Southern Ocean biogeochemical impact on the tropical ocean: Stable isotope records from the Pacific for the past 25,000 years     

Paul Loubere  Samantha Bennett 《Global and Planetary Change》2008,63(4):333-340

Modeling of oceanic nutrient fields indicates that the Southern Ocean may have a strong impact on the chemistry of the thermocline waters which upwell in the eastern tropical oceans and feed biological productivity there. The subantarctic is a primary source of equatorial undercurrent (EUC) waters. The Southern Ocean to equator connection has been shown through modeling to have a potential influence on atmospheric carbon dioxide content via an increase in the efficiency of the tropical biotic pump (silica leakage hypothesis). On the glacial–interglacial timescale the eastern equatorial Pacific (EEP) has a thermocline (EUC) carbon isotope record which is consistent with that idea and a stronger ice age biologic drawdown in the subantarctic. This carbon isotope record features glacial values more positive than those of the Holocene, which is the reverse of what is seen in the non-equatorial, stratified, ocean. We report planktonic carbon isotope records from the Pacific subantarctic in an effort to trace the unique EEP carbon isotope signature to its source. Our results are compatible with the subantarctic as a source of the tropical carbon isotope signature. Analysis of the glacial to Holocene isotopic pattern in terms of causative process indicates that an increased glacial subantarctic biotic pump accounts best for our observations. This supports the hypothesis of Southern Ocean drive on tropical biological production, and potential impact on the global carbon cycle.  相似文献   

The Rural – Edited by Richard Munton     

Katy Bennett 《Area》2009,41(4):476-477

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Internal structure of a barrier beach as revealed by ground penetrating radar (GPR): Chesil beach, UK   总被引：1，自引：0，他引：1  

Matthew R. Bennett  Nigel J. Cassidy  Jeremy Pile 《Geomorphology》2009,104(3-4):218-229

Chesil Beach (Dorset) is one of the most famous coastal landforms on the British coast. The gravel beach is over 18 km long and is separated for much of its length from land by a tidal lagoon known as The Fleet. The beach links the Isle of Portland in the east to the mainland in the west. Despite its iconic status there is little available information on its internal geometry and evolutionary history. Here we present a three-fold model for the evolution of Chesil Beach based on a series of nine ground penetrating radar (GPR) traverses located at three sites along its length at Abbotsbury, Langton Herring and at Ferry Bridge. The GPR traverses reveal a remarkably consistent picture of the internal structure of this barrier beach. The first phase of evolution involves the landward transgression of a small sand and gravel beach which closed upon the coast leading to deposition of freshwater peat between 5 and 7 k yr BP. The second evolutionary phase involves the ‘bulking-out’ of the beach during continued sea level rise, but in the presence of abundant gravel supplied by down-drift erosion of periglacial slope deposits. This episode of growth was associated with a series of washover fans which accumulated on the landward flank of the barrier increasing its breadth and height but without significant landward transgression of the barrier as a whole. The final phase in the evolution of Chesil Beach involves the seaward progradation of the beach crest and upper beach face associated with continued sediment abundance, but during a still-stand or slight fall in relative sea level. This phase may provide further evidence of a slight fall in relative sea level noted elsewhere along the South Coast of Britain and dated to between 1.2 and 2.4 k yr BP. Subsequently the barrier appears to have become largely inactive, except for the reworking of sediment on the beach face during storm events. The case study not only refines the evolutionary picture of Chesil Beach, but illustrates the importance of the subtle interplay between relative sea level and sediment supply in the evolution of a barrier system. In addition, it also illustrates the potential of GPR in resolving the evolutionary history of gravel-rich coastal landforms such as Chesil Beach.  相似文献   

Partitioning geochemistry of arsenic and antimony,El Tatio Geyser Field,Chile     

J.T. Landrum  P.C. Bennett  A.S. Engel  M.A. Alsina  P.A. Pastén  K. Milliken 《Applied Geochemistry》2009

The abundance of As and Sb in aqueous, mineral and biological reservoirs was examined at El Tatio Geyser Field, a unique hydrothermal basin located in the Atacama Desert region of Chile. Here the concentration of total As and Sb in hydrothermal springs and discharge streams are the highest reported for a natural surface water, and the geyser basin represents a significant source of toxic elements for downstream users across Region II, Chile. The geyser waters are near neutral Na:Cl type with ∼0.45 and 0.021 mmol L⁻¹ total As and Sb, respectively, primarily in the reduced (III) redox state at the discharge with progressive oxidation downstream. The ferric oxyhydroxides associated with the microbial mats and some mineral precipitates accumulate substantial As that was identified as arsenate by XAS analysis (>10 wt% in the mats). This As is easily mobilized by anion exchange or mild dissolution of the HFO, and the ubiquitous microbial mats represent a significant reservoir of As in this system. Antimony, in contrast, is not associated with the mineral ferric oxides or the biomats, but is substantially enriched in the silica matrix of the geyserite precipitates, up to 2 wt% as Sb₂O₃. Understanding the mobility and partitioning behavior of these metalloids is critical for understanding their eventual impact on regional water management.  相似文献   

