Introduction

R/V Pelagia Cruise ARCHIMEDES-1

INTRODUCTION

Goals of the ARCHIMEDES-1 cruise Based on the results of previous ALW-NWO funded research, we follow the succession and spatial dynamics of the microbial community in the main deep water masses of the North Atlantic. During the 28 days cruise in the North Atlantic, we study the changes in composition and activity of the prokaryotic (Bacteria, Archaea) community in the two largest but least-known oceanic subsystems, the meso- (150-1000m) and bathypelagic (1000-4000m) realm under pressure conditions as the organisms experience in their environment. Individual main deep water masses of the deep North Atlantic are followed, as determined by Physical Oceanographers, to assess the succession of the prokaryotes inhabiting these waters. The potential effect of pressure on the metabolic rates of deep water bacteria and archaea is largely unknown while 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, can still only be deduced from model predictions in combination with a few actual rate measurements under realistic pressure conditions. 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 pioneered by closely interacting NIOZ scientists and technical personnel.
NIOZ High Pressure Sampler	In situ pressure-retaining systems constructed and manufactured at the Royal NIOZ are used to assess, for the first time ever, cell production, respiration and enzymatic activity of the bulk bacterial and archaeal community and compare these rates with those on decompressed samples. The study is a joint activity of the Departments Biological Oceanography and Physical Oceanography of the NIOZ and is part of the NIOZ sub-theme 'Processes in the dark ocean - POSEIDON)'.