Meteor-Blog 26. July 2008: Tracing microorganisms with microsensors

Planetearth Blog

Does the biodiversity of deep-sea organisms play a role for the climate on Planet Earth? Questions all about marine research will be answered directly aboard of the German research vessel Meteor by cruise leader Prof. Antje Boetius and her crew. In cooperation with the geoportal planeterde.de from 17.07.08 to 24.08.08 they contribute a Science-Blog of METEOR expedition M76/3 GUINECO – MARUM research of fluid and gas seeps on the Westafrican continental margin. Technical highlight of the cruise is the remote-controlled under water robot QUEST4000 by MARUM that will be deployed for taking fauna and sediments samples and conduction of in situ experiments. Go on a dive down to places no other human being has ever seen before: explore the fascinating deep-sea fauna and watch the scientists’ work at gas and fluid seeps deep down on the ocean bottom.

Expedition M76/3b is a collaboration of MARUM – Center for Marine Environmental Sciences at Bremen University and its associated institutes MPI and AWI as well as the French research institute IFREMER and the University of Paris.

More informationen and an overview of all contributions to the Meteor-Blogand expedition M76/3B:

26. July 2008 (Author: Frank Wenzhöfer)

"My name is Frank Wenzhöfer and I am a scientist of the "Microbial Habitat Group" at the Max-Planck-Institute for Marine Microbiology. For twelve years now I am developing and applying in situ technology to better understand the microbial processes at the seafloor. These instruments are exposed to extreme conditions (high pressure, low temperature), and it is this challenge what makes in situ studies so interesting.

With the use of underwater robots (ROVs) and submersibles we are nowadays able to perform measurements at targeted spots on the deep-sea floor. This opportunity to perform measurements at so far unknown ecosystems is what fascinates me and what attracts me to work at sea. Here on board I work with several in situ instruments (microprofiler, benthic chamber and eddy) to gain a better understanding of the biogeochemical processes at the unique ecosystems of the West African margin."

Picture 1: Different microsensors mounted to the underwater pressure cylinder of the in situ microprofiler: oxygen, sulfide, pH, temperature and conductivity

Tracing microorganisms with microsensors

Despite the continuing technical problems with the ROV, we were able to bring one of our instruments - the microprofiler - to the seafloor to perform first in situ measurements. The microprofiler measures geochemical gradients at a high resolution directly at the seafloor and enables us to characterize the chemical milieu of microbial habitats. For yesterday’s deployment with the ROV QUEST, different microsensors were mounted on the pressure cylinder, which carries the electronics for our autonomous system: we use oxygen, sulfide, pH, temperature and conductivity sensors (picture 1). These microsensors are manufactured at our institute (Microsensor Group) and have a tip diameter below 25 µm, which is thinner than a human hair!

Picture 2: The microprofiler deployed on a bacterial mat at the REGAB pockmark

After placing the microprofiler on the seafloor, the microelectrodes move with steps of 150 µm into the sediment. The measured microprofiles provide information on the depth zonation of microbial processes and they can also be used to quantify their activities. During our dive we were able to place the microprofiler on a bacterial mat at 3150 meter water depth (picture 2). By pushing an underwater button the autonomous measurement is activated, and the ROV has time to collect additional samples (sediment cores and mussels). Luckily, the dive time was long enough to perform a complete measuring cycle. Thus we were able to get the first in situ data for this cruise. After the ROV is back on board we download the data and directly analyze the results (picture 3). To compare the in situ and ex situ data we also run lab profiles on retrieved sediment cores. Here you see Petra Ristova (see BLOG of 19.07.) and me preparing new sensors (picture 4).

Picture 3: Typical microsensor data (oxygen-, pH-, sulfide- und temperature profiles), allowing to characterize the geochemical zonation of the seafloor

Picture 4: Preparation of the microsensors (Petra Ristova und Frank Wenzhöfer) for laboratory measurements