Biological pump strength estimated form 234Th in the northwestern North Pacific. [Go to Japanese Website]
What is 234Th (Thorium-234)?
234Th is the short-lived radionuclide (half-life, 24.1 days). This radionuclide is produced in the water column as a dissolved species by radioactive decay of the conservative 238U (half-life, 4.5 billion years) in seawater and is redistributed between the dissolved and particulate phases depending on particule reactivity and the availability of particle surfaces. Therefore, 234Th serves as a valuable tracer for studying the rates of particule-associated scavenging and the subsequent particle export from the euphotic zone (e.g., Buesseler, 1998).
What is biological pump?
Atmospheric CO2 dissolves in the surfece ocean. The dissolved CO2 is assimilated by phytoplankton in the sunlit layer (photosynthesis) and changes to particlate organic carbon (POC). POC sinks from surface to deep ocean. This role exported carbon to the deep ocean is biological pump.
Schematic of carbon cycle in the ocean.
Biological pump strength in the northwestern North Pacific.
The northwestern North Pacific Ocean experiences intense winter cooling and receives large supplies of nutrients though vertical mixing, resulting in high productivety and biological pump strength in spring and summer (e.g., Takahashi et al., 2002). As the results of our study, annual POC flux in this region was estimated to be 31 gC m-2 y-1 (Kawakami and Honda, 2007) and is twice and more higher than average value in the world ocean (13 gC m-2 y-1, Lutz et al., 2007).
Seasonal variability in POC fluxes in the northwestern North Pacific.