Project code: DFG-Fr 1134/12
Coordinator: André Freiwald
Project Staff: Max Wisshak (GZN)
Project Partner: Kirsten + Joachim Jakobsen (Rebikoff-Niggeler Foundation)
Duration: 2006-2009

 
Studies on the various facies of the widespread cool-water carbonate factory in the N-Atlantic are far advanced, however, quantitative data on growth and degradation rates are almost lacking. This project focused on the warm-temperate Azores Archipelago because of its remote location far from land, its poorly studied carbonate environment and because of the easy accessibility to a manned submersible at the island Faial. By covering a wide environmental gradient with respect to light regime and different water-mass properties along a bathymetric transect (0-500 m), we budgeted carbonate-accretion and bioerosion rates with an experimental approach.

Complementing, we undertook detailed morphological and geochemical analyses (stable ¹⁸O and ¹³C isotopes, trace elements) of selected long-living calcareous epibenthos (stylasterids, corals, oysters) for growth-rate analyses and for the detection of subtle climate variability in this area. In this respect, the main focus was laid on the exceptional occurrence of enigmatic deep-water oysters, which we established as a new species Neopycnodonte zibrowii. With the aid of radiocarbon dating, we where able to reveal that these oysters reach a remarkable centennial longevity of more than 400 years and thus range among the longest-lived non-colonial organisms we know on earth. With mainly Mesozoic relatives, this species is aptly called a "living fossil" and occurs in close association with another relict of ancient time, the small crinoid Cyathidium foresti.

The experiment itself comprises quantitative and qualitative monitoring of carbonate production and degradation as well as the recording of in situ environmental data (temperature, salinity and photosynthetically active radiation along with depth). The anticipated results are expected to yield (1) warm-temperate carbonate-production and bioerosion rates, (2) enhanced insight in the suitability of stable isotopes for growth rate studies and high-resolution climate variability analyses, (3) knowledge on the bathymetric as well as biogeographic distribution of bioeroding and carbonate-accreting agents and (4) new insights in the relative contribution of boring organisms versus grazers on different substrate orientations to the process of bioerosion.

The Azores archipelago has been chosen as an ideal site for this experimental approach where K. and J. Jakobsen of the Rebikoff-Niggeler Foundation provide us with the unique chance to carry out a sophisticated bioerosion and carbonate-accretion experiment with the aid of a submersible at comparably very low costs. The modern submersible "Lula" is equipped with high-end video equipment, various sensors and a manipulator and allows us to cover a bathymetric transect reaching down to 500 m water depth. This gives us a maximum of control on the selection of proper experimental sites and a successful and efficient deployment and recovery, respectively.

During September 2006, the experimental frames were successfully deployed in the south Faial Channel in intense collaboration with K. and J. Jakobsen, supported by C. Michels. Two of the panels were positioned at various depth stations between 5 and 500 m water depth and were recovered in 2007 and 2008 after one and two years of exposure, respectively. During a total of 15 missions with research submersible "Lula", selected sample material of calcareous epibenthos, as well as numerous water samples were taken, and the habitat characteristics and faunal diversity was documented.

One month ahead and as a valuable addition to the ongoing project, three further experimental frames were deployed in arctic Spitsbergen at almost 80° northern latitude in the course of the polar expedition of the MS Merian 2/3. In this case, the deployment was carried out with the aid of the approved research submersible "Jago".