Plankton stoichiometry and ocean change

Transcription

1 Plankton stoichiometry and ocean change Impacts of Ocean Change on Primary Producers Ulf Riebesell Ulf Riebesell Joana Barcelos e Ramos, Antje Biermann, Klaus von Bröckel, Jan Czerny, Arne Körtzinger, Sebastian Krug, Michael Meyerhöfer, Marius Müller, Andreas Oschlies, Leibniz Institute of Marine Sciences, IFM-GEOMAR, Kiel Kai Schulz, Julia Wohlers, Eckart Zöllner SOPRAN Mesocosm CO Foto: Mesocosm Facility, 2 perturbation experiment, Baltic Sea, July 2008 University of Bergen, Norway CarboOcean

2 For primary producers the ocean in a high CO 2 world will be different from the present ocean in several respects Atmospheric CO 2 Climate Ocean acidification Ocean warming Seawater CO 2 Temperature Mixing, stratification Circulation Atmospheric deposition Carbonate chemistry Light Nutrients Pelagic Ocean ecosystems biota Stoichiometry (Si/C/N/P/Fe) Rain ratio (CaCO 3 /POC) C-partitioning (POC-DOC-TEP) Nutrient utilization efficiency Carbon sinks & sources

3 Impacts of Ocean Change on Primary Producers Atmospheric CO 2 Overarching questions: Climate Will the future ocean be more or less productive? Will primary producers provide more or less food to higher trophic levels? Seawater CO 2 Carbonate chemistry Temperature Mixing, stratification Light Pelagic ecosystems Ocean biota Circulation Nutrients Atmospheric deposition Will marine biota sequester more or less CO 2? Stoichiometry Rain ratio C-partitioning Carbon sinks & sources Nutrient utilization efficiency Assess OA- and T-driven feedbacks according to Sign of change positive feedback Sensitivity Capacity Longevity negative feedback amplifies initial perturbation dampens initial perturbation level of perturbation needed to trigger a feedback strength of feedback compared to initial perturbation relevant time-scales: permanent vs. transient

4 Responses to ocean acidification/carbonation There will be winners and losers Winners Eelgrass (Zostera) Cyanobacteria Dinoflagellates Filamentous green algae Losers? Coccolithophores Hinga 2002 ph range for maximum growth

5 Responses to ocean acidification/carbonation Calcification e.g. calcareous microalgae Decrease in calcification, slight increase in photosynthesis Riebesell et al. 2000, Zondervan et al. 2001, Sciandra et al. 2003, Delille et al. 2005, Leonardos & Geider 2005, Langer et al. 2006, Feng et al. 2008, Krug et al. unpubl., Müller (talk tomorrow) + weak ++ moderate +++ strong Gephyrocapsa oceanica 1 μm present pco 2 pco 2 photosyn. calcific. Calcidiscus quadriperforatus Coccolithus braarudii

6 Responses to ocean acidification/carbonation e.g. calcareous microalgae Calcification negative + +? Decrease in calcification, slight increase in photosynthesis Riebesell et al. 2000, Zondervan et al. 2001, Sciandra et al. 2003, Delille et al. 2005, Leonardos & Geider 2005, Langer et al. 2006, Feng et al Krug et al. unpubl., Müller (talk tomorrow) Declining strength of carbonate pump increases CO 2 sequestration, but only weak feedback Zondervan et al. 2001, Heinze 2004, Ridgwell et al. 2007, Gehlen et al Open question: Replacement of sensitive species by more robust coccolithophorids or by other groups? see Krug et al. M28 Heinze 2004 CaCO 3 export pco 2atm Ridgwell et al. 2007: PgC until year 3000 corresponding to pco 2 ~15-49 ppm

7 POC POC Responses to ocean acidification/carbonation e.g. calcareous microalgae Ballast effect positive? Klaas & Archer 2002 POC flux correlates closest with CaCO 3 flux Klaas & Archer 2002, Francois et al. 2002, Armstrong et al. 2002, but see Passow 2004 CaCO 3 serves as ballast Reduced calcification may decrease deep flux of POC Present CO 2 High CO 2 CaCO 3 Decreased calcification CaCO 3

8 Responses to ocean acidification/carbonation Stoichiometry negative e.g. calcareous microalgae Enhanced drawdown of C vs. N and P Riebesell et al Enhanced C loss from upper layer also Delille et al Mechanism still unclear present CO 2 2xCO 2 3xCO 2 C/N=6.0 C/N=7.1 C/N=8.0 Riebesell et al. 2007

9 Responses to ocean acidification/carbonation e.g. calcareous microalgae Stoichiometry negative Enhanced drawdown of C vs. N and P Riebesell et al Enhanced C loss from upper layer Delille et al Mechanism still unclear Low to moderate capacity until 2100 Oschlies et al. 2008, see also Matear & McNeil T32 C:N=const. C:N=f(pCO 2 ) Export production Int(del EP) Int(del C storage) Carbon storage Oschlies et al. 2008

10 Transparent Exopolymer Particles (µg Xanthan Equiv. L -1 ) Responses to ocean acidification/carbonation Extracellular C org e.g. calcareous microalgae ppmv CO 2 Enhanced exudation at elevated CO 2, leading to enhanced TEP formation Baltic Sea natural community Engel (2002) Emiliania huxleyi lab culture 100 Heemann et al. (unpubl.) CO 2 (µmol L -1 )

