Jin-Ho Ahn

Reconstructions of ancient atmospheric carbon dioxide (CO2) variations help us better understand how the global carbon cycle and climate are linked. We compared CO2 variations on millennial time scales between 20,000 and 90,000 years ago with an Antarctic temperature proxy and records of abrupt climate change in the Northern Hemisphere. CO2 concentration and Antarctic temperature were positively correlated over millennial-scale climate cycles, implying a strong connection to Southern Ocean proce

Reconstruction of atmospheric CO2 during times of past abrupt climate change may help us better understand climate-carbon cycle feedbacks. Previous ice core studies reveal simultaneous increases in atmospheric CO2 and Antarctic temperature during times when Greenland and the northern hemisphere experienced very long, cold stadial conditions during the last ice age. Whether this relationship extends to all of the numerous stadial events in the Greenland ice core record has not been clear. Here we

We report a decadally resolved record of atmospheric CO 2 concentration for the last 1000 years, obtained from the West Antarctic Ice Sheet (WAIS) Divide shallow ice core. The most prominent feature of the pre‐industrial period is a rapid ∼7 ppm decrease of CO 2 in a span of ∼20–50 years at ∼1600 A.D. This observation confirms the timing of an abrupt atmospheric CO 2 decrease of ∼10 ppm observed for that time period in the Law Dome ice core CO 2 records, but the true magnitude of the decrease re

We have measured the CO 2 concentration of air occluded during the last 40,000 years in the deep Siple Dome A (hereafter Siple Dome) ice core, Antarctica. The general trend of CO 2 concentration from Siple Dome ice follows the temperature inferred from the isotopic composition of the ice and is mostly in agreement with other Antarctic ice core CO 2 records. CO 2 rose initially at ∼17.5 kyr B.P. (thousand years before 1950), decreased slowly during the Antarctic Cold Reversal, rose during the You

Abstract One common assumption in interpreting ice-core CO 2 records is that diffusion in the ice does not affect the concentration profile. However, this assumption remains untested because the extremely small CO 2 diffusion coefficient in ice has not been accurately determined in the laboratory. In this study we take advantage of high levels of CO 2 associated with refrozen layers in an ice core from Siple Dome, Antarctica, to study CO 2 diffusion rates. We use noble gases (Xe/Ar and Kr/Ar), e

Using new and existing ice core CO 2 data from 65 ∼ 30 ka a new chronology for CO 2 is established and synchronized with Greenland ice core records to study how high latitude climate change and the carbon cycle were linked during the last glacial period. Atmospheric CO 2 rose several thousand years before abrupt warming in Greenland associated with Dansgaard‐Oeschger events, 8, 12, 14, 17, four large warm events that follow Heinrich events. The CO 2 rise terminated at the onset of Greenland warm

Abstract We describe a high-precision method, now in use in our laboratory, for measuring the CO 2 mixing ratio of ancient air trapped in polar ice cores. Occluded air in ice samples weighing ∼8–15 g is liberated by crushing with steel pins at −35°C and trapped at −263°C in a cryogenic cold trap. CO 2 in the extracted air is analyzed using gas chromatography. Replicate measurements for several samples of high-quality ice from the Siple Dome and Taylor Dome Antarctic ice cores have pooled standar

During the last glacial period atmospheric carbon dioxide and temperature in Antarctica varied in a similar fashion on millennial time scales, but previous work indicates that these changes were gradual. In a detailed analysis of one event we now find that approximately half of the CO 2 increase that occurred during the 1500‐year cold period between Dansgaard‐Oeschger (DO) events 8 and 9 happened rapidly, over less than two centuries. This rise in CO 2 was synchronous with, or slightly later tha

Climate variables play an important role in the increase of tree ring width (TRW), which is one of the primary paleoclimate signals. In this study, we apply new methods for understanding tree growth responses to climate variables under anthropogenic climate change. This study uses regression and artificial intelligence (AI) modelling techniques to develop a model describing the relationships between climate variables and the tree ring standardised growth index (TRSGI) in northeast South Korea. W

Abstract 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

Atmospheric nitrous oxide (N 2 O) is a greenhouse gas and ozone-depleting substance whose emissions are substantially perturbed by current human activities. Although air trapped in polar ice cores can provide direct information about N 2 O evolution, analytical precision was not previously sufficient for high temporal resolution studies. In this work, we present a highly improved analytical technique with which to study N 2 O concentrations in ancient-air-trapped ice cores. We adopt a melt–refre

Abstract Reconstruction of the long‐term surface temperature history in Antarctica is important for a better understanding of human‐induced climate changes, especially since the Industrial Revolution. We present here a surface temperature history spanning the last century at Styx Glacier, located on the eastern coast of northern Victoria Land, which is reconstructed using borehole logging data. Our results indicate that surface temperatures in the 20th century were 1.7 ± 0.4 °C higher than the l

As the number of mobile nodes registering with a network rapidly increases in Mobile IP, multiple mobility (home or foreign) agents can be allocated to each network in order to improve performance and availability. Previous fault-tolerant protocols to mask failures of the mobility agents have used passive replication techniques. However, they result in high failure-free latency during registration process if the number of mobility agents in the same network increases, and force each mobility age

Abstract Greenhouse gases (GHGs) trapped in ice wedges may provide useful information on biogeochemical environments in ground ice. Previous studies have reported highly elevated CO 2 and CH 4 mixing ratios in ice wedges. However, N 2 O mixing ratios in ice wedges remain unknown. Here, we present CO 2 , CH 4 and N 2 O mixing ratios in bubbles and plausible mechanisms of GHG formation for two lakeside ice wedges at Cyuie village near Yakutsk. The CO 2 gas age corresponds to the Last Glacial Maxim

Degradation of organic carbon stored in permafrost may represent an additional source of atmospheric greenhouse gases (GHGs) in a warming climate. However, there is no clear understanding of how seasonal freeze–thaw affects gas permeability and emission of methane in permafrost soils, in part due to the lack of chemical and physical characterisation of the soils. Here, we report vertical profiles of CO2, CH4 and other soil properties with resolutions of 0.05–0.1 m depth from five soil cores, dri