PRELIMINARY INVESTIGATION ON EOLIAN PARTICULATE FROM WESTERN TERRA NOVA BAY, ANTARCTICA

G. GASPARO'ITO*, S. GUERZONI* *, V. LANDUZZI* *, R. LENAZ* *, U. SIMEONI* * *, M. TAVIANI* * L. TOMADIN** ** and G. VALDRÈ*

* Dipartimento di Scienze Mineralogiche - Università di Bologna, ltaly ** Istituto per la Geologia Marina, C.N.R. - Bologna, Italy

*** Dipartimento di Geologia e Paleontologia - Università di Ferrara, Italy **** Istituto di Mineralogia e Yetrografia - Università di Urbino, Italy

Summary. Wind-blown materials collected by mesh-panels in the lower atmosphere at Terra No- va Bay have been investigated. Roughly estimated dust-loadings range from 1 1 to 1 3 9 nglm 3, i.e. three orders of magnitude lower than in samples collected at mid-latitude. Present data are, on the contrary, much higher than those reported in the antarctic literature. Grain-size, mineralo- gy and elemental analysis point out the important contribution of "giant" particles of local source (from the surrounding ouicrops, moraines and beach deposits). In addition, variable amounts of clay minerals, whose sedimentological signitìcance is under study, were detected. Numerous spherical particles of probable cosmic origin and several biogenic fragments (diatoms) have been recognized.

Riassunto. Materiali eolici daiia bassa atmosfera di Terra Nova Bay sono stati campionati per intercettazione mediante tele. Stime ponderali del particolato recuperato variano d a 1 1 a 1 3 9 nglm 3, e sono di tre ordini di grandezza inferiori a quelli riscontrati alle medie latitudini. Sono tuttavia assai maggiori dei valori riportati nella letteratura sulì'Antartide. Le dimensioni granulo- metriche, la composizione mineralogica ed elementare del particolato hanno messo in evidenza la prevalenza di particelle grossolane di origine locale (da rilievi circostanti e d a depositi morenici e di spiaggia). Sono inqltre sempre presenti modesti tenori di minerali a r d o s i , la cui provenienza deve essere studiata. E stata segnalata la presenza di numerose particelle sferiche di probabile origine cosmica, ed anche di frammenti biogenici (diatomee).

Received November 30, 1988

1. Introduction In order to contribute to the understandine of the i m ~ a c t of wind-blown ~articles "

in Antarctica, an experiment (Eoloantartide Project: Gasparotto et al., in prep.) has been started in Terra Nova Bay (Northern Victoria Land). During the 3rd Italian Expedition (austral summer 1987-88), a station for dust sampling has been located uphill the Italian Base Station, at about 85 m above m.s.1. (Northem Foothills, Victoria Land, Ross Sea, with coordinates Lat. 74' 41' 42" S, Long. 164' 07' 23" E). The station has been secured to the ganitoid bedrock by steel wires (Simeoni and Taviani, in prep.). Its posi- tion was choosen in order to fulfil the following requirements: easy logistics, suitable po- sition on a deglaciated area not far from many potential particle sources, within a radius of about 40 km, including: a vast area of granitoid igneous (Granite Harbour intrusives) and metamorphic bedrocks (Wilson Terrane Metamorphics), young volcanics (including abundant loose pyroclastics) of the Mt. Melbourne (McMurdo Volcanics), moraines, beach . .

deposits, sea spray.

2. Wind in the sedimentary processes of Antarctica Wind is an important geological factor, modeling rock surfaces and contributing to

the formation and transport of clastic sediments. This is especially true for arid and se- miarid regions, such as deserts, where the wind may r e d y be one of the dominant agents

