Magnetotactic bacteria and their magnetofossils in sediments

Earth and Planetary Science Letters, 86 (1987) 389-400 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

389

Ill

Magnetotactic bacteria and their magnetofossils in sediments H. Vali

1,20.

FOrster

2, G.

Amarantidis 2 and N. Petersen 3

1 Institut fiir Technische Chemie, Technische Universitiit Miinchen (F.R, G.) 2 Lehrstuhlfiir Angewandte Mineralogie und Geochemie, Technische Unioersitiit Miinchen (ER. G.) 3 lnstitutfiirAngewandte undAllgemeine Geophysik, Ludwig-Maximilians Universitiit Miinchen (F.R.G.)

Received June 30, 1987; revised version accepted September 14, 1987 Living magnetotactic bacteria from freshwater environments show, under natural and laboratory conditions, a great variety of morphological appearances. Their magnetosomes vary in number, shape, and size. One species of bacteria yields up to 1000 magnetosomes per cell. Individual particles reach a size of up to 200 nm. As a rule, they form elongated chains. In bacteria which are held under laboratory conditions, loop-shaped arrangements and nearly unordered clusters are also found. During the laboratory experiments, different species of bacteria periodically dominated. Freshwater samples always exhibited a great variety of different magnetosomes. On the other hand, samples from marine environment clearly showed the preponderance of one type of particle. These observations may reflect specific properties of the physico-chemical milieu in which the bacteria grew. At the end of our experiments north- and south-seeking bacteria co-existed in roughly equal quantities. Quaternary unconsolidated sediments from the Ammersee (Bavaria) and the Antarctic, Quaternary to Tertiary deep-sea sediments from the Atlantic and Pacific, and Jurassic limestones from the Sonnwendgebirge (Tyrol, Austria) were analyzed for fossil magnetosomes. We found that fossil magnetosomes were morphologically similar to those from living bacteria, but seemed to be corroded in some cases. The observed differences in quantity, size and shape of magnetosomes from various sediments may be influenced by variations in bacterial viability and particle stability at different sites, but are not determined by geographical latitude.

1. Introduction Bacteria which can navigate in the m a g n e t i c field of the e a r t h were first d e s c r i b e d b y Blakem o r e [1]. Their o r i e n t a t i o n is due to chains o f s i n g l e - d o m a i n m a g n e t i t e particles with size between 30 a n d 150 n m [2-5]. T h e b a c t e r i a are a q u a t i c a n d m i c r o a e r o p h i l i c [6,7]. T h e y have b e e n d e t e c t e d in various freshwater, brackish, a n d m a r i n e e n v i r o n m e n t s [1,2,4,8-15]. K i r s c h v i n k [16,17] s u p p o s e d that m a g n e t o s o m e chains, which are p r e s e r v e d in d e e p - s e a s e d i m e n t s after the d e a t h o f bacteria, are the carriers of a stable m a g n e t i c r e m a n e n c e a n d give c h a r a c t e r i s t i c m a g n e t i z a t i o n to the s e d i m e n t in which t h e y are embedded. Electron microscopic and magnetic analysis of the m a g n e t i c fine f r a c t i o n b y Petersen et al. [18] a n d Stolz et al. [14] p r o v e d , t h a t m a g n e Post address: H. Vali, Lehrstuhl ftir Angewandte Mineralogie der Technische Universit~it Miinchen, Lichtenbergstr. 4, D-8046 Garching, F.R.G. 0012-821x/87/$03.50

© 1987 Elsevier Science Publishers B.V.

t o s o m e s i n d e e d occur in d e e p - s e a sediments. It is n o t clear, when m a g n e t o t a c t i c b a c t e r i a first a p p e a r e d in the e a r t h ' s history. B l a k e m o r e et al. [7] a n d F r a n k e l [19] believed that they p o s s i b l y p l a y e d a m a j o r role in the f o r m a t i o n of b a n d e d i r o n f o r m a t i o n s in the A r c h e a n a n d Proterozoic. H e r e we r e p o r t on m a g n e t o s o m e s derived f r o m living freshwater b a c t e r i a which are c o m p a r e d to fossil m a g n e t o s o m e s (Fig. 1, T a b l e 1). Their stability with respect to the p h y s i c o - c h e m i c a l milieu in the s e d i m e n t is discussed.

