Rosa Tedin | Ourense
From Cape Ortegal in Galicia to the tip of Pern in France, the Bay of Biscay is located, encompassing ports and fishing areas of great importance in both countries. Due to this relevance, any variation in the conditions of its waters can have important socio-economic implications. Given this circumstance and the climate change that is occurring, in his doctoral thesis, the researcher from the University of Vigo Xurxo Costoya analyzed the variations in temperature and salinity in recent decades in this gulf and their causes and consequences. The results point to significant changes, including a warming of the surface of the entire bay of 0.26 degrees Celsius per decade.
The thesis, directed by the professors of the University of Vigo Maite de Castro and Moncho Gómez Gesteira, was entitled Thermohaline variability in the Bay of Biscay: causes and physical implications and was presented this year at the Faculty of Sciences on the Ourense campus. Combining databases from the last 40 years of different origins (in situ, reanalysis and satellite data), the researcher from the Department of Applied Physics studied for three years an area that, he points out, despite its relevance from the point of view of physical oceanography “historically is a region that has received less attention if compared to others in the North Atlantic”.
Changes in temperatures, biological changes
The research detected a warming of the surface of the entire bay since 1982 of 0.26 ºC per decade. “The warming is more related to the increase in the duration of the warm season than to the existence of warmer summers or milder winters”, comments Xurxo Costoya. Furthermore, he adds, the months that are affected by the increase in the duration of the warm season (April-June and September-October) have also suffered a significant increase in the number of days with an extremely warm sea surface temperature. The only area in which a cooling was observed during the study since the eighties is the coastal strip under the influence of the fluvial plume formed by the Loire and Gironde rivers during the winter months. “The decrease in temperature in this area was more intense during periods in which the river discharge and the southwest winds are above their average values, for example in the period 2002-2014”, comments the former doctor.
The results obtained during the research indicate that the two most important water masses in the bay, the eastern North Atlantic water mass and the Mediterranean water mass, have experienced significant changes. The first tended to increase its temperature and salinity during the period from 1975 to 2010 and also during the decade 2004-2013. On the contrary, a cooling and also a decrease in salinity were detected in the second during the period from 2004 to 2013. “The main cause of these variations were the changes in the regions where the water masses originate each year, that is, in the vicinity of the Gulf of Cádiz for the Mediterranean water mass and in a region northwest of Galicia for the eastern North Atlantic,” states the researcher.
The process of climate change that affects the planet as a whole, explains Costoya based on his study, “is already being felt in the waters of the Bay of Biscay”. Thus, he points out, “an increase in temperature has been recorded during the last decades in all months of the year”. The rate of warming, he says, was greater in spring and autumn, causing the warm season to last longer in the gulf, which in turn brings with it important consequences in other areas, such as the biological one. In this way, points out the researcher from the Ephyslab Group, “different studies have detected that some species that are important from an economic point of view, such as some tunas (albacore tuna and bluefin tuna), arrive earlier in the Bay of Biscay. Thanks to this thesis we know that this earlier appearance is related to the increase in temperature during spring”. Furthermore, he adds, an increase in extreme events has been observed that would be “behind the variations observed in the spatial distribution of some species, such as some algae, which tend to be located further north, giving way to foreign species from a more tropical environment”. The research also relates this increase in temperature to the fact that the spawning areas of sardines and anchovies are increasingly located further north. In this context, “the results of this thesis will also serve in the future to better understand variations in the populations and phenology of multiple species”, comments Xurxo Costoya.
Application to other areas of the planet
From the point of view of physical oceanography, the results achieved, the researcher comments, “are of great importance since they help to better understand the dynamics of the Bay of Biscay when analyzing this area as a whole”. Thus, he emphasizes, they have shown that, considering that it is a relatively small area, the heterogeneity of the changes is high, even giving rise to trends of opposite sign in nearby areas. In this way, the thesis, he adds, “is a good example of how important it is to analyze the variations at a detailed spatial scale before determining scenarios and policies to mitigate these changes, since although globally it is obvious that there is an increase in the temperature of the oceans, what we observe is a great spatial heterogeneity in these changes”.
Alén de ofrecer unha análise da situación no caso do Golfo de Biscaia, toda a metodoloxía deseñada para realizar os estudos nesta zona aplícase agora a outras áreas do planeta, xa que as bases de datos creadas conteñen información de todos os océanos e ao longo da tese tratouse de desenvolver programas que con pequenos cambios permitisen aplicar as diferentes metodoloxías a outras zonas. “Dada a aceptación da metodoloxía utilizada para calcular eventos extremos de temperatura no océano, esta aplicouse xa na costa oeste da Península Ibérica, na costa de Marrocos e tamén en Canarias, acadando resultados interesantes”, recalca o investigador. Ademais, a raíz do descubrimento do efecto de arrefriamento coma consecuencia dos aportes dos ríos Loire e Gironde, engade, “xa verificamos que este mesmo efecto ocorreu noutras áreas, coma por exemplo no Golfo de Guinea debido ás achegas de auga doce do río Congo ou na plataforma continental de Texas e Louisiana debido ao río Mississippi”.
Source DUVI
