International research questions explanation of oceanic currents' influence on climate

An international study has raised doubts about one of the most accepted theories regarding the functioning of the Atlantic oceanic circulation. The research indicates that the AMOC (Atlantic Meridional Overturning Circulation) maintained its intensity even when there was a reduction in the input of warm and salty water from the Indian Ocean.

This new discovery suggests that the mechanisms regulating planetary climate may be more intricate than previously imagined, and that major ocean currents do not react uniformly to environmental changes.

Sediments accumulated over millions of years were crucial for unraveling the history of the oceans. The AMOC acts as a vast heat transport system, carrying warm surface waters northward and returning cold, denser waters to the depths. This movement impacts temperatures, rainfall regimes, and climate patterns in various global regions.

For many years, scientists believed that the phenomenon known as the 'Agulhas Leak' played a decisive role in this cycle. This current, composed of warm, salty waters from the Indian Ocean passing south of Africa towards the Atlantic, was seen as a vital source of salt for the system. The premise was that this salt would help increase the density of water in the North Atlantic, facilitating its sinking and strengthening deep circulation.

To verify this assumption, scientists examined a time interval between 3.6 and 2.6 million years ago, at the end of the Pliocene. The team analyzed sediments collected in the Agulhas Plateau, an area located approximately 500 kilometers south of South Africa. These seafloor deposits serve as natural records of Earth's history, containing microscopic dinocysts and organic compounds that allowed researchers to reconstruct past ocean conditions, including temperature variations and current movements.

Less water from the Indian Ocean, but AMOC remained strong

The data revealed that about 3.4 million years ago, a subtropical front migrated north. This change resulted in a cooling of approximately 3°C in the Agulhas region, giving it characteristics similar to subpolar zones. Consequently, the flow of warm, salty water from the Indian Ocean to the Atlantic lost vigor and was close to interruption.

According to traditional theory, such a decrease should lead to the weakening of the AMOC. However, geological records presented a different picture. The main findings included: the reduction of the Agulhas Leak during a Pliocene glacial period; the increase in deep water formation in the North Atlantic, even with less salt influx from the Indian Ocean; a reorganization of oceanic circulation covering different areas of the planet; and the confirmation of these patterns through climate simulations.

olhardigital.com.brJuly 29, 12:30

Study points out that prolonged drought contributed to the collapse of ancient Mediterranean civilizations

A new investigation suggests that the combination of various natural climatic cycles may have been a determining factor in the decline of several Bronze Age civilizations, which occurred approximately 3,200 years ago in the Mediterranean area. The study, published in the journal Science Advances, establishes a link between periods of extreme drought and the weakening of societies that were already fragile.

Climatic Research Methodology

Scientists from Stockholm University conducted this research using an advanced climate model capable of recreating the environmental conditions of the last eight millennia. The analysis demonstrated that progressive climatic changes added to shorter-duration natural fluctuations, resulting in an intensification of water scarcity.

The researchers concluded that this scenario reduced the amount of available water, putting pressure on agricultural production and compromising food security, elements that may have led to the simultaneous collapse of distinct civilizations in the eastern Mediterranean.

Detailed Analysis of Droughts

To investigate the causes of droughts in the eastern Mediterranean, PhD student Katherine Power and Professor Qiong Zhang applied the EC-Earth 3.3.1 climate model, usually used in future climate predictions. This time, the tool was used to reconstruct the environment of the last eight thousand years and map long-term patterns.

Katherine Power explained in a note released by Stockholm University that the most severe drought episodes were not the result of a single climatic event. She stated that the most severe droughts occurred when natural climatic cycles operating on different timescales converged, which helps justify the severity of droughts linked to the Late Bronze Age collapse.

Environmental and Historical Impacts

The findings also indicate that the Mediterranean experienced a slow process of drying over millennia, driven by slow changes in Earth's orbit. In parallel, smaller oscillations related to the Atlantic Ocean and the atmosphere affected the intensity of these climatic conditions. While long-term changes allowed some capacity for population adaptation, faster variations could affect vast regions unexpectedly, increasing impacts on communities dependent on agriculture and generating cascading effects.

The scientists identified three major phases of prolonged drought in the eastern Mediterranean, caused by the coincidence of these natural cycles. The most recent occurred concurrently with the decline of several civilizations during the Late Bronze Age. Climate reconstruction shows that the reduction in rainfall began in parts of the Balkans about 3,400 years ago. Around 1100 BC, the decrease in precipitation was already more widespread, and approximately in 1050 BC, the region recorded lower temperatures.

The authors mention that these results are consistent with indirect evidence found in geological formations, such as stalactites, which signal drops of 15% to 30% in rainfall in certain locations. According to Katherine Power, the combination of these processes exceeded a critical limit for water availability in the region, decreasing water and increasing pressure on agriculture and food security in already vulnerable societies.

Additional Factors and Current Relevance

The study also highlights that small changes in the balance between evaporation and precipitation can cause disproportionate consequences for vegetation, food production, and the stability of natural resources, especially when ecosystems and agricultural systems operate near their moisture limits. In addition to climatic influence, the work recalls that other factors, such as technological transformations and invasions attributed to the Sea Peoples, are also linked to the collapse of the civilizations of that era. However, the authors observe that even these population displacements may have been influenced by the climatic conditions faced in their origins.

The researchers emphasize that the findings are important for the present, given that the Mediterranean is considered one of the areas most susceptible to climate change, with projections indicating a hotter and drier future. Katherine Power concludes that understanding the interaction between warming caused by human actions and the natural variability of the Atlantic Ocean will be crucial for assessing drought risks in the coming decades, although more research is needed.