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Orsi, AJ, Cornuelle BD, Severinghaus JP.  2014.  Magnitude and temporal evolution of Dansgaard-Oeschger event 8 abrupt temperature change inferred from nitrogen and argon isotopes in GISP2 ice using a new least-squares inversion. Earth and Planetary Science Letters. 395:81-90.   10.1016/j.epsl.2014.03.030   AbstractWebsite

Polar temperature is often inferred from water isotopes in ice cores. However, non-temperature effects on 3180 are important during the abrupt events of the last glacial period, such as changes in the seasonality of precipitation, the northward movement of the storm track, and the increase in accumulation. These effects complicate the interpretation of 8180 as a temperature proxy. Here, we present an independent surface temperature reconstruction, which allows us to test the relationship between delta O-18(ice) and temperature, during Dansgaard-Oeschger event 8, 38.2 thousand yrs ago using new delta N-15 and delta Ar-40 data from the GISP2 ice core in Greenland. This temperature reconstruction relies on a new inversion of inert gas isotope data using generalized least-squares, and includes a robust uncertainty estimation. We find that both temperature and delta O-18 increased in two steps of 20 and 140 yrs, with an overall amplitude of 11.80 +/- 1.8 degrees C between the stadial and interstadial centennial-mean temperature. The coefficient alpha = d delta O-18/dT changes with each time-segment, which shows that non-temperature sources of fractionation have a significant contribution to the delta O-18 signal. When measured on century-averaged values, we find that alpha = d delta O-18/dT = 0.32 +/- 0.06%(0)/degrees C, which is similar to the glacial/Holocene value of 0.328%(o)/degrees C. (C) 2014 Elsevier B.V. All rights reserved.

Bereiter, B, Shackleton S, Baggenstos D, Kawamura K, Severinghaus J.  2018.  Mean global ocean temperatures during the last glacial transition. Nature. 553:39-+.   10.1038/nature25152   AbstractWebsite

Little is known about the ocean temperature's long-term response to climate perturbations owing to limited observations and a lack of robust reconstructions. Although most of the anthropogenic heat added to the climate system has been taken up by the ocean up until now, its role in a century and beyond is uncertain. Here, using noble gases trapped in ice cores, we show that the mean global ocean temperature increased by 2.57 +/- 0.24 degrees Celsius over the last glacial transition (20,000 to 10,000 years ago). Our reconstruction provides unprecedented precision and temporal resolution for the integrated global ocean, in contrast to the depth-, region-, organism-and season-specific estimates provided by other methods. We find that the mean global ocean temperature is closely correlated with Antarctic temperature and has no lead or lag with atmospheric CO2, thereby confirming the important role of Southern Hemisphere climate in global climate trends. We also reveal an enigmatic 700-year warming during the early Younger Dryas period (about 12,000 years ago) that surpasses estimates of modern ocean heat uptake.

Petrenko, VV, Severinghaus JP, Schaefer H, Smith AM, Kuhl T, Baggenstos D, Hua Q, Brook EJ, Rose P, Kulin R, Bauska T, Harth C, Buizert C, Orsi A, Emanuele G, Lee JE, Brailsford G, Keeling R, Weiss RF.  2016.  Measurements of 14C in ancient ice from Taylor Glacier, Antarctica constrain in situ cosmogenic 14CH4 and 14CO production rates. Geochimica et Cosmochimica Acta. 177:62-77.   10.1016/j.gca.2016.01.004   Abstract

Carbon-14 (14C) is incorporated into glacial ice by trapping of atmospheric gases as well as direct near-surface in situ cosmogenic production. 14C of trapped methane (14CH4) is a powerful tracer for past CH4 emissions from “old” carbon sources such as permafrost and marine CH4 clathrates. 14C in trapped carbon dioxide (14CO2) can be used for absolute dating of ice cores. In situ produced cosmogenic 14C in carbon monoxide (14CO) can potentially be used to reconstruct the past cosmic ray flux and past solar activity. Unfortunately, the trapped atmospheric and in situ cosmogenic components of 14C in glacial ice are difficult to disentangle and a thorough understanding of the in situ cosmogenic component is needed in order to extract useful information from ice core 14C. We analyzed very large (≈1000 kg) ice samples in the 2.26–19.53 m depth range from the ablation zone of Taylor Glacier, Antarctica, to study in situ cosmogenic production of 14CH4 and 14CO. All sampled ice is >50 ka in age, allowing for the assumption that most of the measured 14C originates from recent in situ cosmogenic production as ancient ice is brought to the surface via ablation. Our results place the first constraints on cosmogenic 14CH4 production rates and improve on prior estimates of 14CO production rates in ice. We find a constant 14CH4/14CO production ratio (0.0076 ± 0.0003) for samples deeper than 3 m, which allows the use of 14CO for correcting the 14CH4 signals for the in situ cosmogenic component. Our results also provide the first unambiguous confirmation of 14C production by fast muons in a natural setting (ice or rock) and suggest that the 14C production rates in ice commonly used in the literature may be too high.

