Seasonal and spring interannual variations in satellite-observed chlorophyll-a in the Yellow and East China Seas: New datasets with reduced interference from high concentration of resuspended sediment

Seasonal and spring interannual variations in chlorophyll-a (Chl) and total suspended matter (TSM) in the Yellow and East China Seas through a 10-year period were examined by using new datasets from Yellow Sea Large Marine Ecosystem Ocean Color Project (YOC) algorithms. YOC SCHL calculations are based on a combination of the SeaWiFS standard algorithm and a local empirical algorithm for areas of low and high normalized water leaving radiance 555 nm, respectively. YOC SCHL was lower than the standard SCHL in areas with high concentrations of resuspended sediment, especially along the Chinese and Korean coasts and around the Changjiang Bank from fall to spring. YOC SCHL was high in areas of low TSM in the middle of the Yellow Sea, and off shore of the Changjiang Bank in April, indicating the occurrence of spring blooms. In these areas, TSM was dominated by phytoplankton cells and phytoplankton-related organic particles. Offshore from the Changjiang River mouth and around the Changjiang Bank, YOC SCHL and TSM in March were low and high, respectively, with maximum YOC SCHL values occurring around the Changjiang Bank in May. Spring bloom started with decrease in resuspended sediment concentrations in these areas. During summer, YOC SCHL values were high and TSM concentrations were low; TSM was dominated by organic particles related to phytoplankton activity when Changjiang River diluted water moved from the river mouth to east of the bank. YOC SCHL in spring offshore from the Changjiang River mouth increased significantly during the 10 years, and correspond to an increase in redtide events. In the middle of the Yellow Sea, maximum YOCS CHL in spring increased gradually and significantly during the 10 years. Many of the spatial and temporal variations in YOC SCHL were consistent with a range of earlier in situ descriptions. Our results indicate that the satellite ocean data with proper algorithms is a powerful tool to analyze phytoplankton dynamics in moderate-high suspended sediment area

Particle Distributions and Transport Processes in the East China Sea

MASFLEXプロジェクトの一環として, 東シナ海のPN線を中心とした陸棚, 陸棚斜面, 沖縄舟状海盆, 及び隣接外洋域において粒状懸濁物, 濁度の分布を調べると共に, セディメントトラップ, 濁度計, 流速計の短期・長期係留実験を実施した. その結果, クロロフィル, 生物起源粒状珪素等の分布から陸棚における植物プランクトンの春季増殖, 及び長江沖の高生産力域が明瞭に示された。一方, 陸起源粒状珪素, 濁度等の分布から, 夏季・秋季の陸棚における海底高濁度層の顕著な発達と冬季鉛直混合による内部陸棚域での活発な再懸濁過程が明らかとなった. 沖縄舟状海盆の中・深層における粒子フラックスは, 陸棚上の季節風変動パターン, 台風等との関連が示峻され, 陸棚斜面域における粒子フラックスは内部潮汐の影響を大きく受けていることが示された. これらのことから, 沖縄舟状海盆の中・深層における粒子フラックスは, 海盆表層からの鉛直輸送よりは主に陸棚からの水平輸送によるものと推察された. また, 陸棚域における粒子フラックスと基礎生産量との比較から, 基礎生産量の5～20%程度が沈降粒子として有光層下に運ばれていることが明らかとなった.We have conducted a long- and short-term particulate flux studies using sediment traps together with turbidity and current meters on the shelf, slope, Okinawa Trough in the East China Sea and the adjacent Pacific Ocean. Temporal and spatial variations of suspended matter and turbidity were also studied. The distribution of chlorophyll a and particulate biogenic silica (BSiO_2) showed a phytoplankton spring bloom on the shelf and a high productive area off Changjiang River. On the other hand, the distribution of particulate lithogenic silica (LSiO_2) and turbidity revealed a well-developed bottom turbid layer on the shelf in summer and autumn, and resuspended bottom sediments of the entire water column on the inner shelf, particularly in winter mixing period. The variability of particle fluxes at the deep waters of the Okinawa Trough was seasonally coupled to local climate and oceanographic events such as monsoon wind and typhoon. The variability of particle fluxes on the slope was also influenced by the short-term events such as internal tide. The observation showed that resuspension and near-bottom transport of the sedimented particles from the shelf to the Okinawa Trough may be key processes of cross-shelf transport of biogenic and lithogenic particles. Further, 5-20% of annual primary production was transported into deep layers, indicating that the most of primary production is utilized within the euphotic zone

Image-based goniometric appearance characterisation of bronze patinas

Patinas are a form of metal polychromy used to decorate metallic artworks. Due to the nature of the metallic surface, their colour and gloss is perceived differently when the illumination and viewing directions vary. Sparkle effect on surfaces is a physical phenomenom caused by micro-facets on the surface coating which are also perceived with changing viewing and illumination geometry. In this paper, a method designed for the measurement of sparkle is applied for the goniometric characterisation of bronze patinas. Using a set of six different patinas, in three colours and two surface finishes, it is found that these surfaces exhibit different appearance when illuminated and viewed at different angles. Moreover, the roughness of the patinas is measured and as expected, as the roughness increases the specular reflection peak decreases. The experiment is repeated at two different institutions with different sets of equipment to test its repeatability and robustness. The sparkle is presented as a function of the angle of tilting, and it is characterised by its maximum value and full-width halfmaximum. It is found that the maximum and the roughness have a negative exponential relationship whereas the full-width halfmaximum and the roughness have a linear relationship

Unique Dispersal of the Changjiang-Diluted Water Plume in the East China Sea Revealed from Satellite Monitoring of Colored Dissolved Organic Matter (CDOM)

The optical properties of colored dissolved organic matter (CDOM) in the Changjiang (Yangtze River) plume water were investigated during the summer of 2009 and 2010. The absorption coefficient of CDOM at 325 nm (aCDOM) increased inversely with decreasing sea-surface salinity (SSS), implying that aCDOM can be used as a natural tracer of Changjiang-diluted water (CDW). This aCDOM vs. SSS relationship, however, differed between 2009 and 2010. For mapping the CDW plume, the aCDOM was retrieved from an ocean-color satellite. Values of SSS were also derived from the satellite-retrieved aCDOM using field-based SSS vs. aCDOM relationships. Satellite observations revealed the temporary variable eastward extension of a high aCDOM, low SSS CDW plume in the central East China Sea (ECS) during the summer. The CDW plume during the summer of 2010 extended southeastward from the mouth of the Changjiang (Yangtze River) to almost 26°N. Moreover, the branch of this southeastward CDW plume was seen to extend northeastward to the eastern ECS where the Kuroshio Current flows northeastward along the shelf break. Subsequently, this branch was distributed around southern Kyushu. Satellite observations revealed this unique dispersal of the CDW plume, which illustrates that the aCDOM and SSS from ocean-color satellite data are useful for monitoring the dispersal of this river-water plume

Empirical ocean-color algorithms to retrive chlorophyll-a, total suspended matter, and colored dissolved organic matter absorption coefficient in the yellow and East China Seas

A bio-optical dataset collected during the 1998–2007 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 TChl (regionally tuned Tassan’s Chl-a algorithm) in case-1 waters (TChl2i in case-2 waters), TTSM (regionally tuned Tassan’s TSM algorithm), and Tag440 or Cag440 (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, TChl was not viable in the eastern part of the YECS, which was associated with an inaccurate SeaWiFS Rrs retrieval because of improper atmospheric correction