The Effect of Fang-Liao Earthquake on Particulate Scavenging and Transport Processes in the Gaoping Submarine Canyon Deduced from Pb-210 Observations

Pb-210 were measured on the suspended particulate matter(SPM) and filtered water samples collected from five stations in the Gaoping Submarine Canyon (GPSC) during the 1201 cruise aboard R/V Ocean Researcher III in early January 2007, about two weeks after the Fang-Liao submarine earthquake (M > 6.5) occurred off southwest Taiwan. These stations were selected along the axis of the GPSC, and denoted as CW1 through CW5 sequentially from the shallow part near the mouth of the Gaoping River to the deep-water region of the canyon. The profile results of 210Pb determined from the 1201 cruise are compared with those at the same stations during the 1192 cruise aboard R/V Ocean Researcher III in late November 2006 to decipher the effect of earthquake on the particulate scavenging and lateral transport processes in this study area. The SPM concentrations measured from the 1201 cruise generally display an increase with depth, the values in the bottom water are more one order of magnitude higher than those observed above. The SPM profiles show a decrease away from the shore, the concentrations at CW1, CW2 and CW3 stations are an order of magnitude higher than those at CW4 and CW5 stations. The SPM spatial distribution trend of 1201 cruise is similar with that of 1192 cruise, but the SPM in the bottom water at all stations during 1201 cruise is from several to a few tens times higher than that from 1192 cruise, suggesting the effect of resuspension and slumping processes triggered by this submarine earthquake. The Pb-210 results observed during the 1201 cruise are described as below. The dissolved Pb-210 profiles generally show a decrease with depth, but an inverse trend is found in particulate Pb-210, responding to significant particulate scavenging. The mean values of particulate and dissolved Pb-210 obtained at CW1, CW2 and CW3 stations are respectively around 41-122 and 13-18 dpm/100kg and at other stations about 28-37 and 23-25 dpm/100kg, suggesting an increase toward offshore in dissolved Pb-210 and an inverse trend in particulate Pb-210 which are the same as trends observed from 1192 cruise. On the comparison of averages of particulate and dissolved Pb-210 activities between 1192 and 1201 cruises, the values (dpm/100kg) of particulate phase at all stations determined from 1201 cruise are two times higher than those from 1192 cruise, but the dissolved phase results from two cruise indicate no significant difference. According to the calculation of the particulate Pb-210 removal flux ratios from water column between 1201 and 1192 cruises, the values at CW2 and CW4 stations are around 1.0, and at other stations between 0.74 and 0.84, responding to the SPM dilution and particulate lateral transport processes.