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.     

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.     

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.     

Phytoplankton pigment change as a photoadaptive response to light variation caused by tidal cycle in Ariake Bay,Japan

Underwater light environment and photosynthetic accessory pigments were investigated in Ariake Bay in order to understand how change of the pigments occurs in response to the tidal-induced changes in underwater light conditions. We hypothesize that phytoplankton increases photo-protective pigments and decreases light-harvesting pigments under higher light condition in the mixed layer caused by tidal cycle. Contribution rates of non-phytoplankton particles (a _nph (400–700)) for light attenuation coefficient (K _d ) was highest (32–85%), and those of phytoplankton particles (a _ph (400–700)), dissolved organic matter (a _g (400–700)) and water were 6–32, 6–21 and 5–23%, respectively. Mean K _d was higher during the spring tide (0.55 ± 0.23 m⁻¹) than the neap tide (0.44 ± 0.16 m⁻¹), and the K _d difference was caused by the substances resuspension due to the tidal current. In contrast, ratios of photo-protective pigments (diadinoxanthin and diatoxanthin) per chlorophyll a ((DD+DT)/Chl a) were higher during the neap tide (0.10 ± 0.03 mg mg-Chl a ⁻¹) than the spring tide (0.08 ± 0.03 mg mg-Chl a ⁻¹). And there was significant positive correlation between (DD+DT)/Chl a and mean relative PAR in the mixed layer ($ \overline {I_{mix} } $ \overline {I_{mix} } ). Moreover, there was significant negative correlation between ratios of light-harvesting pigments (fucoxanthin) per Chl a (Fuco/Chl a) and $ \overline {I_{mix} } $ \overline {I_{mix} } . These results suggested that phytoplankton in Ariake Bay increase photo-protective pigments and decrease light-harvesting pigments in the higher light condition of less turbid, shallower mixed layer during neap tide than spring tide.     

<Emphasis Type="Italic">Cochlodinium polykrikoides</Emphasis> red tide detection in the South Sea of Korea using spectral classification of MODIS data

To distinguish true red tide water (particularly Cochlodinium polykrikoides blooms) from non-red tide water (false satellite high chlorophyll water) in the South Sea of Korea, we developed a systematic classification method using spectral information from MODIS level products and applied it to five different harmful algal bloom events. Red tide and nonred tide waters were classified based on four different criteria. The first step revealed that the radiance peaks of potential red tide water occurred at 555 and 678 nm. The second step separated optically different waters that were influenced by relatively low and high contributions of colored dissolved organic matter (CDOM) (including detritus) to chlorophyll. The third and fourth steps discriminated red tide water from non-red tide water based on the blue-to-green ratio in areas with lower and higher contributions of CDOM to chlorophyll, respectively. After applying the red tide classification (using the four criteria), the spectral response of the red tide water, which is influenced by pigment concentration, showed different slopes for the blue and green bands (lower slope at blue bands and higher slope at green bands). The opposite result was found for non-red tide water, due to decreasing phytoplankton absorption and increasing detritus/CDOM absorption at blue bands. The results were well matched with the discoloration of water (blue to dark red/brown) and delineated the areal coverage of C. polykrikoides blooms, revealing the nature of spatial and temporal variations in red tides. This simple spectral classification method led to increase user accuracy for C. polykrikoides and non-red tide blooms (>46% and >97%) and provided a more reliable and robust identification of red tides over a wide range of oceanic environments than was possible using chlorophyll a concentration, chlorophyll anomaly, fluorescence analysis, or proposed red tide detection algorithms.     

An optical model for the remote sensing of coloured dissolved organic matter in coastal/ocean waters

