Since the industrial revolution began, the concentration of carbon dioxide in the atmosphere has increased and it is now more than 50% higher than pre-industrial levels. The oceans absorb about 30% of the carbon dioxide, which reacts with seawater and carbonate ions, resulting in a decrease of seawater pH. As the pH decreases, oceans became more acidic, and the fitness of many marine organisms is negatively impacted in a number of different ways. Corals and shell builders with a calcium carbonate skeleton are harmed, as well as other organisms such as fishes, posing a threat to humanity, since billions of people depend on food from the ocean as their main source of protein and many activities rely on the fish and shellfish living in the ocean, posing a threat to the economy.
Seasonality is a key factor to understand possible climate changes. Indeed, analyses of surface ocean observations from 1982 to 2015 has demonstrated that the seasonal difference in concentration of carbon dioxide has increased globally because of changes in the seasonality of superficial temperature. Climate models show an enhancement in the amplitude of the seasonal cycle of the sea surface in the middle-high latitudes, reaching a difference between summer and winter up to 8°C by the year 2100, implying more substantial stress for organisms sensitive to pH due to change in the seasonal dissolution of the carbon dioxide.
Studying seasonal time series of superficial temperature and pH is thus critical to forecast climatic changes, but the record of seasonality, especially for the pH, does not go far into the past, covering about the last 40 years. Therefore, the challenge of this project was to understand if it is possible to obtain seasonal time series for pH and seawater temperature beyond the instrumental record using recent and fossil shells of brachiopods.
Brachiopods, known also as lamp-shells, are sessile marine organisms, which produce a shell of calcium carbonate. Estimates for pH and temperature can be obtained by measuring the Boron and Oxygen isotopes of the brachiopod shell, after understanding the biological factors affecting the isotopic values. The broad objectives of this project were to study the seasonal signal in shells of brachiopods which live in middle-high latitudes and to understand the meaning of seasonal time series to make correct esteem of past seasonal parameters (pH and Temperature) estimated by analysing fossil shells.
