Comparison of climate model results with European vegetation and permafrost during oxygen isotope stage three

Oxygen isotope stage 3 (OIS3), an interstade between approximately 60,000 and 25,000 yr B.P., presents an ideal opportunity to compare high-resolution climate simulations with the geologic record. To facilitate this comparison, the results of a mesoscale climate model (RegCM2) embedded in the GENESIS GCM are utilized to drive a vegetation model (BIOME 3.5). The BIOME output is then compared with OIS3 compilations derived from pollen. The simulated biomes agree well with the pollen-based biomes in southern Europe; however, disagreements occur in the northern part of the domain. The most striking mismatch involves the distribution of tundra. The models fail to have tundra extend to its observed position as far south as 50°N in central Europe during OIS3. The model also fails to have permafrost extend southward to its observed position between 50°N and 55°N in western Europe during OIS3. A variety of sensitivity experiments are performed to investigate these mismatches. These experiments demonstrate the importance of annual and summer temperatures and the length of the winter season in creating improved matches between the model results and the inferred distributions of vegetation and permafrost in northern Europe.     

Detrital zircon U–Pb geochronology of Permian strata in the Galilee Basin,Queensland, Australia

The late Carboniferous to Triassic tectonic history of eastern Australia includes important periods of regional-scale crustal extension and contraction. Evidence for these periods of tectonism is recorded by the extensive Pennsylvanian (late Carboniferous) to Triassic basin system of eastern Australia. In this study, we investigate the use of U–Pb dating of detrital zircons in reconstructing the tectonic development of one of these basins, the eastern Galilee Basin of Queensland. U–Pb detrital zircon ages were obtained from samples of stratigraphically well-constrained Cisuralian and Lopingian (early and late Permian, respectively) sandstone in the Galilee Basin. Detrital zircons in these sandstones are dominated by a population with ages in the range of 300–250 Ma, and ages from the youngest detrital zircons closely approximate depositional ages. We attribute these two fundamental findings to (1) appreciable derivation of detrital zircons in the Galilee Basin from the New England Orogen of easternmost Australia and (2) syndepositional magmatism. Furthermore, Cisuralian sandstone of the Galilee Basin contains significantly more >300 Ma detrital zircons than Lopingian sandstone. The transition in detrital zircon population, which is bracketed between 296 and 252 Ma based on previous high-precision U–Pb zircon ages from Permian ash beds in the Galilee Basin, corresponds with the Hunter–Bowen Orogeny and reflects a change in the Galilee Basin from an earlier extensional setting to a later foreland basin environment. During the Lopingian foreland basin phase, the individual depocentres of the Galilee and Bowen basins were linked to form a single and enormous foreland basin that covered >300 000 km² in central and eastern Queensland.     

Spreading of submarine slopes caused by trenching

Abstract

Submarine trenching for pipeline installation in potentially unstable sediments has recently been of increasing concern. Although typical pipeline depths are less than 3 or 4 m, trenching operations generally cause local stress concentrations within the sediments and induce excess pore pressures. The result of these stress concentrations and pore pressure increases may be spreading of submarine slumps that can endanger pipelines or other nearby installations. A simplified analytical approach is described to estimate the extent of slump spreading caused by trenching. It is shown that the spreading potential is affected by many geotechnical characteristics of the sediments in addition to geomorphic processes and the oceanographic regimes governing the area. The primary geotechnical factors that influence spreading include the porepressure parameter A_f , the degree of consolidation, the coefficient of earth pressure at rest, and the strength characteristics of the soil. Dimensionless parameters are developed to illustrate graphically the functional relationships among these parameters. A Gulf of Mexico soil profile is used to quantify the spreading phenomenon.     

Aspartic acid racemization in Late Wisconsin Lake Ontario sediments

We have determined aspartic acid racemization and [¹⁴C] ages in sediment from a 17-m piston core recovered from Lake Ontario. This core represents a depositional record extending back into the Late Wisconsin. Total organic radiocarbon ages of the glaciolacustrine lower section of the core are older than the true depositional age. Hence we suggest that these ages do not represent time elapsed since deposition but rather may be up to several thousand years too old due to mixing with ¹⁴C-depleted organic matter and possibly also d-amino acids contained by the glacier and deposited as the glacier receded. Further studies are suggested that might test this hypothesis as well as establish the general applicability of racemization dating to clay sediments.     

Climate change impacts on coral reefs: Synergies with local effects,possibilities for acclimation,and management implications

Most reviews concerning the impact of climate change on coral reefs discuss independent effects of warming or ocean acidification. However, the interactions between these, and between these and direct local stressors are less well addressed. This review underlines that coral bleaching, acidification, and diseases are expected to interact synergistically, and will negatively influence survival, growth, reproduction, larval development, settlement, and post-settlement development of corals. Interactions with local stress factors such as pollution, sedimentation, and overfishing are further expected to compound effects of climate change.     

