The biological pump in the northwestern North Pacific based on fluxes and major components of particulate matter obtained by sediment-trap experiments (1997–2000)

To characterize the export flux of biogenic and lithogenic materials to the ocean interior and evaluate the ability of the biological pump to take up atmospheric CO2 in the northwestern North Pacific, sediment trap experiments were conducted at three stations (station KNOT: 44°N, 155°E; 50N: 50°N, 165°E; station 40N: 40°N, 165°E). The export fluxes showed seasonal variability with a high flux period in summer at station KNOT and in spring and autumn at stations 50N and 40N. The settling particles were mostly biogenic opal, comprising 50% of the total mass flux. The annual average export flux in 1998 was smaller than that in 1999 at the three stations, perhaps a result of the calm 1997/1998 winter associated with an El Niٌo event. Station KNOT had the largest total mass, organic carbon, and opal fluxes and the largest mole ratios of opal to carbonate (opal/CaCO3(mole)) and organic carbon to inorganic carbon (Co/Ci) compared with those at other two stations. These fluxes and ratios in the western, central and eastern parts of the northern North Pacific tended to decrease eastward. It is likely that the intensity of winter mixing or the supply of macro- and micronutrients influences the biogeochemistry of the northern North Pacific. Compared to the export flux of biogenic materials previously observed in the world ocean, the northwestern North Pacific, including the Bering Sea, has high opal/CaCO3(mole) and Co/Ci ratios. Moreover, at station KNOT, the ratio of the organic carbon flux in the deep sea to surface primary productivity (transfer efficiency: TE) was estimated to be approximately 5%, 3%, and 2% at 1000, 3000, and 5000 m, respectively. These values were significantly higher than TE values reported previously in the other oceanic regions. The high Co/Ci ratio and TE lead us to conclude that the biological pump in the northwestern North Pacific works more efficiently to decrease pCO2 in the surface seawater and, consequently, to enhance the uptake of atmospheric CO2 by the ocean.