Ciclo global del carbono Land use change Land sink y su perturbación antropogénica

DEFINITION: within a given reservoir (ocean, land or atmosphere), the excess is the increase in carbon compared to it’s the stock during preindustrial times. WHERE IS IT: everywhere, land, ocean and atmosphere WHERE can you MEASURE IT: atmosphere, and ocean (can be inferred), land is too heterogeneous. DISTRIBUTION:

Anthropogenic CO 2 Budget 1800 to 1994 CO 2 Sources[Pg C] (1) Emissions from fossil fuel and cement production a 244 (2) Net emissions from changes in land-use b 110 (3) Total anthropogenic emissions = (1) + (2)354 Partitioning among reservoirs[Pg C] (4) Storage in the atmosphere c 159 (5) Storage in the ocean d 112 (6) Terrestrial sinks = [(1)+(2)]-[(4)+(5)]83 a: From Marland and Boden [1997] (updated 2002) b: From Houghton [1997] c: Calculated from change in atmospheric pCO 2 (1800: 284ppm; 1994: 359 ppm) d: Based on estimates of Sabine et al. [1999], Sabine et al. [2002] and Lee et al. (submitted) The ocean uptake a great part of C ANT and they storage it. Thanks to them global warming is mitigated Uptake: across the air-sea interface Storage: accumulation in the water column Transport: contrary to trees, oceans move!!, C ANT is redistributed within the oceans

- once in the ocean the CO2 uptaken does not affect the radiactive balance of the Earth - to predict the magnitude of climate change in the future - within the carbon market (Kyoto) is important to know where is stored, important for policy makers - we need to know the magnitude of the sinks and sources, and their variability and factors controlling them - predict the future behavior of the ocean as a sink of CANT within a given emission scenario - to control the effectiveness of the mitigation and control mechanisms as emission policies and sequestering mechanisms

Globally integrated flux: 2.2 PgC yr -1

Preindustrial Flux Anthropogenic Flux

WOCE/JGOFS/OACES Global CO 2 Survey OBJECTIVES: + quantify the CO2 storage in the oceans + provide a global description of the CO2 variables distribution in the ocean to help the development of global carbon cycle models + characterize the transport of heat, salt and carbon in the ocean and the air-sea CO2 exchange.

+ CANT is estimated or inferred, not measured + there are several methods, the most popular is Gruber et al. (1996), back-calculation technique (more during S1). + the CANT signal over TIC is very low 60/2100 = 3%

GSS’96 defined the semiconservative parameter  C*(  ), it depends on the anthropogenic input, thus, the water mass age (  ), and its include the air-sea desequilibrium constant with time:  C*(  ) = C ANT +  C Tdis

To separate the anthropogenic CO 2 signal from the natural variability in DIC. This requires the removal of i)the change in DIC that incurred since the water left the surface ocean due to remineralization of organic matter and dissolution of CaCO 3 (  DIC bio ), and ii)a concentration, DIC sfc-pi, that reflects the DIC content a water parcel had at the outcrop in pre-industrial times, the equilibrium concentration plus any disequilibrium Thus,  C ant = DIC -  DIC bio - DIC sfc-pi = DIC –  DIC bio – DIC  DIC dis Assumptions: natural carbon cycle has remained in steady-state

44.5  5 Pg 44.8  6 Pg 20.3  3 Pg Indian Ocean Pacific Ocean Atlantic Ocean (Sabine et al, Science 2004) Inventory of C ANT for year 1994 = 110 ± 13 Pg C 15% area 25% inventorio SO, south of 50ºS 9% inventory, equal area as NA Kuhlbrodt et al, 2006

Atlantic a Inventory [Pg C] Pacific b Inventory [Pg C] Indian c Inventory [Pg C] Global Inventory [Pg C] Southern hemisphere Northern hemisphere Global47 (42%)45 (40%)20 (18%)112 a) Lee et al. (submitted) b) Sabine et al. (2002) c) Sabine et al. (1999)

Kuhlbrodt et al, 2006 ¿How is C AN T uptaken ? + areas of cooling. + areas where old waters get to the surface ¿ Where is C ANT stored ? where surface waters sink to intermediate and deep --- deep waters formation areas.