2. Methods 2.1. E n r i c h m e n t o f magnetotactic bacteria A glass vessel (10 c m in d i a m e t e r a n d 25 c m in height) was filled with 500 ml o f fresh m u d f r o m a pond near Landshut/Bavaria (sample Pe/May, T a b l e 1). A f t e r settling, a b o u t 2 - 3 c m of clear w a t e r were left a b o v e the m u d . T h e c y l i n d e r was loosely covered a n d k e p t u n d e r d i m m e d d a y l i g h t at r o o m t e m p e r a t u r e (ca. 2 0 - 2 3 ° C ) . It was left to

390

rest during the whole period of the experiment. In contrast to the method described by [10], no further additions of new mud were made. The bacteria were sampled by a magnet which was mounted with the south pole directed down a few millimeters above the water/air interface, where its magnetic field had a magnitude of about 100 Oe. Normally after about half an hour enough bacteria were concentrated in the uppermost layer, forming a muddy cloud just below the water surface, where they could be gently aspirated with a pipette.

2.2. Preparation of bacteria The bacteria were first studied with a phase contrast microscope. To examine the magnetotactic behavior a drop of the bacterial suspension was put onto a glass slide under a cover slip and sealed with paraffin. A drift of bacteria could be observed when a magnetic field of 2 - 4 0 e was applied by means of a pair of Helmholtz coils. For the investigations with the transmission electron microscope (TEM) the bacteria were fixed with 2.5% glutaraldehyde in a 0.1 M cacodylate buffer (pH 7.2), rinsed with water and stained with a 2% uranylacetate solution.

2.3. Preparation of fossil magnetosomes Unconsolidated sediments were prepared using the common methods of clay mineralogy [24]. The carbonate matrix of the consolidated sediments was dissolved with 10% formic acid. Reaction time was about 24 hours. Samples rich in quartz and silicates were then treated for several days with a surplus of 10% N a O H at 7 0 ° C (magnetosomes exposed for several weeks to dilute (1%) and saturated solutions of formic acid and N a O H showed no morphological alterations). Further preparation was similar to that of the loose sediments. The fraction < 60 ~tm was separated by wet screening. From this fraction the magnetic particles were extracted using a special separation apparatus (see [15]). To prevent cross-contamination, in addition to washing with distilled water, the apparatus was cleaned with 10% HC1 after each sample. Beside the biogenic magnetite, the magnetic extract also yielded relatively coarsegrained ferromagnetic detritus, e.g. titanomagnetite and magnetite. Magnetosomes were enriched in the fraction < 0.2/~m of sediments rich in clay minerals. Other ferromagnetic contaminants were almost absent from this fraction. The magnetic fraction was then diluted ap-

Fig. 1. G e o g r a p h i c location of the i n v e s t i g a t e d samples. 1 = So 35, 182-KL, 184-KL; 2 = So 35, 119-KL, 120-KL; 4 = D S D P Leg 73; 5a = A N T - I ; 5b = A N T - I I / 3 ; 6 = Alvin; 7 = Pe, As-86, Sp 1, 2.

3 = So 25;

391 propriately with bidistilled water, dispersed by ultrasonic treatment, and finally mounted on c o p p e r grids for T E M o b s e r v a t i o n . I n a d d i t i o n , t h e m a g n e t i c p h a s e s w e r e a n a l y z e d b y the D e b y e S c h e r r e r m e t h o d a n d s e l e c t e d - a r e a e l e c t r o n diffraction (SAED).

3. R e s u l t s

3.1. Investigations on riving bacteria T w o s a m p l e s w e r e t a k e n , o n e in s p r i n g ( P E / M a y ) a n d o n e in a u t u m n ( P E / S e p t e m b e r ) , a n d h e l d u n d e r l a b o r a t o r y c o n d i t i o n s . A t first,

TABLE 1 Investigated samples (ages of DSDP Leg 73 from [20], Sonnwendgebirge [21-23]) Sample

Locality

Age

Lithology

Pe/May Pe/September

pond near Landshut Bavaria; ca. 200 m 2, depth 1 m

recent

silt, clay, high C-org. concentration

As-86

Ammersee, Bavaria; 48°N, l l ° 1 0 ' E (44.4 m water depth) (23.2 m water depth) (14.4 m water depth) (5.0 m water depth)

subrecent

silt, clay, fine sand

northern North Fiji Basin, southwest Pacific 14°30'S, 177°06'E 14°25'S, 177° 06'E

