5 Isotopic Composition of Seawater 117
that the oceans are only very weakly linked to each other. For equations IV and V,
this would yield:
(El - e.AI) FS1 - (t"2 -el) CI W 1,2
(VIII)
(e2 - e-A2) FS2 - (el - e2) Cl Wl, 2
(IX)
By placing the residence time zNd into equation VIII, the mixing time T between
oceans I and 2 can be derived as follows:
For residence time ~:
~ J
where W 1 = mass of water in ocean i
and FSI = F A I = flux of Nd into the ocean
(C,W, 1 / ' E 2 - - E , "~
(see equation I)
(X)
W,._,)
\e, -
(XI)
Wl.2 = WI/T,
where W I: mass of water in the ocean,
and T : rate of exchange
T = w l/w~,2
(XII)
(Xll) in (XI):
z
~gJ -- EalJ
(XlII)
E-, (Pacific) - -3;
~1 (Atlantic) - - 12.0;
~:A I( Nd into the Atlantic) ~ -14.4 (assuming this corresponds to North
American shales "NASC")
T = 4ZN d ; ('~Nd = 2000 years)
(XIV)
T = 8000 years