Ocean biology: sensitivity to climate change and impacts on atmospheric CO 2

1. nn Ocean biology: sensitivity to climate change and impacts on atmospheric CO2 Irina Marinov (Univ. of Pennsylvania) UW PCC Summer School, WA, September 16th 2010

3. Oceanic carbon pump = Solubility pump + Biological pump Solubility pump Biological pump atmosphere photosynthesis warm Ocean Carbon Storage ocean Respiration (remineralization) cold Store CO2 and nutrients in the deep Store CO2 in the deep

4. The natural ocean carbon: the solubility pump Solubility carbon pump Cold high latitude waters can hold more CO2 than warm low latitude waters. This implies that most CO2 enters the ocean via high latitudes. Here NADW and AABW sink to the bottom of the ocean, taking CO2 with them. This is the solubility pump. A warmer ocean will absorb less CO2(a warm coke loses its CO2 and becomes flat quickly). A positive feedback on atmospheric CO2 ! warm cold Store CO2 in the deep

5. CO2+PO4+NO3+ light organic matter + O2 Photosynthesis: Biological carbon pump Remineralization: Organic matter + O2 CO2+PO4+NO3 (Respiration)

6. CO2+PO4+NO3+ light organic matter + O2 Biological carbon pump PO4, CO2 consumed Store PO4, CO2 PO4, CO2 added to the deep Ocean Carbon Storage (remineralized CO2) Organic matter + O2CO2+PO4+NO3

7. Story 1: How will ocean carbon storage change with changes in ocean ventilation? How will that feedback to atmospheric pCO2? Oceanic natural carbon pumps Store CO2

8. Story2: How will phytoplankton biomass, production and size structure respond to climate change? How will that feedback to atmospheric pCO2? (don’t know yet…) Oceanic natural carbon pumps Store CO2

9. Simplified 2D cartoon of oceanic thermohaline circulation North Atlantic NADW= North Atlantic Deep Water; AABW= Antarctic Bottom Water AAIW = Antarctic Intermediate Water; CDW = Circumpolar Deep water SAMW= Subantarctic Mode Water

10. present Increased Southern Ocean winds (future) Southern Ocean North Atlantic CO2 • Low latitudes CO2 • Low latitudes NADW NADW PO4, CO2 AABW AABW • Most CO2 is stored in the deep ocean. More upwelling (strong winds over Drake passage) results in more CO2 being released to the atmosphere via the Southern Ocean, a decrease in the biological ocean storage and an increase in atmospheric pCO2. • Positive feedback on atmospheric pCO2 !

11. What is the impact of an increase in S. Ocean winds on atmospheric pCO2? North Atlantic • Increasing Southern Ocean winds results in: • more loss of “natural” carbon stored in the deep via stronger CDW, a positive feedback. • more anthropogenic CO2 uptake via stronger SAMW/AAIW, a negative feedback (Russell et al. ‘06) Which one wins ?

12. Changes in the westerlies and atmospheric structure between interglacials and glacials, as proposed by Toggweiler 2008 Warm Interglacials Strength of Westerlies over the Drake passage channel is lower during glacials. Glacials

13. Toggweiler 2006 has a feasible theory to explain glacial-interglacial changes in CO2 and Temperature. Can we apply this to the modern world? Fig 8, Toggweiler et al 2006. Modeled CO2 and T variation. Fig 4, Toggweiler et al 2006. Proposed positive feedback that propels transitions between warm and cold states of the climate system.

14. Increasing Southern Ocean winds increases total ocean carbon storage (due to the biological pump), and decreases atmospheric pCO2. High winds high Kv control pCO2 atm (ppm) Increasing ventilation Oceanic Carbon Storagesoft (PgC) = Total Remineralized carbon in the ocean (PgC) (Marinov et al., 2008a,b)

15. Proposed simple theory fits model results well, but needs generalization! High winds high Kv However, theory assumes fast gas exchange; no CaCO3 or solubility pumps. Next steps: generalize this theory to include the above effects. Non trivial… control pCO2 atm (ppm) Increasing ventilation Oceanic biological Carbon Storage(PgC) Proposed analytic solution: (Marinov et al., 2008a,b)

16. Atmospheric pCO2 is more sensitive (responds more) to changes in ocean biology if deep ocean ventilation is stronger (if Southern Ocean winds increase): high ventilation (high Kv) low ventilation (LL) Oceanic biological Carbon Storage(PgC)

17. High winds -> high ventilation (future) atmospheric pCO2 low ventilation (present) ocean carbon storage (biological pump) • As Southern Ocean winds increase with global warming, the biological ocean carbon storage decreases, further increasing atmospheric pCO2. • the natural biological pump might therefore act as a positive feedback on the system ! Bad News !!!

