Instrument for in situ synchronous measurement of the multi-angle volume scattering function and attenuation coefficient.

An instrument named as Volume Scattering and Attenuation Meter (VSAM) is presented. The VSAM can simultaneously measure the attenuation coefficient and the volume scattering function (VSF) from 10° to 170° with an interval of 10° at 659 nm. Using ultrapure water and NCRM-traceable polystyrene microsphere beads, the VSAM was calibrated, and the conversion factor χbθ for estimating the backscattering coefficient from the backward VSF was obtained based on Mie theory in the laboratory. For χbθ, the average relative deviation was no more than 7.77% in the range of 100°-160° between the modeled result based on VSAM and the theoretical result by Boss. Subsequently, the VSAM and ECO-VSF3 were deployed in situ in Zhanjiang Bay. The backscattering coefficient and VSF at the same angles measured by the two instruments were quite consistent. Some remarkable changes in the shape and magnitude of the VSF profile at different stations were found, with land-based pollutants composing an important suspicious source of these changes.

Approach for estimating the vertical distribution of the diffuse attenuation coefficient in the South China Sea.

The vertical distribution of the diffuse attenuation coefficient K(z, λ) is critical for studies in bio-optics, ocean color remote sensing, underwater photovoltaic power, etc. It is a key apparent optical property (AOP) and is sensitive to the volume scattering function ß(ψ, z, λ). Here, using three machine learning algorithms (MLAs) (categorical boosting (CatBoost), light gradient boosting machine (LightGBM), and random forest (RF)), we developed a new approach for estimating the vertical distribution of Kd(z, 650), KLu(z, 650), and Ku(z, 650) and applied it to the South China Sea (SCS). In this approach, based on in situ ß(ψ, z, 650), the absorption coefficient a(z, 650), the profile depths z, and Kd(z, 650), KLu(z, 650), and Ku(z, 650) calculated by Hydrolight 6.0 (HL6.0), three machine learning models (MLMs) without or with boundary conditions for estimating Kd(z, 650), KLu(z, 650), and Ku(z, 650) were established, evaluated, compared, and applied. It was found that (1) CatBoost models have superior performance with R2 ≥ 0.92, RMSE≤ 0.021 m-1, and MAPE≤ 4.3% and most significantly agree with HL6.0 simulations; (2) there is a more satisfactory consistency between HL6.0 simulations and MLMs estimations while incorporating the boundary conditions; (3) the estimations of Kd(z, 650), KLu(z, 650), and Ku(z, 650) derived from CatBoost models with and without boundary conditions have a good agreement with R2 ≥0.992, RMSE ≤0.007 m-1, and MAPE≤0.8%, respectively; (4) there is an overall decreasing trend with increasing depth and increasing offshore distance of Kd(z, 650), KLu(z, 650), and Ku(z, 650) in the SCS. The MLMs for estimating K(z, λ) could provide more accurate information for the study of underwater light field distribution, water quality assessment and the validation of remote sensing data products.

Highly sensitive gold nanoparticles-modified silver nanorod arrays for determination of methyl viologen.

Gold nanoparticles-modified silver nanorod (AuNPs@AgNR) arrays were fabricated as surface-enhanced Raman spectroscopy (SERS) substrates. The coffee ring effect of the AuNPs@AgNR was explored as a preconcentration method for enriching the target analytes and increasing the "hot spots." Furthermore, methyl viologen (MV) as a toxic herbicide used in agricultural production was successfully determined to investigate the application of the coffee ring effect on AuNPs@AgNR arrays and density functional theory (DFT) was employed to calculate its vibrational modes of corresponding characteristic peaks. Good linearity was obtained in the range 0.10-100 mg/L, and the limit of detection (LOD) of MV was estimated to be 0.01 mg/L, which was lower than the US maximum residue limits (MRLs). This method was also applied to practical detection of MV in river water and apple peel with LODs of 0.10 mg/L and 0.05 mg/L, respectively. SERS results suggest that the coffee ring on AuNPs@AgNR arrays provides a promising way for monitoring environmental pollution and food safety caused by pesticides.

