Transcript - EdShare - University of Southampton

Sea level, meltwater pulses, the overturning
circulation, and climate
Eelco J Rohling
With thanks to
Jenny Stanford, Mark Siddall, Bob Marsh
Stable O isotope records from Greenland (example here is GISP2) through
the last glacial cycle show strong climate variability
Reproduced by permission of American Geophysical Union:
Rahmstorf, S., Timing of abrupt climate change: A precise clock,
Geophys. Res. Lett., 30(10), 1510, 21 May 2003. Copyright [2003]
American geophysical Union.
The “Dansgaard-Oeschger cycle”
warm = interstadial; cold = stadial
Large (order 10°C) temperature shifts
Warming events within time-span of a decade or possibly less
Also sharp coolings, after a more gradual onset of cooling
©Niels Bohr Institutet
CH4 synchronisation
Antarctica
Greenland
How related to climate variability in high southern latitudes?
Reprinted by permission from Macmillan Publishers Ltd: Asynchrony of Antarctic and Greenland climate change
during the last glacial period. Blunier, T; Chappellaz, J; Schwander, J; Daellenbach, A; Stauffer, B; Stocker, T F;
Raynaud, D; Jouzel, J; Clausen, H B; Hammer, C U; Johnson, S J., Nature, v. 394, no. 6695, p. 739-743.
Copyright (1998) Not under CC licence
Frequent and “Square-wave”
Type fluctuations
(DO-events of order 10+oC)
Fewer and temporally more
Symmetrical fluctuations (A-events
of order 3oC)
•
Timing relationship: bipolar see-saw
•
1100 y integration of –ve northern
record giving southern record
[CH4] in air bubbles within all
Ice cores follows DO-style
Variability = synchronisation
criterion!
Most discussed explanations
focus on the North Atlantic
overturning component of the
global ocean conveyor
Courtesy of LDEO
North Atlantic overturning thought to be sensitive to
fresh-water fluxes into the N Atlantic (order 0.1 Sv)
In a bi-stable regime, surpassing of forcing
thresholds would result in rapid circulation change
Reprinted by permission from Macmillan Publishers Ltd: Ocean circulation and climate during the
past 120,000 years, Rahmstorf, S., Nature, vl. 419, no. 6903, p. 207-214. Copyright (2002). Not
under CC Licence
Models suggest that collapse of the
overturn would shut down northward
heat transport, causing abrupt cooling
over N Atlantic sector
(Note: in records, the warmings are
the really sharp events!)
Link to article with figure that
Demonstates the cold nothern
Hemisphere that would result from
overturn shutdown (Figure 3)
Link to article: Global Climatic Impacts of a Collapse of the Atlantic Thermohaline
Circulation., Vellinga, M; Wood, R, A., Climatic Change. Vol. 54, no. 3, p251. Copyright
(2002).
Strongest cases for freshwater dilution concept :
“Heinrich Events” in coldest extreme DO stadials
Widespread IRD deposition - massive iceberg input.
Durations: 550-900 years (Rohling et al., 2003) or
250-750 years (Hemming, 2004).
Max. associated meltwater input into N Atlantic
equivalent to 15 m sea-level rise (Hemming, 2004).
Reproduced by permission of American Geophysical Union: Hemming, S.R., Heinrich events: Massive Llate Pleistocene detritus layers of the North
Atlantic and their global climate imprint. Reviews of Geophysics, v. 42, no. 1, [np]. March 2004. Copyright [2004] American Geophysical Union.
Concepts of what the world may
have looked like:
Schematic overturning in N Atlantic:
DO
interstadial
DO
stadial
“Heinrich
Events”
Reprinted by permission from Macmillan Publishers Ltd: Ocean
circulation and climate during the past 120,000 years, Rahmstorf,
S., Nature. v. 419, no. 6903, p. 207-214. Copyright (2002).
Not under CC Licence
Reproduced by permission of American Geophysical Union: Rahmstorf, S.,
Alley, R., Stochastic resonance in glacial climate Eos, Transactions,
American Geophysical Union, v. 83, no.12, pp.129-135, 19 Mar 2002.
