This issue marks a change in the editorial team of the ICESJournal of Marine Science, in that we have bid farewell to ourformer Editor-in-Chief, Niels Daan, after six years of sterlingservice, and to our Elsevier Publishing Editor, Andrew Richford,after an even longer period of years. Both deserve credit fortheir energy and vision that has left us the legacy of a journalas widely read and cited as the ICES Journal now is, but theyleave a gap that will be a huge challenge for us to meet. However,in my new capacity as Editor-in-Chief and in Els Bosma's capacityas Elsevier's Publishing Editor, I 相似文献
Deep-sea benthic ecosystems are sustained largely by organic matter settling from the euphotic zone. These fluxes usually
have a more or less well-defined seasonal component, often with two peaks, one in spring/early summer, the other later in
the year. Long time-series datasets suggest that inter-annual variability in the intensity, timing and composition of flux
maxima is normal. The settling material may form a deposit of “phytodetritus” on the deep-seafloor. These deposits, which
are most common in temperate and high latitude regions, particularly the North Atlantic, evoke a response by the benthic biota.
Much of our knowledge of these responses comes from a few time-series programmes, which suggest that the nature of the response
varies in different oceanographic settings. In particular, there are contrasts between seasonal processes in oligotrophic,
central oceanic areas and those along eutrophic continental margins. In the former, it is mainly “small organisms” (bacteria
and protozoans) that respond to pulsed inputs. Initial responses are biochemical (e.g. secretion of bacterial exoenzymes)
and any biomass increases are time lagged. Increased metabolic activity of small organisms probably leads to seasonal fluctuations
in sediment community oxygen consumption, reported mainly in the North Pacific. Metazoan meiofauna are generally less responsive
than protozoans (foraminifera), although seasonal increases in abundance and body size have been reported. Measurable population
responses by macrofauna and megafauna are less common and confined largely to continental margins. In addition, seasonally
synchronised reproduction and larval settlement occur in some larger animals, again mainly in continental margin settings.
Although seasonal benthic responses to pulsed food inputs are apparently widespread on the ocean floor, they are not ubiquitous.
Most deep-sea species are not seasonal breeders and there are probably large areas, particularly at abyssal depths, where
biological process rates are fairly uniform over time. As with other aspects of deep-sea ecology, temporal processes cannot
be encapsulated by a single paradigm. Further long time-series studies are needed to understand better the nature and extent
of seasonality in deep-sea benthic ecosystems.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
The formation of incised valleys on continental shelves is generally attributed to fluvial erosion under low sea level conditions. However, there are exceptions. A multibeam sonar survey at the northern end of Australia's Great Barrier Reef, adjacent to the southern edge of the Gulf of Papua, mapped a shelf valley system up to 220 m deep that extends for more than 90 km across the continental shelf. This is the deepest shelf valley yet found in the Great Barrier Reef and is well below the maximum depth of fluvial incision that could have occurred under a − 120 m, eustatic sea level low-stand, as what occurred on this margin during the last ice age. These valleys appear to have formed by a combination of reef growth and tidal current scour, probably in relation to a sea level at around 30–50 m below its present position.
Tidally incised depressions in the valley floor exhibit closed bathymetric contours at both ends. Valley floor sediments are mainly calcareous muddy, gravelly sand on the middle shelf, giving way to well-sorted, gravely sand containing a large relict fraction on the outer shelf. The valley extends between broad platform reefs and framework coral growth, which accumulated through the late Quaternary, coincides with tidal current scour to produce steep-sided (locally vertical) valley walls. The deepest segments of the valley were probably the sites of lakes during the last ice age, when Torres Strait formed an emergent land-bridge between Australia and Papua New Guinea. Numerical modeling predicts that the strongest tidal currents occur over the deepest, outer-shelf segment of the valley when sea level is about 40–50 m below its present position. These results are consistent with a Pleistocene age and relict origin of the valley.
Based on these observations, we propose a new conceptual model for the formation of tidally incised shelf valleys. Tidal erosion on meso- to macro-tidal, rimmed carbonate shelves is enhanced during sea level rise and fall when a tidal, hydraulic pressure gradient is established between the shelf-lagoon and the adjacent ocean basin. Tidal flows attain a maximum, and channel incision is greatest, when a large hydraulic pressure gradient coincides with small channel cross sections. Our tidal-incision model may explain the observation of other workers, that sediment is exported from the Great Barrier Reef shelf to the adjacent ocean basins during intermediate (rather than last glacial maximum) low-stand, sea level positions. The model may apply to other rimmed shelves, both modern and ancient. 相似文献
Urban stormwater runoff could contribute to the deterioration of water quality of a receiving water body. In this research, field studies and laboratory experiments were conducted to assess the microbial contamination resulting from urban stormwater runoff into the Lake Pontchartrain estuary. Fecal coliform, Escherichia coli and enterococci were used as indicator organisms. The specific objectives of the research were to examine the distribution of the indicator organisms in different environmental elements (water column, suspended particles and sediment) and to further investigate the mechanisms related to their fate. Results of the research indicated satisfactory water quality at the study sites during dry weather periods. However, a significant increase was observed in the concentrations of the indicator organisms in the water columns and sediment at specific study sites following a given stormwater event. Three to seven days were needed for the elevated indicator organisms to return back to their background levels in the water column and sediment, respectively. The mechanism of sedimentation contributed to a reduction in the microbial concentration in the water column, as the indicator organisms were found to attach to the suspended particles in the stormwater. The percentage of fecal coliform, E. coli and enterococci attached to the suspended particles was found to be within the range of 9.8–27.5%, 21.8–30.4%, and 8.4–11.5% of the total indicator organisms in the stormwater loaded into the estuary, respectively. About 75–80% of the total indicator organisms remained free-floating for some distance in the water column before dying off. 相似文献
