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111.
Deposition, mineralization, and storage of carbon and nitrogen in sediments of the far northern and northern Great Barrier Reef shelf 总被引:4,自引:0,他引:4
The flow of carbon and nitrogen in sediments of the far northern and northern sections of the Great Barrier Reef continental shelf was examined. Most of the organic carbon (81–94%) and total nitrogen (74–92%) depositing to the seabed was mineralized, with burial of carbon (6–19%) and nitrogen (8–20%) being proportionally less on this tropical shelf compared with other non-deltaic shelves. Differences in carbon and nitrogen mineralization among stations related best to water depth and proximity to river basins, with rates of mineralization based on net ∑CO2 production ranging from 17 to 39 ( mean=23) mmol C m−2 d−1. The overall ratio of O2:CO2 flux was 1.3, close to the Redfield ratio, implying that most organic matter mineralized was algal. Sulfate reduction was estimated to account for ≈30% (range: 6–62%), and denitrification for ≈5% (range: 2–13%), of total C mineralization; there was no measurable CH4 production. Discrepancies between ∑CO2 production across the sediment–water interface and sediment incubations suggest that as much as 5 mmol m−2 d−1 (≈25% of ∑CO2 flux) was involved in carbonate mineral formation. Most microbial activity was in the upper 20 cm of sediment. Rates of net NH4+ production ranged from 1.6 to 2.7 mmol N m−2 d−1, with highly variable N2 fixation rates contributing little to total N input. Ammonification and nitrification rates were sufficient to support rapid rates of denitrification (range: 0.1–12.4 mmol N m−2 d−1). On average, nearly 50% of total N input to the shelf sediment was denitrified. The average rates of sedimentation, mineralization, and burial of C and N were greater in the northern section of the shelf than in the far northern section, presumably due to higher rainfall and river discharge, as plankton production was similar between regions. The relative proportion of plankton primary production remineralized at the seafloor was in the range of 30–50% which is at the high end of the range found on other shelves. The highly reactive nature of these sediments is attributed to the deposition of high-quality organic material as well as to the shallowness of the shelf, warm temperatures year-round, and a variety of physical disturbances (cyclones, trawling) fostering physicochemical conditions favorable for maintaining rapid rates of microbial metabolism. The rapid and highly efficient recycling of nutrients on the inner and middle shelf may help to explain why the coral reefs on the outer shelf have remained unscathed from increased sediment delivery since European settlement. 相似文献
112.
Chris K. Wendt Jason Beringer Nigel J. Tapper Lindsay B. Hutley 《Boundary-Layer Meteorology》2007,124(2):291-304
Fire scars have the ability to radically alter the surface energy budget within a tropical savanna by reducing surface albedo,
increasing available energy for partitioning into sensible and latent heat fluxes and increasing substrate heat flux. These
changes have the potential to alter boundary-layer conditions and ultimately feedback to local and regional climate. We measured
radiative and energy fluxes over burnt and unburnt tropical savanna near Howard Springs, Darwin, Australia. At the burnt site
a low to moderate intensity fire, ranging between 1,000 and 3,500 kW m−1, initially affected the land surface by removing all understorey vegetation, charring and blackening the ground surface,
scorching the overstorey canopy and reducing the albedo. A reduction in latent heat fluxes to almost zero was seen immediately
after the fire when the canopy was scorched. This was then followed by an increase in the sensible heat flux and a large increase
in the ground heat flux over the burnt surface. Tethered balloon measurements showed that, despite the presence of pre-monsoonal
rain events occurring during the measurement period, the lower boundary layer over the burnt site was up to 2°C warmer than that over the unburnt site. This increase in boundary-layer heating when applied to fire scars at the landscape
scale can have the ability to form or alter local mesoscale circulations and ultimately create a feedback to regional heating
and precipitation patterns that may affect larger-scale processes such as the Australian monsoon. 相似文献
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Fitzpatrick Lindsay Titze Daniel Anderson Eric J. Beletsky Dmitry Kelley John G. W. 《Ocean Dynamics》2023,73(7):433-447
Ocean Dynamics - Generally, ports in the North American Great Lakes are not supported with navigational guidance (water level, water temperature, currents, ice) by NOAA’s Great Lakes... 相似文献
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There are recognised benefits to managing fisheries by individual transferable quotas (ITQs), but ITQs may increase incentives to discard fish. 相似文献
120.
Gavin M. Elliott Christian Berndt Lindsay M. Parson 《Marine Geophysical Researches》2009,30(3):207-214
The continental margin of SW Africa is typical of a volcanic rifted margin associated with a hotspot trail characterized by a large volcanic ridge, the Walvis Ridge, defining the hotspot migration, and extensive extrusive volcanism that produced seaward-dipping reflectors (SDR). Previously unpublished seismic data show two significant anomalies of the SW African Margin when compared to other typical volcanic rifted margins: (1) Hyaloclastitic outer highs are rare, and (2) the SDR in the North dip towards the Walvis Ridge. We explain these anomalies by a major transform segment close to the centre of volcanism combined with pulsed volcanism. The Walvis Ridge represents an east-west striking extrusive centre which produced a SDR sequence. Following break-up the northern boundary of the Walvis Ridge became a left lateral transform fault. Our data support the idea that a transform fault system interacting with a ridge jump were responsible for the accretion of the São Paulo Plateau to the American plate. 相似文献