Quaternary/ Tertiary

clay, silt, > 50 wt.% CaCO3, skeletons of organisms

southern Lau Basin, southwest Pacific 22° 00'S, 177 ° 07'-177 °17'W

Quaternary/ Tertiary

clay, silt, > 40 wt.% CaCO3, skeletons of organisms

central Pacific, between Clarion Fracture Zone and Clipperton Fracture Zone; 13 ° -8 ° N, 150 ° -143 ° W

Quaternary

clay, silt, carbonate-free to -poor

DSDP Leg 73 Site: 519-523

southern spur of the Angola deep-sea plain, South Atlantic; 25°_30 °S, 12° W _ 4 ° E

Quaternary/ Tertiary

clay, nannofossil ooze

ANT-I ANT-II/3 1021-1 1174-2

Weddell Sea, Antarctic; 63°_70 °S, 1 0 ° _ 4 5 ° W

subrecent

carbonate-poor to -free

Alvin

Mid-Atlantic; 22 ° N, 44 o W

subrecent

nannofossil ooze, clay

Sp 2

Sonnwendgebirge, Tyrol/Austria

Oxfordian/ Sinemufien

calcium carbonate, M n / F e concretions, small clay content

Sp 1

Sonnwendgebirge, Tyrol/Austria

Oxfordian/ Sinemunen

calcium carbonate with small clay content

/13 /14 /15 /16 So 35 182-KL 184-KL So 35 119-KL 120-KL So 25

133-KL 177-KL 184-KL 315-KL 383-KL

392

spirilli (similar to Aquaspirillum rnagnetotacticum [25]) and cocci (similar to Magnetococcus [10]) could be observed sporadically. After 2-3 days

cocci appeared abundantly which under the light microscope moved with about 20 /~m/s. In the sample PE/May each coccus contained one chain

e

Fig. 2. Cocci after 2-3 days in the laboratory. (a) Mud from May (sample Pe/May); (b) mud from September (Pe/September); (c) cocco after 2 months; (d) parallelly arranged chains of magnetosomes; (e) loopshape arrangement of chains; (f) prismatic magnetosomes prepared by freeze-etching method.

393

consisting of 10-12 short prismatic magnetosomes of about 150 × 120 nm (Fig. 2a). In the sample P E / S e p t e m b e r morphologically similar cocci appeared, but contained 4 chains composed of 7 - 9 magnetosomes each with an octahedral shape and dimensions of 80 × 70 nm (Fig. 2b). Only the development of the sample P E / M a y was observed further. Sporadically, very agile coccoid bacteria appeared, which moved with ca 50 g m / s . After about 2 months, these bacteria occurred in abundance. They possessed up to 200 magnetosomes (Fig. 2c). Typical arrangements were straight, parallel and partially loop-shaped chains, and nearly unordered clusters (Fig. 2c-e). The magnetosomes were prismatic (Fig. 2f) and measured about 130 × 70 nm. The bacteria were covered with numerous fine pili (Fig. 2c). After 4 months a spirillum-like species with a length up to 8 g m dominated. This organism was

morphologically similar to the large cells of A. magnetotacticum [3]. One to three chains of magnetosomes were strung out along the long axis of the cell with about 50 idiomorphic magnetite crystals (Fig. 3a) of 50-80 nm in length (Fig. 3b). The number of bacteria decreased after about 5 months; only few bacteria could be detected after 6 months. The color of the mud changed from greyish yellow to greyish blue (first observed at about 1.5 cm below the m u d / w a t e r interface). After 6 months the putrefaction zone reached the surface of the sediment, and a putrid smell occurred. Shortly before, coccoid cells were observed which moved in both directions along the geomagnetic field lines in roughly equal numbers. During the observation time the p H changed from 7 to 7.5. Other chemical investigations were not performed in order to prevent disturbance of the sample. A similar variety of bacteria was observed under natural conditions (as described from other southwestern German ponds by [4]) by examining freshwater sediments from different depths of water from the Ammersee. Here large spirillum species with cell lengths up to 8 /xm and 1-4 chains of magnetosomes were present. The chains were aligned parallel to the long axis of the cells (Fig. 4a) and consisted of prismatic magnetosomes of ca~ 180 × 100 nm (Fig. 4b). Also, other bacteria occurred which measured 9 g m in length and contained up to 1000 projectile-shaped magnetosomes of 110-150 nm (Fig. 4d). These magnetosomes were arranged in several straight chains parallel to the long axis of the bacteria (Fig. 4c). The pH of the uppermost sediment layer varied between 7.1 and 7.7, the Eh between - 2 4 0 and - 4 2 5 mV; 10 m below the water surface the temperature was about 8 o C.

