GrimseyEM – Grimsey Vent Field, Island – 25.6.201

Hölz, Sebastian

OceanRep

POS524 – GrimseyEM – Grimsey Vent Field, Iceland – 25.6.20182. Weekly ReportAfter we were forced to leave the survey area on the 15. - 16.6 to seek shelter in the nearby Eyja-fordhur fiord, we were able to continue with the scientific work plan on the 16.- 17.06. After return-ing to the area of interest, a further gravity core was taken, several stations were measured usingthe heat probe and 3 OBEM receivers were intended to be redeployed along a longer east-westtransect. Unfortunately, one receiver (RX11) did  not resurface and we were forced to temporarilyabandon the station to continue on with a new transmitter configuration using the MARTEMIS sys-tem, which allows us to increase the depth of investigation. Measurements were obtained along anapproximately 4 km long profile. During the measurements, winds and waves returned and wewere again forced to leave the measurement area to seek shelter in the nearby fiord.After returning to the survey area on 19.06further  measurements  were  conductedusing the heat probe. In the following days,MARTEMIS measurements were conductedalong 20 km profile and two further gravitycores  were  retained.  Subsequently,  theremaining 11 OBEM stations were success-fully retrieved and the exciting search for thelost system began. Surprisingly, the triangu-lation indicated that the station had movedapproximately 1.5 km from its original posi-tion. The next morning. we redeployed theMARTEMIS  transmitter  cage  with  anattached camera system to  search for  thelost  receiver.  After  less  than  an  hour  ofsearching,  we  found  the  station  near  theposition that was indicated by the triangulation. Due to the large distance from the deploymentpoint and the fact that the station is currently upside-down, we infer that it must have been caughtin a net . Unfortunately, we were unable to retrieve the station due to insufficient material on deck.However, we hope to retrieve the station in our 2019 campaign. A first interpretation of the acquired CTD data, which was attached to the MARTEMIS system dur-ing measurements shows significant anomaliesin temperature and salinity in  the unsuspectedregions of the survey area. However, a compar-ison to the CTD data of several OBEM receiversshows that  these  fluctuations  are  not  decisiveindicators  for  hydrothermal  activity,  but  rathertemporary fluctuations in the regional temperat-ure field.  These variations are on the order  of1.0°C / 24h which means that CTD data withoutan adequate regional drift correction are insuffi-cient to detect hydrothermal activity in the area.Fig.  1: Station RX11 on video (top left) and ropes holdingrescue hooks in the foreground.Fig.  2:  Temperature  measured  at  several  stationaryOBEM receivers.A heat probe measurement along one profile shows temperatures of ca. 5°C if the probe is located150m above the seafloor. Along the seafloor, the temperature decreases to approximately 1.5°C.To the east of the known hydrothermal field, background temperatures are measurable within thesediment and a slight increase of temperature is observable at closer distances to the field. Station4, which is located ca. 350m east of the field centre shows a significant temperature increaseabove 70°C that we were unable to resolve with the sensors of the heat probe. Previous measure-ments had only experienced temperatures of 10 – 20°C within the sedimentary cores. In compar-ison,  temperature  values  of  35°C  were  measured  during  this  cruise  which  indicates  that  thehydrothermal field is currently in a more active phase than before.On a final note, we would like to show preliminaryresults of the data measured with the MARTEMISsystem.  Transients  measured  above  the  hydro-thermal  field  (red)  show  significantly  largervoltages  compared  to  the  background  (black)curves acquired at large distances to the hydro-thermal field.  Additionally,  compared to previousmeasurements, the curves are now free of distor-tions that were previously caused by small metalcomponents within the measurement system thathave now been removed. Here we would like toacknowledge the cooperation with the TLZ (spe-cial  thanks  to  Marion  Deckelnick  and  FlorianBeeck …) .  Further results will  be presented inthe cruise report and in the GDY seminar this Fall.Crew, technicians and scientists are all well andexcited  to  return  to  Kiel  to  enjoy  temperaturesabove  the  typical  5°C,  which  accompanied  usthroughout our time at sea.Amir Haroon & Sebastian HölzFig. 3: Profile with six measurements with the heatflow probe (West ↔ East). Stations 1-3 and stations 4 – 6 arelocated to the East and West, respectively, of the hydrothermal field.Fig.  4:  Processed  transients  measured  with  theMARTEMIS system above and away from the hydro-thermal field (red and black, respectively).

2. Wochenbericht POS524

http://oceanrep.geomar.de/43494/7/POS524_WeeklyReport_2.pdf

2. Wochenbericht POS524

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