Abstract. Quantitative information on the vertical distribution of meiofaunal abundances and biomass were obtained from samples collected at 3 bathyal stations in the Eastern Mediterranean Sea located at the same depth but characterized by different food supply. Vertical distribution patterns of nieiofauna were investigated in relation to the biochemical composition of the sediment organic matter (proteins, carbohydrates, and lipids) and compared to benthic bacterial standing stocks. No significant relationship between bacteria and meiofauna was found, whereas a significant relationship between protein and lipid concentrations and total meiofauna density was observed. These data suggest that labile organic matter. considered as material readily aVdihbk to benthic consumers, may be an important factor regulating meiofaunal abundance and vertical distribution in deep-sea sediments. 相似文献
Repeated hydrographic casts, mooring time series and satellite sea surface temperature collected during the CANALES experiment (1996–98) are used to describe the thermohaline circulation in the Balearic Channels (western Mediterranean) and to analyze its variability. Mass transports are estimated by inverse calculations. The role played by each channel in the meridional water exchange is clarified: the Ibiza Channel funnels southward cool, saline, northern waters whereas the Mallorca Channel appears as the preferred route for the northward progression of warm, fresh, southern waters. A neat interannual trend is revealed by the continuous decrease of the amount of Western Mediterranean Intermediate Waters (WIW) brought by the Northern Current, reflecting the increase in temperature of the winter mixed layer in the northern Mediterranean that occurred each year between 1996 and 1998. A clear seasonal signal was also seen in the transport of the Northern Current which decreased from 1 to 1.4 Sv in winter to < 0.5 Sv in summer. The current intensified again in fall. A number of mesoscale eddies, from 20 to 70 km in size, most of them anticyclonic vortex eddies were brought by the unstable Northern Current, these eddies strongly perturbed the water exchange in the Ibiza Channel forcing retroflections of northern waters back to the north-east into the Balearic Current. These eddies either stayed stalled for several months in the Gulf of Valencia to the north of the channel, or were slowly funnelled southward through the channel narrows. A decreasing trend was observed in the mesoscale activity of the Northern Current between 1996 and 1998. Conversely, large, anticyclonic eddies, 150-km diameter, progressively invaded the Algerian Basin to the south of the channels in 1997–98 and forcing northward inflows (up to 0.75 Sv) of fresh and warm waters of Atlantic origin (AW) into the Mallorca Channel. The marked interannual differences observed in both northern and southern eddy activity may be linked to the interannual variability of the large scale thermohaline circulation. 相似文献
Mercury speciation and its distribution in surface and deep waters of the Mediterranean Sea were studied during two oceanographic cruises on board the Italian research vessel URANIA in summer 2003 and spring 2004 as part of the Med Oceaneor and MERCYMS projects. The study included deep water profiles of dissolved gaseous Hg (DGM), reactive Hg (RHg), total Hg (THg), monomethyl Hg (MeHg) and dimethyl Hg (DMeHg) in open ocean waters. Average concentrations of measured Hg species were characterized by seasonal and spatial variations. Overall average THg concentrations ranged between 0.41 and 2.65 pM (1.32 ± 0.48 pM) and were comparable to those obtained in previous studies of the Mediterranean Sea. A significant fraction of Hg was present as “reactive” Hg (average 0.33 ± 0.32 pM). Dissolved gaseous Hg (DGM), which consists mainly of Hg0, represents a considerable proportion of THg (average 20%, 0.23 ± 0.11 pM). The portion of DGM typically increased towards the bottom, especially in areas with strong tectonic activity (Alboran Sea, Strait of Sicily, Tyrrhenian Sea), indicating its geotectonic origin. No dimethyl Hg was found in surface waters down to the depth of 40 m. Below this depth, its average concentration was 2.67 ± 2.9 fM. Dissolved fractions of total Hg and MeHg were measured in filtered water samples and were 0.68 ± 0.43 pM and 0.29 ± 0.17 pM for THg and MeHg respectively. The fraction of Hg as MeHg was in average 43%, which is relatively high compared to other ocean environments. The concentrations reported in this study are among the lowest found in marine environments and the quality of analytical methods are of key importance. Speciation of Hg in sea water is of crucial importance as THg concentrations alone do not give adequate data for understanding Hg sources and cycling in marine environments. For example, photoinduced transformations are important for the presence of reactive and elemental mercury in the surface layers, biologically mediated reactions are important for the production/degradation of MeHg and DGM in the photic zones of the water column, and the data for DGM in deep sea indicate the natural sources of Hg in geotectonicaly active areas of the Mediterranean Sea. 相似文献