Characteristics of subsurface chlorophyll maxima during the boreal summer in the South China Sea with respect to environmental properties.

Characterizing the vertical distribution of chlorophyll a in the water column in each oceanic region is crucial for accurate assessment of depth-integrated phytoplankton biomass. In this study, the characteristics of the subsurface chlorophyll maximum (SCM) in the South China Sea (SCS) during the boreal summer were investigated by using bio-optical and hydrological data collected during four cruises from 2008 to 2015. During the boreal summer, a well-developed SCM layer was found to be a prominent feature in the SCS, with the thickness, depth, and magnitude of the SCM exhibiting large spatial variability. The vertical position of the SCM varied between 11 and 99 m, with an average value of 53 m. Light attenuation played a fundamental role in determining the depth (ZSCM) and magnitude of the SCM (Chlmax), as reflected by their relationships with the euphotic zone depth (Zeu). However, because significant positive correlations were found between ZSCM and the depth of potential density at 23 kg m-3 (Zσ=23), physical processes were inferred to be more important in modulating the fluctuation of ZSCM, especially in open-ocean areas. Anticyclonic eddies, which act to deepen the nutricline by means of isopyncnal displacement, may play a role in aggravating nutrient limitation in the SCM layer, which leads to deepening of ZSCM, weakening of Chlmax, and a fall in the total integrated chlorophyll a within the euphotic layer (ChlintZeu). Knowledge of ocean physical conditions and the variability of ZSCM should be taken into consideration to improve the accuracy of ChlintZeu estimates based on the surface chlorophyll a concentration (Chlsurf), especially when Chlsurf is very low. Our assessment of SCM parameters provides the basis for a better understanding and quantification of their role in primary production estimation within the SCS.

Preparation of a silver nano-tripod structure by a tilting angle deposition technique and its SERS application.

A silver nano-tripod (AgNT) structure with a high-density "hot spots" distribution was fabricated by a tilting angle deposition technique. The electric field simulation distribution showed that the electric field enhancement of the AgNT structures is optimal when the tilting angle is 72°. Such AgNT substrates were successfully obtained experimentally when the included angle between the silver vapor and the normal of the sample platform was set to 86°. R6G and CV were used as probe molecules to investigate the SERS activity of AgNT, which revealed that the detection limits of AgNT for R6G and CV were 2.24×10-8 M and 4.01×10-8 M, the relative standard deviations (RSDs) were 4.26% and 4.44%, and the enhancement factors (EFs) were 9.58×106 and 1.16×107, respectively. The AgNT substrates with simple preparation and high distribution density of "hot spots" illustrate a good application prospect in environmental monitoring.

Development of an In Situ Analyzer Based on Sequential Injection Analysis and Liquid Waveguide Capillary Flow Cell for the Determination of Dissolved Reactive Phosphorus in Natural Waters.

This study presents an innovative technique for the in situ analysis of aquatic biochemical elements detected through wet chemical processes. A new compact in situ phosphate analyzer based on sequential injection analysis, liquid waveguide capillary flow cell and spectrophotometry was developed, and a safe and modular electronics-chemical separation mechanical structure was designed. The sequential injection system of this analyzer was optimized, and the major functions of this analyzer were studied and estimated. With a 10 cm liquid waveguide capillary flow cell and a 6.3 min time cost of detection, the analyzer reaches a detection limit of 1.4 µg·L-1 (≈14.7 nM, [PO43-]) and a consumption of 23 µL at most for each reagent. This analyzer was operated in situ and online during two scientific research cruises in the Pearl River Estuary and northern South China Sea. The advantages of this analyzer include its simple versatile manifold, full automation, low chemical consumption and electronics-chemical separate safe structure. Long-term in situ performance of this analyzer will be validated in the future.

