Transcript Put title here. - Denver Climate Study Group

NATURE
June 1, 2006
THE
CENOZOIC
ARCTIC
OCEAN
Greenhouse to icehouse
in 55 million years
NATIONAL GEOGRAPHIC May 2005
Great Green North
“Was the icy Arctic once a warm soup of life?”
NEW YORK TIMES November 30, 2004
Under All That Ice, Maybe Oil
Need a picture of NYT page
THE AZOLLA STORY
IMPLICATIONS FOR
CLIMATE CHANGE
AND
ARCTIC SOURCE ROCKS
PART 1
CLIMATE CHANGE
FROM GREENHOUSE TO ICEHOUSE
MODERN ICEHOUSE WORLD
bipolar glaciation
MODERN ICEHOUSE WORLD
Arctic
bipolar glaciation
Antarctic
we think of this as ‘normal’…but
bipolar glaciation
geological rare
possibly unique
no previous bipolar glacial state is known from the geological record
icehouse world also characterized by
glacial – interglacial cycles
icehouse world also characterized by
high latitudinal thermal gradient
Mesozoic greenhouse world
differed strongly from the modern icehouse world
• no bipolar glaciation
• low latitude thermal gradient
determining the cause of climate change
is crucial today to
• understand the reasons for
glacials and interglacials
• understand the shift from
greenhouse to icehouse
and to understand where we are going next
so why is the modern icehouse world
geologically rare?
we need to look at two geological
controls on long-term climate change
PART 2
PLATE TECTONICS & MARINE GATEWAYS
HOW TO MAKE AN ICEHOUSE WORLD
STEP ONE
isolate polar regions from warm marine currents
Antarctic
a landmass isolated from warm marine currents
Antarctic
a landmass isolated from warm marine currents
and centred on the South Pole
resulted from separation
of Antarctica from
Australia &
South America
development of circum
Antarctic current
initiation of modern
cold deep-water
oxygen-rich circulation
occurred during the
Eocene to early Miocene
with a major step at the
Eocene/Oligocene
transition
Arctic
An ocean isolated from warm marine currents
Arctic
An ocean isolated from warm marine currents
centred on the North Pole
• basin largely enclosed
• single marine gateway
• freshwater input from rivers
• freshwater input from rivers
• locally lowering salinity
• preventing marine inflow
into central Arctic
plate tectonics resulted in
isolated Arctic Ocean
isolated Antarctic continent
thermal isolation of polar regions depended on
unusual land-sea configuration at both poles at
the same time
but this only provided the background needed
to produce bipolar glaciation
for this to develop we also need to add the
second major parameter to the story………
the atmosphere
PART 3
greenhouse gases
PART 3
greenhouse gases
• CO2 particularly important
• very significant
• today and in the past
atmospheric CO2
now the focus of intense research
the debate is very controversial
atmospheric CO2 through time
atmospheric CO2 through time
Charles Keeling – measured pCO2 over the past 50 years
atmospheric CO2 through time
1958 to present
Mauna Loa, Hawaii and la Jolla
and other locations worldwide
La Jolla Pier California
CO2 values
measured in
parts per million
annual
cyclicity
of 5ppm
due to northern spring drawdown
and autumn/fall CO2 release
increase from
320ppm to
380ppm
we can look at older CO2 values
using air trapped in ice cores
Source: Etheridge et al. 1996, 1998
can include the Keeling data
and rotate the graph
1958
Keeling data
ice core data
Keeling data
how much is
man made?
how much is
natural cyclicity?
