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Short abstract:

Scientists dive in the Baltic Sea to study the environmental repercussions of marine heatwaves with an innovative underwater experiment. In this experiment, marine heatwaves are enacted as a spatial, temporal, and techno-material objects where different oceanic futures become engaged simultaneously.

Long abstract:

This paper draws on ethnographic observations conducted at a marine zoological station in Southern Finland to detail how marine researchers scuba dive to study the effects of marine heatwaves in the Baltic Sea. With its low biodiversity and salinity levels, high pollution, relatively shallow average depth, and the numerous stagnating bays and coves, scientists claim, the Baltic Sea is a “time-machine,” a likely image of what the rest of the oceans will look like in the future. Based on a 100-year-old time series of seawater temperatures, researchers identified increasingly frequent marine heatwaves in the sea near their research station. Crucially, however, the time series did not provide any insights on potential ecological repercussions. The scientist-divers had to negotiate work underwater to setup a very innovative – yet quite precarious – in-situ experiment: They designed incubation chambers to be placed at the seafloor. Thanks to common household floor-heating technology, they simulated heatwaves inside the chambers and monitored bio-chemical processes through regular water sampling. The skills of scientific diving became entangled with the challenges of building underwater incubation chambers (Muka 2023) and maintaining them functional-while-submerged (Jue, 2020). Studying and making marine heatwaves apparent emerges as a temporal and techno-material problem, and as a spatial one too: The peculiar morphology of the Baltic generates micro-climates where water temperatures are regularly in excess of those reached during the heatwaves and of those simulated in the chambers. The experiment becomes a moment and a place where different oceanic futures become engaged simultaneously.