An optical model is developed for the remote sensing of coloured dissolved organic matter (CDOM) in a wide range of waters within coastal and open ocean environments. The absorption of CDOM (denoted as a_g) is generally considered as an exponential form model, which has two important parameters – the slope S and absorption of CDOM at a reference wavelength a_g(λ₀). The empirical relationships for deriving these two parameters are established using in-situ bio-optical datasets. These relationships use the spectral remote sensing reflectance (R_rs) ratio at two wavelengths R_rs(670)/R_rs(490), which avoids the known atmospheric correction problems and is sensitive to CDOM absorption and chlorophyll in coastal/ocean waters. This ratio has tight relationships with a_g(412) and a_g(443) yielding correlation coefficients between 0.77 and 0.78. The new model, with the above parameterization applied to independent datasets (NOMAD SeaWiFS match-ups and Carder datasets), shows good retrievals of the a_g(λ) with regression slopes close to unity, little bias and low mean relative and root mean square errors. These statistical estimates improve significantly over other inversion models (e.g., Linear Matrix-LM and Garver-Siegel-Maritorena-GSM semi-analytical models) when applied to the same datasets. These results demonstrate a good performance of the proposed model in both coastal and open ocean waters, which has the potential to improve our knowledge of the biogeochemical cycles and processes in these domains.     

Phytoplankton absorption and pigment adaptation of a red tide in the Benguela ecosystem

Phytoplankton absorption and pigment characteristics of a red tide were investigated in coastal waters of the southern Benguela. Diagnostic indices indicated that dinoflagellates were the dominant phytoplankton group, with diatoms and small flagellates being of secondary importance. Very high biomass was observed close to the coast where chlorophyll a concentrations of up to 117 mg m^–3 were measured. Both measured (a _ph) and reconstructed pigment absorption (a _pig) displayed an increasing trend with chlorophyll a, while the package effect index (Q^* _a) decreased, indicating increased packaging with an increase in biomass. Proportioning of the total pigment absorption between 400 and 700 nm revealed that chlorophyll a accounted for 39–65% of the absorption, while photosynthetic carotenoids (15–30%) and chlorophyll cs (15–30%) were also prominent in absorbing light for photosynthesis.     

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.     

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。     

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.     

Bio-Optical Properties of Seawater in the Western Subarctic Gyre and Alaskan Gyre in the Subarctic North Pacific and the Southern Bering Sea during the Summer of 1997

Chlorophyll a concentrations (chla) and the absorption coefficients of total particulate matter [a _p()], phytoplankton [a _ph()], detritus [a _d()], and colored dissolved organic matter: CDOM [a _CDOM()] were measured in seawater samples collected in the subarctic North Pacific and the southern Bering Sea during the summer of 1997. We examined the specific spectral properties of absorption for each material, and compared the light fields in the Western subarctic Gyre (area WSG) with those in the Alaskan Gyre (area AG), and the southern Bering Sea (area SB). In the area WSG, the irradiance in the surface layer decreased markedly, indicating high absorption. In the area AG, the radiant energy penetrated deeply, and the chl a and absorption values were low throughout the water column. In the area SB, light absorption was high in the surface layer on the shelf edge and decreased with increasing depth; on the other hand, light absorption was low in the surface layer in the shelf area and increased with increasing depth.     

Comparison of Chlorophyll a Concentrations Obtained with 90% Acetone and N,N-dimethylformamide Extraction in Coastal Seawater

Determinations of Chlorophyll a (Chl a) in eutrophic coastal marine waters were compared using N, N-dimethylformamide (DMF) and 90% acetone techniques. Measured Chl a concentrations ranged from 0.89 to 10.65 μg l₋₁ for 90% acetone extracts and from 0.97 to 12.92 μg l⁻¹ for DMF extracts, respectively, for 24 surface water samples from the Harima-nada, Seto Inland Sea, Japan. Chl a concentrations using DMF as a solvent were consistently higher than those found using 90% acetone (p < 0.001, n= 24). Chl a is thus likely to be underestimated (by 13%) when 90% acetone is used for eutrophic waters. This revised version was published online in July 2006 with corrections to the Cover Date.     

Initial validation of GOCI water products against in situ data collected around Korean peninsula for 2010–2011

