The sea, a sensitive thermometer of climate change, also showed unequivocal signs this year. Monitoring campaigns by CIMA Research Foundation using a CTD probe 1 recorded a significant increase in surface temperatures: from 14 °C in early May to 26.8 °C in early August and 27.7 °C in mid-August. Heatwaves affected not only the surface but also the water column: the thermocline 2 deepened to 122 meters, altering the vertical structure and influencing ecological processes.
Positions of CTD probe casts carried out on 16 July by CIMA Research Foundation, identified on the basis of sea surface temperature detected by Copernicus on 15 July. Warming was so rapid that the thermal front had almost completely disappeared by the following day.
CTD (Conductivity, Temperature, Depth) multiparameter probe of CIMA Research Foundation
These conditions had effects on biodiversity. Fin whales which, according to data from monitoring activities coordinated by CIMA Research Foundation, in recent years had been observed in 150–200 individuals per season (with the exception of 2023, which recorded almost 500 sightings), were only 63 this year, values similar to 2014 and well below average. Conversely, populations of Goose-beaked whales and striped dolphins showed high numbers, with over 4,000 individuals of the latter species. Among the most significant sightings was a leatherback turtle near Corsica, an extremely rare event that in the past twenty years had been documented only a couple of times by CIMA’s monitoring.
Alongside these data, observations also recorded a very weak phytoplankton bloom in March, significantly less intense than the previous year, when marked blooms occurred between March and April with a peak in April and high chlorophyll concentrations. Summer mixing⁴ observed between two heatwaves further highlighted the vulnerability of the marine system to extreme atmospheric conditions.
Sum of chlorophyll concentration obtained by satellite (Copernicus Marine Service), a preliminary indicator of the intensity of the phytoplankton bloom.
This picture suggests that marine warming does not produce uniform effects: some species decrease sharply, others seem to derive temporary benefit from new conditions, outlining a complex reorganization of marine communities.
- The CTD multiparameter probe (Conductivity, Temperature, Depth) is an instrument that measures the electrical conductivity (C), temperature (T) and depth (D) of water. The probe used in CIMA Research Foundation’s monitoring activities reaches depths of up to 1,000 meters and is equipped with an external battery, thereby enabling regular sampling even in extended and prolonged conditions. ↩︎
- The thermocline is the layer of the sea that separates warmer surface waters from colder deep waters. ↩︎