Biogenic Sulfur in the Environment - ACS Publications - American

Chapter 21

Distribution of Biogenic Sulfur Compounds in the Remote Southern Hemisphere 1

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H. Berresheim , M . O. Andreae , G. P. Ayers , and R. W. Gillett

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School of Geophysical Sciences, Georgia Institute of Technology, Atlanta, GA 30332 Max-Planck Institute for Chemistry, Mainz, Federal Republic of Germany Division of Atmospheric Research, Commonwealth Scientific and Industrial Research Organization, Mordialloc, Australia

Downloaded by RUTGERS UNIV on May 29, 2018 | https://pubs.acs.org Publication Date: April 27, 1989 | doi: 10.1021/bk-1989-0393.ch021

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The Southern Ocean south of 40°S has been considered to be a potentially major source of biogenic sulfur compounds to the remote atmosphere due to reported high primary productivity rates and intensive winds in these latitudes. Most of this area is remote from man-inhabited continents. Therefore it offers the possibility to study the natural atmospheric sulfur cycle without major interferences by continental air masses. In this paper we discuss measurements of atmospheric and seawater concentrations of dimethylsulfide (DMS) which were made on a cruise across the Drake Passage and in inshore waters of Antarctica. The annual DMS emission from the Southern Ocean to the atmosphere is estimated to be 0.2 Tmol yr . Some data for atmospheric methylmercaptan (MeSH) concentrations are also reported. We further report measurements of vertical distributions of atmospheric DMS which were made during flights over the west coast of Tasmania. During both field expeditions we also determined the atmospheric concentrations of the DMS oxidation products sulfur dioxide (SO ), methanesulfonic acid (MSA), and non-sea-salt sulfate (nss-SO42-). The results suggest a higher yield of MSA and a lower yield of SO from D M S oxidation compared to other world ocean areas. -1

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The global natural flux of sulfur compounds to the atmosphere has recently been estimated to be about 2.5 Tmol y r (1) which is comparable to the emissions of sulfur dioxide (SO2) from anthropogenic sources (2). A substantial amount of the natural sulfur contribution (0.5-l.z Tmol y r ) is attributed to the emission of dimethylsulfide (DMS) from the world's oceans to the atmosphere (3.4). One of the major uncertainties in this estimate is due to a scarcity of DMS and other sulfur data from the Southern Hemisphere, particularly the Southern Ocean region between about 40°S and the Antarctic continent, which represents about one fifth of the total world ocean area. Very high primary productivity rates have been reported for the coastal and inshore areas around the Antarctic continent (5.6). Recently, high densities of phytoplankton species like Phaeocystis poucheti, which is known to be an important source for marine DMS (7.8) have been observed in the same areas (2). On the other hand, strong winds which are associated with the intensive 1

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0097-6156/89/0393-0352$06.00A) 1989 American Chemical Society

Saltzman and Cooper; Biogenic Sulfur in the Environment ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

21. BERRESHEIM ETAL.

Distribution ofBiogenic Sulfur Compounds

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circum-Antarctic weather systems prevailing between 40°-60°S are very common in these latitudes. One may therefore expect high DMS emission rates from the Southern Ocean, with even a temporary depletion of DMS levels in surface seawater due to strong ventilation, which may significantly contribute to the atmospheric sulfur cycle of the remote Southern Hemisphere. Once DMS is emitted into the atmosphere it will eventually be oxidized by O H or NO3 radicals to sulfur dioxide (SO2), methanesulfonic acid (MSA), ana, via SOo oxidation, to non-sea-salt sulfate (11SS-SO4 -) as major reaction products (e.g. 10,11). The Southern Ocean represents a relatively unpolluted marine environment. It offers a unique possibility to study the natural sulfur cycle in an atmosphere far remote from man-inhabited continents. In this work we compare some of the major results from two field expeditions to the Southern Ocean region. The first expedition was a ship cruise between Punta Arenas/Chile and the west coast of the Antarctic Peninsula, which was conducted during the austral fall season (March 20 - April 28,1986) as part of the United States Antarctic Research Program (USARP). Details of the ship cruise and a complete discussion of the results have been published elsewhere (12). The second expedition consisted of a series of flight measurements off the west and south coast of Tasmania during the austral summer season (December 3-18,1986). We discuss preliminary results from 2 of 8 flights which were conducted in marine air masses behind cold fronts moving over the open ocean.


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Experimental The determination of DMS in seawater and in the atmosphere has been described in detail elsewhere (12-14). Methods used to determine atmospheric concentrations of MeSH, SO2, MSA, and 11SS-SO4 - have also been discussed in previous publications (12.15). A brief summary is presented here. DMS dissolved in seawater was purged from 10-15 ml samples by a helium carrier gas stream, passed through a K2CO3 drying column, and then trapped cryogenically on a chromatography column (15%> OV3 on Chromosorb W AW-DCMS 60/80 mesh) which was immersed in liquid nitrogen. After removal of the liquid nitrogen the DMS was separated from interfering compounds by controlled heating of the G C column and was then detected by flame photometric detection. An atmospheric DMS sample was obtained by preconcentration on ca. 2g gold wool enclosed in a quartz glass sampling tube. Before entering the sampling tube the sample air first passed through a preconditioned scrubber material (5% Na2CX>3 on Anakrom C22, 40/M) mesh) to remove SO2 and strong oxidants like ozone. Samples were taken in duplicate. In the laboratory the DMS was transferred to the G C column after heat desorption from the gold wool under a helium or hydrogen carrier gas flow and then analyzed as described previously. For the analysis of MeSH 1 ml propyliodide vapor was added to the carrier gas prior to the heat desorption step to convert MeSH into ropylmethylsulfide which is more stable and easier to detect. A l l DMS and leSH analyses were calibrated using permeation devices (Metronics, Dynacal). Particle-bound MSA and n s s - S 0 4 " collected in a two-stage aerosol filter sampler using a Nuclepore filter (diameter: 47 mm, nominal pore size: 8.0 /*m) on the first stage and a Zefluor filter (Gelman, diameter: 47 mm, nominal pore size: 2.0 pm) on the second filter stage. The aerosol particles were thereby separated into coarse andfine-modeparticles (particle cutoff diameter: 1.5 nm). SO2 was trapped on a third stage consisting of a K2C03/glycerol impregnated membrane filter (Schleicher and Schuell, FF#2, diameter: 25 mm). The aerosolfilterswere leached out with 10 ml of 18 megohm deionized water. The 2

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impregnated filters were treated with 10 ml of 0.06% H 0 to convert sulfur (IV) to sulfate. A l l solutions were analyzed on a Dionex ion chromatograph (model 2020i). The overall precision of the filter measurements was between 10-20%, with the uncertainty largely due to die filter blank corrections. In this work all concentrations are reported in units of nanomole per cubic meter (nmol nr ) at 20°C and 1013 hPa, and/or as parts per trillion by volume (pptv) with 1 nmol n r corresponding to 24 pptv. 2

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Results and Discussion


Ship Cruise Measurements Figure 1 gives an overview of the cruise tracks and the DMS sampling stations in the Drake Passage and in Bransfield Strait. The land base in Antarctica was Palmer Station on Anvers Island. Most of the measurements were made in open ocean areas (Drake Passage) and in the inshore areas of Gerlache Strait. Ten-day isobaric back-trajectories were calculated for each day of the cruise (Harris, J., personal communication, 1986) indicating that air masses were predominantly advected from the open South Pacific Ocean. Wind velocities over the Drake Passage ranged between 3-30 m s , whereas in the inshore areas they never exceeded 10 m s* . During about 70% of the cruise period the weather was characterized by overcast conditions with occasional snowfall and fog episodes. A high pressure weather situation occurred between April 8-14 which was responsible for sustained cloud-free conditions with intense daylight during this short period. Surface seawater temperatures were typically around 8°C in the Subantarctic and 2°C in the Antarctic and inshore waters, whereas air temperatures were around -0.5°C and showed much less latitudinal difference. Table I summarizes the results of the DMS and MeSH measurements in the major study areas. No significant differences in the concentrations were found between the individual areas. The average surface seawater D M S concentration was 1.80 nmol l " which is comparable to values observed in temperate latitudes and in oligotrophic areas of the world's oceans (!£). This is consistent with lower primary productivity rates in the study areas during austral fall relative to spring and summer conditions (7,17). Exceptionally high DMS concentrations in seawater (6-9 nmol H ) were measured in Gerlache Strait during periods with intense daylight conditions between April 9-14 and April 18-19, which likely caused a strong increase in primary productivity and hence, DMS production rates. Generally the DMS distribution in surface seawater was very patchy, particularly in the inshore areas. No regular diurnal variations were observed. High concentrations were often found in the vicinity of icebergs, which is consistent with reports that sea ice may be an ideal growth medium tor certain algal species (18). Measurements in areas with high krill populations, or in krill-rich water basins at Palmer Station did not show a significant production of DMS by these animals, as one may have suspected from reports about high DMS concentrations in frozen body tissue of krill (12). Only decomposition processes of dead krill produced significant levels of DMS and dimethyldisulfide (DMDS). Both MeSH and DMDS were observed in some seawater samples but could not be quantified due to the lack of a reliable calibration procedure. However, from the obtained chromatograms we estimate the concentrations did not exceed a few percent of those of DMS. The average atmospheric DMS concentration was 4.4 nmol n r (106 pptv), similar to the global mean value over the world's oceans (4.7 nmol nr* 14). MeSH concentrations were mostly below the detection limit (0.03 nmol nr ). Measurable MeSH values were frequently observed in coincidence with high _1

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21. BERRESHEIM ET AL.

Figure 1. Overview of the cruise track in the study area and DMS sampling locations in the Drake Passage and in Bransfield Strait. Cruise legs in the Drake Passage (1986): I, March 21-24, II, March 28-29, III, March 30-31, IV, April 2427; Circles indicate stations including both air and seawater samples, triangles seawater samples only, squares air samples only, and hatched areas represent multiple adjacent stations where air and/or seawater samples were taken. (Reprinted with permission from Ref. 12. Copyright 1987 by the American Geophysical Union).


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Table I. Concentrations of DMS and MeSH in Air and DMS in Surface Seawater in the Cruise Area During Austral Fall Sampling Region

DMS(air) (nmol nr )

DMS(seaw.) MeSH(air)* (nmol I/ ) (nmol nr )

Mean±s.d Range n

4.8+1.9 1.7-8.3 23

1.9±0.5 0.7-3.2 31

Gerlache Strait

Mean±s.d. Range n

4.4±2.5 0.7-9.8 80

1.8±1.2 0.6-8.6 104

Biogenic Sulfur in the Environment - ACS Publications - American

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