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*Subject*: C-14*From*: joos@climate.unibe.ch (Fortunat Joos)*Date*: Wed, 2 Sep 1998 16:17:24 +0200

Dear Jim and Ray, Thank you for sending me your memo dealing with inclusion of C14 in OCMIP/GOSAC. I have the following comments: A) Suess Effect: >14CO2 should actually be constant from 1765 to first bomb test (~1954). > May want to check Enting record to see if this is true. This is not true. Delta-14C the 14C/12C ration have decreased by about 20 permil due to the addition of 14C free fossil fuel. This is the well known Suess Effect. The small decrease in the ratio implies that the total atmospheric 14C inventory has increased by a very similar amount as CO2. This is due to release of 14C from the ocean and the biosphere in response to the fossil perturbation. B) Calculation of 14C inventory and bomb-inventory - --------------------------------------------------- You may add a section (G) in your protocol to clarify how 14C inventory have to be calculated and properly compared with published inventories based on 14C observations. - ----------Section (G) to be added -------------------- (G) Calculation of 14C inventory and bomb-inventory and comparison with observations Inv-DIC-14(fractionation normalized) = Integral(zbottom,0) dz DIC-14 Inv-DIC-14 (denormalized) = Inv-DIC-14(fractionation normalized)/[1-2*(d13C(ocean)+25)/1000] with d13C(ocean)=1 permil : ~average d13C value in the thermocline/ocean. Published inventories such as those of Broecker et al 1985 and Broecker et al, 1995 are for the absolute number of 14C atoms and are thus to be compared with Inv-DIC-14(denormalized). - ----------end Section (G) to be added -------------------- The denormalized inventory is about 5 percent larger than the fractionation normalized inventory. The above equations are motivated by the following relationships: (1) R(normalized)=Rsample*[1-2*(d13Csample+25)/1000] where (2) Rsample= DIC-14/DIC-12~DIC-14/DIC is the isotopic ratio of a sample and R(normalize) is the fractionation corrected ratio as used in the calculation of (3) big Delta 14C = (R(normalized)/Rstd - 1) * 1000 It follows from (1) and (2): (4) DIC-14(sample) = DIC-14(normalized)/[1-2*(d13Csample+25)/1000] and straight forward: (5) Inv-DIC-14 (denormalized) = Inv-DIC-14(normalized)/[1-2*(d13C(ocean)+25)/1000] As we do not carry d13C in the model, we need to define d13C(ocean). d13C in the ocean is in the range of 0-2 permil. Thus potential uncertainties in Inv-DIC-14 (denormalized) related to the choice of d13C(ocean) are up to 0-4 permil, but usually much smaller. This uncertainty is negligible compared to the uncertainties in the observed inventories (10 percent). With best wishes, Fortunat - -- - ---------------------------------------------------------------------------- Fortunat Joos Physics Institute, KUP, Sidlerstr. 5, CH-3012 Bern Phone: ++41(0)31 631 44 61 Fax: ++41(0)31 631 44 05 e-mail: joos@climate.unibe.ch Internet: http://www.climate.unibe.ch/~joos/

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