The pelagic realm

The changes in the North and Baltic Seas during the Anthropocene and their effects on their carbon stores and carbon exchange are to be examined in work package (WP) 1. An increase in total alkalinity (TA) can facilitate seasonal or long-term (> 1 year) CO2 uptake. As a result, carbon storage and export to the deep sea via the shelf pump can be increased, and the effect of atmospheric ocean acidification can be weakened.

In WP 1, new methods are to be applied that directly record the CO2 fluxes on the coast. This is intended to circumvent the uncertainty in the parameterization of the gas transfer and to create a data set that is representative over time (including the variability from hourly to seasonal scales). In addition, the representation for the model is to be made easier so that the CO2 fluxes measured at this location can be scaled up to the entire coastal region.

For this purpose, the Coastal Research Center of the NLWKN provides, among other things, ship-based data for the North Sea, Wadden Sea and estuaries. In addition, precise and high-resolution ship-based transect data of the shipping area on biogeochemistry, nutrients and, in particular, relevant parameters of the carbonate system are collected and validated.


  • Understanding the role of anthropogenic influences on physical and biogeochemical factors that regulate the uptake and storage capacity of CO2 in the water column
  • Influence of TA changes on carbon uptake
  • Characterization of the influence of the assimilation of sulfur on carbon storage as a more resistant, dissolved organic material
  • Input of data from nature measurements into the bidirectionally coupled hydrodynamic-biogeochemical model system FVCOM / ERGOM (e.g. for calibration) (WP 3)

Reasons for change of total alkalinity (TA) in the Baltic Sea as well as past and future effects on carbon storage and export as well as gas exchange with the atmosphere

Work package 1.1 deals in detail with the potential drivers of the recently identified long-term changes in total alkalinity (TA), including anthropogenic eutrophication and potentially increased weathering. The focus here is on the processes along the gradients from land to sea and the gradients at the redox interfaces.


  • Update of the available data on inorganic carbon and inputs into the Baltic Sea
  • Carrying out trend analyzes of total alkalinity (TA) to clarify the significance of external vs. internal sources of alkalinity
  • Assessment of the data on the carbon system with regard to the changed storage capacity and the induced change in the carbon dioxide exchange with the atmosphere
  • Investigation of the carbon system through field expeditions, the observation network in the Baltic Sea and sampling as a supplement to the regular monitoring trips (Baltic Sea monitoring and IOW long-term data collection)
  • Identification of inconsistencies (e.g. systematic errors due to the contribution of organic alkalinity) through overdetermination of the CO2 system and the characterization of stable isotopes
  • Assessment and improvement of the functioning and possible shortcomings of the description of the inorganic carbon system and the source description in the current ERGOM model
  • Operation of the model in an environment with and without a scenario of anthropogenic changes in alkalinity
  • Assessment of changes and variability in surface pCO2 with potential for better verification of the AP 3 model framework

Separation of long-term total alkalinity (TA) trends from seasonal productivity patterns

In work package 1.2, the heterogeneity of the total alkalinity (TA) in coastal systems and its influence on region-specific buffer capacities and thus the overall capacity of the coastal sea to absorb carbon dioxide will be investigated. in particular, the effects of high TA on carbon uptake and storage in the water column will be studied in the southern central North Sea. TA is measured both at the Spiekeroog time series station of the University of Oldenburg and underway during various research cruises using a HydroFIA-TA.

Hourly TA measurements at a tidal inlet in the Wadden Sea in combination with pCO2 and discrete measurements of the carbonate system allow an improved quantification of the land-sea flux of TA and DIC.


