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1.
Atmospheric molar fraction of CO2 (xCO2atm) measurements obtained on board of ships of opportunity are used to parameterize the seasonal cycle of atmospheric xCO2 (xCO2atm) in three regions of the eastern North Atlantic (Galician and French offshore and Bay of Biscay). Three selection criteria are established to eliminate spurious values and identify xCO2atm data representative of atmospheric background values. The filtered data set is fitted to seasonal curve, consisting of an annual trend plus a seasonal cycle. Although the fitted curves are consistent with the seasonal evolution of xCO2atm data series from land meteorological stations, only ship-board measurements can report the presence of winter xCO2atm minimum on Bay of Biscay. Weekly air–sea CO2 flux differences (mmol C·m− 2 day− 1) produced by the several options of xCO2atm usually used (ship-board measurements, data from land meteorological stations and annually averaged values) were calculated in Bay of Biscay throughout 2003. Flux error using fitted seasonal curve relative to on board measurements was minimal, whereas land stations and annual means yielded random (− 0.2 ± 0.3 mmol C·m− 2·day− 1) and systematic (− 0.1 ± 0.4 mmol C·m− 2 day− 1), respectively. The effect of different available sources of sea level pressure, wind speed and transfer velocity were also evaluated. Wind speed and transfer velocity parameters are found as the most critical choice in the estimate of CO2 fluxes reaching a flux uncertainty of 7 mmol C·m− 2·day− 1 during springtime. The atmospheric pressure shows a notable relative effect during summertime although its influence is quantitatively slight on annual scale (0.3 ± 0.2 mmol C·m− 2·day− 1). All results confirms the role of the Bay of Biscay as CO2 sink for the 2003 with an annual mean CO2 flux around − 5 ± 5 mmol C m− 2 day− 1. 相似文献
2.
Air–sea fluxes in the Caribbean Sea are presented based on measurements of partial pressure of CO2 in surface seawater, pCO2sw, from an automated system onboard the cruise ship Explorer of the Seas for 2002 through 2004. The pCO2sw values are used to develop algorithms of pCO2sw based on sea surface temperature (SST) and position. The algorithms are applied to assimilated SST data and remotely sensed winds on a 1° by 1° grid to estimate the fluxes on weekly timescales in the region. The positive relationship between pCO2sw and SST is lower than the isochemical trend suggesting counteracting effects from biological processes. The relationship varies systematically with location with a stronger dependence further south. Furthermore, the southern area shows significantly lower pCO2sw in the fall compared to the spring at the same SST, which is attributed to differences in salinity. The annual algorithms for the entire region show a slight trend between 2002 and 2004 suggesting an increase of pCO2sw over time. This is in accord with the increasing pCO2sw due the invasion of anthropogenic CO2. The annual fluxes of CO2 yield a net invasion of CO2 to the ocean that ranges from − 0.04 to − 1.2 mol m− 2 year− 1 over the 3 years. There is a seasonal reversal in the direction of the flux with CO2 entering into the ocean during the winter and an evasion during the summer. Year-to-year differences in flux are primarily caused by temperature anomalies in the late winter and spring period resulting in changes in invasion during these seasons. An analysis of pCO2sw before and after hurricane Frances (September 4–6, 2004), and wind records during the storm suggest a large local enhancement of the flux but minimal influence on annual fluxes in the region. 相似文献
3.
Ships of opportunity have been used to investigate ocean–atmosphere CO2 fluxes in the English Channel and Southern Bight of the North Sea. Continuous underway measurements of the fugacity of seawater carbon dioxide (fCO2sw), chlorophyll, temperature and salinity have been performed along 26 transects during the spring and autumn periods. The spatial fCO2sw distribution along the Channel and Southern Bight is modulated by the photosynthetic activity, temperature changes and water mixing between inputs from the North Atlantic Ocean and riverine discharges. The seasonal variability of fCO2sw is assessed and discussed in terms of the biology and temperature effects, these having similar impacts. The variation of fCO2sw shows similar interannual patterns, with lower values in spring. The annual average of air–sea CO2 fluxes places the English Channel as neutral area of CO2 uptake. The spring and autumn data allow differentiating between distal and proximal continental areas. The Southern Bight shows a tendency towards net CO2 uptake on the distal continental shelf, whereas the Scheldt and Thames Plumes show a CO2 source behaviour on the proximal continental shelves. 相似文献
4.
