The biogeochemical behavior of dissolved aluminum in the southern Yellow Sea: Influence of the spring phytoplankton bloom

Many recent studies have investigated the nutrient-type profiles of dissolved aluminum (Al) in the ocean. Significant scavenging of dissolved Al can occur during phytoplankton blooms, but the mechanism remains unclear. The distribution of dissolved Al in the southern Yellow Sea (SYS) was investigated in winter and spring 2009. Following measurements at grid stations during the spring sampling cruise, two drifting anchor surveys of more than 100 h were conducted to trace the variation of dissolved Al concentration during the spring phytoplankton bloom (SPB). The concentration of dissolved Al in the SYS decreased from 40 nmol/L in February to 30 nmol/L in March and 10-20 nmol/L in April, while the concentration of Chl a increased from < 2 mu g/L in March to > 4 mu g/L in April. The concentration of dissolved Al in the SYS decreased significantly with the development of the phytoplankton bloom, which indicated biological scavenging of dissolved Al from water column. The proportion of dissolved Al scavenged from water column by different phytoplankton species differed at the two drifting stations, with greater removal efficiency demonstrated by diatoms than dinoflagellates. Phytoplankton samples collected from the Chl a maximum layer were washed with trace metal clean reagent (oxalate-EDTA-citrate, abbreviate as oxalate solution, Tovar-Sanchez et al., 2003) to enable the surface-scavenged (extracellular) and intracellular Al pools associated with phytoplankton to be differentiated. Thirty-nine to ninety-six percent of the total Al was found to be existed in the interior pools, which indicated that biological absorption was the important way to scavenge dissolved Al during phytoplankton blooms in the SYS.