Work Package 2

Scaling upwelling intensity with plankton community production

Work Package Leaders

Description

In contrast to other upwelling systems, phytoplankton biomass in the Humboldt Upwelling System (HUS) does not seem to respond immediately to upwelling intensity. Nutrient supply and primary productivity seem to be out of phase. During winter, when the upwelling intensity is highest and nutrient concentrations at the surface increase, phytoplankton biomass remains low; while in summer, when the upwelling intensity is reduced, the highest accumulations of photosynthetic biomass appear at the surface. There are several factors which might be responsible for this out-of-phase seasonal cycle: (1) reduced incoming irradiance during winter, (2) changes in mixed layer depth, (3) shifts in the nutrient availability (macro- vs micronutrients, such as iron), and (4) increased top-down control by grazers during winter. Since a mechanistical understanding of the linkage between upwelling intensity (including all factors influenced by upwelling) and phytoplankton productivity is still lacking, WP2 aims to address the following questions combining a ship-based expedition and a field mesocosm experiment. In addition, WP2 will be responsible for organizing the mesocosm experiment off the coast of Callao (Lima, Perú) in February-April 2020.

General Questions 

  • What is the functional relationship between upwelling intensity and phytoplankton productivity and the factors controlling it in the HUS?
  • What is the functional relationship between upwelling intensity and export potential and the factors controlling it? Addressed jointly with WP5 during the mesocosm study.
  • How does seasonality affect these functional relationships?
  • Is the mesocosm-derived functional relationship valid in the natural environment?
  • How do the results generated during the CUSCO project compare with those of previous cruises in that area and the previous mesocosm experiment in 2017?
  • Can we make reliable projections on future developments of the HUS productivity under climate change with the new understanding of the processes regulating the relationship between upwelling intensity and productivity?

Research topics

  • Net community production
  • Phytoplankton diversity and community composition
  • Biogeochemical fluxes in the water column and in the sedimented material
  • Phytoplankton physiological responses to different light and nutrient regimes

Expeditions and field experiments

  • MSM80 (FS Maria S Merian): Panama-Chile December 2018- January 2019
  • KOSMOS Peru 2020: Callao, Lima February-April 2020

Design of Mesocosms (Graphic: Rita Erven, GEOMAR)

 

 

 

Ulf Riebesell

Mar Fernández

 

 

KOSMOS Experiment, sunrise in Gando Bay (Photo: Ulf Riebesell)

KOSMOS Experiment (Photo: Ulf Riebesell)