Modeling Low-Oxygen Regions

Transcription

1 Modeling Low-Oxygen Regions Andreas Schmittner College of Oceanic and Atmospheric Sciences Oregon State University 1.How well can global models simulate low- oxygen regions? 2.Long-term projections 3.Variability 4.Coastal ocean oxygen modeling 5.Paleo prespective Ocean Carbon and Biogeochemistry (OCB) summer workshop 2010 Scripps Institution of Oceanography

2 1. How well can global models simulate low-oxygen regions? Stratospheric N2O Sink Fixed UVic Model (Weaver et al. 2001) 2D Energy-Moisture Balance Atmosphere (fixed winds) O2 N2O CO2 CO2 CO2 N2O Winds Fixed Dyn. Thermod. Sea Ice Fixed 3D Ocean (1.8x3.6 deg, 19 levels) 2N2PZD Ocean Ecosystem / Biogeochemistry Model (Schmittner et al GBC) O O2 O2 Plankton DIC PO4 NO3 DIC PO4 NO3 Soil Terrestrial Vegetation / Carbon Cycle (Meissner et al Clim. Dyn.) Nevison et al GBC O2,crit=4±3μM

3 1. How well can global models simulate low-oxygen regions? Schmittner et al. (2007) Paleoceanography

4 1. How well can global models simulate low-oxygen regions? Schmittner et al. (2007) Paleoceanography

5 How well can global models simulate low-oxygen regions? Large scale oxygen distribution can be modeled well Low-oxygen regions not so well. Typically suboxic volume overestimated. Issues: physics (resolution, mixing parameterizations), biology (zooplankton vertical migration,...)

6 2. Long-Term Projections Global Warming until year 4000 Business-as-usual based on burning of all readily available fossil fuel reserves (SRES A2, linear decrease from ) Schmittner et al. (2008) GBC 2. Long-term projections 9ºC Warming Control Sea Ice Disappears Sea Level Rises (only thermal expansion)

7 2. Long-term projections Impacts on Ocean Circulation and dproductivity it NPP doubles New Production Export Production Schmittner et al. (2008) GBC

8 Impact on O and N Cycles 2. Long-term projections Oxygen decreases Suboxic water volume increases Denitrification increases by 350% Nitrogen fixation increases Decrease in NO3 inventory small N2O production increases by 64% (estimated from empirical relation by Nevison et al., 2003) => atmospheric N2O increases by 60 ppb (21%) => additional warming by 0.2ºC Schmittner et al. (2008) GBC

9 2. Long-term projections Dissolved Oxygen Change (%) QuickTime and a BMP decompressor are needed to see this picture. Time (years)

10 2. Long-term projections year m depth

11 Oxygen on σθ=27.0 kg/m 3 year 2100 ΔO2 C:N fixed 2. Long-term projections Effects of C:N changes Gnanadesikan et al. (2007) Ocean Sci. effect reduced upwelling ΔO2 C:N (pco2) Oschlies et al. (2008) GBC

12 Acidification effects (decreased ballasting) Global Tropical Indian 2. Long-term projections Tropical Atlantic Tropical Pacific Hofmann & Schellnhuber 2009 PNAS North Pacific

13 Keeling et al Annu. Rev. Mar. Sci

14 3. Long-Term Projections Dissolved Oxygen is projected to decrease world-wide due to decreased solubility increased stratification / slower circulation Low-oxygen regions will expand, perhaps dramatically increased denitrification increased N2O production (very small positive climate feedback) positive climate feedback) Biological effects of acidification may

15 Variability: Atlantic 3. Decadal variability Fröhlicher et al., 2009, GBC

16 Variability: Pacific 3. Decadal variability Fröhlicher et al., 2009, GBC

17 Variability: Pacific 3. Decadal variability Deutsch et al. (2006) GBC

18 Variability Much of the observed changes due to internal variability Models capture variability in North Atlantic Models underestimate variability in North Pacific

19 Spitz, Batchelder, Koch CIOSS Project 4. Coastal Models

20 4. Coastal Models 2002 GLOBEC - LTOP data Climatology Spitz, Batchelder, Koch CIOSS Project

21 Coastal Models Important to predict local occurrence of Important to predict local occurrence of hypoxia Boundary conditions crucial

22 5. Paleo De Pol-Holz et al. (2006) Emmer and Thrunell (2000) Altabet et al. (2002) Ren et al. (2009) Time

23 5. Paleo LGM preliminary model results Solid Lines Dashed Lines Fe Limitation No Yes Sedim. Denitrification No Yes Time AMOC collapsed not collapsed

24 Difference 5. LGM Paleo Funded by NSF MG&G Chris Somes

25 Paleo Perspective Provides information on past episodes of ocean deoxygenation and effects on biogeochemical cycles (e.g. N-cycle) Models including N-isotopes are now available and can provide quantitative constraints in combination with observations

26 Thanks

27 Paleo: Effects of Ocean Circulation Changes Shutdown of Atlantic Meridional Overturning Circulation Schmittner et al. (2007) Paleoceanography

28 Schmittner et al. (2007) Paleoceanography

29 Comparison with Ice Core Record Time Time Model reproduces N2O amplitude and timescale

30 Atlantic Pacific Schmittner (2005) Nature

31 Productivity Decreases Schmittner 2005 Nature

32 Semidiurnal Diurnal Diurnal

33 δ 15 N Model Somes et al., 2010 GBC subm. Fe εnfix=1.5 UVic Model (Weaver et al. 2001) 2D Energy-Moisture Balance Atmosphere (fixed winds) εdeni=25 εdeni=25 εassim=5 εnfix=1.5 εexcr=6 εassim=5 Dyn. Thermod. Sea Ice 3D Ocean Circulation (MOM) (1-1.8)x3.6, 19 levels 2N2PZD Ocean Ecosystem / Biogeochemistry Model (Schmittner et al GBC) Assumptions: Constant Elemental Ratios No DOM No N-Deposition No River Input of N no fractionation tuned to reproduce global mean 15 N

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