Brook, EJ, Severinghaus JP.  2011.  Methane and megafauna. Nature Geoscience. 4:271-272.   10.1038/ngeo1140   AbstractWebsite
Petrenko, VV, Etheridge DM, Weiss RF, Brook EJ, Schaefer H, Severinghaus JP, Smith AM, Lowe D, Hua QA, Riedel K.  2010.  Methane from the East Siberian Arctic Shelf. Science. 329:1146-1147.   10.1126/science.329.5996.1146-b   AbstractWebsite
Severinghaus, JP, Grachev A, Luz B, Caillon N.  2003.  A method for precise measurement of argon 40/36 and krypton/argon ratios in trapped air in polar ice with applications to past firn thickness and abrupt climate change in Greenland and at Siple Dome, Antarctica. Geochimica Et Cosmochimica Acta. 67:325-343.   10.1016/s0016-7037(02)00965-1   AbstractWebsite

We describe a method for measuring the (40)Ar/(36)Ar ratio and the (84)Kr/(36)Ar ratio in air from bubbles trapped in ice cores. These ratios can provide constraints on the past thickness of the firn layer at the ice core site and on the magnitude of past rapid temperature variations when combined with measured (15)N/(14)N. Both variables contribute to paleoclimatic studies and ultimately to the understanding of the controls on Earth's climate. The overall precision of the (40)Ar/(36)Ar method (1 standard error of the mean) is 0.012parts per thousand for a sample analyzed in duplicate, corresponding to +/-0.6 in in reconstructed firn thickness. We use conventional dynamic isotope ratio mass spectrometry with minor modifications and special gas handling techniques designed to avoid fractionation. About 100 g of ice is used for a duplicate pair of analyses. An example of the technique applied to the GISP2 ice core yields an estimate of 11 +/- 3K of abrupt warming at the end of the last glacial period 15,000 years ago. The krypton/argon ratio can provide a diagnostic of argon leakage out of the bubbles, which may happen (naturally) during bubble close-off or (artifactually) if samples are warmed near the freezing point during core retrieval or storage. Argon leakage may fractionate the remaining (40)Ar/(36)Ar ratio by +0.007parts per thousand per parts per thousand change in (84)Kr/(36)Ar, introducing a possible bias in reconstructed firn thickness of about +2 in if thermal diffusion is not accounted for or +6 in if thermal diffusion effects are quantified with measured (15)N/(14)N. Reproducibility of (84)Kr/(36)Ar measured in air is about +/-0.2parts per thousand (1 standard error of the mean) but is about +/-1parts per thousand for ice core samples. Ice core samples are systematically enriched in (84)Kr/(36)Ar relative to atmosphere by similar to5parts per thousand, probably reflecting preferential size-dependent exclusion of the smaller argon atom during bubble entrapment. Recent results from the Siple Dome ice core reveal two climate events during the last deglaciation, including an 18-in reduction in firn thickness associated with an abrupt warming at sometime between 18 and 22 kyr BP and a partial or total removal of the firn during an ablation event at 15.3 kyr BP. Copyright (C) 2003 Elsevier Science Ltd.

Headly, MA, Severinghaus JP.  2007.  A method to measure Kr/N-2 ratios in air bubbles trapped in ice cores and its application in reconstructing past mean ocean temperature. Journal of Geophysical Research-Atmospheres. 112   10.1029/2006jd008317   AbstractWebsite

We describe a new method for precise measurement of Kr/N-2 ratios in air bubbles trapped in ice cores and the first reconstruction of atmospheric Kr/N-2 during the last glacial maximum (LGM) similar to 20,000 years ago. After gravitational correction, the Kr/N-2 record in ice cores should represent the atmospheric ratio, which in turn should reflect past ocean temperature change due to the dependence of gas solubility on temperature. The increase in krypton inventory in the glacial ocean due to higher gas solubility in colder water causes a decrease in the atmospheric inventory of krypton. Assuming Kr and N-2 inventories in the ocean-atmosphere system are conserved, we use a mass balance model to estimate a mean ocean temperature change between the LGM and today. We measured Kr/N-2 in air bubbles in Greenland (GISP2) ice from the late Holocene and LGM, using the present atmosphere as a standard. The late Holocene delta Kr/N-2 means from two sets of measurements are not different from zero (+0.07 +/- 0.30 parts per thousand and -0.14 +/- 0.93 parts per thousand), as expected from the relatively constant climate of the last millennium. The mean delta Kr/N-2 in air bubbles from the LGM is -1.34 +/- 0.37 parts per thousand. Using the mass balance model, we estimate that the mean temperature change between the LGM ocean and today's ocean was 2.7 +/- 0.6 degrees C. Although this error is large compared to the observed change, this finding is consistent with most previous estimates of LGM deep ocean temperature based on foraminiferal delta O-18 and sediment pore water delta O-18 and chlorinity.

Severinghaus, JP.  2009.  Monsoons and Meltdowns. Science. 326:240-241.   10.1126/science.1179941   AbstractWebsite