How the geology on our doorstep can help inform offshore infrastructure design

In 2023, BGS entered into a data-sharing partnership with Ossian to enhance understanding of the seabed and shallow subsurface conditions across the United Kingdom continental shelf . The partnership granted BGS access to Ossian’s extensive survey data, with the development set to become one of the world’s largest floating wind farms.

In total the lease area covers 858 km² and is located 84 km off Scotland’s east coast. Once glaciated and now submerged at approximately 72 m depth, the site offers a unique opportunity to investigate offshore stratigraphy and geomorphology in a region undergoing rapid environmental and industrial transformation. It also allows researchers to compare findings to Ossian’s parent company SSE Renewables’ other projects in the Firth of Forth: Berwick Bank and Seagreen.

As part of the project, BGS scientists hosted a dedicated workshop attended by members of the Ossian project team, which included a mini-field trip day in Midlothian close to the BGS office in Edinburgh. The field trip allowed the project teams to explore similarities to geological features found onshore and discuss the broader implications for interpreting offshore survey data. By examining glacial deposits, meltwater channels and till sequences in a terrestrial setting, geoscientists can refine offshore geological models and reduce uncertainty in infrastructure design.

A key example observed during the field trip was the heterogeneity of the sediments across relatively small areas, with notable variations in grain size, composition and depositional structure. These complexities mirror the variability of ground conditions found offshore and highlight the importance of detailed site characterisation when planning and constructing marine infrastructure.

To help contextualise the offshore data, the field trip explored several key geological sites in Midlothian, each offering valuable insights into glacial processes and sedimentary environments similar to those observed beneath the sea.

Auchencorth Moss: Black Burn exposure (Local Geodiversity Site)

Auchencorth Moss is an extensive, peat-covered plateau dissected by small streams and drainage channels. The Black Burn site, where a tributary joins the River North Esk near Penicuik, features an exposure of three distinct glacial tills with varying physical characteristics and compositions. Though partially obscured by slope wash and vegetation, the upper sections remain visible and accessible for study. The exposure reveals how glacial processes deposited and reworked sediments, which act as a useful analogue for interpreting stratified units offshore.

Carlops meltwater channel

There is a classic example of a subglacial meltwater channel systems at Carlops, a Geological Conservation Review Site and partially a Site of Special Scientific Interest (SSSI).

The bedrock-cut channels at Carlops exhibit braided forms, rock islands and chute features. These geomorphological structures help explain the evolution of meltwater systems beneath ice sheets, which are also evident in offshore channel features. The site also provides a good opportunity to emphasise the scale of channel features, helping to conceptualise the variability of the offshore landscape.

Hewan Bank

Hewan Bank, an SSSI located close to Roslin Glen, presents a textbook sequence of two tills overlain by sands and gravels. The locality has been used to construct the regional glacial stratigraphy for the Edinburgh and Lothians area.

The debate over whether these represent separate glaciations or complex depositional environments mirrors the interpretive challenges faced offshore, where seismic and core data must be carefully analysed to distinguish between similar units. The wider Roslin Glen area, known for its meltwater gorge and incised meanders, also illustrates the erosional power of glacial meltwater and the formation of geomorphological features that can be traced in offshore bathymetry and sediment records.

Collaboration

The collaboration between Ossian, SSE Renewables and BGS provides important new data that is being used to update baseline geological models for the Central North Sea and the Firth of Forth. These feed into BGS’s publicly available offshore maps and datasets, which support a wide range of users including developers, regulators, researchers and marine planners. Integrating data from offshore wind farms such as Ossian with existing geological frameworks will help to guide future offshore developments and promote the sustainable use of marine resources.

This initiative also builds on BGS’s longstanding relationship with Ossian joint venture partner SSE Renewables and highlights the value of sustained collaboration in delivering large-scale renewable energy projects. The Ossian floating wind farm, which is a joint venture between SSE Renewables, Marubeni and Copenhagen Infrastructure Partners (CIP), is set to deliver up to 3.6 GW of renewable energy, enough to power 6 million homes and offset up to 7.5 million tonnes of carbon emissions, marking a significant step forward in the UK’s journey to net zero.

About the author

Catriona Macdonald
Margaret Stewart