Spatial variability of initial 230Th/232Th in modern Porites from the inshore region of the Great Barrier Reef     

Tara R. Clark  Jian-xin Zhao  Yue-xing Feng  Terry J. Done  Stacy Jupiter  Janice Lough  John M. Pandolfi 《Geochimica et cosmochimica acta》2012

The main limiting factor in obtaining precise and accurate uranium-series (U-series) ages of corals that lived during the last few hundred years is the ability to constrain and correct for initial thorium-230 (²³⁰Th₀), which is proportionally much higher in younger samples. This is becoming particularly important in palaeoecological research where accurate chronologies, based on the ²³⁰Th chronometer, are required to pinpoint changes in coral community structure and the timing of mortality events in recent time (e.g. since European settlement of northern Australia in the 1850s). In this study, thermal ionisation mass spectrometry (TIMS) U-series dating of 43 samples of known ages collected from living Porites spp. from the far northern, central and southern inshore regions of the Great Barrier Reef (GBR) was performed to spatially constrain initial ²³⁰Th/²³²Th (²³⁰Th/²³²Th₀) variability. In these living Porites corals, the majority of ²³⁰Th/²³²Th₀ values fell within error of the conservative bulk Earth ²³⁰Th/²³²Th atomic value of 4.3 ± 4.3 × 10^?6 (2σ) generally assumed for ²³⁰Th₀ corrections where the primary source is terrestrially derived. However, the results of this study demonstrate that the accuracy of ²³⁰Th ages can be further improved by using locally determined ²³⁰Th/²³²Th₀ values for correction, supporting the conclusion made by Shen et al. (2008) for the Western Pacific. Despite samples being taken from regions adjacent to contrasting levels of land modification, no significant differences were found in ²³⁰Th/²³²Th₀ between regions exposed to varying levels of sediment during river runoff events. Overall, 39 of the total 43 ²³⁰Th/²³²Th₀ atomic values measured in samples from inshore reefs across the entire region show a normal distribution ranging from 3.5 ± 1.1 to 8.1 ± 1.1 × 10^?6, with a weighted mean of 5.76 ± 0.34 × 10^?6 (2σ, MSWD = 8.1). Considering the scatter of the data, the weighted mean value with a more conservative assigned error of 25% (i.e. 5.8 ± 1.4 × 10^?6) that encompasses the full variation of the 39 ²³⁰Th/²³²Th₀ measurements is recommended as a more appropriate value for initial ²³⁰Th corrections for U-series dating of most Porites samples from inshore regions of the GBR. This will result in significant improvement in both the precision and accuracy of the corrected ²³⁰Th ages related to those based on the assumed bulk Earth ²³⁰Th/²³²Th₀ value of 4.3 ± 4.3 × 10^?6. However, several anomalously high ²³⁰Th/²³²Th₀ values reaching up to 28.0 ± 1.6 × 10^?6 occasionally found in some coral annual bands coinciding with El Niño years imply high ²³⁰Th/²³²Th₀ sources and highlight the complexities of understanding ²³⁰Th/²³²Th₀ variability. For U-series dating of young coral samples from such sites where anomalous ²³⁰Th/²³²Th₀ values occur, we suggest replicate dating of multiple growth bands with known age difference to verify age accuracy.  相似文献   

(Re-)negotiating access: The politics of researching skills and knowledge for ‘sustainable communities’     

Julie Newton  Alex Franklin  Jennie Middleton  Terry Marsden 《Geoforum》2012,43(3):585-594

The last decade has witnessed a surge of interest in ‘sustainable communities’ within the UK. This has stimulated a plethora of research aimed at acquiring a better understanding of what ‘sustainable communities’ might look like and how they can be achieved. However, this has not been accompanied by a reflection and interrogation of the actual processes, challenges and politics of doing ‘sustainable communities’ research. This paper addresses this gap by highlighting the importance of paying attention to the on-going process of negotiating access when carrying out sustainability research at the community level. We draw on a recent study of skills and knowledge for ‘sustainable communities’ in Stroud Gloucestershire, UK, to illustrate the importance of sensitivity to social relationships throughout and beyond the research trajectory within sustainability research. Our experience raises important questions about the politics of research practices when doing sustainability research ‘with’ communities and the challenges associated with participatory approaches as a means to demonstrate research impact. We argue that in developing a fuller understanding of why and how different types of community level initiatives can contribute to the ‘sustainable communities’ agenda, greater consideration needs to be given to how these community practices can be better supported through the process of doing academic research.  相似文献   

