Mi­cro­pro­filer

The sed­i­ment sur­face is char­ac­ter­ized by steep gradi­ents and an ex­tens­ive spa­tial and tem­poral het­ero­gen­eity. Meas­ure­ments with high tem­poral and spa­tial res­ol­u­tion are cru­cial for the un­der­stand­ing of early di­gen­esis, mi­crobe-en­vir­on­ment in­ter­ac­tions and benthic fluxes. Benthic mi­cro­bial activ­ity is lim­ited by kin­et­ics (avail­ab­il­ity of suit­able mi­crobes/​en­zymes, pH, T, and other mi­croen­vir­on­mental factors) and by mass trans­fer rates (avail­ab­il­ity of the main re­act­ants: e.g. oxy­gen, ni­trate, sulfate, sulf­ide). To de­term­ine mi­cro­bial con­ver­sion rates in sed­i­ments and to get in­sight in their reg­u­la­tion, activ­ity meas­ure­ments must be com­ple­men­ted by char­ac­ter­iz­a­tion of the hab­itat, its mi­croen­vir­on­ments, de­term­in­a­tion of trans­port phe­nom­ena and, ideally, sub­strate avail­ab­il­ity meas­ure­ments. The mi­cro­pro­filer unit en­ables the in situ quan­ti­fic­a­tion of such pro­cesses in en­vir­on­ments where core re­trieval severely al­ters the sed­i­ment, such as in gas-laden cold seeps, the deep sea, or highly dy­namic en­vir­on­ments.

The instrument:
The mi­cro­pro­filer is com­posed of a ti­tanium hous­ing car­ry­ing sensors and data ac­quis­i­tion unit, a mo­tor, a deep sea bat­tery and a frame. The sensors moun­ted on the bot­tom of the device are mainly mi­cro­sensors, small, needle-shaped and ex­tremely sens­it­ive elec­trodes cap­able to de­term­ine geo­chem­ical gradi­ents in wa­ter or in sed­i­ment. They have a tip size of about 5–50 µm, thus non-in­vas­ive meas­ure­ments can be car­ried out. An in­di­vidu­ally as­sembled as­sort­ment of up to 11 mi­cro­sensors, cov­er­ing an area of 180 cm2, can be used sim­ul­tan­eously on the device. Autonom­ous pro­fil­ing can be car­ried out with a spa­tial res­ol­u­tion of >50 µm and a max­imal ver­tical res­ol­u­tion of 20 cm. Cur­rently mi­cro­sensors for O2, H2S, pH, redox, Ca2+, pCO2 and NO3-, and mac­ro­sensors for tem­per­at­ure and con­duct­iv­ity are avail­able for in situ use. From the lin­ear con­cen­tra­tion gradi­ent in the dif­fus­ive bound­ary layer or the steep­est gradi­ent within the sed­i­ment dif­fus­ive fluxes can be cal­cu­lated provid­ing in­form­a­tion on e.g. oxy­gen con­sump­tion rates in deep sea sed­i­ments and sulf­ide pro­duc­tion or con­sump­tion at cold seeps.
The mi­cro­pro­filer unit can be fixed to­gether with any trans­port­a­tion device and ap­plied as re­quired. De­ployed by re­motely op­er­ated un­der­wa­ter vehicles (ROVs) and sub­mers­ibles, which en­able tar­geted and pre­cise po­s­i­tion­ing at se­lec­ted spots un­der visual con­trol, mul­tiple pro­fil­ing de­ploy­ments can be achieved dur­ing one dive. At­tached to a free-fall­ing lander in com­bin­a­tion with benthic cham­bers for com­par­ison of total and dif­fus­ive benthic oxy­gen up­take rates or moun­ted on benthic crawl­ers for ex­tens­ive sea­floor stud­ies. The latest de­vel­op­ment, the newly de­signed x-y-z pro­filer, al­lows in­tens­ive stud­ies of the sea­floor, cov­er­ing an area of up to 625 cm2.