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.

Integrated net primary production during POLARSTERN cruise ARK-XXVII/3 (IceArc) in 2012

Depth-integrated in situ rates were calculated for each environment as a function of the available photosynthetically active radiation (PAR). Irradiance profiles were calculated for each environment (sea ice, melt pond, water under the ice and open water) from the daily average incoming solar shortwave irradiance measured by a pyranometer (Kipp & Zonen, Delft, Netherland) mounted on the ship. We used light attenuation coefficients of 10 m**-1 for snow, 1.5 m**-1 for sea ice (Perovich, 1996) and 0.1 m**-1 for Atlantic-influenced Arctic seawater, based on literature values and observations during the cruise. Planar irradiance was transformed to scalar irradiance according to Ehn and Mundy (2013) and Katlein et al., (2014). Water column production was integrated over the euphotic zone (1% of incoming irradiance) and sea ice production over the ice core thickness. Melt pond coverage and sea ice concentration were taken into account when calculating the total primary production per area.