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1.
The water under the main thermocline in the Japan Sea is a single water mass referred to as the Japan Sea Proper Water. It can be defined as having temperature below 2.0°C, salinity above 34.00%, and dissolved oxygen below 7.0 ml 1−1. In the north most of the water above the potential temperature 0.1°C depth (about 800–1000 m) is a mode water, with σθ of 27.32 to 27.34 kg m−3. North of 40°N it has high oxygen (more than 6.00 ml 1−1) with a distinct discontinuity (oxygen-cline) at the bottom of the mode water. The most probable region for the formation of the water is the area north of 41°N between 132° and 134°E. The deeper water probably is formed in the norther area of 43°N, and directly fills the main part of the Japan Basin north of 41°N and east of 134°E.  相似文献   

2.
Dissolved cadmium and copper concentrations have been determined in 76 surface water samples in coastal and ocean waters around Scotland by anodic stripping voltammetry (ASV). A trace metal/salinity ‘front’ is observed to the west, north and north-east of Scotland separating high salinity ocean water (>35 × 10−3) with low concentrations of dissolved Cd and Cu from lower salinity (<35 × 10−3) coastal water containing higher concentrations of Cd and Cu. Mean Cd concentrations in ocean and coastal waters are 7 ng dm−3 (0·06 n ) and 11 ng dm−3 (0·10 n ) respectively; for Cu the respective levels are 60 ng dm−3 (0·95 n ) and 170 ng dm−3 (2·68 n ). The observed distribution is attributed principally to freshwater runoff and the advection of contaminated Irish Sea water into the study area.  相似文献   

3.
A simple hydraulic model is used to estimate the deep water fluxes of Cretan Deep Water (CDW), through the Cretan Arc Straits and into the Eastern Mediterranean Basins. The input to the model consists of the height of the deep water reservoir above sill depth and its density difference from the overlying water masses. Data from four hydrographic cruises, which took place in 1995, 1991 and 1987, are used to estimate the depth of the reservoir above the sill and the density difference. The results show a significant CDW outflow of 0.75×106 m3 s−1 in early 1995. The outflow of CDW through Kassos Strait, in the east, is 0.53×106 m3 s−1, while 0.22×106 m3 s−1 outflows through the Antikithira Strait in the west. The model results agree with fluxes estimated from current meter observations.The CDW outflow has been neither steady nor uniform during the period 1987–95. In the Kassos Strait, the outflow commenced in 1987 and increased rapidly until 1991; since then, it appears to have stabilised. In the Antikithira Strait, in contrast, the outflow has increased steadily since 1987. Such modifications in the CDW outflow are associated with changes in its hydrographic characteristics. The salinity of CDW increased constantly, by approximately 0.1, between 1987 and 1995 while its temperature warmed, between 1987 and 1991, and then cooled.  相似文献   

4.
The origin and the spreading of the shallow Mediterranean water core (Ms) in the Iberian basin is discussed with a quasi-synoptic hydrographic data set enhanced by chlorofluoromethane (CFM) measurements. Its characteristic density level is found to be σt = 27.4. Characterized by high temperature and CFM values, Ms enters the Iberian basin in the region of Cape St Vincent between depths of 500–750 dbar. A heat anomaly of >11.8 × 109 J m−2 is chosen as the boundary between the presence of Ms and the background field. The core is found in a tongue-like shape as well as in separate isolated eddies of both cyclonic and anticyclonic circulation. Using the optimum multiparameter analysis (Tomczak and Large, 1989, Journal of Geophysical Research, 94, 16141–16149), the North Atlantic Central Water (NACW), which mixes with the Mediterranean outflow to form Ms, turned out to be in the mean 1°C warmer and 0.11 saltier than in regions with minor Mediterranean influence. This points to the Gulf of Cadiz as the origin of Ms, where the Mediterranean oufflows is in contact with NACW of the appropriate characteristics.  相似文献   

