scholarly journals Atmospheric trends of the halon gases from polar firn air

2005 ◽  
Vol 5 (1) ◽  
pp. 937-960 ◽  
Author(s):  
C. E. Reeves ◽  
W. T. Sturges ◽  
G. A. Sturrock ◽  
K. Preston ◽  
D. E. Oram ◽  
...  
Keyword(s):  
Ice Core ◽  
Atmospheric Model ◽  
Polar Regions ◽  
Emission Rates ◽  
Depth Profiles ◽  
Devon Island ◽  
The North ◽  
Global Emission ◽  
Core Project ◽  
Atmospheric Concentrations

Abstract. Four halons (H-1301, H-1211, H-2402 and H-1202) have been measured in air samples collected from polar firn from Dome Concordia (Dome C), Antarctica, from Devon Island, Canada and the North Greenland Ice Core Project (NGRIP) site, Greenland. H-2402 and H-1202 are reported for the first time in firn air. The depth profiles show the concentrations of all four halons to be zero at the base of the firn thus demonstrating their entirely anthropogenic origin. This is the first evidence of this for H-2402 and H-1202. A 2-D atmospheric model was run to produce historical trends in the atmospheric concentrations at the firn sites, which were then input into a firn diffusion model to produce concentration depth profiles for comparison with the measurements. The firn measurements provide constraints on the atmospheric concentrations in both hemispheres which allow the global emission rates and their latitudinal distribution in the atmospheric model to be evaluated. Global emission trends previously determined from measurements at Cape Grim are found to be consistent with the firn data. Further emissions of H-1202 in recent years (late 1980s onwards) are likely to have come from latitudes mostly south of 40° N, but emissions prior to that may have come from further north. Emissions of H-1211 may also have shifted to latitudes south of 40° N during the late 1980s. The firn data is used to derive atmospheric trends in total organic bromine in the form of halons for both polar regions.

scholarly journals Trends of halon gases in polar firn air: implications for their emission distributions

2005 ◽  
Vol 5 (8) ◽  
pp. 2055-2064 ◽  
Author(s):  
C. E. Reeves ◽  
W. T. Sturges ◽  
G. A. Sturrock ◽  
K. Preston ◽  
D. E. Oram ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Ice Core ◽  
Atmospheric Model ◽  
Polar Regions ◽  
Emission Rates ◽  
Atmospheric Concentration ◽  
Depth Profiles ◽  
Devon Island ◽  
The North ◽  
Indirect Evaluation

Abstract. Four halons (H-1301, H-1211, H-2402 and H-1202) have been measured in air samples collected from polar firn from Dome Concordia (Dome C), Antarctica, from Devon Island, Canada and the North Greenland Ice Core Project (NGRIP) site, Greenland. H-2402 and H-1202 are reported for the first time in firn air. The depth profiles show the concentrations of all four halons to be close to zero (i.e. below the detection limit of 0.001 ppt) at the base of the firn thus demonstrating their entirely anthropogenic origin. This is the first evidence of this for H-2402 and H-1202. A 2-D atmospheric model was run with emissions previously derived using archive air measurements from the southern hemisphere mid-latitudes to produce historical trends in atmospheric concentrations at the firn sites, which were then input into a firn diffusion model to produce concentration depth profiles for comparison with the firn measurements. This comparison provides an evaluation of the model-derived atmospheric concentration histories in both hemispheres and thus an indirect evaluation of the emission rates and distributions used in the atmospheric model. Atmospheric concentration trends produced using global emissions previously determined from measurements at Cape Grim are found to be consistent with the firn data from the southern hemisphere. Further emissions of H-1202 in recent years (late 1980s onwards) are likely to have come from latitudes mostly south of 40° N, but emissions prior to that may have come from further north. Emissions of H-1211 may also have shifted to latitudes south of 40° N during the late 1980s. Following comparison of the atmospheric model output with the firn data, modelled atmospheric trends of total organic bromine in the form of halons were derived for both polar regions.

scholarly journals The Recurrence Time of Dansgaard–Oeschger Events and Limits on the Possible Periodic Component

