Prediction of wave pressures on smooth impermeable seawalls

Simple prediction methods are proposed to estimate the wave induced pressures on smooth impermeable seawalls. Based on the physics of the wave structure interaction, the sloped seawall is divided into a total of five zones (zones 1, 2 and 3 during run-up (corresponding pressures are called as positive pressures) and zones 4 and 5 during run-down (corresponding pressures are called negative pressures)) (Fig. 1). Zone 1 (0<z<d−H_i/2), where the wave pressure is governed by the partial reflection and phase shift; Zone 2 (d−H_i/2<z<d), where the effect of wave breaking and turbulence is significant; Zone 3 (d<z<Run-up height), where the pressure is induced by the run-up water; Zone 4 (Run-down<z<d), where the wave pressure is caused by the run-down effect and Zone 5 (0<z<d-Run down), where the negative wave pressures are due to partial reflection and phase shift effects. Here d is the water depth at the toe of the seawall, H_i is the incident wave height and z is the vertical elevation with toe of the seawall as origin and z is positive upward. For wave pressure prediction in zones 1 and 5, the empirical formula proposed by Ahrens et al. (1993) to estimate the wave reflection and Sutherland and Donoghue's recommendations (1998) for the estimation of phase shift of the waves caused by the sloped structures are used. Multiple regression analysis is carried out on the measured pressure data and empirical formulas are proposed for zones 2, 3 and 4. The recommendations of Van der Meer and Breteler (1990) and Schüttrumpf et al. (1994) for the prediction of wave run-down are used for pressure prediction at zone 4. Comparison of the proposed prediction formulas with the experimental results reveal that the prediction methods are good enough for practical purposes. The present study also shows a strong relation between wave reflection, wave run-up, wave run-down and phase shift of waves on wave pressures on the seawalls.     

秦皇岛外海低氧区颗粒物吸收光谱特征

近年来, 渤海夏季低氧现象频发, 引起了人们的广泛关注。然而对该海域低氧形成的机制还未得到充分认识。研究基于在秦皇岛外海的现场观测, 分析了海水中颗粒物吸收光谱特征及其与不同粒径浮游植物叶绿素a (chl a)组成、环境因子的关系, 评估了夏季底层水体脱氧过程中有机物来源与特征。结果显示,夏季秦皇岛外海微型浮游植物chl a占总量的80%。表层水体中, 总颗粒物吸收光谱[a_p(l)]特征由浮游植物色素吸收光谱[a_ph(l)]主导, 在中、底层水体中则由碎屑颗粒物吸收光谱[a_d(l)]主导。垂向上, a_p(440)和a_d(440)均表现为表层<中层<底层。结果还表明, 浮游植物粒径主导秦皇岛外海chl a的光吸收效率, 即a^*_ph(440)。基于三粒级chl a含量, 可利用多元回归预测a_ph(440)。碎屑颗粒物的吸收光谱同样受浮游植物群落、有机质相对含量等的影响。研究结果表明初级生产产生的微型颗粒有机物是底层水体脱氧的主要底物。     

Drag and Sediment Dispersion Over Sand Waves

Estimates of the drag coefficient over sand waves during calm weather in the southern North Sea have been obtained from measurements of the water slope and currents at different heights (z) above the sea-bed using the log profile and momentum balance methods. An observed phase difference between principal terms in the momentum balance equation is examined theoretically. Drag coefficient estimates are found to agree broadly with previous studies. Owing to bedform asymmetry, average drag coefficient values obtained atz=1 m (C₁₀₀) are found to be 0·0021 and 0·0029 for flood and ebb tides, respectively. Systematic changes in bed roughness are not detected. Using a momentum balance approach, the average drag coefficient value (C_d) atz=10 m is found to be 0·0056. Changes in 10-min averageC_dvalues over sand waves during the tidal cycle are found to be small with bedform asymmetry having no detectable effect. Correlation betweenC_dandC₁₀₀is found to be poor and separation of skin friction and form drag terms is not possible with existing measurements. The inclusion of form drag inC₁₀₀values at the present site leads to over-estimation of the bed shear stress ({q) available to mobilize and transport sediment. Mobile sediment, detected through the use of tracers and a transmissometer, was not found to have any measurable effect on eitherC_dorC₁₀₀in calm weather conditions.     

