What caused Glacial-Interglacial CO2 Change?

1
What caused Glacial-Interglacial CO2 Change?
Douglas L. Love Meto 658A Spring 2006
2
Suggested papers
Reviews Archer et al., 2000 Newer
ideas Zeng 2003 Toggweiler et al.
2005 Paillard and Perenin 2005
Broecker and Henderson 1998
Broecker and Peng 1998
3
Archer et al, 2000
David Archer
Arne Winguth
David Lea
Natalie Mahowald
U Chicago
U Wisconsin
UCSB
NCAR
4
Archer et al, 2005

• Glacial pCO2 was 80-90 µatm lower than
  interglacial
• Radiative forcing from CO2 accounts for
• half of climate change
• Tight repeatable

• corellation between
• pCO2
• Ice volume
• Temperature records

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Archer et al, 2005

• Glacial pCO2 was 80-90 µatm lower than in the
  interglacial
• Radiative forcing from CO2 accounts for
• half of climate change
• The terrestrial biosphere and soil carbon
  reservoirs would have to be approximately double
  in size to deplete pCO2 by 80 µatm.
• d13C from deep-sea CaCO3, more 12C rich during
  glacial time, tells us that if anything, the
  terrestrial biosphere released carbon during
  glacial time Shackleton, 1977

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Archer et al, 2000

• Glacial cycles

• Advances and retreats of ice sheets
• Documented by isotopic composition of seawater
• Oxygen in CaCO3
• 16O is selectively sequestered in glacial ice.
• Oceans become enriched in 18O

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Archer et al, 2005

• Clear physical link between Northern Hemisphere
• summer heating and ice sheets
• No easy link from orbital variations to pCO2.
• pCO2 rise clearly precedes the 18O of the
  atmosphere
• by several thousand years
• (an indicator of melted ice sheets)
• Implies that pCO2 is a primary driver of
  melting.
• Alternatively, pCO2 could be driven by changes
  in
• meteorological forcing
• dust delivery of trace metals to the ocean
  surface
• an acausal correlation between Northern
• Hemisphere summer insolation and ice volume

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Archer et al, 2005
Because CO2 is more soluble in colder water,
colder sea surface temperatures could lower
pCO2. However, the magnitude of the glacial
cooling can account for only a small fraction of
the observed pCO2 drawdown.
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Archer et al, 2005
A New model of Ocean and Sediment Geochemistry
- Mechanisms to lower glacial pCO2

• Increase biological activity at surface
• so that Carbon sinks to deep sea
• sediments as particles
• Increase Ocean Inventory of PO43- and NO3-
• Change the ratio of nutrient to C in
  phytoplankton
• Iron limitation of biological production at
  surface indicates a Southern Ocean Biological
  Pump could have intensified in a dustier, more
  iron-rich environment.
• Glacial dust could stimulate the rate of Nitrogen
  fixation, increasing the ocean pool of NO3-

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Archer et al, 2005
A New model of Ocean and Sediment Geochemistry
- Mechanisms to lower glacial pCO2

• 2. Change the pH of the whole ocean
• Convert seawater CO2 into HCO3- and CO3,
• which cant evaporate in the atmosphere.
• pH is regulated by balance between influx of
  dissolved CaCO3 and removal by burial of CaCO3
  sediments.
• Timescale of 5-10 kyears is within observed
  timescales.

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Archer et al, 2005

• 2. Change the pH of the whole ocean
• Conditions under which it could occur
• Glacial rate of weathering is higher
• CaCO3 deposition shifts to deep sea
• Rate of CaCO3 production decreased
• CaCO3 compensation may also affect pCO3 response
  to the biological pump in
  1.
• Results
• burial efficiency would increase
• the Ocean would become more basic
• degradation of biological C in sediments would
  promote Calcite dissolution, further increasing
  Ocean pH.

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Two Caveats
Archer et al, 2005
A New model of Ocean and Sediment Geochemistry
- Mechanisms to lower glacial pCO2
The ocean carbon cycle is a complicated system,
controlled by biological processes we are only
beginning to understand. Thus the formulation of
the model is not completely con-strained by our
understanding of the underlying processes.
Furthermore, we use the model to
predictconditions which we are unable to observe
except indirectly via clues preserved in the
sedimentary record.
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Archer et al, 2005
A New model of Ocean and Sediment Geochemistry
- Mechanisms to lower glacial pCO2 - CO2 pump
scenarios

• Fe fertilization of existing NO3 or PO4 pools
• attains glacial pCO2 values in box models
• But not in circulation models
• 2. Increase NO3- by 50
• Attains glacial pCO2 for a few thousand years
  until CaCO3 compensation lowers Ocean pH.
• Requires a change in the Redfield Ratio.