CO2 partial pressure in surface water was measured in the Northeast Atlantic and in the Hebride Shelf/North Sea area during a cruise with R.V. Poseidon in June 1991. A mean pCO2 of 303 μatm was found in the Atlantic between 50°N and 60°N. For an atmospheric CO2 content of 357.5 ppm(v) this corresponds to a partial pressure difference of −55 μatm. This supports the view that the subarctic Atlantic is a significant sink within the CO2 cycle between the ocean and the atmosphere. A comparison of our measurements with other data reveals that the pCO2 distribution changes significantly during May/June. This explained by seasonal warming, CO2 exchange with the atmosphere and biomass production. The contribution by each of these processes to the seasonal variations is calculated. It was found that during a plankton bloom the production of biomass is the dominating factor and may lower seawater pCO2 by almost 100 μatm. The shelf areas are charactrized by strong pCO2 gradients which are explained by water exchange with the Atlantic, temperature effects and biomass production. 相似文献
5.
During 2004, 10 samplings were performed in order to measure dissolved methane (CH4), carbon dioxide (CO2) and nitrous oxide (N2O) in the surface waters of Río San Pedro, a tidal creek in the salt marsh area of the Bay of Cádiz (SW Spain). The inner partvs of the creek is affected by the inputs coming from an intensive fish farm and the drainage of an extensive salt marsh area.Dissolved CH4, CO2 and N2O concentrations ranged from 11 to 88 nM, 36 to 108 μM and 14 to 50 nM, respectively. Surface waters were in all cases oversaturated with respect to the atmosphere, reaching values of up to 5000% for CH4, 1240% for CO2 and 840% for N2O. Dissolved CH4, CO2 and N2O showed a significant tidal and seasonal variability. Over a tidal cycle, concentrations were always highest during low tide, which points to the influence of the inputs from the fish farm effluent and the drainage of the adjacent salt marsh area, as well as in situ production within the system. Dissolved CH4, CO2 and N2O seasonal patterns were similar and showed maximum concentrations in summer conditions. Using four different parameterizations to calculate the gas transfer coefficients [Liss, P.S. and Merlivat, L., 1986. Air-sea exchange rates: introduction and synthesis. In P. Buat-Ménard (Ed.), The Role of Air-Sea Exchanges in Geochemical Cycling. Reidel, Dordrecht, The Netherlands, p. 113–127.; Clark, J.F., Schlosser, P., Simpson, H.J., Stute, M., Wanninkhof, R., and Ho, D.T., 1995. Relationship between gas transfer velocities and wind speeds in the tidal Hudson River determined by the dual tracer technique. In: B. Jähne and E. Monahan (Eds.), Air-Water Gas Transfer: AEON Verlag and Studio, Hanau, Germany, pp. 785–800.; Carini, S., Weston, N., Hopkinson, G., Tucker, J., Giblin, A. and Vallino, J., 1996. Gas exchanges rates in the Parker River estuary, Massachusetts. Biol. Bull., 191: 333–334.; Kremer, J.N., Reischauer, A. and D'Avanzo, C., 2003. Estuary-specific variation in the air-water gas exchange coefficient for oxygen. Estuaries, 26: 829–836.], the averaged air–water fluxes of CH4, CO2 and N2O from the creek to the atmosphere ranged between 34 and 150 μmol CH4 m− 2 day− 1, 73 and 177 mmol CO2 m− 2 day− 1 and 24 and 62 μmol N2O m−2 day−1, respectively. 相似文献
6.
Genevive Lacroix Kevin Ruddick Youngje Park Nathalie Gypens Christiane Lancelot 《Journal of Marine Systems》2007,64(1-4):66
This paper presents results obtained with MIRO&CO-3D, a biogeochemical model dedicated to the study of eutrophication and applied to the Channel and Southern Bight of the North Sea (48.5°N–52.5°N). The model results from coupling of the COHERENS-3D hydrodynamic model and the biogeochemical model MIRO, which was previously calibrated in a multi-box implementation. MIRO&CO-3D is run to simulate the annual cycle of inorganic and organic carbon and nutrients (nitrogen, phosphorus and silica), phytoplankton (diatoms, nanoflagellates and Phaeocystis), bacteria and zooplankton (microzooplankton and copepods) with realistic forcing (meteorological conditions and river loads) for the period 1991–2003. Model validation is first shown by comparing time series of model concentrations of nutrients, chlorophyll a, diatom and Phaeocystis with in situ data from station 330 (51°26.00′N, 2°48.50′E) located in the centre of the Belgian coastal zone. This comparison shows the model's ability to represent the seasonal dynamics of nutrients and phytoplankton in Belgian waters. However the model fails to simulate correctly the dissolved silica cycle, especially during the beginning of spring, due to the late onset (in the model) of the early spring diatom bloom. As a general trend the chlorophyll a spring maximum is underestimated in simulations. A comparison between the seasonal average of surface winter nutrients and spring chlorophyll a concentrations simulated with in situ data for different stations is used to assess the accuracy of the simulated spatial distribution. At a seasonal scale, the spatial distribution of surface winter nutrients is in general well reproduced by the model with nevertheless a small overestimation for a few stations close to the Rhine/Meuse mouth and a tendency to underestimation in the coastal zone from Belgium to France. PO4 was simulated best; silica was simulated with less success. Spring chlorophyll a concentration is in general underestimated by the model. The accuracy of the simulated phytoplankton spatial distribution is further evaluated by comparing simulated surface chlorophyll a with that derived from the satellite sensor MERIS for the year 2003. Reasonable agreement is found between simulated and satellite-derived regions of high chlorophyll a with nevertheless discrepancies close to the boundaries. 相似文献
7.
Alexandra Weiss Joachim Kuss Gerhard Peters Bernd Schneider 《Journal of Marine Systems》2007,66(1-4):130
Long-term observations of the marine atmospheric boundary layer were performed by an eddy correlation system, which was set-up on a platform in the Baltic Sea. In this experiment the three-dimensional wind vector and the turbulent fluxes of momentum, sensible and latent heat and CO2 were measured for one and a half years. Simultaneously the CO2 partial pressure pCO2 in surface water was measured by a submersible autonomous moored instrument for CO2 at the platform in 7-m depth. The high-resolution eddy correlation measurements of the atmospheric CO2 flux FCO2, together with the measurements of the CO2 partial pressure differences between air and sea ΔpCO2 led to a long-term data set which provided the possibility to investigate the parameterization of the CO2 transfer velocity k as a function of 10-m wind speed u in a statistical manner. From half-hour mean CO2 fluxes and CO2 partial pressure differences, k was calculated using k = FCO2 / (K0ΔpCO2), with K0 the CO2 solubility. The half-hour mean data points, used for the determination of the k–u parameterization, show large scatter. However, assuming a linear, quadratic dependency the analysis yields: k660 = 0.365u2 + 0.46u (k at 20 °C and salinity 35 psu) with a correlation coefficient of r2 = 0.81. The large scatter indicates that the kinetics of the air–sea CO2 transfer velocity is not only a function of the wind speed alone, but might also be controlled by other environmental parameters and mechanisms, such as sea state and surface coverage with surfactants. 相似文献
8.
