Introduction

R/V Pelagia Cruise ARCH-OCEAN

INTRODUCTION

The aim of this cruise is to study the activity of the prokaryotic community in the two largest but least-known oceanic subsystems, the meso- (150-1000m) and bathypelagic (1000-4000m) realm. Our knowledge on the phylogenetic composition of the prokaryotic communities in the dark ocean has substantially advanced over the past decade. Their actual metabolic activities, however, still remain essentially unknown and can only be deduced at the moment from model predictions in combination with a few actual rate measurements under in situ pressure. These model predictions and the few data available indicate that prokaryotic communities in these dark realms of the ocean are more active than commonly measured under decompressed conditions. We directly measure prokaryotic activity under in situ pressure conditions by combining conventional methods to determine the metabolic activity of the bulk prokaryotic (Bacteria and Archaea) community with recent methodological developments on single cell approaches in the deep ocean. In situ pressure-retaining systems are used to assess, for the first time ever, cell production, respiration and ectoenzymatic hydrolytic activity of the bulk prokaryotic community and compare these rates with those on decompressed samples. By combining the recently developed catalyzed reporter deposition fluorescence in situ hydridization (CARD-FISH) with microautoradiography (MICRO-CARD-FISH) we determine the uptake of specific organic compounds by selected Bacteria and the Cren- and Euryarchaea in the meso- and bathypelagic realm and assess their population/group-specific pressure sensitivity. Additionally, samples will be taken to determine viral abundance and diversity in the deep realm of the (sub)tropical Atlantic.