2005 ◽  
Vol 18 (14) ◽  
pp. 2594-2603 ◽  
Author(s):  
Peter D. Ditlevsen ◽  
Mikkel S. Kristensen ◽  
Katrine K. Andersen
Keyword(s):  
Waiting Times ◽  
Ice Core ◽  
Ice Cores ◽  
Recurrence Time ◽  
Objective Criterion ◽  
Climate Signal ◽  
The North ◽  
Climate Shifts ◽  
Isotopic Records ◽  
Core Project

Abstract By comparing the high-resolution isotopic records from the Greenland Ice Core Project (GRIP) and the North Greenland Ice Core Project (NGRIP) ice cores, the common climate signal in the records has been approximately separated from local noise. From this, an objective criterion for defining Dansgaard–Oeschger (DO) events is achieved. The analysis identifies several additional short-lasting events, increasing the total number of DO events to 27 in the period 12–90 kyr before present (BP). The quasi-regular occurrence of the DO events could indicate a stochastic or coherent resonance mechanism governing their origin. From the distribution of waiting times, a statistical upper bound on the strength of a possible periodic forcing is obtained. This finding indicates that the climate shifts are purely noise driven with no underlying periodicity.

scholarly journals The impact of ice layers on gas transport through firn at the North Greenland Eemian Ice Drilling (NEEM) site, Greenland

2014 ◽  
Vol 8 (5) ◽  
pp. 1801-1806 ◽  
Author(s):  
K. Keegan ◽  
M. R. Albert ◽  
I. Baker
Keyword(s):  
Gas Transport ◽  
Ice Core ◽  
Polar Regions ◽  
Air Concentration ◽  
Transport Models ◽  
Transport Dynamics ◽  
The North ◽  
Transition Depth ◽  
The Impact ◽  
North Greenland

Abstract. Typically, gas transport through firn is modeled in the context of an idealized firn column. However, in natural firn, imperfections are present, which can alter transport dynamics and therefore reduce the accuracy of reconstructed climate records. For example, ice layers have been found in several firn cores collected in the polar regions. Here, we examined the effects of two ice layers found in a NEEM, Greenland firn core on gas transport through the firn. These ice layers were found to have permeability values of 3.0 and 4.0 × 10−10 m2, and are therefore not impermeable layers. However, the shallower ice layer was found to be significantly less permeable than the surrounding firn, and can therefore retard gas transport. Large closed bubbles were found in the deeper ice layer, which will have an altered gas composition than that expected because they were closed near the surface after the water phase was present. The bubbles in this layer represent 12% of the expected closed porosity of this firn layer after the firn-ice transition depth is reached, and will therefore bias the future ice core gas record. The permeability and thickness of the ice layers at the North Greenland Eemian Ice Drilling (NEEM) site suggest that they do not disrupt the firn-air concentration profiles and that they do not need to be accounted for in gas transport models at NEEM.

scholarly journals Bayesian analysis of rapid climate change during the last glacial using Greenland δ<sup>18</sup>O data

2010 ◽  
Vol 6 (6) ◽  
pp. 787-794 ◽  
Author(s):  
D. Peavoy ◽  
C. Franzke
Keyword(s):  
Latent Variable ◽  
Model Comparison ◽  
Ice Core ◽  
Greenland Ice Sheet ◽  
Variable Model ◽  
Last Glacial ◽  
The North ◽  
Bayesian Model Comparison ◽  
Core Project ◽  
The Last Glacial

Abstract. We present statistical methods to determine climate regimes for the last glacial period using three temperature proxy records from Greenland: measurements of δ18O from the Greenland Ice Sheet Project 2 (GISP2), the Greenland Ice Core Project (GRIP) and the North Greenland Ice Core Project (NGRIP) using different timescales. A Markov Chain Monte Carlo method is presented to infer the number of states in a latent variable model along with their associated parameters. By using Bayesian model comparison methods we find that a model with 3 states is sufficient. These states correspond to a gradual cooling during the Greenland Interstadials, more rapid temperature decrease into Greenland Stadial and to the sudden rebound temperature increase at the onset of Greenland Interstadials. We investigate the recurrence properties of the onset of Greenland Interstadials and find no evidence to reject the null hypothesis of randomly timed events.

