CO 2 flux in the North Pacific Alan Cohn May 10, 2006.

COCO22 flux in the flux in the

North PacificNorth PacificAlan CohnAlan Cohn

May 10, 2006May 10, 2006

• Oceans contain ~50x as much COOceans contain ~50x as much CO22 as atmosphere as atmosphere

• Mean annual rate of oceanic COMean annual rate of oceanic CO22 uptake by oceans for past few uptake by oceans for past few

decades is estimated at about 2 Pg-C yrdecades is estimated at about 2 Pg-C yr-1-1 (Takahashi et al., 2005) (Takahashi et al., 2005)

• Only a few stations in the ocean COOnly a few stations in the ocean CO22 monitoring network monitoring network

• Researchers have looked at atmospheric time series of COResearchers have looked at atmospheric time series of CO22, , 1313CO2, and CO2, and

OO22 to infer interannual changes in oceanic and terrestrial CO to infer interannual changes in oceanic and terrestrial CO22 uptake uptake

lack of ocean COlack of ocean CO22 time-series limits scientists’ ability to time-series limits scientists’ ability to

estimate interannual changes in oceanic COestimate interannual changes in oceanic CO2 2 uptake uptake

IntroductionIntroduction

Distribution of climatological mean annual sea-air CO2 flux (moles CO2 m-2 yr-1) for reference year 1995 representing non-El Niño conditions. This map yields an annual oceanic uptake flux for CO2 of 2.2 ± 0.4 Pg C yr-1.

http://www.pmel.noaa.gov/pubs/outstand/feel2331/mean.shtml

• I concentrate on North Pacific as it is a region of strong climate variability I concentrate on North Pacific as it is a region of strong climate variability with implications for variability of atmospheric COwith implications for variability of atmospheric CO22

• One of most frequently sampled regions of oceans for COOne of most frequently sampled regions of oceans for CO22 variability and variability and

nutrient chemistry nutrient chemistry

• Strongly influenced by strength of wintertime Aleutian Low through Strongly influenced by strength of wintertime Aleutian Low through changes in surface wind stress, Ekman advection, surface ocean mixing, changes in surface wind stress, Ekman advection, surface ocean mixing, and heat fluxes and heat fluxes

• In winter, surface water pCOIn winter, surface water pCO2 2 values are governed primarily by physical values are governed primarily by physical

processes because of reduced biological activity (McKinley et al., 2006) processes because of reduced biological activity (McKinley et al., 2006)

• Photosynthesis has significant effects on pCOPhotosynthesis has significant effects on pCO2 2 come spring and summer come spring and summer

Why the North Pacific?Why the North Pacific?

• pCOpCO22 of seawater is sensitive function of temperature as well as total of seawater is sensitive function of temperature as well as total

concentration of COconcentration of CO22

TCOTCO22 depends on net biological depends on net biological

community production, rate of community production, rate of upwelling of COupwelling of CO22 rich subsurface rich subsurface

waters, and air-sea COwaters, and air-sea CO22 flux flux

Revelle factor measures sensitivity Revelle factor measures sensitivity of pCOof pCO22 to changes in total CO to changes in total CO22

pCOpCO22 sensitivity sensitivity

• Temperatures lead to low pCOTemperatures lead to low pCO22 in winter and high pCO in winter and high pCO22 in summer, i.e. in summer, i.e.

they’re positively correlated (McKinley et al., 2006)they’re positively correlated (McKinley et al., 2006)

• In mixed layer, lower total COIn mixed layer, lower total CO22 from photosynthesis counteracts effect of from photosynthesis counteracts effect of

seasonal warming on pCOseasonal warming on pCO22

• Influences of SST on surface ocean pCOInfluences of SST on surface ocean pCO22 oppose effects of biological oppose effects of biological

and physical influences on dissolved inorganic carbon (DIC) and physical influences on dissolved inorganic carbon (DIC)

often evident often evident during spring bloomsduring spring blooms

SST vs. BiologySST vs. Biology

• Interannual variability of COInterannual variability of CO22 in surface ocean strongly correlated with in surface ocean strongly correlated with

changes in mixing depth during winter changes in mixing depth during winter

Deep surface-mixed layers can Deep surface-mixed layers can lead to increased COlead to increased CO22 uptake and uptake and

higher levels of photosynthesis higher levels of photosynthesis than during normal years (Quay, than during normal years (Quay, 2002). 2002).

