1. nn Ocean biology: sensitivity to climate change and impacts on atmospheric CO 2 Irina Marinov (Univ. of Pennsylvania) UW PCC Summer School, WA, September 16 th 2010

3. atmosphere ocean Solubility pump Oceanic carbon pump = Solubility pump + Biological pump warm cold Biological pump Store CO 2 and nutrients in the deep Store CO 2 in the deep photosynthesis Respiration (remineralization) Ocean Carbon Storage

4. Solubility carbon pump The natural ocean carbon: the solubility pump warm cold Store CO 2 in the deep Cold high latitude waters can hold more CO 2 than warm low latitude waters. This implies that most CO 2 enters the ocean via high latitudes. Here NADW and AABW sink to the bottom of the ocean, taking CO 2 with them. This is the solubility pump. A warmer ocean will absorb less CO 2 (a warm coke loses its CO 2 and becomes flat quickly). A positive feedback on atmospheric CO 2 !

5. CO 2 +PO 4 +NO 3 + light organic matter + O 2 Organic matter + O 2 CO 2 +PO 4 +NO 3 Biological carbon pump Photosynthesis: Remineralization: (Respiration)

6. PO 4, CO 2 consumed PO 4, CO 2 added to the deep CO 2 +PO 4 +NO 3 + light organic matter + O 2 Organic matter + O 2 CO 2 +PO 4 +NO 3 Biological carbon pump Store PO 4, CO 2 Ocean Carbon Storage (remineralized CO 2 )

7. Oceanic natural carbon pumps Store CO 2 Story 1: How will ocean carbon storage change with changes in ocean ventilation? How will that feedback to atmospheric pCO 2 ?

8. Oceanic natural carbon pumps Store CO 2 Story2: How will phytoplankton biomass, production and size structure respond to climate change? How will that feedback to atmospheric pCO 2 ? (don’t know yet…)

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. Southern Ocean AABW NADW North Atlantic Low latitudes AABW NADW Low latitudes Increased Southern Ocean winds (future) CO 2 Most CO 2 is stored in the deep ocean. More upwelling (strong winds over Drake passage) results in more CO 2 being released to the atmosphere via the Southern Ocean, a decrease in the biological ocean storage and an increase in atmospheric pCO 2. Positive feedback on atmospheric pCO 2 ! PO 4, CO 2 present

11. What is the impact of an increase in S. Ocean winds on atmospheric pCO 2 ? 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 CO 2 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 Glacials Warm Interglacials Strength of Westerlies over the Drake passage channel is lower during glacials.

13. Fig 4, Toggweiler et al 2006. Proposed positive feedback that propels transitions between warm and cold states of the climate system. Fig 8, Toggweiler et al 2006. Modeled CO2 and T variation. Toggweiler 2006 has a feasible theory to explain glacial- interglacial changes in CO 2 and Temperature. Can we apply this to the modern world?

14. (Marinov et al., 2008a,b) Oceanic Carbon Storage soft (PgC) High winds high Kv control Increasing Southern Ocean winds increases total ocean carbon storage (due to the biological pump), and decreases atmospheric pCO 2. Increasing ventilation pCO 2 atm (ppm) = Total Remineralized carbon in the ocean (PgC)

15. (Marinov et al., 2008a,b) Oceanic biological Carbon Storage (PgC) High winds high Kv control Increasing ventilation pCO 2 atm (ppm) Proposed simple theory fits model results well, but needs generalization! Proposed analytic solution: However, theory assumes fast gas exchange; no CaCO 3 or solubility pumps. Next steps: generalize this theory to include the above effects. Non trivial…

16. low ventilation (LL) high ventilation (high Kv) Atmospheric pCO 2 is more sensitive (responds more) to changes in ocean biology if deep ocean ventilation is stronger (if Southern Ocean winds increase): Oceanic biological Carbon Storage (PgC)

17. ocean carbon storage (biological pump) atmospheric pCO 2 (present) (future) High winds -> high ventilation low ventilation As Southern Ocean winds increase with global warming, the biological ocean carbon storage decreases, further increasing atmospheric pCO 2. the natural biological pump might therefore act as a positive feedback on the system ! Bad News !!!

