Showing papers on "North Greenland Ice Core Project published in 2004"

Magnetization of Greenland ice and its relationship with dust content

Abstract: [1] We estimate the concentration of fine magnetic particles in ice samples from the North Greenland Ice Core Project core from the central Greenland ice sheet, using lowtemperature (77K) isothermal remanent magnetization (IRM) analysis and compare it with the mass concentration of aerosol dust. Samples were taken from six climatic intervals, spanning the time from the Holocene (Preboreal) back to the Last Glacial Dansgaard/ Oeschger cycle 5. The mean IRM intensity of the ice varies by a factor of 3 from glacial to interglacial stages, being lower during interglacials. The IRM acquisition curves of the ice do not quite saturate at the maximum available field of 0.8 T and show a relatively broad coercivity, which is compatible with a mixture of maghemite or magnetite and hematite. Comparison of the IRM intensity and total dust mass shows a remarkably good correlation but also reveals a large background magnetization, which may be essentially constant over the different climatic stages. IRM suggests that the dust properties are independent of the background signal and that the dust aerosol has a magnetization within about 30% of pristine loess from the Chinese Loess Plateau, which is considered to have the same source in the same east Asian deserts as dust in Greenland ice. Ice contamination and the flux of extraterrestrial dust particles were considered in order to explain the origin of the background magnetization. Nevertheless, we could not find a convincing explanation for this signal, which represents a considerable part of the IRM signal and is the dominant component during interglacial intervals, without invoking the presence of undetected dust mass. The alternative hypothesis of a varying magnetization of the ice dust at different climatic periods would suggest that different sources of aerosol are active during different climatic periods. This, however, has not proven to be the case so far for studies of the provenance of dust in Greenland ice. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0399 Atmospheric Composition and Structure: General or miscellaneous; 0394 Atmospheric Composition and Structure: Instruments and techniques; KEYWORDS: magnetization, IRM, Greenland, ice core, NorthGRIP, aerosol

A compact high-resolution radar for determining snow accumulation rates

Abstract: Rising sea level has important humanitarian and economic implications Scientists are rigorously investigating the contribution of glacial ice sheets to sea-level rise Knowledge of the mass balance of the ice sheets is important in understanding their dynamics The accumulation rate of snow on ice sheets is an important variable in determining this mass balance The accumulation rate is currently determined using ice cores and pits This is a tedious method to obtain coverage over the entire ice sheet due to the limited number of samples that can be acquired The only practical means of obtaining coverage over a large area would be by means of remote sensing We have developed a wideband radar to map the isochronous layers in the ice sheet This will help reduce the uncertainty associated with sparse sampling of the ice sheet We built a compact FM-CW radar that operates from 500 to 2000 MHz with range resolution of about 10 cm Both the transmitter and receiver were housed in a single Compact PCI chassis We used a YIG oscillator to generate the FM signal The performance of an FM-CW is usually degraded by the nonlinearity of the source We linearized the sweep of the YIG oscillator by means of a phase-locked loop (PLL) We have successfully tested the radar in the lab and we will be performing tests during the 2004 summer field experiments at the Summit camp in Greenland We successfully tested a connectorized version of this radar during the 2003 field experiments at the North Greenland Ice Core Project (NGRIP) camp We were able to map the internal layers up to a depth of about 150 m over a 5-km transect We also conducted detailed snow pit studies at several spots over the transect for correlating the visually determined layers with the radar determined layers We will present the radar design, laboratory test results of its performance, results from the experiments at Summit and a comparison of the radar data with information derived from ice cores and snow pits