Before CO₂ storage begins, the current state of the selected site must be precisely characterised in order to detect, attribute and quantify any changes and damage caused by the exploration and operation of the storage facility.

However, interpreting this baseline data is complicated by the fact that the North Sea is subject to constant change. Changes occurring during the storage operation phase must therefore not automatically be attributed to CO2 storage, as they may equally be triggered by other dynamic factors. These include natural processes, such as the North Atlantic Oscillation, as well as a variety of anthropogenic influences, such as the steadily advancing warming of North Sea water, overfishing and bottom trawling, the expansion of offshore wind farms, the spread of invasive species, and the acidification of North Sea water, which is triggered by the continuous rise in CO₂ concentrations in the atmosphere and in the water. In many cases, it will therefore be difficult to unequivocally attribute a change observed in the local ecosystem to storage operations.

This issue is to be addressed by the baseline study carried out at an early stage as part of the GEOSTOR project. As it will be supplemented at a later stage by the baseline study that the storage operator must carry out in order to apply for a storage licence, it can be used to gain a better understanding of the dynamics of the processes in the study area before storage begins, thereby identifying specific changes that may be triggered by storage operations.

What will be done?

As part of the baseline study, biological, physical and geological processes in Work Area A are being investigated in an integrated manner. The work is being carried out by several project partners, each of whom contributes their specific areas of expertise:

Biodiversity of benthic organisms and communities

Senckenberg am Meer

The endo- and epifaunal communities living in and on the seabed are analysed in terms of their species composition, abundance, biomass and functional characteristics. To this end, systematic sampling using standardised methods (including the van Veen grab and the Baumkurre) is carried out along a spatially high-resolution grid of stations.

In addition, seasonal variations and the presence of Red List and invasive species are recorded. Functional diversity is quantified on the basis of biological traits (e.g. bioturbation potential) and statistically analysed.

Characterisation of natural and anthropogenic seismicity

Kiel University

To assess seismic activity in the study area, national and international earthquake catalogues are being re-evaluated and re-analysed using modern methods. In addition, seismic waveform data from existing monitoring networks are being utilised.

Particular emphasis is placed on distinguishing between natural, induced and anthropogenic seismicity in order to establish a robust reference for the subsequent assessment of potential storage-related events.

Recording of microseismicity and background noise

K.U.M. Environmental and Marine Technology Kiel GmbH & Kiel University

By deploying seismic sensors on the seabed, microseismicity is continuously recorded over extended periods. The sensors are developed and deployed by K.U.M., whilst the data analysis is carried out in collaboration with the Kiel University (CAU).

The aim is to distinguish natural signal sources (e.g. waves, currents) from anthropogenic influences (e.g. shipping traffic, offshore infrastructure) and to establish a high-resolution seismic reference baseline.

Investigation of potential leakage pathways

GEOMAR Helmholtz Centre for Ocean Research Kiel

Natural gas and formation water can escape along old boreholes and at fault zones that extend down to the seabed or are interconnected via permeable layers. At these weak points, leaks of CO₂ and formation water may occur during storage operations, exacerbated by the rise in pressure within the storage facility. In Area A, there is only one old borehole (H15), which, however, extends into the storage formation. Furthermore, a number of faults in the caprock layers extending down to the seabed were identified in GEOSTOR I. During a survey with the FS ALKOR, hydroacoustic measurements are being used to search for natural gas seeps on the seabed. Sediment cores are also being taken there to detect the rise of saline formation water based on the pore water composition. The data obtained in this way can be used to gather initial information on the hydraulic permeability of these structures. Furthermore, the data serves as a baseline for subsequent monitoring, during which these weak points must be specifically monitored in order to identify them at an early stage, and sediment samples taken to analyse the chemical composition of the pore water.

Development of an integrated data management platform

North.io GmbH

All collected data is consolidated and visualised in a central, georeferenced data platform. The platform is developed by North.io and is continuously being expanded.

It integrates both environmental parameters (e.g. temperature, salinity, current) and geological information (e.g. reservoir formation, overburden, fault zones), enabling the creation of a three-dimensional overview of the study area.

Why is that important?

Interpreting environmental changes in the context of CO₂ storage presents significant challenges, as the North Sea is a highly dynamic system. Changes can be caused by both natural processes (e.g. climatic variability, oceanographic fluctuations) and anthropogenic influences (e.g. fishing, offshore wind energy, rising temperatures).

Against this background, a robust baseline is essential in order to:

• clearly attribute changes to storage operations or other influencing factors

• quantitatively assess the natural variability of biological and physical processes

• identify sensitive ecosystem components and potential risk areas at an early stage

• establish the scientific basis for environmental impact assessments and licensing procedures

Furthermore, the baseline study serves as an important supplement to subsequent investigations by potential storage operators, which are required for applying for a storage licence.

What are the expected outcomes?

The baseline study provides a comprehensive, multidisciplinary data set for characterising Work Area A prior to the commencement of any potential storage operations.

Key findings include:

• high-resolution datasets on the biodiversity and functional structure of benthic communities

• a robust reference for natural and anthropogenic seismicity, including microseismicity

• initial quantitative assessments of potential leakage pathways and their hydraulic properties

• an integrated, georeferenced database for the three-dimensional description of the study area

These results form the basis for subsequent work within the project, in particular for the assessment of environmental risks and the development of monitoring strategies. At the same time, they help to reduce uncertainties in the assessment of storage projects and to establish a scientifically sound basis for decision-making regarding potential CO2 storage in the German North Sea.