Fluxes of dissolved inorganic carbon in three estuarine systems of the Cantabrian Sea (north of Spain) 总被引:3,自引:1,他引:2
The diffusive and in situ fluxes of dissolved inorganic carbon (DIC) and total alkalinity (TA) have been measured and an estimation has been made of the water–atmosphere fluxes of CO2 in three estuarine systems of the Cantabrian Sea during the spring of 1998. Each of these systems undergoes a different anthropogenic influence. The diffusive fluxes of dissolved inorganic carbon and total alkalinity obtained present values ranging between 0.54–2.65 and 0.0–2.4 mmol m−2 day−1, respectively. These ranges are in agreement with those of other coastal systems. The in situ fluxes are high and extremely variable (35–284 mmol TA m−2 day−1, 43–554 mmol DIC m−2 day−1 and 22–261 mmol dissolved oxygen (DO) m−2 day−1), because the systems studied are very heterogeneous. The values of the ratio of the in situ fluxes of TA and DIC show on average that the rate of dissolution of CaCO3 is 0.37 times that of organic carbon oxidation. Equally, the interval of variation of the relationship between the benthic fluxes of inorganic carbon and oxygen (FDIC/FDO) is very wide (0.3–13.9), which demonstrates the different contributions made by the processes of aerobic and anaerobic degradation of the organic matter, as well as by the dissolution–precipitation of CaCO3. The water–atmosphere fluxes of CO2 present a clear dependence on the salinity. The brackish water of these systems (salinity<20), where maximum fluxes of 989 mmol m−2 day−1 have been estimated, act as a source of CO2 to the atmosphere. The more saline zones of the estuary (salinity>30) act as a sink of CO2, with fluxes between −5 and −10 mmol m−2 day−1. 相似文献
9.
The variations of the partial pressure of CO2 (pCO2) and related parameters were determined in surface seawater along the Belgian coast, from January 1995 to June 1996, at both daily and seasonal time scales. The distribution of pCO2 in this area is regulated by river input from the Scheldt, biological activity and hydrodynamics. The contribution of each of these processes varies as a function of the considered time scale: (i) the daily variation of pCO2 depends on the tide although modulated by the biological diel cycle; (ii) the seasonal variation of pCO2 depends on the input from the Scheldt and the seasonal variations of phytoplanktonic biomass. During winter, the plume of the river Scheldt is oversaturated in pCO2 with respect to the atmosphere. During spring and summer, phytoplankton blooms occur both in the lower Scheldt estuary and in the river plume and may lead to undersaturation of pCO2 in the easternmost area of the river plume. However, the degradation of phytoplankton induces oversaturation of pCO2, in the westernmost area of the plume. Furthermore, the inter-annual variation of pCO2 depends partly on the fluctuations of the discharge of the Scheldt. Our preliminary results strongly suggest that, on an annual basis, the Scheldt plume behaves as a net source of CO2 to the atmosphere. 相似文献
10.
Dissolved and particulate phases of carbon (DIC, DOC, POC) and nutrients (DIN, DIP, DSi, DON, DOP, PN) were investigated bimonthly from August 1999 to August 2000 to study biogeochemical dynamics of carbon and nutrients in Tapong Bay, a small semi-enclosed and hypertrophic lagoon in southwestern Taiwan. The lagoon has only a tidal inlet for exchanging water between Tapong Bay and Taiwan Strait, which may result in low water exchange rates and various oxygen-deficient conditions in bottom water of the inner bay during warm seasons. The water exchange time of Tapong Bay ranges from 7 days (summer) to 13 days (winter) with a mean of 10 days. Nutrient dynamics were largely ascribed to allochthonous inputs, biological and exported removals in the lagoon. Diffusion fluxes from sediments to overlying water accounted for only about 7.6% of annual DIN inputs and 1.0% of annual DIP inputs. High primary productivity (89 mol C m−2 year−1) supported by abundant nutrients primarily drove the lagoon into a hypertrophic condition as particulate organic matter was derived mainly from biological production. Excess of DIP appeared to occur throughout the study period in the lagoon. Temperature, solar radiation and turbidity, rather than nutrients, perhaps controlled seasonal variations of primary productivity. The net ecosystem production (NEP) derived from daily changes of DOC and POC inventories was about 6.3 mmol C m−2 day−1 that was close to 6.7 mmol C m−2 day−1 simulated from the biogeochemical modeling. Therefore, the net ecosystem production (NEP) rate of organic carbon estimated from the biogeochemical model was reliable, and the NEP was temporally variable with an annual mean of 5.8 mol C m−2 year−1, implying that Tapong Bay was an autotrophic system. Although calcification proceeded pronouncedly in warm seasons, an invasion of CO2 was significant in this system. In terms of nitrogen budget, the annual nitrogen fixation exceeded the annual denitrification with a magnitude of 1.30 mol N m−2 year−1, which may be supported by the abundance of nitrogen fixation microplanktons in the lagoon. 相似文献
11.
