Geological
ObservationsThroughout the course of the work by the team in the fjord, numerous observations were made of the ikaite and the local geology of the upper fjord area. The observations made by the team are presented here with, in many cases some brief discussion.
Syenite/Gneiss Boundary Evidence of an intrusive boundary with a slight cooked margin, (as opposed to a process of fenitization - see Geological Setting section) between the syenite and the gneiss, was best seen at a location on the shoreline just east of the small island. At this location the syenite passes (to the south), into a highly friable rock material containing a very high content of iron, in the form of pyrites.
Field Geology Map The map is only rough, but to produce a better map, would have required considerably more mapping. The main reason for mapping was to look at the predominant jointing patterns, in an attempt to review a possible control on the ikaite column distribution. The mapping whilst generally, not as widespread and detailed as that of Emeleus, was unique in that it mapped the island - which gave us a better control of the syenite/gneiss boundary across the fjord.
However, the map does show the fundamentals:
i) The distribution of ikaite columns lies within the syenite boundary. ii) Our map can be related to that of Emeleus by the similarity of some of the exposure and suggested boundaries. iii) It picks out all the main rock types, although there are many smaller units and a fair number of minerals that have not yet been identified
The water of the upper fjord (referred to as 'the fjord' here after) is strongly stratified both by temperature and salinity. The surface waters of the fjord are almost fresh and relatively warm 8-10 oC. At a depth of between 1-2m a halocline exists which also represented a distinct thermocline, below which the water changes at once to sea water at a much lower temperature of 2-3 oC. This interface made the underwater visibility poor for the first few meters as the two fluids of differing refractive index mixed giving an oily impression.
The bottom of Ikka Fjord is formed predominantly from fine, unconsolidated, black organic rich mud, broken by outcrops of syenite roche moutonnees and frequent glacial dropstones. Where streams flow into the fjord, deltas are formed and the bottom is strewn with boulders and pebbles, which, in the case of the river at the head of the fjord extend over some distance. The bathymetric survey revealed that the waters of the upper fjord are much shallower than those in the surrounding fjords, with a maximum depth of only 26m as opposed to 600m. Through the middle of the long axis of the fjord is found a deeper trench. This trench is broken in two by a shallower platform formed from the delta deposits of the river running down the major faultline on the mid NW side of the fjord. The depth reading revealed that the deposits from the delta at the head of the fjord extend for several hundred meters down the fjord giving a gently sloping profile in this area. Where the deep channel, beyond the delta at the head of the fjord starts, the growth of large ikaite columns has resulted in the construction of a pyramidal structure which is probably not as steeply sided as appears on the DEM as a result of interpolation and contouring.
Ikka Bund (the upper part of Ikka Fjord and survey area within which ikaite is found) is very sheltered from marine forces by its location. Although the tidal range is high, and surface currents are moderate, the tidal action affects only a few meters of surface and below this currents are much gentler to still. The entrance to Ikka Bund is a shallow constriction through the depositional efforts of a stream delta, an exposed roche moutonnee and possibly a terminal moraine. Thus current actions are further subdued and large ice bergs which could damage the columns may ground or miss the narrow entrance and so are mostly excluded.
During the winter months the fresh surface waters freeze down to 60cm. The effect this has on the ikaites is unknown.
Seemingly unrelated to the ikaite deposit was a fine white precipitate seen near the southern limit of the surveyed fjord. Whilst diving in this area on one occasion, the light green, weedy bottom appeared as a meadow with mist collecting in hollows. The hollows were several meters across and 20-30cm deep and the white precipitated could be wafted out of them in the same manner as smoke. Below the precipitate there was no green weed but a black sludge of decaying vegetable matter which itself was easily wafted up into the fjord water.
Ikaite was mapped as occurring exclusively in areas where the underlying geology is, or at least thought to be, the syenite complex, identified from Emeleus (1963) and our own observations. Thus, the first occurrences mapped, start abruptly on the seabed over the rocks of the syenite complex, as the delta deposits thin. The columns were found with varying density down the fjord ceasing at a point where the syenite complex stops against what is probably the gneiss, before the largest NS fault zone mapped by Emeleus (1963) that dissects the mountain ridges on the NW side of the fjord.
Along the length of the surveyed area of the upper fjord, the ikaite was observed to show differing form. Although the ikaite occurrence was a continuum it can be divided into three broad zones, the upper, middle and lower zones. All zones lie within the limits of the syenite intrusion.
Upper Zone In the upper zone, towards the head of the fjord, ikaite forms great towering columns up to 18m high. The roots of these great columns are obscured by talus deposits of mud and fecal products from organisms on the columns. There is variety in the heights and widths of the columns in this area ranging from the small, a few centimetres to a metre in height, to real giants rising from the bottom at 15-18m to within 2-3m of the surface. The largest examples of these have great girth, and are formed from the amalgamation of several individual columns creating an irregular undulating surface. The process of amalgamation was incomplete in some locations, such that structures resembling 'flying buttresses'' were formed.
