Methanesulfonic acidand non-seasalt sulfatein the Vostok ice core:

A glacial/interglacial recordof biogenic sulfur emissions

from the southern ocean

E.S. SALTZMAN and C.D. GERMAIN

Rosenstiel School of Marine and Atmospheric ScienceUniversity of Miami

Miami, Florida 33149

M.R. LEGRAND and C. FENIET-SAIGNE

Laboratoire de Glaciologie et Geophysique de l'EnvironnementSt. Martin d'Heres, France

per billion or more); these samples are not associated withsignificant changes in climate of MSA and most likely reflectepisodic increases in atmospheric sulfate associated with vol-canic eruptions (Legrand and Delmas 1987).

The MSA profile also correlates strongly with climatic changeand shows greater variability than non-seasalt sulfate. Intergla-cial stages (A and G) have concentrations of 5-10 parts perbillion and glacial stages (B, D, and H) have concentrations of25-30 parts per billion. The similarity in general trends be-tween MSA and non-seasalt sulfate suggests that the sulfateaerosols in the central antarctic atmosphere are primarily ofmarine origin.

The observed trend of increasing MSA and non-seasalt sul-fate during colder periods may indicate higher emissions ofDMS from the glacial circumantarctic ocean as a result of eitherincreased biological emissions or increased air/sea exchangedue to higher wind speeds. If fine-particle sulfate aerosol con-centrations were indeed higher in the atmosphere surroundingAntarctica during glacial conditions, as the ice-core data sug-gest, the effect should have been to stabilize the cooler climate.

M.I. BARKOV and V.N. PETROV

Arctic and Antarctic Research InstituteSt Petersburg 199226, Russia

Dimethylsulfide (DMS) is produced biologically in the sur-face oceans by phytoplankton and emitted into the atmospherevia gas exchange. In the atmosphere, DMS is rapidly oxidizedby the hydroxyl ion radical to form methanesulfonic acid(CH-,S0 3 ; MSA) and sulfur dioxide, which is converted, inturn, to sulfuric acid. MSA retains one of the methyl groups ofits DMS precursor, making it potentially useful as a tracer forbiogenic sulfur in marine aerosol and precipitation. Becausenon-seasalt sulfate is the principal source of fine-particle aero-sols and cloud condensation nucleii in the atmosphere, it hasbeen suggested that the atmospheric sulfur cycle may play arole in the long-term control of the radiation budget of the Earth(Shaw 1983; Charlson et al. 1987). This article reports on apreliminary record of MSA and non-seasalt sulfate in the 2,500-meter ice core from Vostok Station, central East Antarctica(78°27'S 106°51'E, elevation 3,488 meters). The Vostok ice corehas been analyzed to investigate the relationship betweenoceanic sulfur emissions and climate change. It contains a160,000-year record covering the last glacial/interglacial climaticcycle (Jouzel et al. 1987; Barnola et al. 1987).

MSA, sulfate, sodium, and calcium concentrations were de-termined by ion chromatography with chemical suppressionand conductivity detection. The record is a composite of sam-ples analyzed at the University of Miami and Grenoble labora-tories. Samples were obtained from the core by subcoring witha mechanical lathe to avoid rinsing the core, a process whichhas been shown to lead to artifacts in the analysis of MSA. Theanalytical techniques and the method of calculation of non-seasalt sulfate have been discussed in detail in Legrand et al.(1991).

The results of this study are shown in the figure. Non-seasaltsulfate concentrations vary from 110-150 parts per billion dur-ing warm interglacial stages (A and G) to 200-250 parts perbillion during cold glacial stages (B, D, and H). A few samplesexhibited unusually high levels of non-seasalt sulfate (350 parts

88

Age (kyr)133356 66107 118 141

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0. 25CL 20

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3502300CL 250

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Depth (m)

Depth profiles of delta 0, non-seasalt (nss) sulfate, MSA, and theratio MSA!non-seasalt sulfate in the Vostok ice core. Upper andlower stage boundaries are marked by vertical lines.

ANTARCTIC JOURNAL

—420—440

E. —4800

—480—500—520

An alternative to changes in the oceanic source might bechanges in the glacial atmospheric circulation of the antarcticregions favoring the inland transport of marine aerosols to thecentral plateau from highly productive high-latitude coastal re-gions. Research is continuing to differentiate between thesescenarios.

The Vostok ice core was analyzed in conjunction with a co-operative agreement between the United States, France, andthe Soviet Union. Financial support was provided by NationalScience Foundation grant DPP 88-20919 and by the FrenchCentre National de la Recherche Scientifique (ATP Phase At-mospherique des cycles Biogeochimiques).