Andrea Riedel Christine Michel Michel Gosselin Bernard LeBlanc 《Journal of Marine Systems》2008,74(3-4):918
An understanding of microbial interactions in first-year sea ice on Arctic shelves is essential for identifying potential responses of the Arctic Ocean carbon cycle to changing sea-ice conditions. This study assessed dissolved and particulate organic carbon (DOC, POC), exopolymeric substances (EPS), chlorophyll a, bacteria and protists, in a seasonal (24 February to 20 June 2004) investigation of first-year sea ice and associated surface waters on the Mackenzie Shelf. The dynamics of and relationships between different sea-ice carbon pools were investigated for the periods prior to, during and following the sea-ice-algal bloom, under high and low snow cover. A predominantly heterotrophic sea-ice community was observed prior to the ice-algal bloom under high snow cover only. However, the heterotrophic community persisted throughout the study with bacteria accounting for, on average, 44% of the non-diatom particulate carbon biomass overall the study period. There was an extensive accumulation of sea-ice organic carbon following the onset of the ice-algal bloom, with diatoms driving seasonal and spatial trends in particulate sea-ice biomass. DOC and EPS were also significant sea-ice carbon contributors such that sea-ice DOC concentrations were higher than, or equivalent to, sea-ice-algal carbon concentrations prior to and following the algal bloom, respectively. Sea-ice-algal carbon, DOC and EPS-carbon concentrations were significantly interrelated under high and low snow cover during the algal bloom (r values ≥ 0.74, p < 0.01). These relationships suggest that algae are primarily responsible for the large pools of DOC and EPS-carbon and that similar stressors and/or processes could be involved in regulating their release. This study demonstrates that DOC can play a major role in organic carbon cycling on Arctic shelves. 相似文献
12.
《Journal of Marine Systems》2006,59(1-2):120-142
Production of calcium carbonate by marine calcifying organisms has been shown to decrease under increasing CO2. This effect appears to be driven by a decrease in [CO32−]. The modelling study here described aims at investigating whether the success of a marine calcifying phytoplankton species, the coccolithophore Emiliania huxleyi, may be tied to [CO32−]. The work highlights the complex interactions between the carbonate system variables and spring blooms, and the possibility of a link to the competition between calcifying vs. non-calcifying species on the Bering Sea shelf. We find that the strong seasonal cycle in [CO32−] is driven primarily by carbon drawdown during spring blooms. The interesting outcome of this work is the fact that E. huxleyi bloom timings always coincide with periods of high [CO32−], which is consistent with studies showing coccoliths malformations and a slowdown in calcification at low [CO32−]. Whether the condition of high [CO32−] can be considered a crucial ecological factor for the success of E. huxleyi, however, remains an open and important question needing further investigation. 相似文献
13.
A new method to calculate the anthropogenic CO2 (ΔDICant) within the water column of the North Atlantic Ocean is presented. The method exploits the equilibrium chemistry of the carbonate system with reference to temperature, salinity and the partial pressure of atmospheric CO2 (pCO2,atm). ΔDICant is calculated with reference to the ventilation ages of water masses derived from tracer data and to the time history of pCO2,atm. The method is applied to data recorded during the WOCE program on the WHP A1/E transect in the North Atlantic Ocean, where we characterise six key water masses by their relationships of dissolved inorganic carbon (DIC) and apparent oxygen utilisation (AOU). The error in determining ΔDICant is reduced significantly by minimising the number of values referred to, especially by avoiding any use of remineralisation ratios of particulate organic matter. The distribution of ΔDICant shows highest values of up to 45 μmol kg−1 in the surface waters falling to 28–33 μmol kg−1 in the Irminger Sea west of the Mid-Atlantic Ridge. The eastern basin is imprinted by older water masses revealing decreasing values down to 10 μmol kg−1 ΔDICant in the Antarctic Bottom Water. These findings indicate the penetration of the whole water column of the North Atlantic Ocean by anthropogenic CO2. 相似文献
14.
