Conclusions
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• Exposed bedrock is identified next to where the two major holes in MS Estonia’s hull are found along the northern side, approximately 69m and 89m from the stern respectively. From ocular inspection of its texture and visible parallel jointing, the bedrock appears to be igneous, likely granite or syenite. Denting in the hull is visible where it comes close to exposed bedrock in-between the two major holes.
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• The sediment thickness model supports previous suggestions that MS Estonia is resting on firm seafloor midship but is poorly supported by soft sediments under the bow section.
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• Using the flat port side as reference, together with the small one-degree trend with lower listing towards the bow, may indicate a gradual deformation of the hull, where the sides are pressed upward from the pressure of the shipwreck’s weight on the seafloor
• MS Estonia lies with the straight part of the fender line aligned ~102°, i.e. with the bow towards east-southeast, and has a trim of ~4.5°±0.3 relative to sea-level. This trim may cause the observed gradual increase of deformation of the shipwreck port side towards the bow.
• The measured listing in this work can be compared with the estimated listing of 120° during the ROV investigations by Rockwater A/S and Smit Tak. Although it has not been possible to verify the accuracy of the initial listing, it seems likely that the shipwreck has changed position over time.
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• A mooring was deployed that measured water column currents at one position over five days. Although there are indications of a compass offset in the moored instrument, the data show strong bottom currents between about 70 and 80m depth, sometimes approaching 1m/s. The depth interval of these bottom currents coincides with a significant turbidity peak in the hydrological data, indicating resuspension and transport of sediments with the bottom currents.
• Although more data covering longer time periods and further analyses are needed to draw firm conclusions on dominating current regimes, the bserved strong bottom currents must be considered when assessing the stability of MS Estonia at her location.
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• A halocline is present between about 60 and 80m depth.
• The boundary between oxic and anoxic conditions in the water column coincided with the halocline, with anoxic conditions prevailing below ~75m depth during the survey.
• MS Estonia was therefore partly in contact with anoxic waters during the survey period. The depth of the halocline (and thus also the depth of the oxycline) can, however, vary significantly over time and oxygen conditions may change rapidly in response to Major Baltic inflows.
• The port aft section of MS Estonia is shallowest, partly rising to a depth of about 57m, implying that this part reaches into the oxic zone. The shipwreck is thus exposed to different conditions with respect to corrosion.
