Mary Jo Spencer

Determination of major ions in snow and ice cores by ion chromatography

Abstract The determination of major anions (Cl − , NO − 3 , SO 2− 4 ) and cations (Na + , NH + 4 , K + , Mg 2+ , Ca 2+ ) in snow and ice cores by ion chromatography at trace level concentrations (ng/g) is presented. Total acidity (H + ) was determined using an acid titration method in order to complete the ionic balance. Unique sampling techniques and sample preparation methods were developed to avoid contamination of the snow and ice samples.

Seasonal and spatial trends in South Greenland snow chemistry

Abstract The spatial, temporal, source and physical controls on chloride, nitrate, sulfate and sodium in south Greenland snow are presented in this paper based on chemical data from snowpit and fresh snow samples. The snowpit samples cover the period June 1982–June 1984 and the fresh surface snow samples represent one storm event sampled over a 38-km traverse from Dye 3 to the southwest. Oxygen isotope dated records of chloride, sodium, excess sulfate and nitrate are discussed with respect to input timing and source. Notably the anthropogenic influx of excess sulfate is apparent in addition to an influx of excess sulfate that coincides with and is attributed to the arrival of the El Chichon cloud in S Greenland. The El Chichon event is also marked by highs in chloride and nitrate. Examination of fresh surface snow reveals geographic, temperature and moisture controls on deposition. Some excess sulfate close to Dye 3 can be attributed to local pollution.

A REVIEW OF CENTRAL ASIAN GLACIOCHEMICAL DATA

The glaciers of central Asia provide suitable locations from which to recover continuous, high-resolution glaciochemical records on a continental scale. Although the glaciochemical investigations undertaken to date in central Asia are few in number and limited in terms of spatial coverage and length of record, some preliminary observations can be made concerning regional and seasonal trends in snow chemistry in this region. The sodium chloride ratio for most snow samples collected in central Asia approaches the ratio found in sea water (0.86 in /Leq kg-I), reflecting a marine source for these constituents. Sodium and chloride concentrations are, on average, 3-10 times higher in the Himalayas than in the Karakoram, demonstrating the greater influence of monsoonal sources of moisture in the Himalayas. Very high sodium concentrations from Khel Khod Glacier probably reflect a local crustal source from surrounding ice-free areas. Low nitrate concentrations were found in snow collected from the southern margin of the Himalayas and high concentrations in snow deposited on the north margin of the Himalayas. This strong regional trend in the spatial distribution of nitrate suggests the influx of continental aerosols, rich in nitrate, originating from the arid regions of central Asia. High calcium concentrations measured in snow from Mount Everest and the north-west corner of China are also indicative of dust derived from the arid regions of central Asia. Very high sulfate concentrations found in snow from the Tien Shan and the Bogda Shan most likely reflect local anthropogenic sources. The altitude effect on isotopic composition is not apparent from snow samples collected in central Asia. Understanding the processes which control the chemical content of snow, the local-to-regiona l scale complexities,

Ice-core Dating and Chemistry by Direct-current Electrical Conductivity

Although quantitative interpretation of the low-frequency electrical conductivity of ice cores from central Greenland is complicated by temperature variations of the measured core, annual layers can be recognized in sections of the core that are not impacted by non-seasonal features. Ambiguities in counting of annual layers can be minimized by comparing the electrical conductivity measurements to measurements of dust concentration and visual stratigraphy. A non-linear relationship between applied voltage and the current measured across two electrodes complicates the quantitative comparison of measurements made with different equipment, but does not affect the overall shape of the observed features .

A GLACIOCHEMICAL SURVEY OF THE SUMMIT REGION. GREENLAND

Spatial representativene ss and an understanding of controls on chemical species distribution are essential requirements of any significant ice core investigation. Snowpit studies provide an essential tool in this process. In preparation for the central Greenland deep drilling effort a series of snowpits was sampled in detail for oxygen isotopes, major anions, major cations, total acidity and radionuclides. The results of this sampling program are used to define: (1 ) the chemical composition of the snow in the region, (2) the input timing and spatial distribution of major chemical species, (3) the potential dependence of

Two-hundred-year record of biogenic sulfur in a south Greenland ice core (20D)