need a better
geological
perspective
we need to go
further back in time
almost half a million years
using Vostok ice cores from the Antarctic
Vostok
Sources: Petit et al. (Nature 1999); Am Ass Adv Science
November 2005; Science November 2005
note the change in CO2 scale
glacial
we see strong fluctuations in
CO2 that correlate closely
with changes in temperature
and glacial-interglacial cycles
interglacial
with CO2 decreasing during glacials due to increased CO2 sequestration by
the colder waters in the oceans
temperature
glacials
glacial
and peaking during interglacials as higher temperatures lead to CO2 release
from the oceans
temperature
interglacials
glacial
interglacial
glacial-interglacial
phases initially
triggered by
Milankovitch cycles
glacial
interglacial
Sources: Am Ass Adv Science November 2005;
Science November 2005
glacial-interglacial
phases initially
triggered by
Milankovitch cycles
reinforced by
resulting CO2
cyclicity due to
ocean dissolution
Sources: Am Ass Adv Science November 2005;
Science November 2005
glacial
interglacial
glacial-interglacial
phases initially
triggered by
Milankovitch cycles
reinforced by
resulting CO2
cyclicity due to
ocean dissolution
with CO2 following
temperature by
about 800 years
Sources: Am Ass Adv Science November 2005;
Science November 2005
glacial
interglacial
today’s situation differs
we are now at 380 ppm
100 ppm higher than
previous 280 ppm peaks
280
380
today’s situation differs
we are now at 280 ppm
100 ppm higher than
previous 280 ppm peaks
and CO2 appears to be
leading temperature
280
380
let’s go
further back
in time
we now need to use proxies to estimate
values of atmospheric CO2
CO2 determined from
boron 11 and
alkenoid carbon isotopes
backed up by other data
into the
Miocene
note change
in CO2 scale
poor data
600
ppm
poor data
Oligocene-mid Miocene
values reach 600 ppm
poor data
extending
further back
into the Eocene
poor data
CO2 values
exceed 1000 ppm
poor data
we see an abrupt fall
in CO2 at the base
Oligocene to below
1000 ppm
coincident with major
development of cold
bottom-water circulation
did this sequester CO2?
coincident with the
onset of modern
cold deep-water
circulation
poor data
climate models also
indicate that full
Antarctic glaciation
cannot occur unless
CO2 ppm is less than
1000 ppm
poor data
major Antarctic glaciation
1200 ppm
1200 ppm
poor data
minor glaciation
1200 ppm
800 ppm
increased glaciation
fall in CO2
800 ppm
poor data
800 ppm
1200 ppm
extensive continental glaciation
fall in CO2
600 ppm
600 ppm
poor data
800 ppm
1200 ppm
can this be used to
predict the effect of
future increases in
CO2 on Antarctic
deglaciation?
600 ppm
poor data
800 ppm
1200 ppm
poor data
preliminary data also
indicate that middle-late
Eocene values fluctuate
strongly
poor data
was this a period of
readjustment?
what were earlier CO2 values?
back into the early Eocene
Sources: Tripati et al. Nature July 2005
Pagani et al. Science July 2005
Pearson & Palmer Nature August 2000
CO2 values reach 3500 ppm
Sources: Tripati et al. Nature July 2005
Pagani et al. Science July 2005
Pearson & Palmer Nature August 2000
so we see a major
decrease at base of the
Middle Eocene from
3500ppm to 600 ppm
Why?
what effect did this
have on temperature?
PART 4
temperature change
from greenhouse
to icehouse
Paleocene temperatures
greenhouse state inherited
from the Mesozoic
Arctic centred on the North Pole
low latitudinal thermal gradient
warm Arctic temperatures
temperatures estimated by
• various marine and terrestrial markers
• oxygen isotopes
• climate models
we can therefore estimate Palaeocene Mean Annual Temperatures
11
23
22
20
26
11
22
24
17
19
17
11
Source: Triparti et al. 2001
16
12
which indicate warm Arctic temperatures
11
23
22
20
26
11
22
24
17
19
17
11
Source: Triparti et al. 2001
16
12
but with seasonality resulting in Arctic environments totally unknown today
11
23
22
20
26
11
22
24
17
19
17
11
16
12
- 24 hour summer daylight and 24 winter darkness
within a region of warm air and sea temperatures
11
23
22
20
26
11
22
24
17
19
17
11
16
12
climate models indicate these
temperatures required about
x10 modern CO2 levels
= about 3500 ppm
climate models indicate these
temperatures required about
x10 modern CO2 levels
= about 3500 ppm
consistent with isotope data
we can also look at
temperature change
through the Cenozoic
cooler
warmer
using oxygen isotopes as a
proxy for temperature
icehouse
these show the
change from
greenhouse to
icehouse
greenhouse
and the Paleocene Eocene Thermal Maximum
which resulted in a
supergreenhouse world
and very high temperatures
including polar regions
Paleocene Eocene Thermal Maximum
triggered by increased greenhouse gases from
• extensive volcanism (Greenland plume)
• release of methane clathrates (hydrates)
supergreenhouse state continued
through the early Eocene
abundant greenhouse gases
high temperatures
but early Eocene supergreenhouse
was followed immediately by
abrupt global cooling
what forced this change?
the massive
decrease in
atmospheric
CO2?