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Archer et al, 2005
A New model of Ocean and Sediment Geochemistry
- Mechanisms to lower glacial pCO2 - CO3 pump
scenarios

• Coral reef hypothesis lowered sea level causes a
  decrease in shallow CaCO3 deposition, which
  drives increased deposition in the deep sea
• Increased pH would lower pCO2
• Not backed up by deep-sea cores
• Rain ratio hypothesis decrease in CaCO3
  production or in-crease in organic carbon
  production could shift Ocean pH.
• A doubling of H4SiO4 could explain it, but cant
  be rationalized.
• Predicted distribution of CaCO3 on seafloor is a
  poor fit.

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Archer et al, 2005
A New model of Ocean and Sediment Geochemistry
Procedures and summaries

• Present Day Ocean simulation
• pCO2 within 2 µatm of observed values
• Distribution of CaCO3 a poor fit

Present-day CaCO3 distribution on seafloor
Modeled Present-day CaCO3 distribution on seafloor
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Archer et al, 2005
A New model of Ocean and Sediment Geochemistry

• The Glacial Ocean model description
• High Lat. Air temperatures 10-15 C colder than
  now
• Tropical cooling 1-2 C cooler from plankton and
  O isotope ratios
• Glacial flow field estimated from best second
  guess velocities
• Atlantic overturning shallower and 30 slower
  than now
• d13C tracer says Southern Ocean was
  high-nutrient, low Oxygen, contradicting Cd data.

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Archer et al, 2005
A New model of Ocean and Sediment Geochemistry

• The Glacial Ocean model results
• Iron flux to sea surface increases by 2.5 goes
  to regions that already receive sufficient iron.
• NO3- decreases from 110 x 1012 mol to 80 x 1012
  mol.
• pCO2 lowered by 8 µatm.
• CO3 and H4SiO4 tweaked until burial rates of
  CaCO3 and SiO2 are those of present day.
• 17 H4SiO4 decrease yields a 70 SiO2 burial
  increase.
• Organic C production increased from 0.198 to
  0.210
• Acidification of ocean overwhelms iron
  fertilization, increasing pCO2 to 280 µatm.

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Archer et al, 2005
A New model of Ocean and Sediment Geochemistry

• Collapse of the terrestrial biosphere
• 13C/12C ratio in deep sea CaCO3 was .4o lower,
  indicating that an isotopically-depleted carbon
  reservoir released 40 x 1015 mol C, raising the
  Ocean-Atmosphere inventory by 1
• Possible sources
• Terrestrial biomass 40 x 1015 mol C
• Soil organic carbon 120 x 1015 mol C
• Sedimentary C on continental shelves

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Archer et al, 2005
A New model of Ocean and Sediment Geochemistry

• Collapse of the terrestrial biosphere
• Reconstructions call for 2-3 x this d13C value.
• Initially raises pC02 to 305 µatm.
• Reaction with CaCO3 will neutralize the added
  CO2
• Lowering to 297 µatm predicts a lowering of 17
• µatm in the future.
• After compensation, pCO2 is 295 µatm.

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Archer et al, 2005
A New model of Ocean and Sediment Geochemistry

• Tropical Temperatures
• Lowering Tropical Sea Surface Temperature by 4C
  decreases pCO2 by 5 µatm.
• Biological production is altered
• Stratification decreases, organic Carbon
  increases.
• SiO2 decreases as H4SiO4 recycling decreases.
• Small increase in pCO2.

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Archer et al, 2005

• Constraints on the cause of glacial/ interglacial
  atmospheric pCO2
• Deglacial increase leads ice volume, eliminating
  sea-level-driven explanations such as submersion
  of continental shelves
• Deglacial transition was slow 6-14 kyears.
• The pCO2 response is much faster.
• Glacial rates of weathering and burial
• were not much different than today.
• Isotopic signatures of C, N, B, Cd, Ba
• Distribution of CaCO3 and SiO2 on sea floor

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Archer et al, 2005
Solution challenge one or more of the basic
assumptions of chemical oceanography!

