₂
₂

10.1002/2013GL058177
Key Points:
• We provide a high-resolution CO
2 record during the cooling event
8200 years ago
•
Compared to centennial variations,
CO
2 change during 8.2 ka is not remarkable
• The sensitivity of CO
2 to the cooling during the 8.2 ka was limited
2
Jinho Ahn
1
, Edward J. Brook
2
, and Christo Buizert
2
1
School of Earth and Environmental Sciences, Seoul National University, Seoul, South Korea,
2
College of Earth, Ocean, and
Atmospheric Sciences, Oregon State University, Corvallis, Oregon, USA
Supporting Information:
•
Readme
• Analytical methods and gas age distribution model
Correspondence to:
J. Ahn, jinhoahn@snu.ac.kr
Atmospheric CO
2 records for the centennial scale cooling event 8200 years ago (8.2 ka event) may help us understand climate-carbon cycle feedbacks under interglacial conditions, which are important for understanding future climate, but existing records do not provide enough detail. Here we present a new CO
2 record from the Siple Dome ice core, Antarctica, that covers 7.4
– 9.0 ka with 8 to 16 year resolution. We observe a small, about 1 – 2 ppm, increase of atmospheric CO
2 during the 8.2 ka event. The increase is not signi fi cant when compared to other centennial variations in the Holocene that are not linked to large temperature changes. Our results do not agree with leaf stomata records that suggest a CO
2 decrease of up to ~25 ppm and imply that the sensitivity of atmospheric CO
2 to the primarily Northern Hemisphere cooling of the 8.2 ka event was limited.
Citation:
Ahn, J., E. J. Brook, and C. Buizert (2014),
Response of atmospheric CO
2 to the abrupt cooling event 8200 years ago,
Geophys. Res. Lett.
, 41 , 604
–
609, doi:10.1002/2013GL058177.
Received 1 OCT 2013
Accepted 16 DEC 2013
Accepted article online 19 DEC 2013
Published online 17 JAN 2014
Accurate understanding of climate-carbon cycle feedbacks is important to better constrain the future climate under continued anthropogenic CO
2 forcing. Model-based estimates for climate sensitivity of the global carbon cycle suggest that climate change will be ampli fi ed by carbon cycle feedback, although the magnitude of these feedbacks remains poorly constrained [ Friedlingstein et al ., 2006]. Although climate models produce quantitative results with plausible mechanisms, tests of the models are limited due to the brevity of the instrumental record. Paleoclimate records, on the other hand, provide long records of natural experiments on variety of time scales and under a variety of climate boundary conditions. In particular, the relationship between abrupt climate change and atmospheric CO
2 is of great interest. This topic has been relatively well studied on multimillennial time scales for the last glacial period and deglacial conditions [ Monnin et al ., 2001;
Ahn et al ., 2004; Ahn and Brook , 2007; Ahn and Brook , 2008; Ahn et al ., 2012a; Bereiter et al ., 2012; Schmitt et al .,
2012]. However, the relationship between CO
2 and abrupt climate change on submillennial time scales or under interglacial climate boundary conditions remains poorly investigated.
The 8.2 ka event is a centennial cooling and drying event, which is the most abrupt climate feature of the
Holocene [ Alley et al ., 1997; Alley and Agustdottir , 2005; Rohling and Paelike , 2005]. The event is pronounced around the circum-North Atlantic region. Well-dated Greenland ice cores show that the cooling event lasted for 160 years [ Thomas et al ., 2007] and was accompanied by a sharp atmospheric CH
4 decrease, indicating that the event was probably at least hemispheric in its extent [ Kobashi et al ., 2007]. It is likely that the 8.2 ka event was related to a reduction of the Atlantic meridional overturning circulation (AMOC) by freshwater discharge from proglacial lakes Agassiz and Ojibway into the Labrador Sea [ von Grafenstein et al ., 1998; Barber et al ., 1999; Teller et al ., 2002; Ellison et al ., 2006; Kleiven et al ., 2008; Pratoreous et al ., 2008; Carlson et al ., 2009;
Hoffman et al ., 2012] and was associated with a total eustatic sea level rise of 0.8
– 2.2 m [ Li et al ., 2012;
Törnqvist and Hijma , 2012]. The freshwater discharge may have reduced northward heat transport by the
AMOC, causing a cooling in the circum-North Atlantic [ Alley et al ., 1997; Barber et al ., 1999]. Model studies indicate that freshwater discharge may have caused the abrupt cooling event [ LeGrande et al ., 2006; Wiersma and Renssen , 2006]. Compared to glacial conditions, climate boundary conditions of the 8.2 ka event (e.g., sea level and ice sheet extent) were not very different from modern ones, although hemispheric seasonality of orbital forcing was different and there still was a small ice sheet in North America [ Carlson et al ., 2008; Renssen et al ., 2009]. Thus, the 8.2 ka event provides an important target for testing climate-carbon cycle models for
AMOC disturbance and associated climate change under interglacial conditions.
