1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Carbon 14, radioactive decay of ocean waters

  1. Nov 17, 2008 #1
    The youngest bottom waters in the North Atlantic had a [delta 14 C] value of approx -70o/oo (o/oo being parts per thousand). Bottom waters in the South Pacific have a [delta 14 C] value of -170o/oo, while bottom waters in the North Pacific had a [delta 14 C] value of -230o/oo.
    a)In the [delta 14 C] notation, the specific sample activity is approximately given by 1+([delta 14 C]/1000). Using this fromula, convert these [delta 14 C] values to specific carbon 14 activities. For this i got north atlantic-> 1+ (-70/1000)=0.93, south pacific->0.83, north pacific->0.77.
    b)Now, assume that a water mass sinks out of the north atlantic at t=0 with the specific activity based on a [delta 14 C] value of -70o/oo. Using the Radioactive Decay equation N=N0e^-(0.693t/(T1/2)), calculate the "age" of the waters in the south pacific and north pacific. recall that T1/2 is half-life and the half-life of carbon is 5,730 years.
    c)The average replacement or residence time for the entire ocean is ~500-1000 years. Please discuss the ages you calculated for north pacific and south pacific waters in the context of this average replacement time.

    Now, i'm stuck on part B i'm not sure whether to put the specific activity values in for N or N0. If i put it in for N and then put 0 for N0 as the initial value it doesn't work obviously. i don't know any guidance or assistance would be much appreciated. thanks
  2. jcsd
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted