Anomalies of oxygen measurements performed with Aanderaa optodes

Abstract

Four sets of measurements performed between 2005 and 2010 in the deep central Atlantic, the deep north-western Mediterranean Sea, and in the Arctic Ocean revealed strange anomalies in the performance of the Aanderaa optode 3830 sensors mounted on RCM11 current meters in low current regimes (current speeds >10 cm s–1). All oxygen datasets collected during these deployments showed significant drops of oxygen (50–100 ìmol) affecting the data stability of the optode sensors in low hydrodynamic conditions. High correlations between all acquired parameters (temperature, turbidity, speed and direction of currents) verified that no unusual event occurred in the mooring areas during the periods of acquisition, although natural events responsible for such abrupt, short and intense oxygen variations cannot be easily identified. Despite the well-known performance of the Aanderaa optodes, these experiments demonstrate that the data acquired by those installed on RCM11s cannot be always reliable, especially in low energy systems (typical for the deep ocean), and that current speeds should always be considered in order to verify the reliability of the data recorded.