M. C. Morrison

Record of Volcanism Since 7000 B.C. from the GISP2 Greenland Ice Core and Implications for the Volcano-Climate System.

Sulfate concentrations from continuous biyearly sampling of the GISP2 Greenland ice core provide a record of potential climate-forcing volcanism since 7000 B.C. Although 85 percent of the events recorded over the last 2000 years were matched to documented volcanic eruptions, only about 30 percent of the events from 1 to 7000 B.C. were matched to such events. Several historic eruptions may have been greater sulfur producers than previously thought. There are three times as many events from 5000 to 7000 B.C. as over the last two millennia with sulfate deposition equal to or up to five times that of the largest known historical eruptions. This increased volcanism in the early Holocene may have contributed to climatic cooling.

Changes in Atmospheric Circulation and Ocean Ice Cover over the North Atlantic During the Last 41,000 Years

High-resolution, continuous multivariate chemical records from a central Greenland ice core provide a sensitive measure of climate change and chemical composition of the atmosphere over the last 41,000 years. These chemical series reveal a record of change in the relative size and intensity of the circulation system that transported air masses to Greenland [defined here as the polar circulation index (PCI)] and in the extent of ocean ice cover. Massive iceberg discharge events previously defined from the marine record are correlated with notable expansions of ocean ice cover and increases in PCI. During stadials without discharge events, ocean ice cover appears to reach some common maximum level. The massive aerosol loadings and dramatic variations in ocean ice cover documented in ice cores should be included in climate modeling.

The atmosphere during the Younger Dryas

One of the most dramatic climate change events observed in marine and ice core records is the Younger Dryas, a return to near-glacial conditions that punctuated the last deglaciation. High-resolution, continuous glaciochemical records, newly retrieved from central Greenland, record the chemical composition of the arctic atmosphere at this time. This record shows that both the onset and the termination of the Younger Dryas occurred within 10 to 20 years and that massive, frequent, and short-term (decadal or less) changes in atmospheric composition occurred throughout this event. Changes in atmospheric composition are attributable to changes in the size of the polar atmospheric cell and resultant changes in source regions and to the growth and decay of continental biogenic source regions.

Greenland ice core “signal” characteristics: An expanded view of climate change

The last millenium of Earth history is of particular interest because it documents the environmental complexities of both natural variability and anthropogenic activity. The authors have analyzed the major ions contained in the Greenland Ice Sheet Project 2 (GISP 2) ice core from the present to {approximately}674 A.D. to yield an environmental reconstruction for this period that includes a description of nitrogen and sulfur cycling, volcanic emissions, sea salt and terrestrial influences. They have adapted and extended mathematical procedures for extracting sporadic (e.g., volcanic) events, secular trends, and periodicities found in the data sets. Finally, by not assuming that periodic components (signals) were {open_quotes}stationary{close_quotes} and by utilizing evolutionary spectral analysis, they were able to reveal periodic processes in the climate system which change in frequency, {open_quotes}turn on,{close_quotes} and {open_quotes}turn off{close_quotes} with other climate transitions such as that between the little ice age and the medieval warm period. 42 refs., 4 figs., 2 tabs.

The variability of biogenic sulfur flux from a temperate salt marsh on short time and space scales

Abstract Three emission chambers were deployed simultaneously to measure rates of emission of dimethyl sulfide, methane thiol and carbonyl sulfide within or across vegetation zones in a New Hampshire salt marsh. Short term (a few hours) variation in fluxes of all S gases from replicate sites were small within a monospecific stand of either Spartina alterniflora or S. patens . The quantity of emergent biomass and the type of vegetation present were the primary factors regulating the rate of emission. Dimethyl sulfide fluxes from the S. alterniflora soils ranged from 800 to 18,000 nmol m −2 h −1 compared to emissions of 25–120 nmol m −2 h −1 from S. patens . This difference was probably due to the presence of the dimethyl-sulfide precursor dimethylsulfoniopropionate which is an osmoregulator in S. alterniflora but not in S. patens . Methane thiol emissions from S. alterniflora were 20–280 nmol m −2 h −1 and they displayed a similar diel trend as dimethyl sulfide, although at much lower rates, suggesting that methane thiol is produced primarily by leaves. Methane thiol emissions from S. patens were 20–70 nmol m −2 h −1 . Net uptake of carbonyl sulfide of 25–40 nmol m −2 h −1 occurred in stands of S. alterniflora while net efflux of 10–36 nmol m −2 h −1 of carbonyl sulfide occurred in stands of S. patens . In general, ranges of emissions of sulfur gases were similar to most other published values.

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.