Evaluating semi-analytical algorithms for estimating inherent optical properties in the South China Sea.

Using large amounts of bio-optical data collected in the South China Sea (SCS) from 2003 to 2016, this study checks the consistency between well-known semi-analytical algorithms (SAAs)-the quasi-analytical algorithm (QAA) and the default generalized inherent optical property (GIOP-DC)-in retrieving the non-water absorption coefficient (anw(λ)), phytoplankton absorption coefficient (aph(λ)) and particulate backscattering coefficient (bbp(λ)) from remote-sensing reflectance (Rrs(λ)) data at 412, 443, 490, 531, and 555 nm. The samples from the SCS are further separated into oligotrophic and mesotrophic water types for the comparison of the SAAs. Several findings are made: First, the values of anw(λ) derived from the two SAAs deliver similar performance, with R2 values ranging from 0.74 to 0.85 and 0.74 to 0.87, implying absolute percent error differences (APDs) from 37.93% to 74.88% and from 32.32% to 71.75% for the QAA and GIOP-DC, respectively. The QAA shows a value of R2 between 0.64 and 0.91 and APDs between 43.57% to 83.53%, while the GIOP-DC yields R2 between 0.76 to 0.89 and APDs between 44.65% to 79.46% when estimating aph(λ). The values of bbp(λ) derived from the QAA are closer to the in-situ bbp(λ) values, as indicated by the low values of the normalized centered root-mean-square deviation and normalized standard deviation, which are close to one. Second, a regionally tuned estimation of aph(λ) is proposed and recommended for the SCS. This consistency check of inherent optical properties products from SAAs can serve as reference for algorithm selection for further applications, including primary production, carbon, and biogeochemical models of the SCS, and can provide guidance for improving aph(λ) estimation.

Estimation of suspended particulate matter in turbid coastal waters: application to hyperspectral satellite imagery.

An empirical algorithm is proposed to estimate suspended particulate matter (SPM) ranging from 0.675 to 25.7 mg L-1 in the turbid Pearl River estuary (PRE). Comparisons between model predicted and in situ measured SPM resulted in R2s of 0.97 and 0.88 and mean absolute percentage errors (MAPEs) of 23.96% and 29.69% by using the calibration and validation data sets, respectively. The developed algorithm demonstrated the highest accuracy when compared with existing ones for turbid coastal waters. The diurnal dynamics of SPM was revealed by applying the proposed algorithm to reflectance data collected by a moored buoy in the PRE. The established algorithm was implemented to Hyperspectral Imager for the Coastal Ocean (HICO) data and the distribution pattern of SPM in the PRE was elucidated. Validation of HICO-derived reflectance data by using concurrent MODIS/Aqua data as a benchmark indicated their reliability. Factors influencing variability of SPM in the PRE were analyzed, which implicated the combined effects of wind, tide, rainfall, and circulation as the cause.

Retrieval of phytoplankton cell size from chlorophyll a specific absorption and scattering spectra of phytoplankton.

Phytoplankton cell size is an important property that affects diverse ecological and biogeochemical processes, and analysis of the absorption and scattering spectra of phytoplankton can provide important information about phytoplankton size. In this study, an inversion method for extracting quantitative phytoplankton cell size data from these spectra was developed. This inversion method requires two inputs: chlorophyll a specific absorption and scattering spectra of phytoplankton. The average equivalent-volume spherical diameter (ESDv) was calculated as the single size approximation for the log-normal particle size distribution (PSD) of the algal suspension. The performance of this method for retrieving cell size was assessed using the datasets from cultures of 12 phytoplankton species. The estimations of a(λ) and b(λ) for the phytoplankton population using ESDv had mean error values of 5.8%-6.9% and 7.0%-10.6%, respectively, compared to the a(λ) and b(λ) for the phytoplankton populations using the log-normal PSD. The estimated values of CiESDv were in good agreement with the measurements, with r2=0.88 and relative root mean square error (NRMSE)=25.3%, and relatively good performances were also found for the retrieval of ESDv with r2=0.78 and NRMSE=23.9%.

