Dr. Nicholas R. Bates Bermuda Biological Station For Research

Dr. Nicholas R. BatesBermuda Biological Station For ResearchBermuda Biological Station For Research

Twenty Years of Oceanic CO2 Observations in the North Atlantic Ocean

at the BATS site

BATSBATS sitesite

Sargasso Sea

Gulf Stream

• Monthly sampling at BATS16 core cruises a year 2-3 validation cruises

• Sampling from 0-4200 m• 24 Hydrostation S cruises

per year.

Bermuda Atlantic Time-series Study(BATS)

Long-term Changes

Bates 2005Bates 2005

Bates 2005Bates 2005

Long-term Changes at BATS

1992 20011985•••

Non-conservative alkalinity decreases due to coccolithophore blooms

Long-term Changes in Seawater pCO2 2

and pH at several sites

-0.0012 yr-1

IPCC Report (in prep); Bates, 2005IPCC Report (in prep); Bates, 2005

+1.5 µatm yr-1

pCO2

+2.2 µatm yr-1

+0.7 µatm yr-1

pH

1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998

420

400

380

360

340

320

300

ppC

OC

O22

(µat

m)

(µ

atm

)

Seawater pCO2

Atmospheric pCO2

Ocean-atmosphere exchanges of CO2

Bates Bates et alet al., 1998a., 1998a

Summer CO2 Efflux

Winter CO2 Influx

North Atlantic subtropical gyre is a net sink for CONorth Atlantic subtropical gyre is a net sink for CO22

Flux = ~0.7 moles COFlux = ~0.7 moles CO2 2 mm22 year year-1-1

Takahashi et al., 2002Takahashi et al., 2002

Red Areas:Red Areas: Oceanic Source of COOceanic Source of CO22

Blue Areas:Blue Areas: Oceanic Sinks of COOceanic Sinks of CO22

Air-sea CO2 fluxes

Air-sea CO2 fluxes

Bates 2005Bates 2005Interannual air-sea CO2 flux ~0.4 to 1.6 moles CO2 yr-1

HurricaneFabian (2003)

HurricaneFelix (1995)

• • 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 TCOSTMW TCO22

Surface TCOSurface TCO22

• • STMW TCO2 (µmoles kg-1 yr-1)TCO2/nTCO2 +2.22 + 0.27 (r2= 0.65)

DO -0.58 + 0.22 (r2= 0.27)

Interannual Variability of CO2

Uptake of anthropogenic CO2

Bates Bates et alet al., 2002., 2002

• Higher winter wind speeds in 1990’s compared to 1980’sGEOSECS data GEOSECS data TTO dataTTO data Keeling dataKeeling data Brewer Brewer data data BATS dataBATS data

* ** **

Non-steady state changes in CO2

* Extensive STMW formation

The sink status in the North Atlantic changed

Bates Bates et alet al., 2002., 2002

N.R. Bates, A.C Pequignet, and R.J. Johnson Bermuda Biological Station For ResearchBermuda Biological Station For Research

Source: Talley, 2000Source: Talley, 2000

North Atlantic Subtropical North Atlantic Subtropical Mode Water (STMW)Mode Water (STMW)

• The magnitude and interannual variability of uptake and storage of carbon dioxide (CO2) and storage into mode

waters are poorly quantified.

STMW Carbon Uptake and Storage

18°C 25°C4°C

STMW in the North Atlantic OceanGeneric winter Generic winter

location of STMW location of STMW formationformation

Geostrophic recirculation Geostrophic recirculation pathways of STMWpathways 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)Images: Thanks to Norm Nelson, UCSB and John Marshall (MIT)

Gulf Gulf StreamStream

Increasing Heat LossIncreasing Heat Loss

18°C 25°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)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 CO2 through gas exchange?• 3. Retention of CO2 or loss from STMW (by mixing)?

40°N40°N20°N20°N

BATSBATS

11

22

33

Causes for changes in CO2?

Bates Bates et alet al., 2002., 2002

Source: Bates Source: Bates et alet al., 2002., 2002

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]

Remineralization?

• STMW TCO2 changes not due to remineralization (i.e., decrease in DO) or sampling of older water.

Bates Bates et alet al., 2002., 2002

C +2.22 (µmoles kg-1 yr -1) Cant +0.90 (µmoles kg-1 yr -1) Cgasex +1.19 + 0.26 (µmoles kg-1 yr -1) (r2= 0.47) Cbio +0.28 + 0.12 (µmoles kg-1 yr -1) (r2= 0.25)

• Low Cbio values indicate that biological processes did not contribute much to the +2.2 µmoles kg-1 yr -1 change in STMW TCO2

Remineralization?

Bates Bates et alet al., 2002., 2002

• Higher winter wind speeds in 1990’s compared to 1980’s

• Higher winter wind speeds in 1990’s compared to 1980’s

Mean winter wind speedMean winter wind speed

Mean annual wind speedMean annual wind speed

GEOSECS data GEOSECS data TTO dataTTO data Keeling dataKeeling data Brewer Brewer data data BATS dataBATS data

CO2 gas flux at the site of STMW formation should increase STMW by 2-3 µmoles kg-1 yr-1.

Increased Gas Exchange?

Bates Bates et alet al., 2002., 2002

• Higher winter wind speeds in 1990’s compared to 1980’sGEOSECS data GEOSECS data TTO dataTTO data Keeling dataKeeling data Brewer Brewer data data BATS dataBATS data

* ** **

Variability of Carbon Storage?

* ** * *

* Extensive STMW formation Bates Bates et alet al., 2002., 2002

Post 1987: CO2 transferred to ocean interior

1960’s, 1970’s, early 1980’s: CO2 in STMW redistributed

Long-term CO2 sink >10 yearsShort-term CO2 sink ~1-4 years

NAO-ve State NAO+ve State

Bates Bates et alet al., 2002., 2002

• 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.

20°N20°N 40°N40°N

~3-11% of annual global CO2 uptake?

Conclusions and Implications: A changed oceanic CO2 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)