Ice cores permit us to directly analyze CO
2 mixing ratios in ancient air with an analytical precision of ~1 ppm
[ Ahn et al ., 2009; Bereiter et al ., 2012]. Previous ice core studies did not directly address the CO
2 change at the
©2013. American Geophysical Union. All Rights Reserved.
AHN ET AL.
604

AHN ET AL.
Geophysical Research Letters 10.1002/2013GL058177
8.2 ka event, mostly because of the low sampling resolution of 100 – 200 years
[ Indermühle et al ., 1999; Flückiger et al .,
2002] and smoothing effects in the fi rn layer by diffusion and gradual bubble close-off [ Spahni et al ., 2003]. In addition, insuf fi cient chronological control has hampered exact comparison of atmospheric CO
2 change, which is normally measured in Antarctic ice cores, with the timing of the 8.2 ka event, which is expressed in Greenland ice cores.
Figure 1.
Atmospheric CO
2 from Siple Dome ice core for 9.0
–
7.3 ka.
(a) Greenlandic temperature proxy, δ 18
O ice from NGRIP ice core [ North
Greenland Ice Core Project members , 2004]. (b) Atmospheric CH
4 records obtained from GISP2, Greenlandic (blue), and Siple Dome, Antarctic (red), ice cores (this study). (c) Atmospheric CO
2 record from Siple Dome ice core,
Antarctica (this study). Yellow box indicates the timing of the 8.2 ka event.
Red triangles represent age tie points. To obtain the GICC05 time scale for
Siple Dome ice records, we adjusted the existing chronology [ Severinghaus et al ., 2009] for synchronization at the age tie points (red triangles).
As an alternative to ice core records, past CO
2 levels can be reconstructed from the density of stomata in fossil leaves [e.g., Beerling et al ., 1995; Wagner et al ., 2004]. A high-resolution stomatabased CO
2 record for the 8.2 ka event obtained from fossil leaves of European tree birches indicates a CO
2 decrease of up to ~25 ppm during 8.4
– 8.1 ka that was associated with the 8.2 ka event
[ Wagner et al ., 2002]. However, the mean sampling resolution of
~110 years and the mean uncertainty of CO
2 estimates of ±10 ppm suggest that this record should be cautiously interpreted, particularly given the relatively short span of the 8.2 ka event [ van Hoof et al ., 2005].
The fact that the estimated CO
2 concentration from the stomata record is higher than that from ice cores by
35
–
40 ppm is also a concern, given that such large interhemispheric gradients in the background preindustrial atmosphere are very unlikely [ IPCC , 2007].
To resolve centennial atmospheric CO
2 variability during the 8.2 ka event, we analyzed the Siple Dome ice core at a very high mean sampling resolution of 8 – 16 years. The modern Siple Dome site has a high snow accumulation rate of 12.4 cm we/yr (water equivalent/year) [ Brook et al ., 2005], higher than those of the Taylor Dome
(6.4 cm we/yr) and Dome C (2.5 cm we/yr) cores, which were previously used for Holocene CO
2 reconstructions
[ Indermühle et al ., 1999; Flückiger et al ., 2002]. The high snow accumulation rate results in a relatively small gas age distribution width [e.g., Schwander et al ., 1997; Buizert et al ., 2012] (Table S1 of the supporting information).
For these reasons, Siple Dome gas records have experienced only minimal smoothing by diffusion and gradual bubble close-off; the width of the age distribution is 42 years (full width at half maximum), compared to
~137 years at Dome C (Table S1 of the supporting information).
Details of the methods for CO
2 analysis are given by Ahn et al . [2009] and in the supporting information. We analyzed Siple Dome ice samples from 107 depth intervals that correspond to ages including the 8.2 ka event.
For most depth intervals, we analyzed two samples from a mean depth range of 7 cm (corresponding to
2.6 years), and we report the mean depths of the replicates (Figure 1). The CO
2 mixing ratios follow the NOAA
WMOX2007 CO
2 mole fraction scale.
