Intensified mid-Holocene Asian monsoon recorded in corals from Kikai Island, subtropical northwestern Pacific

Coupled records of Sr/Ca and oxygen isotope ratios (δ¹⁸O) of coral skeletons have been used to produce quantitative estimates of paleo-sea surface temperature (SST) and δ¹⁸O of surface seawater that can in some cases be converted to sea surface salinity (SSS). Two fossil corals from Kikai Island in the subtropical northwestern Pacific, a location affected by East Asian summer and winter monsoons, were analyzed to investigate differences between mid-Holocene and present-day SST and SSS. At 6180 cal yr BP, SSTs were roughly the same as today, both in summer and winter; δ¹⁸O_seawater and SSS values were higher both in summer (+ 0.5‰, +1.1 psu) and in winter (+ 0.2‰, + 0.6 psu) than modern values. At 7010 cal yr BP, SSTs were slightly cooler both in summer and winter (−0.8 and −0.6 °C), whereas δ¹⁸O_seawater and SSS had higher values in summer (+ 0.3‰, + 0.6 psu) and in winter (+ 0.8‰, + 1.9 psu) than present-day values. These results are consistent with other marine records for the mid-Holocene of the low and midlatitudes in the northwestern Pacific. Such regional conditions indicate that the East Asian summer and winter monsoons were more intense in the mid-Holocene, which was likely a function of the mid-Holocene insolation regime.     

An analytical study of the effect of penetration rate on piezocone tests in clay

Finite element cavity expansion analysis investigating the effect of penetration rate on piezocone tests in clay is presented. A coupled analysis was performed, in which the rate of cavity expansion was linked to the penetration rate of the cone and the cone angle, using the assumption that the deformation was wholly radial, and took place only between the cone tip and the cone shoulder. The soil was modelled using modified cam clay with two sets of parameters and varying values of overconsolidation ratio (OCR). The influence of penetration rate on the stress and pore pressure distributions was examined. For slower penetration rates, the excess pore pressure at the cone shoulder is lower since consolidation is permitted coincident with penetration. The radial profiles of post‐penetration voids ratio demonstrate that partially drained penetration is permitted by volume change in the near field, in addition to radial movement in the far field. The radial distribution of excess pore pressure after slow penetration differs from the undrained case, with a relatively low radial gradient existing at the cone face. As a result, the dissipation curves after slow penetration lag behind those following fast penetration. The cone velocity is made dimensionless by normalizing with the coefficient of consolidation and the cone diameter. ‘Backbone’ curves of normalized velocity against normalized tip resistance and excess pore pressure capturing the transition from undrained to drained penetration are derived. The normalized pore pressure backbone curve is unique, whilst the normalized tip resistance shows a small dependency on OCR. These backbone penetration curves are compared with centrifuge model piezocone tests conducted at varying rates, and subsequent dissipation tests. The numerical and experimental results suggest that the value of consolidation coefficient operative during the dissipation phase is 2–4 times higher than the virgin compression value due to changes in the operative soil stiffness, as demonstrated from the stress paths of individual soil elements. The use of multi‐rate penetration tests to deduce values of consolidation coefficient is discussed, in light of these differences. Copyright © 2005 John Wiley & Sons, Ltd.     

Object Models with Vector Steering

Object models are widely used to model the distribution of facies in a reservoir. Several computer programs exist for modelling fluvial channels or more general facies objects. This paper focuses on a marked point model with objects that are able to orient locally according to a vector field. In this way, objects with locally varying curvature are created. With this kind of objects it is possible to model complex depositional basins, that are not easily modelled with conventional methods. The new object type is called Backbone objects. The objects have a piecewise linear centerline and are able to follow the direction of a three-dimensional vector field locally in lateral and vertical direction. How well the objects follow the vector field is determined by three parameters. Use of different coordinate systems and mapping between the systems make it possible to generate Gaussian random fields that follow the shape and direction of the objects. The Gaussian fields can be used to model petrophysical variables, which is important for fluid flow modelling.     

Inshore fishing interests on the Atlantic coast: Their response to extended jurisdiction by Canada

Atlantic Canada has many small fishing communities where the patterns of fisheries are extremely variable and incomes are generally very low. Federal and provincial governments and fish processing corporations play a pervasive role in a complex set of conflicts and relationships between the different interest groups among the fishermen. This article demonstrates how inshore/nearshore fisheries developed, before and after extended jurisdiction, in relation to developing government policies. Patterns of behaviour so far registered raise questions about alternative consultative frameworks and tenure systems, and associated systems of representation.     

Some Probability Applications to Oil Exploration

In the first part of this paper, a portion of a sedimentary basin is subdivided conceptually into hexagons of equal area. The area of each hexagon is equal to the minimum area an oil field should have to be commercial. Hexagons can be full of oil, or empty. A field size 1 consists of a cell with oil surrounded by six empty cells; a field size 2 consists of two adjacent cells with oil surrounded by eight empty cells, etc. Principles of Percolation Theory are used to determine the probabilility distribution of the areas of the oil fields existing in this portion of the basin. The only piece of information necessary to determine this probability distribution is the Success Ratio (number of successful exploration wells/total number of exploration wells drilled in this portion of the basin). This approach has several practical applications.In the second part of this paper, a probabilistic model is introduced to predict to which extent potential oil traps are filled with oil. The model assumes that the probability that an oil unit will end up in a particular trap, is proportional to the surface area of the trap. The model predicts that independently of the distribution of the trap volumes, there will be a critical trap volume. All the traps having a volume less than this critical volume, will be filled to spill point. An equation is deduced to predict, for all traps having a volume greater than the critical, the volume of oil that can be encountered in the trap, provided the volume of the trap is known.     

