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

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

Long-term Changes Bates 2005

Long-term Changes at BATS Non-conservative alkalinity decreases due to coccolithophore blooms

2 Long-term Changes in Seawater pCO 2 and pH at several sites yr -1 IPCC Report (in prep); Bates, µatm yr -1 pCO µatm yr µatm yr -1 pHpH

pCO 2 (µatm) Seawater pCO 2 Atmospheric pCO 2 Ocean-atmosphere exchanges of CO 2 Bates et al., 1998a Summer CO 2 Efflux Winter CO 2 Influx North Atlantic subtropical gyre is a net sink for CO 2 Flux = ~0.7 moles CO 2 m 2 year -1

Takahashi et al., 2002 Red Areas: Oceanic Source of CO 2 Blue Areas: Oceanic Sinks of CO 2 Air-sea CO 2 fluxes

Bates 2005 Interannual air-sea CO 2 flux ~0.4 to 1.6 moles CO 2 yr -1 Hurricane Fabian (2003) Hurricane Felix (1995)

Mixed layer TCO 2 (µmoles kg -1 yr -1 ) TCO (r 2 = 0.36*) nTCO (r 2 = 0.37*) DO (r 2 = 0.00) STMW TCO 2 Surface TCO 2 STMW TCO 2 (µmoles kg -1 yr -1 ) TCO 2 /nTCO (r 2 = 0.65) DO (r 2 = 0.27) Interannual Variability of CO 2 Uptake of anthropogenic CO 2 Bates et al., 2002

Higher winter wind speeds in 1990’s compared to 1980’s GEOSECS data TTO data Keeling data Brewer data BATS data ***** Non-steady state changes in CO 2 * Extensive STMW formation The sink status in the North Atlantic changed Bates et al., 2002

N.R. Bates, A.C Pequignet, and R.J. Johnson Bermuda Biological Station For Research Source: Talley, 2000 North Atlantic Subtropical Mode Water (STMW) The magnitude and interannual variability of uptake and storage of carbon dioxide (CO 2 ) and storage into mode waters are poorly quantified. STMW Carbon Uptake and Storage

18°C25°C4°C STMW in the North Atlantic Ocean Generic winter location of STMW formation Geostrophic recirculation pathways of STMW 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) GulfStream Increasing Heat Loss

18°C25°C4°C STMW in the North Atlantic Ocean 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)

1. Changing production and/or remineralization of organic matter (sampling older water over time)? 2. Changing flux of CO 2 through gas exchange? 3. Retention of CO 2 or loss from STMW (by mixing)? 40°N20°N BATS Causes for changes in CO 2 ? Bates et al., 2002

Source: Bates et al., 2002 DO µmoles kg -1 yr -1 (r 2 = 0.27) Nitrate µmoles kg -1 yr -1 (r 2 = 0.15) Phosphate µmoles kg -1 yr -1 (r 2 = 0.13) [Temperature °C yr -1 Salinity yr -1 ] Remineralization? STMW TCO 2 changes not due to remineralization (i.e., decrease in DO) or sampling of older water. Bates et al., 2002

 C+2.22 (µmoles kg -1 yr -1 )  C ant (µmoles kg -1 yr -1 )  C gasex (µmoles kg -1 yr -1 ) (r 2 = 0.47)  C bio (µmoles kg -1 yr -1 ) (r 2 = 0.25) Low  C bio values indicate that biological processes did not contribute much to the +2.2 µmoles kg -1 yr -1 change in STMW TCO 2 Remineralization? Bates et al., 2002

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

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

Post 1987: CO 2 transferred to ocean interior 1960’s, 1970’s, early 1980’s: CO 2 in STMW redistributed Long-term CO 2 sink >10 years Short-term CO 2 sink ~1-4 years NAO-ve StateNAO+ve State Bates et al., 2002

Annual global ocean uptake of CO 2 is about 2 Pg C yr -1. Over the last 12 years, the extra uptake of CO 2 into STMW (~ 0.6 to 2.8 Pg C) has the same range as the global annual uptake of CO 2. Since 1988, STMW has taken up ~ 0.05 to 0.23 Pg C yr °N40°N ~3-11% of annual global CO 2 uptake? Conclusions and Implications: A changed oceanic CO 2 sink in 1990’s

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)