in controlling the evolution of the geologica1 landscape. Therefore, it is intuitive the im- portante of the wind also in Antarctica, one of the two largest deserts of the world and the domain of strong winds (Schwerdtfeger, 1984). Differently from warm deserts, the "cold desert" (Markov, 1956) is however largely prevented to be site of major wind- blown sediment transport and landscape modelling because only a smail percent (2-3%) of the whole surface (ca. 1 4 million km ') is exposed, being - at least part of the year - ice or snow free. On deglaciated areas (oases and nunataks) wind is anyway a powerful agent as testified by rock disintegration, abrasion and polishing, ventifacts, eolian pave- ments and other wind-linked phenomena (e.g., Wade, 1945; Webb and McKelvey, 1959; Pewe, 1960; Nichols, 1961a, 1961 b, 1966; Berg and Black, 1966; Tedrow and Ugoli- ni, 1966; Thornbury, 1969; Campbell and Claridge, 1975, 1987; Selby et al., 1973; Selby, 1977; Vennun, 1980; Glasby et al., 1981; Whitney and Splettsteosser, 1982; Orombelli, 1986). Well documented is also the removal and redistribution of even coar- se particles in relation to stroqg winds, with the occasiona1 formation of sand sheets or even dunes (Twenhofel, 1932; Avsiuk et al., 1956; Webb and McKelvey, 1959; McKel- vey and Webb, 1961; Nichols, 1961b, 1966; Allen and Gibson, 1962; Gibson, 1962; Calkin, 1964; McCraw, 1967; Cailleux, 1968; Lindsay, 1973; Murrell, 1973; Selby et al., 1974). Thus, on theoretical grounds, wind-blown particles appear to be a possible contributor to the sedimentaw budeet of Antarctic marine and lacustrine sedimentaw

u

basins. Its actual importance derives also by the fact that the primary fluvio-lacustrine mechanism of transport and unloading of sediment, active at low and middle latitudes, is virtually absent in Antarctica where water is mostly stored as ice and snow; thus. mi- nor sediment sources (such as the eolian one) assume by comparison an enhanced rele- vance, although the overall importance of eolian deposits has been questioned (Nichols, 1953; 1966). Not clear yet is when the maximum transport takes place, because although in winter time the winds would be more favourable for eolian transportation (see, for example, Nichols, 1966), the low temperatures and the snow cover could inhibit the be- drock erosion.

The importance of a wind-blown component is sometimes claimed by authors con- cerned with Antarctic sedimentation (e.g. Barrett et al., 1983); under such respect it is worth to mention the contributions of Bentley (1979), Porter and Beget (1981) and Barret et al. (1984) who carried out grain size, texture and microfabric analyses of sand particles of suspected eolian origin within cores. However, the volumetrical contribution of wind-blown particles to the marine total sedimentary budget cannot match the ones deriving by glacier activity and, increasingly offshore, by biogenic production which lar- gely overwhelm any other sediment supply (e.g., Lisitzin, 1962; Anderson et al., 1979, 1982, 1984; Ledford-Hoffman et al., 1986); wind-blown sedimentation may be quanti- tatively important only in nearshore coastal areas (cf. Barrett et al., 1983).

Different considerations have to be made for submicronic particles transportation to Antarctica. Most of the authors that studied antarctic aerosols underline that the area produces few native aerosols, and that most of them are imported from a distance (Pa- rungo et al., 1979; Parungo et al., 1981 ; Ito, 1985). The particle concentration is extre- mely low and many of the aerosols are so small that they are difficult to capture by impaction (Shaw, 1988). Large (> 0.4, < 2 microns) ~ar t ic les are estimated, in order of importan- ce, to have come from: (i) unidentified sulfate sources; (ii) oceanic sources; (iii) arid re- gions in the southern hemisphere; (iv) extraterrestrial sources, and (v) oases on the continent (Shaw, 1979).

Many attempts have been made to trace increases in global pollution, but very few data are available on pollution problems in the South Pole. Cunningham and Zoller (1981) stated that there was no evidence for a change due to anthropogenic emissions. The sa- me conclusion, at least for trace metals, was drawn by Parungo et al. (1981) and Wolff and Peel (1985).

3. Sampling and analytical procedures To investigate the insoluble particulate from the lower atmosphere of Terra Nova

Bay, a sampling techiqiie by mesh-pannels was adopted. This was already used in or nearby the marine environment and, in spite of the well-known cut-off of finest fractions (Prospero, 1981; Tomadin et al., 1984; Chester, 1986), the collected dust gives relia- ble information on the mineralogy of the wind-blown particulate. In the present case, the local severe conditions enphasize the easy installation of the system, not requiring energy sources and not giving contamination by exhausts.