3.2. Investigation of fossil magnetosomes

1 Fig. 3. (a) "Spirillum" after 4 months; (b) octahedral magnetosomes.

The magnetosomes of the marine and freshwater sediments exhibit prismatic, octahedral, and projectile-shaped contours. Whereas the octahedral and prismatic magnetosomes can form longer chains, the majority of the projectile-shaped occur as single grains of short chains of up to 3 magnetosomes. The chains are arranged mostly in parallel and partially superimpose onto each other. In this way they build up clusters which rendered their identification more difficult (Fig. 5).

394 The Quaternary sediments of the Atlantic and Pacific Ocean predominantly yield octahedral magnetosomes arranged in chains (Fig. 5a, b); partially they showed diffuse boundaries due to adsorption or accretion of small particles (Fig. 5c). Both, the young sediments from the Antarctic (Fig. 5d, e) and the Ammersee contain chains of large prismatic magnetosomes. In magnetic extracts from the Fiji and Lau basins (South Pacific) magnetosomes were found sporadically; chains occurred rarely and were rather short. Often¢ clusters of mineral particles

were observed which were about the size of magnetosomes (Fig. 5f). In addition, grains of superparamagnetic particle size ( < 10 nm) were observed. In the Sonnwendgebirge (Tyrol, Austria) a profile of the Rethian to lower Cretacious was sampled (stratigraphy and age according to [21-23]). F r o m two of the samples magnetosomes could be extracted. Sample Sp 1 was derived from bedded carbonates which can laterally change to Cephalopod limestones (Oxford/Sinemurien). Specimen Sp 2 was derived from a region with hard-ground

a

c

d

1 ~m Fig, 4. Bacteria from the Ammersee. (a) "Spirillum"; (b) large prismatic magnetosomes; (c) bacterium containing up to 1000 projectile-shaped magnetosomes; (d) projectile-shaped magnetosomes.

395

formation (Oxford/Sinemurien: F e / M n concretions and mineralized organisms) which crops out some meters above Sp 1. The magnetic extracts had low concentrations of magnetosomes. Cumulated short chains were the main feature. In both samples prismatic and octahedral shapes occurred (Fig. 6).

3.3. Alterations of magnetosomes Typical alterations could be observed on fossil

I ix

I=/.I

magnetosomes. Magnetosomes derived from fresh mud of the Ammersee (uppermost 5 cm of sediment) showed cracks and dissolution caverns (Fig. 7). The fossils from the deep-sea sediments and from the Sonnwendgebirge partially showed diffuse boundaries and appeared to be smaller than the well preserved ones (Figs. 5b, c and 6b, d). X-ray and electron diffraction revealed that the magnetosomes from the Ammersee consisted of magnetite (a o = 8.397 + 0.006 ,~) throughout.

~11|

Fig. 5. Magnetofossils from marine sediments. (a) Central Pacific, matrix consists of clay minerals; (b) octahedral magnetosomes from the central Pacific; (c): adsorption of small particles; (d), (e) prismatic magnetosomes from the Antarctic; (f) magnetic extract, Fiji Basin.

396

~a

....

OA/zm

Fig. 6. Magnetofossils from diagenetically consolidated carbonates, Jura, Sonnwendgebirge; (a), (b) from carbonate with Fe/Mn concretions; Jura (specimen Sp 2); (c) prismatic shapes, and (d) octahedric shapes from specimen Sp. 1.

According to [26-29] this is typical for magnetosomes of living bacteria. Samples So 25 and Leg 73 yielded mainly maghemite (a 0 = 8.344 + 0.014 A) (Fig. 8). Using selected-area electron diffraction magnetite reflections could be identified. Strikingly, in freshwater and marine sediments both altered and well preserved magnetosomes were observed in the same samples.

4. Discussion Our experiments clearly show that various shapes and sizes of magnetosomes can arise in a very short period of time within one freshwater sample. At the end of the experiment P E / M a y , roughly equal numbers of north- and south-seeking bacteria co-existed in the sample. As a rule,

Fig. 7. Magnetic extract from fresh sediment from the Ammersee showing corrosion.

