Abstract
As the offshore energy sector continues to expand and mature, an increasing number of offshore structures will reach the end of their operational lifetimes in the coming decades. As these installations transition from active use to decommissioning, governments, operators and environmental stakeholders face a growing set of complex decisions. Decommissioning is no longer a purely technical task; it has become an ecological, regulatory and societal balancing act shaped by shifting baselines, evolving policy frameworks and expanding knowledge of marine ecosystems and the ecological functions of offshore structures within them.
This document covers the pre-decommissioning stage and the two decommissioning scenarios - full removal and partial removal - presented in the infographics for offshore wind turbines and offshore platforms in more depth. It first describes what we know about the ecological state of structures prior to decommissioning, providing context for understanding how different measures may affect existing ecological communities. It then outlines the ecological, technical and regulatory considerations that could shape each scenario.
The aim of this background document is not to prescribe a single preferred pathway. Instead, we try to frame the complexity of the choices ahead and emphasise that responsible decommissioning requires adaptive, evidence-based and context-dependent decisions.
So far, the partial removal scenario discussed is a theoretical option that does not yet have regulatory approval in the Dutch North Sea for wind farms (including sub-stations) and nowhere in the OSPAR region for oil and gas installations. For offshore wind, none of the scenarios have proven their technical feasibility in a real-world situation, nor have the impacts of decommissioning been monitored in practice. Where technically feasible, decommissioning approaches should aim to remove as much of the monopile as possible without disturbing the scour protection layer, in order to maximise material recovery while retaining ecological value at the seabed. For platforms, full removal as well as partial removal have been implemented all around the world, but generally without proper monitoring of the ecological effects of different decommissioning options. Hence, we primarily describe ecological effects of decommissioning scenarios (in the Southern North Sea) in terms of loss of the ‘new nature’ that has developed on and around the structures in question. In doing so, we strongly recommend that studies are set up to better understand the actual impacts of various decommissioning options, before it is too late. With current full-removal policies, we risk throwing out the baby with the bathwater.