PART 5
Arctic Coring Expedition (ACEX)
Arctic Coring Expedition (ACEX)
• August – September 2004
Arctic Coring Expedition (ACEX)
• August – September 2004
• first International ODP cruise into the Arctic
• supported by Norwegian and Russian icebreakers
successfully cored the
Lomonosov Ridge
ACEX results
ACEX results
• 1400 ft cored section
• good Paleocene Eocene
section recovered
ACEX results
Azolla event
PETM
ACEX Azolla core
• 8 to 20m metre ACEX core with >90% Azolla
• base not cored
• Azolla occurs as laminated layers
• indicates Azolla deposited in situ
• in a ‘marine’ setting away from shore
Age of the Azolla event
Azolla event also present in Arctic exploration wells
and transported south into Nordic seas
so we can establish the age of the Azolla event
i
Brinkhuis et al., Nature, 2006
Azolla event: summary
base Middle Eocene
lasted about 800,000 years
coeval with onset of Arctic cooling
coeval with onset of Antarctic glaciation
coeval with massive fall in CO2
is this coincidence?
or is there a relationship
between Azolla and CO2?
PART 6
modern and fossil Azolla
what is Azolla?
• floating aquatic freshwater fern
• known from Cretaceous to present
• so we can look at habitats of modern species
fossil Azolla from the Eocene Green River Formation
is identical in morphology to modern Azolla
what do we know about modern Azolla?
fastest growing plant on the planet!
doubles its biomass in 2 to 3 days
widely used as a green biofertilizer for rice fields
why is it a fertilizer?
why does it have
rapid growth?
how can it grow free-floating on water
without soil nutrients?
the key is
Azolla’s leaf
structure
source: Carrapiço, 2002
its leaves are
characterised
by cavities
source: Carrapiço, 2002
leaf cavities
filled with nitrogen
inhabited by a nitrogen-fixing
cyanobacterium (blue-green
alga) Anabaena
source: Carrapiço, 2002
Anabaena symbiont has been passed to
successive generations via Azolla spores
sporocarps
Azolla’s sporophyte
megasporocarp
new sporophyte
megasporocarp’s chamber
megasporocarp’s chamber
fertilization
(Carrapiço, 2006)
for more than hundred million years!
sporocarps
Azolla’s sporophyte
megasporocarp
new sporophyte
megasporocarp’s chamber
megasporocarp’s chamber
fertilization
(Carrapiço, 2006)
so Azolla-Anabaena can fix more
than 1000 kg of atmospheric
nitrogen per acre per year
providing a natural biofertilizer
in the water for rice production
the nitrogen is also available for
rapid growth of the Azolla plant
which can then fix up to 6000 kg of
atmospheric carbon per acre per
year free-floating on water
it is the only known known symbiont of this kind
to summarize
• Azolla floating freshwater fern (no salinity tolerance)
• draws down large quantities of C & N
• doubles biomass in 2 - 3 days…….and
• temperature tolerant
• optimum growth 20 hours of daylight
PART 7
Arctic Eocene model
i
what triggered the Azolla event?
i
what triggered the Azolla event?
• Arctic Basin largely enclosed
following the PETM
i
what triggered the Azolla event?
• Arctic Basin largely enclosed
• high temperature, rainfall & runoff
i
what triggered the Azolla event?
• Arctic Basin largely enclosed
• high temperature, rainfall & runoff
i
• widespread surface freshwater layer
what triggered the Azolla event?
