Climate Impacts on the Southern Ocean Ecosystem(s)
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Transcript of Climate Impacts on the Southern Ocean Ecosystem(s)
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Climate Impacts on the Southern Ocean
Ecosystem(s)Eileen Hofmann, John Klinck, Mike
DinnimanWalker O. Smith
Eugene Murphy, Nadine Johnston, Rachel Cavanaugh (BAS)
SO GLOBEC Investigators
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Presentation Outline
• Background on Southern Ocean GLOBEC program• Southern Ocean food webs• Consider potential climate change
effects on mesopelagic-shelf coupling• Summarize possible effects of climate
change on physical habitat and consequences for biological production and food webs
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UK
AustraliaUS, Germany
Germany
Korea
SO GLOBEC Field Study Sites
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Target Species
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Circumpolar System
Not similar food webthroughout
Considerable heterogeneity in forcingand habitat structure
Regional differences inresponses
Southern Ocean Food Webs
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Upper ocean temperatures have increased by 1ºC in the
last 50 years -WAP most rapidly warming region on
planet
Southern Ocean is Undergoing Major Environmental Changes
Parkinson (2002)
19761978198019821984198619881990199219941996199820002002
Year
Density (no. m-2)
1
10
100
1000
30% decline in Antarctic krill in SouthAtlantic in last 30 years
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What happened in the past?
Harvesting has generated massive perturbations over more than 2
centuries
Fur-sealsFrom 1778; economic extinction
within 35 years
Whales1906 to 1966, residual thereafter
Fin-fish, krillFrom late 1960s, continuing
Top-down effects => Krill surplus?
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Challenges for Southern Ocean
• Climate Impacts• Harvesting effects • Biogeochemistry• Food Webs
Can we develop experimental and modeling programs to address these effects and
interactions at a circumpolar scale?
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What is a Southern Ocean Food Web?
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Is This the Only Food Web?
Ross Sea
Western AntarcticPeninsula
Classical Food Web
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Why the Differences?
HighAntarctic
SubAntarctic
LowProduction High Production
Seasonal length
Differences due toCirculation
Sea-iceBiogeochemistry
ProductionSeasonality
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Mesopelagic Environment
• Region between about 200 m and 700 m
• For much of the Antarctic this is the depth of the continental shelf
• Shelf region is flooded with oceanic water, Circumpolar Deep Water (CDW), between 200-700 m - various forms of CDW
• Provides a direct connection between epipelagic and mesopelagic regions
• Focus on western Antarctic Peninsula
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Shelf depth ~400 m
ACC flows along shelf edge
Deep trenches that provide connections between shelf and oceanic environments
WAP Circulation
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(Klinck et al., 2004)
Southern Ocean Sentinel Workshop Hobart, Tasmania, 20-24 April
2009
Fall 2001 Warm and salty water mass
Floods shelf below 200 m
Extends across shelf atspecific sites
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CDW Effects
Inputs of heat and salt
Surface water abovefreezing in winter
Salt excess Klinck et al. (2004)
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Phytoplankton assemblagedominated by diatoms
CDW - regions of highprimary production
Prezelin et al. (2002)
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Not all parts of the shelf are biologically similar
Biological Hot SpotsBiological Hot Spots
(Costa et al., 2007)
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Climate Change Effects on CDW
• Effects of increased and decreased wind strength and increased transport of Antarctic Circumpolar Current on CDW intrusions onto the WAP shelf • Modified wind scenarios represent
regional effects - positive Southern Annular Mode gives stronger westerlies• Change in ACC transport represents
large-scale circulation effects - global thermohaline circulation
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Circulation Model Characteristics
• ROMS: 4 km horizontal resolution, 24 levels• Ice shelves (mechanical and thermodynamic)• Dynamic sea ice• Bathymetry: ETOPO2v2 + WHOI SOGLOBEC region +
Padman grid + BEDMAP + Maslanyj• Open boundaries: T + S set to SODA, barotropic V
relaxed to SODA, baroclinic V pure radiation• Daily wind forcing from a blend of QSCAT data and
NCEP reanalyses • Other atmospheric parameters from several sources,
including Antarctic Mesoscale Prediction system (AMPS)
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Simulation Configuration
• Track dye concentration as proxy for CDW• Dye concentration off the shelf set to 100 below
200 m and at temperatures > 0ºC• Allow 4-year spin up of circulation model • Simulations begin in January and run for 2 years
that correspond to 2000-2002 • Set up a reference case using current conditions
to provide comparisons
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Model Domain
Includes iceshelves
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Focus onMarguerite Bayand Crystal Sound regionsof WAP
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Dye distribution for current conditions - FebruaryLevel of CDW (210-420 m)
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50% increase in wind speed
20% decrease inwind speed
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20% increase in wind speed
20% increase inwind speed andincrease in ACCtransport
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Vertical dye distribution
Current conditions
50% increase in windspeed
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Vertical temperaturedistribution
Current conditions
50% increase in wind speed
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Summer sea ice distribution
50% increase in windspeed
Current conditions
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Winter sea ice distribution
50% increase in wind speed
Current conditionsSummer sea ice
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Dye concentrationfor Crystal Sound
Inner portion ofWAP shelf
Stronger winds andACC provide more CDW to region
Is this beneficial?
Will region persistas a biological hotspot?
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Summary
• Strong coupling between mesopelaic and epipelagic environments
• Intrusions of CDW are controlling habitat structure and biological production
• Modified by winds and circulation changes• Biological hot spots are coincident with
intrusions of CDW • What are the consequences of changes in
CDW intrusions?• Is this specific to WAP region?
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Biological continuum that is driven by subsurface intrusions of CDW
Prezelin et al. (2004)
Shift to a diatom-dominated system?
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Alternative pathways buffer change - reflect/support long-term change?Need better quantification of alternative pathways
Alternative Food Web Pathways
High krill Low krill
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Salps Zooplankton Krill
P
60%20%
20%
Salps Zooplankton Krill
P
20%
60%20%
P
20%60%20%
Krill
Salps
Benthos
Penguins
Penguins
Krill
Zooplankton Salps
Benthos
Zooplankton
Detritus
Killer Whales
Salps
Zooplankton
Killer Whales
Change in production
Salps Zooplankton Krill
Ballerini et al. (in prep)
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Change in production
Z K
P
Fish Cephalopods
Z K
P
Fish Cephalopods
14% 3%
83%
80% 20%
0%Ballerini et al. (in prep)
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Large-scale distribution of ACC fronts
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Potential Consequences
• Reduction in winter sea ice- current food web components disappear? • Time history of seasonal
heating/cooling of surface layers changed - implications for air-sea exchanges and sea ice formation? • Timing of productivity changed -
same annual production but different time distribution?
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Potential Consequences
• Larger areas of shelf influenced by warm CDW - change in habitat structure and food web linkages?
• Open/close more habitat - more regions where Antarctic krill can reproduce, reduced regions for Adélie penguins?
• More emphasis on benthic system - warmer bottom temperatures
• Mixing processes of CDW still a matter of research and debate - basic physical understanding still needs to be developed
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Relevance to Global Ecosystems
Global carbon budget models lack biological detail
Current models do not capture what is known about SO ecosystems
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• Circumpolar, interdisciplinary program focused on climate interactions and feedbacks to ecosystem function and biogeochemical cycles
• Extend and further develop circulation, ecosystem, and biogeochemical models
• Focus on end-to-end food web models
• Combine food web and biogeochemical communities
Joint program under IMBERand GLOBEC - 10 year effort
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Thank you!
Photos byD. Costa