Gas transfer velocities of CO2 and CH4 in a tropical reservoir and its river downstream 总被引:4,自引:0,他引:4
Frdric Gurin Gwenaël Abril Dominique Sera Claire Delon Sandrine Richard Robert Delmas Alain Tremblay Louis Varfalvy 《Journal of Marine Systems》2007,66(1-4):161
We have measured simultaneously the methane (CH4) and carbon dioxide (CO2) surface concentrations and water–air fluxes by floating chambers (FC) in the Petit-Saut Reservoir (French Guiana) and its tidal river (Sinnamary River) downstream of the dam, during the two field experiments in wet (May 2003) and dry season (December 2003). The eddy covariance (EC) technique was also used for CO2 fluxes on the lake. The comparison of fluxes obtained by FC and EC showed little discrepancies mainly due to differences in measurements durations which resulted in different average wind speeds. When comparing the gas transfer velocity (k600) for a given wind speed, both methods gave similar results. On the lake and excluding rainy events, we obtained an exponential relationship between k600 and U10, with a significant intercept at 1.7 cm h− 1, probably due to thermal effects. Gas transfer velocity was also positively related to rainfall rates reaching 26.5 cm h−1 for a rainfall rate of 36 mm h− 1. During a 24-h experiment in dry season, rainfall accounted for as much as 25% of the k600. In the river downstream of the dam, k600 values were 3 to 4 times higher than on the lake, and followed a linear relationship with U10. 相似文献
15.
Ecophysiological growth characteristics and modeling of the onset of the spring bloom in the Baltic Sea 总被引:1,自引:0,他引:1
The onset of spring bloom in temperate areas is a transition period where the low productive, winter phytoplankton community is transformed into a high productive spring community. Downwelling irradiance, mixing depth and the ability of the phytoplankton community to utilize the light, are key parameters determining the timing of the onset of the spring bloom. Knowing these parameters would thus provide tools for modeling the spring bloom and enhance our knowledge of ecophysiological processes during this period.Our main objective with this study was to provide data for the growth characteristics of some key species forming the spring bloom in the Gulf of Finland, and to apply those results in a simple dynamic model for the onset of the spring bloom, in order to test if the timing of the spring bloom predicted by the models corresponds to field observations. We investigated the photosynthetic characteristics of three diatoms and two dinoflagellates (Chaetoceros wighamii, Melosira arctica, Thalassiosira baltica, Scrippsiella hangoei and Woloszynskia halophila), at low temperatures (4–5 °C). All of these species are common during spring bloom in the Baltic Sea.Cultures of these species were acclimated to different irradiance regimes prior to measurements of photosynthesis, respiration, pigment concentration and light absorption. We did not find a positive relationship between respiration and growth rate, and we hypothesize that this relationship, which is well established at higher temperatures, is negligible or absent at low temperatures (< 10 °C). Photosynthetic maximum (Pm), and maximum light utilization coefficient (α) was lowest and respiration (R) highest in the dinoflagellates.We made a model of the onset of the spring bloom in the western part of Gulf of Finland, using the obtained data together with monitoring data of mixing depth and water transparency from this area. Model results were compared to field observations of chlorophyll-a (Chl-a) concentration. There was a good agreement between the model predictions and the observed onset of the spring bloom for the diatoms. S. hangoei, however, was not able to reach positive production in the model, and W. halophila had the similar growth characteristics as S. hangoei. Consequently, these species must have other competition strategies enabling them to exist and grow during spring bloom. 相似文献
16.