Long-term shoreline retreat rates on Whidbey Island,Washington, USA     

Heather E. Rogers  Terry W. Swanson  John O. Stone 《Quaternary Research》2012,78(2):315-322

Long-term retreat rates of Puget Sound's unconsolidated sediment shorelines have been difficult to quantify, and little systematic research has been completed to constrain retreat in this area. We put forward a new application of cosmogenic ¹⁰Be exposure dating to assess long-term shoreline retreat on Whidbey Island, WA by dating lag boulders exposed on the shore platform as the shoreline erodes. Production of ¹⁰Be in shoreline boulders is modulated by both tidal submergence and topographic shielding from the retreating bluff. By modeling the combined effect of these variables on ¹⁰Be production, the timing of exposure can be determined and used to calculate long-term (10³–10⁴ yr) bluff retreat rates. In rare cases, retreat rates are underestimated due to inherited ¹⁰Be. Within the study area, average retreat rates ranged between 0 and 8 cm yr^? 1. Our results demonstrate the utility of cosmogenic nuclides for determining long-term shoreline retreat rates in areas with thick sediment cover, where large numbers of samples can be collected, and where the pre-depositional history of the boulders is uncomplicated.  相似文献   

Modeling fresh water lens damage and recovery on atolls after storm-wave washover   总被引：1，自引：0，他引：1  

Chui TF  Terry JP 《Ground water》2012,50(3):412-420

The principal natural source of fresh water on scattered coral atolls throughout the tropical Pacific Ocean is thin unconfined groundwater lenses within islet substrates. Although there are many threats to the viability of atoll fresh water lenses, salinization caused by large storm waves washing over individual atoll islets is poorly understood. In this study, a mathematical modeling approach is used to examine the immediate responses, longer-term behavior, and subsequent (partial) recovery of a Pacific atoll fresh water lens after saline damage caused by cyclone-generated wave washover under different scenarios. Important findings include: (1) the saline plume formed by a washover event mostly migrates downward first through the top coral sand and gravel substrate, but then exits the aquifer to the ocean laterally through the more permeable basement limestone; (2) a lower water table position before the washover event, rather than a longer duration of storm washover, causes more severe damage to the fresh water lens; (3) relatively fresher water can possibly be found as a preserved horizon in the deeper part of an aquifer after disturbance, especially if the fresh water lens extends into the limestone under normal conditions; (4) post-cyclone accumulation of sea water in the central depression (swamp) of an atoll islet prolongs the later stage of fresh water lens recovery.  相似文献   

Challenging Sustainability. Urban Development and Change in Southeast Asia – Edited by Tai-chee Wong, Brian J. Shaw and Kim-chuan Goh     

Terry McGee 《Singapore journal of tropical geography》2008,29(1):106-107

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Differential rotation on both components of the pre-main-sequence binary system HD 155555     

N. J. Dunstone  G. A. J. Hussain  A. Collier Cameron  S. C. Marsden  M. Jardine  J. R. Barnes  J. C. Ramirez Velez  J.-F. Donati 《Monthly notices of the Royal Astronomical Society》2008,387(4):1525-1536