The tops of these amalgamated columns are either stump-like with truncated surfaces, or terminate, slightly deeper, in a spectacular cluster of fine spires of differing lengths up to several meters long. The truncated surfaces are thought to represent the limit of growth at any one time. Deeper truncated surfaces may show regrowth. This upper zone was named the 'Cathedral site' by both expeditions as they reminded the onlooker of the Cathedrals at Barcelona and Milan.
In certain places, in all zones, but particularly around the spires of the cathedral site, the ikaite columns have fallen over and frequently the broken lengths lie amongst the remaining spires. Where these fragments lay, they were often seen to heal to the remaining columns, as the spring waters continuing to flow out of the main column cemented them in place with freshly precipitated ikaite. The actively streaming broken stems from which the fragment was derived would themselves heal, but into a bulbous mass many times the diameter of the original column looking like the head of a poppy seed.
The sides of these massive columns, and indeed most of the other columns seen, have varying colours with apparently different forms of calcium carbonate. The hard crust of the columns is formed from a yellow-buff coloured carbonate, presumed to be diagenetic ikaite and the skeletal remains of coralline alga. Growing on this background are commonly, purple lithothamnian algae creating a knobbly calcitic coat. Where columns are cracked, damaged or bored by organisms, fresh, pure white ikaite was seen to grow up the sides of the column in a variety of shapes. Most commonly these ikaite forms are tear-drop or candle flame-like, up to 1m high. In these cases it is believed that the flow of water streaming from the column is affected by Bernoulli drag, causing the flow to lick up the side of the column.
Other examples of side growth forms are like half-bells embedded in the columns, the insides of which display an open honeycomb structure. The observed examples of fresh ikaite, were seen to made up of a matrix of very fine accicular crystals, up to a centimetre in length. The causes of this re-emergence of ikaite form the sides of the older columns is unknown. Suspected possible mechanisms are boring bivalves, or in the case of the larger forms, fractures caused by upending ice or an increase in the internal hydrostatic pressure.
Spring waters and fine bubbles were observed issuing from the fresh ikaite growths on several columns; the mixing of the two fluids, of differing refractive index, causing an oily taint to the water. The gases forming the bubbles, did not appear to be expelled at any pressure and were readily dissolved in the water.
Middle Zone In the middle reaches of Ikka Bund, the second apparent zone, the ikaite was observed growing both directly out of the muddy bottom, but also from the joints in the syenite outcrop on the roche moutonnee. Ikaite was seen to grow in serrated ridges which when they crossed culminated in peaks, seemingly related to a jointing pattern in the syenite. The ikaite columns in this region are typically smaller than that in the 'cathedral site', being usually no more than 3m but occasionally up to 8-10m high. The density of the ikaite is varied, with areas of very infrequent ikaite and areas of relatively dense ikaite growth. Here, in appearance, the columns were more irregular in outline and frequently densely covered in leafy fan-like sea-weed effectively hiding the detail of the column underneath. This gave the impression of the columns being 'dead' with less apparent growth of fresh ikaite.
Some small columns in the mud (30 cm tall by 10 cm across) could be moved in the same manner as the roots of a potted plant. The impression was that the ikaite had formed from water that has found its way through the mud to the surface and precipitation has commenced as this water came into contact with the sea-water. It is suggested that the mechanism by which they become firmly rooted is by the progressive sinking into the mud under their own weight as they grow. It has been alternatively suggested that the above mechanism would be more likely to create a crust of ikaite and the loose columns are 'dead' and merely supported by the mud.
Lower Zone The third zone of ikaite is found towards the seaward limit of the occurrence where the ikaite forms reefs 10--15m across and 5-10m high with shear sides. It is proposed that these reefs be called 'Pauly's Skerries' as opposed to 'atolls' to avoid the confusion with their tropical counterparts. These masses are composed of hard, calcareous material. The whole is largely encrusted in lithothamnian giving an irregular, rugged appearance. Living on and amongst this mass in great numbers are anemones, echinoids, starfish, sea-squirts, brittle stars and many fish - the many organisms of a living reef community.
Around the edges of the skerry, a talus fringe slopes off into the surrounding muddy sea-bed. Within the muddy deposits of the fringe are the rubbly remains of broken reef and column. The skerry appears founded on a syenite roche moutonnee which extends out from under the mass to the east and north. Off the skerry, on the edges of the underlying roche moutonnee, lie small columns growing out of the fringing mud and up the sides of the rock before pointing vertically up into the open water. In other areas off and around the edges of the skerry are found columns in isolation and together in clusters. Notable amongst these are a small version of the many spired 'cathedral' columns, a perfect line of tall columns (up to 5m high) and an area where there is a small forest of finger sized columns.