Punctuated recovery of sediments and benthic infauna: a 19-year study of tailings deposition in a British Columbia fjord.

Sediment organic and metal chemistry, benthic infauna and tissue contaminants surveys have been conducted over 19 years before and following tailings deposition from a metal (Mo, Pb, Zn) mine in Alice Arm, a British Columbia fjord. We found changes in benthic fauna and habitat after tailings disposal to be predictable in terms of sediment chemistry and faunal recolonization. What was not predictable was the timing and extent of slope failure or resuspension following abandonment. These events can have essentially the same or greater effect than the initial tailings disposal and produce long-term unpredictability particular to cases of submarine disposal on slopes. The present study focused on the submarine deposition of 4 x 10(6) tonnes of tailings during an 18-months period ending October 1982. When the mine closed, gross defaunation had occurred at three stations in the tailings path, and two others showed recent defaunation and recolonization. A year later, a large tailings slump near the outfall transported tailings to the deep basin; fauna were impoverished both in the slump region and through most of the deep basin. Declining metal concentrations in surface sediments was accompanied by considerable recovery of fauna 3 years after the mine closed. Nevertheless, fauna at the three stations defaunated at the time of mine closure could still be statistically distinguished from all other stations due to high abundances of small opportunistic polychaetes and bivalves. A resuspension in tailings between 1988 and 1990 coincided with a moderate decline in abundance of all macrofauna taxa. From 1989 to 1995 recovery toward natural sediment conditions was evident as increasing organic content together with the highest faunal biomass values found during the study. Small polychaetes were the first recolonizers in defaunated areas, whereas small bivalves were more tolerant of moderate tailings deposition. By 1989 and 1995 small colonizers had declined and amphipods and larger echinoderms had increased. Dominant species patterns and exceptionally high biomass values in 1995 show that the largest fauna did not recover until much later than smaller taxa. One genus of bivalve (Yoldia spp.) accumulated metals in a pattern similar to the sediment chemistry, indicating that the metals from the most recent mine had entered the benthic food chain. It is not possible to tell from this study whether biota were affected by toxicity from metals. However, many of the observed biotic effects could be caused by physical disruption from tailings.     

A record of Holocene environmental and ecological changes from Wildwood Lake,Long Island,New York

Analyses of pollen, charcoal and organic content in a lake sediment core from Wildwood Lake, Long Island, New York, provide insights into the ecological and environmental history of this region. The early Holocene interval of the record (ca. 9800–8800 cal. a BP) indicates the presence of Pinus rigida–Quercus ilicifolia woodlands with high fire activity. A layer of sandy sediment dating to 9200 cal. a BP may reflect a brief period of reduced water depth, consistent with widespread evidence for cold, dry conditions at that time. Two other sandy layers, bracketed by ¹⁴C dates, represent a sedimentary hiatus from ca. 8800 to 4500 cal. a BP. This discontinuity may reflect the removal of some sediment during brief periods of reduced water depth at 5300 and 4600 cal. a BP. In the upper portion of the record (<4500 cal. a BP), subtle changes at ca. 3000 cal. a BP indicate declining prevalence of Quercus–Fagus–Carya forests and increasing abundance of Pinus rigida, perhaps due to reduced summer precipitation. Elevated percentages of herbaceous taxa in the uppermost sediments represent European agricultural activities. However, unlike charcoal records from southern New England, fire activity does not increase dramatically with European settlement. These findings indicate that present‐day Pinus rigida–Quercus ilicifolia woodlands on eastern Long Island are not a legacy of recent, anthropogenic disturbances. Copyright © 2010 John Wiley & Sons, Ltd.     

Post Gondwana breakup evolution of the SE Australia rifted margin revisited

Low‐temperature thermochronology (LTT) is commonly used to investigate onshore records of continental rifting and geomorphic evolution of passive continental margins. The SE Australian passive margin, like many others, has an elevated plateau separated from the coastal plain by an erosional escarpment, presumed to originate through Cretaceous rifting prior to Tasman Sea seafloor spreading. Previous LTT studies have focused on reconciling thermal histories with development of the present‐day topography. New apatite LTT data along an escarpment‐to‐coast transect define a classic “boomerang” (mean track length vs. fission‐track age), indicating variable overprinting of late‐Palaeozoic cooling ages by a younger, mid‐Cretaceous cooling event. Regionally, however, the boomerang trend diverges NNW away from the coast and crosses the escarpment, implying the underlying thermal history pre‐dates escarpment formation and is largely independent from post‐breakup landscape evolution. We suggest that Cretaceous cooling might relate to erosion of Permo‐Triassic sedimentary cover from a formerly more extensive Sydney Basin.