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The air–sea exchange and oceanic cycling of greenhouse gases (GHG), including carbon dioxide (CO₂), nitrous oxide (N₂O), methane (CH₄), carbon monoxide (CO), and nitrogen oxides (NO_x = NO + NO₂), are fundamental in controlling the evolution of the Earth’s atmospheric chemistry and climate. Significant advances have been made over the last 10 years in understanding, instrumentation and methods, as well as deciphering the production and consumption pathways of GHG in the upper ocean (including the surface and subsurface ocean down to approximately 1000 m). The global ocean under current conditions is now well established as a major sink for CO₂, a major source for N₂O and a minor source for both…

Increasing anthropogenic CO₂ emissions to the atmosphere are partially sequestered into the global oceans through the air-sea exchange of CO₂ and its subsequent movement to depth, commonly referred to as the global ocean carbon sink. Quantifying this ocean carbon sink provides a key component for closing the global carbon budget, which is used to inform and guide policy decisions. These estimates are typically accompanied by an uncertainty budget built by selecting what are perceived as critical uncertainty components based on selective experimentation. However, there is a growing realization that these budgets are incomplete and may be underestimated, which limits their power as a…

Oyster reefs are often referred to as the temperate functional equivalent of coral reefs. Yet evidence for this analogy was lacking for the European native species Ostrea edulis. Historical data provide a unique opportunity to develop a robust definition for this ecosystem type, confirm that O. edulis are large-scale biogenic reef builders, and assess its current conservation status. Today, O. edulis occur as scattered individuals or, rarely, as dense clumps over a few m². Yet historically, O. edulis reef ecosystems persisted at large scales (several km²), with individual reefs within the ecosystems present at the scale of several hectares. Using the IUCN Red List of Ecosystems Framework, we conclude the European…

Anthropogenic activities have impacted marine ecosystems at extraordinary scales. Biogenic reef ecosystems built by the European flat oyster (Ostrea edulis) typically declined before scientific monitoring. The past form and extent of these habitats thus remains unknown, with such information potentially providing valuable perspectives for current management and policy. Collating >1,600 records published over 350 years, we created a map of historical oyster reef presence at the resolution of 10 km² across its biogeographic range, including documenting abundant reef habitats along the coasts of France, Denmark, Ireland and the United Kingdom…