Copyright [2002] American Geophysical Union.
Heinrich Event = interval of high ice-berg
discharge into N Atlantic (IRD deposits and
light surface-water δ18O anomalies)
BUT: Greenland ice-core data show changes of order 10°C or more….
No model gets even close to that.
Link to article with figure that
Demonstates the cold nothern
Hemisphere that would result from
overturn shutdown (Figure 3)
Link to article: Global Climatic Impacts of a Collapse of the Atlantic Thermohaline
Circulation., Vellinga, M; Wood, R, A., Climatic Change. Vol. 54, no. 3, p251. Copyright
(2002).
Courtesy of The Russian Journal of Earth Sciences: Raspopov, O. M., Dergachev, A.V.,
Kolström, T., Kuzmin, A.V., Lopatin, E.V., Lisitsyna, O.V., (2007), Long-term solar activity
variations as a stimulator of abrupt climate change, Russ. J. Earth Sci., 9, ES3002,
Seager & Battista (2006) review data and simulations from coupled GCMs (GFDL, Hadley Centre),
and find:
“In the North Atlantic region, therefore, there is sufficient agreement ... that changes in the THC were
likely involved in abrupt climate changes.
…., changes in the THC, even shutdowns - at least as represented in GCMs - cannot explain the
magnitude of the cooling around the North Atlantic….
…., even on its own home turf, the THC theory falls short of being able to offer a complete
explanation of abrupt climate changes, unless all existing coupled GCMs are significantly in error
….”
Did the THC slow down? Consider the last two big events: H1 and Younger Dryas
YD
H1
IRD
13C
Reproduced by permission of American Geophysical Union: Stanford, J.D., Rohling, E.J.,
Hunter, S.H., Roberts, A.P., Rasmussen, S.O.,Bard, E., McManus, J. and Fairbanks, R.G.,
Timing of meltwater pulse 1a and climate responses to meltwater injections.
Paleoceanography, 21, (4), PA4103. 9 December 2006. Copyright [2006] American
Geophysical Union.
SST
Pa/Th
Pa scavenged/
settles slower than
Th, so if much
lateral advection,
then Pa depleted
(low ratio). If less
lateral advection,
then ratio increases
Reprinted by permission from Macmillan Publishers Ltd: Collapse and rapid resumption of
Atlantic meridional circulation linked to deglacial climate changes. McManus, J F; Francois, R;
Gherardi, J M; Keigwin, L D; Brown-Leger, S., Nature, v.428, no.6985, p.834-837, Copyright
(2004). Not under CC licence
Widespread light benthic 13C and
marked shift in Pa/Th ratios (GGC-5)
suggest strongly reduced NADW flow
starting with the IRD event of H1.
Similar, but less pronounced for YD.
At same time of reduced NADW,
strong surface (SST) cooling.
Q: Is Pa/Th reconstruction supported by other
rate-sensitive proxies?
Yes - new record of magnetic grainsize from Eirik
Drift core TTR-451  strong signal similarity to
Pa/Th in GGC-5.
Both show gradual slowdown over 2kyr or more,
and sharp recovery (vs. abrupt collapse in
models)
YD
H1
Reproduced by permission of American Geophysical Union: Stanford, J.D., Rohling, E.J., Hunter, S.H.,
Roberts, A.P., Rasmussen, S.O.,Bard, E., McManus, J. and Fairbanks, R.G., Timing of meltwater pulse
1a and climate responses to meltwater injections. Paleoceanography, 21, (4), PA4103. 9 December
2006. Copyright [2006] American Geophysical Union.
Q: Is Pa/Th reconstruction supported by other
rate-sensitive proxies?
Yes - new record of magnetic grainsize from Eirik
Drift core TTR-451  strong signal similarity to
Pa/Th in GGC-5.
Both show gradual slowdown over 2kyr or more,
and sharp recovery (vs. abrupt collapse in
models)
YD
Q: Is freshwater driving these things at all ?
i.e., how is it related to documented large
freshwater fluxes (sea level change) ?