18. Le Quere et al (2007) notice a decline in the efficiency of the Southern Ocean carbon sink • Part of the decline is attributed to up to a 30% decrease in the efficiency of the Southern Ocean sink over the last 20 years (Le Quere et al, 2007) • This sink removes annually 0.7 Pg of anthropogenic carbon. • The decline is attributed to the strengthening of the winds around Antarctica which enhances ventilation of natural carbon-rich deep waters. • The strengthening of the winds is attributed to global warming and the ozone hole. Credit: N.Metzl, August 2000, oceanographic cruise OISO-5 Le Quéré et al. 2007, Science

19. Land Ocean Efficiency of Natural Sinks Atmosphere (+ 0.23% y−1) Obs. difference LeQuere et al. 2007 (model) Canadell et al. 2007, PNAS; Raupach, Canadell, LeQuere 2008, Biogeosciences

20. Decline in the Efficiency of Natural CO2-Sinks

21. Story2: How will phytoplankton biomass, production and size structure respond to climate change? How will that feedback to atmospheric pCO2? (don’t know yet…) Oceanic natural carbon pumps Marinov, Doney, Lima, Biogeosciences Discussions, Sept 2010 Store CO2

22. Phytoplankton Groups Fixed C/N/P, Variable Fe/C, Chl/C, Si/C Diazotrophs (C, Chl, Fe) Picoplankton / Coccolithophores (C, Chl, Fe, CaCO3) Diatoms (C, Chl, Fe, Si) Nutrients Ammonium Nitrate Phosphate Silicate Iron CCSM3.1=Dynamic Green Ocean Model (DGOM) Zooplankton (C) Dissolved Organic Material (C, N, P, Fe) Sinking Particulate Material (C, (N, P), Fe, Si, CaCO3, Dust) Moore, Doney & Lindsay, Global Biogeochem. Cycles (2004)

23. Types of phytoplankton we model: 1. Diatoms • Large photosynthetic phytoplankton, 50 mm wide, with SiO2 shells • Best at exporting Carbon to the deep ocean 2. Small phytoplankton (Nano-pico plankton) - get recycled more at surface, less export ex: Coccolithophores • Photosynthetic phytoplankton with CaCO3 shell (nanoplankton, ~10mm wide). • Respond to increased ocean acidity. 3. Diazotrophs bacteria that fix atmospheric nitrogen gas into a more usable form such as ammonia.

24. Biomass (1980-1999 NCAR model mean): Diatom Carbon Diatom relative abundance Small Phyto. Carbon Small Phyto. Carbon Small phytoplankton: better at taking up nutrients in nutrient poor subtropical gyres. Strongly grazed. Diatoms: require higher nutrients to reach their maximal growth rates. Grazed less. Dominant in turbulent conditions or under bloom conditions. Diazotroph Carbon

25. CCSM-3 Carbon-Climate • control & prescribed CO2 emissions (SRES A2) simulations • Increasing atmospheric CO2 => • upper ocean warming & freshening (decr in salinity) • increased stratification Atmospheric pCO2 (ppm) Upper ocean temperature (deg. C) Upper ocean salinity (psu)

26. present (1980-1999) (2080-2099)-(1980-1999) wind stress x  wind stress x wind stress curl  wind stress curl vertical velocity  vertical velocity

27. Increased Stratification with global warming over most of the ocean (due to enhanced temperature) • Less change in Southern Ocean stratification, because of the counteracting impact of stronger winds. Stratification Years (2080-2099) - (1980-1999) Stratification (1980-1999) High mixing Low mixing Q: How will ocean ecology respond to these changes in stratification?

28. Separate ecological biomes (based on physical principles) LL Upwelling Equatorial Subtropical (permanent + seasonal) Subpolar Ice biome * technique as in Sarmiento et al. 2004

29. Ecological Biomes (Present)  Ecological Biomes All biome changes are more pronounced in the Northern Hemisphere !

30. Satellite data suggests that ocean oligotrophic areas are getting larger Irwin et al. 2009 “Are ocean deserts getting larger?” Polovina et al. 2008 “Ocean’s least productive waters are expanding” Increase in the Global area of extreme oligotrophic province in the ocean for SeaWIFS (black) and MODIS/Aqua (grey) Irwin, GRL 2009

31. Increased stratification decreases mixed layer depth: less nutrient supply, more light Tropics/mid-latitudes (nutrient limited) • -Subtropics: nutrient limited; Nutrient decrease will lower Chl and primary productivity • High latitudes: light limited • More light increases Chl and primary productivity in subpolar gyres Higher latitudes (light limited in winter) Doney 2006; Sarmiento et al. 2004 Does this classical picture explain our model results?

