1. Answer the following questions about 238U and 234Th activities in a body of water in the surface ocean with salinity S = 34.0. Assume that U is present in seawater as a conservative ion. The decay constant of 238U is 1.55 1010 yr1. The concentration of 238U is 13.11 nmol/kg.

a. Calculate the activity of 238U (A238) in this seawater in units of dpm/kg (disintegrations per minute per kilogram of seawater).

b. What is the activity of 234Th (A234) in this seawater if 238U and 234Th are in secular equilibrium? Please report your answer in units of dpm/kg.

c. The activity of 234Th (A234) in this body of seawater is 0.66 dpm/kg. Assuming that radioactive decay and scavenging by sinking particles are the only mechanisms that remove 234Th from this water, and that 234Th activity is in steady-state, calculate the scavenging rate constant, k, for 234Th. Report your answer in units of day-1.