Biological Implications of Change in Pacificinfluenced Arctic Marine Ecosystems

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Biological Implications of Change in
Pacific-influenced Arctic Marine Ecosystems
Jacqueline M. Grebmeier Chesapeake Biological
Laboratory University of Maryland Center for
Environmental Science Solomons, Maryland, 20688,
USA
ASLO Web-based Lecture January 2009
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Key Environmental Factors Influencing Arctic
Marine Food webs

• Shrinking sea ice cover - change in proportion of
  sea ice algae and water column algae will likely
  drive significant trophic level changes
• Warming surface seawater - increased microbial
  and zooplankton grazing will limit food reaching
  ocean bottom to feed benthic animals
• Freshening of Arctic seawater - less saline water
  impacts marine biodiversity
• Coastal erosion - changes carbon cycle by
  diluting rich marine carbon with old, refractory
  carbon from land

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OUTLINE

• Changes to the Arctic system reduced sea ice
  type and extent, warming seawater, increased
  freshwater input, increased coastal erosion of
  older terrestrial carbon
• General marine ecosystem structure
• Case studies marine biological changes in the
  Pacific Arctic sector
• Summary

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• Annual sea ice minimum in September, 1979-2008

Pacific Arctic sector
2008

Modified from NSIDC, 2007 see
http//www.nsidc.org
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Seasonal sea ice retreat 1979-2008
NSIDC, 2008 see http//www.nsidc.org

• September is the usual minimum month for sea ice
  retreat and over time, ice is retreating more
• 2007 is the minimum ice retreat on record 2008
  came in 2nd

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Ice-albedo effects cause increased sea ice melt

• polar ice reflects light from sun (high albedo)
• as ice melts, less reflection and more
  absorption by ocean and land, raising
  temperature of both
• ice-albedo feedback is a positive loop,
  resulting in loss sea ice and continued seawater
  warming

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Dramatic decline old, multi-year ice in 2008 vs
2007

• recent reduction in multi-year ice results in
  thinner, first year ice developing in the
  subsequent winter in the open basin and over the
  Arctic continental shelves
• potential impact on production of sea ice and
  open water algae the following spring and summer

NSIDC, 2008 see http//www.nsidc.org
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Increased freshwater input to Arctic Ocean
through river flow and Pacific water input via
Bering Strait

• 60 freshwater to Arctic Ocean from rivers and
  local precipitation
• 40 freshwater to Arctic Ocean from Pacific
  water inflow through Bering Strait, using 32.5
  psu for Pacific water and 34.8 psu for Atlantic
  water
• data collected in 2000s indicate increased
  freshwater input through Bering Strait

Peterson et al. 2002, Shiklomanov et al. 2006
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Permafrost in northern hemisphere melting and
releasing old organic carbon to the marine
environment

• less sea and land ice, more shoreline erosion
• release older, more refractory carbon to ocean,
  dilutes nutrient-rich marine carbon
• also methane and carbon dioxide release is a
  positive feedback to global warming

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Timing and location of ice algae growth depends
on ice cover and light, zooplankton growth
influences food reaching underlying sediments
Wassman et al. 2004
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Arctic Marine Food Web
figure from http//www.arcodiv.org/
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Winners and losers for marine mammals with
changing sea ice cover
Marc Webber
Moore and Huntington 2008
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Sue Moore
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The Pacific Arctic

• highly productive ecosystem under Pacific water
  influence in west
• sea ice important for system
• timing annual production critical for water
  column production, carbon cycling, and
  pelagic-benthic coupling
• short food chains lower trophic level impacts
  cascade efficiently to higher trophic organisms
• potential impacts of change have broad-reaching
  implications for long-term ecosystem structure

courtesy Tom Weingartner and Seth Danielson
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BENTHIC PROCESSES

• Influenced by
• extent and duration of sea ice
• water temperature and salinity
• water column production and grazing
• net carbon flux to the sediments
• sediment grain size
• predator-prey relationships
• Benthic fauna are excellent indicators of
  climate change since they reflect large scale
  changes in biological response
• Pelagic-benthic coupling can be studied via
  underlying sediment processes on various time
  scales
• Sediment metabolism days-to-weeks
• Sediment tracers (e.g. chl a) weeks-to-years
• Benthic faunal populations months-to-years
  (integrators)

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Benthic sampling and collections
0.1 m2 van Veen grab
Benthic sieving
Polychaete
Haps benthic corer
Benthic clams, worms brittle stars
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Nutrient-rich Pacific water important for
variation in water column chlorophyll biomass

• the western side of the northern Bering and
  Chukchi Seas is site for high primary production
  and chlorophyll standing stock due to
  nutrient-rich Pacific water input to the shelf
  system

Grebmeier et al. 2006a
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Sediment community oxygen consumption as an
indicator of carbon supply to the benthos

• spatial patterns indicative of the amount of
  carbon reaching the sediments

Grebmeier et al. 2006a
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Rich benthic communities on the western side of
the Bering/Chukchi Sea system

• carbon export through the water column to the
  benthos supports a rich benthic infaunal system
  in the the Bering and Chukchi ecosystem
• foot prints of high benthic biomass on the
  shallow continental shelves regions are areas of
  high pelagic-benthic coupling and export of
  carbon to sediments

Grebmeier et al., 2006a
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Dominant benthic macroinfaunal taxa by biomass

• differences in dominant benthic macroinfaunal
  type in system are due to variable food supply,
  sediment grain size composition, and
  predator-prey interactions

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Case Study 1 Northern Bering Sea south of St.
Lawrence Island

• Bering Sea shifting towards an earlier spring
  transition between ice-covered and ice-free
  conditions
• Retrospective benthic studies indicate changes
  in both carbon deposition and benthic biomass

modified from Grebmeier et al. 2006b

• Region south of St. Lawrence Island has the
  longest time-series record that indicates a
  change in bivalve species composition and size
  may directly influence the declining populations
  of spectacled eiders

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Threatened spectacled eiders keyed to sea ice and
specific bivalves
courtesy Jim Lovvorn

• threatened spectacled eiders feed on three
  species of bivalves south of the island
• shallow shelf system, high cascade potential
  lower to higher trophic levels
• ocean acidification with increasing CO2 in
  seawater has potential to dissolve bivalve shells

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Tight coupling between walrus and benthic prey
modified from Grebmeier and Dunton 2000
courtesy of Tony Fischbach

• Bivalves are important walrus food, thus changes
  in benthic biomass will cascade efficiently to
  benthic predators,such as walrus

courtesy of Gay Sheffield
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Highest sediment oxygen uptake, an indicator of
carbon deposition to benthos, occurs in May-June
after spring bloom
Cooper et al. 2002
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Highest water column chlorophyll deposition to
benthos in May-June after spring bloom
Cooper et al. 2002
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Settling of spring chlorophyll bloom to the
benthos over two week time period in May 2007 in
the northern Bering Sea is an example of high
export of carbon to the benthos
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Bivalves, amphipods, polychaetes, and brittle
stars dominate benthic infauna

• Dominant bivalve families by abundance and
  biomass Nuculanidae, Nuculidae, and Tellinidae

modified from Grebmeier and Barry 2007
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Potential restructuring of ecosystem with earlier
sea ice retreat and reduction of extent of cold
pool

• earlier shift of air temperature to above
  freezing and associated sea ice melt in spring on
  St. Lawrence Island

• location of cold pool in northern Bering Sea
  critical to maintaining high benthic prey
  populations by exclusion of benthic predators