Wind records were obtained from the meteorological station "Eneide" located very close to the sampling device (Lat. S 74' 41' 37", Long. E 164' 06' 35"). After each sampling period (17-52 hours) the mesh-panels were sealed and sent to the laboratory for analysis. The particulate was collected in an ultrasonic vessel, and the solid and li- quid fractions kept separated for analyses.

Mineralogica1 and chemical analyses' were performed by X-ray diffraction and by SEM and EDS. The analysis of the solubile fraction is underway.

4. Results and discussion 4.1 Surface winds

In Antarctica the surface winds are decisive for outside working and living condi- tions (New Zealand Antarctic Research Programme, 1987). They are also important with respect to the eolian dusts collected by mesh-panels. Anywhere else on the plateau, the surface winds blow persistently from a direction wich depends on the orientation of the ice surface topography. Near the base of a steep mountain massif or the coastal escarp- ments of a plateau, there can be found;

(i) katabatic winds, starting either with a rise of temperature (Foehn-type), or with an arrival of colder air (Bora-like);

(ii) barrier winds, with the air moving essentially parallel to a mountain range or wail;

(iii) frequent calms, also in presence of a large-scale horizontal pressure gradients;

(iv) a "funnel" effect, in coastal regions, between the land and nearby islands, that can affects wind speed and direction more than 100 km downwind (Schwerdtfeger, 1984).

An important parameter is the directional constancy of the wind, called "q", defi- ned by the ratio of the magnitude of the resultant wind (the vector mean of a time series of wind values at a given place and height) divided by the mean wind speed. A value of q = 1 would mean that al1 wind measurements in the respective period of time indicate the same direction, with only a possible variation in speed.

"Surface" winds have to be measured at the 1 0 m leve1 about ground, and reported every three hours.

The frequency of calms (in % of all observations) is also important for windlsam- pling statistics.

4.2 Sampling data Twelwe samples of atmospheric particulate were collected in the period January 26th-

February 2nd, 1988. The measured wind directions and wind speeds show that collec- ted dusts are representative of the average summer antarctic climatology.

Wind conditions and sampling data are reported in Table 1 .

During the total sampling time (335 hours) the following conditions were observed:

(a) 34% of cases with wind direction from the Transanctarctic Mountains (catabatic winds). Representative of this category are severa1 stations near the coast of East Antarc- tica at which much in situ research has been carried out.

Table 1 - Wind conditions, sampling data and dust-loadings of partieulate colieeted by meeh-panels. Terra Nova Bay, Antaretica (January 26th-February 2nd, 1988).

simple Wind coodit. Wind speed Simpling Wei8ht or dust loadin@ N. orev. direci. m18 (houn) dust (ma) ( w l m 3,

O1 variable 52 36.6 18 02 (a) N W 10-13 20 34.1 29 03 W 24 54.3 54 04 W 24 16.6 1 1 05 (b) calm < 2 48 21.8 53 06 calm+NW (4h) 23 10.6 40 07 calm + NW (6h) 24 13.1 30 08 calm 23 33.1 139 09 calm 30 18.8 5 1 10 (C) S-SE 2-5 17 41.8 121 1 1 NW 30 38.5 28 12 variab.lN (9h) 20 38.3 81

(a). (b) nnd ( C ) are the "end-members" mentioned in the text.

(b) 45% of cases with low-intensity winds (< 2m/sec), favourable for indirect tran- sportation of dusts already in suspension in the lower atmosphere;

(C) 7% of winds arriving from the Ross Ice shelf (barrier winds) or the Ross Sea. The barrier winds need particular geographic conditions to be formed; the Transantarc- tic Mountains, south of 77' Lat., are very suitable, but even more south the cpnditions are still favourable for the development of minor barrier winds.

(d) 5% of episodes from other mixed directions. Three samples, selected as representative of contrasting wind conditions during sam-

pling, are the "end-member" of above described situations (see Table 1 and Fig. 1): (a) sample n. 02, with little to ordinary katabatic winds (10-13 mlsec); from N-NW, (b) samples n. 05, collected with calms, for period longer than a day, and low winds

(< 2 mlsec). from heterogeneous directions;

m 1s O 2.5 5.0 - O 5.0 10

K t s

Fig. 1 - Diagram showing directions and wind speed during the coìiection of dust samples N. 2 .5 and 10.

