1. 1/30 IS THERE A HIGHER C ANT STORAGE IN THE INDIAN OCEAN? Estimating the storage of anthropogenic carbon in the subtropical Indian Ocean: a comparison of five different approaches M. Álvarez, C. Lo Monaco, T. Tanhua, A. Yool, A. Oschlies, J. L. Bullister, C. Goyet, N. Metzl, F. Touratier, E. McDonagh, and H. L. Bryden, Biogeosciences, 6, 681-703, 2009. http://www.biogeosciences-discuss.net/6/729/2009/bgd-6-729-2009.html

2. 2/30 C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN 44.5  5 Pg 44.8  6 Pg 20.3  3 Pg Indian Ocean Pacific Ocean Atlantic Ocean (Sabine et al, Science 2004) C ANT inventory referred to 1994 = 110 ± 13 Pg C Indian Ocean contains - 21% of the total C ANT inventory - half of the Atlantic C ANT inventory despite having only 20% less area

3. 3/30 C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN Indian Ocean C ANT vertical distribution  mol/kg (Sabine et al, Science 2004) RedSea /Persian Gulf Intermediate Water Antarctic Intermediate Water (AAIW) AAIW marks the deepest C ANT penetration in the Subtropical gyre No C ANT in deep and bottom waters

4. 4/30 C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN Hypothesis: C ANT penetrates deeper than 1000-1500 m How to assess this question: compare different C ANT methods -> difficult: every method has high uncertainties help: relation of C ANT with tracers (CFC 12, CCl 4 )

5. 5/30 C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN ã On board R/V Charles Darwin, CD139 cruise, 1/3 – 15/4/2002, from Durban to Freemantle ã P.I.: Harry Bryden (National Oceanographic Centre, Southampton, UK) ã Physics: temperature, salinity, ADCP, LADCP ã Chemistry: oxygen, salinity, nutrients, CO 2 (pH & TA, TIC), CFCs (11, 12, 113), CCl 4.

6. 6/30 C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN Salinity (psu) AfricaAustralia NADW AAIW SAMW CDW AABW AAIW SAMW NADW AAIW SAMW AABW NADW AAIW SAMW

7. 7/30 C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN CFC-12 (pmol/kg) CDW AABW NADW AAIW SAMW CDW Africa Australia AAIW SAMW AABW AAIW SAMW

8. 8/30 C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN C ANT TECHNIQUES 1.C ANT SAB99: method by Sabine et al. (GBC,1999), using their  C Dis 2.C ANT LM05: method by LoMonaco et al. (JGR, 2005) 3.C ANT TrOCA: Touratier & Goyet (Tellus, 2007) 4.C ANT TTD 5.C ANT from OCCAM model

9. 9/30 C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN C ANT =  C* -  C Dis = C – AOU/R C – ½(  TA + AOU/R N ) + 106/104 · N* - C 280 –  C Dis ã C is the current total inorganic carbon ã  TA = TA - TA 0, current alkalinity - preformed alkalinity TA 0 = 378.1 + 55.22 · Sal + 0.0716 · PO - 1.236 · Tpot ã AOU is the Apparent Oxygen Utilization, assuming oxygen saturation ã C 280 is the inorganic carbon in equilibrium with the preindustrial atmosphere. C 280 = f (Tpot, Sal, TA 0, pCO 2280 ) from thermodynamic equations pCO 2280 = CO 2 fugacity at a 100% of water vapor pressure in uatm = f(Tpot, Sal, 280) C 280 in GSS96 => constants by Goyet & Poisson (1989) & a constant pCO 2280 = 280 uatm linearilized equation: C 280 = 2072 - 8.982 · (Tpot - 9) - 4.931 · (Sal - 35) + 0.842 · (TA 0 - 2320) ã N* = (0.87 · (NO 3 - 16 · PO 4 + 2.9)) term accounting for the denitrification Back-calculation technique by Sabine et al. (GBC, 1999) to estimate C ANT.

10. 10/30 C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN

11. 11/30 C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN  C Dis is obtained with own CD139 data using CFC 12 ages and limit at 40 years a) Old deep waters, C ANT = 0 =>  C* =  C Dis b) In upper waters, having the age:  C Dis =  C*t| σ=cte  C* t = C - C Bio - C t where C t = f (Tpot, Sal, TA 0, pCO 2t ) pCO 2 in the atmosphere at 2002 – age (t) c) In between => weigthed mean  C* and  C*t|  =cte

12. 12/30 C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN Fig. 4. Air-sea CO2 disequilibrium (  mol kg-1) by  density intervals. Blue points correspond to the values taken directly from SAB99 work, light blue and orange points correspond to the values estimated using the CD139 biogeochemical data, following SAB99 (orange) and combined (light blue) methods. Interpolated points are highlighted with black open circles.