This paper provides initial validation results for GOCI-derived water products using match-ups between the satellite and ship-borne in situ data for the period of 2010?C2011, with a focus on remote-sensing reflectance (R _rs ). Match-up data were constructed through systematic quality control of both in situ and GOCI data, and a manual inspection of associated GOCI images to identify pixels contaminated by cloud, land and inter-slot radiometric discrepancy. Efforts were made to process and quality check the in situ R _rs data. This selection process yielded 32 optimal match-ups for the R _rs spectra, chlorophyll a concentration (Chl_a) and colored dissolved organic matter (CDOM), and with 20 match-ups for suspended particulate matter concentration (SPM). Most of the match-ups are located close to shore and thus the validation should be interpreted limiting to near-shore coastal waters. The R _rs match-ups showed the mean relative errors of 18?C33% for the visible bands with the lowest 18?C19% for the 490 nm and 555 nm bands and 33% for the 412 nm band. Correlation for the R _rs match-ups was high in the 490?C865 nm bands (R²=0.72?C0.84) and lower in the 412 nm band (R²=0.43) and 443 nm band (R²=0.66). The match-ups for Chl_a showed a low correlation (<0.41) although the mean absolute percentage error was 35% for the GOCI standard Chl_a. The CDOM match-ups showed an even worse comparison with R²<0.2. These match-up comparison for Chl_a and CDOM would imply the difficulty to estimate Chl_a and CDOM in near-shore waters where the variability in SPM would dominate the variability in R _rs . Clearly, the match-up statistics for SPM was better with R²=0.73 and 0.87 for two evaluated algorithms, although GOCI-derived SPM overestimated low concentration and underestimated high concentration. Based on this initial match-up analysis, we made several recommendations -1) to collect more offshore under-water measurements of the R _rs data, 2) to include quality flags in level-2 products, 3) to introduce an ISRD correction in the GOCI processing chain, 4) to investigate other types of in-water algorithms such as semianalytical ones, and 5) to investigate vicarious calibration for GOCI data and to maintain accurate and consistent calibration of field radiometric instruments.     

后赤潮过程中现场水样的三维荧光光谱特征分析

对发生在青岛近岸水域的后赤潮过程中赤潮藻密度、藻种进行鉴别的同时,对现场水样的三维荧光光谱进行了测量,获得了一套三维特征荧光数据。分析结果表明,1）当海水中生物密度达到或接近赤潮密度时,Ex最高峰值波长位于245nm,Em最高峰值波长在445nm,激发转折波长在260nm,荧光转折波长在245nm;2）在非赤潮区,Ex...     

The proportions and variations of the light absorption coefficients of major ocean color components in the East China Sea

The East China Sea (ECS),one of the largest continental seas,has dynamic hydrology and complex optical characteristics that make ocean color remote-sensing retrieval difficult.The distributions and proportions of the light absorption coefficients of major ocean color components based on two large-scale investigations in the ECS are presented,showing these features in typical summer and winter seasons.The absorption coefficient a CDOM,a NAP and a phy of colored dissolved organic matter,non-algal particle,and pigment of phytoplankton show a decreasing trend from the coast to the outer shelf.According to the a CDOM distribution at 440 nm,the Changjiang River plume shows an abnormal southeastward transport.An extremely high a NAP value patch at 440 nm is present in the middle coast.The chlorophyll-a-specific phytoplankton pigment absorption (a phy) is much higher in winter than in summer,which may cause serious underestimated results when applying the averaged a phy into remote-sensing algorithms for chlorophyll concentration retrieval.The importance of phytoplankton size was evident in outer shelf waters.The absorption of a CDOM (440) is a dominant component accounting for over half of the total seawater absorption in summer.The a NAP (440) accounts for 64% of the absorption of the ECS coastal area in winter.     

珠江口溶解有机物的遥感动态监测

河口有色溶解有机物（colored dissolved organic matter,CDOM）的分布是各种物理-生物地球化学过程共同作用的结果。为实现河口高动态变化CDOM的监测，遥感是一种重要的手段。由珠江口四个不同季节的航次获得的实测数据，本文构建了一个遥感算法以反演CDOM在400 nm的吸收系数（a_CDOM （400））。该算法使用以波段反射率比值R_rs （667）/R_rs （443）和R_rs （748）/R_rs （412）为自变量。将构建的算法应用于2002-2014年的MODIS/Aqua数据，本文计算了珠江口不同季节的a_CDOM （400）气候态分布。CDOM的分布主要受珠江径流量和区域水下地形特征的影响。沿着垂直于水深梯度的断面，气候态a_CDOM （400）呈指数减少（y=ae^bx,b<0），但不同季节差异很大。珠江口CDOM主要是河流淡水输运而来。其中，富里酸比例随盐度的增加而降低。基于构建的算法、CDOM保守混合方程和径流量，本文由MODIS/Aqua数据进一步估算了2002-2014年夏季和冬季珠江DOC的有效入海浓度和有效入海通量。珠江的有效入海浓度和有效入海通量都与流量存在正相关关系，且在夏季的相关性更明显，R2分别为0.698和0.9657。     

