Marine Chemistry, 20 (1987) 361-376 361 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

F O R M A T I O N OF C H E M O G E N I C C A L C I T E IN S U P E R - A N O X I C S E A W A T E R - - F R A M V A R E N , S O U T H E R N N O R W A Y

LEIF G. ANDERSON and DAVID DYRSSEN

Department of Analytical and Marine Chemistry, Chalmers University of Technology and University of Gothenburg, S-412 96 Gothenburg (Sweden)

JENS SKEI*

Norwegian Institute for Water Research, P.B. 333, Blindern, 00314 Oslo 3 (Norway)

(Received April 17, 1986; revision accepted October 13, 1986)

ABSTRACT

Anderson, L.G., Dyrssen, D. and Skei, J., 1987. Formation of chemogenic calcite in super-anoxic seawater - - Framvaren, southern Norway. Mar. Chem., 20: 361-376.

Framvaren, a super-anoxic fjord in southern Norway, contains 7 8mmoll 1 of sulphide and a total carbonate concentration of 18.5 mmol kg ' in the bottom water. The chemistry of calcium has been studied, considering sources, biogenic and chemical processes and sedimentary sinks. Cal- cium associated with the bacteria biomass at the redox interface (18m depth) appears to be the primary source of dissolved calcium in the deep, anoxic water. Excess calcium and high total carbonate cause supersaturation of calcite, which is precipitated chemogenically. Calcite (and presumably some aragonite) is identified both in sediment trap material and the bottom sediments below the depth of supersaturation.

INTRODUCTION

Biogeochemical processes in super-anoxic water may be quite different from those occurring in oxic or intermittently anoxic environments. High sulphide water characteristically has a low pH, high total carbonate, high nutr ient concentrations and extremely low levels of several trace metals. Marine waters with a redox cline within the euphotic zone create a large biomass due to bacterial activity at the interface (Indreb5 et al., 1979). This pool of labile, organic matter sinks vertically into the sulphidic water, sustaining sulphate reduction. Additionally, the plankton biomass situated above the layer of bacteria contributes to vertical transport of organic matter into the deep water. Anaerobic degradation of organic substances in the water column causes a build-up of high total carbonate, nutrient-rich bottom water. If no complete water exchange occurs a super-anoxic environment develops, with extremely high concentrations of sulphide and total carbonate.

*Present address: Department of Analytical and Marine Chemistry, Chalmers University of' Technology and University of Gothenburg, S-412 96 Gothenburg, Sweden.

0304-4203/87/$03.50 © 1987 Elsevier Science Publishers B.V.

362

I N

Scale 2000 i

INorwa~ i 4000 ~ / l~;w~de',~ /

, ( ;

Fig. 1. Location of study area (O, sampling sites).

The fate of calcium in such environments has not been fully investigated. In normal seawater, calcium carbonate is close to saturat ion with respect to calcite (Broecker, 1974). Hence, small physicochemical changes may be suf- ficient to produce supersaturation. Laboratory experiments have shown that calcite precipitation occurs easily in supersaturated seawater in the presence of nuclei, humic material, etc. (Suess and F/itterer, 1972). In addition to the chemogenically formed calcite, plankton and bacteria may play an important role in the formation of biogenic calcite (Lalou, 1957; Morita, 1980).

Framvaren, southern Norway (Fig. 1), is a super-anoxic fjord with a sill depth of 2 m and a basin depth of 183 m (Skei, 1983a, b). The sulphide concentra- tions in the bottom water are of the order of 7-8 mmol or about 25 times that of the Black Sea. Inflow of oxic seawater to the anoxic layers occurs, par- t icularly at intermediate depths, although the fjord has been permanently anoxic at least since 1850 (see Skei, 1983b, for further details). However, some oxic seawater must regularly penetrate into the super-anoxic bottom water in

363

order to balance the hydrogen sulphide production and keep the sulphate concentration at 50% of that of seawater.

