Microparticle Concentrations Research Articles

Magnetic movement of biological fluid droplets

Magnetic fields can be used to control the movement of aqueous drops on non-patterned, silicon nanowire superhydrophobic surfaces. Drops of aqueous and biological fluids are controlled by introducing magnetizable carbonyl iron microparticles into the liquid. Key elements of operations such as movement, coalescence, and splitting of water and biological fluid drops, as well as electrochemical measurement of an analyte are demonstrated. Superhydrophobic surfaces were prepared using vapor–liquid–solid (VLS) growth systems followed by coating with a perfluorinated hydrocarbon molecule. Drops were made from aqueous and biological fluid suspensions with magnetizable microparticle concentrations ranging from 0.1 to 10 wt%.

Microparticle content records of the Dunde ice core and dust storms in northwestern China

Dust storms are important atmospheric phenomenon in central Asia, particularly in the regions bordering deserts, arid and semi-arid regions. Dust storms occur quite often in northwestern China. There are some research results about past dust storm events using historical archives in China. However, the archives used cover limited time and area. Microparticle concentrations in the Dunde ice cap, Qilian mountain of northwestern China, represent a continuous record of past dust storms. Comparison between dust rain frequency reconstructed from historical archives and the ice core record from the Dunde ice cap demonstrate that the microparticle record in the Dunde ice core is a good indicator of dust storms in northwest China. According to the ice core records, we can reconstruct the dust storm chronology for historical time. During the past 700 years, the dust content fluctuated with time, and lower frequency variations existed. Although the linear trend increased over the past 700 years, dust content was decreasing since the early 1700s. During the Little Ice Age, it was slightly higher corresponding to the cold period.

Seasonal evolution of aerosol stratigraphy in Ürümqi glacier No. 1 percolation zone, eastern Tien Shan, China

AbstractThe processes involved in the evolution of vertical profiles of Mg2+, Ca2+ and microparticle concentrations, as well as their seasonal variation in surface snow, were studied by weekly sampling from September 2003 to September 2004 of a snow pit on Ürümqi glacier No. 1, eastern Tien Shan, China. The development of the microparticle and Mg2+ and Ca2+ stratigraphy in the snow pit is closely related to the physical development of the snow–firn pack. The sampling site is located at 4130 ma.s.l. in the percolation zone of the glacier, and in addition to the effects of sublimation and wind erosion, melting plays a crucial role in both the physical and chemical evolution processes. During the winter, soluble aerosol concentrations in the surface layers are altered slightly by sublimation and wind erosion, and the concentrations are further modified as the wet season begins in late April. In contrast, soluble aerosol stratigraphy in the deeper layers remains relatively unchanged through the winter. In early summer, as melting occurs in the upper part of the snow–firn pack, meltwater carries chemical species to different depths in the underlying snow–firn layers, such that at the end of the ablation season, all of the surface cations might be leached out from the upper layers. In addition, the possible source of calcium and magnesium is discussed in this paper.

Circulating Endothelial Microparticles Are Associated with Vascular Dysfunction in Patients with End-Stage Renal Failure

Endothelial dysfunction and arterial stiffness are major determinants of cardiovascular risk in patients with end-stage renal failure (ESRF). Microparticles are membrane fragments shed from damaged or activated cells. Because microparticles can affect endothelial cells, this study investigated the relationship between circulating microparticles and arterial dysfunction in patients with ESRF and identified the cellular origin of microparticles associated with these alterations. Flow cytometry analysis of platelet-free plasma from 44 patients with ESRF indicated that circulating levels of Annexin V+ microparticles were increased compared with 32 healthy subjects, as were levels of microparticles derived from endothelial cells (three-fold), platelets (16.5-fold), and erythrocytes (1.6-fold). However, when arterial function was evaluated noninvasively in patients with ESRF, only endothelial microparticle levels correlated highly with loss of flow-mediated dilation (r = -0.543; P = 0.004), increased aortic pulse wave velocity (r = 0.642, P < 0.0001), and increased common carotid artery augmentation index (r = 0.463, P = 0.0017), whereas platelet-derived, erythrocyte-derived, and Annexin V+ microparticle levels did not. In vitro, microparticles from patients with ESRF impaired endothelium-dependent relaxations and cyclic guanosine monophosphate generation, whereas microparticles from healthy subjects did not. Moreover, in vitro endothelial dysfunction correlated with endothelial-derived (r = 0.891; P = 0.003) but not platelet-derived microparticle concentrations. In fact, endothelial microparticles alone decreased endothelial nitric oxide release by 59 +/- 7% (P = 0.025). This study suggests that circulating microparticles of endothelial origin are tightly associated with endothelial dysfunction and arterial dysfunction in ESRF.