Reconstruction of pH in the Surface Seawater over the North Pacific Basin for All Seasons Using Temperature and Chlorophyll-<Emphasis Type="Italic">a</Emphasis>

We found a simple function of pH that relates to sea surface temperature (SST, K) and chlorophyll-a (Chl, µg l⁻¹) using measured surface seawater pH, SST and Chl data sets over the North Pacific: pH (total hydrogen scale at 2°C) = 0.01325 SST − 0.0253 Chl + 4.150 (R² = 0.95, p < 0.0001, n = 483). Moreover, evaluating the seasonal variation of pH based on this algorithm, we compared the measured pH with the predicted pH at the observational time series stations in subpolar and subtropical regions. The average of ΔpH (measured - predicted, n = 52) was 0.006 ± 0.022 pH. Therefore, the combination of SST and Chl can allow us to determine the spatiotemporal distribution of pH over the North Pacific. Using the climatological data sets of SST and Chl with our pH algorithms, we have described the seasonal distributions of pH at 25°C (pH₍₂₅₎) and pH in situ temperature (pH_(T)) over the North Pacific surface water.     

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.     

东亚边缘海区浮游植物春华的纬向与年际变化

Combined studies of latitudinal and interannual variations of annual phytoplankton bloom peak in East Asian marginal seas(17°–58°N, including the northern South China Sea(SCS), Kuroshio waters, the Sea of Japan and the Okhotsk Sea) are rarely. Based on satellite-retrieved ten-year(2003–2012) median timing of the annual Chlorophyll a concentration(Chl a) climax, here we report that this annual spring bloom peak generally delays from the SCS in January to the Okhotsk Sea in June at a rate of(21.20±2.86) km/d(decadal median±SD). Spring bloom is dominant feature of the phytoplankton annual cycle over these regions, except for the SCS which features winter bloom. The fluctuation of the annual peak timing is mainly within ±48 d departured from the decadal median peak date, therefore this period(the decadal median peak date ±48 d) is defined as annual spring bloom period. As sea surface temperature rises, earlier spring bloom peak timing but decreasing averaged Chl a biomass in the spring bloom period due to insufficient light is evident in the Okhotsk Sea from 2003 to 2012. For the rest of three study domains, there are no significant interannual variance trend of the peak timing and the averaged Chl a biomass. Furthermore this change of spring phytoplankton bloom timing and magnitude in the Okhotsk Sea challenges previous prediction that ocean warming would enhance algal productivity at high latitudes.     

油藻混合水体遥感反射比光谱分析

辐射传输模式HydroLight是研究水体辐射传输特性的有效工具,同时也是进行石油类水体辐射传输特性的有效模型。本文基于2018年8月在辽宁大连港海域实测的石油类污染水体的表观及固有光学量数据,通过设置不同浓度的配比模拟试验,利用HydroLight对油类物质和藻类物质的单一组分和两者混合水体的遥感反射比（remote sensing reflectance,R_rs）光谱进行了模拟。模拟结果表明：（1）在仅含油类物质单一组分的水体中,R_rs随着油浓度C_oil的变化分为两个特征波段：400~480 nm和480~700 nm。在400~480 nm波段范围内R_rs随C_oil的增加而减小,在480~700 nm随C_oil的增大而增大;（2）在仅含藻类物质的单一成分水体中,叶绿素的光谱特性需要其浓度C_chl达到一定值才能表现出来,在低C_chl时的R_rs光谱特性反映为纯水的光谱特性;（3）在油藻混合水体中,随C_oil的增加会增大叶绿素的R_rs,但不会明显改变叶绿素的R_rs随波长的变化趋势,这说明油藻混合水体的光谱形状主要受叶绿素的影响,油类物质的存在只改变光谱的量值。利用HydroLight对石油类污染水体的R_rs展开研究,有助于丰富水色遥感基础研究,对完善各类水体生物光学模型研究具有重要的理论意义。