18. 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. Le Quéré et al. 2007, Science Credit: N.Metzl, August 2000, oceanographic cruise OISO-5 Le Quere et al (2007) notice a decline in the efficiency of the Southern Ocean carbon sink

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

20. Decline in the Efficiency of Natural CO 2 -Sinks

21. Oceanic natural carbon pumps Store CO 2 Story2: How will phytoplankton biomass, production and size structure respond to climate change? How will that feedback to atmospheric pCO 2 ? (don’t know yet…) Marinov, Doney, Lima, Biogeosciences Discussions, Sept 2010

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

23. 1. Diatoms –Large photosynthetic phytoplankton, 50 mm wide, with SiO 2 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 CaCO 3 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. Types of phytoplankton we model:

24. Biomass (1980-1999 NCAR model mean): Small Phyto. Carbon Diatom Carbon Diazotroph 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. Diatom relative abundance

25. Atmospheric pCO 2 (ppm) CCSM-3 Carbon-Climate control & prescribed CO 2 emissions (SRES A2) simulations Increasing atmospheric CO 2 => upper ocean warming & freshening (decr in salinity) increased stratification Upper ocean temperature (deg. C) Upper ocean salinity (psu)

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

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 (1980-1999) Stratification Years (2080-2099) - (1980-1999) Q: How will ocean ecology respond to these changes in stratification? Low mixing High mixing

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

29.  Ecological Biomes Ecological Biomes (Present) Ecological Biome:control (1980-1999) areas (10 12 m 2 ) % change Climate driven trends Marginal Sea Ice (Ice)N.Hem: 15.1 S.Hem: 25.0 -18.9% -15.4% Contraction Subpolar (SP)N Hem: 17.8 S Hem: 36.5 + 8.9% + 3.5% Expansion Subtropical gyresN Hem: 67.3 S Hem: 95.3 + 4.5% + 1.6% Expansion All biome changes are more pronounced in the Northern Hemisphere !

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

31. Higher latitudes (light limited in winter) Does this classical picture explain our model results? -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 Tropics/mid-latitudes (nutrient limited) Doney 2006; Sarmiento et al. 2004 Increased stratification decreases mixed layer depth: less nutrient supply, more light

32. - Subtropics: nutrient limited; Nutrient decrease will lower Chl and primary productivity Tropics/mid-latitudes (nutrient limited) Increased stratification decreases mixed layer depth: less nutrient supply, more light 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 NO 3 ) 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 in situ Chl + transparency data Effect of SST on Chl

34. Total Primary Prod (PgC/yr) Stratification ( kg/m 3 ) Export Flux (PgC/yr) e-ratio surface NO 3 (mmol/m 3 ) N Hem S Hem global 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 ! Total Carbon (biomass)

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 NO 3 ) 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: Can we understand the response of this system to future changes in climate change by analyzing the underlying model equations ? + complicated equations for particulate organic carbon (POC), etc.

37. Model Phytoplankton Growth Equations (biomass in mol C/m 3 ) Specific Growth Rate: light availability temperature function nutrient functional response I PAR (W/m 2 )= surf irradiance

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. In the 40 o S-40 o N region where background nutrients are below N critical (1.18 mmolNO 3 /m 3 ), a change in nutrients will affect more small than large phytoplankton: Outside 40 o S-40 o N, the opposite is the case. For example, in the GFDL TOPAZ model we can show that: At steady state, the equations translate to:

40. diatoms respond more Small phyto respond more high latitudes: high nutrient zone 40 o S - 40 o N: low nutrient region a nutrient change will affect more small phytoplankton than diatoms. a nutrient change will affect more diatoms than small phytoplankton Critical Nutrient Hypothesis diatoms respond more 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 …

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

42. Summary: Story 1: The sensitivity of atmospheric pCO 2 to changes in ocean biology (and hence the feedback strength) depends on ocean ventilation. The stronger the ventilation, the more sensitive atmospheric pCO 2 is to ocean biology. Increasing Southern Ocean winds act to decrease the biological storage in the Southern Ocean and increase atmospheric pCO 2. 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. Friedlingstein et al. 2006 pCO 2 atm, coupled - uncoupled Land Uptake, coupled (GtC/yr) Land Uptake, coupled - uncoupled Ocean Uptake, coupled - uncoupled Ocean Uptake, coupled (GtC/yr) pCO 2 atm (ppm), coupled Hadley CCSM-1 Hadley UVic “Climate-C cycle feedback analysis: results from the CMIP-4 model intercomparison”

45. Change in land and ocean carbon (GtC): Ocean C sensitivity to atmospheric CO 2 Ocean C sensitivity to climate change Carbon cycle gain, g, along with component sensitivities of climate to CO 2 (α), land and ocean carbon storage to CO 2 (β L, β O ), and land and ocean carbon storage to climate (γ L, γ O ). Calculations are done for year 2100. (Friedlingstein, 2006)