Global terrestrial carbon estimation map ecosystem extents assume

Global terrestrial carbon estimation • map ecosystem extents • assume C storage (t/ha) in: • vegetation • litter • soils LGM terrestrial biosphere: ~750 -1500 Gt smaller? (~35 -70% smaller? ) (Crowley, 1995)

Glacial atmospheric CO 2 lowering must be due to greater storage in ocean Modern surface p. CO 2 (Takahashi et al. , 2002) • at equilibrium, atmospheric p. CO 2 determined by Henry’s Law • p. CO 2 = [CO 2] / K 0 • need mechanisms to lower [CO 2] or raise K 0 (solubility)

dissolved inorganic carbon (DIC): SCO 2 = [CO 2] + [HCO 3 -] + [CO 32 -] ~1% ~90% ~10% where CO 2(aq) + H 2 CO 3 Therefore we can lower [CO 2] by: • decreasing DIC • shifting DIC equilibrium to right • cooling (slightly influences K 1 & K 2) • freshening (slightly influences K 1 & K 2) • alkalinity: DIC change

Temperature & salinity (effects on K values only) LGM temperature (colder) • CO 2 more soluble in cold waters (K 0 ) • DIC also shifts away from CO 2 ([CO 2] ) • could account for -30 ppm LGM salinity (saltier) • CO 2 less soluble in salty waters (K 0 ) • DIC also shifts toward CO 2 ([CO 2] ) • could result in +10 ppmv (Takahashi et al. , 2002)

What else determines the speciation of DIC (at constant T, S)? Electroneutrality In any solution, the sum of cation charges must balance the sum of anion charges Conservative alkalinity Excess of conservative cations over conservative anions (conservative: no [ ] change with p. H, T, or P) Alk = S(conserv. cation charges) - S(conserv. anion charges) = ([Na+] + 2[Mg 2+] + 2[Ca 2+] + [K+]…) - ([Cl-] + 2[SO 42 -]…) 2350 meq/kg

The conservative alkalinity excess positive charge is balanced primarily by three non-conservative acid-base systems: DIC, boron, and water Titration alkalinity Moles of H+ equivalent to the excess of proton acceptors (bases) over proton donors (acids) Alk [HCO 3 -] + 2[CO 32 -] + [B(OH)4 -] + [OH-] – [H+] carbonate alk borate alk water alk DIC therefore shifts to right as conservative alkalinity increases, providing more negative charges

DIC speciation and p. H H+ OH- • p. H and DIC systems “move together” in terms of charge • DIC buffers p. H changes • add strong acid: CO 2 forms, consuming H+, hindering p. H drop

Conservative alkalinity and DIC together • increase Alk/DIC: DIC shifts to right (p. CO 2 drops) • decrease Alk/DIC: DIC shifts to left (p. CO 2 rises) • add Alk/DIC at 1/1: very little change in DIC speciation Ca. CO 3 Dissolution: Alk: DIC 2: 1 Precipitation: Alk: DIC 2: 1 Organic matter Respiration: Alk: DIC Photosynthesis: Alk: DIC CO 2 gas Invasion: Alk: DIC Evasion: Alk: DIC Increase Decrease Lesser increase Lesser decrease

Carbonate system parameters • carbonate system can be reduced to four interdependent, measurable parameters: • DIC • alkalinity • p. CO 2 • p. H • full characterization requires measurement of only two

Some useful approximations DIC [HCO 3 -] + [CO 32 -] Alk carbonate alk = [HCO 3 -] + 2[CO 32 -] Therefore: [HCO 3 -] 2 DIC – Alk [CO 32 -] Alk – DIC And since: p. CO 2 = K 2[HCO 3 -]2 / K 0 K 1[CO 32 -] It follows that: p. CO 2 K 2(2 DIC – Alk)2 / K 0 K 1(Alk – DIC) Using average surface water values: 1% increase in DIC gives ~10% increase in p. CO 2 1% increase in Alk gives ~10% decrease in p. CO 2

Role of seafloor Ca. CO 3: Carbonate compensation DIC removed DIC added Ca. CO 3 dissolves with: • low T • high P • low [CO 32 -] undersaturation supersaturation

Carbonate compensation • say, DIC added to deep ocean at start of glaciation • deep ocean equilibrium shifts to left and CO 32 - drops • seafloor Ca. CO 3 dissolves, releasing Alk: SCO 2 in 2: 1 ratio • pushes equilibrium back to right until CO 32 - recovers • since initial SCO 2 addition was simple rearrangement within ocean, whole ocean has net Alk: SCO 2 gain • at sea surface, this shifts equilibrium to right (CO 2 drops)