WP 4

Observation of upper ocean organic carbon dynamics

Work Package Leaders



Mesoscale eddies are important vehicles for water mass transport from Eastern Boundary Upwelling Systems (EBUS) to the open oligotrophic ocean that can influence biogeochemical cycles on relatively small spatial scales (on the order of 102 km). These water masses are rich in carbon and nutrients affecting both primary production and export fluxes, which has consequences for the distribution of oxygen through locally variable remineralization processes (see figure 1). Since oxygen concentration is one of the major controls for the distribution of larger pelagic organisms, such as zooplankton as well as meso- and epipelagic fish, mesoscale activities in and around EBUS also have socio-economical impacts. However, the larger role of mesoscale eddies in the marine biogeochemichal cycles are still not well constrained.


To gain a better understanding of carbon cycling in and around eddies, research in the Engel lab will focus on three main topics: (i) The distribution of organic carbon by determining the spatial distribution as well as the lateral and vertical fluxes of dissolved and non-sinking organic matter across mesoscale eddies off West-Africa, (ii) organic carbon turn-over by quantifying microbial process rates (primary production, exudation, bacterial production, organic matter degradation and respiration), and (iii) organic carbon tracing by identifying organic biomarkers for water mass transport as well as organic matter production and degradation processes. Understanding the chemical composition, microbial cycling and eddy-driven transport of fresh dissolved and non-sinking organic matter in and out of highly productive EBUS will help us to better estimate climate change impacts on oxygen, nutrient and CO2 fluxes.


General Questions and Research topics

Overall aims:

  • Determine the influence of submesoscale eddies on upper ocean organic carbon distribution
  • Understand the influences of eddy dynamics on microbial productivity and organic matter turn-over
  • Assess the role of EBUS in the lateral supply of organic matter to the central Atlantic Ocean

Current hypotheses:

  • Eddies enhance the lateral transport of organic cabon to the open ocean
  • Reduction of particulate carbon export on the shelf
  • Laterally supplied organic carbon supports net heterotrophy offshore


Figure 1. Schematic showing the interplay between remote physical transport mechanisms and local organic matter remineralization processes creating oxygen and nitrate variability within the oxygen minimum zone off Mauritania. Picture credit: Thomsen et al. (2019).