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

Oceans contain ~50x as much CO 2 as atmosphere Oceans contain ~50x as much CO 2 as atmosphere Mean annual rate of oceanic CO 2 uptake by oceans for past few decades is estimated at about 2 Pg-C yr -1 (Takahashi et al., 2005) Mean annual rate of oceanic CO 2 uptake by oceans for past few decades is estimated at about 2 Pg-C yr -1 (Takahashi et al., 2005) Only a few stations in the ocean CO 2 monitoring network Only a few stations in the ocean CO 2 monitoring network Researchers have looked at atmospheric time series of CO 2, 13 CO2, and O 2 to infer interannual changes in oceanic and terrestrial CO 2 uptake Researchers have looked at atmospheric time series of CO 2, 13 CO2, and O 2 to infer interannual changes in oceanic and terrestrial CO 2 uptake  lack of ocean CO 2 time-series limits scientists’ ability to estimate interannual changes in oceanic CO 2 uptake Introduction

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

I concentrate on North Pacific as it is a region of strong climate variability with implications for variability of atmospheric CO 2 I concentrate on North Pacific as it is a region of strong climate variability with implications for variability of atmospheric CO 2 One of most frequently sampled regions of oceans for CO 2 variability and nutrient chemistry One of most frequently sampled regions of oceans for CO 2 variability and nutrient chemistry Strongly influenced by strength of wintertime Aleutian Low through changes in surface wind stress, Ekman advection, surface ocean mixing, and heat fluxes Strongly influenced by strength of wintertime Aleutian Low through changes in surface wind stress, Ekman advection, surface ocean mixing, and heat fluxes In winter, surface water pCO 2 values are governed primarily by physical processes because of reduced biological activity (McKinley et al., 2006) In winter, surface water pCO 2 values are governed primarily by physical processes because of reduced biological activity (McKinley et al., 2006) Photosynthesis has significant effects on pCO 2 come spring and summer Photosynthesis has significant effects on pCO 2 come spring and summer Why the North Pacific?

pCO 2 of seawater is sensitive function of temperature as well as total concentration of CO 2 pCO 2 of seawater is sensitive function of temperature as well as total concentration of CO 2  TCO 2 depends on net biological community production, rate of upwelling of CO 2 ­rich subsurface waters, and air-sea CO 2 flux  Revelle factor measures sensitivity of pCO 2 to changes in total CO 2 pCO 2 sensitivity

Temperatures lead to low pCO 2 in winter and high pCO 2 in summer, i.e. they’re positively correlated (McKinley et al., 2006) Temperatures lead to low pCO 2 in winter and high pCO 2 in summer, i.e. they’re positively correlated (McKinley et al., 2006) In mixed layer, lower total CO 2 from photosynthesis counteracts effect of seasonal warming on pCO 2 In mixed layer, lower total CO 2 from photosynthesis counteracts effect of seasonal warming on pCO 2 Influences of SST on surface ocean pCO 2 oppose effects of biological and physical influences on dissolved inorganic carbon (DIC) Influences of SST on surface ocean pCO 2 oppose effects of biological and physical influences on dissolved inorganic carbon (DIC)  often evident during spring blooms SST vs. Biology

Interannual variability of CO 2 in surface ocean strongly correlated with changes in mixing depth during winter Interannual variability of CO 2 in surface ocean strongly correlated with changes in mixing depth during winter  Deep surface-mixed layers can lead to increased CO 2 uptake and higher levels of photosynthesis than during normal years (Quay, 2002). Upwelling of CO 2 -rich subsurface waters in winter counteracts effect of cooling on pCO 2 (Takahashi et al., 2005) Upwelling of CO 2 -rich subsurface waters in winter counteracts effect of cooling on pCO 2 (Takahashi et al., 2005) Mixed Layer Variability

Aleutian Low is a wintertime semi-permanent cyclone Strong Low:  strong westerly winds in central N. Pacific  cooler SSTs, deeper mixed layer Strong Low:  strong westerly winds in central N. Pacific  cooler SSTs, deeper mixed layer  enhanced southerly winds in eastern N. Pacific  warmer SSTs, upwelling supressed Strength of Low associated with PDO and ENSO.