13. 13/30 C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN Back-calculation technique by Lo Monaco et al. (JGR, 2005): C ANT = C T – C Bio - C T 0 obs – (C T – C Bio – C 0 obs ) REF C T = measured TIC C Bio = 0.73·(O 2 0 – O 2 ) + 0.5·(TA – TA 0 ) => biological activity variation in TIC TA 0 => preformed TA O 2 0 = O 2 sat –  ·  ·O 2 Sat =>  O 2 = 12% undersaturation K = > mixing ratio of ice-covered water (OMP) C 0 obs => preformed TIC currently observed in the formation area water masses REF = reference water where no C ANT should be detected.

14. 14/30 C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN mixing ratios of southern and northern waters: k(S) + k(NADW) = 1 determined from OMP analysis TA 0 = k(S) TA 0 (S) + k(N) TA 0 (NADW) C 0,obs = k(S) C 0,obs (S) + k(N) C 0,obs (NADW) southern relationships: winter surface data from the Atlantic and Indian oceans (WOCE and OISO cruises) TA 0 (S) = 0.0685 PO + 59.787 S - 1.448  + 217.15 (± 5.5 µmol/kg, r 2 = 0.96, n = 243) C 0,obs (S) = -0.0439 PO + 42.79 S - 12.019  + 739.83 (± 6.3 µmol/kg, r 2 = 0.99, n = 428) northern relationships subsurface data from the North Atlantic and Nordic Seas (WOCE and KNORR cruises) TA 0 (N) = 42.711 S + 1.265  + 804.6 (± 9.3 µmol/kg, r 2 = 0.92, n = 297) C 0,obs (N) = 10.69 S + 0.306 NO + 1631.6 (± 9.2 µmol/kg, r 2 = 0.79, n = 364) Back-calculation technique by Lo Monaco et al. (JGR, 2005)

15. 15/30 C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN Back-calculation technique by Lo Monaco et al. (JGR, 2005): OMP analysis modified from Lo Monaco et al. (JGR, 2005) Endmembers: AAIW, NADW-E, NIDW, Indian Water, WDS/CDW, ISW Weddell Variables: Sal, Tpot, SiO2 and NO Salinity SiO2 NO Tpot

16. 16/30 C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN Back-calculation technique by Lo Monaco et al. (JGR, 2005): OMP Tpot, Sal, SiO 2 NO STD Res. 0.0481 0.0051 1.3 3 R 2 0.9979 0.9967 0.9973 0.9611 (n=1299)

17. 17/30 C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN 2. Back-calculation technique by Lo Monaco et al. (JGR, 2005): OMP NADW contribution Ice-covered SW contribution AfricaAustraliaAfricaAustralia

18. 18/30 C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN REF = NADW= reference water where no C ANT should be detected. Applied to samples with more 50% NADW from OMP analysis (C T – C Bio – C 0 obs ) REF = - 54.4 ± 1.4 umol/kg (LoMonaco JGR2005 -51 umol/kg) Back-calculation technique by Lo Monaco et al. (JGR, 2005): C ANT = C T – C Bio - C T 0 obs – (C T – C Bio – C 0 obs ) REF C ANT = C T – C Bio - C T 0 obs – (- 54.4)

19. 19/30 C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN C ANT TrOCA, Touratier et al (Tellus B, 2007): C ANT = (O 2 + 1.279 · (C T – 0.5 · TA) – exp (7.511-0.01087· θ -781000/TA 2 ))/1.279) C ANT (TrOCA) = (TrOCA – TrOCA 280 ) / a TrOCA = O 2 + a · (C T -1/2 ·TA)a = ψ O2 / [ψ CO2 + ½ ·( ψ H+ − ψ HPO24− )]

20. 20/30 C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN 4. C ANT TTD (Waugh et al., 2004; 2006; Tanhua et al., 2008): - each water sample has its own “age”, i.e. time since it was last in contact with the atmosphere. The sum of all these ages makes the TTD of a water sample - the mean age (  ) and the width of the TTD (  ) are assumed to be of equal magnitude: realistic assumption of the relation between advective and diffusive transport in the Ocean - C ANT is an inert passive tracer where air-sea disequilibrium hasn’t changed over time.

21. 21/30 C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN 5. C ANT OCCAM - global, medium-resolution, primitive equation ocean general circulation model (Marsh et al., 2005). - OCCAM's vertical resolution is 66 levels (5 m thickness at the surface, 200 m at depth), with a horizontal resolution of typically 1 degree. - Advection is 4th order accurate, and the model is time-integrated using a forward leapfrog scheme with a 1 hour time-step. - Surface fluxes of heat and freshwater not specified but are calculated empirically using NCEP-derived atmospheric boundary quantities (Large and Yeager, 2004). - OCCAM incorporates a NPZD plankton ecosystem (Oschlies, 2001; Yool et al., 2007) which drives the biogeochemical cycles of nitrogen, carbon, oxygen and alkalinity.

