Marta Álvarez Rodríguez

1. Asignatura 2.07 Impacto del cambio global en los ciclos del N, P, C y metales CARBON production during the Antropocene: sinks, sources and ocean storage Anthropogenic carbon in the ocean Marta Álvarez Rodríguez IMEDEA, CSIC-UIB Esporles, Mallorca Palma de Mallorca, February 2010

2. Ciclo global del carbono y su perturbación antropogénica +161 1.9 Land sink 5.4 1.7 Land use change 21.9 20 -220 +65 -125 +18 1.6 +100 Global carbon cycle

3. Carbon excess or anthropogenic carbon 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:

4. Anthropogenic CO2 Budget 1800 to 1994 The ocean uptake a great part of CANT 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!!, CANT is redistributed within the oceans a: From Marland and Boden [1997] (updated 2002) b: From Houghton [1997] c: Calculated from change in atmospheric pCO2 (1800: 284ppm; 1994: 359 ppm) d: Based on estimates of Sabine et al. [1999], Sabine et al. [2002] and Lee et al. (submitted)

5. Why is important to know where and how CANT is stored and uptaken by the ocean?? • 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

6. Recent numbers for the ocean uptake of CO2

7. CANT estimation in the ocean: what can you measure? Globally integrated flux: 2.2 PgC yr-1

8. CANT estimation in the ocean: what you CAN NOT measure? Preindustrial Flux Anthropogenic Flux

9. WOCE/JGOFS/OACES Global CO2 Survey 1991-1997 CANT estimation in the ocean: what can you measure? 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.

10. CANT estimation in the ocean: what can you measure? + 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%

11. CANT estimation in the ocean: back-calculation technique Gruber et al (1996) GSS’96 defined the semiconservative parameter DC*(t), it depends on the anthropogenic input, thus, the water mass age (t),and its include the air-sea desequilibrium constant with time: DC*(t) = CANT + DCTdis

12. CANT estimation in the ocean: back-calculation technique Gruber et al (1996) • To separate the anthropogenic CO2 signal from the natural variability in DIC. This requires the removal of • the change in DIC that incurred since the water left the surface ocean due to remineralization of organic matter and dissolution of CaCO3 (DDICbio), and • a concentration, DICsfc-pi , that reflects the DIC content a water parcel had at the outcrop in pre-industrial times, the equilibrium concentration plus any disequilibrium • Thus, DCant = DIC - DDICbio - DICsfc-pi = DIC – DDICbio – DIC280 - DDICdis • Assumptions: • natural carbon cycle has remained in steady-state

13. CANT distribution in the ocean

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

15. CANT distribution in the ocean

16. CANT distribution in the ocean

17. CO2 system in the ocean Revelle factor

18. CO2 system in the ocean Revelle factor

19. CANT distribution in the ocean a) Lee et al. (submitted) b) Sabine et al. (2002) c) Sabine et al. (1999)

20. Kuhlbrodt et al, 2006 CANT distribution in the ocean ¿How is CAN T uptaken ? + areas of cooling. + areas where old waters get to the surface ¿ Where is CANT stored ? where surface waters sink to intermediate and deep --- deep waters formation areas.

21. CANT budgets in the ocean F air-sea = – (Storage + TS + TN) + other terms - F air-sea is the air-sea CO2 flux in the region (positive into the region), - TS and TN 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 CO2, - Other terms: river discharge, biological activity, etc...

22. Bering St. 4x 24.5ºN CANT budgets in the ocean F air-sea = – (Storage + TS + TN) F air-sea = no se puede medir Storage = se puede estimar, dos maneras Transportes = se pueden calcular

23. CANT budgets in the ocean: transport TProp  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 rS,T,P in-situ density

24. where t is time and CANTz dz is the water column inventory of CANT. CANT budgets in the ocean: storage Storage can be mathematically defined as:

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

26. CANT budgets in the ocean: storage Calculated from: - the temporal change of CANT in the mixed layer. - the MPD can be derived from current TIC observations approximated assuming a fully CO2 equilibrated mixed layer keeping pace with the CO2 atmospheric increase.

27. CANT budgets in the ocean: storage

28. CANT budgets in the ocean: storage

29. ± ± 172 111 321 258 Bering St. 4x 24.5ºN ± ± 116 104 630 200 ± ± -288 50 -835 100 CANT budgets in the ocean: air-sea uptake CANT kmol/s

30. Stoll et al. (1996). Álvarez et al. (2003). Rosón et al. (2003). McDonald et al (2003) Holfort et al. (1998). CANT budgets in the ocean: estimates

31. CANT budgets in the ocean: OGCMs Ocean Inversion method • The ocean is divided into n regions

32. CANT budgets in the ocean: OGCMs 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)

33. CANT budgets in the ocean: OGCMs Mikaloff Fletcher et al. (GBC, 2006)

34. CANT budgets in the ocean: OGCMs 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.

35. CANT budgets in the ocean: OGCMs • 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. 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].

36. CANT budgets in the ocean: OGCMs • 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

37. CANT budgets in the ocean: OGCMs • 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)

38. Uptake, storage and transport summary • By taking up about a third of the total emissions, the ocean has been the largest sink for anthropogenic CO2 during the anthropocene. • The Southern Ocean south of 36°S constitutes one of the most important sink regions, but much of this anthropogenic CO2 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 CO2 and thus for the evolution of climate.