Seasonal changes in the abundance and biomass of cyanobacteria (Synechococcus and Prochlorococcus) and picoeukaryotes were studied by flow cytometry in the upper layers of the central Cantabrian Sea continental shelf, from April 2002 to April 2006. The study area displayed the typical hydrographic conditions of temperate coastal zones. A marked seasonality of the relative contribution of prokaryotes and eukaryotes was found. While cyanobacteria were generally more abundant for most of the year (up to 2.4 105 cells mL− 1), picoeukaryotes dominated the community (up to 104 cells mL− 1) from February to May. The disappearance of Prochlorococcus from spring through summer is likely related to shifts in the prevailing current regime. The maximum total abundance of picophytoplankton was consistently found in late summer–early autumn. Mean photic-layer picoplanktonic chlorophyll a ranged from 0.06 to 0.53 µg L− 1 with a relatively high mean contribution to total values (33 ± 2% SE), showing maxima around autumn and minima in spring. Biomass (range 0.58–40.16 mg C m− 3) was generally dominated by picoeukaryotes (mean ± SE, 4.28 ± 0.27 mg C m− 3) with an average contribution of cyanobacteria of 30 ± 2%. Different seasonality of pigment and biomass values resulted in a clear temporal pattern of picophytoplanktonic carbon to chlorophyll a ratio, which ranged from 10 (winter) to 140 (summer). This study highlights the important contribution of picoplanktonic chlorophyll a and carbon biomass in this coastal ecosystem. 相似文献
17.
The potential for carbon export and the role of siliceous plankton in the cycling of C and N was assessed in natural plankton assemblages in the Santa Barbara Basin, California, by examining uptake rates of inorganic carbon, nitrate and silicic acid. In April–August 1997, the concentrations of chlorophyll a, particulate organic carbon, particulate organic nitrogen and biogenic silica were measured twice monthly, and results revealed the occurrence of at least three blooms, the largest in June. Particulate elemental ratios of C, N and Si were similar to ratios of nutrient-replete diatoms, suggesting that they dominated this bloom. Mean integrated rates of carbon, nitrate and silicon uptake during the 4-month study period are similar to other productive coastal and upwelling regions (103, 8.3 and 13 mmol m−2 day−1, respectively). New production rates were twice as high as previously reported in this region and indicate that high rates of new production along eastern boundary currents are not confined to the major coastal upwelling regions. C/NO3−, Si/NO3− and Si/C uptake ratios varied widely, and mean integrated ratios were 14±5.4, 1.6±1.0 and 0.12±0.07 (S.D.), respectively. That mean C/NO3− uptake ratio corresponds to an f-ratio of about 0.5 indicating a large potential for particulate export. Based on the average Si/NO3− and Si/C uptake ratios, diatoms could perform all of the primary production and nitrate uptake that occurred during the study; these rates also suggest that export is controlled by diatoms in this system. The mean Si/C biomass ratio was lower than the mean Si/C uptake ratio, consistent with the preferential export of Si relative to C observed in sediment traps in the basin. The study took place during a period of surface-water warming, with nitrate and silicic acid concentrations decreasing throughout the onset of the 1997–1998 El Niño conditions. Although diatoms contributed less to particulate biomass during the low nutrient conditions, high f-ratios (0.33–0.66) were maintained. 相似文献
18.