5.
In May and September 1999 11 stations were sampled in the southern and central North Sea, located in the German Bight, eastern Oyster Ground and Dogger Bank. The study focused on the influence of particle mixing on transport of chlorophyll a to deeper sediment layers and vertical bacterial distribution (max. DEPTH=10 cm). The sampling stations were chosen to reflect a gradient in environmental conditions in the North Sea. The sampling stations differed in respect to redox potential (eH up to −243 mV in the German Bight and up to 274 mV in the offshore regions), silt content (up to 54% in the German Bight and 0·34% at the northern Dogger Bank) and different proportion of fresh organic material on total organic matter content (C/N ratios ranging from 9·27 in the German Bight up to 1·72 in the offshore sediments). Although bacterial densities (8·55×109 g−1in the German Bight up to 0·35×109 g−1in offshore sediments) were significantly correlated to chlorophyll a content in the sediment (P<0·01), inconsistencies in the temporal pattern of both variables in the surficial sediment layer suggested, that the dynamics of bacterial densities is generally controlled by food supply but also by other variables. The chlorophyll a content in the surficial sediments of the German Bight (up to 1·84 μg g−1) was significantly higher than in the Oyster Ground (up to 0·58 μg g−1) and the Dogger Bank area (up to 0·68 μg g−1). With increasing chlorophyll a input to the benthic realm a subsequent enhanced burial of this compound into deeper sediment layers was expected either by biological (bioturbation) or by physical sediment mixing. However, the vertical profile of chlorophyll a decreased steeply in the sediments of the German Bight. Contrary, subsurface peaks were measured in the offshore areas. It was concluded from these results, that the vertical distribution of organic matter in sediments is less limited by the quantitative input from the water column but concomitant with particle mixing itself. The extent and possible mechanisms of particle mixing in the different study areas in relation to specific environmental factors is discussed.  相似文献   

6.
The ratio of oxygen-18 to oxygen-16 (expressed as per mille deviations from Vienna Standard Mean Ocean Water, δ18O) is reported for seawater samples collected from seven full-depth CTD casts in the northern North Atlantic between 20° and 41°W, 52° and 60°N. Water masses in the study region are distinguished by their δ18O composition, as are the processes involved in their formation. The isotopically heaviest surface waters occur in the eastern region where values of δ18O and salinity (S) lie on an evaporation–precipitation line with slope of 0.6 in δ18O–S space. Surface isotopic values become progressively lighter to the west of the region due to the addition of 18O-depleted precipitation. This appears to be mainly the meteoric water outflow from the Arctic rather than local precipitation. Surface samples near the southwest of the survey area (close to the Charlie Gibbs Fracture Zone) show a deviation in δ18O–S space from the precipitation mixing line due to the influence of sea ice meltwater. We speculate that this is the effect of the sea ice meltwater efflux from the Labrador Sea. Subpolar Mode Water (SPMW) is modified en route to the Labrador Sea where it forms Labrador Sea Water (LSW). LSW lies to the right (saline) side of the precipitation mixing line, indicating that there is a positive net sea ice formation from its source waters. We estimate that a sea ice deficit of ≈250 km3 is incorporated annually into LSW. This ice forms further north from the Labrador Sea, but its effect is transferred to the Labrador Sea via, e.g. the East Greenland Current. East Greenland Current waters are relatively fresh due to dilution with a large amount of meteoric water, but also contain waters that have had a significant amount of sea ice formed from them. The Northeast Atlantic Deep Water (NEADW, δ18O=0.22‰) and Northwest Atlantic Bottom Waters (NWABW, δ18O=0.13‰) are isotopically distinct reflecting different formation and mixing processes. NEADW lies on the North Atlantic precipitation mixing line in δ18O–salinity space, whereas NWABW lies between NEADW and LSW on δ18O–salinity plots. The offset of NWABW relative to the North Atlantic precipitation mixing line is partially due to entrainment of LSW by the Denmark Strait overflow water during its overflow of the Denmark Strait sill. In the eastern basin, lower deep water (LDW, modified Antarctic bottom water) is identified as far north as 55°N. This LDW has δ18O of 0.13‰, making it quite distinct from NEADW. It is also warmer than NWABW, despite having a similar isotopic composition to this latter water mass.  相似文献   