397 8.~,0" I [ q

I

I

I

I

I

I

I

I I H~,gg [31 ]

I

I

•

8.39" =_ 8.38 c" _o 8.37

~-

8.36

~ 8.3S 8.3~.

A I

'33Fe304

10

I

20

30

I

/~0 SO 60 70 Mole per cent Fe203

80

I

90 -y Fe203

Fig. 8. Fossil (A, B) and recent (C) magnetosomes in the diagram of variation of cell dimension with composition in the Fe304-~,-Fe203 (magnetite-maghemite) series (after [30]). A: Leg 73/Angola Basin; B: So 25/Central Pacific; C: Ammersee; with standard deviation.

bacteria which are sampled freshly from freshwater environments in the northern hemisphere, were north-seeking. Simultaneous occurrence of north- and southseeking bacteria has to date only been reported for samples from environments near the geomagnetic equator [11]. Populations with mixed polarities have been generated artificially by intense magnetic field pulses oriented opposite to the original polarization of the bacteria [9,12]. Blakemore [8] observed, that in populations of magnetotactic bacteria which were held in a magnetic field-free space, both polarizations appeared in equal numbers after about one month. Compared to natural environments, in our laboratory experiment the temperature is higher and relatively constant and there is no water exchange. The latter fact leads to alterations of the milieu, which are known to influence the growth of bacteria and the formation of magnetosomes [33]. The laboratory experiment showed that the milieu also influences the magnetotactic properties of the bacteria. In the Ammersee it was recognized that the population density of the bacteria depended on the bathymetry. In the riparian area no bacteria could be found, but with increasing depth of water, the number of bacteria increases. In the pond near Landshut (with a depth of only 1 m on the average) an even distribution was found. We observed that in sediments from relatively stable marine environments only one type of fossil

magnetosome dominated in each sample, whereas in the seasonally instable freshwater environments several types of magnetosomes coexisted. In the samples from the Pacific and the South Atlantic Ocean (Table 1 and Fig. 1) magnetosomes with octahedral shapes dominated (Fig. 5a, b, e), whereas in the Antarctic (samples 1021-1, 1174-2) prismatic shapes (Fig. 5c, d) represented the main fraction. In freshwater environments we found prismatic and octahedral magnetosomes in one and the same locality (samples As 86/13-16). In addition, projectile-shaped magnetosomes were more frequent in freshwater sediments than in marine sediments. The shape and size of magnetosomes did not seem to depend on geographic latitude. We expect, therefore, that the shape and concentration of magnetosomes in a sample provide information on the prevailing milieu. The comparison of fossil magnetosomes with those of the bacteria showed that various shapes are present in both, sediments and living bacteria. However, the fossil magnetosomes are about 10% smaller. The size of the fossil magnetosomes is in the range of single-domain particles as calculated by Butler and Banerjee [34] (Fig. 9). A number of sediments (sample Alvin and those from the Sonnwendgebirge), partly loose, partly diagenetically consolidated, gave negative results. This observation is problematic for magnetostratigraphic investigations of sediments, because magnetosomes are thought to be important carriers of the stable remanence of sediments [16-18]. Possible reasons for the absence of magnetosomes in certain sediments might be: (a) Primary absence of magnetotactic bacteria because of unfavorable living conditions [8]. (b) Lack of formation of magnetosomes in the bacteria, due to the living conditions [7,8,25,33]. (c) Irrecognizability of magnetosomes due to aggregation and superposition with other minerals. (d) Corrosion of magnetosomes a n d / o r their total dissolution. It remains an open question if under a weak external magnetic field over long periods of time (e.g. at reversals) the bacteria cease to produce magnetosomes, thus becoming non-magnetic. Valet and Lai [35] studying the magnetostratigraphy of marine sediments from Crete noticed that

398

(Q)

Length (~m)

Length

Length

(b)

Length

CA]

1.00 0.80 0.60

F~

IO000

tl} I.O0

8000 6000

0.80 0.60

8000 IO000 8000

0.40

4000

0.40

4000

0.20

2000

0.20

0.10 0.08!

'1OOO 'BOO

0.10

0.06

500

0.06

0.041

'400

0.04

0.02

200

0.02

o.o

o12

o:,

0:6

o18

0.08

CentraJ P a c i f i c (Fig. 5a,b) Weddel Sea / A n t a r c t i c a (Fig. 5d,e) Angola Abyssal Plain (Fig. 5f) Sonnwendgeblrge Sp I (Fig. 6c,d) Sonnwendgeblrge Sp 2 (Fig. 6a,b)

HI]

o

o =

2000

~

800

600 40O 2O0

SP r

1.0

O.

