THE IMPACT-FLOOD CONNECTION: DOES IT EXIST?*

In a recent article in Terra Nova, Kristan-Tollmann and Tollmann (1994) suggested that the Biblical Flood can be explained by seven fragments of a comet that impacted the ocean at seven locations on Earth at 03.00h (C.E.T.) on 23 September, 9545 yr BP. We demonstrate that all the ‘geological proofs’ that allegedly support their conclusions are not supported by the available data on impact cratering. Their hypothesis is based on insufficient and ambiguous data, selective citation, and incomplete comprehension of previous research.     

Factors controlling the chemical evolution of travertine‐depositing rivers of the Barkly karst,northern Australia

Groundwaters feeding travertine‐depositing rivers of the northeastern segment of the Barkly karst (NW Queensland, Australia) are of comparable chemical composition, allowing a detailed investigation of how the rate of downstream chemical evolution varies from river to river. The discharge, pH, temperature, conductivity and major‐ion concentrations of five rivers were determined by standard field and laboratory techniques. The results show that each river experiences similar patterns of downstream chemical evolution, with CO₂ outgassing driving the waters to high levels of calcite supersaturation, which in turn leads to widespread calcium carbonate deposition. However, the rate at which the waters evolve, measured as the loss of CaCO₃ per kilometre, varies from river to river, and depends primarily upon discharge at the time of sampling and stream gradient. For example, Louie Creek (Q = 0·11 m³ s^?1) and Carl Creek (Q = 0·50 m³ s^?1) have identical stream gradients, but the loss of CaCO₃ per kilometre for Louie Creek is twice that of Carl Creek. The Gregory River (Q = 3·07 m³ s^?1), O'Shanassy River (Q = 0·57 m³ s^?1) and Lawn Hill Creek (Q = 0·72 m³ s^?1) have very similar gradients, but the rate of hydrochemical evolution of the Gregory River is significantly less than either of the other two systems. The results have major implications for travertine deposition: the stream reach required for waters to evolve to critical levels of calcite supersaturation will, all others things being equal, increase with increasing discharge, and the length of reach over which travertine is deposited will also increase with increasing discharge. This implies that fossil travertine deposits preserved well downstream of modern deposition limits are likely to have been formed under higher discharge regimes. Copyright © 2002 John Wiley & Sons, Ltd.     

Advection in plankton models with variable elemental ratios

As ocean biogeochemical models evolve to permit the elemental composition of plankton populations and dissolved organic matter to vary, each element is normally assigned a separate state variable, which is advected and mixed independently of the others. In a population of cells with varying elemental quotas, the proper currency of the advection operator is subpopulations of similar cells. The spatial gradient in total C, N, or P summed over the spectrum of such subpopulations is identical to that calculated for the population means, so treating the various elements as independent should generally be a valid approximation. However, errors can arise in high-order advection schemes with nonlinear corrector terms, which are not additive across the subpopulations. Some numerical examples indicate that these errors are relatively small [O(10⁻³–10⁻⁴)] but can be as high as O(10⁻²) in certain cases. As grid resolution varies, the error scales approximately to the Courant number.     

Main Species Characteristics of Phytoplankton Spring Blooms in NE Atlantic and Arctic Waters (68–80° N)

A compilation of phytoplankton species abundance data from the spring bloom along the northern Norwegian coast and in the Barents Sea shows that the quantitatively most important species are the prymnesiophyte Phaeocystis pouchetii and the common cold water to temperate diatoms Chaetoceros socialis, Skeletonema costatum sensu lato, Fragilariopsis oceanica, Thalassiosira spp., Chaetoceros furcellatus, Chaetoceros compressus, Chaetoceros debilis and Bacterosira bathyomphala. The relative abundance of diatoms and Phaeocystis varied highly and apparently stochastically between years. P. pouchetii occurred during all stages of the spring bloom and sometimes completely dominated the phytoplankton community. Along the Norwegian coast, the importance of P. pouchetii increased northwards. The species composition in coastal fjords at 70° N is surprisingly similar to that of shelf waters in the Barents Sea (up to 80° N). An exception is S. costatum sensu lato which was seldom observed in Arctic waters. Small flagellates (<10 μm) other than dinoflagellates and P. pouchetii are also important among the Barents Sea spring phytoplankton. Associations of species seem rigid over time and are dominated by C. socialis and P. pouchetii in northern waters. Biogeographical categories of spring bloom species in relation to environmental conditions are discussed.     