Different aspects of reproductive biology of the polychaete Timarete filigera (Delle Chiaje) were studied during a period of 2 years (from September 2002 to August 2003 and from September 2004 to August 2005). Timarete filigera specimens were collected monthly in the port of Bari (South Adriatic Sea, Mediterranean Sea). For population analysis, regenerating and entire specimens were separately analyzed, the regenerating individuals were assigned to different categories related to the region of the body from which they derived. Regenerating individuals were present throughout the year. There were three to four times more individuals deriving from the middle part than the anterior and posterior regenerating portions. From the high percentage of regenerating individuals observed in the T. filigera population, it can be supposed that this species reproduces mainly asexually by schizogenesis. However, histological analysis revealed the presence of female gametes in a few individuals. In contrast, males were never collected, probably due to the limited number of reproductive individuals collected. The abundance has shown wide fluctuations during the year, with a decrease from Winter to Spring. The analysis of the size‐frequency histograms has shown a growing phase of whole specimens from Spring to Winter. The life cycle of the investigated species is discussed with the hypothesis that strategies could be linked to the colonized environments, agamic reproduction coupled with sexual reproduction assures the presence and expansion of the population after the colonization by a limited number of larvae. 相似文献
A repeat hydrographic section has been maintained over two decades along the 180° meridian across the subarctic-subtropical
transition region. The section is naturally divided into at least three distinct zones. In the Subarctic Zone north of 46°N,
the permanent halocline dominates the density stratification, supporting a subsurface temperature minimum (STM). The Subarctic
Frontal Zone (SFZ) between 42°–46°N is the region where the subarctic halocline outcrops. To the south is the Subtropical
Zone, where the permanent thermocline dominates the density stratification, containing a pycnostad of North Pacific Central
Mode Water (CMW). The STM water colder than 4°C in the Subarctic Zone is originated in the winter mixed layer of the Bering
Sea. The temporal variation of its core temperature lags 12–16 months behind the variations of both the winter sea surface
temperature (SST) and the summer STM temperature in the Bering Sea, suggesting that the thermal anomalies imposed on the STM
water by wintertime air-sea interaction in the Bering Sea spread over the western subarctic gyre, reaching the 180° meridian
within a year or so. The CMW in this section originates in the winter mixed layer near the northern edge of the Subtropical
Zone between 160°E and 180°. The CMW properties changed abruptly from 1988 to 1989; its temperature and salinity increased
and its potential density decreased. It is argued that these changes were caused by the climate regime shift in 1988/1989
characterized by weakening of the Aleutian Low and the westerlies and increase in the SST in the subarctic-subtropical transition
region.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
Identification of the distinctive circulation patterns of storminess on the Atlantic margin of Europe forms the main objective of this study; dealing with storm frequency, intensity and tracking. The climatology of the extratropical cyclones that affect this region has been examined for the period 1940–1998. Coastal meteorological data from Ireland to Spain have been linked to the cyclone history for the North Atlantic in the analysis of storm records for European coasts. The study examines the evolution in the occurrence of storms since the 1940s and also their relationship with the North Atlantic Oscillation (NAO). Results indicate a seasonal shift in the wind climate, with regionally more severe winters and calmer summers established. This pattern appears to be linked to a northward displacement in the main North Atlantic cyclone track.
An experiment with the ECHAM4 A-GCM at high resolution (T106) has also been used to model the effect of a greenhouse gases induced warming climate on the climatology of coastal storms in the region. The experiment consists of (1), a 30-year control time-slice representing present-day equivalent CO2 concentrations and (2), a 30-year perturbed period corresponding to a time when the radiative forcing has doubled in terms of equivalent CO2 concentrations. The boundary conditions have been obtained from an atmosphere-ocean coupled OA-GCM simulation at low horizontal resolution. An algorithm was developed to allow the identification of individual cyclone movements in selected coastal zones. For most of the northern part of the study region, covering Ireland and Scotland, results describe the establishment by ca. 2060 of a tendency for fewer but more intense storms.
The impacts of these changes in storminess for the vulnerability of European Atlantic coasts are considered. For low-lying, exposed and ‘soft’ sedimentary coasts, as in Ireland, these changes in storminess are likely to result in significant localised increases in coastal erosion. 相似文献
The polychaete fauna of muddy bottoms off the Rhone delta (NW Mediterranean) was seasonally sampled at two sites at 70 m depth, from 1993 to 1996. During this period, five severe flood events occurred. A clustering analysis (distance coefficient of Whittaker) and three way fixed factor ANOVAs (site x season x year) showed strong year-to-year changes in species density and community structure, changes that masked seasonal variations. Total density increased by a factor of 3 and density of most species significantly increased following the first flooding event. Changes in the community structure were due to the successive dominance of a few species. The opportunistic species, such as Cossura sp., Mediomastus sp. and Polycirrus sp., exhibited peaks in density 1-3 months after the flood. These peaks were followed by a drastic decline. For species with a long life span, such as Sternaspis scutata, a slower but continuous increase in density was observed which was maintained for several months. The density fluctuations of these species exhibited a good correlation with river flow with time lags of 1-2 years. The successional dynamics observed are explained according to the geographical origin of the floods and the biology and feeding ecology of species. 相似文献