Identification of miR-601 as a novel regulator in the development of pancreatic cancer.

Pancreatic cancer (PC) is one of the most aggressive malignancies, with a high mortality. Distant metastasis and recurrence are the main causes of PC-related deaths. MicroRNAs (miRNAs) have been reported in the serum or tumor tissue of cancer patients, including PC, which makes them potential biomarkers. The dysfunction of many miRNAs has been linked to PC occurrence and metastasis. In the current study, we found that miR-601 expression was significantly lower in PC samples, especially in metastatic compared to non-metastatic PC tissues. Gain-of-function and loss-of-function analysis showed that miR-601 suppressed PC cell proliferation and migration. One potential mechanism is that miR-601 inhibited the expression of Sirtuin 1 (SIRT1), which is a well-known regulator of PC development. We found that overexpression of SIRT1 could reverse the effect of miR-601 on PC cells. Our investigation therefore suggests that both miR-601 and SIRT1 are possible biomarkers for the early detection, and targets for the treatment of PC.

Novel method for quantifying the cell size of marine phytoplankton based on optical measurements.

Phytoplankton size is important for the pelagic food web and oceanic ecosystems. However, the size of phytoplankton is difficult to quantify because of methodological constraints. To address this limitation, we have exploited the phytoplankton package effect to develop a new method for estimating the mean cell size of individual phytoplankton populations. This method was validated using a data set that contained simultaneous measurements of phytoplankton absorption and cell size distributions from 13 phytoplankton species. Comparing with existing methods, our method is more efficient with good accuracy, and it could potentially be applied in current in situ optical instruments.

Satellite-observed variability of phytoplankton size classes associated with a cold eddy in the South China Sea.

Ocean-color remote sensing has been used as a tool to detect phytoplankton size classes (PSCs). In this study, a three-component model of PSC was reparameterized using seven years of pigment measurements acquired in the South China Sea (SCS). The model was then used to infer PSC in a cyclonic eddy which was observed west of Luzon Island from SeaWiFS chlorophyll-a (chla) and sea-surface height anomaly (SSHA) products. Enhanced productivity and a shift in the PSC were observed, which were likely due to upwelling of nutrient-rich water into the euphotic zone. The supply of nutrients promoted the growth of larger cells (micro- and nanoplankton), and the PSC shifted to greater sizes. However, the picoplankton were still important and contributed ∼48% to total chla concentration. In addition, PSC time series revealed a lag period of about three weeks between maximum eddy intensity and maximum chlorophyll, which may have been related to phytoplankton growth rate and duration of eddy intensity.

[Construction and application of an onboard absorption analyzer device for CDOM].

Colored dissolved organic matter (CDOM) plays an important role in marine ecosystems. In order to solve the current problems in measurement of CDOM absorption, an automated onboard analyzer based on liquid core waveguides (Teflon AF LWCC/LCW) was constructed. This analyzer has remarkable characteristics including adjusted optical pathlength, wide measurement range, and high sensitivity. The model of filtration and injection can implement the function of automated filtration, sample injection, and LWCC cleaning. The LabVIEW software platform can efficiently control the running state of the analyzer and acquire real time data including light absorption spectra, GPS data, and CTW data. By the comparison experiments and shipboard measurements, it was proved that the analyzer was reliable and robust.

Approach for determining the contributions of phytoplankton, colored organic material, and nonalgal particles to the total spectral absorption in marine waters.