Fig. 2 - Secondary Electron 1mage'(marker 10 pm): Biotite.

(C) sample n. 10, with barrier winds, from E-SE, speed of 2-5 mlsec, and a small marine contribution.

4.3 Dust loading The amount of dusts collected was ranging from 11 and 54 mg during variable sam-

pling time (see Table 1). A comparison with mid-latitude data shows that the weights of collected particulate are three orders of magnitude lower than the average values found in the Mediterranean Sea (Lenaz et al., 1988).

Because of the limits of dust collections made by a mesh technique, the dust loa- dings of Table 1 represent estimates of the lower limit particle concentration in the atmo- sphere of Terra Nova Bay.

A rough estimation of dust loadings (Table 1) was made using the following equa- tion: C (ng/m3) = P / (V . H . A ) , where P is the total weight of the sample, V is the average wind speed (mls); H is the time (s) of each sampling, and A is the area of the mesh-panels (m 2).

Table 2 - Mineralogica1 composition of the particulate (whole sample) collected by mesh-panels.

Sample N. Q1 P1 K-Feld Cal Do1 A M CM

O 1 XX t r tr - - - - X 02 XX X X - - - XX XX 03 XX X X - - X X 04 XX X X - - - X X 05 XX X X - - - X X 06 X - XX - - - - tr 07 XX X X - - - X X 08 X tr tr X X - - X 09 XX X X - - X X XX 10 X tr tr X X - - X 1 1 XX tr tr - X - - X 12 XX X tr - X X X

Qt: quartz; PI: plagioclase; K-feld: K-feldspar; Cal: Calcite; Dol: dolomite; A: amphibole; M: mica; CM: clay minerals; tr: trace; X: present; XX: abundant.

143

O 3 6 9 12 15

E N E R G Y I K V )

Fig. 3 - Zircon (ZrSio 4) (above): Secondaw Elertron Image (marker 10 pm): (below): Backscattered Elec- tron Image.

The average dust loadings were correlated with the wind provenance and speed. In- creasing values have been measured by winds turning from N-NW ( - 3 0 nglm 3, to E- SE (- 120 nglm 3), with variable values for calms and mixed barrierlmarine winds (Ta- ble l ) .

Chester (1986) described a latitudinal contro1 on mass concentrations over the Atlantic Ocean and sorrounding waters, with values decreasing towards the high latitudes. The present investigation gives, on the contrary, higher values in comparison with those pre- viously published on the atmosphere of Antarctica. Here, according to Maenhaut et al. (1979) and Cunningham and Zoiler (1981), the concentration of mineral particulate could fall to values as low as 2 nglm of air. Because of the samplivg site location, close to the Transantarctic mountains, the obtained data indicate a remarkable supply from local sources.

4.4 Mineralogica1 and elemental composition The particulate coilected by mesh-panels is mainly composed by large-sized mate-

ENERGY ( K V )

Fig. 4 - Fe spherical particle (above: Secondary Electron Irnage; marker I gm; below: Backscattered Electron Irnage).

rials (> 4 pm), as was determined splitting by sedimentation each sample in severa1 grain- size fractions. Analytical data of Table 2 show the mineralogy of the whole sample by X-ray diffractometry on dust - and oriented - mounts (smear-slides).

Quartz, feldspars and mica are the most important components of the insoluble par- ticulate. Quartz is generally present in constant amounts. Feldspars (both plagioclase and K-feldspars were determined) and high-cristalline muscovite are - on the contrary - su- bordinate. Calcite and dolomite were recoanized in few samvles and amvhibole in onlv

L,

one case (sample n. 09). Scarce but variable amounts of clay minerals characterize the atmospheric dust of Terra Nova Bay. Their study is presently undenvay, to investigate the possible contribution as natura1 tracers. Analyses by SEM and X-ray energy dispersi- ve spectrometry, have been performed. Minerals like biotite (sample n. 02, Fig. 2) and zircon (sample n. 05, Fig. 3) and moreover numerous spherical particles of variable grain- size (2-20 um) and composition (see Figs. 4 and 5) were recognized. According to Pa- rungo et al. (1981), the most important elements observed in these spherules are Fe (and Si, Al) in Fig. 4, or Mg (and Si, Al) in Fig. 5. The absence of Ni in the elemental