The timing of the 8.2 ka event in our Siple Dome gas records is well constrained by comparison of our new Siple
Dome CH
4 record with the NGRIP (North Greenland Ice Core Project) ice core δ 18
O ice record, which is a proxy for
Greenlandic climate [ North Greenland Ice Core Project members , 2004] (Figure 1) because the abrupt cooling event in Greenland is essentially synchronous with a sharp CH
4 decrease within ±4 years [ Kobashi et al ., 2007].
The synchronized ages are on the GICC05 (Greenland Ice Core Chronology 2005) time scale, which is constructed by annual layer counting and has been widely used for paleoproxy data [ Rasmussen et al ., 2006; see also supporting information] (Figure 1). We also utilized a high-resolution CH
4 record from the GISP2 (Greenland
©2013. American Geophysical Union. All Rights Reserved.
605

AHN ET AL.
Geophysical Research Letters 10.1002/2013GL058177
Ice Sheet Project 2) ice core and correlated it with the Siple Dome record (Figure 1). We fi nd that the CH
4 change in the Siple Dome ice is similar to that of the GISP2 ice with an almost constant offset, supporting the contention that Siple Dome gas records are well preserved and have experienced only minimal fi rn smoothing. The offset in
CH
4 between the GISP2 and Siple Dome records is attributed to the interhemispheric CH
4 gradient caused by the predominance of Northern Hemisphere CH
4 sources [e.g., Etheridge et al ., 1998; Dlugokencky et al ., 2005].
Our new CO
2 record from the Siple Dome core covers 9.0
– 7.3 ka with sampling resolutions of 8 and 16 years for the 8.2 ka event and the other age intervals, respectively (Figure 1). Our new CH
4 during 9.0
– 7.3 ka. Therefore, the CO
2 records from the Siple Dome and GISP2 ice cores clearly de fi ne the timing of the 8.2 ka event, and we observe a slight increase of CO
2 of about 1 – 2 ppm (Gaussian fi lter, 1 σ = 10 – 40 years) during that event compared to the preceding century. We also observe atmospheric CO
2 background variability of 2
–
4 ppm on multidecadal to centennial time scales increase during the 8.2 ka event is similar to multidecadal to centennial
CO
2 variability observed in other parts of the record (Figure 1), which are not associated with large cooling. Our results are not consistent with the ~25 ppm decrease of CO
2 constructed from leaf stomata [ Wagner et al ., 2002].
Smoothing due to diffusion and gradual bubble close-off in the fi rn column is an important consideration when interpreting ice core gas records. At some sites, this process might be expected to remove an abrupt response at the 8.2 ka event. For example, the CH
4 drop at the 8.2 ka-cooling event is estimated to be attenuated by 34~59% in the European Project for Ice Coring in Antarctica Dome C (EDC) core [ Spahni et al .,
2003], a low-accumulation site (Table S1 of the supporting information). At sites like Siple Dome (Table S1 of the supporting information), the in fl uence of smoothing should be signi fi cantly less. In order to quantitatively estimate the smoothing effect in the Siple Dome CO
2 record, we modeled gas diffusion and bubble close-off in the fi rn layer (Figure S3 of the supporting information) to obtain gas age distributions (Figure S4 of the supporting information). We used a 1-D fi rn air transport model [ Buizert et al ., 2012], and details of the modeling are given in the supporting information. We applied the Siple Dome gas age distributions to imaginary square pulses of atmospheric CO
2 with various durations of 50, 100, and 200 years, which are comparable to the ~160 year duration of the 8.2 ka event (Figure 2). We fi nd that the magnitude of the pulse with duration of 50 years is decreased by ~25%, and pulses with durations of 100 and 200 years are recorded in the ice with their full magnitude (orange curves). In good agreement with earlier studies [ Spahni et al .,
2003], we fi nd that at EDC a 100 year event would be recorded in the ice with only half the true atmospheric magnitude (blue curves). This analysis con fi rms that, given our sampling resolution, any centennial scale CO
2 response to the 8.2 ka cooling event would be visible in our records with essentially unattenuated amplitude.
