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Dr. Nicholas R. Bates Bermuda Biological Station For Research

Twenty Years of Oceanic CO 2 Observations in the North Atlantic Ocean at the BATS site. Dr. Nicholas R. Bates Bermuda Biological Station For Research. Bermuda Atlantic Time-series Study. (BATS). • Monthly sampling at BATS 16 core cruises a year 2-3 validation cruises

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Dr. Nicholas R. Bates Bermuda Biological Station For Research

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  1. Twenty Years of Oceanic CO2 Observations in the North Atlantic Ocean at the BATS site Dr. Nicholas R. Bates Bermuda Biological Station For Research

  2. Bermuda Atlantic Time-series Study (BATS) • Monthly sampling at BATS 16 core cruises a year 2-3 validation cruises • Sampling from 0-4200 m • 24 Hydrostation S cruises per year. Gulf Stream BATS site Sargasso Sea

  3. Long-term Changes Bates 2005

  4. Long-term Changes at BATS Non-conservative alkalinity decreases due to coccolithophore blooms • • • 1985 1992 2001 Bates 2005

  5. Long-term Changes in Seawater pCO2 and pH at several sites pCO2 pH +2.2 µatm yr-1 +1.5 µatm yr-1 -0.0012 yr-1 +0.7 µatm yr-1 IPCC Report (in prep); Bates, 2005

  6. Ocean-atmosphere exchanges of CO2 North Atlantic subtropical gyre is a net sink for CO2 420 Summer CO2 Efflux Seawater pCO2 Atmospheric pCO2 400 380 pCO2 (µatm) 360 340 320 Winter CO2 Influx 300 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 Flux = ~0.7 moles CO2 m2 year-1 Bates et al., 1998a

  7. Air-sea CO2 fluxes Red Areas:Oceanic Source of CO2 Blue Areas:Oceanic Sinks of CO2 Takahashi et al., 2002

  8. Air-sea CO2 fluxes Hurricane Fabian (2003) Hurricane Felix (1995) Interannual air-sea CO2 flux ~0.4 to 1.6 moles CO2 yr-1 Bates 2005

  9. Interannual Variability of CO2 Uptake of anthropogenic CO2 STMW TCO2 Surface TCO2 • Mixed layer TCO2 (µmoles kg-1 yr-1) TCO2 +1.20 + 0.35 (r2= 0.36*) nTCO2 +1.19+ 0.25 (r2= 0.37*) DO -0.10 + 0.24 (r2= 0.00) • STMW TCO2 (µmoles kg-1 yr-1) TCO2/nTCO2+2.22+ 0.27 (r2= 0.65) DO -0.58 + 0.22 (r2= 0.27) Bates et al., 2002

  10. Non-steady state changes in CO2 The sink status in the North Atlantic changed • Higher winter wind speeds in 1990’s compared to 1980’s GEOSECS data TTO dataKeeling dataBrewer data BATS data * * * * * * Extensive STMW formation Bates et al., 2002

  11. STMW Carbon Uptake and Storage • The magnitude and interannual variability of uptake and storage of carbon dioxide (CO2) and storage into mode waters are poorly quantified. N.R. Bates, A.C Pequignet, and R.J. Johnson Bermuda Biological Station For Research North Atlantic Subtropical Mode Water (STMW) Source: Talley, 2000

  12. STMW in the North Atlantic Ocean Generic winter location of STMW formation 4°C 18°C 25°C Gulf Stream Geostrophic recirculation pathways of STMW Increasing Heat Loss Interannual variability of STMW formation is primarily associated with climate variability (i.e. North Atlantic Oscillation, NAO) Images: Thanks to Norm Nelson, UCSB and John Marshall (MIT)

  13. STMW in the North Atlantic Ocean 4°C 18°C 25°C Interannual variability of STMW formation is primarily associated with climate variability (i.e. North Atlantic Oscillation, NAO) Images: Thanks to Norm Nelson, UCSB and John Marshall (MIT)

  14. Causes for changes in CO2? • 1. Changing production and/or remineralization of organic matter (sampling older water over time)? • 2. Changing flux of CO2 through gas exchange? • 3. Retention of CO2 or loss from STMW (by mixing)? 2 BATS 3 1 20°N 40°N Bates et al., 2002

  15. Remineralization? DO -0.58 + 0.22 µmoles kg-1 yr-1 (r2= 0.27) Nitrate -0.02 + 0.02 µmoles kg-1 yr-1(r2= 0.15) Phosphate -0.00 + 0.00 µmoles kg-1 yr-1 (r2= 0.13) [Temperature +0.003 + 0.004 °C yr-1 Salinity +0.002 + 0.000 yr-1] • STMW TCO2 changes not due to remineralization (i.e., decrease in DO) or sampling of older water. Bates et al., 2002 Source: Bates et al., 2002

  16. Remineralization? DC +2.22 (µmoles kg-1 yr -1) DCant +0.90 (µmoles kg-1 yr -1) DCgasex +1.19+ 0.26 (µmoles kg-1 yr -1) (r2= 0.47) DCbio +0.28+ 0.12 (µmoles kg-1 yr -1) (r2= 0.25) • Low DCbio values indicate that biological processes did not contribute much to the +2.2 µmoles kg-1 yr -1 change in STMW TCO2 Bates et al., 2002

  17. Increased Gas Exchange? GEOSECS data TTO dataKeeling dataBrewer data BATS data • Higher winter wind speeds in 1990’s compared to 1980’s CO2 gas flux at the site of STMW formation should increase STMW by 2-3 µmoles kg-1 yr-1. Mean winter wind speed Mean annual wind speed • Higher winter wind speeds in 1990’s compared to 1980’s Bates et al., 2002

  18. Variability of Carbon Storage? • Higher winter wind speeds in 1990’s compared to 1980’s GEOSECS data TTO dataKeeling dataBrewer data BATS data * * * * * * * * * * * Extensive STMW formation Bates et al., 2002

  19. NAO-ve State NAO+ve State 1960’s, 1970’s, early 1980’s: CO2 in STMW redistributed Post 1987: CO2 transferred to ocean interior Short-term CO2 sink ~1-4 years Long-term CO2 sink >10 years Bates et al., 2002

  20. Conclusions and Implications: A changed oceanic CO2 sink in 1990’s • Annual global ocean uptake of CO2 is about 2 Pg C yr-1. • Over the last 12 years, the extra uptake of CO2 into STMW (~ 0.6 to 2.8 Pg C) has the same range as the global annual uptake of CO2. • Since 1988, STMW has taken up ~ 0.05 to 0.23 Pg C yr-1. ~3-11% of annual global CO2 uptake? 20°N 40°N

  21. Acknowledgements: Thanks to: A.H. Knap, M. Lomas, R.J. Johnson (BBSR) D.A. Hansell (RSMAS) A.F. Michaels (USC) N. Gruber (UCLA) C.D. Keeling (Scripps)

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