7.
Self-diffusion coefficients of five major ions have been determined by a radioactive tracer method (capillary tube method) in seawater of salinity 34.86 at 25°C. Data are presented for Na+, Ca2+, Cl−, SO42, and HCO3−, which constitute about 95% by weight of sea salt. The influence of temperature and salinity on these coefficients has been studied for Na+ and Cl− which are the major components of sea salt: self-diffusion coefficients of these two ions have been measured in seawater, at different temperatures for a salinity of 34.86 and at different salinities for a temperature of 25°C. Diffusion coefficients of the same ions have been determined at 25°C by using another radioactive tracer method (quasi-steady cell method). In this experiment, seawater ions were allowed to diffuse from natural seawater into dilute seawater. Data have been obtained at 25°C for Na+, Ca 2+, Cl−, SO42− and HCO3−, corresponding to different salinity gradients.  相似文献   

8.
We present a detailed account of the changing hydrography and the large-scale circulation of the deep waters of the Eastern Mediterranean (EMed) that resulted from the unique, high-volume influx of dense waters from the Aegean Sea during the 1990s, and of the changes within the Aegean that initiated the event, the so-called ‘Eastern Mediterranean Transient’ (EMT). The analysis uses repeated hydrographic and transient tracer surveys of the EMed in 1987, 1991, 1995, 1999, and 2001/2002, hydrographic time series in the southern Aegean and southern Adriatic Seas, and further scattered data. Aegean outflow averaged nearly 3 × 106 m3 s−1 between mid-1992 and late 1994, and was largest during 1993, when south and west of Crete Aegean-influenced deep waters extended upwards to 400 m depth. EMT-related Aegean outflow prior to 1992, confined to the region around Crete and to 1800 m depth-wise, amounted to about 3% of the total outflow. Outflow after 1994 up to 2001/2002, derived from the increasing inventory of the tracer CFC-12, contributed 20% to the total, of 2.8 × 1014 m3. Densities in the southern Aegean Sea deep waters rose by 0.2 kg/m3 between 1987 and 1993, and decreased more slowly thereafter. The Aegean waters delivered via the principal exit pathway in Kasos Strait, east of Crete, propagated westward along the Cretan slope, such that in 1995 the highest densities were observed in the Hellenic Trench west of Crete. Aegean-influenced waters also crossed the East Mediterranean Ridge south of Crete and from there expanded eastward into the southeastern Levantine Sea. Transfer into the Ionian mostly followed the Hellenic Trench, largely up to the trench’s northern end at about 37°N. From there the waters spread further west while mixing with the resident waters. Additional transfer occurred through the Herodotus Trough in the south. Levantine waters after 1994 consistently showed temperature–salinity (T–S) inversions in roughly 1000–1700 m depth, with amplitudes decreasing in time. The T–S distributions in the Ionian Sea were more diverse, one cause being added Aegean outflow of relatively lower density through the Antikithira Strait west of Crete. Spreading of the Aegean-influenced waters was quite swift, such that by early 1995 the entire EMed was affected. and strong mixing is indicated by near-linear T–S relationships observed in various places. Referenced to 2000 and 3000 dbar, the highest Aegean-generated densities observed during the event equaled those generated by Adriatic Sea outflow in the northern Ionian Sea prior to the EMT. A precarious balance between the two dense-water source areas is thus indicated. A feedback is proposed which helped triggering the change from a dominating Adriatic source to the Aegean source, but at the same time supported the previous long-year dominance of the Adriatic. The EMed deep waters will remain transient for decades to come.  相似文献   

9.
Water samples from the Tamar Estuary oxidized manganese when supplemented with Mn2+ (2 mgl−1). The rates of oxidation were depressed in the presence of various metabolic inhibitors. The effect of Mn2+ and temperature on the rate of manganese oxidation suggested that a biological process was largely responsible for converting Mn2+ to Mn4+. Rates of manganese oxidation were much higher in freshwater (3·32 μgl−1 h−1 in water containing 30 mgl−1 of suspended matter) than in saline water (0·7 μgl−1 h−1 in water of salinity 32‰) containing the same amount of particulate matter. The rate of manganese oxidation was proportional to the particulate load (up to 100 mgl−1 particulates).  相似文献   

10.
The apparent (stoichiometric) solubility product of calcite in artificial seawater of salinity 35‰ was measured by a saturometer technique. The value of the apparent solubility product was found to be (4·59 ± 0·05) × 10−7 moles/(kilogram of seawater)2 at 25°C with a temperature coefficient of −0·0108 × 10−7/°C between 2 and 25°C. These values are significantly smaller than those found by MacIntyre (1965) and other workers. The effect of these results on the saturation of the oceans with respect to calcite is examined.  相似文献   