During the period 1979-85 a joint international research programme was carried out in Framvaren, with emphasis on biogeochemical processes. As a part of this study, the fate of calcium in the super-anoxic environment was investigated. The vertical distribution of dissolved and particulate calcium in the water column, the origin of the solid calcium phases, their flux rate meas- ured by sediment traps and their incorporation in the bottom sediments are discussed.

MATERIAL AND METHODS

Seawater samples, collected through the ice in February 1985, were analysed for density, calcium, total alkalinity (At) and pH. Total alkalinity and pH were determined hours after collection, while others were determined back at the laboratory in Gothenburg. Total carbonate (Ct) was calculated from total alkalinity and pH using the stability constants together with the total con- centrations of the species included in the alkalinity definition (Dickson, 1981).

The density was determined using a Paar density meter (DMA 50), calcium by a photometric EGTA ti trat ion (Anderson and Gran~li, 1981), total alkalinity by a photometric HC1 t i trat ion (Anderson and Wedborg, 1983) and pH was measured according to Almgren et al. (1975). The precision relative standard deviation (SD) of the methods is 0.05% for density, 0.16% for calcium and 0.1% for total alkalinity. The SD of pH was 0.003 units.

Water was also sampled during June 1979, August 1981, July 1983 and February 1985 for analyses of particulate Ca. The water was pressure-filtered through 0.4pm Nuclepore membrane filters and analysed by X-ray fluore- scence, using a thin-film technique (Price and Calvert, 1973; Price and Skei, 1975; Skei and Melsom, 1982). The samples were rinsed using distilled water to remove sea salt. The results are expressed as #g Ca per litre water filtered.

Cylindrical sediment traps (height 640 mm, diameter 50 mm) were employed in pairs at 20, 40, 80, 120 and 160 m depth on a mooring at the centre of the deep basin (180 m) and in the northern basin (100 m). The trap experiment lasted for 414 days and the traps were emptied five times during this period, by unscrew- ing the bottom part of the trap. The collected sediment and the water above were shaken and poured into a sedimentation chamber, divided into four sections to allow material to be used for various purposes. The subsamples were then filtered and weighed and the filters were subsequently treated with HC1 to remove calcite, after X-ray diffraction identification. One subsample was filtered onto a Nuclepore membrane filter, and then coated with carbon and analysed by scanning electron microscopy (SEM) coupled to an energy-disper- sive X-ray analyser (EDAX).

The bottom sediments were sampled using a gravity corer designed for muddy sediments (NiemistS, 1974). The sediment cores were immediately sliced in 2-cm sections, washed with distilled water, centrifuged to remove salt and

364

TABLE I

The chemistry of the water of Framvaren, southern Norway (February 1985)

Depth Salinity A t pH f C t Ca Ca (35) fl~,l,,.~,, (m) (calc. from (mM~) (at 20°C) (raMw) (mM~) (mM~) (%)

density)

0 5.588 0.315 6.698 0.447 1.632 10.222 0.8 2 11.035 0.780 7.391 0.831 3.240 10.276 ] 1.5 4 11.390 0.722 7.390 0.772 3.345 10.279 9.9 8 14.741 0.969 7.484 1.013 4.337 10.298 20,0

12 15.650 1.114 7.422 1.162 4.589 10.263 26.8 14 18.803 1.348 7.330 1.420 5,497 10.232 28.6 16 18.902 1.293 7.239 1.382 5.546 10.269 22.7 18 20.038 1.633 7.343 1.716 5.885 10,279 36.3 20 20.990 1.819 7.355 1.910 6.221 10.373 40.7 22 21.344 2.132 7.186 2.246 6.340 10.396 31.4 24 21.210 2.167 7.136 2.286 6.261 10.332 27.0 26 21.217 2.381 7.092 2.496 6.282 10.363 25.8 30 21.699 2.850 7.051 2.942 6.405 10.331 26.4 40 21.458 3.393 7.012 3.467 6.354 10.364 27.2 50 21.678 4.142 7.012 4.177 6.446 10,407 33.0 70 21.749 5.879 7,059 5.428 6.490 10.444 49.1 80 22.15 a 7.737 7.048 7.127 6,657 10.519 63.9 90 22.558 12.476 7.055 11.289 6.892 10,693 107.1