In this paper, we derive an unsteady refraction–diffraction model for narrowbanded water waves for use in computing coupled wave–current motion in the nearshore. The end result is a variable coefficient, nonlinear Schrödinger-type wave driver (describing the envelope of narrow-banded incident waves) coupled to forced nonlinear shallow water equations (describing steady or unsteady mean flows driven by the short-wave field). Comparisons with experimental data show that good accuracy can be obtained for cases of nonbreaking wave transformation. Numerical simulations show that the interaction of wave groups with longshore topographic nonuniformities generates strong edge wave resonances, providing a generating mechanism for low-order edge waves. 相似文献
The coupling of physics and biology was examined along a 160 km long transect running out from the north coast of South Georgia Island and crossing the Southern Antarctic Circumpolar Current Front (SACCF) during late December 2000. Surface and near surface potential TS properties indicated the presence of three water types: a near-shore group of stations characterised by water which became progressively warmer and fresher closer to South Georgia, an offshore grouping in which sea surface temperatures and those at the winter water level were relatively warm (1.8°C and 0.5°C, respectively), and a third in which surface and winter water temperatures were cooler and reflected the presence of the SACCF. The transect bisected the SACCF twice, revealing that it was flowing in opposite directions, north-westward closest to South Georgia and south-eastwards at its furthest point from the island. The innermost limb was a narrow intense feature located just off the shelf break in 2000–3500 m of water and in which rapid surface baroclinic velocities (up to 35 cm s−1) were encountered. Offshore in the outermost limb, shown subsequently to be a mesoscale eddy that had meandered south from the retroflected limb of the SACCF, flow was broader and slower with peak velocities around 20 cm s−1. Chlorophyll a biomass was generally low (<1 mg m−3) over much of the transect but increased dramatically in the region of the innermost limb of the SACCF, where a deepening of the surface mixed layer was coincident with a subsurface chlorophyll maximum (7.4 mg m−3) and elevated concentrations down to 100 m. The bloom was coincident with depleted nutrient concentrations, particularly silicate, nitrate and phosphate, and although ammonium concentrations were locally depleted the bloom lay within an elevated band (up to 1.5 mmol m−3) associated with the frontal jet. Increased zooplankton abundance, higher copepod body carbon mass and egg production rates all showed a strong spatial integrity with the front. The population structure of the copepods Calanoides acutus and Rhincalanus gigas at stations within the front suggested that rather than simply resulting from entrainment and concentration within the jet, increased copepod abundance was the result of development in situ. Estimates of bloom duration, based on silicate and carbon budget calculations, set the likely duration between 82 and 122 d, a figure supported by the development schedule of the two copepod species. Given this timescale, model outputs from FRAM and OCCAM indicated that particles that occurred on the north side of South Georgia in December would have been in the central-southern Scotia Sea 2–3 months earlier, probably in sea ice affected regions. 相似文献
Knowledge of marine geological environments in which shallow gas is accumulating is becoming increasingly important in global
studies of climate change because a measurable proportion of the total methane source comes from continental margins. Previous
studies have revealed that coastal environments represent important geological environments where microbial methane is being
generated, is accumulating, and is being released. In the Ría de Pontevedra, at least 4.5 km2 of seafloor in the innermost part of the ría is underlain by sediments containing natural gas. Seismic interpretation contributes
new findings for the definition of periods and geological environments in which the gas could have been generated, and is
accumulating and released in the Ría de Pontevedra. Groundtruthing the seismic data (facies, environments) makes it possible
to identify favourable geological environments for gas generation in the sedimentary infill of the Ría de Pontevedra. Sequence
stratigraphy based on high-resolution seismic profiles and post-Last Glacial Maximum sea-level records makes it possible to
establish the stratigraphic architecture of the ría and to define the periods in which gas could have been generated. The
results of this study show that the sedimentary infill is composed of a fifth-order sequence developed since the Last Glacial
Maximum. Within this sequence, gas appears to have accumulated in the Holocene deposits associated with the latest transgressive
and highstand system tracts. Seismic analysis shows that gas could have been generated in different geological environments
in the Ría de Pontevedra. If coastal environments at times of lower sea level were similar to those of the present, organic-rich
mud deposits (deposited mainly in lakes, estuaries and floodplains) could have survived transgression and remained buried
as potential gas sources in the inner part of the ría. 相似文献
Environmental tracers sampled from the carbonate Madison aquifer on the eastern flank of the Black Hills, South Dakota, USA indicated the approximate locations of four major karst conduits. Contamination issues are a major concern because these conduits are characterized by direct connections to sinking streams, high groundwater velocities, and proximity to public water supplies. Objectives of the study were to estimate approximate conduit locations and assess possible anthropogenic influences associated with conduits. Anomalies of young groundwater based on chlorofluorocarbons (CFCs), tritium, and electrical conductivity (EC) indicated fast moving, focused flow and thus the likely presence of conduits. δ18O was useful for determining sources of recharge for each conduit, and nitrate was a useful tracer for assessing flow paths for anthropogenic influences. Two of the four conduits terminate at or near a large spring complex. CFC apparent ages ranged from 15 years near conduits to >50 years in other areas. Nitrate-N concentrations >0.4 mg/L in groundwater were associated with each of the four conduits compared with concentrations ranging from <0.1 to 0.4 mg/L in other areas. These higher nitrate-N concentrations probably do not result from sinking streams but rather from other areas of infiltration. 相似文献