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1.
Abstract. Dark respiration rates, dissolved inorganic nitrogen (DIN) fluxes and nitrification rates were measured at two sites in the microtidal Sacca di Goro lagoon in September 2000. DIN fluxes correlated with the biomass of the dominant macrofauna species (the amphipod Corophium spp. at station Giralda and the polychaete Neanthes spp. at station Faro). Respiration (> 6 mmol O2 m−2h−1) and ammonium fluxes (> 80μmol N m−2h−1) were higher at station Giralda despite the lower organic matter content (4.5 %) and lower macrofauna biomass (4 g AFDW m−2). At both sites ammonium fluxes were significantly correlated with the biomass of the benthic infauna, but Corophium stimulated ammonium NH4+ fluxes 3-fold compared to Neanthes. The amphipod also enhanced nitrification rates (> 300 μmol N m−2h−1) due to the high density of its burrows, the higher NH4+ regeneration rates and the enhanced oxygen supply to the bacteria.  相似文献   

2.
Abstract. The influence of corallivores on coral community structure of eastern Pacific reefs has been considered less important then that of abiotic oceanographic factors. The data that support this assumption, however, are only available for Central American reefs. To assess the role of predation on hermatypic corals in a different regional reef environment, the abundance, spatial distribution and consumption rate of three corallivores: the echinoid Eucidaris thouarsii (Valenciennes), the asteroid Acanthaster planci (Linnaeus) and the teleostean fish Arothron meleagris (Bloch & Schneider), were estimated at Cabo Pulmo reef, Gulf of California, México (23°25' N, 109°25' W). Statistically, the abundances of the species did not change in any sections of the reef (mean values: E. thouarsii , 0.17 indiv. · m−2; A. planci , 1.9 indiv. · m−2; A. meleagris , 39 indiv. · ha−1). The average daily individual consumption rates of coral were calculated at 1.83 g CaCO3· m−2 for E. thouarsii , 118.4 cm2 for A. planci , and 16.38 g CaCO3· m−2 for A. meleagris , and were lower than those reported for Central American reefs. Considering the mean estimated carbonate production (7.9 kg CaCO3· m−2· a−1), corallivores eliminate less than 4% of the coral standing stock of Cabo Pulmo reef. The low corallivore population density and consumption rates, together with high local coral cover, indicate that corallivores are not key factors determining scleractinian abundance in this marginal reef.  相似文献   

3.
This study describes the macrofauna of the three beaches situated in central Gulf of Gabès (Tunisia): Ouderef, Gabès and Zarrat. The Gulf of Gabès has the largest tides in the Mediterranean and the beaches showed a wide intertidal zone. The beaches were sampled once during the spring low tides of June 2005. A transect was extended at each beach, from above the drift line to below the swash line at five sampled levels; at each level six 0.05 m2 replicates were taken to a depth of 30 cm and sieved through a 1-mm mesh, and the organisms collected and preserved. The three beaches showed a different physical environment. Sediment type was medium sand at the steeper Ouderef beach, fine sands at Gàbes beach, and very fine sands at the flatter Zarrat beach. The total number of species collected was 31: 12 crustaceans, 10 polychaetes, four molluscs and five insects. The supralittoral and mediolittoral zones were very different. The supralittoral zone was dominated by Talitrus saltator and insects. The most abundant mediolittoral species were the amphipod crustacean Bathyporeia guilliamsoniana at Ouderef beach (23069 ind.m−1), the surf clam Donax trunculus at Gabès beach (60711 ind.m−1) and the spionid polychaete Scolelepis mesnili at Zarrat beach (18345.6 ind.m−1).  相似文献   