Using a data set of 1333 samples, we assess the spectral absorption relationships of different wave bands for phytoplankton (ph) and particles. We find that a nonlinear model (second-order quadratic equations) delivers good performance in describing their spectral characteristics. Based on these spectral relationships, we develop a method for partitioning the total absorption coefficient into the contributions attributable to phytoplankton [a(ph)(λ)], colored dissolved organic material [CDOM; a(CDOM)(λ)], and nonalgal particles [NAP; a(NAP)(λ)]. This method is validated using a data set that contains 550 simultaneous measurements of phytoplankton, CDOM, and NAP from the NASA bio-Optical Marine Algorithm Dataset. We find that our method is highly efficient and robust, with significant accuracy: the relative root-mean-square errors (RMSEs) are 25.96%, 38.30%, and 19.96% for a(ph)(443), a(CDOM)(443), and the CDOM exponential slope, respectively. The performance is still satisfactory when the method is applied to water samples from the northern South China Sea as a regional case. The computed and measured absorption coefficients (167 samples) agree well with the RMSEs, i.e., 18.50%, 32.82%, and 10.21% for a(ph)(443), a(CDOM)(443), and the CDOM exponential slope, respectively. Finally, the partitioning method is applied directly to an independent data set (1160 samples) derived from the Bermuda Bio-Optics Project that contains relatively low absorption values, and we also obtain good inversion accuracy [RMSEs of 32.37%, 32.57%, and 11.52% for a(ph)(443), a(CDOM)(443), and the CDOM exponential slope, respectively]. Our results indicate that this partitioning method delivers satisfactory performance for the retrieval of a(ph), a(CDOM), and a(NAP). Therefore, this may be a useful tool for extracting absorption coefficients from in situ measurements or remotely sensed ocean-color data.

An instrument for in situ measuring the volume scattering function of water: design, calibration and primary experiments.

The optical volume scattering function (VSF) of seawater is a fundamental property used in the calculation of radiative transfer for applications in the study of the upper-ocean heat balance, the photosynthetic productivity of the ocean, and the chemical transformation of photoreactive compounds. A new instrument to simultaneously measure the VSF in seven directions between 20° to 160°, the attenuation coefficient, and the depth of water is presented. The instrument is self-contained and can be automatically controlled by the depth under water. The self-contained data can be easily downloaded by an ultra-short-wave communication system. A calibration test was performed in the laboratory based on precise estimation of the scattering volume and optical radiometric calibration of the detectors. The measurement error of the VSF measurement instrument has been estimated in the laboratory based on the Mie theory, and the average error is less than 12%. The instrument was used to measure and analyze the variation characteristics of the VSF with angle, depth and water quality in Daya Bay for the first time. From these in situ data, we have found that the phase functions proposed by Fournier-Forand, measured by Petzold in San Diego Harbor and Sokolov in Black Sea do not fit with our measurements in Daya. These discrepancies could manly due to high proportion of suspended calcium carbonate mineral-like particles with high refractive index in Daya Bay.

Variations in the optical scattering properties of phytoplankton cultures.

The scattering and backscattering coefficients of 15 phytoplankton species were determined in the laboratory using the acs and BB9 instruments. The spectral variability of scattering properties was investigated and the homogenous sphere model based on Mie theory was also evaluated. The scattering efficiencies at 510 nm varied from 1.42 to 2.26, and the backscattering efficiencies varied from 0.003 to 0.020. The backscattering ratios at 510 nm varied from 0.17% to 0.97%, with a mean value of 0.58%. The scattering properties were influenced by algal cell size and cellular particulate organic carbon content rather than the chlorophyll a concentration. Comparison of the measured results to the values estimated using the homogenous sphere model showed that: (1) The model could well reproduce the spectral scattering coefficient with relative deviations of 5-39%, which indicates that cell shape and internal structure have no significant effects on predicting the scattering spectra; (2) Although the homogenous sphere model generally reflected the spectral trend of backscattering spectra for most species, it severely underestimated the backscattering coefficients by 1.4-48.6 folds at 510 nm. The deviations for Chaetoceros sp. and Microcystis aeruginosa were large and might be due to algal cell chain links and intracellular gas vacuoles, respectively.

