Physical oceanography and hydrochemistry measured on water bottle samples during METEOR cruise M10/1

During a R.V. Meteor JGOFS-NABE cruise to a tropical site in the northeast Atlantic in spring 1989, three different vertical regimes with respect to nitrate distribution and availability within the euphotic zone were observed. Besides dramatic variations in the depth of the nitracline, a previously undescribed nose-like nitrate maximum within the euphotic zone was the most prominent feature during this study. Both the vertical structure of phytoplankton biomass and the degree of absolute and relative new production were related to the depth of the nitracline, which in turn was dependent on the occurrence/non-occurrence of the subsurface subtropical salinity maximum (Smax). The mesoscale variability of the nitracline depth, as indicated from a pre-survey grid, and published data on the frequent occurrence of the Smax in tropical waters suggest higher variability of new production and F-ratio than usually expected for oligotrophic oceans. The importance of salt fingering and double diffusion for nitrate transport into the euphotic zone is discussed

The nose: a characteristic inversion within the salinity maximum water in the tropical northeast Atlantic

During leg 1 of Meteor cruise 10 in March/April 1989 at 18 circ N, 30 circ W, the high spatial and temporal resolution of hydrographic CTD-stations indicated that the study site was in a hydrographically complex region in the transition zone between the Canary Current and the North Equatorial Current at the southern boundary of the subtropical gyre. Strong variability was found within the upper 120 m due to interleavings of warmer and saltier subtropical salinity maximum water with colder and less saline upper thermocline water. The interleavings caused unexpected nose-like temperature, salinity, nitrate and oxygen profiles yet not described in the literature. A second variability source was found in the Central Water area, because the study area was situated in the vicinity of the Central Water Boundary dividing North and South Atlantic Central Water. Hydrographic analysis of the study shows that interpretations of biological and chemical data can only be done in conjunction with high resolution CTD-profilin

Physical oceanography during METEOR cruise M10/1

During leg 1 of Meteor cruise 10 in March/April 1989 at 18°N, 30°W, the high spatial and temporal resolution of hydrographic CTD-stations indicated that the study site was in a hydrographically complex region in the transition zone between the Canary Current and the North Equatorial Current at the southern boundary of the subtropical gyre. Strong variability was found within the upper 120 m due to interleavings of warmer and saltier subtropical salinity maximum water with colder and less saline upper thermocline water. The interleavings caused unexpected nose-like temperature, salinity, nitrate and oxygen profiles yet not described in the literature. A second variability source was found in the Central Water area, because the study area was situated in the vicinity of the Central Water Boundary dividing North and South Atlantic Central Water. Hydrographic analysis of the study shows that interpretations of biological and chemical data can only be done in conjunction with high resolution CTD-profiling