• Upwelling of COUpwelling of CO22-rich subsurface waters in winter counteracts effect of -rich subsurface waters in winter counteracts effect of

cooling on pCOcooling on pCO22 (Takahashi et al., 2005) (Takahashi et al., 2005)

Mixed Layer VariabilityMixed Layer Variability

http://www.pmel.noaa.gov/~cronin/encycl/cartoon.jpg

http://www.ecy.wa.gov/programs/sea/coast/storms/weather.htmlhttp://www.ecy.wa.gov/programs/sea/coast/storms/weather.html

Aleutian LowAleutian Low is a wintertime semi-permanent cyclone is a wintertime semi-permanent cyclone

Strong Low: Strong Low: strong westerly winds in central N. Pacific strong westerly winds in central N. Pacific cooler cooler SSTs, deeper mixed layerSSTs, deeper mixed layer

enhanced southerly winds in eastern N. Pacificenhanced southerly winds in eastern N. Pacific warmerwarmer SSTs, upwelling supressed SSTs, upwelling supressed

Strength of Low associated with Strength of Low associated with PDO and ENSO.PDO and ENSO.

• Pacific Decadal Oscillation (PDO) is measure of climate variability with Pacific Decadal Oscillation (PDO) is measure of climate variability with possible impacts on COpossible impacts on CO22 flux; it has a 20 – 30 year period flux; it has a 20 – 30 year periodicity

Positive Phase:Positive Phase:

• SSTs cold, mixing layer deep in central and western North Pacific

PDOPDO

http://tao.atmos.washington.edu/pdo/http://tao.atmos.washington.edu/pdo/

• Warm SSTs in Alaska Gyre, along coast of North America, and into tropics

StrongStrong Low Low

WeakWeak Low Low

PDOPDO

Aleutian LowAleutian Low

• Patra et al. (2005) finds that sea-air COPatra et al. (2005) finds that sea-air CO22 flux over North Pacific is flux over North Pacific is

significantly associated with PDO at 5 months lag significantly associated with PDO at 5 months lag

• Believe that delayed effect may be result of slow response of marine Believe that delayed effect may be result of slow response of marine ecosystems and other environments to changes in climate modeecosystems and other environments to changes in climate mode

PDOPDO• In positive phase, upwelling of high COIn positive phase, upwelling of high CO22 waters suppressed due to waters suppressed due to

anomalously northward wind off of Canada anomalously northward wind off of Canada

• station located near Hawaii is believed to have shifted from a weak CO2 sink to weak source due to increased transport of high salinity waters from the north (Keeling et al., 2004)(Keeling et al., 2004)

• shift may be linked to a possible 1997 regime shift in the PDOshift may be linked to a possible 1997 regime shift in the PDO

PDOPDO

http://kela.soest.hawaii.edu/ALOHA/images/hawaii.jpg

• May also influence pCO2 via changes in ocean circulation

http://tao.atmos.washington.edu/pdo/http://tao.atmos.washington.edu/pdo/

• El Nino-Southern Oscillation (PDO) has its primary signature in El Nino-Southern Oscillation (PDO) has its primary signature in tropics; it has a 3-7 year periodtropics; it has a 3-7 year periodicity

ENSOENSO

• Linked to PDO through the variability of the Aleutian Low Linked to PDO through the variability of the Aleutian Low

• Patra et al. find that COPatra et al. find that CO22 flux over North Pacific is significantly flux over North Pacific is significantly

associated with ENSO at three months lag associated with ENSO at three months lag

http://tao.atmos.washington.edu/pdo/http://tao.atmos.washington.edu/pdo/

http://www.pmel.noaa.gov/~kessler/ENSO/soi-1950-98.gifhttp://www.pmel.noaa.gov/~kessler/ENSO/soi-1950-98.gif

ENSOENSO

PDOPDO

La NinaLa Nina predominates predominates when PDO is in negative when PDO is in negative phase phase

El NinoEl Nino predominates predominates when PDO is in positive when PDO is in positive phase phase

• Upwelling regions in central and eastern equatorial Pacific are a strong Upwelling regions in central and eastern equatorial Pacific are a strong source of COsource of CO22 throughout year throughout year