We present the first measurements of surface differential rotation on a pre-main-sequence binary system. Using intensity (Stokes I) and circularly polarized (Stokes V) time-series spectra, taken over 11 nights at the Anglo-Australian Telescope (AAT), we incorporate a solar-like differential rotation law into the surface imaging process. We find that both components of the young, 18 Myr, HD 155555 (V824 Ara, G5IV + K0IV) binary system show significant differential rotation. The equator–pole lap times as determined from the intensity spectra are 80 d for the primary star and 163 d for the secondary. Similarly, for the magnetic spectra we obtain equator–pole lap times of 44 and 71 d, respectively, showing that the shearing time-scale of magnetic regions is approximately half of that found for stellar spots. Both components are therefore found to have rates of differential rotation similar to those of the same spectral-type main-sequence single stars. The results for HD 155555 are therefore in contrast to those found in other, more evolved, binary systems where negligible or weak differential rotation has been discovered. We discuss two possible explanations for this: first that at the age of HD 155555 binary tidal forces have not yet had time to suppress differential rotation and secondly that the weak differential rotation previously observed on evolved binaries is a consequence of their large convection zone depths. We suggest that the latter is the more likely solution and show that both temperature and convection zone depth (from evolutionary models) are good predictors of differential rotation strength. Finally, we also examine the possible consequences of the measured differential rotation on the interaction of binary star coronae.  相似文献   

Effects of the toxic dinoflagellate Alexandrium tamarense on the greenshell mussel Perna canaliculus     

Islay D. Marsden  Sandra E. Shumway 《新西兰海洋与淡水研究杂志》2013,47(3-4):371-378

Abstract

Oxygen consumption, grazing rate, and byssus production of the greenshell mussel Perna canaliculus were measured following exposure to bloom concentrations (10⁶ cells l^?1 ) of a toxic clone of the dinoflagellate AIexandrium tamarense (GT429), using anon‐toxic clone of the same species (PLY173) as control. Following feeding for 1 h on GT429, mussels (dry weight 54–127 mg) showed significantly increased oxygen uptake at 15°C (0.08 μl O₂ (mg dry tissue weight)^?1 ) compared with control mussels. However, following 24 h recovery, oxygen uptake was similar to initial values in all experimental conditions. The grazing rate of P. canaliculus fed upon toxic clone GT429 was 4.58 ± 0.76 cells mg^?1 h^?1 compared with 1.99 ± 0.47 cells mg^?1 h^?1 for PLY173. On exposure to A. tamarense, mussels maintained normal opening behaviour and there was no change in the byssus production over 24 h. It was concluded that P. canaliculus showed no dramatic physiological effects following short‐term feeding on the toxic strain of A. tamarense. During 2 weeks’ exposure to twice daily bloom concentrations of GT429, there was no mussel mortality. Toxicity in the tissues was 1295 μg STX equivalent per 100 g tissue, levels at which these mussels would be unsuitable for human or animal consumption.  相似文献   

Seasonal variation in the reproductive activity and biochemical composition of the Pacific oyster (Crassostrea gigas) from the Marlborough Sounds,New Zealand     

Jeffrey S. Ren  Islay D. Marsden  Alex H. Ross  David R. Schiel 《新西兰海洋与淡水研究杂志》2013,47(1):171-182

Reproductive cycles of the Pacific oyster Crassostrea gigas (Thunberg) from the Marlborough Sounds, New Zealand, were followed between June 1998 and January 2000. Histological examination of the gonad confirms an annual cycle with a winter inactive period followed by rapid gonad development and a single short spawning period. The population gonad index correlated with seawater temperature and changes in tissue dry weight, condition index, and biochemical components. In winter, few individuals with early gametogenic stages were present and rapid development of primary oocytes (diam. 11 μm) occurred during spring (September‐November). The developmental rate and the diameter of mature oocytes (37 μm) was similar for the 1998 and 1999 seasons. For a standard 110‐mm‐length oyster, maximal tissue body weight and condition index were recorded in December. Rapid weight loss in January was length dependent and was attributed to spawning. Temperature was the environmental variable which best correlated with the timing of gametogenesis. Food availability (phytoplankton biomass) may have been responsible for inter‐annual variations. The biochemical composition (% glycogen, lipid, protein) of separated gonad and somatic tissues were variable seasonally and annually. Gametogenesis (oocyte diameter) was associated with increased gonad protein and glycogen and a decrease in lipid concentrations. These changes are similar to those in Pacific oyster populations from other parts of the world.  相似文献   