Comprehensive 1000 year climatic history from an intermediate-depth ice core from the south dome of Berkner Island, Antarctica: methods, dating and first results

AbstractA 181 m deep ice core drilled in 1994/95 on the south dome of Berkner Island, Antarctica, was analyzed for stable isotopes, major ions and microparticle concentrations. Samples for ion chromatography were prepared by using a novel technique of filling decontaminated sample from a device for continuous ice-core melting directly into the sample vials. The core was dated through identification of volcanic horizons and interpolative layer counting. The core, together with a similar core from the north dome, reveals a 1000 year history of relatively stable climate. Temporal variations in the two cores deviate from each other owing to changing patterns of regional-scale circulation; the best correspondence between them is found for MSA–. δ18O, accumulation rate and a sea-salt proxy show only negligible correlation, which suggests a complex meteorological setting. Increasing annual accumulation is observed for the last 100 years. A period of increased sea-salt concentrations started around AD 1405, as has also been observed in other cores. Microparticle concentrations are on average 1220 particles (&gt;1.0 μm diameter) mL–1; they are enhanced from AD 1200 to 1350, possibly because of a higher atmospheric mineral dust load or because local volcanic activity was stronger than previously thought. Microparticles and NH4+ show marked but multiple and very irregular sub-annual peaks; long-term stacking of 1 year data intervals yields seasonal maxima in austral spring or mid-summer, respectively. Post-depositional redistribution was observed for MSA, NO3– and F– at volcanic horizons.

Evidence of glacial flour in the deepest 89 m of the Vostok ice core

The 3623 m long Vostok ice core is divided into two main parts: (1) from the surface to a depth of 3310 m, the ice layers are undisturbed and may be used to reconstruct the climatic record over the past 420 kyr; (2) from 3538 m to the bottom, the core is made up of accreted ice formed by freezing of the lake. In between, the glacier ice is disturbed by ice dynamics, as shown, for example, by inclined volcanic-ash layers. Microparticle concentrations and distributions as well as ionic and isotopic content were used to subdivide this third section. The identification of layers with bedrock material provides clues as to the entrainment processes at sub-freezing temperatures. Dust concentration and size distribution as well as ionic content are comparable with values found in ice of glacial and interglacial periods. Below 3450 m depth, however, the mode of the volume size distribution clearly shifts from 2.1 μm to 3.4 μm in diameter. Particles as large as 30 μm in diameter are observed and cannot have an aeolian origin. From microscopic observations, we suggest that they originate from the bedrock and represent glacial flour entrained in a shear layer up to 89 m from the glacier sole. This process most likely occurred when the ice sheet was grounded before flowing over the lake.

High-resolution microparticle profiles at NorthGRIP, Greenland: case studies of the calcium–dust relationship

AbstractA novel flow-through microparticle detector was deployed concurrently with continuous flow analyses of major ions during the North Greenland Icecore Project 2000 field season. the easy-handling detector performs continuous counting and sizing. In this deployment the lower size-detection limit was conservatively set to 1.0 μm equivalent spherical particle diameter, and a depth resolution of ≤1cm was achieved for microparticle concentrations. the dust concentration usually followed the Ca2+ variability. Here results are presented from an inspection of the Ca/dust mass ratio in 23 selected intervals, 1.65 m long each, covering different climatic periods including Holocene and Last Glacial Maximum (LGM). A (Ca2+)/(insoluble dust) mass ratio of 0.29 was found for the Holocene and 0.11 for LGM. Changes to the Ca/dust ratio occur on an annual to multi-annual time-scale exhibiting the same pattern, i.e. a lower Ca/dust ratio for higher crustal concentrations. Moreover, the Ca2+/dust ratio may increase significantly during episodic events such as volcanic horizons due to enhanced dissolution of CaCO3. This calls into question the notion of deploying Ca2+ as a quantitative mineral dust reference species and shows the importance of variable source properties or fractionating processes during transport and deposition.