Numerical Modeling of Wave-Enhanced Turbulence in the Oceanic Upper Layer

A coupled model of air-wave-sea interaction is modified based on a new roughness formulation and the latest data. The model parameters for aerodynamic roughness from below (ARB) and wave-dependent roughness from above (ARA, z _0a ) are assumed equal. The combined roughness is assumed to be a function of friction velocity, gravity, air and seawater densities, and wave age (c _w ). The model is used in a study of wave-enhanced turbulence under breaking waves to predict turbulent dissipation (), ARA, and drag coefficient (C _d ). Both waves and shear production are considered as sources of ocean turbulent energy. The atmospheric part of the model is used only to specify a correct condition at the interface. Numerical experiments are performed to study the -distribution, z _0a and C _d , and to compare with data. The major achievement is model verification using all available data. The first full application of this model is in conjunction with an ocean circulation model in a coupled circulation-wave system. Simulations show that the -distribution is strongly dependent on local wind-forced wave heights. For each wind and wave state there is a particular wave-dependent depth that is verified by data. The comparison shows that the model predicted agrees well with the observed of the z ^–4 law distribution of Gargett (1989). Simulations also show that waves have an important role in causing to differ from the classical wall-layer theory and z _0a , with a value of 0.30 for the empirical constant a _a . The model-predicted , z _0a , C _d and C _gd agree well with data.     

Investigation of Cd, Cu, Ni and Th in the colloidal size range in the Gulf of Maine

Size-fractionated seawater samples were collected from the Gulf of Maine to determine the fraction (f_c/d) of total dissolved (< 1 μm) Cd, Cu, Ni and ²³⁴Th in the colloidal size range (1,000 nominal molecular weight, NMW, to 1 μm) using cross-flow filtration. Colloidal Cd, Cu and Ni represents < 1–7% of the total dissolved concentration in these shelf waters and increases with an increase in particle concentration. By comparison, results obtained for particle-reactive ²³⁴Th indicate that < 1–47% of total dissolved is associated with the colloidal size fraction. A revised relationship between the concentration of colloids (C_c) and suspended particles (C_p) is reported (log C_c = 0.66 log C_p −2.01 kg L⁻¹) and used to examine the dependence of f_c/d for these metals on the concentration of suspended particles for C_p = 0.01–100 mg L⁻¹. Results indicate that a significant fraction (˜ 10–30%) of Cd, Cu, Ni and ²³⁴Th in the traditionally defined ‘dissolved’ fraction may exist in the colloidal size range in regions characterized by high particle concentrations (C_p > 1–10 mg L⁻¹), such as in near-shore and estuarine waters.     

利用半透膜渗透装置富集-超声萃取分析表层沉积物间隙水PCBs的方法

本文建立了半透膜渗透装置(semi-permeable membrane device,SPMD)富集-超声萃取-凝胶渗透色谱净化-气相色谱法测定沉积物间隙水中多氯联苯(PCBs)的方法。比较了有机溶剂透析法与超声萃取法从膜袋内提取PCBs的回收率,发现超声萃取法在节省时间和溶剂方面有明显优势。应用凝胶渗透色谱分离与净化SPMD提取物,收集11—17min的流出液能达到最佳分离效果。基于此方法测定了大连湾沉积物间隙水中自由溶解态PCBs的含量(C_(W-SPMD)),同时又分析了沉积物中PCBs的总量(C_(SED))、间隙水中PCBs的含量(有机碳含量校正法,C_(W-SED))和间隙水中PCBs的总含量(离心法,C_(PW))。结果表明,C_(PW)值显著高于C_(W-SED)和C_(W-SPMD)值。因此,考虑到生物可利用性,无论采用沉积物中或者间隙水中的PCBs总量进行污染物生态风险评价均会造成风险被高估,建议采用间隙水中可溶解态含量。     

Spectral absorption coefficient of photosynthetically active pigments in the equatorial Pacific Ocean (165°11–150°W)

