CO 2 flux in the North Pacific Alan

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

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

Introduction • Oceans contain ~50 x as much CO 2 as atmosphere • Mean

Introduction • Oceans contain ~50 x 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) • Only a few stations in the ocean CO 2 monitoring network lack of ocean CO 2 time series limits scientists’ ability to estimate interannual changes in oceanic CO 2 uptake • Researchers have looked at atmospheric time series of CO 2, 13 CO 2, and O 2 to infer interannual changes in oceanic and terrestrial CO 2 uptake

Distribution of climatological mean annual sea air CO 2 flux (moles CO 2 m

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. http: //www. pmel. noaa. gov/pubs/outstand/feel 2331/mean. shtml

Why the North Pacific? • I concentrate on North Pacific as it is a

Why the North Pacific? • 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 • 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 p. CO 2 values are governed primarily by physical processes because of reduced biological activity (Mc. Kinley et al. , 2006) • Photosynthesis has significant effects on p. CO 2 come spring and summer

p. CO 2 sensitivity • p. CO 2 of seawater is sensitive function of

p. CO 2 sensitivity • p. CO 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 p. CO 2 to changes in total CO 2

SST vs. Biology • Influences of SST on surface ocean p. CO 2 oppose

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

Mixed Layer Variability • Upwelling of CO 2 rich subsurface waters in winter counteracts

Mixed Layer Variability • Upwelling of CO 2 rich subsurface waters in winter counteracts effect of cooling on p. CO 2 (Takahashi et al. , 2005) • 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). http: //www. pmel. noaa. gov/~cronin/encycl/cartoon. jpg

Aleutian Low is a wintertime semi permanent cyclone Strong Low: strong westerly winds in

Aleutian Low is a wintertime semi permanent cyclone 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. http: //www. ecy. wa. gov/programs/sea/coast/storms/weather. html

PDO • Pacific Decadal Oscillation (PDO) is measure of climate variability with possible impacts

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

PDO Aleutian Low Strong Low Weak Low

PDO Aleutian Low Strong Low Weak Low

PDO • In positive phase, upwelling of high CO 2 waters suppressed due to

PDO • In positive phase, upwelling of high CO 2 waters suppressed due to anomalously northward wind off of Canada • 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

PDO • May also influence p. CO 2 via changes in ocean circulation •

PDO • May also influence p. CO 2 via changes in ocean circulation • 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 http: //kela. soest. hawaii. edu/ALOHA/images/hawaii. jpg

ENSO • El Nino Southern Oscillation (PDO) has its primary signature in tropics; it

ENSO • El Nino Southern Oscillation (PDO) has its primary signature in tropics; it has a 3 7 year periodicity period • 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 http: //tao. atmos. washington. edu/pdo//

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

PDO ENSO La Nina predominates when PDO is in negative phase El Nino predominates when PDO is in positive phase http: //tao. atmos. washington. edu/pdo// http: //www. pmel. noaa. gov/~kessler/ENSO/soi-1950 -98. gif

Physical Mechanisms • Upwelling regions in central and eastern equatorial Pacific are a strong

Physical Mechanisms • 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 • 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

Takahashi et al. , 2005

Takahashi et al. , 2005

p. CO 2 variability • Many studies have shown increased uptake in tropics and

p. CO 2 variability • Many studies have shown increased uptake in tropics and subtropics in recent decades, but their temporal structures are inconsistent • A few areas show decreasing p. CO 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 http: //www. pmel. noaa. gov/np/images/maps/npacific 6. gif

Summary • Seasonal temperature changes are primary cause for seasonal changes of p. CO

Summary • Seasonal temperature changes are primary cause for seasonal changes of p. CO 2 in subtropical gyres • 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) • Takahashi et al. (2006) find that observed increase in p. CO 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

Conclusion • Important to study seawater chemistry as well as temperature and circulation changes

Conclusion • 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

References Keeling, C. D. , H. Brix, and N. Gruber (2004), Seasonal and long

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¸ GB 4006, doi: 10. 1029/2004 GB 002227. Mc. Kinley, 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 CO 2 flux from atmospheric CO 2 inverse modeling, Global Biogeochem. Cycles, 19, GB 4013, doi: 10. 1029/2004 GB 002257. Quay, P. (2002), Ups and Downs of CO 2 Uptake, Science, 298, 2344. Takahashi, T. , S. C. Sutherland, R. A. Feely, and R. Wanninkhof (2005), Decadal Change of the Surface Water p. CO 2 in the North Pacific: A Synthesis of 35 Years of Observations, submitted to J. Geophys. Res.