首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 250 毫秒
1.
  相似文献   

2.
The distribution of the fugacity of CO2 ( $ f_{{{\text{CO}}_{ 2} }} $ ) and air–sea CO2 exchange were comprehensively investigated in the outer estuary to offshore shallow water region (lying adjacent to the Sundarban mangrove forest) covering an area of ~2,000 km2 in the northern Bay of Bengal during the winter. A total of ten sampling surveys were conducted between 1 December, 2011 and 21 February, 2012. Physico-chemical variables like sea surface temperature (SST), salinity, pH, total alkalinity (TAlk), dissolved inorganic carbon (DIC) and in vivo chlorophyll-a along with atmospheric variables were measured in order to study their role in controlling the CO2 flux. Surface water $ f_{{{\text{CO}}_{ 2} }} $ ranged between 111 and 459 μatm which correlated significantly with the SST (r = 0.71, p < 0.001, n = 62). Neither DIC nor TAlk showed any linear relationship with varying salinity in the estuarine mixing zone, demonstrating the significant presence of non-carbonate alkalinity. An overall net biological control on the surface $ f_{{{\text{CO}}_{ 2} }} $ distribution was established during the study, although no significant correlation was found between chlorophyll-a and $ f_{{{\text{CO}}_{ 2} }} $ (water). The shallow water region studied was mostly under-saturated with CO2 and acted as a sink for atmospheric CO2. The difference between surface water and atmospheric $ f_{{{\text{CO}}_{ 2} }} $ ( $ \Updelta f_{{{\text{CO}}_{ 2} }} $ ) ranged from ?274 to 69 μatm, with an average seaward flux of ?10.5 ± 12.6 μmol m?2 h?1. The $ \Updelta f_{{{\text{CO}}_{ 2} }} $ and hence the air–sea CO2 exchange was primarily regulated by the variation in sea surface $ f_{{{\text{CO}}_{ 2} }} $ , since atmospheric $ f_{{{\text{CO}}_{ 2} }} $ varied over a comparatively narrow range of 361.23–399.05 μatm.  相似文献   

3.
To estimate benthic denitrification in a marginal sea, we assessed the usefulness of \({\text{N}}_{2}^{*}\) , a new tracer to measure the excess nitrogen gas (N2) using dissolved N2 and argon (Ar) with N* in the intermediate layer (26.6–27.4σ θ ) of the Okhotsk Sea. The examined parameters capable of affecting \({\text{N}}_{2}^{*}\) are denitrification, air injection and rapid cooling. We investigated the relative proportions of these effects on \({\text{N}}_{2}^{*}\) using multiple linear regression analysis. The best model included two examined parameters of denitrification and air injection based on the Akaike information criterion as a measure of the model fit to data. More than 80 % of \({\text{N}}_{2}^{*}\) was derived from the denitrification, followed by air injection. Denitrification over the Okhotsk Sea shelf region was estimated to be 5.6 ± 2.4 μmol kg?1. The distribution of \({\text{N}}_{2}^{*}\) was correlated with potential temperature (θ) between 26.6 and 27.4σ θ (r = ?0.55). Therefore, we concluded that \({\text{N}}_{2}^{*}\) and N* can act complementarily as a quasi-conservative tracer of benthic denitrification in the Okhotsk Sea. Our findings suggest that \({\text{N}}_{2}^{*}\) in combination with N* is a useful chemical tracer to estimate benthic denitrification in a marginal sea.  相似文献   

4.
To elucidate the sources and transformations of nitrogen in the South China Sea (SCS), the nitrogen isotopic composition of nitrate (\({\updelta }^{ 1 5} {\text{N}}_{{{\text{NO}}_{ 3} }}\)) was measured in seawater samples from the water column of this marginal sea and the adjacent western North Pacific Ocean (WNP). Comparison of the isotopic signatures from these two locations suggests that the main source of nitrogen into the SCS was nitrate that entered from the WNP through the Luzon Strait. Values of \({\updelta }^{ 1 5} {\text{N}}_{{{\text{NO}}_{ 3} }}\) were generally lower in the SCS than in the WNP, and the \({\updelta }^{ 1 5} {\text{N}}_{{{\text{NO}}_{ 3} }}\) maximum observed in the SCS intermediate water was lower than the corresponding WNP maximum. This pattern is attributed to mixing within the SCS in combination with the outflow of SCS intermediate water to the WNP. A mass balance model indicates that atmospherically derived N (a combined input of new nitrogen from marine N2 fixation and atmospheric deposition) supplied approximately 6% of the particulate nitrogen exported from the euphotic zone to the deep SCS. This supply of isotopically light nitrogen cannot, however, explain the low and downward-decreasing δ15N that has been previously observed in sinking particles of the deep SCS. We propose that an alternative explanation might be a downward-increasing ratio of isotopically light NH4 +-N to organic N due to the degradation of organic N within the sinking particles (i.e., relative enrichment of the NH4 +) and also particle incorporation of excreted ammonium from zooplankton.  相似文献   