1. Ocean circulation models are more diffusive than
   the modern ocean, underestimating the pCO2
   sensitivity to the biological pump
2. Increase the glacial NO3- inventory beyond the
   PO43- limitation, assuming the Redfield N/P
   number was different in glacial time.
3. Double the inventory of H4SiO4 in the ocean,
   raising the pH of the deep ocean.

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Greenhouse puzzles Part 2Secondary sources

• A silicon-induced alkalinity pump hypothesis,
  Marine Inorganic Chemistry/ Department of
  Chemical Oceanography, The Ocean Research
  Institute ORI, University of Tokyo, Japan
  http//www.ori.u-tokyo.ac.jp/en/special/topics_4/t
  opics-e.htm
• (refers to Broecker and Peng, Part 2 1994 version
  as Archers World. Also references Martin,
  J.H., The Iron Hypothesis)
• Field-based Atmospheric Oxygen Measurements and
  the Ocean Carbon Cycle, PHD Thesis by Britton
  Bruce Stephens, Chapter 6, The Influence of
  Antarctic Sea Ice on Glacial-Interglacial CO2
  Variations
• Modeling of marine biogeochemical cycles with an
  emphasis on vertical particle fluxes, PhD Theis
  by Regina Usbeck,
• http//www.awi-bremerhaven.de/GEO/Publ/PhDs/RUsbec
  k/RUsbeck.html
• Zeng, Ning, Glacial-Interglacial Atmospheric CO2
  Change - the Glacial Burial Hypothesis.
  http//www.atmos.umd.edu/zeng

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Greenhouse puzzles Part 2Secondary sources

• ORI biological pump model of atmospheric CO2
  variability
• Stephens Harvardton-Bear index
• Actual atmospheric CO2 change /
• potential change due to cooling of
  low-latitude surface box
• Usbeck compares others works with recent
  estimates of total Corg
• accumulation
• Zeng Ocean d13C, .35o,
• land-carbon difference (Holocene - LGM) 460

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Substitute or correct paper?
The sequence of events surrounding Termination II
and their implication for the cause of
glacial-interglacial CO2 changes
Wallace S. Broecker and Gideon M. Henderson,
Paleoceanography, V 13 , No 4, PP. 352-364,
August 1998
Wallace Broecker, Lamont-Doherty
Gideon Henderson, now at Oxford
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Broecker and Henderson, 1998

• Clues from the Vostok ice core
• Antarctic Temperature and atmospheric CO2
  increased together for 8000 years, bounded by
• A drop in dust flux at the onset
• A drop in d18O at the finish
• A similar lag between dust flux and
  foraminiferal d18O in the Southern Ocean
  indicates that the d18O in Vostok ice is a valid
  proxy for ice volume.
• Synchronous changes in CO2 and Southern
  Hemisphere temperatures preceded melting of
  Northern Hemisphere ice
• Nutrient reorganization in North Atlantic occurs
  with or after the sea level rise

28
Broecker and Henderson, 1998

• Clues from the Vostok ice core
• The previous observations eliminate many
  scenarios proposed to explain the CO2 rise
• Those which rely on sea level change
• Conveyor-related nutrient redistribution
• North Atlantic cooling
• Southern Ocean scenarios become the front
  runners.
• The most popular, Iron fertilization, has 2
  problems
• Much of the dust demise occurs prior to the
  change in CO2, so there must be a threshold value
  above which it does not increase.
• The CO2 rise continues for 4-5 kyr after the dust
  flux has fallen to zero.

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Broecker and Henderson, 1998

• Clues from the Vostok ice core
• Problems with iron fertilization causing the
  rise in CO2 may be solved if the increased iron
  supply in dust caused higher rates of nitrogen
  fixation during Glacial periods.
• In this case, residence time of oceanic nitrate
  of a few thousand years would enable decreasing
  productivity to be a global rather than a local
  phenomenon
• This would explain the slow rampup of
  atmospheric CO2.