Kalle Olli Annemarie Clarke sa Danielsson Juris Aigars Daniel J. Conley Timo Tamminen 《Journal of Marine Systems》2008,73(3-4):284
In many parts of the world coastal waters with anthropogenic eutrophication have experienced a gradual depletion of dissolved silica (DSi) stocks. This could put pressure on spring bloom diatom populations, e.g. by limiting the intensity of blooms or by causing shifts in species composition. In addition, eutrophication driven enhanced diatom growth is responsible for the redistribution of DSi from the water phase to the sediments, and changes in the growth conditions may be reflected in the sediment diatom stratigraphy.To test for changes in diatom communities we have analyzed four sediment cores from the Baltic Sea covering approximately the last 100 years. The sediment cores originate from the western Gulf of Finland, the Kattegat, the Baltic Proper and the Gulf of Riga. Three out of the four cores reveal only minor changes in composition of diatom assemblages, while the Gulf of Riga core contains major changes, occurring after the second World War. This area is set apart from the other Baltic Sea basins by a high frequency of low after spring bloom DSi concentrations (< 2 µmol L− 1) during a relatively well defined time period from 1991–1998. In 1991 to 1993 a rapid decline of DSi spring concentrations and winter stocks (down to 5 µmol L− 1) in the Gulf was preceded by exceptionally intense diatom spring blooms dominated by the heavily silicified species Thalassiosira baltica (1991–1992; up to 5.5 mg ww L− 1). T. baltica has been the principal spring bloom diatom in the Gulf of Riga since records began in 1975. DSi consumption and biomass yield experiments with cultured T. baltica suggest that intense blooms can potentially exhaust the DSi stock of the water column and exceed the annual Si dissolution in the Gulf of Riga. The phytoplankton time series reveals another exceptional T. baltica bloom period in 1981–1983 (up to 8 mg L− 1), which, however, took place before the regular DSi measurements. These periods may be reflected in the conspicuous accumulation of T. baltica frustules in the sediment core corresponding to ca. 1975–1985. 相似文献
19.
X.A. Padin G. Navarro M. Gilcoto A.F. Rios F.F. Pérez 《Journal of Marine Systems》2009,75(1-2):280-289
An empirical algorithm has been developed to compute the sea surface CO2 fugacity (fCO2sw) in the Bay of Biscay from remotely sensed sea surface temperature (SSTRS) and chlorophyll a (chl aRS) retrieved from AVHRR and SeaWiFS sensors, respectively. Underway fCO2sw measurements recorded during 2003 were correlated with SSTRS and chl aRS data yielding a regression error of 0.1 ± 7.5 µatm (mean ± standard deviation). The spatial and temporal variability of air–sea fCO2 gradient (ΔfCO2) and air–sea CO2 flux (FCO2) was analyzed using remotely sensed images from September 1997 to December 2004. An average FCO2 of ? 1.9 ± 0.1 mol m? 2 yr? 1 characterized the Bay of Biscay as a CO2 sink that is suffering a significant long-term decrease of 0.08 ± 0.05 mol m? 2 yr? 2 in its capacity to store atmospheric CO2. The main parameter controlling the long-term variability of the CO2 uptake from the atmosphere was the air–sea CO2 transfer velocity (57%), followed by the SSTRS (10%) and the chl aRS (2%). 相似文献
20.
Literature data from 1905/06, 1912/13 and 1949/50 were compared with recent data (2001–2003) from Kiel Bight in order to investigate changes in phytoplankton composition and biomass, which may serve as indicators of environmental changes. In terms of biomass, diatomophyceae and dinophyceae are by far the most important groups. Their ratio is still close to unity. The share of diatomophyceae increased strongly in years with exceptionally high summer blooms (2001) or exceptionally early spring blooms (2003). The summer and autumn blooms of Chaetoceros and Skeletonema, detected in the early 20th century, are replaced by other diatoms (Cerataulina pelagica, Dactyliosolen fragilissimus, Proboscia alata, Pseudo-nitzschia spp.). Chaetoceros and Skeletonema are still important components of the spring blooms. Now as before, the autumn blooms are dominated by Ceratium spp., sometimes also by diatoms. Newly appearing bloom-forming species are mostly potentially toxic (Dictyocha speculum, Prorocentrum minimum, Pseudo-nitzschia spp.). The total phytoplankton biomass has roughly doubled in the course of the last century. The reference condition for phytoplankton biomass in Kiel Bight in the sense of the Water Framework Directive was defined at 55 mg C m− 3 (± 10%, annual mean). The mean annual biomass of diatomophyceae and dinophyceae was 25 mg C m− 3 (± 40%) for each, indicating that the sum of their carbon biomass amounted to 90% (± 10%) of the total phytoplankton biomass on an annual average. Diatomophyceae represented at least 80% of carbon biomass in the spring bloom peak at the beginning of the 20th century. 相似文献