Antarctic phytoplankton ecology and biogeochemistry

CO2 uptake by phytoplankton in the Southern Ocean is mainly constrained by limited trace metal input, in particular iron and manganese. As trace metal bioavailability is determined by its chemistry and biological uptake strategies, biological activities also change trace metal chemistry in seawater. The major goal of the EcoTrace group is to understand how global change will affect Southern Ocean phytoplankton ecology and biogeochemistry. The consequences of climatic changes, particularly on the supply and cycling of iron and other trace metals (manganese, zinc, cobalt) and their effect on Southern Ocean productivity, are essential to understanding the complex balance of biogeochemical cycles and climate feedback mechanisms. Predictions of how Antarctic phytoplankton may respond to these perturbations at the cellular and ecosystem levels are a significant challenge in global change research.

Team

Dr. Scarlett Trimborn - Head of the group
Dr. Silke Thoms - Cell modeler
Christian Völkner - Chemical engineer
Ricarda Kluge - Biological technician

Doktorandinnen:
Alexandra Bettinelli
Elisabeth Rosselli
Jasmin Stimpfle

Master Studentin:
Diya Pallipad

We contribute to the program-oriented research within the Helmholtz Society:

Topic 6: Marine and Polar Life: Sustaining Biodiversity, Biotic Interactions, and Biogeochemical Functions

  • Subtopic 6.2 Adaptation of marine life: from genes to ecosystems
  • Subtopic 6.3 The future biological carbon pump

Competences

The EcoTrace group follows a multidisciplinary laboratory and field work approach, integrating marine biology and chemistry, to obtain a process-based understanding:

  • In situ sampling of natural phytoplankton communities and their physiological characterization together with the detailed analysis of seawater chemistry enable us to identify primary and secondary parameters driving the Southern Ocean ecosystem.

  • Manipulation experiments with natural phytoplankton assemblages simulating predicted climate change scenarios unravel future effects on Southern Ocean species composition, productivity and biogeochemistry.

  • Laboratory experiments with ecological relevant species provide a mechanistic understanding on physiological processes (photosynthesis, carbon and trace metal uptake) in response to climate change.

  • Competition experiments examine how resource limitation (trace metals) and species interactions affect Southern Ocean phytoplankton community structure. 

  • Mathematical models provide a process understanding on the dynamic regulation of photosynthesis and carbon acquisition for the different phytoplankton functional types in response to light and nutrient (including trace metals) limitation. The model development on the cellular level also includes the habitat of phytoplankton such as the brine channel formation in sea ice as a habitat for sea-ice associated algae.

  • Our results are exploited in multidisciplinary contexts ranging from physiological to ecological processes, which in turn facilitates the development and validation of cell models.

Tools

Chlorophyll a fluorescence and computational approaches to assess photosynthesis

Combining laboratory experiments, theoretical and computational approaches we are investigating how trace metal limitation (such as Fe, Zn and Mn) affects the photosynthetic efficiency of phytoplankton key species. Based on our current understanding of the photosynthetic reactions, we are developing dynamical models of the main mechanisms and processes in photosynthetic electron transport. These models describe all intermediary steps from photon absorption and charge separation at photosystem II up to the reduction of the terminal electron carrier ferredoxin at the end of the electron transport chain. We are studying how alternative electron flow pathways affect the synthesis of ATP and production of the reducing equivalent NADPH driving the fixation of carbon. We provide a theoretical framework to test our hypotheses on intrinsic mechanisms associated with the acclimation of algal cells to different trace metal supply in combination with fluctuations of light.

Contact: Dr. Silke Thoms   Dr. Scarlett Trimborn

Ultra-Clean Sampling device

Our Ultra-Clean-CTD setup enables us to sample the water column for all kind of trace elements, in particular tracemetals as for example iron, manganese, cobalt, copper, cadmium, nickel and zinc. The EcoTrace group works primarily in the Southern Ocean, therefore our main interest is the analysis of iron, manganese, cobalt and zinc in dissolved and particulate samples in the picomolar range. Our Ultra-Clean sampling system consists of three major parts: 

  1. The Ultra-Clean-CTD rosette

The characterization of the water chemistry and sampling for trace elements is possible through the use of titanium and plastic instead of steel. Sensor wise the CTD is equipped with two temperature sensors, two conductivity cells, a pressure sensor, an oxygen sensor, a transmissometer, a fluorescence sensor, a photosynthetically active radiation (PAR) sensor and an altimeter. All sensors have a titanium housing and are rated to 6000 m or deeper. For water sampling, the rosette is equipped with 24x 14L bottles made of PVC and titanium with butterfly closures.

     2. Winch Container

The Ultra-Clean-CTD comes with its own winch build in a 20” sea container to protect the winch and cable from environmental influences. Instead of a normal steel cable the winch has 8000m of a synthetic robe. This mobile winch is designed to be as flexible as possible and therefore we are able to take our Ultra-Clean-Sampling equipment to all kind of research platforms and are not limited to one specific vessel.

    3. Clean Room Container

The Ultra-Clean-CTD setup comes with its own clean room build in a 20” container to ensure biggest mobility and flexibility. The clean room is completely metal free, there are no open metal surfaces in the clean room. Besides the space to mount all 24 bottles from the CTD on one wall, the container has two workbenches and a third open working area, which is flushed with clean air. To introduce the bottles in the clean room, the container is equipped with an extra air lock. Inside this air lock the CTD bottles are washed with deionized water to rinse down salt water and dust. 

Since 2022, we have used this Ultra Clean Sampling device successfully during the Polarstern expeditions the GEOTRACES Process Study PS133 Island Impact and the GEOTRACES cruise ArcWatch 2.

Trace metal analytical pipeline

In the EcoTrace working group we have various techniques and know how to analyze all types of trace metal samples using GEOTRACES protocols and standards, be it water samples, particle samples or even tissue and feces samples.

Water samples
To analyze the trace metal content of seawater samples they first need to be preconcentrated and matrix components such as Na, Mg, Ca and Cl need to be removed. Both steps are done with the ESI seaFast system via a chelating resin. After elution of the concentrated trace metals from the column the trace element concentrations in sub nanomolar range can be precisely and accurately assessed.

Particulate samples
In order to analyze particulate trace metal samples we use a DAS 30 from Picotrace to perform an acid digestion with concentrated acids under pressure. Therefor samples are placed in 30 mL Teflon vials. A mixture of strong acids like HNO3 and HF depending on the sample material is added. The vials will be closed and heated up to 180 °C for several hours. After digestion the acid is evaporated and the sample resuspended in 2% HNO3 and will be measured via ICP-MS.

Contact: Dr. Christian Völkner    Dr. Scarlett Trimborn

Determination and characterization of iron and ligands via voltammetry

The working group EcoTrace has got several voltammeters from Metrohm (VA-Stand 663) and Bioanalytical Systems (EC Epsilon). With those we can determine the chemical speciation of iron as well as the concentration of humic acid-like substances using competitive ligand exchange–adsorptive cathodic stripping voltammetry (CLE-AdCSV).

Contact: Dr. Christian Völkner    Dr. Scarlett Trimborn