Web­log 11

Chief sci­en­tist leg 4
Frank Wenz­hoefer
f.wenz­hoefer.d at
me­ri­an.brie­se-re­se­arch.de
Whe­re is Ma­ria S. Me­ri­an?
Weblog 11
30.11. - 05.12.


30.11.2009

On No­vem­ber 30 the AUV-team con­ti­nued with their suc­cess sto­ry. AUV-dive 27 was the lon­gest mis­si­on pos­si­ble. Af­ter 9 hours and 39 km of sur­vey the AUV re­tur­ned to sur­face with al­most em­pty bat­te­ries. Half way to the sur­face the bat­te­ry ca­pa­ci­ty was then too low to keep the com­mu­ni­ca­ti­on avail­able and the ve­hi­cle so­le­ly sur­faced with its po­si­ti­ve buoyan­cy. Howe­ver, du­ring its dive the AUV map­ped the nort­hern, wes­tern and sou­thern rim of the mud vol­ca­no and thus we have co­ve­r­ed al­most the ent­i­re geo­struc­tu­re, only a small area in the eas­tern part is mis­sing. The ba­thy­me­try map re­vea­led that the Ams­ter­dam mud vol­ca­no is a com­plex struc­tu­re with a rough cen­ter, a smoo­ther ou­ter area towards west, sur­roun­ded by a rough rim. The high-re­so­lu­ti­on data enable as also to iden­ti­fy sin­gle struc­tu­res.
Fig. 1a : 2-D Ba­thy­me­try map of the cen­ter and north-west area of the Ams­ter­dam mud vol­ca­no; 0.5 m raw-Grid, sin­gle fil­te­ring (Sour­ce: Ma­rum, Bre­men)

Fig. 1b: 3-D view of the cen­ter area; 0.5 m raw-Grid, sin­gle fil­te­ring, sca­le in­cre­ments 10m (Sour­ce: Ma­rum, Bre­men)
Fig. 2a De­tai­led 3-D image of the seaf­loor struc­tu­res in the mud vol­ca­no can­ter; 0.5 m raw-grid, sin­gle fil­te­ring, sca­le in­cre­ments 2.5m (Sour­ce: Ma­rum, Bre­men)
Fig. 2b: De­tai­led 3-D image of a sin­gle geo­struc­tu­re; 0.5 m raw-grid, sin­gle fil­te­ring, sca­le in­cre­ments 1m (Sour­ce: Ma­rum, Bre­men)
ROV dive 257 was only short and had to be stop­ped at 500m wa­ter depth. The ma­ni­pu­la­tor still does not work pro­per­ly; ano­ther night of re­pair for some of the pi­lots. We used the time to take a TV-MUC samp­le from the sur­roun­ding area to get a re­fe­rence samp­le. We choo­se a site with a nor­mal se­di­ment tem­pe­ra­tu­re pro­fi­le but du­ring the TV-MUC sur­vey se­veral black patches were vi­si­ble in­di­ca­ting that this site is still in­flu­en­ced by the mud vol­ca­no ac­tivi­ty.


On De­cem­ber 1 du­ring ROV dive 258 we were then able to collect se­di­ments from the mud vol­ca­no cen­ter. Lar­ge patches of grey se­di­ments, even so­me­ti­mes with small whi­te bac­te­ri­al mat patches, co­ve­r­ed this part of the mud vol­ca­no. Using our Lift to bring ad­di­tio­nal in­stru­ments to the seaf­loor, like the bent­hic cham­ber and bla­de co­rers, we were able to collect sam­ples for all groups on board.


The next two days were cha­rac­te­ri­zed by bad wea­ther preven­ting any AUV or ROV dive. Thus the­se days were used to per­form ad­di­tio­nal heat flow mea­su­re­ments, which will help us to bet­ter de­fi­ne the ac­tive area of the mud vol­ca­no. Fur­ther Pa­ra­sound tran­sect were used to map the gas fla­res sin­ce Mi­ri­am Rö­mer found out that the seeps were not con­stant­ly emit­ting gas but show­ed some pe­ri­ods of quiet­ness. In to­tal 34 fla­res could be de­tec­ted by Mi­ri­am clus­te­ring in three sites. Be­si­des the strong fla­res seen, which of­ten reach up to 750m into the wa­ter co­lumn, se­veral wea­ker fla­res, ex­ten­ding bet­ween 100 and 500 m into the wa­ter co­lumn were de­tec­ted.
Fig 3: Dis­tri­bu­ti­on of gas fla­res at the Ams­ter­dam mud vol­ca­no (Sour­ce: Mi­ri­am Rö­mer, Ma­rum Bre­men)
Fig 4 Screen­shot sho­w­ing se­veral fla­res ex­ten­ding in to the wa­ter co­lumn (Sour­ce: Mi­ri­am Rö­mer, Ma­rum Bre­men)
On De­cem­ber 4 we once again de­ploy­ed our lift sys­tem pa­cked with se­veral in situ tools to take sam­ples from the se­di­ment are­as bet­ween the grey and black se­di­ment patches. The idea was to com­pa­re the geo­che­mi­cal zo­na­ti­on, bent­hic flu­xes and fau­na (from mi­cro to mar­co) com­po­si­ti­on from the dif­fe­rent ha­bi­tats. Howe­ver, ROV dive 259 had to be ab­or­ted due to tech­ni­cal pro­blems with the ROV. Af­ter re­co­gni­zing that the ROV-team nee­ds a lon­ger time pe­ri­od to re­pair Quest, the Lift was re­leased and re­co­ve­r­ed.

The evol­ved time was then used to map the mud vol­ca­no Athi­na with Pa­ra­sound for gas fla­res and to per­form a TV-MUC tran­sect to se­arch for gas emit­ting sites and to map the ha­bi­tats. A strong fla­re at in the cen­ter of Athi­na was found by Pa­ra­sound and TV-MUC.
Fig. 5: Parasound image showing a strong flare at the center as well as a weak flare at the rim (Source: Miriam Römer, Marum, Bremen)


Sin­ce the wea­ther si­tua­ti­on im­pro­ved on De­cem­ber 5 and the re­pairs on Quest were fi­nis­hed ano­ther last dive on Ams­ter­dam was pla­ned to re­co­ver the co­lo­niza­t­i­on ex­pe­ri­ments and Ho­mer Be­a­con pla­ced two weeks ago du­ring our first ROV dive. Un­for­t­u­n­a­te­ly the dive had to be ab­or­ted again at 500 m wa­ter depth due to tech­ni­cal pro­blems and thus we have to lea­ve the in­stru­ments at the seaf­loor for lon­ger. The re­mai­ning time be­fo­re we have to lea­ve the working area the next day was used with Pa­ra­sound map­ping of the Thes­sa­lo­ni­ki and Kula mud vol­ca­noes.


Frank Wenz­hö­fer

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