• Arctic Basin largely enclosed
• high temperature, rainfall & runoff
i
• widespread surface freshwater layer
• atmosphere rich in C & N
• abundant nutrients flushed into basin
ideal conditions for opportunistic Azolla
i
model of Azolla growth and deposition
model of Azolla growth and deposition
local anoxia
variable water stratification and bottom water anoxia
model of Azolla growth and deposition
Azolla deposited in anoxic conditions
and was therefore able to drawdown carbon
Azolla model of climate change
•
Azolla blooms widespread in Arctic
freshwater surface layers
• occurred episodically for about 800,000 years
resulting in massive
carbon drawdown
and the onset of cooling
triggering the shift
from supergreenhouse
towards the modern
icehouse state at
base Middle Eocene
we can estimate amount of carbon
from modern Azolla production
•
6000 kg of carbon per acre each year
•
= 6000,000 kg of carbon per acre in 1000 years
Source: ACEX scientists preliminary unpublished data
carbon drawdown for Azolla event
• TIME: up to 800,000 years
• AREA: up to 4,000,000 sq km
carbon drawdown for Azolla event
• TIME: up to 800,000 years
• AREA: up to 4,000,000 sq km
easily sufficient to change CO2 from 3500 to 650 ppm
even with time and area strongly scaled down
so the Azolla event could
have triggered the initial shift
from a greenhouse world towards
our modern icehouse planet!
PART 8
implications for Arctic petroleum
Arctic petroleum resources are
now becoming very significant
and controversial…..
TIME MAGAZINE
October 1 2007
Who Owns the Arctic?
Fight for the Top of the World
could the Azolla interval provide
a source for Arctic petroleum?
Azolla event - implications for Arctic petroleum
• large amount of C possibly deposited in Arctic Basin
•
unusual source – includes cyanobacterial symbiont
Azolla event - implications for Arctic petroleum
•
occurs at ACEX location near central Arctic
•
also present in numerous Alaskan and Canadian wells
northern Alaska
Canadian Beaufort
Chukchi Sea
Bujak well database
extends data points
beyond ACEX
ACEX
• Canadian Beaufort
• northern Alaska
• Chukchi Sea
northern Alaska
Canadian Beaufort
Chukchi Sea
ACEX
in a variety of
environments
Canadian Beaufort: 28 wells in various deltaic facies
northern Alaska and Chukchi Sea
• 27 wells away from the delta
• various nearshore to offshore locations
Mikkelsen 13-9-19
Alaska well
4500'
Gam ma Log
0
(API)
150
Azolla and PETM events exactly
the same age as in the ACEX cores
based on palynological zones
4460
T6
4750'
TEU
4837.0
T4b
5000'
5100.0
T4a
5250'
Azolla event
Azolla
5260.0
T3(iii)
5500'
5550
T3(ii)
5690.0
5750'
T3(i)
6000'
PETM event
T2(ii) PETM
6050.0
6250'
T2(i)
6500'
6642.0
source Bujak unpublished data
Mikkelsen 13-9-19
Alaska well
4500'
both events are also characterised
by distinctive high-gamma curves
Gam ma Log
0
(API)
150
4460
T6
4750'
TEU
4837.0
T4b
5000'
5100.0
T4a
5250'
Azolla event
Azolla
5260.0
T3(iii)
5500'
5550
T3(ii)
5690.0
5750'
T3(i)
6000'
PETM event
T2(ii) PETM
6050.0
6250'
T2(i)
6500'
6642.0
Canadian and Alaskan well data
age and source rock
potential are consistent
with preliminary
ACEX results
indicates a possible
Arctic-wide
source rock
indicates a possible
Arctic-wide
source rock
gas prone with minor
mixed oil/gas potential
TOC up to 5.5%
onset of maturation
about 0.8% Ro
but we don’t know its
geographic extent
northern Alaska
Canadian BMB
Chukchi Sea
ACEX
so we need to
extend database
into other Arctic
areas
and finally………..
did Azolla really change the Earth from
a supergreenhouse to icehouse state?
the answer has important implications for
past & modern climate change which are crucially significant today
not only for
the Arctic
but for the
entire planet
thank you