The erosion rates of cohesive sediments in Venice lagoon,Italy     

Carl L. Amos  G. Umgiesser  C. Ferrarin  C.E.L. Thompson  R.J.S. Whitehouse  T.F. Sutherland  A. Bergamasco 《Continental Shelf Research》2010

The stability of cohesive sediments from Venice lagoon has been measured in situ using the benthic flume Sea Carousel. Twenty four stations were occupied during summertime, and a sub-set of 13 stations was re-occupied during the following winter. Erosion thresholds and first-order erosion rates were estimated and showed a distinct difference between inter-tidal and sub-tidal stations. The higher values for inter-tidal stations are the result of exposure that influences consolidation, density, and organic adhesion. The thresholds for each state of sediment motion are well established. However, the rate of erosion once the erosion threshold has been exceeded has been poorly treated. This is because normally a time-series of sediment concentration (C) and bed shear stress (τ₀(t)) is used to define threshold stress or cohesion (τ_crit,z) and erosion rate (E). Whilst solution of the onset of erosion, τ_crit,0, is often reported, the evaluation of the erosion threshold variation through the process of erosion (eroded depth) is usually omitted or not estimated. This usually leads to assumptions on the strength profile of the bed which invariably has no credibility within the topmost mm of the bed where most erosion takes place. It is possible to extract this information from a time-series through the addition of a step in data processing. This paper describes how this is done, and the impact of this on the accuracy of estimates of the excess stress (τ₀(t)–τ_crit,z) on E.  相似文献   

K‐Ar ages of Cainozoic volcanic suites,Bowen‐St Lawrence Hinterland,North Queensland (with some implications for petrologic models)     

F. L. Sutherland  D. Stubbs  D. C. Green 《Australian Journal of Earth Sciences》2013,60(7-8):447-460

Thirty K‐Ar dates on Cainozoic volcanic rocks lying at the north end of the Bowen Basin suggest that several episodes of volcanism took place at major structural weaknesses. The oldest volcanism (ca 54 m.y.) was located outside the basin structure. The main volcanism (Nebo and East Clermont Provinces) extended from early Oligocene (34–35 m.y.) to mid‐Cainozoic time (21–22 m.y.?). Isolated Pliocene activity is tentatively suggested by dates on Mt St Martin (ca 3 m.y.).

Dating of the Nebo central volcano (31–33 m.y.) supports the model of Wellman &; McDougall, with volcanic activity related to migration of Australia northwards over a mantle magma source. Consideration of the Nebo dates with those of other central volcanoes in north Queensland, suggests that central felsic activity was surrounded by broad zones of peripheral eruptives, petrologically zoned from outer undersaturated basalts to inner saturated basalts. These zones (super provinces) delineate the size and profile of underlying magma sources and appear to trend back in time and space to sea‐floor spreading episodes in the Coral Sea—southeastern Papua region (55 m.y.).

The basalt dates also assist in fixing periods of lateritization (mid‐Oligocene) and in determining approximate minimum erosion rates in the northern Bowen Basin since the Eocene (3–5m/m.y.).  相似文献   

Late thermal events based on zircon fission track ages in northeastern New South Wales and southeastern Queensland: Links to Sydney Basin seismicity?     

F. L. Sutherland 《Australian Journal of Earth Sciences》2013,60(5):461-470

Zircon, concentrated from basaltic terrains in northeastern New South Wales and southeastern Queensland, reveals some unexpectedly young fission track peaks. Between 2 to 13 Ma in age, these peaks are younger than known Tertiary basaltic ages from these regions which match older fission track peaks. Analysis of the fission track data suggests that the young dates are probably not reset ages due to recent heating events such as bush fires, but more likely mark thermal resetting by later volcanic eruptions.

