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Arendal, Norway

Huang Z.,Geoscience Australia | Nichol S.L.,Geoscience Australia | Harris P.T.,GRID Arendal | Caley M.J.,Australian Institute of Marine Science
Marine Geology

Submarine canyons influence oceanographic processes, sediment transport, productivity and benthic biodiversity from the continental shelf to the slope and beyond. However, not all canyons perform the same function. The relative influence of an individual canyon on these processes will, in part, be determined by its form, shape and position on the continental margin. Here we present an analysis of canyon geomorphic metrics using an updated national dataset of 713 submarine canyons surrounding mainland Australia. These metrics (attributes) for each canyon are used to classify them into canyon types across a hierarchy of physical characteristics separately for shelf-incising (n. =. 95) and slope-confined (blind; n. =. 618) canyons. We find that the canyon metrics describe a wide variety of canyon form and complexity that is consistent with a population of canyons that has evolved at different rates around the Australian margin since the break-up of Gondwana. The large number of slope-confined canyons is interpreted to reflect dominance of slope mass-wasting processes over erosive turbidity flows from fluvial and shelf sources on an arid continent. The distribution of submarine canyons around the Australian margin is not regular, with clusters occurring in the east, southeast, west and southwest where the margin is steepest. The classification result provides a quantitative framework for describing canyon heterogeneity for application in studies of geological controls on individual canyons, canyon oceanography and canyon biodiversity. © 2014 Published by Elsevier B.V. Source

Tesi T.,CNR Marine Science Institute | Tesi T.,Oregon State University | Goni M.A.,Oregon State University | Langone L.,CNR Marine Science Institute | And 11 more authors.
Global Biogeochemical Cycles

Outcrops of old strata at the shelf edge resulting from erosive gravity-driven flows have been globally described on continental margins. The reexposure of old strata allows for the reintroduction of aged organic carbon (OC), sequestered in marine sediments for thousands of years, into the modern carbon cycle. This pool of reworked material represents an additional source of 14C-depleted organic carbon supplied to the ocean, in parallel with the weathering of fossil organic carbon delivered by rivers from land. To understand the dynamics and implications of this reexposure at the shelf edge, a biogeochemical study was carried out in the Gulf of Lions (Mediterranean Sea) where erosive processes, driven by shelf dense water cascading, are currently shaping the seafloor at the canyon heads. Mooring lines equipped with sediment traps and current meters were deployed during the cascading season in the southwestern canyon heads, whereas sediment cores were collected along the sediment dispersal system from the prodelta regions down to the canyon heads. Evidence from grain-size, X-radiographs and 210Pb activity indicate the presence in the upper slope of a shelly-coarse surface stratum overlying a consolidated deposit. This erosive discontinuity was interpreted as being a result of dense water cascading that is able to generate sufficient shear stress at the canyon heads to mobilize the coarse surface layer, eroding the basal strata. As a result, a pool of aged organic carbon (14C = -944.5 24.7‰; mean age 23,650 3,321 ybp) outcrops at the modern seafloor and is reexposed to the contemporary carbon cycle. This basal deposit was found to have relatively high terrigenous organic carbon (lignin = 1.48 0.14 mg/100 mg OC), suggesting that this material was deposited during the last low sea-level stand. A few sediment trap samples showed anomalously depleted radiocarbon concentrations (14C = -704.4 62.5‰) relative to inner shelf (14C = -293.4 134.0‰), mid-shelf (14C = -366.6 51.1‰), and outer shelf (14C = -384 47.8‰) surface sediments. Therefore, although the major source of particulate material during the cascading season is resuspended shelf deposits, there is evidence that this aged pool of organic carbon can be eroded and laterally advected downslope. © 2010 by the American Geophysical Union. Source

Harris P.T.,Geoscience Australia | Macmillan-Lawler M.,GRID Arendal | Rupp J.,Wildlife Conservation Society | Baker E.K.,University of Sydney
Marine Geology

