SUBMICROMETER PARTICLES IN NORTHWEST PACIFIC COASTAL ENVIRONMENTS - ABUNDANCE, SIZE DISTRIBUTION, AND BIOLOGICAL ORIGINS

Submicrometer particles (SMP) are suggested to be a critical component for organic matter transitions in seawater, but little is known about variations and controls of SMP in coastal systems. We examined vertic al and horizontal distributions of SMP (0.4-1 mu m in equivalent spher ical diameter as measured by a resistive pulse particle counter) and b iological variables (chlorophyll a concentration, abundance of bacteri a, and heterotrophic nanoflagellates) in northwest Pacific coastal env ironments. The abundance and total volume of SMP in the upper 200 m va ried in the range of 5 x 10(4)-3 x 10(7) particles ml(-1) and 4 x 10(3 )-3 x 10(6) mu m(3) ml(-1), respectively. Over a large trophic gradien t (Chl a, 0.02-4 mu g liter(-1)), the total volume of SMP was strongly positively correlated with Chi a concentration (r = 0.90, P < 0.0001, n = 47) and with other microbial variables (r = 0.84-0.90), consisten t with a hypothesis that SMP dynamics are closely related to microbial food-web processes. Notably, size distribution of SMP in upper waters often exhibited a distinctive peak at a size range of 0.6-0.7 mu m, w hich was most pronounced in productive nearshore waters and became les s evident with depth and with distance from the shore. A sonication ex periment revealed that the 0.6-0.7-mu m particles are primarily nonliv ing. We hypothesize that SMP, particularly the 0.6-0.7-mu m component, are directly produced by biological processes. Our data suggest that SMP are a highly reactive and abundant component of detrital colloids and play important roles in material cycles within coastal systems.