100 22.73 ~ 16,332 7.067 14.468 7.112 10.951 147.1 110 22.892 17.873 7.095 15.726 7.074 10.816 170.7 130 23.2F 19,639 6.986 b 17.680 7.247 10.928 (149.1) 150 23.523 20.675 7,050 18.167 7.342 10.924 181,8 160 c 23.67 a 20.649 6.970 b 18.528 7.342 10,856 (151,0} 170 23.807 20,644 7.048 18.211 7.393 10.869 18t.2

a Calculated from depth profile. b Low values due to oxidation. c Sediment particles observed in sample bottle.

analysed by neutron activation for calcium and 29 other elements. 5-cm sec- tions of selected cores were squeezed in a nitrogen glove-box to obtain pore water for analyses of pH, alkalinity and calcium.

TABLE II

Calcium, total alkal ini ty and pH outside and inside sediment traps, Framvaren, southern Norway

Depth (m) Outside trap Inside trap

Ca (mM) At (mM) pH Ca (mM) At (mM) pH

80 6. 789 8.88 7.14 6.687 8.41 6,93 120 7.435 18.99 6.91 7.435 19.15 6.92 160 7.510 21.05 7.02 7.510 21.36 6.94

365

FRAIVAREN 1 9 3 1 - 1 9 8 5 St .F1

40

"~ BO

cz 120

J60

200

6 12 18 24 30

Sal . o/oo

°~ "z . .

°° o.

~- °° . ° m

|

Fig. 2. Vertical salinity distr ibution in Framvaren (data from 1931 85).

FRAHVAREN "1979-:1985

St .F1

120

~SO

• -- H2S mmol/l 0 2 4 S

A -- 02 micromol/1 130 260 390

40 m u

m m m

80 • •

8 10

520 BSO , , . ~ '

• !

• !

i l

II l U I •

I I II

5

FRAMVAREN ~.979 1985

S t . . F t

PO4-P mtcromol/l BO 90 120

! - -

0 30 o ~' '

40 ~ J

80 J

120 ]

160 1

2O0 2OO

Fig. 3. Vertical dis tr ibut ion of oxygen, sulphide and phosphate (data from 1979-85).

150

366

F R A M V A R E N 2 0 . 2 . 8 , 5

St .F1

4 0

8O

£z

~ 1 2 0

1 6 0

C t , m ~ : r o m o l / k q

0 ~ 8 1; '

2 0 0 - - -

I~.; 2 0

Fig. 4. Vertical distribution of total carbonate {data from February 1985).

RESULTS

The results are presented in Tables I and II.

Basic water chemistry

The salinity profile in Framvaren shows a very fresh surface water with a strong halocline down to approximately 20m the (Fig. 2). Deeper than 20m the salinity is fairly constant with a slow increase downwards. At a depth of 75-90 m the increase is somewhat larger, indicating an interface between two water masses.

At 18 m, in the lower part of the halocline, the water becomes anoxic. Deeper than this there is an increase in hydrogen sulphide, reaching 7-8mM below 130m. The decay of organic matter reflected in the oxygen/sulphide and nu- trient (represented here by phosphate) profiles (Fig. 3) is also stressed by the total carbonate profile (Fig. 4), which reaches concentrations exceeding 18 mmol kg- 1 seawater in the deepest waters.

The normalized calcium profile (normalized to salinity 35 in order to avoid changes due to salinity variations) also increases somewhat with depth down to ~100m (Fig. 5). The pH is low over the entire water column (< 7.5) and reaches a minimum in the deep water. Nevertheless the concentration of CO~- in the deep water increases sufficiently for the solubility product of CaCO~ to be exceeded, giving calcite saturat ion values of close to 200% below 100 m

367

5 0 ,

Z "1-

1 0 o .

uJ

2 0 0

Q NORMALIZED CALCIUM (mmole/kg) 1 0 , 0 1 0 . 5 1 1 .0

i I i

"~g CALCITE SATURATION (%) 5 0 1 O0 1 5 0

i I I

'Z 2 0 0 d

Fig. 5. Vertical profile of normalized calcium and calcite sa tura t ion in Framvaren (normalized to a salinity of 35%o) (data from February 1985).