The sharp decrease of the Siple Dome CH
4
(Figure 1) con fi rms that the smoothing of gas records in the Siple
Dome ice is minimal on centennial time scales and supports our estimation of gas smoothing as discussed above. We also convolved the stomatal records from the work of Wagner et al . [2002] with the Siple Dome gas age distribution (Figure 3). If the stomatal CO
2 reconstruction represented the true atmospheric CO
2 variations, then the convolved record shows how it would be recorded in the ice core. We observe that the smoothing would not signi fi cantly change the magnitude of the putative CO
2 decrease at the 8.2 ka event derived from the stomatal data (Figure 3). The Antarctic ice cores and the stomatal records represent opposite hemispheres, yet the offset is too large to be attributed to the interhemispheric gradient, which is currently ~2.5 ppm and would have been smaller during the preanthropogenic period [ IPCC , 2007, p. 517].
Given the small difference among the three different ice core CO
2 records and our assessment of fi rn smoothing, we conclude that the elevated CO
2 levels and high amplitude variability in the stomatal CO
2 reconstruction [ Wagner et al ., 2002] do not represent variations in the background atmosphere and are more likely representative of other factors that impact stomatal density and/or very local variations in CO
2
.
The atmospheric CO
2 concentration changes through carbon exchanges with ocean and land. Many of the processes that control the carbon fl uxes are sensitive to temperature. Ice core records for the late Holocene show positive correlations between CO
2 and climate proxies from the Northern Hemisphere on centennial time scales [ MacFarling Meure et al ., 2006; Ahn et al ., 2012b] probably because carbon emissions from land
[ MacFarling Meure et al ., 2006; Gerber et al ., 2003] or from both land and oceans [ Ahn et al ., 2012b] are
©2013. American Geophysical Union. All Rights Reserved.
606

Geophysical Research Letters 10.1002/2013GL058177
300
250
200
150
100
50
0
−200 −100 0 100
Time (years)
200 300
Figure 2.
Illustration of the effect of smoothing in the fi rn on Siple
Dome ice core CO
2 record. Three gray lines indicate imaginary atmospheric CO
2 peak lasting (top) 200, (middle) 100, and (bottom)
50 years, respectively. Orange (blue) curves represent the effect of fi rn smoothing on Siple Dome (EDC) ice core record.
positively linked with surface temperatures.
An ensemble reconstruction by Frank et al .
[2010] fi nds a positive global carbon cycle sensitivity of 7.7 ppm (with a range of
1.7
– 21.4) CO
2 per °C for the late Holocene.
Although the average global temperature change at the 8.2 ka event is not well known, paleoclimatic data and model results indicate that the magnitude of cooling in the
Northern Hemisphere is greater than that of warming in the Southern Hemisphere
[ Wiersma and Renssen , 2006], and therefore, we might expect a small decrease in CO
2 associated with the event due to surface temperature forcing by reduced carbon emissions from land and increased dissolution of atmospheric CO
2 in ocean as we observe for the late Holocene [ MacFarling
Meure et al ., 2006; Ahn et al ., 2012b; Gerber et al ., 2003].
Previous studies for the last glacial and deglacial periods indicate that long Greenlandic stadials (cold periods) and associated major Antarctic warmings accompanied reductions in AMOC and CO
2 increases of up to
20~40 ppm on multimillennial time scales [ Monnin et al ., 2001; Ahn and Brook , 2008; Ahn et al ., 2012a; Bereiter et al ., 2012; Indermühle et al ., 2000; Marchitto et al ., 2007]. These CO
2 increases are often attributed to upwelling of CO
2
-rich deep water in the Southern Ocean [ Marchitto et al ., 2007; Anderson et al ., 2009]. The small increase of 1 – 2 ppm during the 8.2 ka event could perhaps be attributed to a weaker version of mechanism operating during the deglaciation and glacial period, where CO
2 rises during stadial periods. However, direct
AHN ET AL.
Figure 3.
Comparison of CO
2 records from leaf stomata and ice core records. (a) Atmospheric CH
4 from Siple Dome ice core, Antarctica (this study). The timing of the 8.2 ka event is indicated with the yellow box. The atmospheric CH
4 decrease is essentially synchronous with the abrupt cooling in Greenland at the 8.2 ka event [ Kobashi et al ., 2007]. (b)
Reconstructed atmospheric CO
2 indicate the mean CO
2 records from leaf stomata [ Wagner et al ., 2002]. Black solid line and dashed gray lines concentration and uncertainty range, respectively. The orange curve represents the stomata CO
2 record convolved with the gas age distribution of Siple Dome ice core. (c) Ice core CO
2
Taylor Dome and Dome C records (see Figure S3 of the supporting information).
records from Siple Dome (red, this study), Taylor Dome (green), and Dome C (brown), Antarctica. We added an interlaboratory offset of 1.5 ppm CO
2 on the
©2013. American Geophysical Union. All Rights Reserved.
