Frontiers of instability in marine ecosystems and carbon export (Marine Frontiers)

Marine Frontiers is an innovative project that will push the frontiers of knowledge on the limits to stability in marine ecosystem functioning. It will introduce, for the first time in a global model, three triggers of widespread mortality: viruses, early life cycles, and microplastic pollution, and test the impact of extreme conditions that are plausible for the coming Century.

Marine ecosystems keep the concentration of atmospheric CO2 about 200 parts per million (ppm) lower than it would be otherwise. Marine ecosystems were not stable in the geological past. They contributed and possibly triggered massive Ocean Anoxic Events. Global marine ecosystem models used for climate study have been shown to underestimate variability in a range of variables, including variability in carbon and oxygen fluxes over multiple time and space scales, and variability in plankton biomass. The incapacity of the current generation of ocean carbon models to reproduce observed variability means instabilities in marine ecosystems and associated carbon fluxes have never been adequately explored.

Mortality processes are critical in the ocean because the biomass turns over very quickly. Yet mortality processes have received little attention so far. Recent advances in observation technology (particularly genomics and automated imaging) and in knowledge have highlighted processes that could radically alter mortality processes in the ocean. Marine Frontiers will attempt, for the first time, to model three of the most important triggers of mortality, in order to explore the stability of marine ecosystems in a changing environment.

Marine Frontiers will expand mortality processes in the NEMO-PlankTOM model using theory, observations, and new computing methods. A new framework for representing marine ecosystems is proposed through the representation of Particle Functional Types (PtclFTs) that include living particles such as phytoplankton, zooplankton, and bacteria, as well as dead particles such as virus, microplastics, and organic aggregates of different size.

Viruses will be introduced as a new PtclFT of inert properties. Viruses will be parameterised with a reproduction and decay rates based on recent insights from ocean observations.

Early life cycles will be introduced for crustaceans, jellyfish, and pteropods, initially through the explicit representation of the eggs, the larvae and the adult stages, but with optimisation of model resources in a second stage.

Microplastics will be introduced as a new PtclFT of inert properties, using an ocean influx based on observations and a decay rate optimised to the observed distribution. Microplastics will penetrate the food chain through incidental grazing by zooplankton, causing physical damages and chemical poisoning.

An advanced approach to validate the model will be developed using emergent properties of the ecosystem functioning such as the North/South ratio in chla, the maximum intensity of the Spring bloom, patchiness, and trophic pyramids. This is in addition to standard validation biogeochemical fields (nutrients, carbon, biomass). Emergent properties and theoretical analysis of the strengths of food webs will also serve to establish precursor indicators for instabilities.

The model will then be used to explore the sensitivity of marine ecosystems and resulting carbon export to growing external pressures from climate change, ocean acidification, microplastic pollution, fisheries, and combined stressors.

This highly ambitious project builds on nine "Greenocean" Workshops led by the project Principal Investigator (PI), and international collaborations with experts at the forefront of understanding and observing marine ecosystems. The PI is a world leader who has demonstrated experience in leading cutting-edge research. She is a Fellow of the Royal Society, a highly cited researcher for 2018 & 2019, and has won seven Prizes and Medals for her work.