H1
Reproduced by permission of American Geophysical Union: Stanford, J.D., Rohling, E.J., Hunter, S.H.,
Roberts, A.P., Rasmussen, S.O.,Bard, E., McManus, J. and Fairbanks, R.G., Timing of meltwater pulse
1a and climate responses to meltwater injections. Paleoceanography, 21, (4), PA4103. 9 December
2006. Copyright [2006] American Geophysical Union.
Courtesy of AGU: Stanford, J.D., Rohling, E.J., Hunter, S.H., Roberts, A.P., Rasmussen, S.O.,
Bard, E., McManus, J. and Fairbanks, R.G. (2006) Timing of meltwater pulse 1a and climate
responses to meltwater injections. Paleoceanography, 21, (4), PA4103.
Barbados
sea-level
data (new
datings)
Rate of
sea-level
change
THC
intensity
proxies
Heavy line: GRIP on
new GICC05
timescale
Comparison layer-counted GICC05 timescale with Barbados sea-level record shows:
... the ~20m magnitude mwp-1a did NOT coincide with Bölling warming
(even when pushing the confidence limits, they are 300 years separated)
Instead, melt input started during Bölling (…warming caused melting…!), and the massive peak
meltwater flux coincides with abrupt (but rather unimpressive) 200y Older Dryas cooling event
Strong indications of local freshwater dilution in Nordic Seas during H events (Lekens et al., 2006)
Is this (location) what controls
the THC, rather than sheer
magnitude and rate of input?
Caption: Distribution of 18O anomalies
in the Nordic Seas during Heinrich
events and between 33 and 35 cal kyr
B.P. measured on N. pachyderma (s).
No corrections made for global ice
volume and temperature effects.
Reproduced by permisson of American Geophysical Union:
Lekens, W.A.H., Sejrup, H.P., Haflidason, H., Knies, J.,
Richter, T., Meltwater and ice rafting in the southern
Norwegian Sea between 20 and 40 calendar kyr B.P.;
implications for Fennoscandian Heinrich events
Paleoceanography, v. 21, no. 3, PA3013. 9 September
2006. Copyright [2006] American Geophysical Union.
Strong indications of local freshwater dilution in Nordic Seas during H events (Lekens et al., 2006)
Is this (location) what controls
the THC, rather than sheer
magnitude and rate of input?
Moore (2005) and Tarasov &
Peltier (2005) ascribe YD to a
relatively small surface
(iceberg) meltwater flux into
Nordic Seas (from Arctic).
Also, Jennings et al. (2006) a
detected YD meltwater signal
on SE Greenland shelf.
Caption: Distribution of 18O anomalies
in the Nordic Seas during Heinrich
events and between 33 and 35 cal kyr
B.P. measured on N. pachyderma (s).
No corrections made for global ice
volume and temperature effects.
Reproduced by permisson of American Geophysical Union:
Lekens, W.A.H., Sejrup, H.P., Haflidason, H., Knies, J.,
Richter, T., Meltwater and ice rafting in the southern
Norwegian Sea between 20 and 40 calendar kyr B.P.;
implications for Fennoscandian Heinrich events
Paleoceanography, v. 21, no. 3, PA3013. 9 September
2006. Copyright [2006] American Geophysical Union.
So how do H events in general relate to global sea-level variations?
CH4 synchronisation
Antarctica
Greenland
First: consider climate variability in high southern latitudes:
Frequent and “square-wave”
type fluctuations
(DO-events of order 10+°C)
Fewer and temporally more
symmetrical fluctuations
(A-events of order 3°C) of order
3°C)
• Timing relationship; bipolar
see-saw
• 1100 y integration of -ve
northern record giving southern
record
[CH4] in air bubbles within all
ice cores follows DO-style
variability
Reprinted by permission of Macmillan Publishers Ltd: Asynchrony of Antarctic and
Greenland climate change during the last glacial period. Blunier, T; Chappellaz, J;
Schwander, J; Daellenbach, A; Stauffer, B; Stocker, T F; Raynaud, D; Jouzel, J;
Clausen, H B; Hammer, C U; Johnson, S J., Nature, v. 394, no. 6695,
p. 739-743. Copyright (1998) Not under CC licence
Greenland-Antarctic phase relationships confirmed,
by analyses of both types of signals within a single
sample set from a sediment core taken from 3150 m
waterdepth off Portugal (MD952042).