607

Geophysical Research Letters 10.1002/2013GL058177 comparison is dif fi cult due to different durations of the cold events (millennial versus centennial) and different boundary conditions (glacial versus interglacial), and as we point out above, the 2 ppm fl uctuation does not appear to be anomalous with respect to times without large cooling.
Multiple model simulations for land and oceanic carbon during a reduced AMOC under late Holocene climate boundary conditions show that the terrestrial CO
2 creased CO
2 source overcompensates the oceanic sink, resulting in in-
[ Obata , 2007; Menviel et al ., 2008; Bozbiyik et al ., 2011]. However, another simulation indicates that terrestrial carbon processes could act as a sink [ Köhler et al ., 2005]. We also note that the change in atmospheric
CO
2 in the models depends on the shape (e.g., continual versus abrupt change) and amplitude of freshwater discharge. The magnitude and timing of the freshwater discharge fl ux associated with the 8.2 ka event is not well constrained [ Törnqvist and Hijma , 2012; Carlson and Clark , 2012]. However, estimates based on sea level rise at Louisiana [ Li et al ., 2012] and the Netherlands [ Hijma and Cohen , 2010] suggest that the magnitude was 0.09
–
0.25 sverdrup (Sv) (1 Sv = 10
6 m
3 s
1
) for 100 years and 0.06
– 0.15 Sv for 300 years, respectively [ Törnqvist and
Hijma , 2012; Carlson and Clark , 2012], comparable to the fl ux ranges in the modeling of Köhler et al . [2005] and
Bozbiyik et al . [2011] that did not impact atmospheric CO
2 for 100 – 200 years. Thus, the weak and/or gradual freshwater discharge might have not been suf fi cient to change atmospheric CO
2 during the 8.2 ka event.
Understanding the response of the global carbon cycle to climate change is important for predictions of future warming. Our results provide a target for climate-carbon cycle models with a new important constraint on Holocene climate-carbon cycle feedbacks during abrupt climate change associated with ocean circulation changes as might be expected in the future associated with a weakened AMOC [ IPCC , 2007].
Acknowledgments
We thank Michael Kalk, James Lee, and
Logan Mitchell for analytical assistance and the staff of the National Ice Core
Lab for ice sampling and curation. We also thank Andreas Schmittner for helpful discussions. Financial support was provided by National Science
Foundation grant OPP 0944764-ANT to
E.B. and the NOAA Climate and Global
Change Fellowship Program to C.B., administered by the University
Corporation for Atmospheric Research.
This work was also supported by Basic
Science Research Program through the
National Research Foundation of Korea, funded by the Ministry of Education,
Science and Technology (2011-
0025242), and Korea Meteorological
Administration Research and
Development Program under grant
CATER 2012-7030 to J.A.
The Editor thanks Andrei Demekhov and an anonymous reviewer for their assistance in evaluating this paper.
AHN ET AL.
Ahn, J., and E. J. Brook (2007), Atmospheric CO
2
Ahn, J., and E. J. Brook (2008), Atmospheric CO
2 and climate from 65 to 30 ka B.P, Geophys. Res. Lett.
, 34 , L10703, doi:10.1029/2007GL029551.
and climate on millennial time scales during the last glacial period, Science , 322 , 83
–
85.
Ahn, J., M. Wahlen, B. L. Deck, E. J. Brook, P. A. Mayewski, K. C. Taylor, and J. W. C. White (2004), A record of atmospheric CO
2 during the last
40,000 years from the Siple Dome, Antarctica ice core, J. Geophys. Res.
, 109 , D13305, doi:10.1029/2003JD004415.
Ahn, J., E. J. Brook, and K. Howell (2009), A high-precision method for measurement of paleoatmospheric CO
2
J. Glaciol.
, 55 , 499
–
506.
Ahn, J., E. J. Brook, A. Schmittner, and K. Kreutz (2012a), Abrupt change in atmospheric CO
L18711, doi:10.1029/2012GL053018.
2 in small polar ice samples, during the last ice age, Geophys. Res. Lett.
, 39 ,
Ahn, J., E. J. Brook, L. Mitchell, J. Rosen, J. R. McConnell, K. Taylor, D. Etheridge, and M. Rubino (2012b), Atmospheric CO
2 over the last 1000 years: A high-resolution record from the West Antarctic Ice Sheet (WAIS) Divide ice core, Global Biogeochem. Cycles , 26 , GB2027, doi:10.1029/2011GB004247.
