How will biogeochemical processes in the ocean respond to surface warming? Anja Engel Alfred Wegener Institute for Polar and Marine Research (AWI)

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1 How will biogeochemical processes in the ocean respond to surface warming? Anja Engel Alfred Wegener Institute for Polar and Marine Research (AWI)

2 The Naked Earth The Discovery of Global Warming Air traps the heat from the sun It s the water vapour and the CO 2.. CO 2 and temperature. That s the feedback! Joseph Fourier Pictures:wikipedia John Tyndall Svante Arrhenius

3 Future projections of GHG Emissions and Global Mean temperature IPCC, synthesis report (2007)

Surface temperature -projected Changes until 2100- IPCC-A1F1 Scenario business as usual Largest

4 Surface temperature -projected Changes until IPCC-A1F1 Scenario business as usual Largest temperature changes are expected for the northern hemisphere Exceptional strong warming may occur in the Arctic Ocean

5 Biogeochemistry and surface warming outline: Sea Surface Warming feedback Surface Ocean Physics: Mixed layer depth Stratification strength Nutrients Light Ice coverage Direct Temperature Effects: Plankton Metabolism Primary & Secondary Production POM-DOM Partitioning Organic Matter Remineralisation Biogenic Silica Dissolution feedback Marine Biogeochemistry

6 Increase in surface ocean stratification Low Latitude and Temperate Ocean High Latitude Ocean Sea ice nutrient reservoir nutrient reservoir nutrient reservoir nutrient reservoir Thermocline Pycnocline/The rmocline Thermocline Temperature Ø Nutrients Œ Temperature Ø Light Ø Present Future Present Future

7 stratification reduces primary production (in warm regions) Net primary production (NPP) anomaly follows changes in stratification patterns Behrenfeld et al. (Nature, 2006)

8 Changes in annual average SST between 1994 and 2004 Changes in annual average NPP between 1994 and 2004 For 74% of the permanently stratified ocean, NPP and SST changes are inversely related Behrenfeld et al. (Nature, 2006)

9 What to expect for the polar Oceans? % more open water Arrigo et al. 2008

10 What to expect for the polar Oceans? Arrigo et al Difference in NPP Extended season

11 Direct effects of Temperature on biology -metabolic processes- Bacterioplankton Phytoplankton Zooplankton Q 10 :2-3 Q 10 :1-2 Q 10 : Enzymatic Reaction Rate Arrhenius-type increase Q 10 Temperature Protein denaturation

12 temperature sensitivity of Bacterial Production in the ocean Polar Seas Temperate & Low Latitude Seas Kirchman et al Kirchman et al. (Nature, 2009)

13 temperature sensitivity of Bacterial Production in the ocean Polar Seas Temperate & Low Latitude Seas Kirchman et al Temperature

14 temperature sensitivity of Bacterial Production in the ocean? Polar Seas Temperate & Low Latitude Seas Hypothesis: The balance between Primary and Secondary (Bacterial) Production is primarily determined by the availability of nutritious DOM Kirchman et al. 2009

15 ( ) Project: Temperature effects on DOM-POM-partitioning Riebesell & Engel DIC/DIN/DIP Phytoplankton Zooplankton Source of DOM: - Phytoplankton Sink of DOM: - Bacterial Production - DOM aggregation DOM sinks and sources display different temperature-sensitivities DOM Bacteria TEP Aggregation Sinking Hypothesis: DOM-POM partitioning is temperature-sensitive

16 Aquashift: experimental design of mesocosm studies temperature increase above baseline(mean 92-02) 1400 l mesocosms actual temperatures Sommer et al (2007)

17 Aquashift: Temperature effect on phytoplankton blooms Chlorophyll a Bloom peak: -1.3 d/ 1 C 8 C 6 C 4 C 2 C Wohlers et al. (2009)

18 Aquashift: Temperature effect on phytoplankton blooms Temperature accelerates nutrient draw-down Nitrate: -1d/ C Phosphate: -0.7d/ C 22µM NO 3 0.9µM PO 4 +6 C +4 C +2 C +0 C Wohlers et al. (2009)

19 Aquashift: Temperature effect on phytoplankton blooms No temperature effect on total yield of PN and POP PN: -1d/ C POP: -0.7d/ C 0.9µM PO 4 22µM NO 3 Wohlers et al. (2009)

20 loss DIC 2 C TOC DIC max POC 8 C Settling loss

21 Temperature control Of heterotrophy Bacterial Secondary Production increases with temperature Community Respiration >3µm increases with temperature Wohlers et al. (2009)

22 organic matter degradation in aggregates 20 µm Piontek et al (AME, 2009)

23 Remineralisation of Biogenic silica with bacteria without bacteria Faster dissolution of silica from diatom frustules after bacterial degradation of organic surface coating Bidle & Azam (Nature 1999)

24 Remineralisation of Biogenic silica with bacteria Dissolution of diatom frustules without bacteria 8 C 2 C Faster dissolution of silica from diatom frustules after bacterial degradation of organic surface coating Piontek et al (AME, 2009) Bidle & Azam (Nature 1999)

25 What we learned from Aquashift: Warming leads to: Higher partitioning of carbon into DOM that satisfies increased bacterial carbon demand and supports microbial metabolic activity (growth & remineralisation). Earlier onset and higher activity of microbial heterotrophic community that enhances organic matter remineralisation and reduces net DIC draw down. Stimulation of microbial loop that results in reduced carbon export (particularly for cold system).

26 Summary: warming effects on biogeochemical cycling CO 2 CO 2 CO 2 CO 2 Zoo micro Zoo micro H + remineralisation remineralisation Phytoplankton DOM Bacteria Phytoplankton DOM Bacteria Zoo meso /Aggregates Export nutrients Deeper, colder mixed layer Zoo meso /Aggregates Export nutrients Shallower, warmer mixed layer Present day Future scenario

27 Temperature effects on a Global scale Inreased Organic Matter Recycling Reduced Organic Matter Export Export Production : Total Production Temperature Laws et al. 2000

28 What do we need to know better? Will warming alter the balance between primary and bacterial production in the polar ocean? How will the increased amount of respiratory CO 2 affect ocean acidification projections? Will the ocean ecosystems change from a CO 2 sink to a CO 2 source? How large is the feedback to atmospheric CO 2 concentration?

29 How will biogeochemical processes in the ocean respond to surface warming? Acknowledgements: Ulf Riebesell, Julia Wohlers, Judith Piontek, Nicole Händel, Ullrich Sommer, Peter Fritsche, Petra Breithaupt, Mascha Wurst

Lakes, Primary Production, Budgets and Cycling

OCN 401-Biogeochemical Systems Lecture #10 (9.22.11) Lakes, Primary Production, Budgets and Cycling (Schlesinger: Chapter 7) 1. Primary Production and Nutrient Cycling in Lakes Physical aspects and nomenclature