More than 99 % of Ascension Island’s territorial area is comprised of ocean. The ocean plays a key role in regulating Ascension’s climate, holds much of its biodiversity, and is a source of recreation and food for the Island’s human population. In 2019, the waters around Ascension Island were designated as one of the world’s largest marine protected areas (MPA), covering the entirety of the Territory’s 445,000 km2 Exclusive Economic Zone. However, despite strong protections from fishing extractive activities, the MPA remains potentially at risk from external pressures from climate change.
As part of the CRACAB project, a team of marine ecosystem modellers from Plymouth Marine Laboratory have carried out the first detailed climate change assessment for the Ascension Island MPA and the wider tropical central Atlantic region. The team, led by Dr Lee de Mora, used state-of-the-art global ocean circulation models to predict how a range of ocean biophysical variables, such as temperature, salinity, pH, productivity and nutrient concentrations would change over the period 2015-2100, under a range of different CO2 emission scenarios. They also examined how a key current system – known as the Atlantic equatorial undercurrent (AEU) – which flows to the north of Ascension would respond to projected warming.
Warmer, more acidic and less productive
The modelling results that Ascension’s surface marine waters are expected to become warmer, more acidic, less nutrient rich and less productive by the end of the century, with the effects being more severe under pessimistic ‘business as usual’ emissions scenarios. The AEU is also projected to weaken over this period, which may have a number of implications for Ascension’s marine ecosystem. For example, the AEU has been shown to play a role in transporting bringing oxygenated water to the tropical subsurface layer which may in turn effect the vertical niche of pelagic fish, such as tunas.
The full report can be downloaded here: