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1988 -core Records and —Potential for a Proxy Ozone Record Paul Andrew Mayewski University of Maine, [email protected]

Mary Jo Spencer

William Berry Lyons

Mark S. Twickler

J. Dibb

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Repository Citation Mayewski, Paul Andrew; Spencer, Mary Jo; Lyons, William Berry; Twickler, Mark S.; and Dibb, J., "Ice-core Records and Ozone Depletion—Potential for a Proxy Ozone Record" (1988). Earth Science Faculty Scholarship. 225. https://digitalcommons.library.umaine.edu/ers_facpub/225

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Figure 2. Twin Otter aircraft with antenna mounts for Kansas radar.

A method has been devised for comparing the shape of the bottom echo with that of a simulated pulse whose shape de- pends on the roughness parameters: standard deviation of height and autocorrelation function of height. With this method, we made roughness estimates for some of the bottom surface in the Downstream B area. Figure 1. University of Kansas radar mounted on a sled. We have developed a two-dimensional, matched-filter method for removing the hyperbolas characteristic of point-target echoes from the bottom of the . This method replaces a hy- perbola with a single image point at the location of the scat- the bottom echoes (at depths of roughly 1.1 kilometers), and terer. With such a method, the shape of the bottom may be also the internal layers. The "A scope" displays allowed es- more readily interpreted, and weak target echoes are not cov- timates of the roughness at the ice/bedrock interface. ered up by strong hyperbolic echoes from nearby targets. Plans for the 1988 field season are to conduct application- Other project participants are S. Rao, 0. Sit, S. Xie, and W. oriented measurements at the Siple Upstream B (USB). Xin. Measurements will be made of a 35-by-8 kilometer area from This reasearch was suported by National Science Foundation a Twin Otter aircraft, supplemented by sled measurements. grant DPP 83-00340.

Ice-core records and itored sites. We propose that measurements of nitrate and/or chloride in polar /ice samples may provide proxy records ozone depletion—Potential of ozone depletion because of the role these species play in for a proxy ozone record the ozone cycle (e.g., see summary review by Schoeberl and Krueger 1986). Heterogeneous chemical reactions in the ant- atmosphere involving catalyzing agents such as chlorine PAUL A. MAYEWSKJ, MARY Jo SPENCER, monoxide, bromine monoxide, and/or nitrogen oxides are known W.B. LYONS, MARK S. TWICKLER, and J. DIBB to be effective in reducing ozone concentrations through their effect on the general reaction: oxygen plus ozone forms 202 Glacier Research Group (e.g., McElroy et al. 1986a). Removal of nitrogen oxides by Institute for the Study of Earth, , and Space condensation from polar stratospheric (e.g., Toon et al. University of New Hampshire 1986; McElroy et al. 1986b; Crutzen and Arnold 1986) triggered Durham, New Hampshire 03824 particularly by cooling in the stratosphere helps set the stage for more efficient removal of ozone by reactions with chlorine monoxide and bromine monoxide (e.g., McElroy et al. 1986a). Time-series of the ionic composition in polar ice cores can These reactions may result in increased concentrations of ni- provide detailed direct and proxy records of seasonal to mu - trate and chloride in polar snow/ice cores. lenial scale fluctuations in climate, atmospheric chemistry, and An ozone proxy pilot study. In 1984, we conducted a detailed volcanic activity. Even though problems of species-source links glaciochemical program that included collecting a 201-meter and air/snow fractionation have not all been entirely resolved, core, collecting snowpit-samples, and taking surface-snow the fact remains that ice cores currently hold the best hope of samples at a site 500 kilometers from the , in the retrieving detailed paleoatmospheric records. While direct links Dominion Range (85°15S 166°10E, mean elevation, 2,700 me- between the chemistry in ice cores and the ozone depletion ters above level). (See figure 1.) This site lies along the phenomenon cannot be guaranteed, ice-core records provide contact between the Transantarctic and the east the only means by which signals related to the ozone cycle antarctic ice sheet and provides an excellent site for monitoring can be produced for pre-measurement periods or for unmon- the interaction of coastal and inland air masses. This site is

64 ANTARCTIC JOURNAL

/ Syowa James Ross ) 200

I South Pole 9OW- £

Rossice S Dominion Range S. Dome C 0 Shelf -C kl\" 0 Northern Victoria 00 km Dumont d Urville L

Figure 1. Location .

also located within the area affected by the austral spring "ozone • hole." The low mean annual , -38.8°C, and rel- atively low accumulation rate (approximately equivalent to 4 centimeters of ) make the site ideal for the recovery of relatively long-period, undisturbed paleoatmospheric records. We established the dating for the core by counting annual 3) maxima in chloride, nitrate, and sodium as well as by using 4- lead-210, and total beta-activity measurements. Unfortunately, 0 the upper 18 meters (AD 1984-1910) of the core were lost, due - 50- to , while being transported from McMurdo Station, , to Port Hueneme, California. Fortunately, a 6-me- ter (3-centimeter sample interval) snowpit is available to fill in the detail for the period AD 1984-1910. While the complete interpretation of the full AD 1984 to approximately 1050 BC composite snowpit/ record will be dealt with in future papers, examination of the general 0 I I trends in the time-series of nitrate ion and chlorine ion (figure 2) reveals the following: -38 • a marked increase in nitrate ions is apparent as of approx- imately AD 700, • the period AD 1984-1910 (6-meter snowpit) is characterized by higher nitrate-ion values than any other period of similar o -40 duration in the record, and • the chlorine-ion record shows only minor variations. 0 In an attempt to explain the trend in nitrate ionization, the a) potential sources of this species to the Dominion Range site -42 need to be examined. These sources include: 0 • nitrogen fixation by lightning at tropical and/or mid- C) sites (Legrand and Delmas 1986); 0 • volcanic activity; -44 • ionization via solar related phenomena (Zeller and Parker 1981); • production via thermonuclear detonations (Holdsworth 1986); • anthropogenic, and -461 I I I I I I 1 1 • temperature controls on condensation. 1400 700 0 700 1400 Some of these sources do not appear to be important in ex- BC AD plaining the observed trend in nitrate ionization. For example, Yea no evidence exists for trends in either lighting and/or volcanic source nitrate that match the observed record. Trends in nitrate Figure 2. Dominion Range nitrate (in micrograms per kilogram), ionization attributed to fluctuations in solar activity (e.g., Par- chloride (in micrograms per kilogram), and delta oxygen-18 (in parts ker, Zeller, and Cow 1982) are controversial (Risbo, Clausen, per thousand, %a) time series for the period AD 1984 to approxi- and Rasmussen 1981; Herron 1982; Legrand and Delmas 1984, mately 1050 BC. 1986) and do not explain the trend in the Dominion Range record. Thermonuclear sources are thought to have been sig-

1988 REVIEW 65 nificant from the 1950s to 1970s due to extensive atmospheric core could be linked to condensation in the strat- testing (Holdsworth 1986), however, for other periods the source osphere. is probably negligible. Sources for chloride ion to the antarctic include: volcanic The input of anthropogenically derived nitrate to the Do- activity, marine input, and fallout of hydrogen chloride from minion Range site cannot be assessed in any straight-forward polar stratospheric clouds (e.g., Toon et al. 1986). The relatively manner at this time. In southern , however, a two- weak trend in the chloride record does not necessarily allow fold increase in nitrate since AD 1955 and a threefold increase the differentiation of all of these sources. Volcanic inputs are in sulfate since AD 1900 has been documented and attributed usually seen as discrete signals as opposed to trends. The other to anthropogenic activity (Mayewski et al. 1986). It has been two sources could produce trends in the record depending assumed that because the vast majority of fossil fuels are con- upon, respectively, changes in the circulation intensity of ma- sumed in the Northern Hemisphere that Antarctica has not rine air masses and changes in temperature and overall com- been affected by anthropogenically derived nitrate or sulfate position of associated polar stratospheric clouds. Notably odd (Wolff and Peel 1985). Notably there is no increase in sulfate nitrogen is expected to be removed more efficiently than chlor- in the Dominion Range record throughout the period of nitrate ine gases from polar stratospheric clouds (Wofsy et al. 1988) increase although other sources of sulfate could potentially and, therefore, the trend in chloride may not be expected to mask an anthropogenic signal. To estimate the significance of be as dramatic as that in nitrate. the anthropogenic source of nitrate ions to the Antarctic, we Plots of nitrate and chloride from the 6-meter snowpit record can draw upon a knowledge of documented trends in nitrous compared to mean ozone concentrations (figure 3) measured oxide and lead. Pearman et al. (1986) using polar ice core data at South Pole (Komhyr, Grass, and Leonard 1986) and Syowa propose an approximately 8 percent increase in nitrous oxide Station (Sekiguchi 1986) for the same time periods reveal in- due to fossil-fuel combustion since AD 1600 which is similar teresting similarities in trend. We stress here oniv the general to nitrous oxide emission data model calculations made by Hao correspondence between trends in nitrate and chlorine ioni- et al. (1987) for the period AD 1860 to present. Boutron and zation and annual minima in ozone concentrations since the Patterson (1987) have recently argued that 80 percent of the Dominion Range is located 500 kilometers north of the closest lead found in the antarctic troposphere is anthropogenic and ozone minitoring site, South Pole. Differences in ozone con- that lead levels have risen fivefold since the Holocene. Through centration and hence relationship to nitrate and/or chloride for the last 200 years, Greenland lead values have risen approxi- any one time period could differ significantly from site to site mately 200 times (Murozumi, Chow, and Patterson 1969; Ng due to distance from the center of the polar vortex (e.g., and Patterson 1981). If we use the ratio Greenland-lead-in- McCormick and Larsen 1986). Is the general relationship in crease to antarctic-lead-increase (200:5) as a rough approxi- figure 3 coincidence or causality? We suggest that there is mation of the differences expected in anthropogenic effect significant potential for future study. between the two hemispheres and assume that the same gen- Further confirmation that there may be an association be- eral relationship holds for nitrate, we would expect approxi- tween nitrate precipitated onto the antarctic ice sheet and the mately a 2.5 percent increase due to anthropogenic activity for ozone cycle comes from the geographic distribution of rela- nitrate in Antarctica. Neither analogy explains the approximate tively recent nitrate values. The increase inland observed along twofold increase in nitrate since the early 1800s that is observed the Dumont dUrville-Dome C traverse (Legrand and Delmas in the Dominion Range record. It should be noted, however, 1985) and the relatively low concentrations measured from also that neither analogy provides definitive evidence of the coastal sites [e.g., mean 16 micrograms per kilogram on James increased flux of nitrate to the Antarctic due to anthropogenic Ross Island (Aristarain, Delmas, and Briat 1982); mean 40 mi- sources because of differences in transport style (lead analogy) crograms per kilogram on the Ross (Herron 1982) and and atmospheric residence time (nitrous oxide analogy) com- mean 42 micrograms per kilogram in northern Victoria Land pared to nitrate. (Allen et al. 1985)] compared to inland sites [e.g., range 65- As noted by Toon et al. (1986) and Hamill, Toon, and Turco 130 micrograms per kilogram at South Pole (Legrand and Del- (1986), polar stratospheric clouds which form at temperatures mas 1984) and range 35-265 micrograms per kilogram from of approximately 190°K could be composed of as much as 50 the Dominion Range (this study)] all tend to suggest that ni- percent nitric acid/water. Therefore, recent cooling of the strat- trate has a source which first enters the interior portions of osphere such as that observed over Syowa Station for the pe- Antarctica. Recent work which indicates that stratospheric air riod AD 1974-1985 (Chubachi 1986) could possibly have resulted descends during periods of ozone depletion (Hofman et al. in increased condensation of nitric acid in polar stratospheric 1988; Parrish et al. 1988) coupled with the knowledge that the clouds. Hofman et al. (1988) and Parrish et al. (1988) note that annual maximum in nitrate is an austral spring phenomenon during the period of ozone depletion, and within the geo- further substantiates the link between increases in nitrate in graphic area affected by the depletion, lower stratospheric air the ice sheet and ozone depletion at 12-20 kilometer altitude. appears to be transported downward. Thus, fallout of the con- Toward a more perfect ozone proxy record. While the Dominion densed nitric acid from polar stratospheric clouds may, in fact, Range record discussed in this paper is suitable as a pilot study be occurring directly onto the antarctic ice sheet particularly it cannot provide the quality of record needed to firmly dem- at as high as 85°S where the tropopause may be fairly onstrate and develop a proxy record of ozone depletion. How- close to the surface of the ice sheet. ever, South Pole provides an optimal site for such a study Examination of the Dominion Range oxygen record because: (figure 2) reveals a trend toward more negative values starting • it is within the ozone hole; at approximately the same time as the beginning of the increase • records of mean monthly total ozone are available that ex- in nitrate ionization. If the nitrate ionization trend we observe tend back to the period prior to the dramatic depletion (Kom- reflects the rate of condensation of nitric acid in polar strato- hyr et al. 1986); spheric clouds and the trend in nitrate is controlled by cooling • atmospheric column temperatures are available to compare in the stratosphere, the oxygen isotope signal measured in our with oxygen isotope measurements from snow/ice cores;

66 ANTARCTIC JOURNAL 350 would be extremely valuable for establishing the validity of oo any proxy relationship with ozone depletion. 325 Some nitrate measurements have been conducted at South \/ \F."\/\V Pole by Zeller and Parker (1981), Parker et al. (1982), and Le- a grand and Delmas (1984). These studies while all extremely valuable do not provide the appropriate data necessary to test a) 300 C for a proxy ozone record since the studies were developed for 0 (a) other purposes. The time-series of nitrate from these earlier 0 275 studies are either too low in resolution, are not substantiated 0 by companion measurements, and/or the measurements cover H0 too short a time period. 250 During the 1988-1989 austral summer we plan to sample a 6-10-meter snowpit covering several decades from a site 10- 225 I I1 1I 40 kilometers from South Pole to examine this issue further. 62 66 70 74 78 82 86 This site is close enough to South Pole so that the results can be directly compared with the South Pole records of ozone but 400 far enough away so that local contamination is minimized (Mayewski et al. 1987). Potentially this record could provide D details concerning the onset and temporal characteristics of 0 ozone depletion. Such future studies could dramatically ex- 300 /\, , C pand our spatial and temporal understanding of this problem. 0 N.J Z % (b) Acknowledgements. We would like to thank j.V. James (Glacier 0 Research Group), H. Rufli (), B. Koci and S. Wat- 0 son (Polar Ice Coring Office) for their help and friendship in 200 the field. PICO ably recovered the core. P. Grootes (University of ) kindly provided the iostopic oxygen-18 anal- 62 66 70 74 78 82 86 yses. We appreciate several useful suggestions made by B. Mosher. Thanks are also due VXE-6. 20 This research was supported by National Science Founda- tion grants DPP 84-00574, DPP 84-11108, and DPP 85-13699. 0 60 0 00 0 (c) Z 40 References 80 62 66 70 74 78 82 86 Allen, B., P.A. Mayewski, W.B. Lyons, and M.J. Spencer. 1985. Cia- ciochemical studies and estimated mass balance for Rennick Glacier 0 area, Antarctica. Annals of Glaciology, 7, 1-6. Aristarain, A.J., R.J. Delmas, and M. Briat. 1982. Snow chemistry of James Ross Island (), 1982. Journal of Geophysical Research, 87, 11,004-11.012. (d) Boutron, C.F., and C.C. Patterson. 1987. Relative levels of natural and anthropogenic lead in recent Antarctic snow. Journal of Geophysical Research, 92, 8454-8464. 62 66 70 74 78 82 86 Chubachi, S. 1986. On the cooling of stratospheric temperature at Year Syowa Station, Antarctica. Geophysical Research Letters, 13, 1221-1223. Crutzen, P.J., and F. Arnold. 1986. Nitric acid formation in the Figure 3. (a) South Pole mean October to February total ozone Antarctic stratosphere: A major cause for the springtime "ozone values (Komhyr et al. 1986), (b) Syowa Station October monthly hole," , 324, 651-655. total ozone (Sekiguchi 1986), (C) Dominion Range springtime (an- Hamill, P., O.B. Toon, and R.P. Turco. 1986. Characteristics of polar nual maxima) in nitrate, and (d) Dominion Range springtime (annual stratospheric clouds during the formation of the Antarctic ozone maxima) in chloride. (ppb denotes parts per billion.) hole. Geophysical Research Letters, 13, 1288-1291. Hao, W.M., S.C. Wofsy, M.B. McElro y, J.M. Beer, and M.A. Togan. 1987. Sources of atmospheric nitrous oxide from combustion. Journal of Geophysical Research, 92, 3098-3104. • mean annual temperatures (approximately - 59°C) assure Hofmann, D.J., J.M. Rosen, and J.W. Harder. 1988. Aerosol mea- preservation of the chemical record; surements in the winter/spring Antarctic stratosphere, 1. Correlative • stratigraphic markers such as oxygen , total beta- measurements with ozone. Journal of Geophysical Research, 93, 665- activity, and stratigraphy have been demonstrated to pro- 676. vide excellent chronological control over periods of decades; Herron, M.M. 1982. Impurity source of F, Cl , NO, , and SO2 in and Greenland and Antarctic . Jniriial of Geep/ulsical Research, 87, 3052-3060. • accumulation rates of approximately 0.26 centimeters per Holdsworth, G. 1986. Evidence for a link between atmospheric ther- year snow equivalent are low enough to allow the collection monuclear determinations and nitric acid. Nature, 324, 551-553. of decadal records from snowpits and shallow cores with Komhyr, W.D., R.D. Grass, and R.K. Leonard. 1986. Total ozone resolution on the order of 10-15 samples per year. We sug- decrease at South Pole, Antarctica, 1964-1985. Geophysical Research gest that nitrate and chloride measurements from South Pole Letters, 13, 1,248-1,251.

1988 REVIEW 67 Legrand, M., and R.J. Delmas. 1984. The ionic balance of Antarctic ancient Arctic and Antarctic ice. Geochimica et Cosmochimica Acta, 45, snow: A 10-year detailed record. Atmospheric Environment, 18, 1,867- 2,109-2,121. 1,874. Parker, B.C., E.J. Zeller, and A.J. Gow. 1982. Nitrate fluctuation in Legrand, M., and R.J. Delmas. 1985. Spatial and temporal variations Antarctic snow and : Potential sources and mechanisms of for- of snow chemistry in Terre Adelie Coast, Antarctica. Annals of Gla- mation. Annals of Glaciology, 3, 243-248. ciology, 7, 20-25. Parrish, A., R.L. Zafra, M. De Jaramillo, B. Connor, P.M. Solomon, Legrand, M., and R.J. Delmas. 1986. Relative contributions of tropos- and J.W. Barrett. 1988. Extremely low N 20 concentrations in the pheric and stratospheric sources to nitrate in Antarctic snow. Tellus, springtime stratosphere at McMurdo Station, Antarctica. Nature, 38B, 236-249. 332, 53-55. Mayewski, P.A., W.B. Lyons, M.J. Spencer, M. Twickler, W. Dans- Pearman, G.I., D. Etheridge, F. de Silva, and P.J. Fraser. 1986. Evi- gaard, B. Koci, C.I. Davidson, and R.E. Honrath. 1986. Sulfate and dence of changing concentrations of atmospheric CO,, N 20 and CH4 nitrate concentrations from a South Greenland ice core. Science, 232, from air bubbles in Antarctic ice. Nature, 320, 248-250. 975-977. Risbo, T., H.B. Clausen, and K.L. Rasmussen. 1981. Supernovae and Mayewski, PA., M.J. Spencer, W.B. Lyons, and M. Twickler. 1987. nitrate in the . Nature, 294, 637-639. Seasonal and spatial trends in south Greenland snow chemistry. Schoeberl, M.R., and A.J. Krueger. 1986. Overview of the Antarctic Atmospheric Environment, 21, 863-869. ozone depletion issue. Geophysical Research Letters, 13, 1,191-1,192. McCormick, M.P., and J.C. Larsen. 1986. Antarctic springtime mea- Sekiguchi, Y. 1986. Antarctic ozone change correlated to the strato- surements of ozone, nitrogen dioxide and aerosol extinction by SAM spheric temperature field. Geophysical Research Letters, 13, 1,202-1,205. II, SAGE, and SAGE II. Geophysical Research Letters, 13, 1280-1283. loon, O.B., P. Hamill, R.P. Turco, and J. Pinto. 1986. Condensation McElroy, M.B., R.J. Salawitch, and S.C. Wofsy. 1986a. Antarctic 03: of HNO3 and HC1 in the winter polar stratospheres. Geophysical Chemical mechanisms for the spring decrease. Geophysical Research Research Letters, 13, 1,284-1,287. Letters, 13, 1,296-1,299. Wofsy, S.C., M.J. Molina, T.J. Salawitch, L.E. Fox, and M.B. McElroy. McElroy, M.B., R.J. Salawitch, S.C. Wofsy, and J.A. Logan. 1986b. 1988. Interactions between HCI, NO N, H2O ice in the Antarctic strat- Reduction of Antarctic ozone due to synergetic interactions of chlor- osphere: Implications for ozone. Journal of Geophysical Research, 93, ine and bromine. Nature, 321, 759-762. 2,442-2,450. Murozumi, M., T.J. Chow, and C.C. Patterson. 1969. Chemical con- Wolff, E.W., and D.A. Peel. 1985. The record of global pollution in centrations of pollutant lead aerosols, terrestrial dusts and seasalts polar snow and ice. Nature, 313, 535-540. in Greenland and Antarctic snow strata. Geochimica et Cosmochimica Zeller, E.J., and B.C. Parker. 1981. Nitrate ion in Antarctic firn as a Acta, 33, 1,247-1,294. marker for solar activity. Geophysical Research Letters, 8, 895-898. Ng, A., and C.C. Patterson. 1981. Natural concentrations of lead in

Detailed glaciochemical investigations for time periods of 10 to 100,000 years. Analysis of the physical and chemical components of ice and snow such as: stratigra- in southern Victoria Land, Antarctica— phy, stable isotopes, radio-nuclides, and primary anions and A proxy climate record cations can all be very effective in determining, on seasonal to multi-year levels, extremely detailed proxy records of climatic change, atmospheric chemistry, and volcanic activity. The production of climatic change records using time-series PAUL A. MAYEWSKI and MARK S. TWICKLER retrieved from ice cores has seen minimal application in the Transantarctic Mountains even though glacial geologic studies Glacier Research Group in this area provide one of the primary bases for understanding Institute for the Study of Earth, Oceans, and Space the glacial . Notably while the glacial geo- University of New Hampshire logic records provide relatively low-resolution, long-period Durham, New Hampshire 03824 records, the ice core records could provide an excellent view of an albeit shorter period but with relatively high resolution. Therefore, detailed ice-core records provide the resolution nec- Advances in climate prediction depend on a knowledge of essary to assess, expand, and utilize the longer, less-detailed historical climatic sequences ranging in scale from decades to glacial geologic records and more importantly allow us to com- millennia. Proxy data produced by , , tree rings, pare in detail the modern environment in Antarctica with the glacier fluctuations, and ice and snow cores are valuable in the paleoenvironment adding significantly to our understanding construction of climatic sequences when direct observations of of global change. the atmosphere are either spatially or temporally lacking. Links Three primary ice core sites were chosen for investigation between proxy data and the atmosphere generate the most during the 1987-1988 field season: the Royal Society Range, confidence when actual components of climate are preserved head of Emmanuel Glacier (approximately 78°07S approxi- in the proxy medium. mately 161°35E, approximate elevation 3,000 meters); the As- The best preserved data pertaining to former climate is found gaard Range, head of Newall Glacier (approximately 77°37S in the time-series available from snow and ice cores retrieved approximately 162°30E, approximate elevation 1,700 meters); from appropriately chosen glaciers. Records from polar and and the Convoy Range in the general area of Staten Island high-altitude, low- to middle-latitude glaciers have proven Heights/Dotson (approximately 76°50S approximately valuable in obtaining time series relatable to climatic change 161°30E, approximate elevation 1,500 meters).

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