The Boiling Sea of Panarea
Off the eastern coast of Panarea, the smallest of the Aeolian Islands, the sea appears to boil. Columns of gas bubbles rise continuously from the seafloor, a dramatic display of the active volcanic system that lies mostly submerged beneath the Tyrrhenian Sea. This activity is centered in a shallow area, between 10 and 35 meters deep, among a cluster of rocky islets—Dattilo, Bottaro, and Lisca Bianca—that are remnants of an ancient volcanic crater.
The vented gas is predominantly carbon dioxide, making up over 98% of the emissions. It originates from a deep geothermal reservoir where temperatures range from 220 to 350°C. This CO2, along with smaller amounts of hydrogen sulfide (H2S), hydrogen chloride (HCl), and other gases, is released from the seafloor through fissures and hydrothermal chimneys. The hydrogen sulfide is responsible for the distinct sulfurous smell often present at the surface. This intense degassing is part of a large hydrothermal system covering about 70 square kilometers. A significant gas eruption in November 2002 created a new submerged crater 20 meters long and 7 meters deep near the islet of Bottaro, showing the dynamic nature of this volcanic complex.
An Acidic Future
The constant stream of volcanic CO2 profoundly alters the local seawater chemistry. As the CO2 dissolves, it forms carbonic acid, drastically lowering the water's pH. While typical seawater pH is around 8.1, measurements taken directly at the Panarea vent sites have recorded values as low as 5.8 to 6.5. This localized, intense ocean acidification creates a unique natural laboratory for scientists studying the potential effects of global climate change on marine ecosystems.
The impact on marine life is clear. In the most acidic zones immediately surrounding the vents, the seafloor is often bare, colonized only by specialized microbes. Calcifying organisms—those that build shells or skeletons from calcium carbonate—are particularly vulnerable. Studies on Mediterranean corals, such as Balanophyllia europaea and Astroides calycularis, transplanted along the pH gradient show that their ability to regenerate tissue after injury is significantly reduced in the low-pH, high-CO2 water. The acidic conditions make it harder for these animals to build and maintain their structures. In contrast, some non-calcifying organisms like certain algae and the seagrass Posidonia oceanica can sometimes tolerate or even benefit from the elevated CO2 levels. By observing which species survive, which struggle, and which thrive, researchers learn about the potential long-term winners and losers in a future, more acidic ocean.