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Millennial-scale Dynamics of Continental Peatlands in Western Canada: Pattern, Controls and Climate Connection Zicheng Yu Lehigh University Bethlehem, Pennsylvania QUEST Workshop on CH4 & Wetlands 14-16 June 2004, Bristol, UK Acknowledgements Dale Vitt, Kel Wieder, Merritt Turetsky, Dave Beilman, Ilka Bauer, Mike Apps, Celina Campbell, and Ian Campbell for sharing slides, data and ideas. Climate Change Action Fund (Canada) and National Science Foundation (US) for funding. Outline of Talk Overview of continental peatlands in western Canada Accumulation pattern & trajectories Possible climate & global C cycle connections Conclusions Peatland Types in Western Canada Bogs (treed) Permafrost peatlands Open fens Treed fens Peatland Distribution % Cover Total peatland area = 365,160 km2 (21% landbase) 63% fens 28% permafrost bogs 9% non-permafrost bogs Vitt et al. (2000) Peatland Carbon Storage 14 C Storage (Pg) 12 10 8 6 4 2 Parkland Mid-boreal High boreal Montane Subarctic Arctic Total = 48 Pg 0 Vitt et al. (2000) Fens are more important C pool and have larger area than bogs in continental Canadian peatlands, as well as bigger CH4 emitters, but we know much less about these ecosystems than bogs in general Outline of Talk Overview of continental peatlands in western Canada Accumulation pattern & trajectories Possible climate & global C cycle connections Conclusions Why accumulation pattern matters? Exponential Cumulative Mass (g.cm-2) 120 (Convex) 100 80 Linear 60 40 (Concave) 20 Logarithmic 0 0 4 Time (ka) 8 12 Because: Observed pattern Infer & understand the processes Projecting future dynamics/trajectories Cumulative peat mass (g/cm2) Concave Pattern from Oceanic Bogs 0 Draved Mose, Denmark (data from Aaby & Tauber, 1975) 5 (assuming constant PAR and decay) 10 15 20 25 0 1000 2000 3000 4000 5000 Age (calendar year BP) “apparent” C accumulation rate 6000 7000 Study Sites 5 sites with hiresolution peat core analysis Basal dates from ~80 paludified peatlands Loss-on-Ignition from Upper Pinto Fen 1-cm LOI n=20 dates also, 2-cm macro 2-cm isotopes Yu et al. 2003 Peat Depth-Age Curve: Convex at UPF Opposite to welldocumented “concave” pattern Yu et al. 2003 What Does This Indicate? 0 Cumulative Peat Mass (g/cm2) UPF: Convex Pattern 10 20 30 0 Causes? 1000 2000 3000 4000 5000 6000 Age (cal yr BP) • decreasing peat-addition rates from acrotelm, and/or • increasing catotelm decomposition rate A Simple Extended Model Followed the suggestion by Clymo (2000; Quebec Meeting), dM p * e b*t * M , dt where M = cumulative peat mass; p = eventual PAR; = catotelm decomposition rate; and b = PAR coefficient. This equation has an analytical solution, p M ( ) * (e b*t e *t ) . b Yu et al. 2003 Peat Mass (g/cm2) Sensitivity to Changes in Decay & PAR 0 0 10 10 -50% PAR +50% Decay 20 20 30 30 40 40 -50% Decay 50 50 +50% PAR 60 60 0 1000 2000 3000 4000 Age (cal BP) 5000 6000 0 1000 2000 3000 4000 5000 6000 Age (cal BP) Yu et al. 2003 Change in PAR over Time 1.0 PAR modifier = exp[-b*t] Change in PAR PAR0.8 decrease from initial 192 to eventual 26 g/m2/yr could explain the observed pattern 0.6 -1 191.8 g m-2 yr-1 200 PAR Modifier Peat-Addition Rate (g m-2yr-1) 250 150 100 0.000185 yr (-50% b) 0.4 0.2 50 26.0 g m-2 yr-1 0.0 0 0 2000 4000 Age (cal BP) 6000 0.000555 yr-1 (+50% b) 0 2000 b=0.00037 yr-1 4000 6000 Time (years) Yu et al. 2003 Summary I The model suggests that unidirectional decrease of PAR from 192 to 26 g m-2 yr-1 over that 5400-yr period at UPF could result in the observed convex pattern. Autogenic drying trend resulted from fen height growth gradually isolates peat surface from water and nutrient sources, causing decreased production, especially for water-demanding rich fen species - esp. in moisture-limiting continental regions. This analysis indicates that continental peatlands with convex pattern may reach their growth limit sooner than previous model predicts. Convex Pattern @ Other Sites I (Kubiw et al. 1989) Convex Pattern @ Other Sites II Western Canada: Slave Lake Bog (Kurry & Vitt 1996) Southwestern Finland: Pesansuo raised bog (Ikonen, 1993) Western Siberia: Salym-Yugan Mire (Turunen et al. 2001) Convex Pattern from Regional Sites (Yu & Vitt, in prep) Outline of Talk Overview of continental peatlands in western Canada Accumulation pattern & trajectories Possible climate & global C cycle connections Conclusions Climate Proxy from UPF (Yu et al. 2003) UPF (Yu et al. 2003) W. Canada Global Climate & C Cycle Connections? Bond et al. 2001 Yu et al. 2003 Indermuhle et al. 1999 Chappellaz et al. 1997 Brook et al. 2000 Summary II Peat accumulation in western Canada shows sensitive response to Holocene climate variability at millennial time scale. Peatland carbon dynamics may connect to change in atmospheric CO2 concentrations (Peatlands in western Canada contain ~50 Pg C, which is equivalent to ~25 ppm CO2 if all remained in the atmosphere). Are there similar pattern in other peatlands of northern latitudes? Pervasive Climate Controls of Peatland Dynamics A thawed bog shows similar millennial-scale variations Patuanak Bog (internal lawn) Connection of Siberian Peatland Initiations and Atmospheric CH4 N = ~200 Smith et al. 2004 Bill Ruddiman’s hypothesis: CO2 increase since 8 ka: caused by deforestation; CH4 increase since 5 ka: caused by rice cultivation Allogenic and Autogenic Controls of Peatland Dynamics: a conceptual model Autogenic drying Climate wetting Climate fluctuations Yu et al. 2003 Conclusions • The different accumulation pattern observed in continental peatlands suggests these peatlands follow different trajectories historically and may respond to climate change differently (compared to well-studied bogs); • Continental peatlands appear to show sensitive responses to subtle millennial-scale moisture changes during the Holocene; • Fens seem to be more variable in C accumulation and more sensitive (less self-regulating) to climate variations than bogs; • Northern peatlands might have had detectable impacts on atmospheric CO2 and CH4 concentrations during the Holocene. Suggestions • Develop scaling-up models to take advantage of detailed inventory results from western Canada or other regions for regional CH4 emission estimates by peatland types (as a validating tool for global model?); • Confirm the extent of past climate – peatland – global C cycle connections, particularly using multiple proxies from paired lakepeatland approach (lakes for independent climate reconstructions); • Understand implications of permafrost (intact, thawing, and thawed) peatlands (and fen-bog transition) for CH4 emission/budget – permafrost is one of the biggest surprises to come in peatland C dynamics; • Integrate/reconcile down-core paleo data with present-day instrumental C flux measurements.