Spectral absorption coefficients of total particulate material and detritus were measured throughout the euphotic zone along the equator between 165°E and 150°W and during time-series for each of these two longitudes in October 1994 (JGOFS-FLUPAC cruise). The sum of pigments obtained by spectrofluorometry (tChla=DV−chla+Chla) was used for normalization (and was also compared to fluorometric and HPLC measurements as an intercalibration study). In order to assess the specific absorption coefficient of photosynthetically active pigments (aps) from the pigment-specific absorption coefficient for phytoplankton (a_ph^*), we made a multiple regression analysis of measured phytoplankton absorption spectra onto publishedin vivo spectra of pure pigments. This made it possible to calculate the concentrations of photoprotective carotenoids (tPPC) when HPLC measurements were not available and thus to subtract their contribution to absorption from the total phytoplanktonic absorption coefficient (a_ph). Methodological uncertainties in both coefficients used for calculating absorption coefficients and in pigment measurements are discussed. Pigments and absorption measurements made during the cruise enabled us to describe two typical trophic regimes in the equatorial Pacific ocean: oligotrophic waters of the ”warm pool“ west of 170°W and high-nutrient, low-chlorophyll waters (HNLC) of the upwelling east of 170°W. The vertical decreasing gradient of a_ph^* from the surface to the deep chlorophyll maximum (DCM) was due to a high tPPC/tChla ratio at the surface and was higher in the oligotrophic (0.14-0.065 m² mg (tChla)⁻¹ biomass dominated byProchlorococcus, rich in zeaxanthin) than in the mesotrophic area (0.07-0.06 m2 mg (tChl a)-' biomass dominated by picoeucaryotes). Below the DCM,a_ph^* reached a similar minimum value in both oligotrophic and mesotrophic areas.a^*_ps varied less than a^*_ph from the surface layer to the DCM in both oligotrophic and mesotrophic areas. The difference in a^*_ph and a^*_ps from west to east of the transect could be interpreted as a shift in the phytoplankton composition, with a dominance of procaryotes in the west and a dominance of eucaryotes in the upwelling area. Higher aps in well-lit typical oligotrophic waters indicated that phytoplankton communities dominated byProclorococcus might be more efficient for capturing light usable for photosynthesis than those present in the HNLC situation.     

CDOM and its contribution to the underwater light climate of a shallow, microtidal estuary in south-western Australia

Light attenuation (K_d) of photosynthetically active radiation (PAR) by chromophoric dissolved organic matter (CDOM), total suspended solids (TSS) and chlorophyll a (Chl a) were measured at nine stations along an estuarine gradient in the Swan River, Western Australia, over 15 months. There were strong spatial gradients associated with the marine-freshwater transition along the 32 km of estuary sampled, as well as seasonal gradients mainly associated with rainfall, 80% of which occurs between May and September. CDOM absorbances at 440 nm reached a maximum of 10.9 m⁻¹ with the freshwater inflow but concentrations of suspended matter remained low throughout the sampling period (1.0–21.0 mg l⁻¹) under the diurnal tides of the estuary. CDOM was the dominant constituent of K_d and a stepwise multiple regression showed that 66% (p < 0.0001) of the variation in K_d can be explained by CDOM and an additional 8% (p < 0.0001) by TSS. As a consequence of this result, analysis into the influence of river discharge rates on CDOM absorbance levels was examined for 2002 using data collected during this study, and for 2000 and 2001 using historical dissolved organic carbon (DOC) and river discharge data. The outcome of this analysis infers that greater river discharge rates result in increased CDOM absorbances in the Swan River estuary.     

Chlorophyll-specific absorption coefficients and pigments of phytoplankton off Sanriku, northwestern North Pacific

The variety in shape and magnitude of thein vivo chlorophyll-specific absorption spectra of phytoplankton was investigated in relation to differences in pigment composition off Sanriku, northwestern North Pacific. Site-to-site variations of the absorption coefficients,a _ph ^* (λ), and pigment composition were clearly observed. At warm-streamer stations, higher values ofa _ph ^* (440) anda _ph ^* (650) were found with relatively high concentrations of chlorophyllb (a green algae marker). At stations located in the Oyashio water (cold streamer),a _ph ^* (440) values were lower and fucoxanthin (a diatom marker) concentrations were higher, compared to the other stations. The peak in the absorption spectra at the Oyashio stations was shifted toward shorter wavelengths, which was probably due to the presence of phaeopigments. In a Kuroshio warm-core ring, the magnitude ofa _ph ^* (440) was in between those at the warm-streamer and Oyashio stations, and the diagnostic pigment was peridinin (a dinoflagellate marker). These findings indicated that major differences in phytoplankton absorption spectra of each water mass were a result of differences in the phytoplankton pigment composition of each water mass, which was probably related to the phytoplankton community.     