Alley, R. B., and A. M. Agustdottir (2005), The 8k event: Cause and consequences of a major Holocene abrupt climate change, Quat. Sci. Rev.
,
24 , 1123 – 1149.
Alley, R. B., P. A. Mayewski, T. Sowers, M. Stuiver, K. C. Taylor, and P. U. Clark (1997), Holocene climatic instability: A prominent, widespread event 8200 years ago, Geology , 25 , 483 – 486.
Anderson, R. F., S. Ali, L. I. Bradtmiller, S. H. H. H. Nielsen, M. Q. Fleisher, B. E. Anderson, and L. H. Burckle (2009), Wind-driven upwelling in the
Southern Ocean and the deglacial rise in atmospheric CO
2
, Science , 323 , 1443 – 1448.
Barber, D. C., et al. (1999), Forcing of the cold event of 8,200 years ago by catastrophic drainage of Laurentide lakes, Nature , 400 , 344
–
348.
Beerling, D. J., H. H. Birks, and F. I. Woodward (1995), Rapid late-glacial atmospheric CO
2 record of fossil leaves, J. Quat. Sci.
, 10 , 379
–
384.
changes reconstructed from the stomatal density
Bereiter, B., D. Lüthi, M. Siegrist, S. Schüpbach, T. F. Stocker, and H. Fischer (2012), Mode change of millennial CO
2 glacial cycle associated with a bipolar marine carbon seesaw, Proc. Natl. Acad. Sci. U.S.A.
, 109 , 9755
–
9760.
variability during the last
Bozbiyik, A., M. Steinacher, F. Joos, T. F. Stocker, and L. Menviel (2011), Fingerprints of changes in the terrestrial carbon cycle in response to large reorganizations in ocean circulation, Clim. Past , 7 , 319
–
338.
Brook, E. J., J. W. C. White, A. S. M. Schill, M. L. Bender, B. Barnett, J. P. Severinghaus, K. C. Taylor, R. B. Alley, and E. J. Steig (2005), Timing of millennial-scale climate change at Siple Dome, West Antarctica, during the last glacial period, Quat. Sci. Rev.
, 24 , 1333
–
1343.
Buizert, C., et al. (2012), Gas transport in fi rn: Multiple-tracer characterization and model intercomparison for NEEM, Northern Greenland,
Atmos. Chem. Phys.
, 12 , 4259
–
4277.
Carlson, A. E., and P. U. Clark (2012), Ice sheet sources of sea level rise and freshwater discharge during the last deglaciation, Rev. Geophys.
, 50 ,
RG4007, doi:10.1029/2011RG000371.
Carlson, A. E., A. N. Legrande, D. W. Oppo, R. E. Came, G. A. Schmidt, F. S. Anslow, J. M. Licciardi, and E. A. Obbink (2008), Rapid early Holocene deglaciation of the Laurentide ice sheet, Nat. Geosci.
, 1 , 620
–
624.
Carlson, A. E., P. U. Clark, B. A. Haley, and G. P. Klinkhammer (2009), Routing of western Canadian Plains runoff during the 8.2 ka cold event,
Geophys. Res. Lett.
, 36 , L14704, doi:10.1029/2009GL038778.
Dlugokencky, E. J., R. C. Myers, P. M. Lang, K. A. Masarie, A. M. Crotwell, K. W. Thoning, B. D. Hall, J. W. Elkins, and L. P. Steele (2005), Conversion of NOAA atmospheric dry air CH
4
2005JD006035.
mole fraction to a gravimetrically prepared standard scale, J. Geophys. Res.
, 110 , D18306, doi:10.1029/
Ellison, C. R. W., M. R. Chapman, and I. R. Hall (2006), Surface and deep ocean interactions during the cold climate event 8200 years ago,
Science , 312 , 1929 – 1932.
Etheridge, D. M., L. P. Steele, R. J. Francey, and R. L. Langenfelds (1998), Atmospheric methane between 1000 A.D. and present: Evidence of anthropogenic emissions and climatic variability, J. Geophys. Res.
, 103 , 15,979 – 15,993.
©2013. American Geophysical Union. All Rights Reserved.
608

AHN ET AL.