5.
Isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs) and alkenones were analyzed in sediment samples retrieved from Ocean Drilling Program Site 1241 covering the last 150000 years to understand the hydrological evolution of the eastern Pacific warm pool (EPWP). GDGT and alkenone concentrations showed higher values in marine isotope stage (MIS)-2 and MIS-6, which suggests the enhancement of primary production at glacial maxima. $ {\text{TEX}}_{86}^{\text{H}} $ - and $ U_{ 3 7^\prime }^{\text{K}} $ -derived temperature depicted different temperature evolutions. $ U_{ 3 7^\prime }^{\text{K}} $ -derived temperature was marked by small variation during the glacial–interglacial cycles, whereas $ {\text{TEX}}_{86}^{\text{H}} $ -derived temperature showed pronounced glacial–interglacial variation that was similar to Mg/Ca-derived temperature records from nearby cores in the EPWP. Given that enhanced primary production during glacial maxima suggests nutricline shoaling, unchanged $ U_{ 3 7^\prime }^{\text{K}} $ over glacial–interglacial cycles can be interpreted as the shift of alkenone production depth. $ {\text{TEX}}_{86}^{\text{H}} $ seems not to be influenced by glacial–interglacial changes in nutricline depths, recording an integrated temperature in surface and thermocline water. The shallow nutricline in the EPWP during glacial maxima most likely reflected the intense formation of Antarctic intermediate water.  相似文献   

6.
The \textU\textK￠37 {\text{U}}^{{{\text{K}}\prime}}_{{37}} index has been widely applied for sea surface temperature (SST) reconstruction in open ocean environments, but has inherently limited applications at smaller, regional scales including some marginal seas where both historical and reconstructed SST records are urgently needed for understanding regional climate evolution. We determined the spatial distribution of alkenone contents in surface sediments from the southern Yellow Sea to assess the regional \textU37\textK￠ {\text{U}}_{{{37}}}^{{{\text{K'}}}} —SST relationship for paleo-SST reconstructions. C37:2 and C37:3 alkenones were detected at all 36 sites covering most of the southern Yellow Sea. Alkenone content ranges from 17 to 1,063 ng/g, with high values (ca. 400 to 1,000 ng/g) at deep water sites and a decreasing trend shoreward. For six samples at shallower depths near the coast and further offshore, the values were too low for statistical evaluation. This spatial pattern of alkenone contents is consistent with existing knowledge on the spatial distribution and productivity of alkenone-producing coccolithophorid species in the region. There is a significant positive relationship ( \textU37\textK￠ = 0.059\textSST - 0.350 {\text{U}}_{{{37}}}^{{{\text{K'}}}} = 0.059{\text{SST}} - 0.350 , R = 0.912, n = 30) between the \textU37\textK￠ {\text{U}}_{{{37}}}^{{{\text{K'}}}} values and satellite-derived annual mean SSTs (0 m) for the last 27 years, providing support for the application of a region-specific \textU37\textK￠ {\text{U}}_{{{37}}}^{{{\text{K'}}}} index as paleothermometer in the southern Yellow Sea. However, the slope of the southern Yellow Sea calibration (0.059) is considerably larger than that of the well-known global core-top calibration (0.033). This implies that global SST trends may not adequately encompass regional SST patterns and/or that environmental factors other than temperature may gain importance in explaining coccolithophore dynamics in marginal seas.  相似文献   

7.
If knowledge of our theories on the directivity of tsunamis had received worldwide attention, the following operations could have been carried out internationally just after the large earthquake of 19 September 1985 which occurred near Acapulco, Mexico. Having found the great circle, “line S” which is perpendicular to the coast around Acapulco, we could have calculated the angles between line S and line A and between line S and line D, where line A and line D are the great circle connecting Acapulco and Auckland, New Zealand and that connecting Acapulco and Duke of York Island (Chile), respectively. The resultant angles are 30?43′ and 41?49′(>68?48′/2), we could thereafter neglect the eastern half of the offshore energy flux. When we assume that the speed of trans-Pacific tsunami is 400 knots, the probability that the actual tsunami will come earlier than the calculated arrival time proves to be $$\frac{1}{{\sqrt {2\pi } }}\int_{ - {\text{ }}\infty }^{ - {\text{ }}0.689} {e^{ - t^{{2 \mathord{\left/ {\vphantom {2 2}} \right. \kern-\nulldelimiterspace} 2}} } dt = 0.2454} $$ Contact with New Zealand prior to the forecasted arrival time was essential, but the tsunami attention for the Japanese coast was unnecessary. Without such application of our directivity theories, frequent fruitless warnings will be issued for future trans-Pacific tsunamis. Quick improvements in warning procedures are required.  相似文献   

