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Preliminary results of the Black Sea SAR project

Jan-Hendrik Körber
MARUM - Center for Marine Environmental Sciences
Faculty of Geosciences, University of Bremen

In advance to the MSM 15/2 cruise to Ukrainian and Georgian parts of the Black Sea in May 2010 approximately 120 ENVISAT Advanced Synthetic Aperture (ASAR) Image Mode Precision images (IM_P) with a resolution of about 30 m were analyses in order to identify sites where natural oil seepage occurs. All images were loaded to a geographic information system and analysed manually. The origins of potential natural oil slicks (OSOs) were marked in an image specific point shape file. All resulting point shape files were overlaid to identify OSO cluster. The cluster identification was done manually, since we struggled to get as nice results as you achieve applying the dendrogram and cluster analysis. (I believe it’s mainly due to the fact that we do not have knowledge on surface currents and possible depth dependent deflections of bubble plumes).
In the Ukrainian parts of the Black Sea many potential OSOs were identified upon first image analyses, however no site showing persistent slicks could be identified. Also, no evidence for oil seepage in Ukrainian waters was found during the cruise, though many sites of gas seepage have been found and were known before.
The situation is different for Georgia. The analysis of 40 ASAR IM_P scenes in the study area yielded clear evidence for oil seepage between 2003 and 2010 (the years images were available for). In the following a number of figures illustrating preliminary results of the image analyses, cruise MSM15/2 and archived data from the cruises M72/3 in 2007(Bohrmann et al. 2008) and TTR15 (IOC Technical Series No. 72) in 2005 are shown.

The image analyses allowed identifyingg 8 sites where natural oil seepage occurs (Fig. 1). The most pronounced oil slicks and the highest persistency of oil slicks were found above two structures named Colkheti Seep and Pechori Mound, followed by site G1. Sites G2 to G6 do not show oil slicks on most of the analysed images, but the occurrence of seepage seems very likely. Tab. 1 gives an overview of how many images covering the different sites were available and how many of them showed oil slicks. Plate 1.1 and 1.2 present sub-scenes of ASAR images showing oil slicks at the different sites. The most prominent sites are Colkheti Seep and Pechori Mound which are shown in detail in Fig. 2, 3 and 4. These sites have been known from previous cruises (to my knowledge they were first mentioned in the TTR-15 cruise report 2005, but Gerhard and Heiko might prove me wrong).
Oil seepage has been observed at Colkheti Seep during one ROV dive in 2007 and the presence of oil in the shallow sediments was proven by gravity coring in 2005, 2007 and 2010. From cruise M72/3 (2007) hydroacoustic data acquired with the PARASOUND echosounder is available and a number of acoustic anomalies were detected. This anomalies do not appear as clear ‘flares’ but are rather blurred or undefined features and might thus not be useful to pinpoint locations of gas emanation. However, they are plotted in all following figures. Beside these sites, four distinct flares at Colkheti Seep and two at Pechori Mound were found. Their locations are indicated on all maps as well. Plate 2a) to c) shows sample echograms of these flares. The location where oil and gas seepage was documented during a ROV dive in 2007 is also indicated on Fig. 2 and 3. During MSM15/2 cruise last year surfacing oily bubbles were observed (see Plate 3a) and b)). This location is marked in the figures, too.

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