Global perspective of nitrate flux in ice cores

The relationships between the concentration and the flux of chemical species (Cl{sup {minus}}, NO{sub 3}{sup {minus}}, SO{sub 4}{sup 2{minus}}, Na{sup +}, K{sup +}, NH{sub 4}{sup +}, Mg{sub 2+}, Ca{sup 2+}) versus snow accumulation rate were examined at GISP2 and 20D in Greenland, Mount Logan from the St. Elias Range, Yukon Territory, Canada, and Sentik Glacier from the northwest end of the Zanskar Range in the Indian Himalayas. At all sites, only nitrate flux is significantly ({alpha}=0.05) related to snow accumulation rate. Of all the chemical series, only nitrate concentration data are normally distributed. Therefore the authors suggest that nitrate concentration in snow is affected by postdepositional exchange with the atmosphere over a broad range of environmental conditions. The persistant summer maxima in nitrate observed in Greenland snow over the entire range of record studied (the last 800 years) may be mainly due to NO{sub x} released from peroxyacetyl nitrate by thermal decomposition in the presence of higher OH concentrations in summer. The late winter/early spring nitrate peak observed in modern Greenland snow may be related to the buildup of anthropogenically derived NO{sub y} in the Arctic troposphere during the long polar winter. 58 refs., 3 figs., 4 tabs.

Emissions of biogenic sulfur gases from Alaskan tundra

Fluxes of the biogenic sulfur gases carbonyl sulfide (COS), dimethyl sulfide (DMS), methyl mercaptan (MeSH), and carbon disulfide (CS2) were determined for several freshwater and coastal marine tundra habitats using a dynamic enclosure method and gas chromatography. In the freshwater tundra sites, highest emissions, with a mean of 6.0 nmol m−2 h−1 (1.5–10) occurred in the water-saturated wet meadow areas inhabited by grasses, sedges and Sphagnum mosses. In the drier upland tundra sites, highest fluxes occurred in areas inhabited by mixed vegetation and labrador tea at 3.0 nmol m−2 h−1 (0–8.3) and lowest fluxes were from lichen-dominated areas at 0.9 nmol m−2 h−1. Sulfur emissions from a lake surface were also low at 0.8 nmol m−2 h−1. Of the compounds measured, DMS was the dominant gas emitted from all of these sites. Sulfur emissions from the marine sites were up to 20-fold greater than fluxes in the freshwater habitats and were also dominated by DMS. Emissions of DMS were highest from intertidal soils inhabited by Carex subspathacea (150–250 nmol m−2 h−1). This Carex sp. was grazed thoroughly by geese and DMS fluxes doubled when goose feces were left within the flux chamber. Emissions were much lower from other types of vegetation which were more spatially dominant. Sulfur emissions from tundra were among the lowest reported in the literature. When emission data were extrapolated to include all tundra globally, the global flux of biogenic sulfur from this biome is 2–3 × 108 g yr−1. This represents less than 0.001% of the estimated annual global flux (∼50 Tg) of biogenic sulfur and <0.01% of the estimated terrestrial flux. The low emissions are attributed to the low availability of sulfate, certain hydrological characteristics of tundra, and the tendency for tundra to accumulate organic matter.

Greenland Ice Core Greenland Ice Core "Signal" Characteristics: An Expanded View of Climate Change

The last millenium of Earth history is of particular interest because it documents the environmental complexities of both natural variability and anthropogenic activity. The authors have analyzed the major ions contained in the Greenland Ice Sheet Project 2 (GISP 2) ice core from the present to {approximately}674 A.D. to yield an environmental reconstruction for this period that includes a description of nitrogen and sulfur cycling, volcanic emissions, sea salt and terrestrial influences. They have adapted and extended mathematical procedures for extracting sporadic (e.g., volcanic) events, secular trends, and periodicities found in the data sets. Finally, by not assuming that periodic components (signals) were {open_quotes}stationary{close_quotes} and by utilizing evolutionary spectral analysis, they were able to reveal periodic processes in the climate system which change in frequency, {open_quotes}turn on,{close_quotes} and {open_quotes}turn off{close_quotes} with other climate transitions such as that between the little ice age and the medieval warm period. 42 refs., 4 figs., 2 tabs.

Greenland ice core {open_quotes}signal{close_quotes} characteristics: An expanded view of climate change

The last millenium of Earth history is of particular interest because it documents the environmental complexities of both natural variability and anthropogenic activity. The authors have analyzed the major ions contained in the Greenland Ice Sheet Project 2 (GISP 2) ice core from the present to {approximately}674 A.D. to yield an environmental reconstruction for this period that includes a description of nitrogen and sulfur cycling, volcanic emissions, sea salt and terrestrial influences. They have adapted and extended mathematical procedures for extracting sporadic (e.g., volcanic) events, secular trends, and periodicities found in the data sets. Finally, by not assuming that periodic components (signals) were {open_quotes}stationary{close_quotes} and by utilizing evolutionary spectral analysis, they were able to reveal periodic processes in the climate system which change in frequency, {open_quotes}turn on,{close_quotes} and {open_quotes}turn off{close_quotes} with other climate transitions such as that between the little ice age and the medieval warm period. 42 refs., 4 figs., 2 tabs.