22. 22/30 C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN C ANT vertical distributions pCFC12 & pCCl 4 SAB99LM05 Troca TTD OCCAM

23. 23/30 C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN C ANT mean profile differences

24. 24/30 C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN Neutral density layers & salinity Africa Australia Bottom AAIW SAMW Deep Surface

25. 25/30 C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN C ANT mean inventories

26. 26/30 pCFC-12 Revelle = 10 C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN Surface, SAMW waters and upper AAIW Revelle = 13 Fig. 10. Partial pressure of CFC-12 (ppt) and CANT estimates (mmol kg-1) for upper waters with potential temperature higher than 5ºC, pressure higher than 200 dbar and CFC-12 age less than 30 years. Also shown in black is the atmospheric evolution of CFC-12 and CANT using Revelle factors of 10 and 13 (see text for details), some time markers are shown.

27. 27/30 C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN Deep and bottom waters Fig. 11. a) Partial pressure of CFC-12 (ppt) and b) partial pressure of CCl4 (ppt) versus CANT (  mol kg-1) estimates for deep waters with potential temperature lower than 5ºC, pressure higher than 200 dbar and CFC-12 age higher than 40 years. In the case of CCl4, the temperature limit is 3ºC. Also shown in black are the atmospheric evolution of CFC-12, CCl4 and CANT using Revelle factors of 10 and 13 (see text for details), some time markers are shown.

28. 28/30 Table 1. Mean  standard deviation C ANT specific inventory (molC m -2 ) by water masses in the subtropical Indian Ocean for the different methods here evaluated. Mean and standard deviation values were obtained randomly modifying the initially calculated single C ANT values by  5  mol kg -1. A set of 100 perturbations were done for the five methods. The standard deviation for each layer is weighted by the layer contribution to the total section area. See text for the acronyms. N/D stands for not determined. Values between brackets correspond to the LM05 method assuming a 100% oxygen saturation in equation (7),  =0. UpperSAMWAAIWDeepBottomTotal* SAB99N/D 8.5  0.58.1  0.40  0.50.3  0.223.9  2 LM05N/D 11  0.711  0.5 0.6  0.4 (0.5  0.4) 1.2  0.3 (0.0  0.3) 30.8  2.5 (29.5  2.5) TrOCAN/D 8.4  0.59.4  0.51.9  0.51.4  0.328.1  2.2 TTD 7.2  0.79.3  0.69.3  0.52  0.41.3  0.228.9  2.3 OCCAM 6.9  1.59.3  0.87.6  0.50.5  0.1000024.4  2.8 * The total specific inventory is calculated as the sum of the SAMW, AAIW, Deep and Bottom contributions plus 7 molC m -2, i.e., the TTD and OCCAM mean specific inventory for the upper layer. C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN Inventories

29. 29/30 This work investigates the C ANT penetration and inventory in the subtropical Indian Ocean along 32ºS calculated with data collected in 2002. Five different methods are compared and discussed: three carbon-based methods (  C*, LM05 and TrOCA), TTD and a simulation from the OCCAM global model. Comparatively, the  C* method seems to yield too shallow penetration of C ANT, with no or very low C ANT detected in deep or bottom waters, mainly due to the formulation and assumptions of  CTdis. Our results indicate that SAB99  CTdis values are inconsistent with the current air-sea CO2 disequilibrium found in current Indian Ocean winter  CTdis values. Although this could also be misleading taking into account that water masses are usually formed in particular times and areas of the ocean. Previous estimates of C ANT inventory in the subtropical Indian Ocean with the  C* method appear to be underestimates. Considering the C ANT estimates derived from those methods consistent with the tracer distributions and the knowledge about water masses, our best estimate for the mean C ANT specific inventory is 28  2 molC m-2 which compares with 24  2 molC m-2 from  C*, 17% higher. C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN Conclusions

30. 30/30 C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN Hypothesis: C ANT penetrates deeper than 1000 m (Sabine et al 1999) How to assess this question: difficult: every method has uncertainties help: relation of C ANT with tracers (CFC 12, CCl 4 ) seems to be hinted by any other method absolutely true, no method is perfect questions still arise, saturation, mixing, etc.. community should combine methods and time-evolution studies at specially sensitive regions OPEN DISCUSSION: KEY REGION ….. THE SO

31. 31/30 C ANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN Discusión: ¿Cuáles son las asunciones de cada método? ¿nos creemos el desequilibrio? ¿Qué método os parece el más fiable? ¿Se os ocurre como evaluar los métodos de otra manera?