Oxygen and trace gases in the tropical southeastern Pacific - Cruise No.M90 - October 28 - November 28, 2012 - Cristobal (Panama) - Callao (Peru) (English)

During cruise M90 a combined chemical, physical oceanographic and biological research cruise was carried out in the eastern tropical Pacific in order to obtain a better understanding of the dynamics and variability of tropical oxygen minimum zones within the framework of the SFB 754 (Climate Biogeochemical interactions in the tropical Oceans). The main goal of cruise M90 was the quantification of the longer periodic variability in the oxygen minimum zone of the tropical South Pacific. The longer periodic changes can be determined in comparison to earlier measurements made on the same sections. A special focus was on the role of large-scale circulation as well as the role of eddy processes for the changes in oxygen and the ventilation of the oxygen minimum zone. The measurements on sections along 85°50W, 6°S, 16°45S and the survey of eddies included hydrographic measurements (CTD-rosette, ADCP), as well as oxygen, nutrients, stable isotope compositions of silicate and nitrate measurements. In addition nitrous oxide, short lived nitrogenous compounds and redox-sensitive species were measured to identify key microbial processes occurring in the Oxygen Minimum Zone (OMZ). The ADCP measurements with the 75 kHz and the 38 kHz ADCP provided good current measurements down to about 1200 m depth and were a good measurement component to identify the location of the eddies. All planned important measurements could be carried out and the survey of 3 eddies let to additional valuable data sets.