The young ages decrease southwards from Queensland through northern New South Wales and trend toward seismic zones within the Sydney Basin in the Newcastle, Blue Mountains and Illawarra regions. A model based on northward motion of the Australian plate over a hot asthenospheric source (0.75° latitude/Ma over 12 Ma)) predicts the positions of most young zircon ages to within ± 70 km in latitude when projected from seismic sites at Newcastle and Bowral‐Robertson.

A minor hot spot source is proposed, some 250 km across, which triggered isolated basaltic and zircon‐bearing eruptions every few million years and now underlies the southern Sydney Basin. This would bring Sydney Basin seismicity into line with other seismic zones known at present hot spot positions across southeastern Australia and the Tasman Sea. It raises questions concerning activation of local seismicity, potential for volcanic risk and distribution of young uplift in the Sydney region. Similar studies are needed to test other puzzling seismic zones (e.g. the Dalton‐Gunning Zone).  相似文献   

Stable carbon isotope distribution of particulate organic matter in the ocean: a model study   总被引：4，自引：0，他引：4  

Matthias Hofmann  Dieter A. Wolf-Gladrow  Taro Takahashi  Steward C. Sutherland  Katharina D. Six  Ernst Maier-Reimer 《Marine Chemistry》2000,72(2-4)

The stable carbon isotopic composition of particulate organic matter in the ocean, δ¹³C_POC, shows characteristic spatial variations with high values in low latitudes and low values in high latitudes. The lowest δ¹³C_POC values (−32‰ to −35‰) have been reported in the Southern Ocean, whereas in arctic and subarctic regions δ¹³C_POC values do not drop below −27‰. This interhemispheric asymmetry is still unexplained. Global gradients in δ¹³C_POC are much greater than in δ¹³C_DIC, suggesting that variations in isotopic fractionation during organic matter production are primarily responsible for the observed range in δ¹³C_POC. Understanding the factors that control isotope variability is a prerequisite when applying δ¹³C_POC to the study of marine carbon biogeochemistry. The present model study attempts to reproduce the δ¹³C_POC distribution pattern in the ocean. The three-dimensional (3D) Hamburg Model of the Oceanic Carbon Cycle version 3.1 (HAMOCC3.1) was combined with two different parametrizations of the biological fractionation of stable carbon isotopes. In the first parametrization, it is assumed that the isotopic fractionation between CO₂ in seawater and the organic material produced by algae, _P, is a function of the ambient CO₂ concentration. The two parameters of this function are derived from observations and are not based on an assumption of any specific mechanism. Thus, this parametrization is purely empirical. The second parametrization is based on fractionation models for microalgae. It is supported by several laboratory experiments. Here the fractionation, _P, depends on the CO₂ concentration in seawater and on the (instantaneous) growth rates, μ_i, of the phytoplankton. In the Atlantic Ocean, where most field data are available, both parametrizations reproduce the latitudinal variability of the mean δ¹³C_POC distribution. The interhemispheric asymmetry of δ¹³C_POC can mostly be attributed to the interhemispheric asymmetry of CO₂ concentration in the water. However, the strong seasonal variations of δ¹³C_POC as reported by several authors, can only be explained by a growth rate-dependent fractionation, which reflects variations in the cellular carbon demand.  相似文献   

The IRAS PSCz dipole     

M. Rowan-Robinson  J. Sharpe  S. J. Oliver  O. Keeble  A. Canavezes  W. Saunders  A. N. Taylor  H. Valentine  C. S. Frenk  G. P. Efstathiou  R. G. McMahon  S. D. M. White  W. Sutherland  H. Tadros  S. Maddox 《Monthly notices of the Royal Astronomical Society》2000,314(2):375-397