Minor and trace elements in some meteoritic minerals

The mineral phases including olivine, orthopyroxene, clinopyroxene, troilite, nickel-iron, plagioclase, chromite and the phosphates were separated from several meteorites. These were a hypersthene chondrite (Modoc), a bronzite chondrite (Guareña), an enstatite chondrite (Khairpur), and two eucrites (Haraiya and Moore County); diopside was separated from the Nakhla achondrite. The purified minerals were analyzed for trace and minor elements by spark source mass spectrometry and instrumental neutron activation analysis. On the meteorites examined our results show that Co, Ni, Cu, Ge, As, Ru, Rh, Pd, Sn, Sb, W, Re, Os, Ir, Pt and Au are entirely or almost entirely siderophile; Na, Rb, Sr, Y, Ba and the rare earth elements lithophile; Se chalcophile. The transition elements So, Ti, V, Cr and Mn are lithophile in most stony meteorites, but show chalcophile affinities in the enstatite chondrites (and enstatite achondrites), as do Zn, Zr and Nb. In the ordinary chondrites Ga shows both lithophile and siderophile affinities, but becomes entirely siderophile in the enstatite chondrites. Molybdenum and tellurium show strong siderophile and weaker chalcophile affinity. The lithophile elements are distributed among the minerals according to the crystallochemical factors, the most effective controlling factor being ionic size.     

Satellite-derived vegetation index and cover type maps for estimating carbon dioxide flux for arctic tundra regions

The spatial variability and co-variability of two different types of remote sensing derivatives that portray vegetation and geomorphic patterns are analyzed in the context of estimating regional-scale CO₂ flux from land surfaces in the arctic tundra. For a study area encompassing the Kuparuk River watershed of the North Slope of Alaska, we compare satellite-derived maps of the normalized difference vegetation index (NDVI) generated at two different spatial resolutions to a map of vegetation types derived by image classification of data from the Landsat multispectral scanner (MSS). Mean values of NDVI for each cover type stratum are unique (with the exception of moist acidic tundra and shrubland types). Based on analysis of semi-variograms generated for SPOT-NDVI data, most of the vegetation cover and landform features of this arctic tundra landscape have spatial dimensions of less than 1 km. Thaw lakes on the coastal plain and glacial depositional landforms, such as moraines in the foothills, seem to be the largest features, with vegetation units having dimensions no larger than 700 m. Frequency distributions of NDVI and vegetation types extracted for sampling transects flown by an aircraft sensing CO₂ flux, relative to distributions for the entire Kuparuk River watershed, suggest a slight sampling bias towards greater cover of mesic wet sedge tundra and thaw lakes and associated lower NDVI values. The regional pattern of NDVI for the North Slope of Alaska corresponds primarily to differences between the two major physiographic provinces of this region.     

Using fuzzy logic for modeling aquifer architecture

Modeling the geologic architecture of an aquifer and visualizing its three-dimensional structure require lithologic data recorded during well drilling. Uncertainties in layer boundaries arise due to questionable quality of drilling records, mixing during the drilling process, which results in blurred contacts, and natural heterogeneity of the geologic materials. An approach for modeling and visualizing the spatial distribution of aquifer units three-dimensionally based on fuzzy set theory is developed. An indicator is defined for evaluating the possibility of aquifer existence based on fuzzy set theory and probability principles. A specific interpolation method for aquifer 3D spatial distribution requiring only very basic borehole log data is proposed. A 3D modeling and visualization system for aquifers is also developed, which can implement basic GIS functions, like borehole identification and cross-section creation. The methodology developed is tested using real borehole lithology data available for an aquifer in British Columbia, Canada.

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Suspended sediment source apportionment in Chesapeake Bay watershed using Bayesian chemical mass balance receptor modeling

A Bayesian chemical mass balance approach was used to estimate the contributions of potential sources into the suspended sediments in the Mill Stream, a tributary of Chesapeake Bay in Maryland, US. The Bayesian approach allows us to incorporate the uncertainties as a result of measurement errors in the elemental profiles of sources and suspended sediments in the stream and also the heterogeneities of the elemental profiles among samples into the analysis and provides us with probability densities representing the contribution of each source. Based on the obtained results, river bank erosion is the major source of sediments with a contribution estimated to range from 83% to 99% with a 95% credible interval. Also, a 95% credible interval in a range of 0.06% to 8% for cropland and 0.1% to 14% for forestland was provided. Hence, while the contribution of sediments from cropland or forestland cannot be ruled out, the model does not definitively demonstrate a significant contribution from either source. Copyright © 2012 John Wiley & Sons, Ltd.     

Fossil spreading center and faults within the Panama Fracture Zone

The north/south-trending Panama Fracture Zone forms the present eastern boundary of the Cocos Plate, with the interplate motion being right-lateral strike-slip. This fracture zone is composed of at least four linear troughs some hundreds of kilometers in length. Separate active or historic faults undoubtedly coincide with each trough. The greatest sediment fill is found in the easternmost trough. Surface and basement depths of the western trough are generally greater than those of the other three; the western trough contains the least sediment, and is most continually linear. Morphology and sediments suggest that the principal locus of strike-slip movement within the fracture zone probably migrated incrementally westward from one fault-trough to another. From north to south, the fracture zone apparently narrows from the continental intersection to approximately 5°30N, and again widens from about 5°N to at least 3°N. Residual E/W-trending magnetic anomalies are centered between two of the four troughs; sea floor spreading in a north-south direction is interpreted to have occurred between 5°30N and 7°N from 4.5 m.y. ago to 2 m.y. ago, with the symmetric center roughly coinciding with a rift valley at 6°10N, 82°30W.