4.
Abstract. A seasonal sampling program of five stations off the Island of Rhodes (SE Aegean Sea) was carried out in 1983–1984. Temperature, salinity, Secchi disk transparency, P-PO4, N-NO3, N-NO2, N-NH3, Si-SiO2, and chl a were measured and phytoplankton species recorded. Cell concentrations and chl a varied seasonally. with the highest values in summer (l.2 times 104 -1--1 total mean cells; 0.13 mgam-3 total mean chl a ) and the lowest in winter (2.3 times 103, 1--1 total mean cells; 0.06 mg.m-- total mean chl a ). A variation in cell abundance among stations was also noted. Quantitative relationships among the recorded taxa showed that diatoms and dinoflagellates were richer in species composition (88 and 58 total species, respectively) than coccolithophores (8 species) and other flagellates (8 species). Comparison of phytoplankton samples from different depths and stations by cluster analysis showed an irregularity or discontinuity in species associations. The SE Aegean Sea was characterized as oligotrophic on the basis of the estimated nutrient and phytoplankton concentration levels.  相似文献   

5.
The 3rd Chinese National Arctic Research Expedition(CHINARE–Arctic III) was carried out from July to September in 2008. The partial pressure of CO2(pCO2) in the atmosphere and in surface seawater were determined in the Bering Sea during July 11–27, 2008, and a large number of seawater samples were taken for total alkalinity(TA) and total dissolved inorganic carbon(DIC) analysis. The distributions of CO2 parameters in the Bering Sea and their controlling factors were discussed. The pCO2 values in surface seawater presented a drastic variation from 148 to 563 μatm(1 μatm = 1.013 25×10-1 Pa). The lowest pCO2 values were observed near the Bering Sea shelf break while the highest pCO2 existed at the western Bering Strait. The Bering Sea generally acts as a net sink for atmospheric CO2 in summer. The air-sea CO2 fluxes in the Bering Sea shelf, slope, and basin were estimated at-9.4,-16.3, and-5.1 mmol/(m2·d), respectively. The annual uptake of CO2 was about 34 Tg C in the Bering Sea.  相似文献   

6.
Abstract. Coastal Patagonian sea waters had been differentially nutrient-enriched to determine (i) the magnitude of the algal biomass supported and (ii) which species were able to best compete for the available nutrients. Nitrogen was found to be the nutrient limiting growth of the natural phytoplankton population. The addition of NO3 at 25 μg at 1-1 led to a 10 to 30 μg 1-1 increase in chlorophyll a in all but those treatments containing trace metal additions. The best yield coefficients were obtained when a chelator (EDTA) was added with NO3. A pool of nine diatom species were common in the N03 supplemented waters and the addition of vitamins along with NO3 allowed two of the nine species to dominate.  相似文献   

7.
The present case study evaluates the downward longwave radiation at the surface (DLR) in several high‐resolution (≈1°) general circulation models (GCMs) using surface observations from a semiarid continental site in New South Wales, Australia (Uardry, 34.39°S, 142.30°E). This site is located on a large grassland plain uniform in both its land use and landcover type, and is therefore particularly well suited for a comparison with GCM grid mean values. Monthly averages of newly constructed clear‐sky and all‐sky DLR climatologies and the resulting cloud‐radiative forcing are compared. It is shown that the GCMs exceed the observed DLR under cloud‐free conditions by 10–20 W m−2 at this semiarid site on an annual basis, with a strong seasonal dependence. The calculated clear‐sky fluxes are overestimated during the warmer summer season, with large absolute values of DLR, while the biases are reduced in the colder and dryer winter season with smaller fluxes. This gives direct support for recent evidence that the DLR model biases depend systematically on the thermal and humidity structure of the cloudless atmosphere. Fluxes from strongly emitting atmospheres tend to be overestimated, but may be underestimated from atmospheres with smaller emission. This points to common problems inherent in the simulation of the emission from the cloudless atmosphere in current longwave radiation codes.
The comparisons of the all‐sky climatologies at Uardry show that the clear‐sky biases are partly masked in the models with an insufficient cloud‐radiative forcing, thereby counterbalancing the excessive DLR of the cloud‐free atmosphere. On the other hand, when the cloudradiative forcing is improved, the biases in the cloud‐free atmosphere become fully apparent in the all‐sky fluxes.  相似文献   

