIR results suggest that internal condensation reactions reduce the amount of surface reaction sites and are partly responsible for the reactivity decrease with depth. The high content of Al in sedimentary BSi is likely caused by precipitation of dissolved silica with Al dissolved from minerals in sediment. Nonbiogenic silica as coatings or detritals are partly responsible for the solubility and reactivity decrease of BSi in sediments. One order of magnitude different rate constants measured in Norwegian Sea and Southern Ocean sediment trap material support the so-called opal paradox—that is, high BSi accumulation rates in sediments in spite of low BSi production rates in surface waters of the Southern Ocean.
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  • 10
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    Hot vents in an ice-cold ocean: Indications for phase separation at the southernmost area of hydrothermal activity, Bransfield Strait, Antarctica (2001)
    Elsevier
    In:  Earth and Planetary Science Letters, 193 (3-4). pp. 381-394.
    Details
    Publication Date: 2016-11-15
    Description: During the expeditions ANT-XV/2 with R/V Polarstern in 1997/98 and NBP 99-04 with R/V IB N.B. Palmer in 1999, the first samples of hydrothermally influenced sediments of Bransfield Strait were obtained at Hook Ridge, a volcanic edifice in the Central Basin of the Strait. The vent sites are characterized by white siliceous crusts on top of the sediment layer and temperatures measured immediately on deck are up to 48.5°C. The shallow depth of these vent sites (1050 m) particularly controls the chemistry of the pore fluids that are enriched in silica and sulfide and show low pH values. Chloride is depleted up to 20% and the calculated hydrothermal endmember concentration is in the range of 1–84 mM. Since other mechanisms for Cl depletion can be ruled out clearly, the composition of this fluid is attributed to phase separation. While the Cl-depleted fluid is emanating at Hook Ridge, a Cl-enriched fluid can be identified in the adjacent King George Basin. Using a p,x diagram the two corresponding endmember concentrations reveal that the phase separation takes place at subcritical conditions (total depth: ∼2500 m), probably along the whole volcanic edifice
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