ENERGY ( K V )

Fig. 5 - Si, Al spherical particle (above: Secondary Electron Image; marker 1 pm; below: Backscatiered Electron Image). Noie the biogenic particle in the lower part of ihe photograph.

composition do not permit to refer the spherules to micrometeorites. Particles with only Fe and Si have already been detected in the atmopheric particulate of Antarctica (Parun- go et al., 1979). Considering however the absence of micropedogenetic features as weli as of high-temperature and vapor-phase patterns, a cosmic origin as siderite andlor side- rolite seems probable.

In the sample n. 10, collected with prevailing E-SE winds (Ross Sea), some organic Si-.and P- rich particles were obsemed (see Figs. 5 - particvlar - and 6). Organic mate- rial from aerosol particles (5-7 um in diameter) was studied by Saxena et al. (1985), who was able to recognize abundant organic materia1 such as phytoplancton, and to rela- te its origin to the Ross Sea. Rare siliceous ceii walis belonging to some unknown dia- toms have been found in sample n. 10 (Fig. 5), pending their exact taxonomic position, a tentative suggestion is that they represent remobilized pack-ice flora.

,o X)

ENERGY (UV)

Fig. h - Biogenic particle (ahove: Secondary Electron Image; marker 10 pm; below: Backscattired Elrc- tron Imagr).

The mineralogy of the present atmospheric dust permits to recognize that the main source of the largest particles are the Transantarctic Mountains. The outcrops of Terra Nova Bay, dominated by granitoids and metamorphics (Skinner, 1983; Carmignani et al., 1988), are in fact the most important suppliers of the wind-blown rnaterials collected by mesh-panels during the investigated period. Moreover other potential sources of dust particles are morain deposits, modern and raised beaches (Nichols, 1966).

More difficult to explain is the presence of carbonates in some eolian dust (Table 2). Severa1 possibilities of surlìcial dissolution and precipitation have been discussed (Carnpbelì and Claridge, 1987), even if of local significante. Another possible source, however, could be the marble beds of the Priestley Schist oucropping at Cape Sastrugi and Mt. Browning (Skinner, 1983).

No evidence of anthropogenic components in the sarnples was detected, in relation to the grain-size range of collected particulate.

5. Conclusions

Eolian dust collected by mesh-panels at Terra Nova Bay were investigated. Dust- loadings, mineralogical and elementai composition have been related with prevailing winds during the sampling period. The measured dust-loadings show an increase with winds turning frorn N-NW ( - 30 nglrn 3, to E-SE ( - 120 nglm 3), and variable values related to calms and mixed barrierlrnarine winds. All these values are higher than data reported in the literature for the Antarctica. This fact is depending on the different sampling me- thod here adopted and on the location of the station, which is very close to the Transan- tarctic Mountains.

The present data enphasize the importante and the composition of "giant" particles of "local" source. However, the constant presence of small amounts of clay minerals, will permit to investigate the possible "remote" source of the finest wind-blown materials.

The analytical data available up to now show a moderate eolian supply to the present sedimentation of the investigated area.

Acknowledgementa. We thank M. Righini and E. Guzzini for their cooperaiion in assembling the station. - C. Giudici, R. Ocone and A. Pellegrini provided meteorological records. G. Marozzi cooperate i n photogra-

phic work. This is 1GM scientific contribution n. 705.

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Giorgio Gasparotto and Giovanni Valdré, Dipartimento di Scienze Mineralogiche, Università di Bologna, P.za di Porta S. Donato. 40126 Bologna, Italy.

Stefano Giierzoni, Vladimiro Landuzzi, Renzo Lenaz and Marco Taviani, Istituto per la Geologia Marina (C.N.R.). via Zamboni 65, 40127 Bologna, Italy.

Umberto Simeoni. Dipartimento di Geologia e Paleontologia, Università di Ferrara, Corso Ercole I d'Este 32, 44100 Ferrara, Italy.

Luciano Tomadin, Istituto di Mineralogia e Petrografia. Università di Urbino, via M. Oddi 14, 61029 Urbino, Italy.