We use the PSC z IRAS galaxy redshift survey to analyse the cosmological galaxy dipole out to a distance of 300  h ¹ Mpc. The masked area is filled in three different ways, first by sampling the whole sky at random, secondly by using neighbouring areas to fill a masked region, and thirdly using a spherical harmonic analysis. The method of treatment of the mask is found to have a significant effect on the final calculated dipole.
The conversion from redshift space to real space is accomplished by using an analytical model of the cluster and void distribution, based on 88 nearby groups, 854 clusters and 163 voids, with some of the clusters and all of the voids found from the PSC z data base.
The dipole for the whole PSC z sample appears to have converged within a distance of 200  h ¹ Mpc and yields a value for , consistent with earlier determinations from IRAS samples by a variety of methods. For b =1, the 2 range for ₀ is 0.431.02.
The direction of the dipole is within 13° of the cosmic microwave background (CMB) dipole, the main uncertainty in direction being associated with the masked area behind the Galactic plane. The improbability of further major contributions to the dipole amplitude coming from volumes larger than those surveyed here means that the question of the origin of the CMB dipole is essentially resolved.  相似文献   

Calibration techniques and sampling resolution requirements for groundtruthing multibeam acoustic backscatter (EM3000) and QTC VIEW™ classification technology     

T.F. Sutherland  J. Galloway  R. Loschiavo  C.D. Levings  R. Hare 《Estuarine, Coastal and Shelf Science》2007,75(4):447-458

Both acoustic and sediment surveys were carried out in the Broughton Archipelago, British Columbia, in order to map a former aquaculture site and calibrate acoustic surveys with georeferenced sediment properties. The acoustic surveys included EM3000 Multibeam (including backscatter) and QTC VIEW™ (Series IV) technologies, while the geotechnical survey entailed Van Veen grab sampling of surface sediments and associated analyses. The two acoustic technologies were consistent in their ability to identify distinct regions of seafloor characterized by rock outcrops, consolidated substrates, or gel-mud depositional fields. Both multibeam backscatter data and QTC VIEW™ number-coded classifications were extracted across a range of circular areas located at each georeferenced sampling station (radii: 2, 3, 4, 5, 8, 12, 16, 20 m). Statistical correlations were observed between backscatter and certain geotechnical properties, such as sediment porosity, sediment grain size fractions (<2 μm, silt content), and particulate sulfur concentration. The areal resolution of backscatter extraction was explored in terms of determining a sensitive calibration technique between backscatter and sediment properties. In general the highest r² values between backscatter and sediment variables were observed across extraction radii between 8 and 20 m. Such groundtruthing techniques could be used to interpolate seafloor characteristics between sampling stations and provide a steering tool for sampling designs associated with benthic monitoring programs.  相似文献   

Internal wave excitation from a collapsing mixed region     

B.R. Sutherland  M.R. Flynn  K. Dohan 《Deep Sea Research Part II: Topical Studies in Oceanography》2004,51(25-26):2889

The collapse of a uniform density fluid (a “mixed region”) into a surrounding ambient fluid with complex stratification is examined by way of laboratory experiments and fully nonlinear numerical simulations. The analysis focuses upon the consequent generation of internal gravity waves and their influence upon the evolution of the collapsing mixed region. In experiments and simulations for which the ambient fluid has uniform density over the vertical extent of the mixed region and is stratified below, we find the mixed region collapses to form an intrusive gravity current and internal waves are excited in the underlying stratified fluid. The amplitude of the waves is weak in the sense that the intrusion is not significantly affected by the waves. However, scaling the results to the surface mixed layer of the ocean we find that the momentum flux associated with the waves can be as large as 1 N/m². In simulations for which the ambient fluid is stratified everywhere, including over the vertical extent of the mixed region, we find that internal waves are excited with such large amplitude that the collapsing mixed region is distorted through strong interactions with the waves.  相似文献   

The East Greenland Coastal Current: Structure, variability, and forcing     

David A. Sutherland  Robert S. Pickart 《Progress in Oceanography》2008,78(1):58-77

