Question #4 - Thorium Problem

Benthic food chains in the deep sea are severely limited by the rain of organic matter (aka food) that settles out of the top 100m of the water column. Construct a steady state ²³⁴Th IPOLA mass balance to estimate the flux of particles into the deep ocean. Work first in moles ²³⁴Th, then convert the ²³⁴Th particulate flux into an organic matter flux.

Then, assuming all the organic matter flux gets deposited to the ocean floor, calculate the gross vertical accretion rate of the deep ocean sediments.

Describe how you would then measure the net accretion rate for comparison.

Useful Information

²³⁸U Activity = 41.8 Bq m^-3

²³⁴Th Activity Dissolved = 11.3 Bq m^-3

²³⁴ Th Activity Particulate = 3.5 Bq m^-3

²³⁸U half life = 4.5 billion years

²³⁴Th half life = 24 days

Organic matter concentration = 100 mg m^-3 and a bulk density of 1.5 g cm^-3

*Bq defined as # of atoms disintegrating in a second.