Anthropogenic CO 2 invasion

I. Anthropogenic CO 2 uptake

Tacoma, WA (1891)

A. “Perturbed” carbon cycle (1990s) Pre-industrial Anthropogenic Anthro Sources: Fossil fuels: 244 GtC Deforestation: ~140 GtC Anthro Sinks: Ocean: 118  19 GtC (~30%) Reforestation: ~100 GtC (~25%) Atmosphere: 165 GtC (~45%)

Pre-anthropogenic ocean:atmosphere DIC:CO 2 >60:1 (98%) Anthropogenic ocean:atmosphere uptake ~0.7:1 (40%) What limits ocean uptake of CO 2 ? How do we measure ocean uptake? What is the equilibrium capacity for uptake? What are the kinetic constraints?

B. Measuring ocean uptake 1. Direct measurement measure increase of DIC over time get expected rate of change from Revelle Factor measureable but small compared to spatio-temporal variability

2. Isolating anthro component of DIC inventory if pre-industrial preformed DIC were known, then it could be subtracted from observed preformed DIC pre-industrial preformed DIC estimated by additionally considering ventilation age (complicated)

Spatial pattern: Revelle Factor higher values mean smaller DIC rise for a given pCO 2 rise higher DIC waters have higher Revelle Factor (high lats) at constant Alk, adding DIC shifts equilibrium to left, towards CO 2 (aq) keeps equilibrium pCO 2 high and limits uptake of CO 2 Sabine et al. (2004) Science

low latitude surface has more uptake due to lower Revelle Factor (lower DIC) greater penetration into subtropical gyres and NADW Sabine et al. (2004) Science

Water column inventory of anthropogenic CO 2

C. Ocean’s equilibrium uptake capacity 1. DIC buffer ocean’s uptake capacity is large due to reaction with DIC calculate equilibrium uptake using Revelle Factor for top 75 m in equilibrium: 8% in ocean (ignoring land) for entire ocean volume: 81% in ocean timescale depends on mixing (e-folding ~300 y) since Revelle Factor rises as DIC rises, capacity will decrease in future

2. CaCO 3 buffer dissolution of seafloor CaCO 3 raises Alk:DIC 2:1 this drives DIC away from CO 2 (aq) and allows more uptake total ocean uptake now ~90% timescale depends on pore water diffusion and dissolution kinetics (e-folding ~4000 y)

3. Weathering buffer reaction with all CaCO 3 on land still leaves 8% in atmosphere silicate weathering ultimately removes rest of perturbation

Remaining in atmosphere ~50% after 400 y ~20% after 2000 y ~8% after 40,000 y

IPCC4 II. Ocean acidification CO 2 addition shifts DIC away from CO 3 2- and OH - (lower pH) surface pH has already dropped by 0.1 at constant Alk, 2X pCO 2 (560 ppm): CO 3 2- ↓30%, pH ↓0.3

aragonite lysocline has shoaled by o(100 m) in Indo-Pacific slight buffering due to reduced calcification (alkalinity gain) greater buffering possible via sediment dissolution (longer) Feely et al. (2004) Science