8.
The life habits and microhabitat selection of speleophilic gobiid fishes were investigated on the Balearic Island of Ibiza (western Mediterranean Sea). Corcyrogobius liechtensteini (Kolombatović, 1891) was the most frequent species within submarine crevices, cavities and caves. Didogobius splechtnai Ahnelt & Patzner, 1995 co-occurred with C. liechtensteini in several cases but showed a clear spatial separation based on a different microhabitat preference. The microhabitat selection of both species was confirmed by habitat-choice experiments in anaquarium. Corcyrogobius liechtensteini was frequent in depths between 5 m and 25 m and attained abundances of 14.2 individuals · m−2. This species inhabited the ceilings and upper parts of the walls within the caves. D. splechtnai was mainly found between 7 m and 11 m and showed abundances of approximately 2 indivi-duals · m−2. This species occupied the fine sediment bottoms in the innermost parts of crevices and caves. The growth and the maximum age of both species were determined by length-frequency distributions. The overall sex ratio from catches of three different years are given for C. liechtensteini .  相似文献   

9.
Abstract. Spongaster tetras tetras Ehrenberg has long been considered by palaeontologists as a species indicative of warm (>21 C) sea-surface temperatures (SSTs) and tropical/subtropical conditions. However. a comparison of the Plio-Pleistocene record of S. t. tetras in the eastern equatorial Pacific (Ocean Drilling Program Hole 677A) with CaCO3, δ18O, and δ13C records reveals that S. t. tetras is most commonly present during periods of intense upwelling, often coinciding with isotopically identified glacial stages. when surface productivity and salinity are high, and SST is expected to be relatively low. Maximum S. t. tetras abundance (1.8% of radiolaria counted) occurred during a cool interglacial. when productivity and salinity were high, wind-driven upwelling intense, and SST relatively warmer than during glacial maxima. It appears that in the eastern equatorial Pacific upwelling system, SSTs are generally too cold (<21 C) for S. t. tetras to survive; however, S. t. tetras can tolerate (with populations <0.7%) cold SSTs if productivity and salinity are increased (due to upwelling), and flourishes (>0.7–> 1.8%) if this is coupled with relatively warm SSTs. This micropalaeontological study Corroborates the findings of an earlier research program on living S. t. tetras cultures (Anderson et al ., 1989a.b, c).  相似文献   

10.
Sedimentary marine systems are often highly productive and perform important nutrient regeneration functions as they efficiently decompose organic material. In recent years the role of habitat effects and of species composition in ecosystem functioning has become of interest. Estuarine environments are frequently subject to considerable anthropogenic pressures whilst supporting a variety of habitats ranging from well sorted soft muds through biogenically stable sediments to highly mobile coarse sands. There is therefore considerable spatial complexity in habitat type and faunal composition. This study set out to observe the effects of altering the topographical habitat features of an estuarine mudflat on a range of porewater nutrient concentrations (NH4+, NO3−, NO2−, PO43− and SiO) collected from four depths (3, 5, 9, and 12 cm) and on faunal composition. Two treatments (Shelled Nets and Net Controls) were used to alter the topography from simple mud to a mussel shell crumble and were compared to un-manipulated Control areas. Sediment granulometry and organic matter content analyses alongside biological traits analysis of the fauna were also conducted.
Differences were observed in porewater nutrient concentrations between the Control and both netted treatments at 5 cm depth only; the species diversity and abundance were also different in the netted treatments compared to the Controls, although no difference between the two manipulated treatments were observed. The changes in faunal composition were attributed solely to the altered topography and the observed nutrient changes were attributed to the faunal alteration rather than the topographical manipulation.  相似文献   

11.
Abstract. A number of recent studies based on hydrographic observations and modelling simulations have dealt with the major climatic shift that occurred in the deep circulation of the Eastern Mediterranean. This work presents hydrographic observations and current measurements conducted from 1997 to 1999, which reveal strong modifications in the dynamics of the upper, intermediate and deep layers, as well as an evolution of the thermohaline characteristics of the deep Aegean outflow since 1995. The reversal of the circulation in the upper layer of the north/central Ionian is worthy of note. The observations indicate a reduction of Atlantic Water in the northern Ionian with an increase on the eastern side of the basin. In the intermediate layer, the dispersal path of the Levantine Intermediate Water (LIW) is altered. Highly saline (>39.0) and well-oxygenated intermediate waters were found near the Western Cretan Arc Straits. They flow out from the Aegean, thus interrupting the traditional path of the LIW, and spread prevalently northwards into the Adriatic Sea. In the deep layer, dense waters, exiting from the Adriatic (σø−29.18 kg · m−3), flow against the western continental margin in the Ionian Sea at a depth of between 1000–1500 m. Dense waters of Aegean origin (> 29.20 kg · m−3), discharged into the central region of the Eastern Mediterranean during the early stages of the transient, propagate prevalently to the east in the Levantine basin and to the west in the northern Ionian Sea. Near-bottom current measurements conducted in the Ionian Sea reveal unforeseen aspects of deep dynamics, suggesting a new configuration of the internal thermohaline conveyor belt of the Eastern Mediterranean.  相似文献   