(Fig. 5). The saturat ion of calcite is based on the solubility product determined by Mucci (1983).

Particulate constituents in the water

Analyses of particulate matter in the water column include the elements calcium, aluminium and phosphorus. Normally, calcium and phosphorus are present in biogenic material in seawater (Price and Skei, 1975), being abundant in the euphotic zone. Additionally, calcium is incorporated in detrital silicates (feldspars, etc.) in a Ca/A1 ratio of 0.16 (mol/mol) in the local granite (farsun- dite) of the drainage area of Framvaren.

The Ca/A1 ratio in the particulate matter above the redoxcline in Framvaren is about 0.5 (mol/mol), at the redoxcline 1-1.5, and also in the bottom water about 0.5. This implies that at all depths calcium is present in amounts larger than that residing in detrital silicates. The maximum excess calcium occurs close to the redox interface (Fig. 6). The depth profile of particulate phosphorus (Fig. 7) indicates that this is the depth corresponding to the maximum of particulate organic matter. Measurements of ATP (adenosine triphosphate) as an indicator of living biomass show a vertical distribution close to that of particulate phosphorus (Skei, 1983a).

Calcium in sediment traps

Sediment traps were employed at various depths in the fjord. With weak HC1 treatment of the sediment trap material, effervescence was observed and a

368

FRAMVAREN I 9 7 9 - :1985

St .F~

E]

40

80

120

160

200

.... Ca (P) (nmol/l)

I00 200 300 400 500

i s ] 4

b

E

, I

t1( ! r t1(t~ I

i I

n * i

i(

Fig. 6. Par t icula te calcium in the water of F ramvaren (data from 1979~85).

40

8O

[:3 120

180

200

FRAMVAREN ~979- :[985

St .F1

140 280 420 560 700

t t ~

Fig. 7. Par t icu la te phosphorus in the water of F ramvaren (data from 1979-85).

369

5 0 p m 2 0 p m I I I I

2 0 p m 1 0 p m I I I I

Plate 1. SEM photographs of calcite (or aragonite) crystals collected in sediment traps at 160m depth: (a) a cluster of calcite crystals at 550 × magnification; (b) two types of precipitates, (i) well crystall ine calcite and (ii) structureless, oolithic precipitate (aragonite ?); (c) a close-up of the button-like precipitate; (d) details of the calcite crystal shapes (3000 x magnification).

370

weight loss in the material was recorded. To verify the presence of calcite in the traps, X-ray diffraction analyses were done, showing the characteristic calcite peaks at d = 2.49 and 3.03A. Furthermore, selected samples were analysed by scanning electron microscopy (SEM) and energy-dispersive X, ray analyses (EDAX). Plate 1 shows crystals of calcite and presumably some oolitic aragonite. The EDAX analyses of the crystals gave only calcium, excluding the possible presence of mixed carbonates (Mg, Mn, etc.). HC1 treatment produced no significant weight loss for material in traps a t 20, 40 and 80m depth. Traps at 120 and 160m, however, which were employed in the supersaturated water, clearly showed the presence of calcite (and presumably some aragonite). Fluxes of CaCO~ were calculated for the periods 19.9-29.11.83 and 29.11.83-3.5.84, representing an autumn situation and a winter/spring situation. Samples from other seasons were unfortunately frozen during storage; as a result, the pre. cipitation of calcite is enhanced due to supersaturation of the enclosed brine (Richardson, 1976).

For the two periods with unfrozen samples, the calculated fluxes of CaCO3 at 160m depth were 2 3 m g m - ~ d a y L1 (autumn) and 21mgm-2day ~I (winter/ sp~ng). It appears that there are small seasonal changes in the flux of CaCO~ to the bottom sediments. The concentration of CaCO3 in the sediment trap material was 20 and 16%, respectively, which corresponds well with that found in the near surface sediments of the deep basin.

