The vertical attenuation of irradiance as a function of turbidity: a case of the Huanghai(Yellow) Sea in spring

The planar photosynthetically available radiation (PAR),turbidity and concentration of chlorophyll a (chl a),were measured at 26 stations in the Huanghai (Yellow) Sea during a cruise of China SOLAS from 19 to 27 March 2005.Due to low chl a (<0.35 mg·m^-3) in upper layers (above 5 m),suspended particulate matter became the major factor that influenced the turbidity in early spring.The calculated vertical diffuse attenuation coefficient of PAR,K_PAR,varied with water depths with a maximum value in the upper 5 m layer.The mean K_PAR in survey area was 0.277±0.07 m^-1 that is considerably higher than most of the other case 2 waters.Within the survey area,K_PAR also showed distinct regional characteristics,corresponding to the distribution of turbidity.Based on measurements,the relationship between K_PAR and turbidity as well as chl a was established.It was suggested that suspended particulate matter plays an important role in light attenuation in the Huanghai (Yellow) Sea in spring.