Journal ArticleDOI
Past Temperatures Directly from the Greenland Ice Sheet
Dorthe Dahl-Jensen,Klaus Mosegaard,Niels S. Gundestrup,Gary D. Clow,Sigfus J Johnsen,A. W. Hansen,Niels Balling +6 more
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TLDR
A Monte Carlo inverse method has been used on the temperature profiles measured down through the Greenland Ice Core Project (GRIP) borehole, at the summit of the Greenland ice Sheet, and the Dye 3 borehole 865 kilometers farther south, resulting in a 50, 000-year-long temperature history at GRIP and a 7000-year history at Dye3.Abstract:
A Monte Carlo inverse method has been used on the temperature profiles measured down through the Greenland Ice Core Project (GRIP) borehole, at the summit of the Greenland Ice Sheet, and the Dye 3 borehole 865 kilometers farther south. The result is a 50, 000-year-long temperature history at GRIP and a 7000-year history at Dye 3. The Last Glacial Maximum, the Climatic Optimum, the Medieval Warmth, the Little Ice Age, and a warm period at 1930 A.D. are resolved from the GRIP reconstruction with the amplitudes -23 kelvin, +2.5 kelvin, +1 kelvin, -1 kelvin, and +0.5 kelvin, respectively. The Dye 3 temperature is similar to the GRIP history but has an amplitude 1.5 times larger, indicating higher climatic variability there. The calculated terrestrial heat flow density from the GRIP inversion is 51.3 milliwatts per square meter.read more
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Posted ContentDOI
Constraints on glacier flow from temperature-depth profiles in the ice. Application to EPICA Dome C.
TL;DR: In this article, the authors used Monte Carlo methods to search the parameters' space of the model, compare the model output with the temperature data, and find probability distributions for the unknown parameters.
Posted ContentDOI
Planktic foraminifera and structure of surface water masses at the SW Svalbard margin in relation to climate changes during the last 2000 years
TL;DR: In this paper, the authors present a high-resolution record of properties in the subsurface (250-100m), near surface (100-30m), and surface (30-0m) water masses at the SW Svalbard margin in relation to climate changes during the last 2000 years.
Dissertation
The sensitivity of marine-terminating glaciers to model parameters and geometry
Abstract: Greenland outlet glaciers are among the largest contributors to global sea level rise. With high velocities and calving rates, they discharge large amounts of glacial ice into the ocean. During the last two decades, the mass loss of these glaciers has increased dramatically. Jakobshavn Isbræ recently experienced dramatic acceleration to peak velocities of 17 km yr−1; in contrast to other fast Greenland glaciers, its high velocities have persisted. Many studies have explained the observed acceleration with increased ocean water temperatures, increased surface runoff and reduced buttressing by sea ice. However, it is still not completely understood how external factors, such as changes by the atmosphere and ocean, impact marine-terminating glaciers. Here, the impact of ice temperature, basal sliding, crevasse water depth, submarine melt rate, and buttressing by sea ice on glacier properties is studied with a numerical flowband model. A sensitivity study is conducted on an idealized marine-terminating glacier and on Jakobshavn Isbræ. Changes to the driving as well as internal parameters of the ice flow model have a great impact on the idealized glacier. Whilst a change in crevasse water depth, buttressing by sea ice, and submarine melt impact the thickness and length proportionally, basal sliding and ice rheology influence rather the shape of the glacier. The ice temperature is represented by the rate factor, a complex parameter, found to influence the glacier in opposing ways through its control on the viscosity and lateral resistance. The study of Jakobshavn Isbræ shows that stabilization at pinning points dominates the impact of parameter uncertainties. The grounding line position can therefore be stable for hundreds of years, while the thickness of the glacier continues adjusting to previous perturbations. This adjustment may eventually lead to a dramatic change of the grounding line position. It is therefore crucial for ice sheet models to involve centennial to millennial time-scales.
Dissertation
Comparison of MODIS LST and SSM/I melt detection products on the Greenland ice sheet
TL;DR: In this article, passive microwave and thermal IR satellite products are compared based on their ability to detect melt occurrence on the Greenland ice sheet, and the 2006 and 2007 melt seasons are examined for differences in the melt onset, duration, and extent of the products, as well as their effectiveness of detection over different regions of the ice sheet.
Journal ArticleDOI
Anthropogenic activity and millennial climate variability affect Holocene mercury deposition of an alpine wetland near the largest mercury mine in China.
TL;DR: In this article , the atmospheric Hg depositional fluxes during the Holocene using a 450-cm alpine wetland sediment core taken from the Jiulongchi wetland, which is only 65 km to the Wanshan Mercury Mine.
References
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Journal ArticleDOI
Decadal Trends in the North Atlantic Oscillation: Regional Temperatures and Precipitation
TL;DR: An evaluation of the atmospheric moisture budget reveals coherent large-scale changes since 1980 that are linked to recent dry conditions over southern Europe and the Mediterranean, whereas northern Europe and parts of Scandinavia have generally experienced wetter than normal conditions.
Journal ArticleDOI
Heat flow from the Earth's interior: Analysis of the global data set
TL;DR: In this paper, a new estimate of the Earth's heat loss based on a new global compilation of heat flow measurements comprising 24,774 observations at 20,201 sites is presented, which when areally weighted yield a global mean of 87 mW m -2 and a global heat loss of 44.2 x 10 2 W, an increase of some 4-8% over earlier estimates.
Journal ArticleDOI
Monte Carlo sampling of solutions to inverse problems
Klaus Mosegaard,Albert Tarantola +1 more
TL;DR: In inverse problems, obtaining a maximum likelihood model is usually not sucient, as the theory linking data with model parameters is nonlinear and the a posteriori probability in the model space may not be easy to describe.
Journal ArticleDOI
Arctic Environmental Change of the Last Four Centuries
Jonathan T. Overpeck,Konrad A Hughen,D. Hardy,Raymond S. Bradley,R. Case,M. A. Douglas,Bruce P. Finney,K. Gajewski,Gordon C. Jacoby,Anne E. Jennings,Scott F. Lamoureux,A. Lasca,Glen M. MacDonald,J.J. Moore,Michael Retelle,S. Smith,Alexander P. Wolfe,G. Zielinski +17 more
TL;DR: A compilation of paleoclimate records from lake sediments, trees, glaciers, and marine sediments provides a view of circum-Arctic environmental variability over the last 400 years.
Journal ArticleDOI
Climate instability during the last interglacial period recorded in the GRIP ice core
TL;DR: Isotope and chemical analyses of the GRIP ice core from Summit, central Greenland reveal that climate in Greenland during the last interglacial period was characterized by a series of severe cold periods, which began extremely rapidly and lasted from decades to centuries.