The concentration of methanesulfonic acid (MSA) was determined in a shallow south central Greenland ice core (20D). This study provides a high-resolution record of the DMS-derived biogenic sulfur in Greenland precipitation over the past 200 years. The mean concentration of MSA is 3.30 ppb (σ = 2.38 ppb, n = 1134). The general trend of MSA is an increase from 3.01 to 4.10 ppb between 1767 and 1900, followed by a steady decrease to 2.34 ppb at the present time. This trend is in marked contrast to that of non-sea-salt sulfate (nss SO42−), which increases dramatically after 1900 due to the input of anthropogenic sulfur. The MSA fraction ((MSA/(MSA + nss SO42−))* 100) ranges from a mean of 15% in preindustrial ice to less than 5% in recent ice. These MSA fractions suggest that approximately 15 to 40% of the sulfur in recent Greenland ice is of biological origin. It is suggested that there is a significant low-latitude component to the biogenic sulfur in the core and that variations in the MSA fraction reflect changes in the relative strengths of low- and high-latitude inputs. The data show no evidence for a strong dependence of dimethyl sulfide (DMS) emissions on sea surface temperature during the last century. There is also no indication that the yield of MSA from DMS oxidation has been altered by increased NOx levels over the North Atlantic during this period.

Seasonal metal remobilization in the sediments of Great Bay, New Hampshire

Abstract Concentrations of dissolved iron, manganese, molybdenum, copper, and organic carbon (DOC) were measured in the pore waters from surficial sediments of a temperate estuary to delineate seasonal metal remobilization from 1978 through 1980. Iron and DOC data were collected for 31 months and covaried inversely and exponentially. Iron dissolution occurred during the spring and during periods of active bioturbation with concentrations as high as 18 mg 1 −1 . Iron values were low during winter due to oxidation to ferric oxides. The lack of active bioturbation during the summer of 1978 allowed for the nearly complete removal of iron as a monosulfide precipitate. However, bioturbation resumed during the summer of 1979 and 1980 and dissolved iron concentrations as high as 10 mg 1 −1 were observed at those times. The iron and DOC data were a qualitative measure of bioturbation activity. Dissolved manganese, molybdenum, and copper data were collected for 18 months during 1978 and 1979. All three metals displayed spring maxima covariate with iron, suggesting that they behaved chemically like iron and/or were associated with iron- or manganese-rich phases during this time of the year. In general, manganese and molybdenum varied temporally with iron while copper concentrations mimicked iron variations only during the spring.

Ice-core sulfate from three northern hemisphere sites: Source and temperature forcing implications

Abstract Comparison of ice-core nss sulfate records (two sites in Greenland and one in the North Pacific) with temperature change records for the regions including these core sites provides further confirmation that change in the concentration of anthropogenic sulfate has had a significant effect on regional temperature during at least the period ∼ ad 1940–1970 over at least the Atlantic portion of the Arctic. Using the ad 1880–1985 portion of our ice-core records as an analog, we provide a test of the potential temperature depression caused by non-seasalt (nss) sulfate aerosols over Greenland during the period ∼ ad 700–1900 concluding that the anthropogenic era is unique by comparison. Statistical examination of this record allows a determination of the relative contributions of volcanic vs biogenic source nss sulfate during this period plus a characterization of the variability in these two sources.

A Northern Hemisphere Volcanic Chemistry Record (1869-1984) and Climatic Implications using a South Greenland Ice Core

The effect of volcanic emISSIOn of acidic aerosols on climate is well documented. The presence of acid droplets in the stratosphere can reduce transmissivity and hence decrease surface temperatures. Since the amount and chemical composition of erupted material has important effects on regional climate, knowledge of past volcanic events is of extreme importance. Detailed glaciochemical records provide the only milieu wherein the geochemistry of paleovolcanic events can be fully documented. We present a detailed sulfate and chloride record from an ice core drilled at site 20 D, 40 km SW of Dye 3 in southern Greenland. The record spans the time period 1869-1984 with chemical analyses of approximately eight samples per year. Time series decomposition and locally weighted scatter plot smoothing techniques were used to extract long term trends from the data so that individual volcanic eruptions could be documented. A number of events identified here have been unnoticed previously and a high percentage of the major chemical signatures documenting these events is associated with large decreases in temperature in the latitudinal zone 60-90 oN. Many authors have pointed out that the amount of volcanic acids such as HCI and H2S04 injected into the atmosphere has a very important influence on global climate, yet this volcanic input has been difficult to quantify prior to -1960. Our data help to alleviate this problem. These individual events can be compared to available frost tree ring data from North America, further establishing a volcanism--climatic linkage.

Nitrate concentrations in snow from remote areas: implication for the global NO x flux

Increased emissions of nitrogen compounds to the atmosphere by human activities have been well documented. However, in order to better quantify these anthropogenic emissions, better knowledge of natural emissions rates must be known. In addition, variation in natural emissions through time should be documented. In this note we present data collected and/or analyzed by us for NO3− in recent snow from remote regions of the world. We also summarize existing data sets from other remote regions. This is done to establish a better understanding of NO3− deposition rates in these regions as well as to add more information to our global understanding of NO3− deposition.