Researchers from the Geological Survey of Israel have identified climate cycles and their effects on the accumulation of sand and clay at the bottom of the Mediterranean Sea, combining historical findings and astronomical theory
Dr. Yoav Ben Dor, Geological Survey of Israel
About a hundred years have passed since the cluster man, scientist, engineer, and Serbian astronomer Milotin Milankovic published his groundbreaking ideas about how slight changes in the Earth's orbit in space affect the Earth's climate. In those days and during the period that preceded them, evidence began to be published from all over Europe, and later also from the "New World", which indicated the possibility that significant parts of the continental surfaces in the northern hemisphere of the earth were once covered by a thick layer of ice. Massive rocks resting on level plains, round lakes and wide valleys characterized by the shape of the letter U, have led naturalists of various schools to claim that great masses of ice shaped the still landscape, but have long since disappeared. It is understood that in those days the scientists did not have the ability to determine the age of the phenomenon (or, in the professional terminology, "date" it), but from a historical review of various writings, as well as from an archaeological study of the remains of human activity, it was clear that these were long periods of time of thousands of years, stretching beyond to the limits of human history. At the same time, the researchers stood helpless in the face of the attempt to explain how such a phenomenon is possible, and many times publications that dealt with these aspects were abandoned or considered exceptional. Many aspects of the fields of human knowledge at that time were still in their infancy, and various issues that seem clear to us today, such as the age of the earth and the age of the solar system were still far outside the realm of known knowledge.
The revolutionary idea proposed by Milankovic regarding climate change, matured in his mind during a lengthy detention he was sentenced to as a Serbian citizen who fell into the territories of the Austro-Hungarian Empire during the First World War. At the foundation of the theory is the understanding that tiny changes in the Earth's orbit in space, which are reflected in the angle of inclination of the Earth's axis of rotation in relation to the milka plane (the plane on which the Earth moves in relation to the Sun), in the direction the axis of rotation points (to which star the north points), and in the degree The ellipticity of its orbit around the sun is what affects the angle and amount of radiation that reaches it from the sun and as a result causes dramatic changes in the global climate the country In this way, suggested Milankovitch, differences in the amount of radiation the Earth receives each year, and differences in the amount of radiation received by the entire hemisphere (Northern or Southern Hemisphere) change the Earth's temperature in time spans of thousands of years. The heating and cooling processes of different areas of the earth, which last for thousands of years, eventually cause the expansion and contraction of the area covered by the permafrost (the ice caps around the poles) and the cyclical appearance of ice ages. The key point, according to Milankovitch's idea, is a cooling of the northern hemisphere in a way that allows the snow front to spread south and survive until the next winter, without melting during the summer. The snow that accumulates turns into ice, which in turn contributes to cooling and reducing radiation, and this is because ice returns radiation to space more effectively than land or water, so that with the expansion of the ice caps, additional cooling occurs, which in turn allows the accumulation of additional ice that contributes to strengthening the process. This type of process is known as positive feedback, in which each of the steps in the process contribute to each other, so that the process "reinforces itself". Milankovitch made the calculations according to the existing knowledge about the Earth's orbit, and came to the conclusion that the Earth's climate "pulses" according to the cycles and rhythms defined by the Earth's movement in space. Unfortunately, Milankovitch passed away before his theory was accepted by the scientific community, as it did not yet have the scientific tools to prove or disprove it. Beyond the language limitations, which were largely resolved thanks to the translation of his writings into English at the Hebrew University of Jerusalem, the main difficulty of the scientific community in accepting Milankovitch's theory about the connection between the Earth's movement in space and the ice ages was the inability to determine the age of sedimentary rocks that contain climatic information . At the same time, since the publication of the theory, many confirmations have been found in the sediments of caves and lakes and even in sediments that accumulate on the seabed. In 1976, three researchers led by JD Hays published a groundbreaking study in which they analyzed a cross-section of sediments from the Atlantic Ocean that was sampled through drilling, and covers about half a million years from the present (that is, during the drilling, sedimentary materials whose age ranged from 500,000 years before the present to the present day were extracted from the seabed). In the section of the sediment sampled in the drilling, the researchers found skeletons of tiny creatures (plankton), which absorb essential elements from the ocean water. The researchers determined the age of the sediments in the section proposed from the drilling, and also measured the isotopic composition of oxygen in the skeletons of the creatures, and identified a clear cycle characterized by a number of durations (wavelengths) of approximately 100, 42 and 23 thousand years. Finding such conclusive evidence of consistent periodicity in an independent cross-section of sediment accumulated on the sea floor provided clear evidence of the influence of the Earth's astronomical motion characteristics on global climate. This concept has been getting stronger since then thanks to many additional findings from various sites in the world, including the concentrations of carbon dioxide found in gas bubbles in ice cores in Greenland and Antarctica.
Despite the clear effect of the Earth's motion on the climate, the relationship between it and other complex processes on the Earth's surface is not always clear, and Milankovitz cycles are used by us to prove the role of this climatic cycle in various processes. An example of the effect of climate change on sedimentary rocks that accumulated off the coast of Israel during the 5 million years before the present was recently published by three researchers from the Geological Survey of Israel (Sirota, Ben Dor and Gabirtzman) in the scientific journal Basin Research. This newspaper deals with sedimentary basins, which are low places in which substances called sediments (or sediments) accumulate, which harden over time and turn into rocks called sedimentary rocks (sedimentary rocks). Some of these sediments come from nearby land via rivers and streams (drift of sand and mud) and some are created in the sea itself, for example, from animal skeletons or salt and gypsum that sink directly from very salty bodies of water.