To ensure that the sediment traps do not create a micro-environment which favours precipitation of calcite within the trap, calcium, pH and alkalinity were measured in the water inside and outside the traps. Table II indicates that there are no significant differences in the results obtained inside and outside the trap. Hence, it is concluded that the observed calcite crystals in the traps in the bottom water are not formed due to a sampling artifact.

Calcium in the bottom sediments

The source rock in the area, farsundite, is a monzonitic-granitic, feldspar- rich rock with a calcium content of 1.5%, Analysis of three sediment cores from various water depths (19.5, 100 and 179 m)indicated large variations in calcium content (Fig. 8). The cores from 19.5 and 100 m depth, both above the super- saturat ion zone of calcite, showed a calcium content close to 1% and no vertical change. This is presumably detrital calcium, mainly residing in the feldspars. The core from the deep basin, however, is highly enriched in calcium in the upper 30 cm, corresponding to the black sediments deposited during the stagnation period since 1850. Analyses of pore water in the sediments show a slight depletion of calcium relative to the bottom water.

The enrichment of calcium in the core from the deep basin, but not in the shallow cores, suggests that the sediments in the deep basin receive calcium from an additional source. X-ray diffraction of the sediments shows strong reflections for calcite. If we assume that the calcium content in the detrital

371

E 0

-1- I-.- 0_ i..u a

C a ( % )

0 5 10 I I !

O-

10-

2 0

3 0 -

4 0 -

5O

Fig. 8. Distribution of calcium in three sediment cores taken at different water depths in Fram- varen. (o) 19.5m, (O) 100m and (Q) 179m depth.

f r ac t ions m a y a c c o u n t for 1% Ca, the sur face sed iments con ta in ~ 8% Ca or ~ 20% calci te , in a g r e e m e n t wi th the sed iment t r ap data .

DISCUSSION

By ob ta in ing da t a f rom the w a t e r column, the compos i t ion of se t t l ing part i- cles and the unde r ly ing b o t t o m sediments , an a t t e m p t is made to e luc ida te the fa te of ca lc ium in a super -anoxic eny i ronmen t . Conven ien t ly , the f jord may be subdiv ided into four com pa r t m en t s :

(I) The oxic su r face l aye r (0-18m) co r r e spond ing to the eupho t i c zone where p roduc t i on of o rgan ic m a t t e r occurs (p l ank ton and bacter ia) . W a t e r exchange occurs regu la r ly .

372

(II) The intermediate anoxic zone (18-100 m) where mineralization of organ- ic matter, release of inorganic carbon and precipitation of metal sulphides occur. Gradients are governed by occasional inflow of water.

(III) The super-anoxic bottom water (100-180m) with relatively long re- sidence time. Small gradients indicate a well mixed water mass.

(IV) The bottom sediments, the ultimate sink or the potential source of various components (Skei, 1983a).

Biogenic calcite formation

Specific groups of plankton build a calcite skeletal (coccolithophorids, fora- minifera) or an aragonitic shell (pteropods). A major consti tuent of biogenic particles settling through the water column of the ocean is carbonate tests (Honjo et al., 1982). The survival of such particles in the water column depends on their residence time, which again partly depends on the grazing by zoo- plankton and incorporation of biogenic calcium in faecal pellets (Honjo, 1976). It is unlikely that calcite situated in the hard parts of organisms is to any large extent dissolved in the underlying waters, especially in Framvaren where the water depth is less than 200m. Hence, it is assumed that calcite tests are incorporated in the bottom sediments where corrosion of calcite may occur in the strongly anoxic environment. The pore water of the sediments is slightly depleted in calcium, suggesting that any calcium formed due to corrosion of biogenic calcite is removed from solution.

Gephyrocapsa (Coccolithus) huxleyi is a common plankton form in Nor~ wegian fjords and extensive blooms are frequently observed, particularly in late summer. Such blooms give a characteristic green colour to the water which is easily recognizable. These blooms have never been observed by us in Framvaren, but has in the fjord outside. However, even if the in situ production of gephyrocapsids in Framvaren is very low, plankton may be passively trans- ported into the fjord. Consequently, biogenic calcite of planktonic origin may contribute to the elevated concentrations of particulate calcium above the pycnocline and sometimes, depending on the density of the inflowing water~ provide biogenic calcium to the intermediate anoxic zone.