The top of the skerry almost breaks surface at low spring tides. On the upper surface a 'powdery' ikaite settles amongst the older rock mass as a calcareous whiting - 'powder snow ikaite' named by the Danish expedition. Some impression of the internal form of the skerry is gained from study of its top. The inside is believed to be at least a partly formed porous mass of ikaite, the exterior stabilised by coralline algae. The remains of two echinoids were seen on top of the skerry partially encrusted in fresh ikaite and along the coralline sides, other shelled organisms were seen to have been incorporated into the mass. Processes such as this may well be adding to, and stabilising the structure.
It is suggested that the reason that the top of the skerry almost reaches the surface, whilst the terminated columns in the upper zone only reach to about minus 3m, is due to a gradient of fresh water. The depth of fresh water decreasing away from the main river input at the head of the fjord (see below diagram). This, further points to the control on the height of the columns as being the fresh water layer and not the effect of ice.
Diagram of Freshwater / Sea water Gradient
The surrounding topography varies along the length of the occurrence and may well account for the differing form of ikaite precipitated. Where the largest columns are found at the top of the fjord, the topography on both sides is at its steepest and highest. In this area hydrostatic pressure is likely also to be at its greatest. Moving down fjord along the occurrence, the topography drops down on both sides, but particularly on the north west side as the major fault zone dissects the ridge. The fault zone has been deeply eroded and contains a stream, draining the ridge side and lowering the water table down to the delta. Across this zone of dropping topography the density and size of the ikaite column is at its lowest despite their being a number of roche moutonnee on the bed of the fjord. Minimum hydrostatic pressure is located at the small delta on the north side of the fjord which emanated from the large fault valley. In the region of the fault zone the skerries could conceivably be formed from a much more disseminated seepage of spring water from the tectonically fractured syenite. This would result in a mass of ikaite precipitation and amalgamation to form the skerries.
The columns are colonised by marine life, apparently making an ideal substrate. There is clear stratification in density and variety of life forms up and down the shafts of the columns presumably related to the changing amounts of penetrative light.
The tops of the columns, particularly the largest columns in the deepest waters, are bare of lithothamniam and other algal forms. They are 'grazed' by echinoids and sea-cucumbers with the occasional anemone and sea-squirt. It is the tips of the columns that show the most fresh ikaite growth possibly accounting for the lack of sessile organic growth.
The presence of echinoids at the tops of most of the columns, again indicates that the columns grow up to a point which always has a sea water covering - echinoids are stenohaline indicators, not being able to exist in either brackish or fresh water.
At greater depth, the biota changes, grading into the Knobbly purple lithothamniam which densely covers most of columns exterior surface. There are again many echinoids, anemones and tube worms. Fresh ikaite is much less abundant restricted to 'candle flame' and the half-bell forms. One possible mode of formation of these ikaite growths could be through the action of boring bivalves, which breach the hard external crust allowing the fluids inside to leak out and precipitate fresh ikaite.
Lateral dissection of a small fallen column (60cm x 15cm) exposed some of the internal characteristics of the columns. The cleaned section revealed an external crust, approximately 1cm thick that was apparently laminated. The outer edge was encrusted with the lithothamnian algae. The internal structure, was a more porous pumice-like texture, with a central pale coloured flame shape structure. The cross section of the column revealed irregular pipes running up through the centre of the column. The pipes and porous nature may represent the path of fluids. A boring bivalve was found in the sawn section, having bored at an angle to the sides to nearly the heart of the column. Whilst the animal is alive it may actively prevent its opening to the water from being sealed by ikaite, but when it dies precipitation of ikaite from this point may well commence.
The maps produced constitute a first attempt to understand the spatial arrangement of the ikaite deposits of Ikka Fjord. The resolution of the GPS/sonar device used was deemed to be within the plotable accuracy of the maps and the dives performed to quantitatively assess the quality of the maps produced by sonar, seem at this stage to reinforce these findings.
The ikaite was apparently growing over springs issuing from the bottom of the fjord. Springs that monopolise joints and fractures within the syenite complex. In areas where there was no obvious outcrop of syenite, ikaite columns were still seen to have been formed, growing out of the muddy bottom. The limit of growth indicated by the truncated columns is believed to be related to the halocline as opposed to erosion by ice.
The ikaite itself appears to be confined by the bedrock geology, forming only within the outcrop of the syenite intrusion beginning soon after delta deposits thin away and ending at the gneiss boundary. Within this occurrence the ikaite is found in three zones which differ in the size and form of the resulting deposit, large columns near the top of the fjord, smaller more isolated columns through the middle of the occurrence and skerry forming ikaite near the lithological boundary/unconformity. Why there should be variation in form is not known but differences in bed form, spring water flow rates and hydrostatic pressure controlled by the nature of the fjords topography is suggested.
Within the individual zones ikaite further displays a great variety of morphological forms. A significant control on form is believed to be, the encrusting marine life, particularly the coralline algae which serve to preserve the columns in stable calcite.
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