We present the first digital seafloor geomorphic features map (GSFM) of the global ocean. The GSFM includes 131,192 separate polygons in 29 geomorphic feature categories, used here to assess differences between passive and active continental margins as well as between 8 major ocean regions (the Arctic, Indian, North Atlantic, North Pacific, South Atlantic, South Pacific and the Southern Oceans and the Mediterranean and Black Seas). The GSFM provides quantitative assessments of differences between passive and active margins: continental shelf width of passive margins (88km) is nearly three times that of active margins (31km); the average width of active slopes (36km) is less than the average width of passive margin slopes (46km); active margin slopes contain an area of 3.4millionkm2 where the gradient exceeds 5°, compared with 1.3millionkm2 on passive margin slopes; the continental rise covers 27millionkm2 adjacent to passive margins and less than 2.3millionkm2 adjacent to active margins. Examples of specific applications of the GSFM are presented to show that: 1) larger rift valley segments are generally associated with slow-spreading rates and smaller rift valley segments are associated with fast spreading; 2) polar submarine canyons are twice the average size of non-polar canyons and abyssal polar regions exhibit lower seafloor roughness than non-polar regions, expressed as spatially extensive fan, rise and abyssal plain sediment deposits - all of which are attributed here to the effects of continental glaciations; and 3) recognition of seamounts as a separate category of feature from ridges results in a lower estimate of seamount number compared with estimates of previous workers. © 2014. Source

Langenheim V.E.,U.S. Geological Survey | Wright T.L.,Chevron | Okaya D.A.,University of Southern California | Yeats R.S.,Oregon State University | And 3 more authors.

Industry seismic reflection data, oil test well data, interpretation of gravity and magnetic data, and seismic refraction deep-crustal profiles provide new perspectives on the subsurface geology of San Fernando Valley, home of two of the most recent damaging earthquakes in southern California. Seismic reflection data provide depths to Miocene-Quaternary horizons; beneath the base of the Late Miocene Modelo Formation are largely nonreflective rocks of the Middle Miocene Topanga and older formations. Gravity and seismic reflection data reveal the North Leadwell fault zone, a set of down-to-the-north faults that does not offset the top of the Modelo Formation; the zone strikes northwest across the valley, and may be part of the Oak Ridge fault system to the west. In the southeast part of the valley, the fault zone bounds a concealed basement high that influenced deposition of the Late Miocene Tarzana fan and may have localized damage from the 1994 Northridge earthquake. Gravity and seismic refraction data indicate that the basin underlying San Fernando Valley is asymmetric, the north part of the basin (Sylmar subbasin) reaching depths of 5-8 km. Magnetic data suggest a major boundary at or near the Verdugo fault, which likely started as a Miocene transtensional fault, and show a change in the dip sense of the fault along strike. The northwest projection of the Verdugo fault separates the Sylmar subbasin from the main San Fernando Valley and coincides with the abrupt change in structural style from the Santa Susana fault to the Sierra Madre fault. The Simi Hills bound the basin on the west and, as defined by gravity data, the boundary is linear and strikes ~N45°E. That northeast-trending gravity gradient follows both the part of the 1971 San Fernando aftershock distribution called the Chatsworth trend and the aftershock trends of the 1994 Northridge earthquake. These data suggest that the 1971 San Fernando and 1994 Northridge earthquakes reactivated portions of Miocene normal faults. © 2011 Geological Society of America. Source

van Oort B.,CICERO Center for International Climate and Environmental Research | Bhatta L.D.,International Center for Integrated Mountain Development | Baral H.,Center for International Forestry Research | Rai R.K.,A+ Network | And 3 more authors.
Ecosystem Services

Human activities and climate change are key factors impacting ecosystem functions and its goods and services, which are important to the livelihoods of mountain communities. In Nepal, community based ecosystem management has been widely adopted as a way to secure local management and empowerment, but local knowledge, perceptions and values of ecosystem change and services are often ignored, and perhaps inadequately understood, in decision-making processes at district or national level. Our objective therefore was to develop a multi-method approach to support mapping of ecosystem services and assessing their local values. Local perceptions of ecosystem use, change and values were identified using participatory mapping, key informant and focus group discussions, and an extensive household survey carried out in the upstream Koshi River basin. Results were cross-validated with scientific literature, statistics and remote sensing data. Key ecosystem services identified are water, agricultural produce, and various forest products, most of which show a declining trend. We demonstrate that the use of different methods and levels of input results in different and complementary types of insights and detail needed for balanced and informed decision-making regarding sustainable management of ESs to secure current and future livelihoods and ecosystem functioning. © 2014 Elsevier B.V. Source

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