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Broecker and Henderson, 1998
Timing is everything for Broecker and Henderson.
More comfortable than their predecessors with
relating time markers, their whole theoretical
setup is based on these time relationships.
O2 created by photosynthesis has the Isotopic
composition of surface seawater, which is
controlled by global ice volume. Turnover time
is 1-2 kyears. Therefore, d18Oatm should have
risen 1.4o with d18Oocean.
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Broecker and Henderson, 1998
The first assumption is that variation in ocean
surface d18O is the only contributor to changes
in d18Oatm.
They then claim that the Dole Effect, where the
atmosphere is enriched in 18O by 23.5o over the
ocean, keeps it steady.
They then present similar offsets between events
as indicating a good correlation.
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Broecker and Henderson, 1998

• Broeckers Bipolar Seesaw concept is also an
  important consideration, where deepwater
  formation alternates between the North and South
  Atlantic. This eliminates mechanisms that occur
  only in the North Atlantic.
• Cooling in the Southern Ocean at the same time
  as CO2 is falling is considered as a cause, but
  is nowhere strong enough to cause the observed
  drop.
• Changing the productivity or alkalinity is also
  suggested as a control of Oceanic CO2.
  Observations indicate that these changes moved in
  the opposite direction.
• Nitrogen fixation by iron fertilization is
  considered, but the residence time for NO3 is too
  long to keep it locally confined.

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Broecker and Henderson, 1998 Tentative
conclusions

• d18O constrains the rise in atmospheric CO2 to
  have preceded the melting of the North American
  ice sheets.
• This eliminates seal level change, North Atlantic
  Nutrient redistribution, and North Atlantic
  cooling as causes.
• Iron fertilization cant explain
• Southern Ocean paleoproductivity
• the long duration of the CO2 rise
• Increased dust flux in the glacials caused more
  nitrogen fixation,
• which allowed a greater CO2 drawdown in surface
  waters.
• Long residence time of NO3 in ocean explains how
  CO2 can continue to increase after the dust flux
  ix zero, and means productivity changes can be
  global.

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Newer ideas 1 Zeng, Ning, Glacial-Interglacial
Atmospheric CO2 Change - the Glacial Burial
Hypothesis
Readily available from http//www.atmos.umd.edu/
zeng
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Newer ideas 1 Zeng, N

• Advancing ice sheets buried vegetation and soil
  carbon accumulated during warm periods.
• Simulation over 2 cycles found a 547 Gt carbon
  release, resulting in a 30 ppmv increase in
  atmospheric CO2, the remainder absorbed by the
  Ocean.
• Atmospheric d13C drops by .3o at deglaciation,
  followed by a rapid rise to a high interglacial
  value, in response to oceanic warming and
  regrowth on land.
• With other ocean-based mechanisms, offers a full
  explanation of the observed atmospheric CO2
  change.

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Newer ideas 1 Zeng, N
Fig. 8. Modeled atmospheric CO2 (a) and land
carbon storage (b) from the control run and 5
sensitivity experiments described in the text
control is in black line, SST in green, CO2v120
in yellow, SoilD5h in red, Soil D20k in blue, and
WarmGlac in purple. The largest change of a 55
ppmv deglacial CO2 increase is due to a cooler
glacial ocean in addition to the land carbon
release (green) and a 40 ppmv increase due to a
long delayed regrowth (blue).
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Newer ideas 1 Zeng, N
Data from Table 1 Land carbon difference,
Holocene - LGM
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Newer ideas 1 Zeng, N

• Look for it
• On the ground
• Back in time
• In the models
• In comparisons

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Newer Ideas 2 Paillard and Perenin
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Newer Ideas 2 Paillard and Perenin

• Glacial bottom waters
• were possibly much more saline
• May have an unsuspected large density
• Glacial deep stratification could account for the
  difference.
• Ice formation around Antarctica involves
• Brine rejection over the Continental Shelves
• Is directly linked to changes in
• Sea Ice Formation
• Antarctic ice-sheet extent

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Kitchen Experiment mixing saline water
Cold 30 salt water
They mixed immediately.
Warm 10 salt water
42
Newer Ideas 2 Paillard and Perenin
43
From Wikipedia
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Newer ideas 3

• Toggweiler, JR, GFDL,
• Climate change from below
• Quaternary Science Reviews 24 (2005) 511-512

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Newer ideas 3 Toggweiler, Climate Change from
below

• Adkins et al, 2002, showed bottom waters around
  Antarcti-ca are significantly saltier than the
  rest of the ocean, appar-ently from accumulation
  of brine during sea ice production.
• This shows that the glacial deep ocean was more
  stably stratified than it is today.
• Geothermal heat would have slowly warmed it from
  below, destabilizing it, like a discharging
  capacitor.
• Just 2C is enough to destabilize it.
• This would take 10,000 years.
• This matches
• Heinrich Events in the North Atlantic.
• Bond cycles in Greenland Ice Cores
• Bi-polar seesaw between Greenland and Antarctica
• He gives several examples separated by 7000
  years.

