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Carbonate Compensation, Answers:
The steady-state (default) value of [CO32-] in the model deep ocean is ~100 Mol kg-1. The initial deep [CO32-] s, after making the changes to [DIC], are, in each case: (a) ~140 Mol kg-1 (b) ~170 Mol kg-1 (c) ~70 Mol kg-1 and (d) ~50 Mol kg-1. The model does converge back towards the steady-state value of ~100 Mol kg-1 after each perturbation, and final values are more or less the same in each run.
[NB. 1 Mol kg-1 H" 1 mMol m-3 = 0.001 Mol m-3].
Lysocline depths immediately after the changes are (a) a deepening to >4 km following a doubling of [CO32-]; (b) a shallowing to <1.5 km following a halving of [CO32-].
The size of the CaCO3 burial flux is (a) ~1 Gt C yr-1 immediately after doubling of deep [CO32-], which exceeds the river flux of ~0.24 Gt C yr-1; and (b) ~0.1 Gt C yr-1 immediately after halving of deep [CO32-], which is less than the river flux of 0.24 Gt C yr-1. They do agree qualitatively with the schematic.
[NB. The constancy of the burial flux during the first 5 ky is an artefact of the model construction, which prevents the lysocline from being so shallow as to lie within the surface or middle boxes]
From visual inspection of the plots, it appears that it takes about 13 ky to return to steady-state after [CO32-] has been doubled, and somewhat greater than 20 ky to return to steady-state after [CO32-] has been halved. These durations are not dissimilar to the literature carbonate compensation times of 6-14 thousand years. It should be noted, however, that the system returns asymptotically to equilibrium and so it is in fact meaningless to talk about a response time unless it is precisely defined. In practise it is necessary to use some sort of more quantitative metric, such as the time to remove 90% of the original perturbation, or the e-folding response time (the latter is more commonly used).
Adding 2000 Gt C into135x1016 m3 equals a perturbation of about 0.123 Mol m-3 (about 123 Mol kg-1) to the DIC concentration. Increasing deep [DIC] by this amount causes the lysocline depth to shallow to <1.5 km, and deep [CO32-] to decrease to <50 Mol kg-1, i.e. less than half its steady-state value. Carbonate compensation brings [CO32-] back towards its steady-state value of about 100 Mol kg-1, but does not do the same for deep [DIC]. The final value of deep [DIC] is nearly 2500 Mol kg-1, approximately 200 Mol kg-1 higher than the value before the perturbation was made (~2300 Mol kg-1). ,@BD " ´m_N<*_#hCTh6xCJH*OJQJ^JaJ#hCTh6xCJH*OJQJ^JaJ hCTh6xCJOJQJ^JaJh6xCJOJQJ^JaJ#h6xhiCJH*OJQJ^JaJ#hCThiCJH*OJQJ^JaJ#hCThiCJH*OJQJ^JaJ hCThiCJOJQJ^JaJhiCJOJQJ^JaJ hCThP&CJOJQJ^JaJhCThP&5>*CJ^JaJh6x5>*CJ^JaJhCThKw=5>*CJ^JaJBDr
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Increasing deep [DIC] by 30 Mol kg-1 and deep [Alk] by 60 Equiv kg-1 causes the lysocline to fall by about 1 km, so that its initial value is 3.4 km (compared to its steady-state value of 2.4 km). Multiplying by the ocean volume of 135x1016 m3 gives the quantity of 4 x1016 Mol (i.e. 40 GMol) of CaCO3 that would have to be added in order to drop the CCD by 1km.
References.
Zeebe & Westbroek (2003) A simple model for the CaCO3 saturation state of the ocean: The Strangelove, the Neritan, and the Cretan Ocean. Geochem. Geophys. Geosyst., 4, 1104, doi:10.1029/2003GC000538.
Archer et al (1998) X,^,`,d,f,0-2-4-j-z-~-----------.*.-.0.ｯpp_NN_@@h?"CJOJQJ^JaJ hCThCJOJQJ^JaJ hCThxCJOJQJ^JaJ#h6xh@CJH*OJQJ^JaJh@CJOJQJ^JaJh-@CJOJQJ^JaJ hCTh@CJOJQJ^JaJhxCJOJQJ^JaJh/|CJOJQJ^JaJ#hCTh/|CJH*OJQJ^JaJ#hCTh/|CJH*OJQJ^JaJ hCTh/|CJOJQJ^JaJ0.=.^._.a....................//䳢䔃qbPBhh~CJOJQJ^JaJ#hCThCJH*OJQJ^JaJh-@CJH*OJQJ^JaJ#hJ{h-@CJH*OJQJ^JaJ h-@h-@CJOJQJ^JaJh-@CJOJQJ^JaJ hCTh?"CJOJQJ^JaJ#hJ{h?"CJH*OJQJ^JaJh@CJOJQJ^JaJ hCThCJOJQJ^JaJh?"CJOJQJ^JaJh#CJOJQJ^JaJ/////-/H/I////////88898:8W8ݽwddbUGUG7hCThCT6OJQJ^JhhCThCTH*OJQJ^JhCThCTOJQJ^JU$hCThCTB*OJQJ\^Jph'hCThCT6B*OJQJ\^Jph'hCThCT5B*OJQJ\^JphhCThCTH*OJQJ\^JhCThCTOJQJ\^JhCThCTOJQJ^Jh#hCTh5CJOJQJ^JaJ#hCThP&5CJOJQJ^JaJ hCTh?"CJOJQJ^JaJDynamics of fossil fuel CO2 neutralization by marine CaCO3. Global Biogeochem. Cycles, 12, 259-276;
Sundquist (1990) Influence of deep-sea benthic processes on atmospheric CO2. Phil. Trans. R. Soc. Lond. Ser. A, 331, 155-165.
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