11 Responses to ocean acidification/carbonation e.g. calcareous microalgae Extracellular C negative org ? Enhanced exudation at elevated CO 2, leading to enhanced TEP formation Present CO 2 High CO 2 Accelerating aggregation and sinking of organic matter Engel et al. 2004, Schartau et al Uncertainties: longevity (transient responses?) Arrigo (2007)

12 glacial present Responses to ocean acidification/carbonation Nitrogen fixation e.g. calcareous microalgae projected 2100 Trichodesmium (diazotrophic cyanobaterium) Enhanced N 2 fixation by Trichodesmium Hutchins et al. 2007, Barcelos e Ramos et al. 2007, Levitan et al Common phenomenon among all diazotrophs? See Czerny et al. T11 Hutchins et al. 2007

13 Responses to ocean acidification/carbonation Nitrogen fixation e.g. calcareous microalgae Trichodesmium (diazotrophic cyanobaterium) Enhanced N 2 fixation by Trichodesmium Barcelos e Ramos et al. 2007, Hutchins et al. 2007, Levitan et al Common phenomenon among all diazotrophs? See Czerny et al. T11 Barcelos e Ramos et al. 2007

14 Responses to ocean acidification/carbonation Nitrogen fixation e.g. calcareous microalgae N:P Trichodesmium (diazotrophic cyanobaterium) Enhanced N 2 fixation by Trichodesmium Barcelos e Ramos et al. 2007, Hutchins et al. 2007, Levitan et al Common phenomenon among all diazotrophs? See Czerny et al. T11 C:P C:N Barcelos e Ramos et al. 2007

15 Responses to ocean acidification/carbonation Nitrogen fixation negative ++ +? C:N=f(pCO 2 ). C:N=f(pCO 2 ) + N 2 fix=g(pco 2 ) Trichodesmium (diazotrophic cyanobaterium) Enhanced N 2 fixation by Trichodesmium Barcelos e Ramos et al. 2007, Hutchins et al. 2007, Levitan et al Common phenomenon among all diazotrophs? See Czerny et al. T11 Oschlies et al. unpubl. ~ 6 PgC until 2100 Low capacity (model assumes shallow remineralisation) (feedback kills itself: enhanced N 2 fixation more DIN reduced N 2 fixation does Tricho-derived org. matter sink?

16 Responses to ocean warming Nutrient supply ++ ±0 ++ Reduced mixing, lower nutrient supply, decreased productivity e.g. Bopp et al. 2001, Boyd & Doney, 2002, Sarmiento et al. 2004, Schmittner et al. 2008, Schneider et al Schneider et al. 2008

17 Responses to ocean warming Nutrient supply +++ ±0 ++ Nut. utiliz. efficiency negative Reduced mixing, lower nutrient supply, decreased productivity e.g. Bopp et al. 2001, Boyd & Doney, 2002, Sarmiento et al. 2004, Schmittner et al. 2008, Schneider et al Reduced mixing, increased light availability, increased productivity Doney 2006

18 Responses to ocean warming Auto- vs.heterotrophy Expected: bacterial degradation increases stronger than primary production Q 10 = rate increase for 10 C temperature increase DIC/DIN/DIP 1<Q 10 <2 2<Q 10 <3 Phytoplankton Zooplankton 1<Q 10 <2 Temperatures: ambient +2 C +4 C +6 C DOM 2<Q 10 <3 Bacteria Detritus Sinking Kiel in-door mesocosms

19 Responses to ocean warming Auto- vs.heterotrophy positive Expected: bacterial degradation increases stronger than primary production DIC etc. = absolute change in pool size Red arrows = temp. - sensitive processes ambient temp. Observed: enhanced community respiration (R), DOC exudation (E), TEP formation (A) decreased sinking (S) decreased DIC drawdown elevated temp. DIC DIC P E P DOC DOC E A POC POC A DIC DIC P E P DOC DOC E A POC POC A R R S S R R S S Thermocline Thermocline Wohlers et al. subm.

20 Responses to ocean warming Nutrient inventories?? Decreased deep ocean ventilation expands oxygen minimum zones (OMZ) Matear & Hirst 2003 Decreases N inventory due to denitrification and anammox Increases P and Fe release from anoxic sediments

21 Impacts of Ocean Change on Primary Producers Responses to ocean acidification/carbonation Calcification negative + +? Ballast effect positive? Stoichiometry negative Extracellular C org negative ? Nitrogen fixation negative ++ +? (Trace) nutr. speciation Production of CR gases presentations by H. de Baar and E. Breitbarth (yesterday) see presentation by F. Hopkins (tomorrow) Responses to ocean warming Nutrient supply +++ ±0 ++ Nutr. utiliz. efficiency negative Nutrient inventory?? Auto- vs. heterotrophy. positive

22 Impacts of Ocean Change on Primary Producers Responses to ocean acidification Feedback sign Calcification negative Ballast effect positive Stoichiometry negative Extracellular C org negative Nitrogen fixation negative Responses to ocean warming Feedback sign Nutrient supply Nutr. utiliz. efficiency negative Nutrient inventory? Auto- vs. heterotrophy. positive Overarching questions: Will the future ocean be more or less productive? Less in low latitudes, more in high latitudes Will primary producers provide more or less food to higher trophic levels? Probably less (higher turnover in microbial loop), less nutritious Will marine biota sequester more or less CO 2? Possibly more, may partly compensate for decrease in physical carbon pump

23 Impacts of Ocean Change on Primary Producers Major uncertainties Short-term (stress) vs. acclimated responses Species (strain)-specific differences Synergetic effects with other stressors (e.g. warming) Single species vs. community level responses Physiological and genetic adaptation Species replacement vs. loss of ecosystem functionality