32. Increased stratification decreases mixed layer depth: less nutrient supply, more light Tropics/mid-latitudes (nutrient limited) • - Subtropics: nutrient limited; Nutrient decrease will lower Chl and primary productivity • The response to climate change in low/mid-latitudes: • Nutrients become more limiting: Diatoms decrease, partially replaced by small phytoplankton (less mixing and less vertical supply of NO3) • Overall total chlorophyll and primary production decrease • e-ratio decreases - increased surface recycling

33. Global phytoplankton decline over the past century (Boyce et al. Nature 2010) Increases in Temp are associated with decreases in phytoplankton Chl. What is the underlying mechanism? 1899-2009 Effect of SST on Chl in situ Chl + transparency data

34. However … More increase in stratification in the N Hemisphere -> larger drop in nutrients, production and export ratio compared to Southern Hemisphere. Very different responses in NH and SH ! S Hem N Hem global Stratification (kg/m3) surface NO3 (mmol/m3) Total Carbon (biomass) Total Primary Prod (PgC/yr) Export Flux (PgC/yr) e-ratio

35. Classical “expected” response to climate change in the Northern Hemisphere: • Nutrients become more limiting. Diatoms decrease, partially replaced by small phytoplankton (less mixing and less vertical supply of NO3) • Overall total chlorophyll and primary production decrease • e-ratio decreases - increased surface recycling • “Unexpected” Southern hemisphere response to climate change: • Less increase in stratification due to stronger S Ocean winds! • Subtropical-subpolar S Ocean front shifts southward and upwelling/temperature increase locally • More upwelling means that diatoms do better relative to small phyto; slight increases in chlorophyll and production; e-ratio decrease minimal !

36. Biogeochemical Model Equations: Grazing: + complicated equations for particulate organic carbon (POC), etc. • Can we understand the response of this system to future changes in climate change by analyzing the underlying model equations ?

37. Model Phytoplankton Growth Equations (biomass in mol C/m3) Specific Growth Rate: light availability temperature function IPAR(W/m2)= surf irradiance nutrient functional response

38. Assume that climate change results changes in light, nutrients and temperature. What is the impact on phytoplankton biomass S and L? If the model is simple enough we can calculate analytically each of these terms at steady state ! Q: Will a given change in nutrients change more S or L, i.e., will

39. For example, in the GFDL TOPAZ model we can show that: • In the 40oS-40oN region where background nutrients are below Ncritical (1.18 mmolNO3/m3), a change in nutrients will affect more small than large phytoplankton: • Outside 40oS-40oN, the opposite is the case. At steady state, the equations translate to:

40. Critical Nutrient Hypothesis • Critical nutrient hypothesis: In the 40S-40N biome, climate driven decreases in nutrients (due to increased stratification) have a larger impact on small phytoplankton than on diatom biomass.The opposite is the case in high nutrient high latitudes. (NCAR, GFDL) • Similar analysis about temperature and light variations in the model … 40oS - 40oN: low nutrient region a nutrient change will affect more small phytoplankton than diatoms. diatoms respond more Small phyto respond more Small phyto respond more high latitudes: high nutrient zone a nutrient change will affect more diatoms than small phytoplankton diatoms respond more

41. New satellite backscattering method aims to separate size structure (shown are SeaWIFS 1997-2007 means) Pico (0.5-2um) particle number Nano (2-20um) particle number Micro (20-50um) Kostadinov et al. 2010

42. Summary: • Story 1: • The sensitivity of atmospheric pCO2 to changes in ocean biology (and hence the feedback strength) depends on ocean ventilation. The stronger the ventilation, the more sensitive atmospheric pCO2 is to ocean biology. • Increasing Southern Ocean winds act to decrease the biological storage in the Southern Ocean and increase atmospheric pCO2. Positive feedback. • Story 2: • Increasing oceanic stratification in low and mid-latitudes results in a relative increase in small phytoplankton and a decrease in diatoms. Therefore, e-ratio decreases globally and ocean carbon storage is less efficient: positive feedback. • This effect is less pronounced in the Southern Hemisphere, because of the counteracting effect of increasing S. Ocean winds (smaller positive feedback) • On-going work to calculate the relative impacts of temperature, nutrients and light on different species, and the relative changes in the species with warming.

43. Thank you …

44. pCO2atm (ppm), coupled pCO2atm, coupled - uncoupled Land Uptake, coupled - uncoupled Land Uptake, coupled (GtC/yr) Hadley Ocean Uptake, coupled - uncoupled Ocean Uptake, coupled (GtC/yr) Hadley Friedlingstein et al. 2006 CCSM-1 “Climate-C cycle feedback analysis: results from the CMIP-4 model intercomparison” UVic

45. Change in land and ocean carbon (GtC): Ocean C sensitivity to climate change Ocean C sensitivity to atmospheric CO2 Carbon cycle gain, g, along with component sensitivities of climate to CO2 (α), land and ocean carbon storage to CO2 (βL, βO), and land and ocean carbon storage to climate (γL, γO). Calculations are done for year 2100. (Friedlingstein, 2006)