Summary of Research Summary of Research on Climate Change on Climate Change

Feedbacks in the ArcticFeedbacks in the Arctic

Erica BettsErica Betts

April 01, 2008April 01, 2008

Issues relating to climate Issues relating to climate change in the Arcticchange in the Arctic

Thawing of permafrost Thawing of permafrost – Increased carbon emissions (sink to source)Increased carbon emissions (sink to source)

Boreal forests move northwardBoreal forests move northward– Surface albedo changeSurface albedo change– respiration rate change (tundra to forest respiration rate change (tundra to forest

vegetation change)vegetation change)– change in energy flux (vegetation changes)change in energy flux (vegetation changes)

Soil subsidence due to melting of ice in Soil subsidence due to melting of ice in permafrost soilspermafrost soils

Changing snow coverChanging snow cover– Change in surface hydrologyChange in surface hydrology– Change in surface temperaturesChange in surface temperatures

IntroductionIntroduction

ArcticArctic PermafrostPermafrost Boreal ForestBoreal Forest PeatlandsPeatlands

ArcticArctic Arctic tundra soils contain 14% of the global Arctic tundra soils contain 14% of the global

soil carbon pool.soil carbon pool. Significant heterogeneity in CO2 release Significant heterogeneity in CO2 release

patterns as a result of plant species patterns as a result of plant species differences (root respiration, litter quality differences (root respiration, litter quality for decomposition, etc.) as well as soil for decomposition, etc.) as well as soil variations (moisture content, size of active variations (moisture content, size of active layer, etc.)layer, etc.)

Need for further studies relating below Need for further studies relating below ground respiration patterns to vegetation ground respiration patterns to vegetation patternspatterns

Better understanding of winter and summer Better understanding of winter and summer variations in respirationvariations in respiration

Arctic tundra: regional studyArctic tundra: regional study Water vapor and CO2 exchange measured by Water vapor and CO2 exchange measured by

eddy covariance method in 24 ecosystems along eddy covariance method in 24 ecosystems along the Arctic coastthe Arctic coast

Variations in ecosystem exchange across the Variations in ecosystem exchange across the region controlled by differences in net uptake of region controlled by differences in net uptake of CO2 due to photosynthesis rather than by CO2 due to photosynthesis rather than by differences in ecosystem respirationdifferences in ecosystem respiration

Daytime CO2 related mainly to differences in LAI, Daytime CO2 related mainly to differences in LAI, nighttime CO2 efflux related to LAI and soil nighttime CO2 efflux related to LAI and soil moisturemoisture

Temperature had no effect on regional patterns of Temperature had no effect on regional patterns of respiration during the growing seasonrespiration during the growing season

Water vapor and CO2 fluxes poorly coupled Water vapor and CO2 fluxes poorly coupled because water vapor exchange largely because water vapor exchange largely determined by evaporation from mosses and CO2 determined by evaporation from mosses and CO2 exchange controlled by vascular plant activityexchange controlled by vascular plant activity

PermafrostPermafrost

Permafrost (permanently frozen Permafrost (permanently frozen ground) is a large carbon reservoir ground) is a large carbon reservoir rarely incorporated into analysis of rarely incorporated into analysis of changes in global carbon reservoirschanges in global carbon reservoirs

Yedoma is a type of permafrost Yedoma is a type of permafrost comprised of 2-5% carbon and 50-comprised of 2-5% carbon and 50-90% ice. Covers more than 1 million 90% ice. Covers more than 1 million kmkm22 of Siberia and Central Alaska of Siberia and Central Alaska

Ground Temperature Profile

PermafrostPermafrost Estimate that carbon reservoir in frozen yedoma Estimate that carbon reservoir in frozen yedoma

to be ~500Gt, another ~400Gt in non-yedoma to be ~500Gt, another ~400Gt in non-yedoma permafrost, and 50-70 Gt in peatlandspermafrost, and 50-70 Gt in peatlands

Organic matter in Yedoma decomposes quickly Organic matter in Yedoma decomposes quickly when thawed resulting in respiration rates of 10-when thawed resulting in respiration rates of 10-40 g carbon/m40 g carbon/m33 initially and then 0.5-5g initially and then 0.5-5g carbon/mcarbon/m33 per day over several years per day over several years– If these rates are sustained, most carbon will be If these rates are sustained, most carbon will be

released within a centuryreleased within a century– Carbon in frozen yedoma is preserved for tens of Carbon in frozen yedoma is preserved for tens of

thousands of yearsthousands of years Yedoma carbon is decomposed by microbes Yedoma carbon is decomposed by microbes

under anaerobic conditions – this produces under anaerobic conditions – this produces methanemethane– During a lake freeze/thaw cycle associated with During a lake freeze/thaw cycle associated with

migration, ~30% of yedoma carbon is decomposed by migration, ~30% of yedoma carbon is decomposed by microbes and converted to methanemicrobes and converted to methane

PermafrostPermafrost

Permafrost carbon is depleted in Permafrost carbon is depleted in radiocarbon (14C)radiocarbon (14C)

Methane, CO2, and DOC have Methane, CO2, and DOC have radiocarbon age reflecting the time radiocarbon age reflecting the time when the yedoma was formed in the when the yedoma was formed in the glacial ageglacial age

This differentiates the permafrost This differentiates the permafrost carbon signal from other reservoirscarbon signal from other reservoirs