scholarly journals Anatomy of a Dansgaard‐Oeschger warming transition: High‐resolution analysis of the North Greenland Ice Core Project ice core

2009 ◽  
Vol 114 (D8) ◽  
Author(s):  
Elizabeth R. Thomas ◽  
Eric W. Wolff ◽  
Robert Mulvaney ◽  
Sigfus J. Johnsen ◽  
Jorgen P. Steffensen ◽  
...  
Keyword(s):  
High Resolution ◽  
Ice Core ◽  
The North ◽  
High Resolution Analysis ◽  
Resolution Analysis ◽  
Core Project ◽  
North Greenland

scholarly journals Tree ring effects and ice core acidities clarify the volcanic record of the 1st millennium

2014 ◽  
Vol 10 (2) ◽  
pp. 1799-1820
Author(s):  
M. G. L. Baillie ◽  
J. McAneney
Keyword(s):  
Tree Ring ◽  
Ice Core ◽  
Ice Cores ◽  
Volcanic Eruptions ◽  
Environmental Response ◽  
West Antarctic Ice Sheet ◽  
The North ◽  
West Antarctic ◽  
Core Project ◽  
The Antarctic

Abstract. Various attempts have been made to link tree-ring and ice-core records, something vital for the understanding of the environmental response to major volcanic eruptions in the past. Here we demonstrate that, by taking note of the spacing between events, it is possible to clarify linkages between tree-response, as witnessed by frost rings in bristlecone pines from Western North America and volcanic acid deposition in ice cores. The results demonstrate that in the 6th and 7th centuries of the current era, and presumably for all earlier dates, the key European ice chronologies from the North Greenland Ice Core Project, namely Dye3, GRIP, NGRIP and NEEM appear to have been wrongly dated by 7 years, with the ice dates being too old. Similar offsets are observed for the Antarctic Law Dome and West Antarctic Ice Sheet Divide WDC06A ice-core chronologies that have been linked to the Greenland record. Importantly, the results clarify which frost rings in bristlecone pines are related to volcanic activity and which may be the result of other causes. In addition, it is possible to show that ice core researchers have used inappropriate linkages to tree effects to justify their chronology.

scholarly journals 20th century trends and budget implications of chloroform and related tri-and dihalomethanes inferred from firn air

2006 ◽  
Vol 6 (10) ◽  
pp. 2847-2863 ◽  
Author(s):  
D. R. Worton ◽  
W. T. Sturges ◽  
J. Schwander ◽  
R. Mulvaney ◽  
J.-M. Barnola ◽  
...  
Keyword(s):  
20Th Century ◽  
Atmospheric Model ◽  
Model Fit ◽  
Anthropogenic Sources ◽  
Anthropogenic Emissions ◽  
Natural Origin ◽  
Devon Island ◽  
The North ◽  
Dronning Maud Land ◽  
Concentration Depth Profiles

Abstract. Four trihalomethane (THM; CHCl3, CHBrCl2, CHBr2Cl and CHBr3) and two dihalomethane (DHM; CH2BrCl and CH2Br2) trace gases have been measured in air extracted from polar firn collected at the North Greenland Icecore Project (NGRIP) site. CHCl3 was also measured in firn air from Devon Island (DI), Canada, Dronning Maud Land (DML), Antarctica and Dome Concordia (Dome C), Antarctica. All of these species are believed to be almost entirely of natural origin except for CHCl3 where anthropogenic sources have been reported to contribute ~10% to the global burden. A 2-D atmospheric model was run for CHCl3 using reported emission estimates to produce historical atmospheric trends at the firn sites, which were then input into a firn diffusion model to produce concentration depth profiles that were compared against the measurements. The anthropogenic emissions were modified in order to give the best model fit to the firn data at NGRIP, Dome C and DML. As a result, the contribution of CHCl3 from anthropogenic sources, mainly from pulp and paper manufacture, to the total chloroform budget appears to have been considerably underestimated and was likely to have been close to ~50% at the maximum in atmospheric CHCl3 concentrations around 1990, declining to ~29% at the beginning of the 21st century. We also show that the atmospheric burden of the brominated THM's in the Northern Hemisphere have increased over the 20th century while CH2Br2 has remained constant over time implying that it is entirely of natural origin.

