Climate‑Driven Transitions in Marine Biogeochemistry and Coral Ecosystems

Session speakers and talk titles: Prof. James Rae (University of St Andrews): Tipping points in marine biogeochemistry, induced by circulation and calcification Oceanic carbon uptake plays a critical role in modulating atmospheric CO2 and ameliorating future warming. However paleo records show that the ocean has the ability to switch rapidly into modes of carbon release. Here, we highlight two such modes, one triggered by changes in ocean circulation, the other by calcifying plankton. First, we show how abrupt changes in AMOC during the last deglaciation led to circulation change and carbon release in both the Southern Ocean and the North Pacific, resulting in multi-decadal to centennial scale CO2 rise. Second, we describe an unexpected feedback in pelagic calcification following past acidification and warming events, which lowered ocean alkalinity and thus delayed CO2 and climate system recovery. Each of these results in additional CO2 rise and so, if triggered in the future, could lead to prolonged and exacerbated global warming. Dr Seb Hennige (University of Edinburgh): Predicting loss of cold-water coral habitats – an in situ – ex situ – in silico approach Here we use a novel approach with 3D printed calcium carbonate ‘mini-reefs’ to visualise how vulnerable cold-water coral habitats will collapse in response to ocean acidification through the process of Coralporosis on dead coral framework. Experimental ex situ data will be combined with existing in situ evidence to create the first in silico (computer based) model of cold-water coral reefs, where future habitat loss and timescales of such loss can be quantified. As the dead coral becomes more porous, they become unable to support the weight of the live coral above them, leading to habitat crumbling and loss. These in silico models will allow us to quantify how projected climate change scenarios will lead to habitat loss over known timescales to increase our understanding of what CWC reefs of the future will look like, when these changes may occur on an ecosystem scale, and how quickly that will happen.