Activation of platelets by in vitro whole blood contact with materials: Increases in microparticle, procoagulant activity, and soluble P-selectin blood levels

Non-adherent platelets and plasma were analyzed for evidence of platelet activation after whole blood contact with materials under conditions of low shear for one hour at 37°C. The contact involved adding heparinized whole blood to small diameter tubes that were connected to two arms extending from a rocking platform. For all surfaces (polyethylene, polypropylene, Silastic™, PVA hydrogel) tested there was strong evidence of platelet activation in the bulk blood: platelet-derived microparticles, procoagulant platelet membranes and soluble P-selectin levels. Flow cytometric quantification of microparticles (MPs) was highly sensitive and entailed the direct determination of microparticle concentrations as opposed to the traditional quantification of microparticle percentages (relative to total number of MPs and platelets). Whole blood contact with polypropylene surfaces led to the greatest drops in bulk platelet counts and also to the lowest increases in microparticle concentrations. Flow cytometry was also used to assess procoagulant levels (annexin V binding) within a light scatter region known to contain platelets and some large microparticles. All surfaces were noted to generate a significant procoagulant population that was, based on forward light scatter, mostly very small platelets or large microparticles. In contrast, most of the P-selectin positive platelets were averaged sized. Lastly, all surfaces generated soluble P-selectin levels that were approximately double the level (25 ng ml-1) noted in the resting whole blood samples. In addition to our previous reports, these findings support the observation that there is strong evidence of platelet activation in the bulk that we anticipate will ultimately lead to more relevant in vitro testing of the compatibility of platelets towards materials.

Evaluation of microparticles released from an adsorber used for low density lipoprotein apheresis.

Microparticle (MP) released from a DALI 750 Adsorber column for low density lipoprotein apheresis, which is used in a direct hemoperfusion system, was evaluated. The numbers of MP were measured by a light blockage method in the effluents from the column during the rinsing (priming) procedure using a priming solution, and the simulated treatment procedure using a physiologic saline solution as a substitute for whole blood. An unacceptable number of MP were released from the column during the simulated treatment after rinsing with an amount of solution prescribed by the manufacturer. MP concentrations (mean values of three experiments) in the initial 300 ml of the effluent were 639.9, 75.1, and 3.6 pieces/ml for > or = 5 microm, > or = 10 microm, and > or = 25 microm, respectively, and neither the result for > or = 5 microm nor for > or = 10 microm meets the requirement for solutions for injection defined in the United States Pharmacopoeia XXIII or the British Pharmacopoeia of 1993. Furthermore, a large number of MP still remained in the column after all the simulated operations. These findings suggest that the column has a potential to release an unacceptable number of MP into the patient during treatment. Further investigation on the influence of the MP released into the patient's circulation is necessary.

Crystal-size and microparticle record in the ice core from Dome Summit South, Law Dome, East Antarctica

An investigation of crystal-size and microparticle variations has been carried out for the 1196 m ice core retrieved from Dome Summit South (DSS) near the summit of Law Dome, East Antarctica. Results show that for ice deposited during the Holocenr (depth &amp;lt;1103 m), microparticle concentrations are low. Variations of crystal size with in the Holocenc ice are due to growth with time at a temperature-dependent rate, and recrystallisation as a consequence of the ice flow. in the DSS ice core the highest microparticle concentration occurs close to the depth (1133 M) at which oxygen isotope ratios exhibit the greatest negative values, i.e. the Last Glaciol Maximum (LGM). Also at this depth, crystal size reduces sharply from a general crystal growth trend above to near minimum core values below. For ice originating during the LGM, the concentration of particles is an order of magnitude greater than the mean Holocene concentration. Laboratory annealing tests at -1 °C confirm the retarded crystal growth in the high-microparlicle-concent ration ice.