11.
Atlantic Water flow through the Barents and Kara Seas   总被引：2，自引：0，他引：2  
The pathway and transformation of water from the Norwegian Sea across the Barents Sea and through the St. Anna Trough are documented from hydrographic and current measurements of the 1990s. The transport through an array of moorings in the north-eastern Barents Sea was between 0.6 Sv in summer and 2.6 Sv in winter towards the Kara Sea and between zero and 0.3 Sv towards the Barents Sea with a record mean net flow of 1.5 Sv. The westward flow originates in the Fram Strait branch of Atlantic Water at the Eurasian continental slope, while the eastward flow constitutes the Barents Sea branch, continuing from the western Barents Sea opening.About 75% of the eastward flow was colder than 0°C. The flow was strongly sheared, with the highest velocities close to the bottom. A deep layer with almost constant temperature of about −0.5°C throughout the year formed about 50% of the flow to the Kara Sea. This water was a mixture between warm saline Atlantic Water and cold, brine-enriched water generated through freezing and convection in polynyas west of Novaya Zemlya, and possibly also at the Central Bank. Its salinity is lower than that of the Atlantic Water at its entrance to the Barents Sea, because the ice formation occurs in a low salinity surface layer. The released brine increases the salinity and density of the surface layer sufficiently for it to convect, but not necessarily above the salinity of the Atlantic Water. The freshwater west of Novaya Zemlya primarily stems from continental runoff and at the Central Bank probably from ice melt. The amount of fresh water compares to about 22% of the terrestrial freshwater supply to the western Barents Sea. The deep layer continues to the Kara Sea without further change and enters the Nansen Basin at or below the core depth of the warm, saline Fram Strait branch. Because it is colder than 0°C it will not be addressed as Atlantic Water in the Arctic Ocean.In earlier decades, the Atlantic Water advected from Fram Strait was colder by almost 2 K as compared to the 1990s, while the dense Barents Sea water was colder by up to 1 K only in a thin layer at the bottom and the salinity varied significantly. However, also with the resulting higher densities, deep Eurasian Basin water properties were met only in the 1970s. The very low salinities of the Great Salinity Anomaly in 1980 were not discovered in the outflow data. We conclude that the thermal variability of inflowing Atlantic water is damped in the Barents Sea, while the salinity variation is strongly modified through the freshwater conditions and ice growth in the convective area off Novaya Zemlya.  相似文献   

12.
North Pacific Tropical Water (NPTW) is characterized as a subsurface salinity maximum flowing in the North Equatorial Current and is the main source of salt for the North Pacific. We briefly describe the climatological features of its formation and circulation, and then examine temporal changes in its properties associated with the climate regime shift in the 1970s. We use a variety of data, which include the repeat hydrographic sections along 130°E, 137°E, 144°E and 155°E meridians, the hydrographic data from the Hawaii Ocean Time-series, the World Ocean Atlas 1994, and available gridded data of wind stress and evaporation. The classical idea that NPTW originates from the zone of the highest sea surface salinity at 20°–30°N centered around the international date line and spreads along the isopycnal geostrophic flow patterns is confirmed. Further, it is shown that the meridional extent of NPTW along 137°E is from 10°N to 23°N on average and the highest salinity core lies at about 15°N and 24.0σθ, and that the portion of NPTW north (south) of about 15°N originates from the formation region west (east) of the date line. NPTW in the 137°E section changed remarkably associated with the mid-1970s regime shift. North of 15°N NPTW increased both in its salinity and thickness while to the south of 15°N only its salinity increased and its thickness remained unchanged. The westward geostrophic velocity is increased significantly in both the southern and northern parts of NPTW. The northern thickening and speedup and the southern speedup increased NPTW transport across 137°E. The changes in the thermohaline forcing such as evaporation and Ekman salt convergence in the NPTW formation region possibly contributed to the increases in salinity in the southern part of NPTW, but not to that of the northern part. On the other hand, the increased Ekman pumping accounts for the increase of the NPTW inventory and transport at 137°E. The increased salinity of NPTW at 137°E, especially its northern portion, was presumably caused by an increase in its formation rate rather than changes in the sea surface salinity in its formation region; the thicker the NPTW layer is, the saltier is the core that tends to survive the mixing processes.  相似文献   

