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Salinity and water stratification are also sharply increasing. Temperature record also for the Mediterranean

The 'ocean fever' is still rising. In 2023 temperatures have risen recording a new record in water warming, with an increase in heat content, stratification and salinity. This is what emerges from the study “New Record Ocean temperatures and related climate indicators in 2023” published in the journal “Advances in Atmospheric Science” and conducted by an international team of scientists, coordinated by IAP-CAS (Institute of Atmospheric Physics of the Chinese Academy of Sciences) and composed of American scientists from NCEI-NOAA (National Centers for Environmental Information of the National Oceanic and Atmospheric Administration), New Zealand, French and, for Italy, by Simona Simoncelli of the National Institute of Geophysics and Volcanology (INGV) and Franco Reseghetti of the National Agency for new technologies, energy and sustainable economic development (ENEA).
In 2023, the ocean water temperature, which cover the 70% of the planet and they absorb approximately the 90% of the heat caused by global warming, increased by a value between 9 (according to NOAA calculation) and 15 (IAP-CAS calculation) ZettaJoule compared to 2022 in the layer between 0 and 2000 meters deep: to give you an idea, 1 ZettaJoule is equivalent to double the amount of energy that powers the world economy every year. The different results seem to be mainly attributable to the different data quality control procedures and calculation methodologies.
In addition to the general warming of the waters, Very strong anomalies were also found in ocean surface temperatures, with unexpected values ​​attributable in this case not only to global warming, but also to the short-term thermal fluctuations of the Pacific Ocean due to the transition of the La Niña and El Niño phenomena, starting from May 2023.
The overall warmer waters produced by the combination of these factors can change weather patterns worldwide. In particular, the variation in atmospheric precipitation and the evaporation of surface water alter the salinity of the ocean, whereby salty areas continue to become saltier and fresher water areas continue to decrease in salinity, with direct consequences on marine life, ocean currents and interactions with the atmosphere.
Less dense, warmer and less salty waters tend to remain on the surface and are unable to transport heat, carbon dioxide and oxygen to deeper waters, with serious consequences for animal and plant life in the ocean. In this case, we are talking about "stratified" waters: according to the study just published, even in the last year stratification has further increased compared to 2022.
Due to warmer ocean waters, excess heat and moisture enter the atmosphere due to evaporation of surface waters, making storms more violent, with stronger rain and winds and, therefore, with a greater risk of flooding, even on Italian territory.
In this global scenario, the Mediterranean Sea in 2023 confirmed itself as the fastest warming basin among those analyzed in the study, reaching the highest thermal value since the beginning of modern recordings.
“In 2023, INGV and ENEA continued, as part of the MACMAP project financed by INGV, to collect temperature data of the Mediterranean waters on a seasonal basis, in particular of the Ligurian and Tyrrhenian Seas along the Genoa-Palermo route, thanks to the collaboration with the shipping company Grandi Navi Veloci (GNV)”, explains Simona Simoncelli, INGV researcher and co-author of the study. “The analysis of these temperature data, as well as those collected at a depth of 400 meters by the CNR-ISMAR buoy in the Strait of Sicily, indicates a clear warming in the water layer between 2013 and 150 meters below sea level since 450. depth, which then extended to deeper (up to 700 meters) and more northern waters. In this case between 2013 and 2016 the warming was above 0.4 °C, followed by a slight decrease and a stationary period. The water temperature has started to increase again since 2021, reaching its record, for the moment, in September 2023.".
“Continuing to systematically monitor the seas, specifically the Mediterranean Sea, by measuring the values ​​of some parameters such as temperature, salinity, PH and oxygen, remains the only way to consolidate knowledge on the subject and improve the reliability of the forecasts that at the moment they are not as accurate as necessary and desired, even if there is a clear trend of temperature growth", he adds Franco Reseghetti, ENEA researcher and co-author of the study.
“The Mediterranean strongly influences life in the countries bordering it: from agriculture, to fishing, to hydrology, to weather evolution, to the health of populations. Continuing to monitor it is the key to contributing to understanding the effects of global warming, raising awareness in society of this emergency and stimulating the adoption of necessary adaptation and mitigation measures. We must always keep in mind that due to this phenomenon enormous material damage is recorded every year all over the world, often accompanied by the loss of human lives.", the researchers conclude.

Link to the study
IMOcean warming 2023 1Figure 1: Progressive ocean heat content since the late 50s, based on the two datasets used in the study. The reference line corresponds to the average ocean temperature calculated for the period 1981-2010 and the difference compared to this value is shown. Blue bars indicate colder waters than the 1981-2010 average, while red bars represent warmer waters. The upper graph shows the results of IAP, the lower one shows NOAA. Ocean warming 2023 2 Figure 2: Total variation in sea surface temperature (Sea Surface Temperature - SST) from 1955 to 2023 obtained from the analysis of data (1 m) of the first level of the IAP/CAS grid. The black line represents the annual value and the red line represents the monthly value. The anomalies always relate to the reference period 1981-2010. The annual change in SST is shown in the inner panel, with 2023 values ​​shown in black.  Ocean warming 2023 3Figure 3: Temperature along the MX04 Genoa–Palermo transect (western Mediterranean) recorded with XBT probes launched from ships of opportunity and monthly average temperature values ​​400 m from the Sicilian Channel buoy. (a) XBT traces in the Tyrrhenian Sea and the Ligurian Sea. (b) Hovmöller plot of mean MX04 temperature anomalies over the period 1999–2023 calculated by subtracting the 1981–2010 baseline of IAP/CAS data. (c) MX04 average temperature values ​​calculated in the 100–700 m layers, and monthly average temperature values ​​at 400 m from the Sicilian Channel buoy, between 2004 and 2023, with error bars representing the relative deviations standard.