Spatial variability of phytoplankton absorption coefficients and pigments off Baja California during November 2002

We have estimated the spatial variability of phytoplankton specific absorption coefficients (a* _ph ) in the water column of the California Current System during November 2002, taking into account the variability in pigment composition and phytoplankton community structure and size. Oligotrophic conditions (surface Chl < 0.2 mg m⁻³) dominated offshore, while mesotrophic conditions (surface Chl 0.2 to 2.0 mg m⁻³) where found inshore. The specific absorption coefficient at 440 [a* _ph (440)] ranged from 0.025–0.281 m²mg⁻¹ while at 675 nm [a* _ph (675)] it varied between 0.014 and 0.087 m²mg⁻¹. The implementation of a size index based on HPLC data showed the community structure was dominated by picoplankton. This would reduce the package effect in the variability of a* _ph (675). Normalized a _ph curves were classified in two groups according to their shape, separating all spectra with peaks between 440 and 550 nm as the second group. Most samples in the first group were from surface layers, while the second group were from the deep chlorophyll maximum or deeper. Accessory photoprotective pigments (APP) tended to decrease with depth and accessory photosynthetic pigments (APS) to increase, indicating the importance of photoprotective mechanisms in surface layers and adaptation to low light at depth. Samples with higher ratios of APP:APS (>0.4) were considered as phytoplankton adapted to high irradiances, and lower ratios (<0.26) as adapted to low irradiances. We found a good relationship between APP:APS and a* _ph (440) for the deeper layer (DCM and below), but no clear evidence of the factors causing the variability of a* _ph (440) in the upper layer.     

Influence of non-photosynthetic pigments on light absorption and quantum yield of photosynthesis in the western equatorial Pacific and the Subarctic North Pacific

Regional variations in the contribution of non-photosynthetic pigments (ā _np^*) to the total light absorption of phytoplankton (ā _ph^*) and its influence on the maximum quantum yield of photosynthesis (φ _m) were investigated. In the western equatorial Pacific, the surface ā _np^* : ā _ph^* ratio was higher in the western warm pool than that in the upwelling region. This difference appears to be attributable to severe nitrate depletion and higher percentage of prokaryotes, which can accumulate very high concentrations of zeaxanthin in the western warm pool. In the subarctic North Pacific, the ā _np^* : ā _ph^* ratio was expected to be higher in the Alaskan Gyre where the thermocline is sharper and iron limitation may possibly be more severe than in the Western Subarctic Gyre. However, the ratio was actually higher in the Western Subarctic Gyre, contradictory to our expectations. This east-west variation appears to be attributable to changes in the taxonomic composition; cyanobacteria were more abundant in the Western Subarctic Gyre. The values of ā _np^* : ā _ph^* and its vertical variations were relatively small in the subarctic North Pacific compared to those in the western equatorial Pacific. These inter-regional variations appear to be attributable to the lower solar radiation intensity, smaller percentage of cyanobacteria, and relatively strong vertical mixing in the subarctic North Pacific. The spatial variations in ā _np^* : ā _ph^* significantly influence φ _m. In comparison with φ _m based on the total light absorption (φ _{m ph}), the values corrected for the contribution of non-photosynthetic pigments (φ _{m ps}) showed an increase in both the western equatorial Pacific and the subarctic North Pacific.     

An evaluation of inversion models for retrieval of inherent optical properties from ocean color in coastal and open sea waters around Korea

This study was aimed to investigate three inversion models (currently in use with Moderate Resolution Imaging Spectroradiometer and Sea-viewing Wide Field-of-view Sensor data processing), namely constrained Linear Matrix (LM), Quasi-analytical algorithm (QAA) and GSM semi-analytical models (GSM). These models were applied to large bio-optical data sets (collected from coastal and open sea waters around Korea) to retrieve inherent optical properties (IOPs) such as absorption coefficients of phytoplankton (a _ph ), colored dissolved and detrital organic matters (a _cdm ), and particulate backscattering coefficient (b _bp ) at five wavelengths (412, 443, 490, 510, and 555 nm). The derived IOP products were compared with in situ a _ph , a _cdm and b _bp coefficients measured for the same remote sensing reflectance (R _rs (λ)) data sets used in the models and the uncertainties of the three models were assessed based on the standard statistical procedures (mean relative error MRE, root mean square error RMSE, slope, and coefficient of determination R ²). It was found that all the three models tended to yield significant errors with varying magnitude at different wavelengths. Overall performance of the models assessed based on the above statistical means was found in the following order: LM > GSM > QAA for retrieving the a _ph , LM > GSM > QAA for retrieving the a _cdm , and QAA > GSM > LM for retrieving the b _bp . Our analyses suggest that these models will require additional refinements with a full parameterization by a fully suited data set in order to produce accurate retrievals of IOPs in coastal and open sea waters around Korea.     

