Summary

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Together with organic matter export from the surface ocean, microbial respiration in the mesopelagic realm (~200m – 1000m) determines the long-term storage of carbon in the ocean, the extent of mesopelagic deoxygenation and, ultimately, the levels of carbon dioxide in the atmosphere. Yet, microbial respiration remains one of the least constrained metabolic rates in the Earth System, with mismatches between inverse model predictions, in situ budgets and in vitro observations of an order of magnitude. These mismatches stem from the difficulties in quantifying microbial respiration rates in the dark ocean. However, with the dawn of novel in situ technologies such as optodes, in situ incubators, gliders, and floats, we are now able to determine mesopelagic microbial respiration with unprecedented spatial and temporal coverage. However, whilst technologies have advanced substantially, efforts to bring all the data together across depth-, size-, and time-scales are still lacking.

This working group will bring together experts in observation, experimentation, data analyses, and modelling to systematically compile and compare data sets of mesopelagic microbial respiration in order to constrain respiration uncertainties and improve quantifications of organic matter flux and remineralisation rates. A final outcome will be to improve projections of the effects of global change on the decline of oxygen in the world’s oceans, with implications for fisheries and food security. The outputs of ReMO will have a high impact on future ocean research as they will enable efficient use of the wealth of data currently collected by autonomous instruments in the oceans.

1. Identify, quantify and prioritise gaps in our knowledge, and prepare an action plan to reduce these gaps by reviewing available information on mesopelagic respiration.

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2. Develop a global dataset of mesopelagic respiration estimates, derived from the range of ecological and biogeochemical techniques available, in order to create a resource for validation of biogeochemical models including Earth System Models used for climate projection.

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3. Produce a new synthesis of open ocean mesopelagic respiration.

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4. Produce a best practice manual of techniques and approaches to determine mesopelagic respiration, and make recommendations as to which is the most appropriate method or combination of methods for a particular application, including best practice on how to reconcile approaches across time and space scales.

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5. Build capacity, share knowledge and transfer technical skills, particularly to scientists in developing nations.

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