13.
The Upper Gulf of California is the shallow (depth <30 m), tidal area at the head of the Gulf of California. It is an inverse estuary, due to the high evaporation rate (E1·1 m year−1) and almost nil freshwater input from rainfall and the Colorado River. Historical and recent hydrographic data show that the area is almost vertically well-mixed throughout the year, that the horizontal distribution of properties follows the bathymetry, and that the hydrography has a strong annual modulation. As in other negative estuaries, the year-round salinity increase toward the head causes the density to do likewise, despite the seasonally reversing temperature gradient. The pressure gradient thus formed leads to water-mass formation and gravity currents (speed 0·1 ms−1), both in winter and in summer. In winter, the high salinity water sinks beyond 200 m, while in summer it only reaches a depth of 20–30 m. The gravity currents appear to be modulated by the fortnightly tidal cycle, with events in neap tides. This phenomenon causes the presence, at least during neap tides, of slight stratification (Δσt≈−0·2).  相似文献   

14.
We proposed an empirical equation of sea surface dimethylsulfide (DMS, nM) using sea surface temperature (SST, K), sea surface nitrate (SSN, μM) and latitude (L, °N) to reconstruct the sea surface flux of DMS over the North Pacific between 25°N and 55°N: ln DMS = 0.06346 · SST − 0.1210 · SSN − 14.11 · cos(L) − 6.278 (R2 = 0.63, p < 0.0001). Applying our algorithm to climatological hydrographic data in the North Pacific, we reconstructed the climatological distributions of DMS and its flux between 25 °N and 55 °N. DMS generally increased eastward and northward, and DMS in the northeastern region became to 2–5 times as large as that in the southwestern region. DMS in the later half of the year was 2–4 times as large as that in the first half of the year. Moreover, applying our algorithm to hydrographic time series datasets in the western North Pacific from 1971 to 2000, we found that DMS in the last three decades has shown linear increasing trends of 0.03 ± 0.01 nM year− 1 in the subpolar region, and 0.01 ± 0.001 nM year− 1 in the subtropical region, indicating that the annual flux of DMS from sea to air has increased by 1.9–4.8 μmol m− 2 year− 1. The linear increase was consistent with the annual rate of increase of 1% of the climatological averaged flux in the western North Pacific in the last three decades.  相似文献   

15.
Phytoplankton community composition, productivity and biomass characteristics of the mesohaline lower Neuse River estuary were assessed monthly from May 1988 to February 1990. An incubation method which considered water-column mixing and variable light exposure was used to determine phytoplankton primary productivity. The summer productivity peaks in this shallow estuary were stimulated by increases in irradiance and temperature. However, dissolved inorganic nitrogen loading was the major factor controlling ultimate yearly production. Dynamic, unpredictable rainfall events determined magnitudes of seasonal production pulses through nitrogen loading, and helped determine phytoplankton species composition. Dinoflagellates occasionally bloomed but were otherwise present in moderate numbers; rainfall events produced large pulses of cryptomonads, and dry seasons and subsequent higher salinity led to dominance by small centric diatoms. Daily production was strongly correlated (r = 0·82) with nitrate concentration and inversely correlated (r = −0·73) with salinity, while nitrate and salinity were inversely correlated (r = −0·71), emphasizing the importance of freshwater input as a nutrient-loading source to the lower estuary. During 1989 mean daily areal phytoplankton production was 938 mgC m−2, mean chlorophyll a was 11·8 mg m−3, and mean phytoplankton density was 1·56 × 103 cells ml−1. Estimated 1989 annual areal phytoplankton production for the lower estuary was 343 gC m−2.  相似文献   