Geophysical Research Letters 10.1002/2013GL058177
Flückiger, J., E. Monnin, B. Stauffer, J. Schwander, and T. F. Stocker (2002), High-resolution Holocene N
2
O ice core record and its relationship with CH
4 and CO
2
, Global Biogeochem. Cycles , 16 (1), 1010, doi:10.1029/2001GB001417.
Frank, D. C., J. Esper, C. C. Raible, U. Büntgen, V. Trouet, B. Stocker, and F. Joos (2010), Ensemble reconstruction constraints on the global carbon cycle sensitivity to climate, Nature , 463 , 527
–
530.
Friedlingstein, P., et al. (2006), Climate-carbon cycle feedback analysis: Results from the C4MIP model intercomparison, J. Clim.
, 19 ,
3337
–
3353.
Gerber, S., F. Joos, P. Brügger, T. F. Stocker, M. E. Mann, S. Sitch, and M. Scholze (2003), Constraining temperature variations over the last millennium by comparing simulated and observed atmospheric CO
2
, Clim. Dyn.
, 20 , 281
–
299.
Hijma, M. P., and K. M. Cohen (2010), Timing and magnitude of the sea-level jump precluding the 8200 yr event, Geology , 38 , 275 – 278.
Hoffman, J. S., A. E. Carlson, K. Winsor, G. P. Klinkhammer, A. N. LeGrande, J. T. Andrews, and J. C. Strasser (2012), Linking the 8.2 ka event and its freshwater forcing in the Labrador Sea, Geophys. Res. Lett.
, 39 , L18703, doi:10.1029/2012GL053047.
Indermühle, A., et al. (1999), Holocene carbon-cycle dynamics based on CO
2 trapped in ice at Taylor Dome Antarctica, Nature , 398 , 121
–
126.
Indermühle, A., E. Monnin, B. Stauffer, T. F. Stocker, and M. Wahlen (2000), Atmospheric CO
2
Taylor Dome ice core, Antarctica, Geophys. Res. Lett.
, 27 , 735
–
738.
concentration from 60 to 20 kyr BP from the
IPCC (2007), Climate Change: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the
Intergovernmental Panel on Climate Change , edited by S. Solomon et al., Cambridge Univ. Press, New York.
Kleiven, H. F., C. Kissel, C. Laj, U. S. Ninnemann, T. O. Richter, and E. Cortijo (2008), Reduced North Atlantic Deep Water coeval with the glacial lake Agassiz freshwater outburst, Science , 319 , 60
–
64.
Kobashi, T., J. P. Severinghaus, E. J. Brook, J.-M. Barnola, and A. M. Grachev (2007), Precise timing and characterization of abrupt climate change 8200 years ago from air trapped in polar ice, Quat. Sci. Rev.
, 26 , 1212
–
1222.
Köhler, P., F. Joos, S. Gerber, and R. Knutti (2005), Simulated changes in vegetation distribution, land carbon storage, and atmospheric CO
2 response to a collapse of the North Atlantic thermohaline circulation, Clim. Dyn.
, 25 , 689
–
708.
in
LeGrande, A. N., G. A. Schmidt, D. T. Shindell, C. V. Field, R. L. Miller, D. M. Koch, G. Faluvegi, and G. Hoffmann (2006), Consistant simulations of multiple proxy responses to an abrupt climate change event, Proc. Natl. Acad. Sci. U.S.A.
, 103 , 837
–
842.
Li, Y.-X., T. E. Törnqvist, J. M. Nevitt, and B. Kohl (2012), Synchronizing a sea-level jump, fi nal Lake Agassiz drainage, and abrupt cooling 8200 years ago, Earth Planet. Sci. Lett.
, 315-316 , 41
–
50.
MacFarling Meure, C., D. Etheridge, C. Trudinger, P. Steele, R. Langenfelds, T. van Ommen, A. Smith, and J. Elkins (2006), Law Dome CO
2
, CH
4 and N
2
O ice core records extended to 2000 years BP, Geophys. Res. Lett.
, 33 , L14810, doi:10.1029/2006GL026152.
Marchitto, T. M., J. L. Scott, J. D. Ortiz, J. Flückiger, and A. van Geen (2007), Marine radiocarbon evidence for the mechanism of deglacial atmospheric CO
2 rise, Science , 316 , 1456
–
1459.
Menviel, L., A. Timmermann, M. Mouchet, and O. Timm (2008), Meridional reorganizations of marine and terrestrial productivity during
Heinrich events, Paleoceanography , 23 , PA1203, doi:10.1029/2007PA001445.