AX%BI Rat%o (B/L) + A o o o

~

o12

o:,

'" o16

0.8

.o

Axlal RatLo I~/k) o D a * o

Coccus, octahedral magn. (Fig. 2a,c) Splrlllum, prismatic magn. (Fig. 3) Coccus, prismatic magn. (Fig. 2b,d) Bacterium, prismatic magn. (Fig. 4a,b) Bact., cone-shaped magn. (Fig. 4c,d)

Fig. 9. Grain size distribution of magnetosomes. (a) Fossil magnetosomes; (b) magnetosoInes from living bacteria• The length and width of the individual grains were measured from T E M micrographs and plotted as shown. Boundaries between the two-domain (TD), single-domain (SD), and superparamagnetic (SP) stability fields were drawn according to the calculations of [34].

the intensity of strong field-induced magnetization becomes very small at reversal boundaries, which is evidence for a decrease of the amount of magnetic material in these intervals. Since the intensity of the earth's magnetic field becomes very small during a field reversal and, assuming that the magnetization of the sediments studied by Valet and Lai [35] is carried essentially by magnetosomes, this could be due to either an extermination of magnetic bacteria during a period of very low magnetic field strength or a termination of the production of magnetosomes by the bacteria. The latter suggestion, however, contradicts the experimental results [8] showing that cultured magnetotactic bacteria did not lose their ability to produce magnetosomes under laboratory conditions in zero magnetic field but acquired mixed polarities. The alteration of magnetosomes, extracted from fresh mud from the Ammersee (Fig. 7) showed that magnetosomes are sensitive to corrosion. This is also demonstrated by the fact that no magnetosomes could be extracted from the mud held un-

der laboratory conditions only a short while after the bacteria had died out. This is possibly due to reducing conditions at the end of the experiment. Corresponding observations of detritic magnetite and titanomagnetite indicate that these minerals are unstable under reducing conditions [36]. Often sulfurization of magnetite and titanomagnetite was observed, which was attributed to reducing conditions during sedimentation [37]. Demitrack [38] described Greigite crystals (Fe3S4) from lacustrine sediments, which were morphologically similar to magnetosomes. X-ray and selected-area electron diffraction examination of magnetosomes from freshwater sediments yielded magnetite only, whereas marine environments showed nearly complete maghemitization of the original magnetite. We suggest that the magnetosomes (originally magnetite under ocean floor conditions) are maghemitized similar to the gradual alteration of the titanomagnetites contained in ocean floor basalts, where an increasing transformation with age into titanomaghemite is observed [39]. The mixed occurrence of altered

399 a n d preserved m a g n e t o s o m e s could be due to biot u r b a t i o n of the sediments. A n o t h e r aim of this work was to trace the occurrence of m a g n e t o t a c t i c bacteria back i n the earth's history b y their fossil magnetosomes. W e could prove that m a g n e t o s o m e s existed already i n the Jurassic. However, n o particles could b e detected in older sediments, so far. This is possibly due to diagenetic or m e t a m o r p h i c alteration of the samples. If it were possible to find m a g n e t o s o m e s in older sediments, interesting questions could be answered, e.g. whether the genesis of b a n d e d iron f o r m a t i o n s might be due to the occurrence of m a g n e t o t a c t i c bacteria i n the Proterozoic.

Acknowledgements We are very grateful to L. B a c h m a n n ( I n s t i t u t fiir Technische Chemie, T U M i i n c h e n ) for his very instructive discussions a n d support. W e t h a n k G. M o r t e a n i (Institut ftir A n g e w a n d t e Mineralogie u n d Geochemie, T U Mtinchen) for his interest i n the progress of our investigations. W e received the samples from the A m m e r s e e from J. Miiller, from the S o n n w e n d g e b i r g e from G. Spielvogel a n d S. Leue (Institut ftir A n g e w a n d t e u n d AUgemeine Ingenieurgeologie, T U Mtinchen). T h e " A l v i n " samples were k i n d l y m a d e available to us b y S. H u m p h r i s (Woods Hole O c e a n o g r a p h i c I n s t i t u tion). The samples from the A n t a r c t i c we received from G. Troll ( I n s t i t u t ftir Mineralogie u n d Petrographie, L M U Mtinchen). W e t h a n k the D F G for financial support.

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