8.
Izvestiya, Atmospheric and Oceanic Physics - From the ERA5 reanalysis data, the time series of the first coefficients ( $$C_{0}^{0}$$ , $$C_{1}^{0}$$ , $$C_{1}^{1}$$ , $$S_{1}^{1}$$ , $$C_{2}^{0}$$...  相似文献   

9.
We investigated the spatial distribution of glycerol dialkyl glycerol tetraethers (GDGTs), alkenones, and polyunsaturated fatty acids in particulate organic matter collected at four sites along a depth transect from the continental shelf to the Okinawa Trough in the East China Sea during the spring bloom in 2008. The maximum alkenone concentration appeared in the top 25?m at all sites and the $ U_{37}^{{{\text{K}}'}} $ values were consistent with in situ water temperatures in the depth interval, suggesting that the alkenones were produced mainly in surface water. At the slope and shelf sites, GDGTs in the water column showed a concentration maximum at 74?C99?m depth, and the $ {\text{TEX}}_{86}^{\text{H}} $ agreed with in situ water temperatures, suggesting the in situ production of GDGTs in the depth interval. The low-salinity surface water above 20?m depth was characterized by low GDGT concentrations and low $ {\text{TEX}}_{86}^{\text{L}} $ -based temperatures, suggesting either the production of GDGTs in winter season or the lateral advection of GDGTs by an eastward current. At the slope and Okinawa Trough sites, TEX86-based temperatures were nearly constant in the water column deeper than 300?m and corresponded to temperatures at the surface and near-surface waters rather than in situ temperatures. This observation is consistent with a hypothesis that Thaumarchaeota cells produced in surface waters are delivered to deeper water and also indicates that the residence time of suspended GDGTs in the deep-water column is large enough to mix the GDGTs produced in different seasons.  相似文献   

10.
This study presents sand activation depth (SAD) measurements recently obtained on two contrasting beaches located along the Atlantic coast of France: the gently sloping, high-energy St Trojan beach where wave incidence is usually weak, and the steep, low-energy Arçay Sandspit beach where waves break at highly oblique angles. Comparisons between field measurements and predictions from existing formulae show good agreement for St Trojan beach but underestimate the SAD on the Arçay Sandspit beach by 40–60%. Such differences suggest a strong influence of wave obliquity on SAD. To verify this hypothesis, the relative influence of wave parameters was investigated by means of numerical modelling. A quasi-linear increase of SAD with wave height was confirmed for shore-normal and slightly oblique wave conditions, and a quasi-linear increase in SAD with wave obliquity was also revealed. Combining the numerical results with previously published relations, both a new semi-empirical and an empirical formula for the prediction of SAD were developed which showed good SAD predictions under conditions of oblique wave breaking. The new empirical formula for the prediction of SAD (Z 0) takes into account the significant wave height (H s), the beach face slope (β) and the wave angle at breaking (α), and is of the form $ Z_{0} = 1.6\tan {\left( \beta \right)}H^{{0.5}}_{{\text{s}}} {\sqrt {1 + \sin {\left( {2\alpha } \right)}} } This study presents sand activation depth (SAD) measurements recently obtained on two contrasting beaches located along the Atlantic coast of France: the gently sloping, high-energy St Trojan beach where wave incidence is usually weak, and the steep, low-energy Ar?ay Sandspit beach where waves break at highly oblique angles. Comparisons between field measurements and predictions from existing formulae show good agreement for St Trojan beach but underestimate the SAD on the Ar?ay Sandspit beach by 40–60%. Such differences suggest a strong influence of wave obliquity on SAD. To verify this hypothesis, the relative influence of wave parameters was investigated by means of numerical modelling. A quasi-linear increase of SAD with wave height was confirmed for shore-normal and slightly oblique wave conditions, and a quasi-linear increase in SAD with wave obliquity was also revealed. Combining the numerical results with previously published relations, both a new semi-empirical and an empirical formula for the prediction of SAD were developed which showed good SAD predictions under conditions of oblique wave breaking. The new empirical formula for the prediction of SAD (Z 0) takes into account the significant wave height (H s), the beach face slope (β) and the wave angle at breaking (α), and is of the form . The use of a dataset from the literature demonstrates the predictive skill of these new formulae for a wide range of wave heights, wave incidence and beach gradients.  相似文献   