The subtidal circulation of the southeast Greenland shelf is described using a set of high-resolution hydrographic and velocity transects occupied in summer 2004. The main feature is the East Greenland Coastal Current (EGCC), a low-salinity, high-velocity jet with a wedge-shaped hydrographic structure characteristic of other surface buoyancy-driven currents. The EGCC was observed along the entire Greenland shelf south of Denmark Strait, while the transect north of the strait showed only a weak shelf flow. This observation, in conjunction with water mass considerations and other supporting evidence, suggests that the EGCC is an inner branch of the East Greenland Current (EGC) that forms south of Denmark Strait. It is argued that bathymetric steering is the most likely reason why the EGC apparently bifurcates at this location. Repeat sections occupied at Cape Farewell between 1997 and 2004 show that the alongshelf wind stress can have an influence on the structure and strength of the EGCC and EGC on timescales of 2-3 days. Accounting for the wind-induced effects, the volume transport of the combined EGCC/EGC system is roughly constant (∼2 Sv) over the study domain, from 68°N to Cape Farewell near 60°N. The corresponding freshwater transport increases by roughly 60% over this distance (59-96 mSv, referenced to a salinity of 34.8). This trend is consistent with a simple freshwater budget of the EGCC/EGC system that accounts for meltwater runoff, melting sea-ice and icebergs, and net precipitation minus evaporation.  相似文献   

Maada’oonidiwag gete-dibaajimowen (“sharing old stories”): reflections on a place-based reparatory research partnership in Nbisiing Anishinaabeg Territory     

Hemsworth  Katie  Greer  Kirsten  Paulin  Megan  Sutherland  Kiethen  McLeod Shabogesic  Joan 《GeoJournal》2021,87(2):267-280

In this paper, we reflect on an emerging community-based partnership rooted in place-based reparative research. Braiding knowledges (Atalay, 2012) from Nbisiing Anishinaabeg communities, northern Ontario universities, and multi-scalar museums, the partnership focuses on repatriation, reparative environmental histories, and action-based research in the context of settler colonialism and climate change. We reflect on ongoing projects that attempt to put Anishinaabe gikendaasowin (knowledge) into action alongside historical geographical research. We discuss how the partnership resonates with community geography values of relationship, collaboration, equity, and reciprocity, and urge non-Indigenous geographers to acknowledge how Indigenous knowledges and approaches have shaped these ideas long before geography became a discipline. We contend that historical geographers have a deeper role to play in community geography scholarship, citing examples of two projects related to (1) repatriation of Anishinaabeg cultural heritage and (2) storymapping through historical Geographic Information Systems (HGIS). However, we argue, geographers must continue to acknowledge their own positionality in a discipline that was built through settler colonial violence and knowledge production. Finally, we reflect on the role of academic institutions in facilitating First Nation-university-museum partnerships through access to funding, space, and databases, while addressing the challenges of relying on institutional support for reparatory and decolonizing projects.

  相似文献   

Distinguishing between natural and aquaculture-derived sediment concentrations of heavy metals in the Broughton Archipelago, British Columbia   总被引：5，自引：0，他引：5  

Sutherland TF  Petersen SA  Levings CD  Martin AJ 《Marine pollution bulletin》2007,54(9):1451-1460

Marine sediment samples were collected in the Broughton Archipelago, British Columbia, to assess the use of a geochemical normalization technique in the identification of a chemical tracer of aquaculture waste material. Zinc and copper were suggested as tracers of feed pellets, while copper was considered an indicator of anti-foulant agents used on netpen systems. The sediment samples were analyzed for carbon, nitrogen, organic matter, water, trace-element, and free sulfide concentrations, and sediment grain-size distribution. Sediment texture analysis revealed a wide range of substrate types from sand to silty loam categories. Strong relationships between sediment texture, sediment porosity, and organic content were observed across both near-field and far-field stations. Excess zinc and copper sediment concentrations, identified using a lithium-normalization technique, were restricted to near-field sampling stations (0 and 30m from netpen systems). The relationships between these metal tracers and organic content and sulfur concentrations were explored to account for variations in sediment concentrations of zinc and copper.  相似文献