References

Barnola, J.M., D. Raynaud, Y.S. Korotkevich, and C. Lorius. 1987. Vos-tok ice core provides 160,000-year record of atmospheric CO 2 . Nature,329, 408-413.

Charison, R.J., J.E. Lovelock, M.O. Andreae, and S. Warren. 1987Oceanic phytoplankton, atmospheric sulphur, cloud albedo and cli-mate. Nature, 326, 655-661.

Jouzel, J., C. Lorius, J.R. Petit, C. Genthon, N.I. Barkov, V.M. Kotly-akov, and V.M. Petrov. 1987 Vostok ice core: A continuous isotopetemperature record over the last climatic cycle (160,000 years). Nature,329,403-408.

Legrand, M.R., and R.J. Delmas. 1987 A 220-year continuous recordof volcanic I-1 2SO4 in the Antarctic ice sheet. Nature, 327, 671-676.

Legrand, M.R., C. Feniet-Saigne, E.S. Saltzman, C.D. Germain, N.J.Barkov, and VN. Petrov. 1991. An ice core record of oceanic emissionsof dimethylsuiphide during the last climatic cycle. Nature, 350, 144-146:1 Shaw, G.E. 1983. Biocontrolled thermostasis involving the sul-fur cycle. Climatic Change, 5, 297-303.

Development of laserice-cutting apparatus

EDWARD ZELLER, GISELA DRESCHHOFF, and CLAUDE M. LAIRD

Radiation Physics LaboratorySpace Technology Center

University of KansasLawrence, Kansas 66045

During the 1990-1991 field season at Windless Bight nearRoss Island, our team introduced the use of a 25-watt contin-uous infrared carbon-dioxide laser as a field device to cut in-dividual firn cores for sample preparation. The test was suc-cessful and permitted this device to be employed on a routinebasis in field operations. The advantage of carbon-dioxide, lasercutting systems is that the beam is emitted at an infrared wave-length, which is absorbed in a very short distance in ice. Wewere able to demonstrate conclusively that the laser beam cancut cleanly and rapidly through both firn and ice and that itcan be manipulated efficiently with standard optical systems.

Subsequently, upon our return to the laboratory at the Uni-versity of Kansas, we tested the system on a 10-centimeterdiameter ice core from the Greenland ice sheet taken at a depthof about 170 meters (Koci personal communication). The corewas supplied to us by P. Grootes. In this case, cutting wasperformed in an open freezer. The initial temperature of thecore was approximately -20 °C. Total power output used wasabout 15 watts. The cutting was performed without opticalcondensers; we used the beam directly from the laser and wereable to slice off a 5-centimeter segment of the core withoutshattering or fragmentation of any kind. The cut was about 2millimeters wide and could have been reduced to half thatwidth with an optical system. A videotape taken in the labo-ratory at the time of the cutting experiment was prepared andsent to the Division of Polar Programs at the National ScienceFoundation and to the Polar Ice Coring Office.

In the process of completing this experiment, we determinedthat it would be possible to develop an optical system thatwould permit the beam to be rotated in a circular path, a motionthat could be used for cutting deep ice cores. With minor mod-ifications, this system could be used in fluid-filled holes as wellas in open holes.

The fact that the laser beam cuts entirely by melting andexerts no torque on the ice at the cutting surface, greatly re-duces the potential for fracturing and breakage of the core dur-ing drilling. Even more important, because the beam can bedeflected at 90° to the drilling directions, the ice core can be cutoff at the bottom of the hole by the beam. This has the effectof greatly reducing stress on the core at the time it is lifted freeof the bottom of the hole. Finally, contamination is avoided,first because the laser beam cannot introduce chemical contam-ination and, second, because the infrared wavelengths used fordrilling are too long to cause significant radiolytic breakdown.Thus, chemical alterations of all types are kept to an absoluteminimum.

In construction of a prototype, the rotating mass of the op-tical system and the thin-walled core barrel will be so low thatonly the lightest of anti-torque systems must be used. Theentire drill assembly including the laser, optics, core barrel andscavenger pump system can be expected to weigh less than 90kilograms and can be supported on a light-weight cable thatmust include electrical conductors for the 28-volt power supplyto the laser. Power requirements are modest. Electrical powerto the completed system can be supplied by a 3,000-watt gen-erating facility and should be fully adequate for all operationsincluding drilling and hoisting of the drill and core barrel as-sembly.

The simplest drill design is shown in figure 1. In this design,the carbon-dioxide laser is mounted vertically in the boreholeand a rotating head containing deflecting mirrors is attached sothat the laser beam can be directed down against the ice andturned in a circle by a small, low-power, direct-current motor.In principle, it is possible to design the drill so that the radiusof the core is adjustable, but we propose to build a system witha fixed-core diameter (most probably 10 centimeters).

1991 REVIEW 89