Zooplankton data of M83/1

Oxygen-deficient waters in the ocean, generally referred to as oxygen minimum zones (OMZ), are expected to expand as a consequence of global climate change. Poor oxygenation is promoting microbial loss of inorganic nitrogen (N) and increasing release of sediment-bound phosphate (P) into the water column. These intermediate water masses, nutrient-loaded but with an N deficit relative to the canonical N:P Redfield ratio of 16:1, are transported via coastal upwelling into the euphotic zone. To test the impact of nutrient supply and nutrient stoichiometry on production, partitioning and elemental composition of dissolved (DOC, DON, DOP) and particulate (POC, PON, POP) organic matter, three nutrient enrichment experiments were conducted with natural microbial communities in shipboard mesocosms, during research cruises in the tropical waters of the southeast Pacific and the northeast Atlantic. Maximum accumulation of POC and PON was observed under high N supply conditions, indicating that primary production was controlled by N availability. The stoichiometry of microbial biomass was unaffected by nutrient N:P supply during exponential growth under nutrient saturation, while it was highly variable under conditions of nutrient limitation and closely correlated to the N:P supply ratio, although PON:POP of accumulated biomass generally exceeded the supply ratio. Microbial N:P composition was constrained by a general lower limit of 5:1. Channelling of assimilated P into DOP appears to be the mechanism responsible for the consistent offset of cellular stoichiometry relative to inorganic nutrient supply and nutrient drawdown, as DOP build-up was observed to intensify under decreasing N:P supply. Low nutrient N:P conditions in coastal upwelling areas overlying O2-deficient waters seem to represent a net source for DOP, which may stimulate growth of diazotrophic phytoplankton. These results demonstrate that microbial nutrient assimilation and partitioning of organic matter between the particulate and the dissolved phase are controlled by the N:P ratio of upwelled nutrients, implying substantial consequences for nutrient cycling and organic matter pools in the course of decreasing nutrient N:P stoichiometry.

Biological and chemical oceanographic profiles from the equatorial Atlantic

The volume presents planktological and chemical data collected during cruise No. 51 of RV "Meteor" to the equatorial Atlantic (FGGE '79) from February to June 1979. A standard section along the meridian 22° W across the equator was sampled ten times between 2° S and 3° N. Together with a temperature and salinity profile, concentrations of oxygen, nutrients and chlorophyll a were analyzed in water samples down to a depth of 250 m. Solar radiation and light depths were measured for determination of primary productivity of the euphotic zone according to the simulated in situ method. Zooplankton biomass was estimated in 5 depth intervals down to 300 m by means of a multiple opening and closing net equipped with a mesh size of 100 µm.