According to an international study involving CIM researcher Paula Diz. The study helps improve understanding of the mechanisms that regulate the planet’s climate
The Marine Research Centre (CIM) of the University of Vigo is participating in an international study led by the University of Bern, Switzerland, which provides important new insights into the evolution of Earth’s climate and the role of the Atlantic Ocean in intensifying ice ages. The study, published last friday in the journal Nature Communications and involving Paula Diz from the CIM’s Geological Oceanography and Biogeochemistry group, shows that around one million years ago the weakening of deep currents in the North Atlantic was a key factor in the transition to longer and more intense glacial cycles.
These results contribute to a better understanding of the mechanisms that regulate the planet’s climate and provide relevant clues about its future evolution.
The ocean as a climate archive
The research team, led by Iván Hernández-Almeida from the Past Global Changes research network based at the University of Bern, analysed marine sediments extracted from the North Atlantic, south of Iceland, which act as a natural archive of more than one million years of climate history. These sediments preserve microfossils and geochemical signals that allow reconstruction of past conditions such as temperature and oxygen content in the ocean.
Through geochemical measurements of oxygen-sensitive elements such as manganese and phosphorus, together with the analysis of fossil microorganisms from the seafloor —benthic foraminifera, studied by Paula Diz—, the team was able to reconstruct the evolution of oxygen supply in the deep North Atlantic between 1.1 million and 800,000 years ago.
Fewer currents, more global cooling
The results indicate that the massive input of freshwater from melting glaciers weakened deep ocean circulation. This process reduced oxygen transport to the seafloor and promoted carbon accumulation in the deep ocean.
In addition to low oxygen levels, which had severe consequences for deep-sea ecosystems, this weakening favoured the accumulation of dissolved carbon from the microbial decomposition of dead organisms.
As a result, the amount of CO₂ that could be released into the atmosphere decreased, contributing to global cooling and the expansion of ice sheets. The study fills an important knowledge gap, as previous research had mainly focused on the Southern Ocean. The new data show that deep circulation and oxygen conditions also changed significantly in the North Atlantic, indicating that both polar regions contributed simultaneously to the transformation of glacial cycles.
Warning signal for future changes in the Atlantic
Beyond its relevance for understanding the past, this research provides a warning signal for the future. Current climate models predict a possible weakening of Atlantic currents due to global warming and increased melting in Greenland.
The study shows that even during much colder phases of the Earth, changes in freshwater input were enough to alter deep water transport in the North Atlantic, with devastating and irreversible impacts on climate and biodiversity. This highlights the sensitivity of the system, which could also respond significantly under present-day conditions.
In a next phase, the research team aims to analyse how deep circulation and oxygen content in the North Atlantic changed during other warm and cold periods in Earth’s history, in order to better understand when these shifts in equilibrium occur.
In this context, the findings highlight the high sensitivity of the ocean system and its capacity to trigger significant climate changes, with potentially irreversible impacts on climate and marine biodiversity.
The CIM holds the CIGUS recognition from the Xunta de Galicia, certifying the quality and impact of its research, and its activity is co-funded by the European Union through the ERDF 2021–2027 Programme.
Source: DUVI