Magnetic measurements of Greenland and Himalayan ice-core samples

This paper summarizes Isothermal Remanence (IRM300mT) measurements from Holocene ice-core samples from two contrasting glaciological regimes: (i) the Greenland ice sheet and (ii) a Himalayan glacier. Cores had been previously characterized in terms of chronologies, geochemistry and, for the Himalayan core, microparticle concentrations. Six samples from the Greenland 20-D ice core from the time period AD 1876-1983 did not yield magnetic measurements above instrumental noise-level. Significant Isothermal Remanence measurements (IRM300mT) were obtained from some levels in the Himalayan ice core. Scanning electron microscopy and EDAX analyses indicate weathered crustal material. The techniques used require ice-core samples with relatively high dust loadings and/or larger volume ice samples.

Climatic and environmental records in Guliya Ice Cap

The Guliya Ice Cap is the largest (with a total area of 376.1 m2 and an area cf 131 2 m2 at the flat top), highest (6 700 m a. s.l.) and coldest (with an ice temperature of -19℃ at 10 m depth) ice cap found in Central Asia so far. From 1990 to 1992, the oxygen isotope ratios, microparticle concentrations, anions, cations of a large number of samples from snow pits and ice cores were analysed to study the climatic and environmental characteristics of the Guliya Ice Cap. Being frozen to bedrock and with extremely low ice temperature, the ideal climatic and environmental informarion was recorded in Guliya Ice Cap. The distinct annual and seasonal cycle characteristics of the oxygen isotope ratio, microparticle concentration, anion and cation provide bases to date precisely the high-resolution time series in the ice cap. Oxygen isotope ratios decreased, microparticle concentrations and various chemical elements increased in the colder periods, while oxygen isotope values increased, microparticle concentrations and various chemical elements decreased during warmer periods, and the interpretation of various abrupt events will be the key to restore systematically various kinds of climatic and environmental information recorded in this ice cap. The records in the Guliya ice cores indicate that climatic wanning which happened in the middle 1980s was one of the most impressive events during the past several decades.

Recent ice-core climate records from the Cordillera Blanca, Peru

Ice cores recently drilled to bedrock on the col of Huascarán (9°06′ S, 77°36′ W, 6047 m a.s.l.) offer the potential for a long, annually resolved climate record from tropical South America. This paper presents the record from 1950 to 1993 preserved in microparticle and nitrate concentrations and oxygen-isotopic ratios. Average monthly temperatures from a satellite-linked automatic weather station installed on nearby Hualcán in 1991 are presented. Annual temperatures from local high-altitude meteorological stations, along with the annual Huascarán isotopic record, show a warming trend over the last two decades. The marked preservation of the climate record in oxygen-isotopic ratios on Huascarán is absent at lower-elevation sites, which have been affected by the recent warming. This paper demonstrates the establishment of a time-scale for the Huascarán core, the preservation of the climatic signal with depth and the linkage of the ice-core “proxy-climate” parameters with measured climatic variations.

Recent ice-core climate records from the Cordillera Blanca, Peru

Ice cores recently drilled to bedrock on the col of Huascarán (9°06′ S, 77°36′ W, 6047 m a.s.l.) offer the potential for a long, annually resolved climate record from tropical South America. This paper presents the record from 1950 to 1993 preserved in microparticle and nitrate concentrations and oxygen-isotopic ratios. Average monthly temperatures from a satellite-linked automatic weather station installed on nearby Hualcán in 1991 are presented. Annual temperatures from local high-altitude meteorological stations, along with the annual Huascarán isotopic record, show a warming trend over the last two decades. The marked preservation of the climate record in oxygen-isotopic ratios on Huascarán is absent at lower-elevation sites, which have been affected by the recent warming. This paper demonstrates the establishment of a time-scale for the Huascarán core, the preservation of the climatic signal with depth and the linkage of the ice-core “proxy-climate” parameters with measured climatic variations.

Quantitative determination of circulating platelet microparticles by flow cytometry

Platelet microparticles are vesicles derived from the plasma membrane of platelets activated by a variety of agonists. To assess the extent of platelet activation, we recently developed a new and simple method of quantitating circulating microparticles in plasma by flow cytometry using the murine monoclonal antibody against glycoprotein IIb-IIIa (NNKY1-32). Using 2-μm fluorescent calibration beads, we succeeded in evaluating the absolute level of circulating microparticles. We determined the microparticle concentrations in 10 patients with arterial occlusive disease and in nine normal healthy donors, to determine whether the detection of microparticles would be useful in assessing the degree of platelet activation in clinical disorders. Microparticle levels were significantly higher in patients not treated with anti-thrombotic drugs than in normal healthy donors ( P < 0.001), but not significantly higher in patients with vascular prostheses who had received anti-thrombotic drugs. These observations suggest the usefulness of microparticle quantitation in assessing the platelet activation in arterial occlusive diseases.

THE MICROPARTICLE CONCENTRATION MEASUREMENT AND ITS CLIMATIC IMPLICATIONS IN AN ICE CORE FROM COAST AREA,ANTARCTICA

The microparticle concentration in an ice core from coast area, East Antarctica, has been measured by a Coulter counter and optic counting. It is proposed in the present paper that the microparticle concentrations in different areas are different, especially from the coast to the inland in Antarctica. After its comparison with microparticle concentrations from other cores, it is also proposed that there is a lag between the coldest climate (i. e. 18 ka B. P.) and the highest microparticle concentration.

Wisconsin/W�rm glacial stage ice in the subtropical dunde ice cap, China

The insoluble microparticle concentrations and size distributions and oxygen isotope abundances (δ18 0) in two 1-meter ice cores from the margin of the Dunde ice cap (38° 06 'N; 96° 24 'E; 5325 masl) drilled in 1986 and three ice cores drilled to bedrock at the summit of the ice cap in 1987 suggest the presence of Wisconsin/Wurm Glacial Stage (LWGS) ice in the subtropics. A Sino-American research group recovered three ice cores 136, 138 and 139 m in length from the summit of the Dunde ice cap in the Qilian Shan which are providing long, high temporal resolution climatic and environmental records for the NE section of the Tibetan Highlands. Particulate concentrations, conductivity and δ18 0 are the ice core constituents best established as indicators of the glacial/interglacial transition. The analyses of two shallow cores from the margin reveal a 14-fold increase in particulate concentration which is correlative with a 1% to 5% decrease (more negative) in δ18 0. The lower 10 to 13 m of three ice cores drilled to bedrock at the summit contain a ten-fold increase in dust (both soluble and insoluble) and a 1.2% decrease in oxygen isotopes. Additionally, the morphological properties of the particles in the LWGS ice are identical to those of the thick, extensive loess deposits of central china which accumulated during the cold, dry glacial stages of the Pleistocene. When the climatic and environmental records are fully extracted from the three deep cores they will provide a very detailed record of variations in particulates (soluble and insoluble), stable isotopes, net balance, pollen and perhaps atmospheric gases of CO2 and methane through the Holocene into the last glacial in the subtropics on the climatically important Tibetan Plateau.

Shallow-Core Analysis and Pit Studies at Siple Station, Antarctica: Implications for Extraction of a 500 Year Proxy Climate Record (Abstract)