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Newer ideas 3 Toggweiler, Climate Change from
below

• This injects salt into the upper North Atlantic,
  kick-starting thermohaline circulation.
• Reinvigorated circulation warms up Greenland and
  the North Atlantic.
• This confirms the finding that the warmest
  intervals in Greenland occur during the
  interstadials that follow Heinrich and Antarctic
  Intervals.
• This contradicts the prevailing view
• these events are caused by fresh water input
• Explains why interstadials after Heinrich events
  are longer and warmer than others.

47
Newer ideas 3 Toggweiler, Climate Change from
below

• Short paper.
• Is it the right one?
• So I wrote and asked!

Woah! Preprint!
48
Newest ideas yet
49
Newest ideas yet Toggweiler et al

• Another new idealized general circulation model
  explains
• tight correlation between atmospheric CO2 and
  Antarctic temp
• lead of Antarctic temp over CO2 at terminations
• Shift of oceans d13C minimum from N. Pacific to
  Atlantic sector of the southern Ocean
• Changes occur at transitions between on and off
  states of the southern overturning circulation.

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Newest ideas yet Toggweiler et al
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Newest ideas yet Toggweiler et al
Proposal overturnings occur in nature through a
positive feedback that involves mid-latitude
westerly winds.

• Glacial climates seem to have equatorward-shifted
  westerlies which allow more respired CO2 to
  accumulate in the deep ocean.
• Warm climates like the present have poleward
  shifted westerlies that flush respired CO2 out of
  the deep ocean.

52
Newest ideas yet Toggweiler et al
Contains 6 pages of good references at the end.
53
But wait theres MORE!

• A silicon-induced alkalinity pump hypothesis
• The Ocean Research Institute, University of Tokyo

In order to maintain atmospheric CO2 at 190-200
ppm, alkalinity and pH in the surface ocean must
be higher by 85 µeq/L and .14 units,
respectively.
Proposal species change in phytoplankton
produced only 20-25 Carbonate plus Opal during
ice ages vs 90 now. Quotes Broecker and Peng
54
and more!

• Carbon Storage on exposed continental shelves
  during the glacial-interglacial transition
• Montenegro et al

• Up to 10,000 years before present,
  time-dependent estimate of inundated carbon is in
  good agreement with the increase in the
  atmospheric reservoir.
• Carbon stock of the LGM exposed shelves cannot be
  ignored and merits more detailed attention from
  modelling and reconstructions.
• Quotes Zeng (2003)

55
and Still more!
A movable trigger Fossil fuel CO2 and the onset
of the next glaciation Archer and Ganopolski
Uses models of how much CO2 and cooling is
required to start an ice age to predict how soon
the next ice age will come, considering how much
CO2 we have/will put in the atmosphere. A
carbon release from fossil fuels of 500 Gton C
could prevent glaciation for the next 500,000
years.The duration and intensity of the
projected interglacial period are longer than
have been seen in the last 2.6 million
years. Quotes Archer et al, Broecker and
Henderson, and Paillards PhD thesis
56
one more
Glacial HiccupsDidier Paillard

• The climate instability of glacial times probably
  resulted frm abrupt switches in ocean
  circulation.
• Figure shows Climate (temperature) stability as a
  function of freshwater input at high latitudes in
  the North Atlantic.
• unperturbed present-day state
• Last Glacial Maximum
• An intermediate situation 50,000 years ago.
  Dansgaard-Oeschger events
• Figure shows Climate
• Quotes himself.

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And finally,

• Aric Global Climate Change Student Guide
• Palaeoclimatic Change CO2 Feedbacks
• Reviews the many hypotheses of the causes of CO2
  changes, and the phase relationships of CO2, ice
  volume and termperature, that have passed through
  many stages over the last decade or so.
• Gives a review of all factors involved, with
  equations.

Ocean SCO2 profile
Ocean d13C profile
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Conclusions

• There are many partial solutions
• This problem is a hard nut to crack.
• Truth, however, is elusive prey
• - Sandra Collins, Pittsburgh Post-Gazette, March
  26 2005