Aggregation of montmorillonite and organic matter in aqueous media containing artificial seawater     

Yoko Furukawa  Janet L Watkins  Jinwook Kim  Kenneth J Curry  Richard H Bennett 《Geochemical transactions》2009,10(1):2-11

Background  

The dispersion-aggregation behaviors of suspended colloids in rivers and estuaries are affected by the compositions of suspended materials (i.e., clay minerals vs. organic macromolecules) and salinity. Laboratory experiments were conducted to investigate the dispersion and aggregation mechanisms of suspended particles under simulated river and estuarine conditions. The average hydrodynamic diameters of suspended particles (representing degree of aggregation) and zeta potential (representing the electrokinetic properties of suspended colloids and aggregates) were determined for systems containing suspended montmorillonite, humic acid, and/or chitin at the circumneutral pH over a range of salinity (0 – 7.2 psu).  相似文献   

Identification and occurrence of 25-norbenzohopanes in biodegraded bitumen from Palaeozoic carbonates in northern Alberta     

Barry Bennett  Chunqing Jiang  Stephen R. Larter 《Organic Geochemistry》2009,40(6):667-670

In addition to the previously reported 25-norhopanes and 25-norhopanoic acids, for the first time we report the identification of 25-norbenzohopanes. The hydrocarbon composition of the bitumen from Palaeozoic carbonates in northern Alberta displays molecular evidence for severe levels of biodegradation characterised by the removal of C₃₀–C₃₅ hopanes. Biodegradation is also indicated by the removal of C₃₂ and C₃₃ benzohopanes. The appearance of C₃₁ and C₃₂ 25-norbenzohopanes corresponds to the decrease in C₃₂ and C₃₃ benzohopanes, suggesting that 25-norbenzohopanes originate by demethylation of benzohopane counterparts. Demethylation at C-10 in the hopanoids affects a broader class of compounds that so far includes the hopanes and hopanoic acids, as well as the benzylated hopanoid species.  相似文献   

Comparison of pelagic and nepheloid layer marine snow: implications for carbon cycling   总被引：5，自引：0，他引：5  

Barbara Ransom  Kevin F. Shea  Patti Jo Burkett  Richard H. Bennett  Roy Baerwald 《Marine Geology》1998,150(1-4):39-50

Marine snow from upper and mid-water (i.e., pelagic) depths on the California margin is texturally and compositionally different from that traveling in the nepheloid layer. Transmission electron microscopy shows that pelagic marine snow consists primarily of bioclasts (e.g., diatom frustules, foram tests), organic matter, and microbes. These components are entrained as discrete particles or small aggregates μm in diameter) in a loose network of exocellular, muco-polysaccharide material. Clays are infrequent but, when present, are constituents of comparatively compact organic-rich microaggregates. Microbes are abundant and appear to decrease in number with increasing water depth. In contrast, marine snow aggregates collected from just above the sea floor in the nepheloid layer are assemblages of clay particles, clay flocs, and relatively dense clay–organic-rich microaggregates in an exocellular organic matrix. Bioclasts and microorganisms occur only rarely. The prevalence of clay–organic-rich aggregates in the nepheloid layer suggests that, prior to final deposition and burial, marine snow from the pelagic zone is subject to disaggregation and recombination with terrigenous detrital material near or at the sea floor. Results have significant implications for the accumulation and burial rates of organic carbon on continental margins and the aging and bioavailability of sedimentary organic matter. Samples examined were collected offshore of northern and central California.  相似文献   

Long-Period Magnetotelluric Measurements Near the Central California Coast: A Land-Locked View of the Conductivity Structure Under the Pacific Ocean   总被引：2，自引：0，他引：2  

R. L. Mackie  B. R. Bennett  T. R. Madden 《Geophysical Journal International》1988,95(1):181-194

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Match probability statistics and gamma-ray burst recurrences in the BATSE catalog     

Sun Hong Rhie  David Bennett 《Astrophysics and Space Science》1995,231(1-2):27-30

We developmatch probability statistics to test the recurrences of gamma-ray bursts in the BATSE catalog 1B and 2B. We do not find a signal of repetitions at the match level of 10^–3.  相似文献   

An Array Experiment with Magnetic Variometers Near the Coasts of South-east Australia     

F. E. M. Lilley  D. J. Bennett 《Geophysical Journal International》1972,29(1):49-64

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