Two cores, 302 and 132 m long, were drilled 1.5 km up-wind from Siple Station (75°55'S, 84°15'W) during the 1985–86 austral summer. These cores are expected to contain an annually resolvable 500 year record of atmospheric constituents. The entire length of these cores will be analyzed for insoluble particulate concentrations, liquid conductivity, and oxygen-isotope ratios. Anion concentrations (Cl−, SO42−) will be measured in selected sections. The extraction of a proxy climate history from these cores requires an assessment of the temporal quality and the spatial variability of the preserved record. This paper presents this assessment, which is based upon an extensive investigation of both pit and shallow-core (20 m) records.To complement the two deeper cores, eight 20 m cores were drilled and three pits were sampled. The pits were excavated up-wind of the drill site at distances between 0.5 and 1.0 km. In the central pit, 2.8 m deep, walls A and C (each 1 m wide) were positioned parallel to the prevailing wind, with wall B (4 m wide) perpendicular to the prevailing wind. The stratigraphy of wall B was mapped and continuous vertical profiles of samples were collected for microparticle concentrations (MPC), oxygen-isotopic ratios (δ18O), anion chemistry (AC) and liquid conductivity (LC). Three 20 m cores, each associated with a vertical profile of pit samples, were drilled 0.5 m behind wall B. In addition, part of one core was sampled for beta radioactivity in order to isolate the 1965–66 horizon which resulted from atmospheric thermonuclear testing. Pits 2 and 3 were both 2 m deep and consisted of two 1 m wide perpendicular walls. Each wall was sampled for MPC, δ18O, LC and AC, and one 20 m core was drilled behind each wall. The visible stratigraphy of both walls in pit 3 was mapped. Densities were measured in each pit. The results from the pit and shallow-core analyses lead to the following conclusions.The high frequency of storm events, often associated with winds in excess of 50 knots, leads to substantial drifting. The result is that stratigraphic features in the uppermost annual layer (e.g. crusts, mass-loss layers, hard layers, etc.) exhibit substantial vertical deviations and, on occasion, are laterally discontinuous. Substantial variation may occur over very short distances: e.g. a 2 cm thick melt feature pinched out over a distance of 10 cm. Interestingly, the stratigraphy in firn older than 1 year exhibits much less lateral variation. In fact, several distinct visible stratigraphic features can be correlated among most of the shallow cores and the two deeper cores. Examples will be presented. These features provide excellent time-stratigraphic markers for cross-core comparisons. Of special interest is the presence of a major melt feature, first reported by Swiss investigators in 1983. This feature, present at four different drill sites, allows time-stratigraphic correlation and yields nearly identical 10 year accumulation rates for all four sites. Such spatial continuity means that accumulation histories reconstructed from the two deeper cores should be representative of this area.The MPC measurements (particles per ml of water) are the lowest that have been measured. No measurements of atmospheric particulate concentrations are available, but the low concentrations probably result from the high annual accumulation (∼0.55 m a−1, water equivalent), which dilutes the atmospheric input signal of particulates preserved in the firn. Swiss investigators reported similar results for the dilution of volcanic acids (e.g. SO42−), which muted the conductivity signals in a 201 m Siple Station core. The low concentrations make particles difficult to use for dating Siple cores. On the other hand, the low background levels of particulates may make Siple Station an excellent site for monitoring major atmospheric turbidity events (e.g. prolonged periods of desertification or volcanic activity).The high annual accumulation leads to the excellent preservation of the δ18O annual signal. The annual δ18O signal ranges from 15‰ at the surface to 8‰ at 122 m, so it is probable that the annual δ18O signal will be preserved over the entire 500 year record, allowing nearly absolute dating of the core.The potential of a nearly absolute time-scale, coupled with detailed particulate, liquid-conductivity and δ18O histories, should provide the first proxy climate record from this area. This 500 year history will complement similar records anticipated from the Antarctic Peninsula (∼73° S) and that recently constructed from the James Ross Island ice cap. A more global climatic picture of the last 500 years may be obtained when these high-resolution Antarctic ice-core records are integrated with non-polar records (e.g. the Quelccaya ice cap, Peru, and the Dunde ice cap, China) of similar quality.

Shallow-Core Analysis and Pit Studies at Siple Station, Antarctica: Implications for Extraction of a 500 Year Proxy Climate Record (Abstract)

