Researchers from the Geoma Group (Marine and Environmental Geology, cover photo) have been studying the topography of the Interior Basin of Galicia (Figure 1) for years, a deep submarine depression of more than 3000 meters deep that extends from north to south about 100 kilometers from the Galician coast with the aim, among others, of advancing in the reconstruction of the climate from sediments and oceanographic data. As a result of this work, the team has just confirmed periodic arrivals of freshwater masses to this entire extension during the last 80,000 years, which highlights the importance of this area for unraveling one of the great enigmas of Quaternary era climatology: what causes and how the disintegration of the North Polar Ice Cap that periodically floods the North Atlantic with a veritable armada of icebergs occurs.
The results will be published in the next issue of the prestigious scientific journal Earth and Planetary Science Letters and are now available in the online version of the journal. “This work is important for better understanding what the consequences would be and how the climate change that would occur if the trend of global warming of anthropogenic origin continues,” says Daniel Rey, principal investigator of the Geoma group, while explaining that the melting of the North Atlantic ice blocks leaves a remnant of debris – small particles that result from the erosion of rocks – on the bottom of the central Atlantic area – called the Ruddiman Belt – which abruptly alters the deep ocean circulation and changes the Earth’s climate.
Figure 1. Position of the sedimentary core studied in the Interior Basin of Galicia with the ice masses referred to and the Channel River
Unexpected discoveries
The researcher of the Do*Mar excellence doctoral program of the Campus do Mar Maider Plaza-Morlote and the rest of the co-authors of the article (colleagues from Geoma and also from the universities of Aveiro, the National University of Australia and the State of Rio de Janeiro) were studying the remains left by the melting of these icebergs, under the GALINCLIMARCH National Plan project directed by Professor Daniel Rey, when they discovered the trace left by river waters originating from the melting of the continental ice masses that occupied the northern half of Europe during the last glaciation.
“The discovery corroborates the hypothesis that the melting of the North Atlantic ice masses is the result of an abrupt climate change, rather than its cause”, emphasizes Plaza-Morlote, who explains that during the last glaciation, the coalescence of the ice masses that occupied the British Isles and the Fennoscandian shield (formed by the Scandinavian Peninsula, the Kola Peninsula, Karelia and Finland) occurred in the North Sea Basin. This circumstance channeled the drainage of the Central European rivers towards a single channel called the Channel River, thus creating one of the largest river systems that have ever existed on the European continent. “This reorganization of the river systems gave rise to very important discharges of freshwater into the Bay of Biscay. What was not known until now is that the flow of these discharges was so important as to reach the northwest of the peninsula, which demonstrates their capacity to disturb the deep ocean circulation”, explains the author.
Magnetic properties of sediments
The detection of freshwater masses was possible by combining the study of magnetic properties and the elemental and isotopic composition of the sediment through specific indicators called paleoclimatic proxies. “All ocean waters transport in suspension a set of very small magnetic particles of nanometric scale resulting from the erosion of rocks in their source areas. The geology of each area naturally produces a set of nano minerals with unique magnetic properties that allow them to be identified in the sedimentary record”, explain the members of Geoma, a driving group and international reference in the use of these techniques to produce non-nutrient-based proxies useful in paleoceanography. The development and calibration of this type of proxies is one of the challenges facing the discipline in order to be able to quantify paleoceanographic parameters in the next decade.
A unique enclave ideal for climate studies
The work also highlights the uniqueness of the sedimentary records of the Interior Basin of Galicia, a morphostructural feature of the Galician Continental Margin that is between 2800 and 4000 meters deep and that forms a wide trough-shaped valley 100 km wide by 400 km long that extends between the continental shelf of Galicia and the so-called Western Banks -Banco Galicia and the submarine reliefs of Vasco de Gama and Oporto-. “Its geographical location is ideal for studying the drastic changes in ocean circulation that take place during glacial/interglacial cycles and its distance from large ice masses acts as a low-frequency filter that only records the most important ice discharge events, providing clearer paleoclimatic signals”, emphasize the authors of the study.
Source: duvi.