Another more important source of biogenic calcite in Framvaren may be of bacterial origin. The precipitation of calcite is common among microorganisms (Lalou, 1957; Morita, 1980). It is also well known that bacteria can bind cations, including calcium ion (adsorption onto the surface, binding to proteins, etc.). Greenfield (1963) noted that dead cells can take up as much calcium as living cells, thereby indicating that the uptake of calcium is not dependent on meta- bolic processes. The redox interface in Framvaren is a site of great bacteria] activity due to the presence of photosynthetic purple bacteria, sulphate-reducm ing bacteria and Thiobacillus (Skei, 1986). A sharp maximum of ATP is obser- ved at this interface (Skei, 1983a), as well as elements like particulate pho- sphorus, beside calcium (Figs: 6 and 7). Additionally, in particulate matter

373

cations like potassium and magnesium also increase at the interface, suggest- ing binding or adsorption to bacteria. It is therefore concluded that the major- ity of the part iculate calcium appearing at the redoxcline is bound to bacteria and that this represents a large biogenic calcium source in Framvaren.

Fluxes and breakdown of organic matter

Assuming that the biogenic calcite in skeletal forms, advected into Fram- varen, is incorporated to a large extent into the sediments, the fate of organic- ally bound calcium should be considered. The small size of bacterial cells should result in a long residence time in the water column and considerable remineralization. The steep vertical gradients of nutrients, total carbonate and sulphide suggest that the major part of the breakdown of organic mat ter takes place in the water column above 100 m. Below 100 m the sediments are likely to play a more important role as a source of sulphide and alkalinity due to a large bottom area compared to the volume of the water. It must be assumed that calcium is released when the bacterial biomass disintegrates. The concentra- tions of dissolved calcium increase vertically and it occurs at concentrat ions exceeding the normalized value of open ocean water (10.28mMw, see Fig. 5).

Sediment traps at 20 and 80 m, collecting material in the productive summer season (May-July, 1983), showed an 80% decrease in carbon flux between 20 and 80m depth. Only an 18% decrease was observed between 80 and 160m depth. During this period most of the mineralization takes place in compart- ment (II), the intermediate anoxic zone between 18 and 100 m depth, assuming that no significant advection of water occurred at depth. The vertical distribu- tion of normalized calcium (Fig. 5) shows a similar trend, with a distinct increase down to 100 m and more or less constant concentrat ions below. If, on the other hand, water exchange down to 100 m depth is a regular feature, the different chemistry between compartments (II) and (III), where compartment (III) is in an approximate steady state, may be explained.

Chemogenic calcite precipitation

In natural seawater, chemogenic calcium carbonate formation is rare. How- ever, under very special conditions it might occur, e.g. during evaporat ion in tropical latitudes or during sea ice production. When sea ice is formed, brine is trapped in channels between the ice crystals. The lower the temperature the ice is exposed to, the more concentra ted the brine becomes, and at a given temperature the solubility product of, e.g., calcium carbonate is exceeded (Richardson, 1976). In anoxic seawater the solubility product might be ex- ceeded as the concentra t ion of carbonate is increased by the large mineraliza- tion rate in comparison to the venti lat ion of the water. The excess calcium in the deep water of Framvaren is assumed to be the result of mineralization of organic mat ter of bacterial origin, where calcium ions are loosely adsorbed o1" bound to proteins in bacteria. Dissolution of calcite from skeletal material in

374

Ca~l iss

CH=O(org.) • ~hSO~" *

CaCOI ( s ) * ' / IH " - Ca ~ ' *

2 HCO~" * v~ MS

I 0,)

:(l~)

Fig. 9. Schematic diagram of the sources of calcium and the processes occurring in the respective compartments (I, II, III and IV) in the super-anoxic fjord, Framvaren, southern Norway.

the sediments and diffusion of calcium into the bottom water is not likely to be important as the calcium content in the pore water is lower than in the bottom water. Any solubilized calc iumin the sediment appears to be removed from the pore water by in situ precipitation.

