Message from the new Editor-in-Chief     

Joji Ishizaka 《Journal of Oceanography》2015,71(2):161-161

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Announcement     

Joji Ishizaka 《Journal of Oceanography》2016,72(5):663-663

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Empirical ocean-color algorithms to retrieve chlorophyll-a, total suspended matter, and colored dissolved organic matter absorption coefficient in the Yellow and East China Seas   总被引：4，自引：1，他引：3  

Eko Siswanto  Junwu Tang  Hisashi Yamaguchi  Yu-Hwan Ahn  Joji Ishizaka  Sinjae Yoo  Sang-Woo Kim  Yoko Kiyomoto  Keiko Yamada  Connie Chiang  Hiroshi Kawamura 《Journal of Oceanography》2011,67(5):627-650

A bio-optical dataset collected during the 1998?C2007 period in the Yellow and East China Seas (YECS) was used to provide alternative empirical ocean-color algorithms in the retrieval of chlorophyll-a (Chl-a), total suspended matter (TSM), and colored dissolved organic matter (CDOM) absorption coefficients at 440 nm (ag₄₄₀). Assuming that remote-sensing reflectance (Rrs) could be retrieved accurately, empirical algorithms for T_Chl (regionally tuned Tassan??s Chl-a algorithm) in case-1 waters (T_Chl2i in case-2 waters), T_TSM (regionally tuned Tassan??s TSM algorithm), and T_ag440 or C_ag440 (regionally tuned Tassan??s or Carder??s ag₄₄₀ algorithm) were able to retrieve Chl-a, TSM, and ag₄₄₀ with uncertainties as high as 35, 46, and 35%, respectively. Applying the standard SeaWiFS Rrs, T_Chl was not viable in the eastern part of the YECS, which was associated with an inaccurate SeaWiFS Rrs retrieval because of improper atmospheric correction. T_Chl behaved better than other algorithms in the turbid case-2 waters, although overestimation was still observed. To retrieve more reliable Chl-a estimates with standard SeaWiFS Rrs in turbid water (a proxy for case-2 waters), we modified T_Chl for data with SeaWiFS normalized water-leaving radiance at 555 nm (nLw₅₅₅) > 2 mW cm^?2 ??m^?1 sr^?1 (T_Chl2s). Finally, with standard SeaWiFS Rrs, we recommend switching algorithms from T_Chl2s (for case-2 waters) to MOC_Chl (SeaWiFS-modified NASA OC4v4 standard algorithm for case-1 waters) for retrieving Chl-a, which resulted in uncertainties as high as 49%. To retrieve TSM and ag₄₄₀ using SeaWiFS Rrs, we recommend empirical algorithms for T_TSM (pre-SeaWiFS-modified form) and MT_ag440 or MC_ag440 (SeaWiFS Rrs-modified forms of T_ag440 or C_ag440). These could retrieve with uncertainties as high as 82 and 52%, respectively.  相似文献   

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

Young Baek Son  Joji Ishizaka  Jong-Chul Jeong  Hyun-Choel Kim  Taehee Lee 《Ocean Science Journal》2011,46(4):239-263

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.  相似文献   

Assessment of carbon- and fluorescence-based primary productivity in Ariake Bay,southwestern Japan     

S.C. Tripathy  J. Ishizaka  T. Fujiki  T. Shibata  K. Okamura  T. Hosaka  T. Saino 《Estuarine, Coastal and Shelf Science》2010

A comparative account of primary productivity (PP), in the characteristically turbid and highly dynamic waters of Ariake Bay, measured by ¹³C uptake and fast repetition rate fluorometer (FRRF) was conducted to ensure compatibility between the two methods. Estimates from both methods depicted strong linearity for both short-term (r² > 0.90) and daily (r² = 0.42–0.93) measurements, except in the near-surface (∼0 m) layer. ¹³C-based short-term (1 h; in situ) PP estimates showed similar magnitudes and trend with the instantaneous PP measured by FRRF concurrently. Whereas, unlike short-term measurements, the daily PP estimates from both methods showed large difference, with FRRF-based time integrated daily PP resulting in 1.09–1.82 times higher than the carbon-based daily (24 h; simulated in situ) PP. This difference between daily PP estimates was mainly due to: (1) the temporal variation of water column chlorophyll a (Chl a) because of frequent moving of water mass, and (2) the dissimilarity in ambient light field conditions between the two methods. Results revealed that considering the above two environmental factors invariable over a daylength, fairly close approximation of daily PP, compared to ¹³C-based daily PP, could be obtained from FRRF. Hence, FRRF-based daily PP can be considered as more realistic in this highly dynamic water body like Ariake Bay where water column parameters are subjected to strong temporal variation. The relationship between Chl a-specific photosynthetic rate (P^B) and the corresponding photosynthetically active radiation (PAR) in the water column (PAR–P^B relationship) was found to be linear for FRRF and curvilinear for ¹³C-based measurements in the near-surface layer, for the same intensities of incident PAR, and this is thought to be the primary basis for the higher difference in PP estimates at the near-surface layer. Considering the minor variations in FRRF-based time series of PAR–P^B relationships, a combined and/or instantaneous PAR–P^B relationship in combination with incubation Chl a and light field condition was used to obtain fairly close estimates of daily water column integrated PP from FRRF.  相似文献   