16.
Biweekly composite averages of the standing stock of sea-surface chlorophyll (SSC) were derived from SeaWiFS satellite ocean-color data at 44 benthic sampling stations occupied along the continental slope and rise by the Deep Gulf of Mexico Benthos (DGoMB) program. At the 22 DGoMB sites north of 26°N and west of 91°W in the NW Gulf of Mexico, annual average SSC was 0.19 mg m−3, ranging at most locations from annual highs of about 0.3 mg m−3 in November–February to lows of about 0.1 mg m−3 in May–August. Comparison of three years of SeaWiFS data (January 1998–December 2000) showed little inter-annual variation at these NW Gulf stations. In contrast, at the 22 NE Gulf sites north of 26°N and east of 91°W, SSC averaged 2.8 times higher than in the NW Gulf, showing also strong inter-annual variation. Maxima in the NE region occurred in November–February and also during summers. The summer maxima were associated with Mississippi River water transported offshore to the east and southward by anticyclonic eddies in the NE Gulf. The apparent increases in SSC in June–August at NE Gulf stations reached average monthly concentrations >50% greater than in November–February. Based on a primary productivity model and a vertical flux model, the calculated export of particulate organic carbon (POC flux reaching the seafloor) was estimated as 18 mg C m−2 day−1 at the 22 NE Gulf stations, and 9 mg C m−2 day−1 at the 22 NW Gulf stations. These estimates are comparable to fluxes measured by benthic lander by others in the DGoMB program, which may drive the differences in west versus east bathymetric zonation and community structure of macrobenthos that were sampled with large box corers by others in the DGoMB program.  相似文献   

17.
Seasonal and diurnal reduced sulfur gas emissions were measured along a salinity gradient in Louisiana Gulf Coast salt, brackish and freshwater marshes. Reduced sulfur gas emission was strongly associated with habitat and salinity gradient. The dominant emission component was dimethyl sulfide (average: 57·3 μg S m−2 h−1) in saltmarsh with considerable seasonal (max: 144·03 μg S m−2 h−1; min: 1·47 μg S m−2 h−1) and diurnal (max: 83·58 μg S m−2 h−1; min: 69·59 μg S m−2 h−1) changes in flux rates. Hydrogen sulfide was dominant (average: 21·2 μg S m−2 h−1, max: 79·2 μg S m−2 h−1; min: 5·29 μg S m−2 h−1) form in brackishmarsh and carbonyl sulfide (average: 1·09 μg S m−2 h−1; max: 3·42 μg S m−2 h−1; min: 0·32 μg S m−2 h−1) was dominant form in freshwater marsh. A greater amount of H2S was evolved from brackishmarsh (21·22 μg S m−2 h−1) as compared to the saltmarsh (2·46 μg S m−2 h−1) and freshwater marsh (0·30 μg S m−2 h−1). Emission of total reduced sulfur gases decreased with decrease in salinity and distance inland from the coast. Emission of total reduced sulfur gases over the study averaged 73·3 μg S m−2 h−1 for the saltmarsh, 32·1 μg S m−2 h−1 for brackishmarsh and 2·76 μg S m−2 h−1 for the freshwater marsh.  相似文献   

18.
Brood sizes of 1259 adult female Euphausia pacifica and Thysanoessa spinifera were measured during 48 h incubations (10 °C, ±0.5 °C) on 27 oceanographic cruises between July 1999 and September 2004. The data set includes measurements from several stations off Newport, Oregon (Newport Hydrographic line, 44°39′N) made over a 5-year period and measurements from 14 more extensive cruises at stations representative of continental shelf, slope, and oceanic waters off Oregon and California, USA. E. pacifica had similar brood sizes at inshore (<200 m) and offshore (>200 m) stations with an average of 151 and 139 eggs brood−1 fem−1, respectively. T. spinifera brood sizes were considerably higher at inshore stations—particularly at Heceta Bank (44°N) and south of Cape Blanco (42°50′N)—than at offshore stations, 155 and 107 eggs brood−1 fem−1, respectively. Average brood sizes of E. pacifica increased during the study period, from 125 (in 2000) to 171 eggs brood−1 fem−1 (in 2003). Average percentage of carbon weight invested in spawning (reproductive effort) was higher in E. pacifica (14%) than in T. spinifera (6%), because both species have similar brood size but T. spinifera females are larger than E. pacifica females and produce smaller eggs. Reproductive effort for both species was higher during summer 2002, probably associated with anomalous cool subarctic waters and high chl-a concentration observed during that summer. Brood sizes and chl-a values remained relatively high in 2003–2004 compared to the 1999–2001 period. Geographical and temporal variability in brood sizes for both species were significantly correlated with in situ measurements of chl-a concentration but not with sea surface temperature. No gravid females were collected during late autumn and winter cruises, thus the spawning season along the Oregon coast appears to extend from March through September for both species. However, T. spinifera usually starts reproductive activity earlier in the spring (March) than E. pacifica. Both species had their highest brood sizes in summer during the period of most intense upwelling, which is associated with an increase in regional phytoplankton standing stock.  相似文献   