Optical properties of the red tide in Isahaya Bay,southwestern Japan: Influence of chlorophyll a concentration

Remote sensing reflectance [R _rs(λ)] and absorption coefficients of red tides were measured in Isahaya Bay, southwestern Japan, to investigate differences in the optical properties of red tide and non-red tide waters. We defined colored areas of the sea surface, visualized from shipboard, as “red tides”. Peaks of the R _rs(λ) spectra of non-red tide waters were at 565 nm, while those of red tides shifted to longer wavelengths (589 nm). The spectral shape of R _rs(λ) was close to that of the reciprocal of the total absorption coefficient [1/a(λ)], implying that the R _rs(λ) peak is determined by absorption. Absorption coefficients of phytoplankton [a _ph(λ)], non-pigment particles and colored dissolved organic matter increased with increasing chlorophyll a concentration (Chl a), and those coefficients were correlated with Chl a for both red tide and non-red tide waters. Using these relationships between absorption coefficients and Chl a, variation in the spectrum of 1/a(λ) as a function of Chl a was calculated. The peak of 1/a(λ) shifted to longer wavelengths with increasing Chl a. Furthermore, the relative contribution of a _ph(λ) to the total absorption in red tide water was significantly higher than in non-red tide water in the wavelength range 550–600 nm, including the peak. Our results show that the variation of a _ph(λ) with Chl a dominates the behavior of the R _rs(λ) peak, and utilization of R _rs(λ) peaks at 589 and 565 nm may be useful to discriminate between red tide and non-red tide waters by remote sensing.     

基于浮游植物吸收的海洋初级生产力模型的不确定性分析

Satellite-derived phytoplankton pigment absorption(a_(ph)) has been used as a key predictor of phytoplankton photosynthetic efficiency to estimate global ocean net primary production(NPP). In this study, an a_(ph)-based NPP model(Ab PM) with four input parameters including the photosynthetically available radiation(PAR), diffuse attenuation at 490 nm(K_d(490)), euphotic zone depth(Z_(eu)) and the phytoplankton pigment absorption coefficient(a_(ph)) is compared with the chlorophyll-based model and carbon-based model. It is found that the Ab PM has significant advantages on the ocean NPP estimation compared with the chlorophyll-based model and carbonbased model. For example, Ab PM greatly outperformed the other two models at most monitoring sites and had the best accuracy, including the smallest values of RMSD and bias for the NPP estimate, and the best correlation between the observations and the modeled NPPs. In order to ensure the robustness of the model, the uncertainty in NPP estimates of the Ab PM was assessed using a Monte Carlo simulation. At first, the frequency histograms of simple difference(δ), and logarithmic difference(δ~(LOG)) between model estimates and in situ data confirm that the two input parameters(Z_(eu) and PAR) approximate the Normal Distribution, and another two input parameters(a_(ph) and K_d(490)) approximate the logarithmic Normal Distribution. Second, the uncertainty in NPP estimates in the Ab PM was assessed by using the Monte Carlo simulation. Here both the PB(percentage bias), defined as the ratio of ΔNPP to the retrieved NPP, and the CV(coefficient of variation), defined as the ratio of the standard deviation to the mean are used to indicate the uncertainty in the NPP brought by input parameter to Ab PM model. The uncertainty related to magnitude is denoted by PB and the uncertainty related to scatter range is denoted by CV.Our investigations demonstrate that PB of NPP uncertainty brought by all parameters with an annual mean of5.5% covered a range of –5%–15% for the global ocean. The PB uncertainty of Ab PM model was mainly caused by a_(ph); the PB of NPP uncertainty brought by a_(ph) had an annual mean of 4.1% for the global ocean. The CV brought by all the parameters with an annual mean of 105% covered a range of 98%–134% for global ocean. For the coastal zone of Antarctica with higher productivity, the PB and CV of NPP uncertainty brought by all parameters had annual means of 7.1% and 121%, respectively, which are significantly larger than those obtained in the global ocean. This study suggests that the NPPs estimated by Ab PM model are more accurate than others, but the magnitude and scatter range of NPP errors brought by input parameter to Ab PM model could not be neglected,especially in the coastal area with high productivity. So the improving accuracy of satellite retrieval of input parameters should be necessary. The investigation also confirmed that the SST related correction is effective for improving the model accuracy in low temperature condition.     