scholarly journals Objective identification of climate states from Greenland ice cores for the last glacial period

2010 ◽  
Vol 6 (3) ◽  
pp. 1209-1227 ◽  
Author(s):  
D. J. Peavoy ◽  
C. Franzke
Keyword(s):  
Ice Core ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Cores ◽  
Glacial Period ◽  
Last Glacial Period ◽  
Last Glacial ◽  
The North ◽  
Core Project ◽  
The Last Glacial

Abstract. We present statistical methods to systematically determine climate regimes for the last glacial period using three temperature proxy records from Greenland: measurements of δ18O from the Greenland Ice Sheet Project 2 (GISP2), the Greenland Ice Core Project (GRIP) and the North Greenland Ice Core Project (NGRIP). By using Bayesian model comparison methods we find that, in two out of three data sets, a model with 3 states is very strongly supported. We interpret these states as corresponding to: a gradual cooling regime due to iceberg influx in the North Atlantic, sudden temperature decrease due to increased freshwater influx following ice sheet collapse and to the Dansgaard-Oeschger events associated with sudden rebound temperature increase after the thermohaline circulation recovers its full flux. We find that these models are far superior to those that differentiate between states based on absolute temperature differences only, which questions the appropriateness of defining stadial and interstadial climate states. We investigate the recurrence properties of these climate regimes and find that the only significant periodicity is within the Greenland Ice Sheet Project 2 data at 1450 years in agreement with previous studies.

scholarly journals 20th Century trends and budget implications of trihalomethanes and dihalomethanes inferred from North GRIP firn air

2006 ◽  
Vol 6 (1) ◽  
pp. 701-754
Author(s):  
D. R. Worton ◽  
W. T. Sturges ◽  
J. Schwander ◽  
R. Mulvaney ◽  
J.-M. Barnola ◽  
...  
Keyword(s):  
20Th Century ◽  
Atmospheric Model ◽  
Model Fit ◽  
Anthropogenic Sources ◽  
Anthropogenic Emissions ◽  
Natural Origin ◽  
Devon Island ◽  
The North ◽  
Dronning Maud Land ◽  
Concentration Depth Profiles

Abstract. Four trihalomethane (THM; CHCl3, CHBrCl2, CHBr2Cl and CHBr3) and two dihalomethane (DHM; CH2BrCl and CH2Br2) trace gases have been measured in air extracted from polar firn collected at the North Greenland Icecore Project (NGRIP) site. CHCl3 was also measured in firn air from Devon Island (DI), Canada, Dronning Maud Land (DML), Antarctica and Dome Concordia (Dome C), Antarctica. All of these species are believed to be almost entirely of natural origin except for CHCl3 where anthropogenic sources have been reported to contribute ~10% to the global burden. A 2-D atmospheric model was run for CHCl3 using reported emission estimates to produce historical atmospheric trends at the three firn sites, which were then input into a firn diffusion model to produce concentration depth profiles that were compared against the measurements. The anthropogenic emissions were modified in order to give the best model fit to the firn data at NGRIP, Dome C and DML. As a result, the contribution of CHCl3 from anthropogenic sources, mainly from pulp and paper manufacture, to the total chloroform budget appears to have been considerably underestimated and was likely to have been close to ~40% at the maximum in atmospheric CHCl3 concentrations around 1990, declining to ~19% at the beginning of the 21st Century. We also show that the atmospheric burden of the brominated THM's in the northern hemisphere have increased over the 20th Century while CH2Br2 has remained constant over time implying that it is entirely of natural origin.

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