Possibility of recent changes in vertical distribution and size composition of chlorophyll-a in the western North Pacific region     

Hiroshi Ishida  Yutaka W. Watanabe  Joji Ishizaka  Toshiya Nakano  Naoki Nagai  Yuji Watanabe  Akifumi Shimamoto  Nobuhiro Maeda  Michimasa Magi 《Journal of Oceanography》2009,65(2):179-186

Our analysis of the last three decades of retrospective data of vertical distributions and size composition of chlorophyll-a (Chl-a) over the western North Pacific has revealed significant changes of three indices related to Chl-a during summer season, as follows: (1) decreasing linear trend of the proportion of Chl-a in surface layer to that of the whole water column by 0.4 and 2.3% year⁻¹ in the subtropical area along 137°E (STA₁₃₇) during 1972 to 1997 and in the Kuroshio Extension area along 175°E (KEA₁₇₅) during 1990 to 2001; (2) increasing linear trend of the depth of subsurface Chl-a maximum (DCM) by 0.4 and 2.6 m year⁻¹ in STA₁₃₇ and KEA₁₇₅; and (3) decreasing linear trend of larger-size Chl-a (>3 μm) by 0.1 and 2.5% year⁻¹ in STA₁₃₇ and KEA₁₇₅, respectively. Water density (σ _θ ) at 75 m depth had also decreased by 0.006 and 0.05 year⁻¹ in STA₁₃₇ and KEA₁₇₅, respectively. The ratio of biogenic opal to biogenic CaCO₃ in the sinking flux decreased by 0.015 year⁻¹ in the subtropical region from 1997 to 2005. These findings may indicate that the subsurface chlorophyll maximum is deepening and larger phytoplankton such as diatoms has been decreasing during the past decade, associated with the decreasing density of surface water caused by warming in the western North Pacific, especially in the summer.  相似文献   

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

Hiroaki Sasaki  Akihiko Tanaka  Mitsunori Iwataki  Yasuharu Touke  Eko Siswanto  Chun Knee Tan  Joji Ishizaka 《Journal of Oceanography》2008,64(4):511-523

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.  相似文献   

Satellite detection of red tide in Ariake Sound, 1998–2001     

Joji Ishizaka  Yasuhisa Kitaura  Yasuharu Touke  Hiroaki Sasaki  Akihiko Tanaka  Hiroshi Murakami  Toshikazu Suzuki  Kazumi Matsuoka  Hideaki Nakata 《Journal of Oceanography》2006,62(1):37-45

High resolution SeaWiFS data was used to detect red tide events that occurred in the Ariake Sound, Japan, a small embayment known as one of the most productive areas in Japan. SeaWiFS chlorophyll data clearly showed that a large red tide event, which damaged seaweed (Nori) cultures, started early in December 2000 in Isahaya Bay, expanded to the whole sound and persisted to the end of February 2001. The monthly average of SeaWiFS data from May 1998 to December 2001 indicated that the chlorophyll peaks appeared twice a year, in early summer and in fall, after the peaks of rain and river discharge. The SeaWiFS data showed that the red tide event during 2000–2001 winter was part of the fall bloom; however, it started later and continued significantly longer than other years. Satellite ocean color data is useful to detect the red tide; however the algorithms require improvement to accurately estimate chlorophyll in highly turbid water and in red tide areas.  相似文献   

Size-Fractionated Primary Production Estimated by a Two-Phytoplankton Community Model Applicable to Ocean Color Remote Sensing   总被引：3，自引：0，他引：3  

Takahiko?KamedaEmail author  Joji?Ishizaka 《Journal of Oceanography》2005,61(4):663-672

In order to estimate primary production from ocean color satellite data using the Vertical Generalized Production Model (VGPM; Behrenfeld and Falkowski, 1997), we propose a two-phytoplankton community model. This model is based on the two assumptions that changes in chlorophyll concentration result from changes of large-sized phytoplankton abundance, and chlorophyll specific productivity of phytoplankton tends to be inversely proportional to phytoplankton size. Based on the analysis of primary production data, P _opt ^B , which was one parameter in the VGPM, was modeled as a function of sea surface temperature and sea surface chlorophyll concentration. The two-phytoplankton community model incorporated into the VGPM gave good estimates in a relatively high productive area. Size-fractionated primary production was estimated by the two-phytoplankton community model, and P _opt ^B of small-sized phytoplankton was 4.5 times that of large-sized phytoplankton. This result fell into the ranges observed during field studies.  相似文献   

Arctic hazes in summer over Greenland and the North American Arctic: II. Nature and concentrations of accumulation-mode and giant particles     

Yutaka Ishizaka  Peter V. Hobbs  Lawrence F. Radke 《Journal of Atmospheric Chemistry》1989,9(1-3):149-159

Airborne measurements made during August 1985 over Greenland and its environs show that both accumulation-mode (0.1 m D2.0 m) and giant (D2 m) particles were present in relatively high concentrations in arctic haze layers and that the accumulation-mode particles dominated light scattering. Particles with diameters (D) between 1 and 4 m consisted predominately of mixed materials, small and dense inclusions, and probably organic compounds containing sulfur. Many of the particles from 0.1 to 1 m in diameter were also of mixed composition, with sulfuric acid, ammonium sulfate and organics probably the dominant constituents.  相似文献