Stable Isotopic Composition of Particulate Organic Carbon in the Caspian Sea

The data on the isotopic composition of particulate organic carbon (δ¹³C_POC) in the Caspian Sea water in summer–autumn 2008, 2010, 2012, and 2013 are discussed in the paper. These data allowed as to reveal the predominant genesis of organic carbon in suspended particulate matter of the active seawater layer (from 0 to 40 m). The δ¹³C_POC =–27‰ (PDB) and δ¹³C_POC =–20.5‰ (PDB) values were taken as the reference data for terrigenous and planktonogenic organic matter, respectively. Seasonal (early summer, late summer, and autumn) variations in the composition of suspended particulate matter in the active sea layer were revealed. A shift of δ¹³C_POC towards greater values was seen in autumn (with a slight outburst in the development (bloom) of phytoplankton) in comparison with summer (with large accumulations and an extraordinary phytoplankton bloom confined to the thermocline area). The seasonal dynamics of autochthonous and allochthonous components in the suspended particulate matter of the Middle and Southern Caspian Sea was studied with the use of data on the concentration of particulate matter and chlorophyll a, the phytoplankton biomass and the POC content.     

Determination of the chlorophyll-a concentration vertical profile by the spectra of incident solar radiation in the ocean

Methods of rapid analysis of the chlorophyll-a concentration vertical profile by the spectra of incident solar radiation are suggested. The methods are applicable for the ocean layerz=20–80 m containing waters of type 1 (by Morel's classification). Testing of the methods underin situ conditions showed that they can be used to reconstructC _ch(z) profiles, with a relative error of 10% and a root-meansquare error of 20–30% at most, provided the data are calibrated using field observations conducted at two or three sites in the test area.Translated by Vladimir A. Puchkin.     

Contrasting behaviour of trace metals in the Scheldt estuary in 1978 compared to recent years

Dissolved and particulate trace metals (Cu, Cd, Pb, Zn, Ni, Fe and Mn) measured at six stations along the Scheldt estuary in October/November 1978 are compared with more recent data. Based on Ca content in the suspended matter, three distinct geochemical regions could be distinguished: the upper estuary (salinity 1–7) dominated by fluvial mud, mid-estuary (salinity 7–17) where the composition of the suspended matter remained relatively constant, and the lower estuary where marine mud prevailed. Re-suspension of sediments is the major factor controlling the composition of the particles in the upstream region. Anoxic conditions prevailed in the upper part of the estuary extending to a salinity of 15 in 1978, while at present the seaward boundary of the anoxic water body is located at less saline waters. Furthermore, the present-day metal load is much lower than in 1978. As a consequence of the changed situation, maxima in dissolved concentrations of redox-sensitive metals in the mid/lower estuary have moved as well, which affects the trace metal re-distribution pattern. In the anoxic zone, exchange processes between dissolved and particulate metal fractions were strongly redox regulated, with Fe and Mn as excellent examples. Iron was removed from the dissolved phase in the early stages of mixing resulting in an increase in the suspended particulate matter of the leachable ‘non-residual' Fe fraction from 2 to 3.5%. Due to its slower kinetics, removal of Mn from solution occurred in mid-estuary where oxygen concentrations increased. Cu, Cd and Zn on the contrary were mobilised from the suspended particles during estuarine mixing. External inputs of Pb, and to a lesser extent of Cu, in the lower estuary resulted in the increase of their particulate and the dissolved concentrations. Calculated K_d (distribution coefficient) values were used to assess the redistribution between the dissolved and particulate phase of the investigated metals. Due to the existence of the anoxic water body in the upper estuary, the importance of redox processes in determining the K_d values could be demonstrated. The sequence of K_d values in the upper estuary (Fe, Cd, Zn, Pb > Cu > Ni, Mn) is significantly different from that in the lower estuary (Fe > Mn > Pb, Ni, Zn, Cu, Cd). Thus, in such a dynamic estuary single metal-specific K_d values cannot be used to describe redistribution processes.     

