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  • 1
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    Estimate of mid-Pliocene Paleo-pCO2 for ODP Hole 130-806 (Table 1) (1996)
    PANGAEA
    In:  Supplement to: Raymo, Maureen E; Grant, B; Horowitz, Michael; Rau, Greg H (1996): Mid-Pliocene warmth: stronger greenhouse and stronger conveyor. Marine Micropaleontology, 27(1-4), 313-326, https://doi.org/10.1016/0377-8398(95)00048-8
    Details
    Publication Date: 2024-01-09
    Description: Three million years ago, prior to the onset of northern hemisphere glaciation, global mean temperatures may have been as much as 3.5 °C warmer than at present. We present evidence, based on the carbon isotopic composition of marine organic matter, that atmospheric CO2 levels at this time were on average only about 35% higher than the preindustrial value of 280 ppm. We also present carbon isotopic evidence for stronger thermohaline circulation in the Atlantic Ocean during the warmest intervals and propose that the North Atlantic “conveyor belt” may act as a positive feedback to global warming by enhancing sea ice retreat and decreasing high latitude albedo. Based on our results, it seems unlikely that the mid Pliocene warm period was a doubled CO, world.
    Keywords: -; 130-806; AGE; Carbon/Nitrogen ratio; COMPCORE; Composite Core; DEPTH, sediment/rock; DSDP/ODP/IODP sample designation; Joides Resolution; Leg130; North Pacific Ocean; Ocean Drilling Program; ODP; Partial pressure of carbon dioxide (ambient atmosphere); Sample code/label; Sea surface temperature, annual mean; δ13C, dissolved inorganic carbon; δ13C, organic carbon
    Type: Dataset
    Format: text/tab-separated-values, 571 data points
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    DATA PANGAEA
  • 2
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    On the Limitations and Implications of Modeling Heat Transport in Porous Aquifers by Assuming Local Thermal Equilibrium (2021)
    Details
    Publication Date: 2021-10-15
    Description: Heat transport in natural porous media, such as aquifers or streambeds, is generally modeled assuming local thermal equilibrium (LTE) between the fluid and solid phases. Yet, the mathematical and hydrogeological conditions and implications of this simplification have not been fully established for natural porous media. To quantify the occurrence and effects of local thermal disequilibrium during heat transport, we systematically compared thermal breakthrough curves from a LTE with those calculated using a local thermal nonequilibrium (LTNE) model, explicitly allowing for different temperatures in the fluid and solid phases. For the LTNE model, we developed a new correlation for the heat transfer coefficient representative of the conditions in natural porous aquifers using six published experimental results. By conducting an extensive parameter study (〉50,000 simulations), we show that LTNE effects do not occur for grain sizes smaller than 7 mm or for groundwater flow velocities that are slower than 1.6 m day−1. The limits of LTE are likely exceeded in gravel aquifers or in the vicinity of pumped bores. For such aquifers, the use of a LTE model can lead to an underestimation of the effective thermal dispersion by a factor of up to 30 or higher, while the advective thermal velocity remains unaffected for most conditions. Based on a regression analysis of the simulation results, we provide a criterion which can be used to determine if LTNE effects are expected for particular conditions.
    Keywords: 551 ; local thermal nonequilibrium ; thermal dispersion ; modeling advective heat transport ; local thermal equilibrium ; porous aquifer
    Language: English
    Type: map
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    CITATION GEO-LEO
  • 3
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    CO2aq-dependent photosynthetic 13C fractionation in the ocean: A model versus observations (1997)
    AGU (American Geophysical Union)
    In:  Global Biogeochemical Cycles, 11 . pp. 267-278.
    Details
    Publication Date: 2018-03-14
    Description: A theoretical model of CO2aq-dependent phytoplankton carbon isotope fractionation (єp) and abundance (δ13Corg) is compared to observed isotopic trends with temperature and [CO2aq] in the ocean. It is shown that the model's δ13Corg response to surface ocean temperature and to [CO2aq] can simulate observed trends when the other independent model variables (phytoplankton cell growth rate, cell size, cell membrane CO2 permeability, and enzymatic isotope fractionation) are held at realistic, constant values. The possible contribution made by each of these variables to the residual scatter in δ13Corg about its trends with temperature and [CO2aq] is quantified, thus estimating a maximum isotopic sensitivity to changes in each of these variables. The model response to growth rate and especially cell size, however, appears to be unrealistically high. This may occur because the net isotopic effects of such factors may be attenuated through dependent and isotopically offsetting variations among variables. The model's indicated sensitivity to such factors as CO2 permeability, enzymatic fractionation, cell size, and cell surface area/volume provides mechanisms whereby changes in species composition can play a significant role in affecting observed variations in oceanic δ13Corg. Overall, the model is consistent with earlier suggestions that marine δ13Corg and єp variability can be explained by carbon isotope fractionation evoked by CO2aq-dependent phytoplankton. This has important implications for interpreting carbon isotopic variability encountered in plankton and their organic constituents in the present-day ocean and in the marine sedimentary record.
    Type: Article , PeerReviewed
    Format: text
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    PAPER (OCEANREP)
  • 4
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    A model of photosynthetic 13C fractionation in marine phytoplankton based on diffusive molecular CO2 uptake (1996)
    Inter Research
    In:  Marine Ecology Progress Series, 133 . pp. 275-285.
    Details
    Publication Date: 2018-05-08
    Description: A predictive model of carbon isotope fractionation (sigma p) and abundance (delta13C phyto) is presented under circumstances where photosynthesis is strictly based on CO2(aq) that passively diffuses into marine phytoplankton cells. Similar to other recent models, the one presented here is based on a formulation where the expression of intracellular enzymatic isotope fractionation relative to that imposed by CO2(aq) transport is scaled by the ratio of intracellular to external [CO2(aq)], ci/ce. Unlike previous models, an explicit calculation of ci is made that is dependent on ce as well as cell radius, cell growth rate, cell membrane permeability to CO2(aq), temperature, and, to a limited extent, pH and salinity. This allows direct scaling of ci/ce to each of these factors, and thus a direct prediction of sigma p and delta13C phyto responses to changes in each of these variables. These responses are described, and, where possible, compared to recent experimental and previous modeling results.
    Type: Article , PeerReviewed
    Format: text
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    PAPER (OCEANREP)
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