High-resolution Holocene N2O ice core record and its relationship with CH4 and CO2

Fig. 2 Dome C long term trends of CO2, CH4, and N2O High-resolution Holocene N2O ice core record and its relationship with CH4 and CO2
Global Biogeochemical Cycles, Vol. 16, No. 1, March 2002.

Jacqueline Flückiger, Eric Monnin, Bernhard Stauffer, Jakob Schwander, Thomas F. Stocker
Climate and Environmental Physics, Physics Institute,
University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland


Jérôme Chappellaz, Dominique Raynaud, Jean-Marc Barnola
CNRS Laboratoire de Glaciologie et de Géophysique
de l'Environnement, Grenoble, France

ABSTRACT:
Nitrous oxide (N2O ) concentration records exist for the last 1000 years and for time periods of rapid climatic changes like the transition from the last glacial to today's interglacial and for one of the fast climate variations during the last ice age. Little is known, however, about possible N2O variations during the more stable climate of the present interglacial (Holocene) spanning the last 11 thousand years. Here we fill this gap with a high resolution N2O record measured along the EPICA Dome C Antarctic ice core. On the same ice we obtained high resolution methane and carbon dioxide records. This provides the unique opportunity to compare variations of the three most important greenhouse gases (after water vapour) without any uncertainty in their relative timing. The CO2 and CH4 records are in good agreement with previous measurements on other ice cores. The N2O concentration started to decrease in the early Holocene and reached minimum values around 8 kyr BP. (less than 260 ppbv) before a slow increase to its preindustrial concentration of about 265 ppbv.

DATA:
Download the EPICA Dome C N2O, CO2, and CH4 data and data description from the WDC Paleo Archive.

Fig. 1 Dome C CO2 , CH4, N2O, and deuterium for the Holocene. Fig. 1.
Dome C CO2 (yellow triangles), CH4 (blue diamonds), N2O (red circles) and deuterium (top trace) [Jouzel et al., 2001] records for the Holocene time period. The CO2, N2O and, CH4 measurements are plotted together with their analytical reproducibility (1s). Smoothed splines were calculated according to Enting [1987] with cut off periods of 3000 yr for CO2, 3000 yr (solid line) and 1500 yr (dashed line) for N2O and 1500 yr for CH4, highlighting long-term trends of the three greenhouse gases. For CO2 and N2O it is believed that the splines with cut off periods of 3000 yr represent the long time trends of the atmospheric concentration. The CH4 spline was calculated with a smaller cut off period (1500 yr) due to a much shorter lifetime of CH4 compared to CO2 and N2O. N2O variations as indicated by the spline with a cut off period of 1500 yr are at the limit of significance given the analytical uncertainty of the data. The time scale for the ice and the enclosed air (which is younger than the surrounding ice because it is enclosed at the bottom of the firn layer) in years before 1950, is based on the time scale by Schwander et al. [2001]. The uncertainty of the absolute time scale for the ice is estimated to ±200 yr. The gas-ice age difference is about 2000 yr with an estimated uncertainty of about 10%. As all three gas records were measured on the air bubbles of the same core, there is no uncertainty in the relative timing of the gas records.
Fig. 2 Dome C long term trends of CO2, CH4, and N2O
Fig. 2.
Comparison of the Dome C long term trends of CO2 (top trace, yellow line), CH4 (middle trace, blue line), and N2O (bottom trace, red line) from Fig. 1 with previously published CO2 and CH4 data and published source distribution calculations for CH4. The disagreement between the CO2 data measured along the Taylor Dome ice core, Antarctica (black diamonds, plotted on the original Taylor Dome time scale) [Indermühle et al., 1999] and the Dome C CO2 trend in the time period 4 to 8 kyr BP can probably be attributed to differences in the time scales of the two ice cores [Stauffer et al., submitted, 2001]. For CH4 the Dome C trend agrees well with CH4 results from the Antarctic ice cores D47 (black triangles) and Byrd (black circles), as well as with results from the GRIP ice core, Greenland (grey circles) when taking the interpolar difference into account [Chappellaz et al., 1997]. However, the used timescales are not synchronized. The GRIP, D47, and Byrd results are shown on a synchronized GRIP time scale [Chappellaz et al., 1997; Schwander et al., 1997], while the Dome C data are plotted on the original Dome C time scale [Schwander et al., 2001]. Additionally to the long term trends of CO2, CH4 and N2O, previously published source distribution calculations deduced from the interpolar gradient of CH4 are shown for the periods 2.5-5 kyr BP, 5-7 kyr BP, and 9.5-11.5 kyr BP [Chappellaz et al., 1997]. Black bars represent the tropical source (30°S to 30°N), grey bars the source of the mid to high northern latitudes (30°N to 90°N). The source of the mid to high southern latitudes (30°S to 90°S) was assumed to be constant over the Holocene time period (15 Tgyr-1) and is, therefore, not shown in the figure. Comparison of the long term trends of CH4 and N2O to the CH4 source distributions for the above mentioned time periods show that CH4 was mainly controlled by drying of the tropics while N2O seems more related to the mid to high northern latitudes. Not shown are the source distribution calculations for the time period 0.25-1 kyr BP because tentative results deduced from the gradient between the Dome C and the GRIP CH4 measurements indicate a different source distribution than found by Chappellaz et al. [1997].
Fig. 3 Dome C N2O data compared to non-sea-salt calcium (nss-Ca2+) and nitrate (NO3-)
Fig. 3.
Dome C N2O data compared to non-sea-salt calcium (nss-Ca2+) and nitrate (NO3-) measured along the same core for two depth interval of rapid shifts in the N2O concentration. The two depth intervals 165 to 210 m (a) and 355 to 400 m (b), centered around 3 and 10 kyr BP, respectively, on the gas age scale are marked as grey shaded areas in the N2O overview (c). nss-Ca2+ is shown in (a) and (b) as 2 cm mean (middle trace, grey line) and 55 cm mean (middle trace, green line). NO3- was only measured in the deeper interval (b) and is plotted as 10 cm mean (top trace, grey line) and 55 cm mean (top trace, blue line). The N2O results (red circles) are complemented by the mean values over the corresponding depth interval (grey dashed line). Neither non-sea-salt calcium (nss-Ca2+) nor NO3- show an abrupt shift in the same depth interval as the N2O record. It is, therefore, unlikely that the shifts in the N2O record are due to an artefact produced by chemical compounds.

To read or view the full study, please visit the AGU website.
It was published in Global Biogeochemical Cycles, Vol. 16, No. 1, March 2002.


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29 April 2002