Effects of ocean acidification & warming on organic matter production

Transcription

1 Effects of ocean acidification & warming on organic matter production : Possible changes in biological carbon pump efficiency Ja-Myung Kim PICES 2015 Annual Meeting October Qingdao China

2 Atmosphere Surface ocean CO 2 CO 2 (µm) C:N ratio Carbon overconsumption? Phytoplankton Org C CO DOC 1500 POC:DOC ratio Carbon sequestration enhancement? Biological pump POC 2000 Sediments Depth (m)

3 Controlled in-situ mesocosm experiment

4 Experimental approaches Natural env. Big bags Bottles Open ocean monitoring Coastal in-situ perturbation Lab cultures Molecular mechanisms

5 Experimental approaches Similarity Natural env. Big bags Bottles in-situ perturbation expt. Mesocosm Control Observation on multidisciplinary parameters

6 Mesocosm Experiments Adjacent areas of the Arctic Ocean North Pacific

7 Mesocosm System Jangmok, Geoje island, Korea

8 Experimental conditions Combined effects of seawater pco 2 concentration & temperature 400 ppm 950 ppm 950 ppm Ambient temp. Ambient temp. 3 o C higher temp. Control Acidification Greenhouse

9 Experimental set up: pco 2 adjustment 2 m 950 ppm pco L

10 Homogeneous mixing

11 Temperature adjustment Nutrient addition N ~33 µm P ~ 2.5 µm Si ~50 µm Water bath + 3 o C

12 Total organic carbon production TOC production (μmol kg -1 ) Control Acidification Greenhouse N depleted Day

13 % ratio of DOC to TOC production % (DOC dayn / TOC day20 ) Control Acidification Greenhouse N depleted Day

14 DOC production process in marine system Production Consumption DIC Phytoplankton Virus Microzooplankton DOC Bacteria Sinking particles Macrozooplankton

15 The most likely mechanism of enhanced DOC production Production Virus DIC Phytoplankton Grazing-induced production Microzooplankton DOC Bacteria Sinking particles Macrozooplankton

16 The most likely mechanism of enhanced DOC production 1.2 Growth rate (d -1 ) ppm 750 ppm Skeletonema costatum major prey DOC Kim et al Limnol. Oceanogr. Grazing-induced production Heterotrophic dinoflagellates ~ 90% of the total carbon biomass of microzooplankton 0

17 The most likely mechanism of enhanced DOC production Control Acidification Greenhouse Grazing-induced production Grazing rate (d -1 ) Day Abundance (x10 4 cells L -1 ) Heterotrophic dinoflagellates Day

18 DOC production (μmol kg -1 ) Another possible mechanism Extracellular DOC release Control Literature Acidification Greenhouse Extracellular release of photosynthetic products was enhanced in warm ocean conditions : Zlotnik and Dubinsky 1989,Morán et al Photosynthetic activity increase N depleted Day POC production (μmol kg -1 )

19 Enhanced DOC production under warm ocean condition ΔDOC = ΔTOC - ΔPOC Wohlers et al Indoor-mesocosm Baltic seawater (winter/spring) Diatom (S. costatum) dominated Ctrl TOC build-up POC build-up Net build-up of TOC was NOT markedly affected by changes in temperature. Yet, after the biomass peak, an enhanced accumulation of DOC occurred at high Temp. + 6 o C * Underlying Mechanism High respiratory consumption of organic C relative to autotrophic production

20 Atmosphere Surface ocean CO 2 DIC:DIN ratio Carbon overconsumption? vs. POC:DOC ratio Carbon sequestration enhancement? Phytoplankton DOC Org C Biological pump POC Strengthening of biological carbon removal efficiency CO 2 Sediments

21 The molar ratio of C to N ± 0.3 This study ΔC (μmol kg -1 ) ΔN (µmol kg -1 ) Riebesell et al ppmv ppmv ppmv

22 CO2 effect Temp. effect Partitioning Elemental ratio ΔTOC ΔPOC ΔDOC ΔTOC:N (or ΔDIC) (or ΔDIC:N) This study Engel et al Riebesell et al Wohlers et al Taucher et al Engel/Czerny et al Biermann et al. 2015

23 CO 2 Photosynthesis Respiration Microbial pump Weakening of biological carbon removal efficiency? Org C microbes Biological pump CO 2 RDOM slow cycle up to millennia POC Jiao et al Nature reviews

24 Conclusion 1. Elevated seawater pco 2 concentration and temperature stimulated two main processes responsible for enhancing DOC production (release by grazers and the extracellular release by phytoplankton). 2. An increase in the DOC:POC production ratio implies a shift in the organic carbon flow from particulate to dissolved forms under future ocean condition. 3. Excess DOC production may act as a positive feed back to increase the atmospheric CO 2 (if the produced DOC is labile and rapidly transformed into inorganic carbon by microbial degradation).