Benthic δ18O signal ~identical in SW Pacific core
MD972120 off New Zealand (~1200 m depth)
Surface foraminiferal δ18O: DO-style signal
Bottom-dwelling foraminiferal δ18O: AA-style signal
From: Pahnke, K., Zahn, R., Elderfield, H., Schulz, M., (2003) 340,000-year centennial-scale
marine record of Southern Hemisphere climatic oscillation Science, v. 301, no. 5635, p.
948-952, Reprinted with permission from AAAS. This figure may be used for non-commercial
classroom purposes only. Any other uses requires the prior written permission from AAAS.
Structure so prevalent that it is even preserved in
the 57-record stack of Lisiecki and Raymo
(2005)
Use of coral-reef data allows first estimate of
sea-level (ice volume) component in the benthic
δ18O signals
 High amplitude shifts with timing that looks
like AA climate variability !
From: Shackleton, N J., (2000) The 100,000-year ice-age cycle identified and found to lag
temperature, carbon dioxide, and orbital eccentricity. Science. v. 289, no. 5486, p. 1897-1902.
Reprinted with permission from AAAS. This figure may be used for non-commercial, classroom
purposes only. Any other uses requires the prior written permission from AAAS.
International Glaciological Society: A numerical investigation of ice-lobe permafrost interaction
around the southern Laurentide ice sheet. Cutler, Paul M; MacAyeal, Douglas R; Mickelson,
David M; Parizek, Byron R; Colgan, Patrick M, Journal of Glaciology, vol.46, no.153, pp.311-325,
Copyright (2000).
Independent validation from the Red Sea sea-level calibration
Why is the Red Sea sensitive
to sea level?
• highly evaporative (2.06 m/yr)
• very limited catchment for run off
• very limited communication with open ocean:
narrow (20km) and shallow (137m) strait
• at 137 m, depth of the sill is very close to the
glacial/ interglacial sea-level range
Small strait limits water exchange. Any reduction in
the strait profile further reduces the exchange. That:
• increases residence time of water in basin
• extends exposure to high evaporation
• consequently enhances salinity and 18O in the
basin.
Link to article (Figure 1) Map of
Red Sea bathymetry and surrounding
topography. Note the small surface
area of the Red Sea rainfall catchment
marked by the bold dashed line
From: Understanding the Red Sea response to sea level.
Siddall, Mark; Smeed, David A; Hemleben, Christoph; Rohling,
Eelco J; Schmelzer, Ina; Peltier, William R .Earth and Planetary
Science Letters, v. 225, no. 3-4, p. 421-434,
So, Red Sea 18O records predominantly reflect sea-level change (dominant cause
of change in the strait profile)
How to quantitatively express this influence?
• develop a realistic model for the hydraulic control of exchange transport through the Strait
• couple this to a basin representation which includes algorithms for calculating 18Owater and
18Ocalcite
• develop the relationship between changes in sea-level and change in 18Ocalcite
• transform planktonic foraminiferal 18O records from central Red Sea to sea-level change
records
Link to article figure (7) The changing
Δsalinity/Δδ18Oseawater with respect
to sea level. Shows strong negative
trend between salinity/oxygen, which
Allows oxygen to be used as a proxy
for measuring past sealevels.
From: Understanding the Red Sea response to sea level.
Siddall, Mark; Smeed, David A; Hemleben, Christoph; Rohling,
Eelco J; Schmelzer, Ina; Peltier, William R .Earth and Planetary
Science Letters, v. 225, no. 3-4, p. 421-434,
2 sigma confidence limit for sea-level variations inferred from oxygen
isotopes is ±12m
(based on ± 2ºC uncertainty in temperature, changes in evaporation between
2.8m y-1 and 1.4m y-1, and changes in relative humidity between 60% and
80%, the modern seasonal extremes).
Relationship sea-level and millennial-scale climate changes during last glacial cycle
Sea-level record based on
central Red Sea planktonic
O-isotope data shows:
 Large changes (order 30
m), in agreement with
maximum amplitudes
suggested by coral data
 Antarctic-type rhythm of
change, very similar to deepsea benthic O-isotope data
Reprinted by permission of Macmillan Publishers Ltd:
Sea-level fluctuations during the last glacial cycle. Siddall, M;
Rohling, E J; Almogi-Labin, A; Hemleben, C; Meischner, D;
Schmelzer, I; Smeed, D A., Nature, v. 423 ,no. 6942,
p. 853-858, Copyright (2003) not under CC licence.
Relationship sea-level and millennial-scale climate changes during last glacial cycle
-40
24m
35m
40m
47m
-37
-38
-60
-70
-39
-80
-40
-90
-100
f
A1
A2
b

-50

H4
12
-60
A3
-41
A4
-42
error bars: ± 1
 : 3 pt. (~500y) mov. avg.
-40
88

H5
H6?
-36
-38
14
14
12
-70
-40
-80
-42
-90
f
-100
Southern Ocean
IRD & 18O shifts
sea level (m below present)
23m
30m
-50
-30
Reprinted by permission of Macmillan
Publishers Ltd: Similar meltwater
contributions to glacial sea level changes
from Antarctic and northern ice sheets
Rohling, Eelco J; Marsh, Robert; Wells,
Neil C; Siddall, Mark; Edwards, Neil R
Nature, v. 430, no. 7003, p. 1016-1021,
Copyright (2004) Not under CC Licence
24m
32m
17m
32m
a
c
53°S
41°S
35000
-44
SA3
GISP2 18O (‰ VSMOW)
sea level (m below present)
-30
BYRD 18O (‰ VSMOW)
In terms of sea level, we find large-amplitude shifts, of similar order to those derived from deconvolved
deep-sea δ18O records (Cutler et al., 2003). Typically ~ 30 m in roughly 2kyr.
SA4
SA5
-0.9‰
-0.5‰
-0.7‰
40000
45000
50000
-0.5‰
55000
-0.5‰
60000
65000
age (cal yr BP) to the GISP2 age model of Blunier et al (1998)
Note ~coincidence of major rises (which last ~1500 y) with periods marked by H-events in N Atlantic, and
IRD and light surface-water δ18O in Southern Ocean (S.O. data after Kanfoush et al., 2000)
Note: co-registered signals in Iberian Margin core MD95-2042 (Shackleton et al., 2000)
demonstrate clearly that THC collapses of H events (negative benthic 13C spikes) occupy
final phase of sea-level rise (shifts to light benthic 18O)
But: was there sea-level rise before H1 as well?
Reproduced by permission of American Geophysical Union: Shackleton, N.J., Hall,
M.A., Vincent, E., Phase relationships between millennial-scale events 64,00024,000 years ago Paleoceanography, v. 15, no. 6, p. 565-569. 25 July 2000.
Copyright [2000] American Geophysical Union.
Looks like it:
roughly 20m in roughly 2 kyr
Reprinted by permission of Macmillan Publishers Ltd: Similar meltwater contributions to glacial sea level
changes from Antarctic and northern ice sheets Rohling, Eelco J; Marsh, Robert; Wells, Neil C; Siddall,
Mark; Edwards, Neil R. Nature, v. 430, no. 7003, p. 1016-1021, Copyright (2004) Not under CC Licence
Hemming (2004) calculates that H events may explain a maximum of 15m
sea-level rise (but some would argue only 1-2m; Roche et al., 2004).
Then:
Q: Where might pre-HE sea-level rises originate from?
A component from Antarctica (e.g. Kanfoush et al., 2000; Rohling et al.,
2004)?
But note: changes in general too large to explain as AA variability
!! New evidence shows melt-water release from the southern margin of the
Laurentide ice sheet, following an AA-style timing !
Hill et al. (2006): melt-signal from southern Laurentide margin (via
Mississippi) agrees more with AA climate rhythm than D-O rhythm
(hard relative timing constraint, based on palaeomagnetic Laschamp event)
Reproduced by permission of American Geophysical Union: Hill, H.W., Flower, B.P., Quinn, T.M.,
Hollander, D.J., Guilderson, T.P., Laurentide ice sheet meltwater and abrupt climate change during
the last glaciation. Paleoceanography, v. 21, no. 1, 9 pp. 18 February 2006. Copyright [2006]
American Geophysical Union.
My speculation:
Observed: AA climate changes are very similar to
atmospheric CO2 changes (Siegenthaler et al., 2005)
Might AA climate signal/rhythm be a (CO2 related?) “global” background climate
signal, and the sharp D-O variability in the North a superimposed pattern?
From: Urs S., Stocker, T.F., Monnin, E., Lüthi, D., Schwander, J., Stauffer, B., Raynaud, D., Barnola, J-M., Fischer, H., Masson-Delmotte, V., Jouzel, J., (2005) Stable Carbon
Cycle–Climate Relationship During the Late Pleistocene. Science v 310, p 1313-1317. Reprinted with permission from AAAS. These figures may be used for non-commerical,
classroom purposes only. Any other uses requires the prior written permission from AAAS.
Conclusions
• AA climate & CO2 signal represents the underlying “global” climate variability
• Global ice-volume fluctuations seem to be closely tied to this AA climate (and
global CO2) rhythm
• Ice volume reductions at S Laurentide margin seem to have followed the (AAtype) rhythm
• We cannot exclude that there may have been AA melt contributions
• Speculation: maybe ice-sheet melting (summer) globally (?) related to an
underlying (CO2 related?) global climate signal, as recorded in AA.
• In Northern Hemisphere, the abrupt D-O style variability may be a
superimposed, winter-dominated signal (for seasonal idea, see: Rohling et al., 2003;
Denton et al., 2005; Seager and Battisti, 2006)
• THC rather insensitive to plain bulk and rate of meltwater additions
• THC may be more sensitive to (much smaller) freshwater input targeted into
the critical Nordic Seas
Copyright statement
•
This resource was created by the University of Southampton and released as an open educational resource through the
'C-change in GEES' project exploring the open licensing of climate change and sustainability resources in the Geography,
Earth and Environmental Sciences. The C-change in GEES project was funded by HEFCE as part of the JISC/HE
Academy UKOER programme and coordinated by the GEES Subject Centre.
•
This resource is licensed under the terms of the Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales
license (http://creativecommons.org/licenses/by-nc-sa/2.0/uk/).
•
However the resource, where specified below, contains other 3rd party materials under their own licenses. The licenses
and attributions are outlined below:
•
The University of Southampton and the National Oceanography Centre, Southampton and its logos are registered trade marks of the University. The University reserves all
rights to these items beyond their inclusion in these CC resources.
•
The JISC logo, the C-change logo and the logo of the Higher Education Academy Subject Centre for the Geography, Earth and Environmental Sciences are licensed under
the terms of the Creative Commons Attribution -non-commercial-No Derivative Works 2.0 UK England & Wales license. All reproductions must comply with the terms of that license.
•
All content reproduced from copyrighted material of the American Geophysical Union (AGU) are subject to the terms and conditi ons as published at: http://www.agu.org/pubs/authors/usage_permissions.shtml AGU content may be
reproduced and modified for non-commercial and classroom use only. Any other use requires the prror written permission from AGU.
•
All content reproduced from the American Association for the Advancement of Science (AAAS) may be reproduced for non commercial classroom purposes only, any other
uses requires the prior written permission from AAAS.
•
All content reproduced from Macmillan Publishers Ltd remains the copyright of Macmillan Publishers Ltd. Reproduction of copyrighted material is permitted for noncommercial personal and/or classroom use only. Any other use requires the prior written permission of Macmillan Publishers Ltd