12.
Sevim Polat 《Marine Ecology》2002,23(2):115-126
Abstract. The monthly changes in chlorophyll a , phytoplankton abundance and nutrient concentrations at two stations, one at the inshore and the other at the deep waters of the northern part of İskenderun Bay, were investigated between 1994 – 1995. The vertical distribution of nutrients and phytoplankton biomass were also studied at the deep station. The concentrations of NO3+NO2-N, PO4-P and SiO4-Si of surface water at both stations were 0.31 – 1.63 µg-at · l-1, 0.08 – 0.60 µg-at · l-1 and 0.50 – 2.7 µg-at · l-1, respectively. The highest concentrations were measured at the inshore station and clear differences were found between the inshore and deep-water stations. Chlorophyll a concentrations ranged from 0.17 to 2.78 µg · l-1 and the highest value was measured in March. At the inshore station, which was affected by land run-off, phytoplankton abundance reached the highest value (21,308 cells · l-1) in October 1995, with a marked dominance of Pseudonitzschia pungens (20,200 cells · l-1). The nutrient and chlorophyll a concentrations at the inshore station were higher than those at the deep station. One reason for this is the land-based nutrient input into the coastal area here. In spite of these effects, the bay is not eutrophicated because of circulation events in the northeastern Mediterranean.  相似文献   

13.
The wind dependence of sea‐ice motion was studied on the basis of ice velocity and wind observations, and weather model output. The study area was a transition zone between open water and the ice‐covered ocean in the northern Baltic Sea. In the centre of the basin the sea‐ice motion was highly wind‐dependent and the linear relationship between the wind and the drift velocities explained 80% of the drift's variance. On the contrary, the wind‐drift dependence was low near the coast. The wind‐drift coherence was significant over a broader frequency range in the central part of the basin than for the coastal drift. The ice motion was simulated by a numerical model forced with five types of wind stress and with two types of current data, and the outcome was compared with the observed buoy drift. The wind and the wind‐induced surface current were the main factors driving the ice in the basin's centre, while internal ice stresses were of importance in the shear zone near the fast ice edge. The best wind forcing was achieved by applying a method dependent on atmospheric stability and ice conditions. The average air–ice drag coefficient was 1.4×10−3 with the standard deviation of 0.2×10−3. The improvement brought about by using an accurate wind stress was comparable with that achieved by raising the model grid resolution from 18 km to 5 km.  相似文献   

14.
Sub‐gridscale processes take place throughout the global atmosphere. Yet they have been neglected in traditional estimates of the global energy cycle on the ground that they can be treated as molecular heat fluxes. This view may cause quantitative underestimates of the efficiency of the global circulation of the atmosphere. In Part I of this two-part study we revisit the classical theory, beginning with the local energy equations. Similar to Lorenz we introduce a barotropic reference pressure p r and define a generalized field equation for the integrand of available potential energy, without reference to hydrostasy. The emerging energy quantity is new in that it comprises not only the classical correlation between efficiency factor and enthalpy but also an additional potential that depends upon p r . We then perform mass-averaging over the scale of contemporaneous global models (40‐400 km) and come up with averaged field energy equations, valid at the gridscale. Additional global and time-averaging of these removes all divergences and tendencies and yields two equations for the global energy reservoirs. The available potential energy reservoir is fed by gridscale plus sub-gridscale generation. The kinetic energy reservoir is tapped by gridscale plus sub-gridscale dissipation. Exchange between the reservoirs is carried by both gridscale and sub-gridscale conversion terms ( C grid, C sub ). Generation, conversion and dissipation fluxes are complete, as compared to the approximate quantities in the traditional formulation of the energy cycle. This approach allows to fully exploit Lorenz's original concept. The gridscale equations derived will be the basis for evaluating numerically the classical Lorenz terms plus a couple of new global conversion fluxes, notably C sub, to be presented in Part II of this study.  相似文献   