San Diego trough geotechnical test area     

Terry Carius  Adrian F. Richards 《Marine Georesources & Geotechnology》2013,31(4):345-369

Abstract

The San Diego Trough Geotechnical Test Area, located about 24 km southwest of San Diego in a water depth of about 1.2 km, lies near the base of the Coronado Escarpment directly north of the Coronado Fan. A new bathymetric map delineates a shallow basin in the soft, highly plastic, clayey silts flooring the Test Area. Measurements of shear strength by vane and static cone pene‐trometer, and bulk density by nuclear densitometer, were made in place from the submersible Deep Quest. Sixteen short (< 1.6 m) gravity cores were collected from ships.

The geotechnical properties show little areal variation and generally change uniformly with depth within the 55 km² Test Area. Silt is the predominant grain size, averaging about 62%. In‐place bulk density shows little change with increasing depth, values range from 1.23 to 1.26 Mg/m³; laboratory density values increase with depth, ranging from 1.30 to 1.52 Mg/m³ between the surface and a depth of about 1.1 m. The difference between the in place and laboratory values may indicate sampling densification of the cored sediment. Water content in the cores decreases uniformly within the range of 249 to 43% dry weight. Shear strength increases linearly with depth. The laboratory shear strength values are lower than the in place values, which range from 4 kPa at the surface to about 29 kPa at a depth of 3.27 m. Predictor equations relate Atterberg limits, bulk density, water content, and laboratory and in place shear strength to depth. Sedimentation‐compression e log p curves have an equivalent compression index of 1.5 to nearly 2. Excluding rurbidite layers and sampling disturbance effects, all cores indicate a uniform depositional environment in the surface to 1.6 m of sediment sampled. The geotechnical properties indicate that the sediments in the west central and southwest parts of the Test Area exhibit vertical heterogeneity due to thin silt‐sand layers, presumably of turbidity current origin, that originated from the Coronado Canyon.  相似文献   

Prehistorical frequency of high‐energy marine inundation events driven by typhoons in the Bay of Bangkok (Thailand), interpreted from coastal carbonate boulders          下载免费PDF全文

James P. Terry  Kieran Dunne  Kruawun Jankaew 《地球表面变化过程与地形》2016,41(4):553-562

Rapidly rising populations of low‐lying megacities in Asia mean that understanding the potential risk of coastal flooding by storm surge is of paramount concern. The city of Bangkok and the wider Chao Phraya River delta at the head of the Gulf of Thailand is a region topographically vulnerable to coastal flooding, but without the record of a high‐energy marine inundation (HEMI) event in historical time owing to the atypical path that a typhoon must take to be able to produce such an event. This work builds upon previous findings that identified coastal depositional evidence for HEMI events in the form of coastal carbonate boulders (CCBs) located on Ko Larn Island in the eastern Bay of Bangkok. The HEMI events were most likely driven by typhoons and the CCBs are therefore interpreted as typhoon deposits. Through uranium/thorium dating, it is revealed that from ad 1400 to ad 1600 the Bay of Bangkok possibly experienced a phase of relatively heightened storm impact. During this period, the frequency of typhoon‐driven HEMI events was approximately four events in 200 years. Waves generated onshore minimum flow velocities (MFVs) in excess of 5 m/s. Such exceptional MFVs are unlikely to be produced during the annual northeast monsoon, but are consistent with typhoon‐impacted coastlines elsewhere in the tropical Asia–Pacific region where similar CCB evidence exists. Since ad 1600, the Bay of Bangkok has enjoyed a relatively quiescent phase, recording less frequent HEMI events and of lower magnitude. However, the re‐occurrence of a typhoon‐driven HEMI event on the scale of the prehistorical events that emplaced carbonate boulders at elevation on Ko Larn Island would threaten low‐lying coasts in the Bay of Bangkok, including the Chao Phraya delta, with potentially damaging inundation. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献