Two cores, 302 and 132 m long, were drilled 1.5 km up-wind from Siple Station (75°55'S, 84°15'W) during the 1985–86 austral summer. These cores are expected to contain an annually resolvable 500 year record of atmospheric constituents. The entire length of these cores will be analyzed for insoluble particulate concentrations, liquid conductivity, and oxygen-isotope ratios. Anion concentrations (Cl−, SO4 2−) will be measured in selected sections. The extraction of a proxy climate history from these cores requires an assessment of the temporal quality and the spatial variability of the preserved record. This paper presents this assessment, which is based upon an extensive investigation of both pit and shallow-core (20 m) records. To complement the two deeper cores, eight 20 m cores were drilled and three pits were sampled. The pits were excavated up-wind of the drill site at distances between 0.5 and 1.0 km. In the central pit, 2.8 m deep, walls A and C (each 1 m wide) were positioned parallel to the prevailing wind, with wall B (4 m wide) perpendicular to the prevailing wind. The stratigraphy of wall B was mapped and continuous vertical profiles of samples were collected for microparticle concentrations (MPC), oxygen-isotopic ratios (δ18O), anion chemistry (AC) and liquid conductivity (LC). Three 20 m cores, each associated with a vertical profile of pit samples, were drilled 0.5 m behind wall B. In addition, part of one core was sampled for beta radioactivity in order to isolate the 1965–66 horizon which resulted from atmospheric thermonuclear testing. Pits 2 and 3 were both 2 m deep and consisted of two 1 m wide perpendicular walls. Each wall was sampled for MPC, δ18O, LC and AC, and one 20 m core was drilled behind each wall. The visible stratigraphy of both walls in pit 3 was mapped. Densities were measured in each pit. The results from the pit and shallow-core analyses lead to the following conclusions. The high frequency of storm events, often associated with winds in excess of 50 knots, leads to substantial drifting. The result is that stratigraphic features in the uppermost annual layer (e.g. crusts, mass-loss layers, hard layers, etc.) exhibit substantial vertical deviations and, on occasion, are laterally discontinuous. Substantial variation may occur over very short distances: e.g. a 2 cm thick melt feature pinched out over a distance of 10 cm. Interestingly, the stratigraphy in firn older than 1 year exhibits much less lateral variation. In fact, several distinct visible stratigraphic features can be correlated among most of the shallow cores and the two deeper cores. Examples will be presented. These features provide excellent time-stratigraphic markers for cross-core comparisons. Of special interest is the presence of a major melt feature, first reported by Swiss investigators in 1983. This feature, present at four different drill sites, allows time-stratigraphic correlation and yields nearly identical 10 year accumulation rates for all four sites. Such spatial continuity means that accumulation histories reconstructed from the two deeper cores should be representative of this area. The MPC measurements (particles per ml of water) are the lowest that have been measured. No measurements of atmospheric particulate concentrations are available, but the low concentrations probably result from the high annual accumulation (∼0.55 m a−1, water equivalent), which dilutes the atmospheric input signal of particulates preserved in the firn. Swiss investigators reported similar results for the dilution of volcanic acids (e.g. SO4 2−), which muted the conductivity signals in a 201 m Siple Station core. The low concentrations make particles difficult to use for dating Siple cores. On the other hand, the low background levels of particulates may make Siple Station an excellent site for monitoring major atmospheric turbidity events (e.g. prolonged periods of desertification or volcanic activity). The high annual accumulation leads to the excellent preservation of the δ18O annual signal. The annual δ18O signal ranges from 15‰ at the surface to 8‰ at 122 m, so it is probable that the annual δ18O signal will be preserved over the entire 500 year record, allowing nearly absolute dating of the core. The potential of a nearly absolute time-scale, coupled with detailed particulate, liquid-conductivity and δ18O histories, should provide the first proxy climate record from this area. This 500 year history will complement similar records anticipated from the Antarctic Peninsula (∼73° S) and that recently constructed from the James Ross Island ice cap. A more global climatic picture of the last 500 years may be obtained when these high-resolution Antarctic ice-core records are integrated with non-polar records (e.g. the Quelccaya ice cap, Peru, and the Dunde ice cap, China) of similar quality.

Climatic Records from the Dunde Ice Cap, China

Results from the first glaciological investigation of the Dunde ice cap demonstrate that a long, highly temporally resolvable climatic ice-core record is preserved in this ice cap. Measurements of stratigraphy, microparticle concentrations, liquid conductivity, and oxygen-isotope ratios from three snow pits in 1984 suggest that the annual accumulation is approximately 200 mm (water equivalent). Measurement of microparticle concentrations and conductivities of pit samples collected in 1986 confirm the existence of annual dust layers and an annual accumulation rate of ∼200 mm/year over the past 5 years. Bore-hole temperatures of –5.4°C at 30 m indicate that the ice cap is polar. Mono-pulse radar depth determinations yield an average thickness of 140 m, which (coupled with the smooth bedrock topography and the current accumulation rate) suggest that the Dunde ice cap should contain at least a 3000 year climatic record. A drilling program to recover that record from this subtropical location is planned for 1987.