19.
Macroalgae biomass and concentrations of nitrogen, phosphorus and chlorophyll a were determined weekly or biweekly in water and sediments, during the spring-summer of 1985 in a hypertrophic area of the lagoon of Venice. Remarkable biomass production (up to 286 g m−2 day−1, wet weight), was interrupted during three periods of anoxia, when macroalgal decomposition (rate: up to 1000 g m−2 day−1) released extraordinary amounts of nutrients. Depending on the macroalgae distribution in the water column, the nutrients released in water varied from 3·3 to 19·1 μg-at litre−1 for total inorganic nitrogen and from 1·8 to 2·7 μg-at litre−1 for reactive phosphorus. Most nutrients, however, accumulated in the surficial sediment (up to 0·640 and to 3·06 mg g−1 for P and N respectively) redoubling the amounts already stored under aerobic conditions, Phytoplankton, systematically below 5 mg m−3 as Chl. a, sharply increased up to 100 mg m−3 only after the release of nutrients in water by anaerobic macroalgal decomposition. During the algal growth periods, the N:P atomic ratio in water decreased to 0·7, suggesting that nitrogen is a growth-limiting factor. This ratio for surficial sediment was between 6·6 and 13·1, similar to that of macroalgae (8·6–12·0).  相似文献   

20.
Continental margins exert a strong influence on global biogeochemical cycles; however there have been relatively few attempts to quantify either the magnitude or nature of temporal variability in material fluxes. At present here are no reports on nutrient fluxes at the mouth of the Gulf of California (GC) so further information is needed to provide estimated values from direct measurements. From 1995–1999 during five cruises covering all seasons, seawater samples were collected and measured the nutrient content from the surface to the bottom (some deeper than 2500 m) from a repeated hydrographic sections at the mouth of the GC. This chemical and physical database is unique because it covers an area with important biogeochemical signs, which has been detected as one of the highest in primary productivity of the world oceans. These sections are perpendicular to the coastlines of the Mexican states of Baja California Sur (BCS) and Sinaloa. In this section, the most dynamic area was the surface waters in February 1999 with strong geostrophic currents and temperatures of 20 ± 1.5 °C; salinity 35.091 ± 0.156; pH 8.16 ± 0.13; phosphate 0.85 ± 0.42 μM, nitrate + nitrite 2.35 ± 2.94 μM, and ammonia 2.00 ± 1.25 μM (average ± standard deviation).Geostrophic velocities were computed from high-resolution CTD sections across the entrance to the GC. During winter and spring, the outflow occurred near BCS and the inflow occurred either through the center of the section and/or along the Sinaloa coast. Both inflow and outflow cores were 45 km wide and extended deeper than 700 m. Summer and fall showed a complex pattern, alternating cores of inflow and outflow but with inflow along Sinaloa on all cruises. The maximum flow into the Gulf occurs during May in the center of the section while outflow was concentrated along BCS. Mascarenhas et al. [Mascarenhas, A., Castro, R., Collins, C.A., Durazo, R., 2004. Seasonal variation of geostrophic velocity and heat flux at the entrance to the Gulf of California, Mexico. Journal Geophysical Research, 2124.] calculated the section mean geostrophic velocity that was composed of two alternating cores of inflow and outflow. The two cores that were adjacent to either coast were broader and contained the highest inflow (0.40 m s− 1) and outflow (− 0.25 m s− 1) velocities, supporting the general idea of inflow along the Sinaloa and an outflow along BCS.The highest nutrient fluxes occur during El Niño conditions in November 1997 with outflows as high as 54.5 Tg yr− 1 for Phosphate, 43.0 Tg yr− 1 for Nitrate and 31.7 Tg yr− 1 for Ammonia, this values were at least three times higher than in February 1999.  相似文献   

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