Detailed visual seabed survey at drilling site 7218/11-1
Detailed visual seabed survey at drilling site 7218/11-1
Detailed visual seabed survey at drilling site 7218/11-1
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Figure2. ROVtransectsandrecordsof spongesfound<strong>at</strong> Darwinduringthe baseline<strong>survey</strong>in 20<strong>11</strong>. Therel<strong>at</strong>ive<br />
amountsof the variousc<strong>at</strong>egoriesof spongedensitiesare shownin the pie chart.Sedimentsamplesweretaken<br />
<strong>at</strong> the red dots (axescrosses).TheSPUDloc<strong>at</strong>ion is markedwith a blue triangle (seearrow). Figurefrom DNV<br />
(20<strong>11</strong>).<br />
The baseline <strong>survey</strong> did not reveal the presenceof soft or hard corals <strong>at</strong> the Darwin field.<br />
Furthermore,no red-list specieswere identified. The specieswith the highestregistereddensities<br />
were the squ<strong>at</strong> lobster Munida spp. as well as spongespeciessuch as Geodia. Rel<strong>at</strong>ively high<br />
densitiesof soft bottom spongespecieswererecordedin the area, with 85.2%of the benthichabit<strong>at</strong><br />
containing "sc<strong>at</strong>tered" to "high densities"of sponges.Darwinhad the highestrecordingsof sponge<br />
densities,rel<strong>at</strong>iveto other nearbyfields<strong>survey</strong>edin 20<strong>11</strong>. (text modifiedfrom DNV20<strong>11</strong>).<br />
Qualit<strong>at</strong>iveabundanceclassesappliedby DNVare: 1. Singlespecimen/rare, 2. Sc<strong>at</strong>tered,3. Common<br />
and4. Highdensity.Illustr<strong>at</strong>ionsof thesedensityclassific<strong>at</strong>ionsare givenin Section2, M<strong>at</strong>erialsand<br />
methods.<br />
1.2.2 Additional studies 2012<br />
Basedon the resultsfrom the BaselineSurvey,duringthe planningof the well RENASaskedDNVto<br />
go deeperinto the d<strong>at</strong>a and try to identify areaswith low densityof spongeswere a CTSsolution<br />
could be deployedfor cuttingsdeposition.In addition SINTEFwas askedto model the spreadingof<br />
cuttingsby different cuttingshandlingsolutions.<br />
DNV(2012) summarizetheir findings:"Thescopeof work wasto assessthe distribution of deepsea<br />
sponges<strong>at</strong> Darwinby d<strong>at</strong>a interpol<strong>at</strong>ions.Byusingspongedensityd<strong>at</strong>a from the BarentsSea<strong>visual</strong><br />
<strong>survey</strong>20<strong>11</strong>, interpol<strong>at</strong>ed maps were made, showingcalcul<strong>at</strong>edvaluesof spongedensitiesin the<br />
<strong>drilling</strong> area.Backgroundd<strong>at</strong>a like spongedensitiesfrom other fields and sedimentsamplingd<strong>at</strong>a<br />
was included in the evalu<strong>at</strong>ion of the sponge situ<strong>at</strong>ion <strong>at</strong> the Darwin field". DNV have made<br />
recommend<strong>at</strong>ionsfor loc<strong>at</strong>ionsfor drill cutting depositionth<strong>at</strong> were estim<strong>at</strong>edto havethe lowest<br />
impacton the spongeassemblages .<br />
Akvaplan-niva AS, 9296 Tromsø<br />
6 www.akvaplan.niva.no
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