Grebmeier et al. 2006, Science 311
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Decline in sediment oxygen uptake (indicator of
carbon supply) and benthic macrofaunal biomass SW
of St. Lawrence Island over time
Grebmeier et al. 2006b
modified from Simpkins et al. 2003
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Seawater warming and northward fish movement
Surface Seawater Temperature (5 m)
2000
2001
2002
2003
2004
Sockeye Salmon Survival
High Survival
Low Survival
courtesy Ed Farley/NOAA
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10 Million new Salmon in the northern Bering Sea
in 2004 coincident with increased northward
movement of pollock
Pink salmon
Pollock
courtesy Jack Helle/NOAA
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Case 2 Chirikov Basin, Northern Bering Sea in
the 1980s

• high amphipod populations in sediments
• coincident large populations of migrating gray
  whales that suction up mud to feed on benthic
  amphipods

Gray whale sightings
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Cases 2 (cont.)-Drop in Benthic Productivity in
1990s

• Highsmith and Coyle (1992) report evidence of 30
  amphipod production downturn from 1986-88
• decline of ampeliscid amphipod biomass at 4 time
  series stations (Moore et al. 2003) subsequently
  supported at more stations in the region (Coyle
  et al. 2007)
• LeBoeuf et al. 2002 suggest this amphipod
  decline in the Chirikov Basin as causal to gray
  whale mortalities
• Shift gray whales north of Bering Strait
  normally prefer feeding in ice-free areas

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Case 3 Time series site BS5 shifted from
amphipods to polychaetes in early 2000 (see
previous time series figure for station location)
PhotoArt Howard/ PolarPalooza
courtesy Xuehua Cui
Shorthorn sculpin
Live ampharetid worm
gt40 ampharetid worms

• observed shift in infaunal dominance at time
  series site BS5 in western Chirikov Basin in
  early 2000s from ampeliscid amphipod dominance
  (gray whale food) to polychaete dominance
  (sculpin food, see photos above)
• ampharetid polychaetes build strong tubes this
  change in dominant species coincident with
  increase in silt and clay content of sediments

10 cm
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The Western Arctic Shelf-Basin Interactions (SBI)
Project

• SBI Arctic / global change project 2002-2004 map
• intensive field studies during the record summer
  sea ice retreat
• investigating production, transformation and
  fate of carbon at the shelf-slope interface in
  the northern Chukchi and Beaufort Seas
• downstream of the productive shallow western
  Arctic shelves
• prelude to understanding the impacts of a
  potential warming of the Arctic

Grebmeier and Harvey 2005
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Case 4 Surface seawater warming in summer 2004
vs 2002 coincided with extensive sea ice retreat
and observations of abandoned baby walruses
Cooper et al. 2006 Aquat. Mammals, 32

• walrus feed on the shallow Arctic shelves
• red squares in left figures are abandoned
  walrus pups due to rapid ice retreat observed
  during SBI cruises

SST August 12-16, 2004
photo by Ev Sherr
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Local Alaskan Communities are concerned by
unpredictability of ice conditions and resulting
impact on subsistence hunting, lifestyle and the
associated ecosystem response
photos courtesy Gay Sheffield, ADFG
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"Alaska Natives and Climate Change"
http//passporttoknowledge.com/polar-palooza/fla
sh/healy03a.php
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Summary

• decreasing sea ice, increasing heat and
  freshwater transport in the Pacific-influenced
  Arctic, along with coastal erosion, will change
  marine carbon cycle and biodiversity
• continental shelf regions in northern Bering Sea
  and Chukchi Seas are experiencing earlier spring
  transition between ice-covered and ice-free
  conditions and increasing seawater temperatures
• changes in the timing of primary productivity and
  zooplankton grazing over shelf will change carbon
  export to the benthos and trophic structure
• currently carbon deposition occurs over
  days-weeks in May-June in the northern Bering Sea
  as the spring bloom settles to the bentho
• some time series sites indicate change in carbon
  deposition, benthic biomass and infaunal
  dominance
• time-series observation sites are critical for
  identifying ecosystem status and trends with
  environmental change

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courtesy of Jim Swift
Support from U.S. National Oceanic and
Atmospheric Administration, National Science
Foundation, Office of Naval Research, and the
North Pacific Research Board
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