Monnin, E., A. Indermühle, A. Dällenbach, J. Flückiger, B. Stauffer, T. F. Stocker, D. Raynaud, and J.-M. Barnola (2001), Atmospheric CO
2 concentrations over the last glacial termination, Science , 291 , 112
–
114.
North Greenland Ice Core Project members (2004), High-resolution record of northern hemisphere climate extending into the last interglacial period, Nature , 431 , 147
–
151.
Obata, A. (2007), Climate-carbon cycle model response to freshwater discharge into the North Atlantic, J. Clim.
, 20 , 5962 – 5976.
Pratoreous, S. K., J. F. McManus, D. W. Oppo, and W. B. Curry (2008), Episodic reductions in bottom-water currents since the last ice age, Nat.
Geosci.
, 1 , 449 – 452.
Rasmussen, S. O., et al. (2006), A new Greenland ice core chronology for the last glacial termination, J. Geophys. Res.
, 111 , D06102, doi:10.1029/2005JD006079.
Renssen, H., H. Seppä, O. Heiri, D. M. Roche, H. Goosse, and T. Fichefet (2009), The spatial and temporal complexity of the Holocene thermal maximum, Nat. Geosci.
, 2 , 411 – 414.
Rohling, E. J., and H. Paelike (2005), Centennial-scale climate cooling with a sudden cold event around 8,200 years ago, Nature , 434 , 975
–
979.
Schmitt, J., et al. (2012), Carbon isotope constraints on the deglacial CO
2 rise from ice cores, Science , 336 , 711 – 714.
Schwander, J., T. Sowers, J.-M. Barnola, T. Blunier, A. Fuchs, and B. Malaizé (1997), Age scale of the air in the summit ice: Implication for glacialinterglacial temperature change, J. Geophys. Res.
, 102 , 19,483 – 19,493.
Severinghaus, J. P., R. Beaudette, M. A. Headly, K. Taylor, and E. J. Brook (2009), Oxygen-18 of O
2 on the terrestrial biosphere, Science , 324 , 1431 – 1434.
records the impact of abrupt climate change
Spahni, R., J. Schwander, J. Flückiger, B. Stauffer, J. Chappellaz, and D. Raynaud (2003), The attenuation of fast atmospheric CH
4 recorded in polar ice cores, Geophys. Res. Lett.
, 30 (11), 1571, doi:10.1029/2003GL017093.
variations
Teller, J. T., D. W. Leverington, and J. D. Mann (2002), Freshwater outbursts to the oceans from glacial Lake Agassiz and their role in climate change during the last deglaciation, Quat. Sci. Rev.
, 21 , 879 – 887.
Thomas, E. R., E. W. Wolff, R. Mulvaney, J. P. Steffensen, S. J. Johnsen, C. Arrowsmith, J. W. C. White, B. Vaughn, and T. Popp (2007), The 8.2 ka event from Greenland ice cores, Quat. Sci. Rev.
, 26 , 70 – 81.
Törnqvist, T. E., and M. P. Hijma (2012), Links between early Holocene ice-sheet decay, sea-level rise and abrupt climate change, Nat. Geosci.
,
5 , 601 – 606.
van Hoof, T. B., K. A. Kaspers, F. Wagner, R. S. W. van de Wal, W. M. Kürschner, and H. Visscher (2005), Atmospheric CO
2 during the 13 century AD: reconciliation of data from ice core measurements and stomatal frequency analysis, Tellus, Ser. B , 57 , 351 – 355.
th von Grafenstein, U., H. Erlenkeuser, J. Muller, J. Jouzel, and S. Johnson (1998), The cold event 8200 years ago documented in oxygen isotope records of precipitation in Europe and Greenland, Clim. Dyn.
, 14 , 73 – 81.
Wagner, F., B. Aaby, and H. Visscher (2002), Rapid atmospheric CO
2
Acad. Sci. U.S.A.
, 99 , 12,011 – 12,014.
changes associated with the 8,200-years-B.P. cooling event, Proc. Natl.
Wagner, F., L. L. R. Kouwenberg, T. B. van Hoof, and H. Visscher (2004), Reproducibility of Holocene atmospheric CO
2 records based on stomatal frequency, Quat. Sci. Rev.
, 23 , 1947 – 1954.
Wiersma, A. P., and H. Renssen (2006), Model-data comparison for the 8.2 ka BP event: con fi rmation of a forcing mechanism by catastrophic drainage of Laurentide Lakes, Quat. Sci. Rev.
, 25 , 63 – 88.
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