Physical oceanography and hydrochemistry measured on water bottle samples during METEOR cruise M10/1, supplement to: Koeve, Wolfgang; Eppley, Richard W; Podewski, Sigrid; Zeitzschel, Bernt (1993): An unexpected nitrate distribution in the tropical North Atlantic at 18°N, 30°W - implications for new production. Deep Sea Research Part II: Topical Studies in Oceanography, 40(1-2), 521-536

• Main Authors: Koeve, Wolfgang, Eppley, Richard W, Podewski, Sigrid, Zeitzschel, Bernt
• Format: Dataset
• Language: English
• Published: PANGAEA - Data Publisher for Earth & Environmental Science 1993
• Subjects: Event label; Date/Time of event; Latitude of event; Longitude of event; Elevation of event; DEPTH, water; Temperature, water; Salinity; Density, sigma-theta 0; Ammonium; Oxygen; Nitrate and Nitrite; Nitrite; Phosphate; Silicate; Chlorophyll a; Nanoflagellates, heterotrophic; Cyanobacteria; Bacteria; Eukaryotes; Carbon, organic, particulate; Nitrogen, organic, particulate; Suspended matter, total; Primary production of carbon per hour; CTD/Rosette; CTD; Calculated; Colorometric analysis, manual; Oxygen, Winkler Culberson, 1991, WOCE Report 68/91; Chemiluminescence NO2/NO3; Continuous Flow Automated Analysis Gordon et al., 1993, WOCE Tech Rpt 93-1; Chlorophyll a, fluorometric determination Grasshoff et al., 1983, Chemie GmbH; Epifluorescence microscopy; Optical microscopy; Carbon/nitrogen analyser GF/F filtered; Gravimetric analysis GF/F filtered; 14C uptake; M10/1; Meteor 1986; Joint Global Ocean Flux Study JGOFS; North Atlantic Bloom Experiment, 1989-1991 NABE; Sigrid; North Atlantic; Northeast Atlantic
• Online Access: https://dx.doi.org/10.1594/pangaea.66484; https://doi.pangaea.de/10.1594/PANGAEA.66484

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.