• Kuroshio Current and extension are strong COKuroshio Current and extension are strong CO22 sink in winter due sink in winter due

primarily to cooling, and a weak source in summer due to warming primarily to cooling, and a weak source in summer due to warming

• Western subarctic areas are strong COWestern subarctic areas are strong CO22 source in winter because of source in winter because of

convective mixing of waters rich in respired COconvective mixing of waters rich in respired CO22 and nutrients and nutrients

become strong sink in winter since nutrients help fuel become strong sink in winter since nutrients help fuel intense photosynthesis intense photosynthesis

Physical MechanismsPhysical Mechanisms

Takahashi et al., 2005Takahashi et al., 2005

• Many studies have shown increased uptake in tropics and subtropics in Many studies have shown increased uptake in tropics and subtropics in recent decades, but their temporal structures are inconsistent recent decades, but their temporal structures are inconsistent

• A few areas show decreasing pCOA few areas show decreasing pCO22; these are in or near the Bering ; these are in or near the Bering

and Okhotsk Seas due to increased biological activity and Okhotsk Seas due to increased biological activity

may be result of changing may be result of changing nutrient supplies caused by nutrient supplies caused by changes in land hydrology or changes in land hydrology or by increases in river or by increases in river or airborne inputs of nutrientsairborne inputs of nutrients

http://www.pmel.noaa.gov/np/images/maps/npacific6.gif

pCOpCO22 variability variability

• Seasonal temperature changes are primary cause for seasonal changes Seasonal temperature changes are primary cause for seasonal changes of pCOof pCO22 in subtropical gyres in subtropical gyres

• Takahashi et al. (2006) find that observed increase in pCOTakahashi et al. (2006) find that observed increase in pCO22 is not is not

affected significantly by SST changes, but is primarily due to change in affected significantly by SST changes, but is primarily due to change in seawater chemistry most likely by uptake of atmospheric COseawater chemistry most likely by uptake of atmospheric CO2 2

• Changes in total COChanges in total CO22 concentration caused by winter upwelling and concentration caused by winter upwelling and

springtime plankton blooms are primary cause for seasonal changes in springtime plankton blooms are primary cause for seasonal changes in sub-polar and polar regions (Takahashi et al., 2006)sub-polar and polar regions (Takahashi et al., 2006)

SummarySummary

• Important to study seawater chemistry as well as temperature and Important to study seawater chemistry as well as temperature and circulation changes throughout world’s oceans, as these can affect future circulation changes throughout world’s oceans, as these can affect future uptake or outgassing of COuptake or outgassing of CO22

• Vital to understand role of various mechanisms for changes in COVital to understand role of various mechanisms for changes in CO2 2 flux in flux in

order to accurately quantify potentially changing role of the ocean as a sink order to accurately quantify potentially changing role of the ocean as a sink for future climate scenarios for future climate scenarios

ConclusionConclusion

References

Keeling, C.D., H. Brix, and N. Gruber (2004), Seasonal and long-term dynamics of the upper ocean carbon cycle at Station ALOHA near Hawaii, Global Biogeochem. Cycles, 18¸ GB4006, doi:10.1029/2004GB002227.

McKinley, G.A., T. Takahashi, E. Buitenhuis, F. Chai, J.R. Christian, S.C. Doney, M.-S. Jiang, K. Lindsay, J.K. Moore, C. Le Quéré, I. Lima, R. Murtugudde, L. Shi, and P. Wetzel (2006), North Pacific Carbon Cycle Response to Climate Variability on Seasonal to Decadal Timescales, submitted to J. Geophys. Res. Oceans

Patra, P., S. Maksyutov, M. Ishizawa, T. Nakazawa, T. Takahashi, and J. Ukita (2005), Interannual and decadal changes in the sea-air CO2 flux from atmospheric CO2 inverse modeling, Global Biogeochem. Cycles, 19, GB4013, doi:10.1029/2004GB002257.

Quay, P. (2002), Ups and Downs of CO2 Uptake, Science, 298, 2344.

Takahashi, T., S.C. Sutherland, R.A. Feely, and R. Wanninkhof (2005), Decadal Change of the Surface Water pCO2 in the North Pacific: A Synthesis of 35 Years of Observations, submitted to J. Geophys. Res.