F air-sea = – (Storage + T S + T N ) + other terms - F air-sea is the air-sea CO 2 flux in the region (positive into the region), - T S and T N respectively refer to the net transport of carbon across the southern and northern boundaries of the area (positive into the region). - The storage term (always negative) stands for the accumulation of anthropogenic CO 2, - Other terms: river discharge, biological activity, etc...

4x24.5ºN BeringSt. F air-sea = – (Storage + T S + T N ) F air-sea = no se puede medir Storage = se puede estimar, dos maneras Transportes = se pueden calcular

T Prop  is the property transport from Vigo to Cape Farewell over the entire water column Prop  the property concentration v  velocity orthogonal to the section, ESENCIAL  S,T,P  in-situ density

Storage can be mathematically defined as: where t is time and  C ANTz dz is the water column inventory of C ANT.

The Mean Penetration Depth (MPD) of C ANT using the formula by Broecker et al. (1979) is: where C ANTz and C ANTml are the C ANT concentrations at any depth (z) and at the mixed layer (ml), Assuming that C ANT is a conservative tracer (not affected by biology) that has reached its “transient steady state” (profile with a constant shape)

Calculated from: - the temporal change of C ANT in the mixed layer. - the MPD can be derived from current TIC observations approximated assuming a fully CO 2 equilibrated mixed layer keeping pace with the CO 2 atmospheric increase.

4x24.5ºN BeringSt. 172       200 C ANT kmol/s

Álvarez et al. (2003). Stoll et al. (1996). Rosón et al. (2003). McDonald et al (2003) Holfort et al. (1998).

Ocean Inversion method The ocean is divided into n regions

The inversion finds the combination of air-sea fluxes from a discrete number of ocean regions that optimally fit the observations: Cj = Carbon signal due to gas exchange calculated from observations at site j s i = Magnitude of the flux from region i H i,j = The modeled response of a unit flux from region i at station j, called the basis functions E = Error associated with the method Mikaloff Fletcher et al. (GBC, 2006)

Figure 4. Global map of the time integrated (1765–1995) transport (shown above or below arrows) of anthropogenic CO2 based on the inverse flux estimates (italics) and their implied storage (bold) in Pg C. Shown are the weighted mean estimates and their weighted standard deviation.

Figure 5. Uptake, storage, and transport of anthropogenic CO2 in the Atlantic Ocean (Pg C yr −1 ) based on (a) this study (weighted mean and standard deviation scaled to 1995), (b) the estimates of [Álvarez et al., 2003], where the transport across 24°N was taken from Rosón et al. [2003], (c) Wallace [2001], where the transport across 20°S was taken from Holfort et al. [1998], and (d) Macdonald et al. [2003], where the transports across 10°S and 30°S were taken from Holfort et al. [1998], and the transport across 78°N was taken from Lundberg and Haugan [1996]. - Difficult to compare: OGCMs=>mean values, data=> no seasonal or temporal integration - agreements and discrepancies - OGCMs trp at 76ºN not robust, but Trp at more southern latitudes are quite robust and in agreement with data.

Air-Sea CANT uptake: total uptake 2.2  0.25 PgC/yr referred to 1995 greatest uptake in SO, 23% of the total flux, but high variability from models considerable uptake in the tropics reduced uptake at mid latitudes, but here is the greatest storage high uptake in regions where low CANT waters get to surface

CANT transport: calculated from divergence of the fluxes SO: large uptake with low storage, drives a high northward flux towards the equator, half the uptake is stored, rest transported SO: transport with SAMW and AAIW, 50% total transport from SO goes into Atlantic oc., stored in subtropics high storage at midlatitudes in SH due to transport from SO not from air-sea uptake NA: high uptake in mid and high latitudes, divergence in transports, high storage (NADW formation)

By taking up about a third of the total emissions, the ocean has been the largest sink for anthropogenic CO 2 during the anthropocene. The Southern Ocean south of 36°S constitutes one of the most important sink regions, but much of this anthropogenic CO 2 is not stored there, but transported northward with Sub- Antarctic Mode Water. Models show a similar pattern, but they differ widely in the magnitude of their Southern Ocean uptake. This has large implications for the future uptake of anthropogenic CO 2 and thus for the evolution of climate.