Pacific Decadal Oscillation (PDO) is measure of climate variability with possible impacts on CO 2 flux; it has a 20 – 30 year period Pacific Decadal Oscillation (PDO) is measure of climate variability with possible impacts on CO 2 flux; it has a 20 – 30 year periodicity Positive Phase: SSTs cold, mixing layer deep in central and western North Pacific PDO Warm SSTs in Alaska Gyre, along coast of North America, and into tropics

Strong Low Weak Low PDO Aleutian Low

Patra et al. (2005) finds that sea-air CO 2 flux over North Pacific is significantly associated with PDO at 5 months lag Patra et al. (2005) finds that sea-air CO 2 flux over North Pacific is significantly associated with PDO at 5 months lag Believe that delayed effect may be result of slow response of marine ecosystems and other environments to changes in climate mode Believe that delayed effect may be result of slow response of marine ecosystems and other environments to changes in climate mode PDO In positive phase, upwelling of high CO 2 waters suppressed due to anomalously northward wind off of Canada In positive phase, upwelling of high CO 2 waters suppressed due to anomalously northward wind off of Canada

(Keeling et al., 2004) station located near Hawaii is believed to have shifted from a weak CO 2 sink to weak source due to increased transport of high salinity waters from the north (Keeling et al., 2004) shift may be linked to a possible 1997 regime shift in the PDO shift may be linked to a possible 1997 regime shift in the PDO PDO May also influence pCO 2 via changes in ocean circulation

El Nino-Southern Oscillation (PDO) has its primary signature in tropics; it has a 3-7 year period El Nino-Southern Oscillation (PDO) has its primary signature in tropics; it has a 3-7 year periodicity ENSO 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 CO 2 flux over North Pacific is significantly associated with ENSO at three months lag Patra et al. find that CO 2 flux over North Pacific is significantly associated with ENSO at three months lag

ENSO PDO La Nina predominates when PDO is in negative phase El Nino predominates when PDO is in positive phase

Upwelling regions in central and eastern equatorial Pacific are a strong source of CO 2 throughout year Upwelling regions in central and eastern equatorial Pacific are a strong source of CO 2 throughout year Kuroshio Current and extension are strong CO 2 sink in winter due primarily to cooling, and a weak source in summer due to warming Kuroshio Current and extension are strong CO 2 sink in winter due primarily to cooling, and a weak source in summer due to warming Western subarctic areas are strong CO 2 source in winter because of convective mixing of waters rich in respired CO 2 and nutrients Western subarctic areas are strong CO 2 source in winter because of convective mixing of waters rich in respired CO 2 and nutrients  become strong sink in winter since nutrients help fuel intense photosynthesis Physical Mechanisms

Takahashi et al., 2005

Many studies have shown increased uptake in tropics and subtropics in recent decades, but their temporal structures are inconsistent Many studies have shown increased uptake in tropics and subtropics in recent decades, but their temporal structures are inconsistent A few areas show decreasing pCO 2 ; these are in or near the Bering and Okhotsk Seas due to increased biological activity A few areas show decreasing pCO 2 ; these are in or near the Bering and Okhotsk Seas due to increased biological activity  may be result of changing nutrient supplies caused by changes in land hydrology or by increases in river or airborne inputs of nutrients pCO 2 variability

Seasonal temperature changes are primary cause for seasonal changes of pCO 2 in subtropical gyres Seasonal temperature changes are primary cause for seasonal changes of pCO 2 in subtropical gyres Takahashi et al. (2006) find that observed increase in pCO 2 is not affected significantly by SST changes, but is primarily due to change in seawater chemistry most likely by uptake of atmospheric CO 2 Takahashi et al. (2006) find that observed increase in pCO 2 is not affected significantly by SST changes, but is primarily due to change in seawater chemistry most likely by uptake of atmospheric CO 2 Changes in total CO 2 concentration caused by winter upwelling and springtime plankton blooms are primary cause for seasonal changes in sub-polar and polar regions (Takahashi et al., 2006) Changes in total CO 2 concentration caused by winter upwelling and springtime plankton blooms are primary cause for seasonal changes in sub-polar and polar regions (Takahashi et al., 2006) Summary

Important to study seawater chemistry as well as temperature and circulation changes throughout world’s oceans, as these can affect future uptake or outgassing of CO 2 Important to study seawater chemistry as well as temperature and circulation changes throughout world’s oceans, as these can affect future uptake or outgassing of CO 2 Vital to understand role of various mechanisms for changes in CO 2 flux in order to accurately quantify potentially changing role of the ocean as a sink for future climate scenarios Vital to understand role of various mechanisms for changes in CO 2 flux in order to accurately quantify potentially changing role of the ocean as a sink for future climate scenarios Conclusion

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: /2004GB 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: /2004GB Quay, P. (2002), Ups and Downs of CO2 Uptake, Science, 298, 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.