Boreal Forest

Boreal forestBoreal forest

Boreal forest region occupies 12-14 Boreal forest region occupies 12-14 million km2 or 10% of vegetated million km2 or 10% of vegetated surface of the globesurface of the globe

Boreal forest region dominates Boreal forest region dominates terrestrial interactions with the terrestrial interactions with the Earth’s climate north of 50Earth’s climate north of 50°°NN

Global warming expected to be most Global warming expected to be most pronounced in the high latitudes of pronounced in the high latitudes of the northern hemispherethe northern hemisphere

Boreal forestsBoreal forests Account for ~20% of the world’s reactive Account for ~20% of the world’s reactive

soil carbon poolsoil carbon pool Has been estimated that understory could Has been estimated that understory could

contribute more than 1/3 of forest contribute more than 1/3 of forest photosynthesisphotosynthesis

Predominant understory type are mosses Predominant understory type are mosses which insulate the soil (reduce soil temp.), which insulate the soil (reduce soil temp.), absorb atmospheric nutrients and absorb atmospheric nutrients and decompose very slowlydecompose very slowly

Climate warming likely to reduce Climate warming likely to reduce productivity of mossesproductivity of mosses

Schuur and TrumboreSchuur and Trumbore Second paper detailed current research to Second paper detailed current research to

determine rates of respiration of various determine rates of respiration of various components of the boreal forest ecosystemcomponents of the boreal forest ecosystem– Specifically difference in autotrophic and heterotrophic Specifically difference in autotrophic and heterotrophic

respirationrespiration Difference between net ecosystem uptake of C Difference between net ecosystem uptake of C

(photosynthesis) and release of C (respiration) = (photosynthesis) and release of C (respiration) = NEE (determines if ecosystem is a source or sink)NEE (determines if ecosystem is a source or sink)

Difficulty in separating components of an Difficulty in separating components of an ecosystem and determining rates of respirationecosystem and determining rates of respiration

This paper looks at separating plant and microbial This paper looks at separating plant and microbial respiration from total soil respirationrespiration from total soil respiration

Methodology and ResultsMethodology and Results Different sources (microbes vs. plant roots) are Different sources (microbes vs. plant roots) are

expected to respire C with differing isotopic expected to respire C with differing isotopic signaturessignatures– Measurements should show differing concentrations of Measurements should show differing concentrations of

14C as a result of utilizing different stores of carbon.14C as a result of utilizing different stores of carbon.– Residence time is largest factor determining 14C Residence time is largest factor determining 14C

concentration in carbon pool.concentration in carbon pool. Expected that root respiration would have 14C Expected that root respiration would have 14C

isotope values similar to atmospheric isotope values similar to atmospheric concentrations – not the caseconcentrations – not the case– Carbon fueling root respiration is up to several years oldCarbon fueling root respiration is up to several years old

Heterotrophic respiration pools from carbon Heterotrophic respiration pools from carbon stores averaging a residence time of 10 yearsstores averaging a residence time of 10 years

Heterotrophic respiration accounts for over half of Heterotrophic respiration accounts for over half of total soil respirationtotal soil respiration

PeatlandsPeatlands Peatland ecosystems cover 25-30% of boreal Peatland ecosystems cover 25-30% of boreal

forest region globallyforest region globally Southernmost occurrence of permafrost is Southernmost occurrence of permafrost is

restricted to peatlandsrestricted to peatlands Records show increases in near-surface Records show increases in near-surface

permafrost temperatures over past several permafrost temperatures over past several decades in response to changing air temperatures decades in response to changing air temperatures and snow cover – this has triggered widespread and snow cover – this has triggered widespread permafrost degradationpermafrost degradation

Recent study by Turetsky et al. 2007 found that Recent study by Turetsky et al. 2007 found that loss of surface permafrost in peatlands increases loss of surface permafrost in peatlands increases net carbon storage as peat accumulation is net carbon storage as peat accumulation is increasedincreased– CH4 emissions increase and in around 70 years, offset CH4 emissions increase and in around 70 years, offset

carbon sink in terms of radiative forcingcarbon sink in terms of radiative forcing

Barrow, Alaska

Effects of Permafrost Melt on Effects of Permafrost Melt on InfrastructureInfrastructure

Effects of Effects of Permafrost Permafrost

Melt on Melt on InfrastructureInfrastructure

SnowSnow Landscape patterns of tundra snow cover develop Landscape patterns of tundra snow cover develop

from wind distribution of snow rather than from from wind distribution of snow rather than from spatial variability in precipitationspatial variability in precipitation

Blowing snow can cause 10-50% of the snowfall to Blowing snow can cause 10-50% of the snowfall to be returned to atmosphere by sublimation of the be returned to atmosphere by sublimation of the wind-blown snow particleswind-blown snow particles

Increased vegetation (larger vegetation types) Increased vegetation (larger vegetation types) results in greater snow depth accumulation results in greater snow depth accumulation resulting in increased runoff from snow melt (w/no resulting in increased runoff from snow melt (w/no increase in precipitation)increase in precipitation)

Change in surface albedo and energy exchangeChange in surface albedo and energy exchange Increased snow thickness increases ground Increased snow thickness increases ground

temperatures and decreases conductive heat flow temperatures and decreases conductive heat flow to the atmosphereto the atmosphere

Shorter periods of snow cover (longer snow-free Shorter periods of snow cover (longer snow-free periods) lead to more solar radiation absorbed by periods) lead to more solar radiation absorbed by land surface and longer growing seasonland surface and longer growing season

Questions?Questions?