The international BIOCAL expedition, led by the Institute of Environmental Science and Technology of the Universitat Autònoma de Barcelona (ICTA-UAB), provided new evidence on the phenomenon of "atlantification" of the Arctic Ocean, a process related to climate change that involves the progressive invasion of Atlantic waters into the polar Arctic Ocean.

The campaign collected samples to study the change in marine biodiversity through the analysis of calcifying planktonic organisms. Calcifying planktonic organisms contribute to the regulation of atmospheric CO₂ and seawater chemistry. These organisms form calcium carbonate shells and are particularly sensitive to ocean acidification and climate change.

During this past August and September, the oceanographic research vessel Sarmiento de Gamboa sailed from Vigo (Spain) to Reykjavik (Iceland), after sampling through the archipelagos of the Azores (subtropics) and Svalbard (polar), analysing the North Atlantic and South Arctic Oceans.

Water and sediment samples were collected throughout the journey, and in-situ experiments were performed to assess marine biodiversity and biogeography and their role in the carbon cycle, with a particular focus on calcifying plankton. Research in regions of different latitudes, from the warmest areas of the Atlantic to the cold waters of the Arctic, allowed the scientific team to gather evidence of the impact of "atlantification" on the physicochemical characteristics of water and on pelagic ecosystems.

"The intrusion of Atlantic waters is turning the Arctic into an ocean that is becoming warmer and less saline due to the accelerated melting of ice. In addition, this intrusion is rapidly changing the marine ecosystems and species distribution of the Arctic," explains Patrizia Ziveri, oceanographer at ICTA-UAB and chief scientist of the campaign. This phenomenon changes the primary and secondary productivity and allows species from more temperate latitudes to expand their habitat northwards, generating food competition and predation on Arctic species.

In the Svalbard archipelago, scientists observed calcifying plankton species of coccolithophores, shelled pteropods and foraminifera (the 3 main calcifying groups) at the edge of their usual geographic range, in addition to higher-than-average surface temperatures over the past 22 years for August and September. The extensive area studied in the campaign from subtropical to polar regions allowed scientists to observe the overall signature of climate change on the biogeography of common calcifying planktic species.

This project is based on the evidence that marine biodiversity loss represents one of the greatest threats to the oceans, but most knowledge comes from large macro-groups and animals. Anthropogenic climate change and environmental degradation are generating alarming effects, such as ocean warming, acidification, stratification and deoxygenation, affecting both small plankton and fish. Despite humanity's clear dependence on the oceans, the consequences of these changes on biodiversity are still not fully understood, particularly at the food web level.

This expedition involved a multidisciplinary team of scientists (ICTA-UAB, Scripps Institution of Oceanography, University of Oxford and Rowan University): oceanographers, biologists, geologists, and environmental and social science specialists from several countries. The Research Group on Marine and Environmental Biogeosciences (MERS) of ICTA-UAB organized and led the campaign with its members: Patrizia Ziveri, Michaël Grelaud, Stéphanie Birnstiel, Arturo Lucas, Thais Peixoto Macedo, Athina Kakelou, Fernando Ruiz and Meryem Upson (visiting student from Utrecht University). In addition, sampling was conducted to identify key biogeochemical processes affected by climate change and to study the distribution and impact of pollutants in the marine environment.

Logbook and more details of the BIOCAL campaign at https://arcg.is/0n8GKn