Chemical hydrography and chlorophyll a distribution in the East China Sea in summer: implications in nutrient dynamics

Abstract A survey of the chemical hydrography and Chla distribution in the middle and outer shelves of the East China Sea was carried out in July 1992. Very high standing stock of Chia (30–110 mg m−2) and supersaturation of oxygen (up to 130%) were observed in the plume of the Changjiang Diluted Water, which was enriched in nitrate and silicate but depleted in phosphate. Beneath the plume, a strong depletion in oxygen and an accompanied enrichment in nitrate as well as phosphate were evident. The rich phosphate in the subsurface water may have been crucial in supporting the rapid phytoplankton growth in the overlying water. The Taiwan Current Warm Water (TCWW) occupied most of the shelf to the south and to the east of the plume. The negative relationships between nitrate and temperature suggest that the nutrient-laden Kuroshio Sub-surface Water from the slope was the main source of nutrients for the TCWW. The input of the slope water to the shelf was probably facilitated by countercurrents associated with the Kuroshio upwelling northeast of Taiwan and the mesoscale eddy at the shelf-break east of the Changjiang river mouth. Yet another source of nutrients for the TCWW was revealed by the positive deviations from the mixing trend. These nutrients that may have originated from local remineralization accounted for up to 30% of the total nutrients in the bottom water on the middle shelf. Compared with the Changjiang river plume, the TCWW was relatively poor in Chia, except in the upwelling region off northern Taiwan where vertical mixing was strong. The nutrients in the subsurface layer of the TCWW further away from Taiwan were generally not available for phytoplankton uptake in the euphotic zone in summer. However, the reserved nutrients could have supported a phytoplankton bloom subsequent to strong vertical mixing.

[1]  P. Williams,et al.  Overall planktonic oxygen and carbon dioxide metabolisms: the problem of reconciling observations and calculations of photosynthetic quotients , 1991 .

[2]  Kon‐Kee Liu,et al.  Distribution of Organic Carbon in the KEEP Area Continental Margin Sediments , 1992 .

[3]  A. Kaneko,et al.  The characteristic distribution of silica over the East China Sea shelf slope , 1994 .

[4]  R. Wanninkhof.  Relationship between wind speed and gas exchange over the ocean , 1992 .

[5]  J. Edmond,et al.  Chemical dynamics of the Changjiang estuary , 1985 .

[6]  S. Chao,et al.  Response of Kuroshio upwelling to the onset of the northeast monsoon in the sea north of Taiwan: Observations and a numerical simulation , 1992 .

[7]  Yang Zuo-sheng,et al.  Transport and deposition of river sediment in the Changjiang estuary and adjacent continental shelf , 1985 .

[8]  S. Chao.  Circulation of the East China Sea, a numerical study , 1990 .

[9]  Min-Pen Chen,et al.  The Distributions of Calcareous Nannofossils and Grain Size in the Surface Sediments of the East China Sea and Their Relationship to the Current Pattern , 1995 .

[10]  Fei Zunle.  An analysis on the formation mechanism of the distribution of high content of chlorophyll-a in the continental shelf edge waters of East China Sea , 1992 .

[11]  Robert C. Beardsley,et al.  Discharge of the Changjiang (Yangtze River) into the East China Sea , 1985 .

[12]  R. Limeburner,et al.  Comparison of winter and summer hydrographic observations in the Yellow and East China Seas and adjacent Kuroshio during 1986 , 1994 .

[13]  J. Strickland.  A practical hand-book of seawater analysis , 1972 .

[14]  Joe Wang,et al.  The exchange of Kuroshio and East China Sea shelf water , 1990 .

[15]  Joe Wang,et al.  Blocking of the Kuroshio by the continental shelf northeast of Taiwan , 1993 .

[16]  Gwo-Ching Gong,et al.  The Year-Round Upwelling at the Shelf Break Near the Northern Tip of Taiwan as Evidenced by Chemical Hydrography , 1992 .

[17]  R. Limeburner,et al.  The structure of the Kuroshio southwest of Kyushu: velocity, transport and potential vorticity fields , 1992 .

[18]  Y. Chen.  Summer Phytoplankton Community Structure in the Kuroshio Current-Related Upwelling Northeast of Taiwan , 1992 .

[19]  T. Tang,et al.  Observations of the countercurrent on the inshore side of the Kuroshio northeast of Taiwan , 1993 .

[20]  S. Pai,et al.  Variability of the chemical hydrography at the frontal region between the East China Sea and the Kuroshio north-east of Taiwan , 1991 .

[21]  J. P. Riley,et al.  Effects of acidity and molybdate concentration on the kinetics of the formation of the phosphoantimonylmolybdenum blue complex , 1990 .

[22]  Yuan-hui Li.  Material Exchange Between the East China Sea and the Kuroshio Current , 1994 .

[23]  G. Gong,et al.  Determination of dissolved oxygen in seawater by direct spectrophotometry of total iodine , 1993 .

[24]  R. Aller,et al.  Early chemical diagenesis, sediment-water solute exchange, and storage of reactive organic matter near the mouth of the Changjiang, East China Sea , 1985 .

[25]  G. Gong,et al.  Prediction of nitrate concentration from two end member mixing in the southern East China Sea , 1995 .

[26]  Joe Wang,et al.  The intrusion of the Kuroshio across the continental shelf northeast of Taiwan , 1992 .