The researchers analyzed the data obtained from the gas drilling off the coast of Israel, in the Levant Basin (the maritime space between Israel, Egypt and Cyprus), where most of the sediment materials are those that came from the nearby continents. The researchers found that the amounts of sand and clay vary, indicating changes in the importance of the processes that provide sediment materials to the Levant Basin. The purpose of the study was to understand the origin of these exchanges - to what extent they are affected by the growth of the Nile fan, one of the largest rivers in the world that drains the northeastern part of the African continent, and to what extent they are affected by past climate changes.
"We were able to quantify the distribution of sand in the sediment that accumulated in the eastern Mediterranean over the past five million years, and we wanted to check the relationship between the changes we found between the amount of sand and clay (fine-grained mud) and the processes that affected the area," says Dr. Ado Sirota, a researcher at the Israel Geological Survey. who led the study. "Since most of the sediment that fills the eastern Mediterranean comes from the Nile, the change in the distribution of sand over the years indicates A change in the nature of the alluvium that is carried from the sources of the Nile in equatorial Africa and the Ethiopian plateau to the Mediterranean Sea, a distance of about 7000 km. We especially wanted to check what are the processes that enable the transport of significant amounts of sand in the maritime space to a distance of hundreds of kilometers from the mouth of the river." The research was led by Dr. Sirota in collaboration with Dr. Yoav Ben Dor, in the research laboratory of Prof. Zohar Gvirtzman. Dr. Ben Dor specializes in the analysis of time series (data arranged in an orderly sequence according to the date of their appearance), and assisted in processing the data and analyzing it using computational tools. "The analysis of the time series was not an easy challenge," explains Dr. Yoav Ben Dor. "The data was not always complete or uniformly arranged in the various drillings, and we were required to analyze, understand and prepare it even before we could investigate it. After pre-processing, we examined the data using several methods from the field of time series in order to understand the central patterns of the cycles and their statistical significance (to what extent The results can be "trusted", or we should suspect that they appeared by chance)".
Prof. Zohar Gebirtzman's research laboratory at the Israel Geological Survey has been focusing on the study of sedimentary basins and the Mediterranean basin in particular for many years. "The study of sedimentary basins is an infrastructural study that affects many fields in theoretical and applied geology. For example, understanding the processes that shaped the earth's crust in areas that were stretched in the distant past as a result of the activity of tectonic plates, understanding the path of movement of seismic waves (waves that carry energy) of earthquakes, finding Gas and oil deposits, assessment of geological risks that may rupture infrastructures such as pipelines gas or communication cables, and other issues that come up from time to time, such as burying excess carbon dioxide in the depths of the earth," Prof. Gvirtzman adds. "In the current study, we wanted to understand the geological processes that control the transport of sand over hundreds and thousands of kilometers in the maritime space. How far will the sand migrate on the seabed and how does it depend on the dynamics of rivers and climate changes."
Within the period examined, which includes the Pliocene and Pleistocene periods (between 5.3 million years before our time and today), the researchers identified patterns typical of "Milankovitch cycles", which have a typical cycle of 100 and 400 thousand years. The identification of the cyclical phenomenon in the layers that accumulated on the bottom of the Mediterranean so long ago illustrates the connection between Milankovitch's theory regarding the amount of radiation reaching the earth and the ice ages and between the dynamics of sediment transport in large rivers such as the Nile. In fact, based on the identification of the climatic cycle, the researchers proposed that the distribution of sand in the Levant basin is directly affected by cyclical changes in the hydrological characteristics of the Nile, which receives its water from the rain that falls on the Ethiopian level, and is in turn affected by changes in global climate patterns over geological ages according to changes in the amount and distribution of radiation that the Earth receives. This hydrological variation translates into changes in the flow of sand carried by the river to the eastern Mediterranean. The progression of climatic processes that originate in the Ethiopian plateau, through the transport of sediment along thousands of km, to the eastern Mediterranean Sea shows the importance of studying sedimentary sections in understanding the relationship between the Earth's climate and large systems of sediment transport, which in turn also affect the climate, through processes of carbon accumulation and removal from the atmosphere.
In addition to the cyclical changes between sand and clay that were discovered in most of the examined section, a widespread sand unit was found in the upper part of the area, indicating the advance of the Nile delta into the Levant basin, and how the presence of a large river near the deposit basin affects the accumulation of alluvial materials. The researchers calculated and found that a river like the Nile results in a "blurring" of part of the climatic signal in the sediment transport process, and therefore short cycles of less than 40 thousand years were not observed in the sediment cross-section, while long cycles of 100 to 400 thousand years were well preserved.
Figure 5: The main cycles identified in the various drillings in the Levant Basin. Short cycles are not prominent because of the sediment transport processes that result in a "blurring" of the transport process from the Nile to the basin, while the long cycles are well preserved in the sediment cross section. From Sirota et al., 2024.
In addition to the sensational discovery of climatic cycles during this period in the area, this is the first study to document the mud of the Levant Basin floor beyond the upper few meters, which were already sampled in several previous studies. The sedimentary section examined here to a depth of several hundred meters is the first evidence of the processes that fed the Levant basin with sand and clay for the past 5 million years, a combination of a large river and climate change. The researchers point out that the very identification of "Milankovitch cycles" in such an early period, in the Pliocene (2.6-5.3 m.s.), is an important contribution to the pool of human knowledge about climate and the environment.
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One response
interesting and important,
And yet it is appropriate that the respected researchers do not confuse the concepts
Between an era and a period, since it is accepted that the earth entered an ice age
About 35 million years ago, after Antarctica was already "sitting" on the South Pole
And after Asia, Europe and America "closed" on the North Pole,
A situation that resulted in the accumulation of glaciers at the poles that spread south and north,
Because of the glacial Milankovitz cycle, they retreat during warm periods,
Periods not "Era", the confusion of terms is common
And it is fitting that learned researchers will not mistake him...