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Marine sediments explain how parts of the northeastern region of Brazil have become semi-arid

Publicado em 22 junho 2021

Rainfall associated with the Intertropical Convergence Zone (ITCZ), the convergence zone of trade winds and rising air around the Earth near the equator, affects the food and water safety of approximately one billion people worldwide. It contains about 11% of Brazil’s population and is concentrated in four provinces in the northeastern region: Rio Grande do Norte, Ceara, Piauí and Maranhão. The wide strips of these states have a semi-arid climate, with about half of the annual rainfall occurring only two months (March and April) when the rainforest reaches the southernmost tip of the northeastern region. .. For the rest of the year, the rainforest zone will move further north. For example, it is the cause of peak rainfall in the Venezuelan coastal areas in July and August.

Predicting the future behavior of precipitation in these semi-arid areas is fundamental to allowing society to predict the potential for changes in rainfall patterns due to ongoing climate change. A study by Cristiano Chiessi, a professor at the University of Sao Paulo (USP) in Brazil, and collaborators found that precipitation in the northern part of the northeastern region of Brazil has been for the past 5,000 years, in contrast to the important paradigm of paleoclimatology. It is shown that it has decreased systematically. This revised view of what happened in the past helps you create more realistic scenarios of what might happen in the future.

Articles about research are published in Paleoceanography and paleoclimatology.. This study was supported by FAPESP.

“According to a general paradigm, the rainforest zone has moved south over the last 5,000 years. Instead, the latitude range has shrunk to oscillate within a narrower band,” Chiessi said. Told Agência FAPESP.

Valuable information about the response of the climate system to various conditions is recorded in geological sediments deposited on the seafloor. The study includes three independent indicators of precipitation from sediments collected along the mouth of Parnaiva on the border between Piauí and Maranhão.

“We analyzed the ratio of levels of chemical elements in titanium and calcium. Titanium comes from rock erosion on the continent and calcium comes from the shells of marine life,” Kiessi said. “We also estimated the rate at which continental sediments accumulate on the seafloor and the composition of hydrogen isotopes in continental plant waxes found in marine sediments. These three datasets, along with analysis of numerical climate model output, Showed a tropical contraction. Rain zones for the last 5,000 years, rather than the proposed southward movement. “

The study also shows that the surface temperature distributions of the two hemispheres are an important factor in the location of the rainforest zone, as opposed to the general paradigm.

“According to the paradigm, the southward movement of the rainforest was due to the gradual increase in radiation the southern hemisphere received from the sun during the summer. The opposite occurred in the northern hemisphere, with the northward movement of the rainforest. More and more hindered, but two weaknesses in this model were noted, “said Chiessi. “The first was the assumption that the location of the rainforest zone was determined by the surface temperature distributions of both hemispheres. This does not necessarily respond linearly to the distribution of solar radiation. The second is the paradigm. The evidence to support this is almost alone in the northern hemisphere. There was no evidence of movement in the southern hemisphere. “

Solar radiation underwent the described changes, but he continued, the hemispherical response was different due to the difference in area between each continent and the sea (continents are more than the sea to changes in solar radiation). Reacts fast). “Therefore, we need to revise the paradigm that has influenced paleoclimatology for 20 years,” he said.

Numerical climate models suggest that by the end of this century, the latitude vibration range of the rainforest zone will shrink, further reducing rainfall in the northeastern region of Brazil, with potentially serious social and environmental consequences. doing. However, when the Atlantic meridional overturn (AMOC) became significantly weaker and reached the turning point predicted in another study by Kiessi, South Atlantic warming outweighed North Atlantic warming. rain South facing belt. “This will have a negative impact on different parts of the world, but in Brazil it will prevent even greater reductions in precipitation in the northeastern part of the world,” he said.


Researcher: Climate change will reposition the Earth’s rainforest zone


For more information:
CM Chiessi et al, Metaphase-Late Holocene Contraction of the Intertropical Convergence Zone in Northeastern South America, Paleoceanography and paleoclimatology (2021). DOI: 10.1029 / 2020PA003936

Additional information is available at. agencia.fapesp.br/23134/

 

Quote: Marine sediments explain how parts of the northeastern region of Brazil became semi-arid (2021, 22 June). Obtained from https: //phys.org/news/2021-06-marine-sediments-brazil-northeast-region.html on June 22, 2021.

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Marine sediments explain how parts of the northeastern region of Brazil have become semi-arid.

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