[Variations in the optical absorption and attenuation properties of cultured phytoplankton and their relationships with cell size].

The spectral absorption and attenuation coefficients of 16 phytoplankton species were measured in the laboratory using acs instrument. Ancillary measurements included particle size distribution and chlorophyll a concentration (Chl a). The results indicated that both algal cell size and Chl a were the two major factors dominating the magnitudes of the spectral absorption and attenuation coefficients. The spectral behaviors of attenuation spectra were dominated by algal cell size, the relationship of them didn't follow the monotonic function. Both the ratio of absorption in blue and red waveband and the spectral slope of absorption coefficient were influenced by the product of algal cell density and squares of cell size rather than algal cell size alone. The relationship between algal cell size and both absorption and attenuation spectra would be interpreted by Mie theory for homogenous sphere, which imply that the heterogeneity and non-spherical shape in algal cell morphology and internal structure have little effect on the inherent association among them.

[Validation and analysis of water column correction algorithm at Sanya Bay].

Water column correction has been a substantial challenge for remote sensing. In order to improve the accuracy of coastal ocean monitoring where optical properties are complex, optical property of shallow water at Sanya Bay and the suitable water column correction algorithms were studies in the present paper. The authors extracted the bottom reflectance without water column effects by using a water column correction algorithm which is based on the simulation of the underwater light field in idealized water. And we compared the results which were calculated by the model and Christian's model respectively. Based on a detailed analysis, we concluded that: Because the optical properties of Sanya Bay are complex and vary greatly with location, Christian's model lost its advantage in the area. Conversely, the bottom reflectance calculating by the algorithm based on the simulation of the underwater light field in idealized water agreed well with in situ measured bottom reflectance, although the reflectance was lower than in situ measured reflectance value between 400 and 500 nm. So, it is reasonable to extract bottom information by using the water column correction algorithm in local bay area where optical properties are complex.

Variation of particulate organic carbon and its relationship with bio-optical properties during a phytoplankton bloom in the Pearl River estuary.

In this study, variations in the particulate organic carbon (POC) were monitored during a phytoplankton bloom event, and the corresponding changes in bio-optical properties were tracked at one station (114.29°E, 22.06°N) located in the Pearl River estuary. A greater than 10-fold increase in POC (112.29-1173.36 mg m⁻³) was observed during the bloom, with the chlorophyll a concentration (Chl-a) varying from 0.984 to 25.941 mg m⁻³. A power law function is used to describe the relationship between POC and Chl-a, and the POC:Chl-a ratio tends to change inversely with Chl-a. Phytoplankton carbon concentration is indirectly estimated using the conceptual model proposed by Sathyendranath et al. (2009), and this carbon is found to contribute 47.21% (±10.65%) to total POC. The estimated carbon-to-chlorophyll ratio of phytoplankton in diatom-dominated waters is found to be comparable with results reported in the literature. Empirical algorithms for determining the concentrations of Chl-a and POC were developed based on the relationships of these variables with the blue-to-green reflectance ratio. With these bio-optical models, the levels of particulate organic carbon and Chl-a could be predicted from the radiometric data measured by a marine optical buoy, which showed much more detailed information about the variability in biogeochemical parameters during this bloom event.

[Progress in Teflon AF LWCC/LCW applications].

Teflon AF is chemically very inert, quite physically and optically stable, a highly vapor-permeable polymer with optical transparency through much of the UV-Vis region and with an RI lower than that of water, so Teflon AF LWCC/LCW (Long path-length liquid waveguide capillary cell/liquid core waveguides) has been used with a range of different detection techniques, including absorbance spectroscopy, fluorescence spectroscopy, Raman spectroscopy, and gas sensor. The present article describes the properties and the aspects of Teflon AF LWCC/LCW instrumentation and applications. And finally,the future prospect and outlook of Teflon AF LWCC/LCW is also discussed.