15.
The rôle of thermodynamics in the oceanic general circulation is investigated. The ocean is regarded as an open dissipative system that exchanges heat and salt with the surrounding system. A new quantitative method is presented to express the rate of entropy increase for a large‐scale open system and its surroundings by the transports of heat and matter. This method is based on Clausius's definition of thermodynamic entropy, and is independent of explicit expressions of small‐scale dissipation processes. This method is applied to an oceanic general circulation model, and the entropy increase rate is calculated during the spin‐up period of the model. It is found that, in a steady‐state, the entropy increase rate of the ocean system is zero, whereas that of the surroundings shows positive values, for both heat and salt transports. The zero entropy increase rate of the ocean system represents the fact that the system is in a steady‐state, while the positive entropy increase rate in the surroundings is caused by irreversible transports of heat and salt through the steady‐state circulation. The calculated entropy increase rate in the surroundings is 1.9×1011 W K−1, and is primarily due to the heat transport. It is suggested that the existence of a steady‐state dissipative system on the Earth, from a living system to the oceanic circulation, has a certain contribution to the entropy increase in its nonequilibrium surroundings.  相似文献   

16.
Reverse tip jets are strong low-level winds with easterly component that form near the southern tip of Greenland. In the present study, a reverse tip jet case which occurred from 21 to 22 December 2000 was examined to clarify its fine structure using a numerical model with a horizontal resolution of 3 km. The reverse tip jet, showing the supergeostrophic wind speed with a maximum wind speed in excess of 45 m s−1, extended from the east coast of Greenland to the west of Cape Farewell with anticyclonic curvature. A cloud free region coincided with the jet indicated that there was a mesoscale downdraft. Along the eastern edge of the jet, a banded cloud formed between the upstream easterly wind and the colder northerly wind that is a part of the jet and is located along the east coast. This cloud was associated with large gradients in surface wind speed, temperature, moisture, and heat flux. A maximum surface total heat flux of 300 W m−2 coincided with the location of the jet. It is suggested that the orographic deflection by Greenland's large-scale topography as well as small-scale downslope winds behind mountains with fiords causes the reverse tip jet.  相似文献   

17.
Abstract. The removal of glycine and glucose by freshly collected adult Mytilus edulis was determined using radiolabeled substances added to ambient concentrations of dissolved organic materials in freshly collected natural sea water. Uptake rates were calculated for substrate concentrations of 0.5 μM glycine and 1.0 μM glucose and were compared with the animals' energy and nitrogen demands as measured by oxygen consumption and ammonia excretion rates. Respiration and ammonia excretion rates as well as cither glycine or glucose removal were all determined for the same animals. The mean respiration rate was 670μl O2 g-1h-1, the mean ammonia excretion rate 1.95 μg-at NH4-g-1 h-1. The calculated uptake rates were 0.48 μmol -g-1-h-1 for free amino acids and 0.44 μmol-g-1 h-1 for free simple sugars. Such uptake rates could have contributed roughly 13% of the mussels' energy requirements or 10% of the mussels' nitrogen requirements assuming the following conditions: 0.5 μM concentration of free amino acids, 1.0μM concentration of simple sugars, uptake of total amino acids at a rate based on a weighted removal rate of glycine, alanine, serine, and glutamic acid, and uptake of simple sugars at a rate equal to that of glucose removal. It is apparent that simple organic substances dissolved in sea water may be of some benefit to mussels, especially when the substances occur in concentrations typical of coastal sea water.  相似文献   