11.
Leont’yev  I. O. 《Oceanology》2022,62(2):258-264
Oceanology - The depth of closure $${{h}_{*}}$$ limits the area of significant morphological changes in a beach profile on an annual time scale, and the prediction of $${{h}_{*}}$$ is important for...  相似文献   

12.
The temporal variation of the partial pressure of carbon dioxide in surface seawater of Iyo Nada in the western Seto Inland Sea was measured by infrared absorption of carbon dioxide (CO2) in air equilibrated with seawater. The variation of from January to late May in 1994 was relatively small (from 270 to 340 atm). on the contrary, the measured in September 1993 ranged from 200 to 450 atm. It seems that the relative high observed in the north and the south of Iyo Nada in September were caused by destruction of a stratification owing to tidal currents at straits between Hiroshima Bay and Iyo Nada and Hayasui Straits, respectively. The low observed in the central Iyo Nada in September was ascribed to a tidal front where high concentrations of chlorophyll-a and a relation between and chlorophyll-a in negative sense were found. Except the observation in the north of Iyo Nada in September, the in the surface seawater of Iyo Nada were lowe than the atmospheric (about 367 atm). The results obtained by this work and Kimotoet al. (1993) lead to the conclusion that Iyo Nada acts as a sink of the atmospheric CO2 on the average.  相似文献   

13.
Water surface elevations(t), vertical surface velocities and vertical surface acceleration of wind-generated waves have been measured in a laboratory wind wave channel by using resistance-type wave gauges combined with an electronic differentiation circuits. Probability distributions of the values of(t), , and have been determined from the wave records.In an initial stage of wave generation,i.e., when wind waves are generated at short fetches and low wind speeds, the observed distributions for(t), and are appreciately good fit to the distributions given by successive sum of a Gram-Charlier series, which has been derived following the formulation ofLonguet-Higgins (1963), by taking the weakly nonlinear effect into account.However, when wind waves develop with increasing wind speeds and fetches, the observed distributions deviate gradually from the Gram-Charlier series. Particularly, the deviations are remarkable for the distribution of .When the wind speed increases, the observed distributions of(t), and show the following characteristics: (i) the skewnesses of the distributions of(t) and decrease slightly, (ii) the skewness of changes, at some wind speed, from positive small values to relatively large negative values, (iii) the kurtosis of the distribution of(t) decreases slightly but that of increases slightly and these characteristics seem to depend not so much on fetches, (iv) the kurtosis of the distribution of increases rapidly.  相似文献   

14.
A formulation for the aerodynamic roughness length of air flow over wind waves $$z_0 = \gamma {\text{ }}u_* /\sigma p$$ which was proposed by Toba (1979) and Toba and Koga (1986) from dimensional considerations with some data analysis, is shown to correspond with a formulation for irregular solid surfaces $$(z_0 /h) = a(h/l)^{1 + \beta } $$ which resulted from work by Woodinget al. (1973) and Kustas and Brutsaert (1986);u * is the friction velocity,σ p the spectral peak frequency of wind waves,h the mean height of the solid obstacles,l the mean distance between their crests, andα,Β, andγ are constants. This correspondence is reached by the existence of a statistical 3/2-power law and an effective dispersion relationship for wind waves. Because both approaches of parameterizingz 0 were arrived at independently, they provide each other mutual reinforcement.  相似文献   

15.
A series of measurements of winds and wind-waves were carried out in wind-wave flumes. A data analysis based on the hypothesis of local equilibrium yielded a new empirical formula on the controversial quantity of roughness heightz 0 over the water surface: , where the nondimensional roughness height is defined bygz 0/u * 2 and the wave-wind parameterũ byω p u */g, g being the gravitational acceleration,u * the friction velocity of air,ω p the peak frequency of wind-wave spectra. The obtained formula is compared with Charnock's (1955) and Toba's (1979) proposals; is constant in the former and inversely proportional toũ in the latter. As in Toba's, this formula immediately leads to a practically important conclusion that the drag coefficientC d depends not merely on the usual variableU 10 (wind velocity at 10m height over the water surface), but also on the surface state represented by wind-waves. An explicit expression is provided for the drag coefficient incorporating the wave-wind parameter; it covers the range ofC d calculated from most of the previous drag formulas, by varying the wave-wind parameter.  相似文献   