The excess concentrations of calcium and total carbonate in the deep water and the pore water of the sediments result in supersaturation of calcite follow- ed by precipitation. In addition, several factors strongly suggest chemogenic calcite formation:

(i) Weak acid treatment (HC1) of sediment trap material gave effervescence and weight loss in samples from 100 m and deeper but not at shallower depths.

(ii) SEM/EDAX analyses of sediment trap material from depths below 1OO m showed crystalline particles containing calcium (Plate 1). X-ray diffraction analyses indicated calcite.

(iii) Sediment cores taken from depths below 100m are highly enriched in calcium in that part of the core representing material deposited since the fjord became fully marine and permanently anoxic (since 1850). Sediment cores from shallow water showed no changes in calcium with depth (Fig. 8) and represent calcium in the source rock and in skeletal biogenic material. The increase of calcium towards the surface of the deep basin core may either be explained by a more extensive chemogenic calcite formation in recent years, due to an increased calcium to carbonate solubility product, or dissolution of chemo- genic and biogenic calcite at depth in the core, followed by upward migration of calcium and reprecipitation at the sediment-water interface.

375

CONCLUSION

A n a t t e m p t h a s b e e n m a d e to o u t l i n e t h e f a t e o f c a l c i u m in a s u p e r - a n o x i c f jo rd , F r a m v a r e n in s o u t h e r n N o r w a y . A s c h e m a t i c d i a g r a m (Fig . 9) i l l u s t r a t e s t h e s o u r c e s o f c a l c i u m a n d t h e p r o c e s s e s i n f l u e n c i n g t h e b e h a v i o u r o f c a l c i u m in d i f f e r e n t c o m p a r t m e n t s o f t h e f jo rd . C a l c i u m in t h e s o u r c e r o c k ( f a r s u n d i t e ) a n d in b i o g e n i c s k e l e t a l m a t e r i a l u n d e r g o l i t t l e c h a n g e in t h e w a t e r c o l u m n a n d a r e i n c o r p o r a t e d in t h e s e d i m e n t s ( c o m p a r t m e n t IV). B a c t e r i o l o g i c a l l y a s s o c i a t e d c a l c i u m is f o r m e d a t t h e i n t e r f a c e b e t w e e n c o m p a r t m e n t s (I) a n d (II) a n d is r e g e n e r a t e d w h e n t h e o r g a n i c m a t t e r b r e a k s d o w n in c o m p a r t m e n t s (II) a n d (III) . D u e to l i t t l e w a t e r e x c h a n g e in c o m p a r t m e n t (III) , s u p e r s a t u r a t i o n of c a l c i t e o c c u r s a n d c h e m o g e n i c c a l c i t e is fo rmed . S e d i m e n t a t i o n o f c h e m o g e n i c c a l c i t e c a u s e s a n e n r i c h m e n t o f c a l c i t e in t h e s e d i m e n t s ( c o m p a r t m e n t IV), w h e r e d i a g e n e t i c p r o c e s s e s m a y r e d i s t r i b u t e t h e c a l c i u m .

ACKNOWLEDGEMENTS

T h e m a r i n e r e s e a r c h a t t h e D e p a r t m e n t o f A n a l y t i c a l a n d M a r i n e C h e m i s t r y is s u p p o r t e d by t h e S w e d i s h N a t u r a l S c i e n c e R e s e a r c h C o u n c i l . T h e R o y a l N o r w e g i a n C o u n c i l fo r S c i e n t i f i c a n d I n d u s t r i a l R e s e a r c h a n d N o r w e g i a n I n s t i t u t e for W a t e r R e s e a r c h ( N I V A ) h a v e f i n a n c i a l l y s u p p o r t e d t h e F r a m - v a r e n p r o j e c t . O n e o f t h e a u t h o r s (J .S.) is g r e a t l y i n d e b t e d to t h e U n i v e r s i t y o f G o t h e n b u r g for a 4 - m o n t h g u e s t p r o f e s s o r s h i p .

REFERENCES

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