Excess of bottom-released methane in an Arctic shelf sea polynya in winter

Latent heat polynyas are regions generating strong ice formation, convection and extensive water mass formation. Here we report on the effects of these processes on resuspension of sediments and subsequent methane release from the seafloor and on the resulting excess methane concentration in surface water on a polar shelf during winter. The study is based on measurements of concentration and δ¹³C values of methane, water temperature, salinity, light transmission and sea ice data collected in March 2003 in Storfjorden, southern Svalbard. In winter, strong and persistent northeasterly winds create polynyas in eastern Storfjorden and cause ice formation. The resulting brine-enriched water cascades from the Storfjordbanken into the central depression thereby enhancing the turbulence near the seafloor. A distinct benthic nepheloid layer was observed reflecting the resuspension of sediments by the cascading dense bottom water. High concentrations of ¹³C-depleted methane suggest submarine discharge of methane with the resuspended sediments. As the source of the submarine methane, we propose recent bacterial methanogenesis near the sediment surface because of extremely high accumulation rates of organic carbon in Storfjorden. Convective mixing transports newly released methane from the bottom to the sea surface. This eventually results in an excess concentration in surface water with respect to the atmospheric equilibrium, and a sea-air flux of methane during periods of open water. When a new ice cover is formed, methane becomes trapped in the water column and subsequently oxidized. Thus, the residual methane is strongly enriched in ¹³C in relation to the δ¹³_CCH4${\delta }^{13}{\mathrm{C}}_{{\mathrm{CH}}_4}$ signature of atmospheric methane. Our results show that latent heat polynyas may induce a direct pathway for biogases like methane from sediments to the atmosphere through coupling of biogeochemical and oceanographic processes. Extrapolating these processes to all Arctic ocean polynyas, we estimate a transfer of CH₄ between 0.005 and 0.02 Tg yr⁻¹. This is not a large contribution but the fluxes from the polynyas are 20–200 times larger than the ocean average and the methane evasion process in polynyas is certainly one that can be altered under climate change.     

The challenge to detect and attribute effects of climate change on human and natural systems

Future scenarios of the energy system under greenhouse gas emission constraints depict dramatic growth in a range of energy technologies. Technological growth dynamics observed historically provide a useful comparator for these future trajectories. We find that historical time series data reveal a consistent relationship between how much a technology’s cumulative installed capacity grows, and how long this growth takes. This relationship between extent (how much) and duration (for how long) is consistent across both energy supply and end-use technologies, and both established and emerging technologies. We then develop and test an approach for using this historical relationship to assess technological trajectories in future scenarios. Our approach for “learning from the past” contributes to the assessment and verification of integrated assessment and energy-economic models used to generate quantitative scenarios. Using data on power generation technologies from two such models, we also find a consistent extent - duration relationship across both technologies and scenarios. This relationship describes future low carbon technological growth in the power sector which appears to be conservative relative to what has been evidenced historically. Specifically, future extents of capacity growth are comparatively low given the lengthy time duration of that growth. We treat this finding with caution due to the low number of data points. Yet it remains counter-intuitive given the extremely rapid growth rates of certain low carbon technologies under stringent emission constraints. We explore possible reasons for the apparent scenario conservatism, and find parametric or structural conservatism in the underlying models to be one possible explanation.     

Sila dialogues on climate change: Inuit wisdom for a cross-cultural interdisciplinarity

This research begins with the recognition that climate change researchers have become interested in Inuit ecological observations because of the importance of northern changes on the global climate system, but this research often marginalizes Inuit understandings of these climate-related changes. The direct translation of the Inuktitut term Sila in much of this research is a case study in this methodological problem. In contrast to climate research translations of Sila as weather, ethnographies of Inuit conceive of Sila as a spiritual power that is related to the weather. These diverging interpretations of Sila reflect the difficulty of conducting cross-cultural research. To mitigate this difficulty a dialogue was engaged with Inuit concerning their experience of climate change in relation to the different Inuit and Western understandings of Sila. The central goals of this paper are to clearly define Sila so as to identify implications it may have for Western approaches in conducting cross-cultural climate research, and, in the process, to begin a cross-cultural dialogue that aims at an agreed upon understanding of climate change that is respectful of different knowledges.     

Gas-Phase Formation of Water-Soluble Organic Compounds in the Atmosphere: A Retrosynthetic Analysis

Atmospheric particles contain a myriad of organiccompounds, including many multifunctional,water-soluble organic compounds. Many of thesecompounds are postulated to be secondary of origin. This work investigates the possible precursors ofseveral classes of multifunctional, water-solublesecondary organic compounds by analyzing the pathwaysleading to their formation, based on known gas-phasereactions. The analysis is termed `retrosynthetic'due to the backward direction of the analysis, fromproducts to precursors. Pathways for multi-functionalcompounds were generated combinatorially, consideringthe formation of one functional group at a time.Many multifunctional organic compounds with carboxylicacid, carbonyl, and hydroxy functional groups werefound to be first- or second-generation products ofcommon anthropogenic and biogenic volatile organiccompounds such as alkanes, alkenes, aromatics, andcyclic alkenes. The estimated yields of water-solubleorganic compounds from primary precursors ranged fromless than 1% to over 10%, based on stoichiometricconsiderations. The SOA formation index, whichcombines the concepts of yields and rates, was used tocompare the feasibility of the retrosyntheticpathways. Many of the candidate pathways involve theisomerization reaction of alkoxy radicals andoxygenated intermediate products such asmonocarboxylic acids and hydroxyaldehydes.