16.
Park  Yu-Hyeon  Kim  Hyung Jeek  Son  Ju Won  Yoo  Chan Min  Khim  Boo-Keun 《Ocean Science Journal》2019,54(3):487-495
Ocean Science Journal - This study evaluates the application of biomarkerbased temperature proxy data (alkenone with its resultant $$U_{37}^{K'}$$ index and glycerol dialkyl glycerol tetraether...  相似文献   

17.
In-water algorithms for OCTS standard products were developed using in situ data and installed for operationally processing at NASDA/EOC. This paper describes the in-water algorithms Version 1.0 for chlorophylla concentration, pigment concentration, and attenuation coefficient at a wavelength of 490 nm. The selected OCTS standard algorithms (Ver. 1.0) are as follows:   相似文献   

18.
Most of reported harmful algal blooms(HABs)of microalgae(75%)have been caused by dinoflagellates.Studies on the negative effects of HABs have generally focused on animals,valuable organisms in particular,and environmental factors such as dissolved oxygen and nutrients,but relatively fewer on community level,particularly that using metagenomic approach.In this study,we reported an investigation on the effects of a HAB caused by the dinoflagellate Prorocentrum donghaiense on the species diversity and community structure of the dinoflagellate sub-community via a pyrosequencing approach for the samples taken before,during,and after the bloom season of P.donghaiense in the East China Sea.We sequenced partial 28S rRNA gene of dinoflagellates for the field samples and evaluated the species richness and diversity indices of the dinoflagellate community,as a sub-community of the total phytoplankton.We obtained 800185 valid sequences(categorized into 560 operational taxonomic units,OTUs)of dinoflagellates from 50 samples and found that the biodiversity of dinoflagellate community was significantly reduced during the blooming period in comparison to that in pre-and after-blooming periods,as reflected in the four diversity indices:the species richness expressed as the number of OTUs,Chao1 index,Shannon index(evenness),and Gini-Simpson index.These four indices were all found to be negatively correlated to the cell density of the bloom species P.donghaiense.Correlation analyses also revealed that the P.donghaiense cell abundance was correlated negatively with NO3--N,and NO2--N,but positively with total nitrogen(TN)and total phosphorus(TP).Principal coordinates analysis(PCoA)showed that the community structure of dinoflagellates was markedly different among the different sampling periods,while the redundancy analysis(RDA)revealed P.donghaiense abundance,salinity,NO3--N,and SiO32-were the most four significant factors shaping the dinoflagellate community structure.Our results together demonstrated that HABs caused by the dinoflagellate P.donghaiense could strongly impact the aquatic ecosystem on the sub-community level which the blooming species belongs to.  相似文献   

19.
A mathematical model of attached bacterial dynamics based on microcolonization was devised using data obtained from a bog. Bacterial samples obtained from any natural water body can be examined by this model with the method of non-linear least squares. The model comprises three bacterial processes; i.e., (1) the attachment rate which was dependent on time after submergence by adsorption onto the substratum surface, and both (2) growth and (3) detachment rate which were dependent on the number of bacterial cells in the microcolony. The population dynamics are expressed as $$\frac{{dC_i }}{{dt}} = - g_i C_i + g_{i - 1} C_{i - 1} - b_i C_i + b_{i + 1} C_{i + 1} + a_i F_i ,$$ where suffixi denotes cell number in each microcolony,C i is microcolony number on the substratum,F i is bacterial clump drifting in the water column,a i , g i andb i are the rate coefficients of attachment, growth and detachment. The growth rate was reciprocally proportional to the cell number in the microcolony. The detachment was shown to increase up to a maximum, and then to decrease as the number of bacterial cells increased in each microcolony.  相似文献   

20.
The relationship between the scale of the spectral minimum of the first differences in temperature fluctuationsL and the local value of the Väisälä-Brunt frequencyN has been analysed using the results of more than 600 soundings made in various regions of the world's oceans. Allowing for the series of theoretical and experimental indications of the fact that the vertical scaleL at the boundary between the fine structure and microstructure in the ocean exists under the effect of processes of breaking of internal waves and hydrodynamic instability with the formation of turbulent patches, and using the energy relationships, the relationship for a solitary patch has been derived through the determining parameters. Based on two expressions forL, derived experimentally and using the energy estimations, the relationships for the averaged rate of absorption of the wave field energy by patches and the coefficient of the density vertical diffusion are derived, which do not contradict a series of independent estimations fromin situ measurements.Translated by Mikhail M. Trufanov.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号