Dr. Nicholas R. Bates Bermuda Biological Station For Research Bermuda Biological Station For Research Twenty Years of Oceanic CO 2 Observations in the North Atlantic Ocean at the BATS site
Dec 24, 2015
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)