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
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.