18.
This paper discusses numerical simulation of the first day of the 1990 winter icing and storms project's (WISP) Valentine's day storm (VDS) case with the Purdue mesoscale model (PMM) and comparison of the results to aircraft, satellite, radiometer and other observations. This situation is marked by many observations of supercooled liquid water (SLW) contents of 0.2 g m−3 to 0.3 g m−3 by the WISP research aircraft. The PMM was initialized with the ECMWF analysis for 13 February 1990 at 0000 GMT and used to make an 18-h forecast with output every 6 h. This paper focuses on comparison of the forecast to observations made at about 1800 GMT since the aircraft encountered significant amounts of SLW during its flight between 1723 GMT and 1928 GMT. Dual channel radiometer, satellite visible imagery, and other observational data sources are also utilized. For this study, the PMM includes a new stable cloud parameterization that is discussed here. In it, cloud water and ice are explicitly calculated while rain and snow are implicitly handled. Between 0 and − 40 °C, cloud water and cloud ice can coexist; the conversion of cloud water to cloud ice is governed by the depositional growth rate of ice crystals whose concentration is diagnosed on the basis of temperature. After accounting for precipitation, a saturation adjustment is done to remove either supersaturated vapor or subsaturation in the presence of cloud drops. In mixed phase conditions, both saturation vapor pressure and the apportionment of condensate into ice or liquid are on a mass-weighted basis according to the existing amounts of ice and liquid or on the basis of temperature if there is neither.  相似文献   

19.
G. J. Herndl    J. Faganeli    N. Fanuko    P. Peduzzi  V. Turk 《Marine Ecology》1987,8(3):221-236
Abstract. The interdependences between phytoplankton standing crop, bacterial biomass and the dissolved organic matter (DOM) pool in the water column were investigated and related to sediment parameters in a shallow marine bay (Bay of Piran, Northern Adriatic Sea) over an annual cycle. Bacterioplankton density varied between 1–10 × 105 cells ml-1, with lowest density observed in March corresponding to the low Chi a concentrations during this period. Generation times as determined by dialysis incubations ranged between 4h (June) and 82 h (March). Mean bacterial secondary production rates during summer were about 40 mg C m-1 d-1 and 5mg C m-3.d-1 during winter. With a short time lag, DOM concentrations followed the fluctuation in Chi a.
Sediment oxygen demand measurements revealed a mean mineralization rate of about 260 mg C m-2 d-1 during summer and 100–200 mg C m-2 d-1 in winter. Sediment bacterial density varied between 108 - 109 cells g (sediment dry wt)-1 in the top 5 cm sediment layer or, in terms of biomass, 4.3 g C m-l during summer and 0.6 g C m-2 during winter. Highest concentrations of DOM in pore waters were measured in September, coinciding with high rates of sediment oxygen demand.  相似文献   

20.
Abstract. Recent findings indicate that heterotrophic bacteria and not phytoplankton are the most numerous biomass components even in the euphotic zone of oligotrophic, open oceans. In this study it was hypothesized that the microbial biomass components change within a few hundred meters as oligotrophic water flows across the reef and becomes enriched with nutrients. Along a trophic gradient, four stations at the Atlantic Barrier Reef off Belize (Central America) were sampled for microbial biomass components. Phytoplankton biomass (measured as chlorophyll a) ranged from the most oligotrophic station (St. 1) to the most eutrophic station (St. 4) from 6.9–415.5 μg CI"' (assuming a C:chl a ratio of 30): heterotrophic bacterial biomass increased 4-fold (from 10.1–46.4μg C 1-1), heterotrophic nanoflagellate (HNAN) biomass increased from 4.6-19ug C 1-1, and cyanobacteria from 0.9-4.5 μg C-1-1. Production estimates derived from seawater cultures revealed a 5-fold increase in bacterial production from the oligotrophic station (3.7 ug C 1-1 d-1) to the eutrophic St. 4 (17.8ug C-1-d1-1)- Cyanobacterial production rose from 1.1–3.5ug C-1–d-1 and HNAN production from 0.65-1.13 μg C-1-1 -d-1. While cyanobacteria contributed between 13 and 20% to the autotrophic plankton component in the oligotrophic waters, their contribution dropped to about 1 % at the eutrophic stations.  相似文献   

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