124 research outputs found
The Evolution and Climate of the Greenland Ice Sheet as seen in Ice Core δ18O
第3回極域科学シンポジウム 横断セッション「海・陸・氷床から探る後期新生代の南極寒冷圏環境変動」11月26日(月) 国立国語研究所 2階講
Molecular diffusion of stable water isotopes in polar firn as a proxy for past temperatures
Polar precipitation archived in ice caps contains information on past
temperature conditions. Such information can be retrieved by measuring the
water isotopic signals of and in
ice cores. These signals have been attenuated during densification due to
molecular diffusion in the firn column, where the magnitude of the diffusion is
isotopologoue specific and temperature dependent. By utilizing the differential
diffusion signal, dual isotope measurements of and
enable multiple temperature reconstruction techniques. This
study assesses how well six different methods can be used to reconstruct past
surface temperatures from the diffusion-based temperature proxies. Two of the
methods are based on the single diffusion lengths of
and , three of the methods employ the differential diffusion
signal, while the last uses the ratio between the single diffusion lengths. All
techniques are tested on synthetic data in order to evaluate their accuracy and
precision. We perform a benchmark test to thirteen high resolution Holocene
data sets from Greenland and Antarctica, which represent a broad range of mean
annual surface temperatures and accumulation rates. Based on the benchmark
test, we comment on the accuracy and precision of the methods. Both the
benchmark test and the synthetic data test demonstrate that the most precise
reconstructions are obtained when using the single isotope diffusion lengths,
with precisions of approximately 1.0\,^\mathrm{o}\mathrm{C}. In the benchmark
test, the single isotope diffusion lengths are also found to reconstruct
consistent temperatures with a root-mean-square-deviation of
0.7\,^\mathrm{o}\mathrm{C}
Greenland during the last interglacial:the relative importance of insolation and oceanic changes
Insolation changes during the Eemian (the last interglacial period,
129 000–116 000 years before present) resulted in warmer than present
conditions in the Arctic region. The NEEM ice core record suggests
warming of 8 ± 4 K in northwestern Greenland based on stable water
isotopes. Here we use general circulation model experiments to investigate
the causes of the Eemian warming in Greenland. Simulations of the atmospheric
response to combinations of Eemian insolation and preindustrial oceanic
conditions and vice versa are used to disentangle the impacts of the
insolation change and the related changes in sea surface temperatures and sea
ice conditions. The changed oceanic conditions cause warming throughout the
year, prolonging the impact of the summertime insolation increase.
Consequently, the oceanic conditions cause an annual mean warming of 2 K at
the NEEM site, whereas the insolation alone causes an insignificant change.
Taking the precipitation changes into account, however, the insolation and
oceanic changes cause more comparable increases in the precipitation-weighted
temperature, implying that both contributions are important for the ice core
record at the NEEM site. The simulated Eemian precipitation-weighted warming
of 2.4 K at the NEEM site is low compared to the ice core reconstruction,
partially due to missing feedbacks related to ice sheet changes and an
extensive sea ice cover. Surface mass balance calculations with an energy
balance model further indicate that the combination of temperature and
precipitation anomalies leads to potential mass loss in the north and
southwestern parts of the ice sheet. The oceanic conditions favor increased
accumulation in the southeast, while the insolation appears to be the
dominant cause of the expected ice sheet reduction. Consequently, the Eemian
is not a suitable analogue for future ice sheet changes
Bubble observations and analysis of the Renland ice core
Bubbles in ice cores store various information about climate conditions during densification and pore close-off in former times. Very recently it was shown that bubbles can additionally be used as marker for cumulated strain within the ice. Bubble studies on the Renland ice core are from particular interest: the Renland ice core includes the oldest bubbly ice retrieved so far in ice core drilling projects and it contains bubbly ice that has been exposed to tremendous deformation and thinning. The Renland ice core of 584 m length was drilled through the ice cap during May-June 2015 in the framework of RECAP (Renland ice cap drilling project). The ice shows no clathrate formation. Preliminary considerations suggest Holocene and Glacial ice with Eemian ice close to bedrock.
Core sections of the Renland ice core from selected depth intervals are measured with the means of X-ray computer tomography using the core-scale AWI-ICE CT. The measurements are performed with a spatial resolution of 15µm and provide 3d- bubble arrangements. Different bubble shape factors, bubble volume (porosity), bubble centre distributions and bubble next neighbor functions are derived. We present first depth profiles of these parameters and discuss the results in context of deformation mechanism and paleo climate. It will contribute to reconstruct the complex deformation history of the Renland ice cap
Does socially differentiated cardiac rehabilitation affect the use of healthcare services after myocardial infarction?:A 10-year follow-up study
Melt layer statistic of two firn cores recently drilled at Dye3 and South Dome in the dry snow zone of Southern Greenland
In the last couple of years remote sensing data have shown large areas of wet snow in the Southern part of the Greenland ice sheet. These melt features are attributed to the overall warming trend. Persistent warming implies changes in the firn layer as well. Even in areas of the dry snow zone one can observe sporadically a few ice lenses within the firn column indicating refrozen meltwater from warm events in the past.
In our contribution we want to close the gap between investigations of firn cores drilled in the 70's and the observational record of remote sensing data over the last decade in South Greenland. The focus lies on firn of the dry snow zone which is sensitive against changes in a warming atmosphere and cold enough to prevent a longway percolation path of meltwater to several firn layers.
To this end we had drilled two 45m-long firn cores at the former drilling sites of DYE3 (65°11'N, 43°49'W) and South Dome (SD) (63°32'N, 44°34'W) during a aircraft-supported field campaign 2012. The retrieved 3inch-firn core segments of 1m length are measured by a X-ray-scanning routine with the means of the core-scale AWI-ICE-CT. The 2d-density fields are calculated and allow to distinguish between refreezing meltwater and compacted firn. The depth-scales are converted to time-scales by using DEP (dielectric profiling) and (in case of DYE3) discrete sampled d18O measurements. Number density of melt layers and relative amount of melt show an synchronized behavior with an general increase over the last 30 years. Local maxima are observed in both sites at around 6-9m and 25m at DYE3 and 5-8m, 22m and 40m at SD
Ice-core data used for the construction of the Greenland Ice-Core Chronology 2005 and 2021 (GICC05 and GICC21)
We here describe, document, and make available a wide range of data sets used for annual-layer identification
in ice cores from DYE-3, GRIP, NGRIP, NEEM, and EGRIP. The data stem from detailed measurements
performed both on the main deep cores and shallow cores over more than 40 years using many different
setups developed by research groups in several countries and comprise both discrete measurements from cut ice
samples and continuous-flow analysis data.
The data series were used for counting annual layers 60 000 years back in time during the construction of
the Greenland Ice-Core Chronology 2005 (GICC05) and/or the revised GICC21, which currently only reaches
3800 years back. Now that the underlying data are made available (listed in Table 1) we also release the individual
annual-layer positions of the GICC05 timescale which are based on these data sets.
We hope that the release of the data sets will stimulate further studies of the past climate taking advantage of
these highly resolved data series covering a large part of the interior of the Greenland ice sheet
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