  • Identification and quantification of the influence of the primary production on local formation of total alkalinity in the southern North Sea.
  • Investigation of the effects of high total alkalinity on carbon uptake and storage in the water column
  • Comparison of study results with those of work package 1.1 (Baltic Sea and Skagerrak)
  • Evaluation of the role of surplus/deficit TA on the seasonal and long-term absorption and storage capacity of CO2 of seawater.
  • Provision of regional maps of TA and DIC as well as an overview of seasonal changes and longer-term (> 1 year) changes in coastal and near-coastal regions

Sulfurization as a mechanism for storing carbon as a resistant dissolved organic material (DOM)

Dissolved organic matter (DOM) in the ocean is one of the largest carbon stores in the ocean. DOM contains more carbon than all the vegetation on our planet. Sulfurization, the abiotic reaction of reduced inorganic sulfur compounds with organic material, is a process that increases the stability of DOM in the ocean.

The main objective of this work package is to clarify how extensive sulfurization occurs in the sulfidic sediments of the Baltic and North Seas and the sulfidic basins of the Baltic Sea, and whether the organic sulfur compounds formed here contribute to the large-scale accumulation of DOM. In particular, two overarching questions will be addressed. How does the benthic sulfur cycle affect DOM sulfurization and the formation and stability of refractory dissolved organic matter (RDOM) as a carbon sink, and how do climate change processes affect the export of RDOM to the North Atlantic and their exchange between the Baltic and North Seas? Experimental approaches are combined with large-scale sampling and time series to address these questions.


  • Determination of sulfur incorporation and decomposition rates under different environmental conditions by laboratory experiments with water and sediment samples
  • Simulation of the spectrum of environmental conditions in sulfidic basins of Baltic Sea and Wadden Sea sediments by sulfurization experiments
  • Test and quantitatively evaluate the stability of newly formed dissolved organic sulfur compounds under pelagic conditions

Understanding the role of physical processes in the CO2 exchange between atmosphere and ocean along the gradient from land to sea and its sensitivity to climate change

This work package will apply new and sophisticated methods to directly quantify CO2 exchange and identify direct physical controlling processes. In addition, work package 1.4 focuses on quantifying the physical and biogeochemical processes that influence the uptake or release of CO2 from or to the atmosphere in coastal waters and nearshore marine areas.

An eddy covariance (EC) system at the Spiekeroog (TSS) monitoring station will provide high-resolution measurements in the tidally influenced region on air-sea gas exchange. Atmospheric eddy covariance (EC) has become the preferred method for direct measurement of air-sea exchange of heat, momentum, and gas because it is non-invasive (unlike flotation chambers), reliable for long-term field deployments, and not dependent on assumptions about the structure of the boundary layer at the sea surface.


  • Determination of the influence of air-water CO2 exchange on lateral fluxes of dissolved inorganic carbon in the Wadden Sea-North Sea transition zone
  • Investigation of extreme events such as storm surges, high wind periods, and algal blooms to assess the significance of the influence on gas exchange rates in nearshore areas
  • Investigation of the influence of upwelling and downwelling of water bodies on CO2 exchange between air and sea and on carbon storage

In-situ pelagic processes and pelagic-benthic coupling as a modulator of alkalinity

The pelagic system controls biogeochemical processes in sediments via the export of carbon, which leads to its temporary or permanent burial. These processes are under the biogeochemical influence of anthropogenic and climatic changes. Measurements of combined stable water isotope ratios in natural waters can be used to track water masses in coastal and nearshore regions. These variables are influenced only by physical processes and allow us to distinguish between freshwater and nearshore end-members. They can therefore help disentangle the complex flow in tidal regions such as the Wadden Sea.


  • Characterization of the variability of carbon sinks, sources, and transformations in the pelagic realm using stable carbon isotope ratios of DIC and DOC
  • Investigation of the dissolution and precipitation of calcium carbonate and the interaction between the atmosphere and the ocean
  • Determination of the coupling between benthic and pelagic reaction spaces and element transports


Dr. Yoana Voynova Coordinator work package 1

Helmholtz-Zentrum Hereon

Phone: +49 4152 87 2377

E-mail contact
Prof. Dr. Gregor Rehder Coordinator work package 1

Leibniz-Institut for Baltic Sea Research Warnemünde (IOW)

Phone: +49 381 5197 336

E-mail contact