Climate Impacts on the Southern Ocean Ecosystem(s)
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Transcript of Climate Impacts on the Southern Ocean Ecosystem(s)
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
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
UK
AustraliaUS, Germany
Germany
Korea
SO GLOBEC Field Study Sites
Target Species
Circumpolar System
Not similar food webthroughout
Considerable heterogeneity in forcingand habitat structure
Regional differences inresponses
Southern Ocean Food Webs
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
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?
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?
What is a Southern Ocean Food Web?
Is This the Only Food Web?
Ross Sea
Western AntarcticPeninsula
Classical Food Web
Why the Differences?
HighAntarctic
SubAntarctic
LowProduction High Production
Seasonal length
Differences due toCirculation
Sea-iceBiogeochemistry
ProductionSeasonality
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
Shelf depth ~400 m
ACC flows along shelf edge
Deep trenches that provide connections between shelf and oceanic environments
WAP Circulation
(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
CDW Effects
Inputs of heat and salt
Surface water abovefreezing in winter
Salt excess Klinck et al. (2004)
Phytoplankton assemblagedominated by diatoms
CDW - regions of highprimary production
Prezelin et al. (2002)
Not all parts of the shelf are biologically similar
Biological Hot SpotsBiological Hot Spots
(Costa et al., 2007)
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
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)
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
Model Domain
Includes iceshelves
Focus onMarguerite Bayand Crystal Sound regionsof WAP
Dye distribution for current conditions - FebruaryLevel of CDW (210-420 m)
50% increase in wind speed
20% decrease inwind speed
20% increase in wind speed
20% increase inwind speed andincrease in ACCtransport
Vertical dye distribution
Current conditions
50% increase in windspeed
Vertical temperaturedistribution
Current conditions
50% increase in wind speed
Summer sea ice distribution
50% increase in windspeed
Current conditions
Winter sea ice distribution
50% increase in wind speed
Current conditionsSummer sea ice
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?
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?
Biological continuum that is driven by subsurface intrusions of CDW
Prezelin et al. (2004)
Shift to a diatom-dominated system?
Alternative pathways buffer change - reflect/support long-term change?Need better quantification of alternative pathways
Alternative Food Web Pathways
High krill Low krill
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)
Change in production
Z K
P
Fish Cephalopods
Z K
P
Fish Cephalopods
14% 3%
83%
80% 20%
0%Ballerini et al. (in prep)
Large-scale distribution of ACC fronts
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?
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
Relevance to Global Ecosystems
Global carbon budget models lack biological detail
Current models do not capture what is known about SO ecosystems
• 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
Thank you!
Photos byD. Costa