Partitioning particulate absorption coefficient into contributions of phytoplankton and nonalgal particles: A case study in the northern South China Sea

We measured the absorption coefficients of suspended particles (a_p(λ)) during three cruises from coastal waters to open ocean in the northern South China Sea (NSCS). The absorption contributions of phytoplankton (a_ph(λ)) and nonalgal particles (a_NAP(λ)) were determined using the methanol extraction method. Based on the dataset of about 360 samples, we examined the spectral relationships of the particle absorption coefficients. The results show that a_p(λ) spectra are well linearly correlated with a_p(443) over the wavebands between 420–650 nm; a_ph(λ) could be well expressed as the second-order quadratic equations of a_ph(443) among the blue-green wavebands, and a_NAP(λ) follows the general exponential function. Based on these spectral relationships, a model was proposed for partitioning the total particulate absorption coefficients into the contributions of phytoplankton and nonalgal particles using the nonlinear optimization method. The model was validated by comparing the computed results with in situ absorption coefficients. In some wavebands, such as 412 nm, 443 nm, 490 nm and 683 nm, we obtained good correlations with the percentage root mean square error (RMSE) values being controlled within 25% and the slopes being closer to 1.0. For samples from coastal waters, the discrepancy was a little large, which might be due to the higher absorption contributions from certain pheopigments. Overall, this model provides us much insight into phytoplankton absorption retrieval from in situ measurements and remote sensing ocean color data.     

Analysis of estuarine colour components during non-monsoon period through Ocean Colour Monitor

Simultaneous acquisition of water samples, radiance and irradiance measurements were carried out from 40 stations in the Mandovi–Zuari estuaries during February to May 2002. From the samples collected, inherent and apparent optical properties (IOP and AOP) such as absorption coefficient (a), upwelling diffuse attenuation coefficient (k_u) and subsurface reflectance (R) were derived. Using these optical properties, radiative transfer at each water column is examined. On the basis of the radiative transfer outcome, band-ratio algorithms are derived for three optically active substances (OAS), viz, chlorophyll-a, suspended sediment and coloured dissolved organic matter (CDOM). The respective algorithms are 670/555, 490/670 and 412/670 nm for chlorophyll-a, suspended sediment and CDOM. These algorithms are applied to Ocean Colour Monitor (OCM), onboard Indian Remote Sensing Satellite (IRS)-Polar Satellite Launch Vehicle (P4), scenes (digital data), to synoptically analyze these OAS. The synoptic analysis of OAS revealed different hydrodynamic characteristics of the estuaries during non-monsoon seasons.     

Anthropogenic CO2 fluxes in the Otranto Strait (E. Mediterranean) in February 1995

This study presents the distribution and fluxes of dissolved inorganic carbon (C_T), total alkalinity (A_T) and anthropogenic carbon (C_ant) along the Otranto strait, during February 1995. Based on a limited number of properties (temperature, dissolved oxygen, total alkalinity and dissolved inorganic carbon), the composite tracer TrOCA was used to estimate the concentration of anthropogenic CO₂ in the Otranto strait.Total alkalinity exhibits high values and weak variability throughout the water column of the strait, probably associated with the dense water formation processes in the Adriatic basin that induce a rapid transport of the coastal alkalinity to the deep waters. Elevated C_ant concentrations and high anthropogenic pH variations are observed in the bottom layer of the strait, associated with the presence of Adriatic Deep Water (ADW). The study shows that large amounts of C_ant have penetrated the highly alkaline Eastern Mediterranean waters, thereby causing a significant pH reduction since the pre-industrial era.Estimates of the transports of C_T and C_ant through the strait indicate that during February 1995, the Adriatic Sea imports through the Otranto strait natural and anthropogenic carbon and acts as a net sink of carbon for the Ionian Sea. The anthropogenic carbon that is imported to the Adriatic Sea represents less than 1% of the net C_T inflow. The Levantine Intermediate Water (LIW) contributes to about one-third of the total C_T and C_ant inflow. Although the amounts of C_ant annually transported by LIW and ADW are almost equal, the contribution of C_ant to the C_T transported by each water mass is slightly higher in ADW (3.1%) than in LIW (2.6%), as a result of its higher mean C_ant concentration. The ADW, despite its weak contribution to the total outflow of C_ant, has a vital role for the sequestration and storage of the anthropogenic carbon, as this water mass is the main component of the Eastern Mediterranean Deep Waters and, thus, the anthropogenic CO₂ is transferred in the deep horizons of the Eastern Mediterranean, where it remains isolated for many years.