Points along the Brazilian coast release greenhouse gases

. Oct 15, 2018
brazilian coast santos Craters on the Brazilian coast release greenhouse gases

Two research groups – one from São Paulo and another from Rio Grande do Sul – have identified almost 2,000 craters in the seabed of parts of Brazil’s south-eastern and southern coast, around 200 kilometers from the mainland. Approximately 230 meters wide and 90 meters deep, these deepsea holes, known as pockmarks, are formed by the eruption of gases from the seabed, mainly methane (CH4), one of the causes of the greenhouse effect. However, it is estimated that most of the methane is consumed by bacterias and other organisms in the ocean, before making it to the atmosphere.

There is yet to be any data about the contribution of seabed craters off the Brazilian coast to the country’s total emission of greenhouse gases, which in 2014 stood at 2 billion tons, the equivalent of around 5 percent of the world’s total, in accordance with the Ministry of Science, Technology, Innovation, and Communications. Produced mainly by farming and the treatment of waste, methane contributes to 24 percent of total emissions (the volume of gas which remains in the atmosphere after subtracting the total emissions of carbon taken from human activity, such as the restoration of forests).

Carbon dioxide (CO2), mainly caused by the combustion of fossil fuels, accounts for 64 percent of total emissions; nitrous oxide (N2O), from the fertilization of soil, makes up 12 percent. Methane lasts much less time in the atmosphere than CO2, but its capacity to retain heat is 21 times higher, while N2O is 310 times higher than CO2.

</span></p> <div id="attachment_9877" style="width: 1034px" class="wp-caption alignnone"><img aria-describedby="caption-attachment-9877" loading="lazy" class="size-large wp-image-9877" src="" alt="Two thousand recently identified craters on the Brazilian coast release greenhouse gases" width="1024" height="496" srcset=" 1024w, 300w, 768w, 610w, 2048w" sizes="(max-width: 1024px) 100vw, 1024px" /><p id="caption-attachment-9877" class="wp-caption-text">Sea bottom profile (Brazilian coast). IO-USP</p></div> <p><span style="font-weight: 400;">The methane produced at the bottom of the ocean from the decomposition of organic material, mainly in craters, which reaches the sea&#8217;s surface, is estimated to contribute somewhere between 1 and 5 percent of global emissions of the gas in the atmosphere. These estimates are according to research carried out by the Max Planck Institute for Marine Microbiology and the Center for Marine Environmental Studies (Marum) of the University of Bremen, both in Germany, published in 2013 in Nature Geoscience.</span></p> <p><span style="font-weight: 400;">&#8220;Recent studies suggest that methane seeps at depths over 100 meters rarely reach the ocean surface,&#8221; says geologist Anthony Rathburn, a professor at California State University, in the United States. &#8220;The dissolved methane is frequently oxidized, forming CO<sub>2</sub></span><span style="font-weight: 400;">, by the action of microorganisms, in the water column.&#8221; the CO<sub>2</sub></span><span style="font-weight: 400;"> is also consumed by marine organisms before reaching the atmosphere.</span></p> <p><span style="font-weight: 400;">These underwater craters may have a financial value, as they can indicate the occurrence of natural gas reserves. In 2011 and 2013, researchers from the Pontifical Catholic University of Rio Grande do Sul (PUC-RS) and Petrobras mapped around one thousand underwater craters off the southern Brazilian coast and used them to identify hydrocarbon reserves in the Pelotas water basin, an area of 250 square kilometers to the south of the state of Rio Grande do Sul.</span></p> <p><span style="font-weight: 400;">&#8220;Based on preliminary studies, we believe that this area is a large reserve of natural gas which could be explored in the future,&#8221; says chemist Luiz Frederico Rodrigues, researcher of the Institute of Petroleum and Natural Resources of PUC-RS. Crystalline solids were found in the sediments. These carbohydrates, formed by water and gases, hold large quantities of methane, as described in an article from September 2017 in the <a href=";script=sci_arttext">Brazilian Geophysics Journal</a>.</span></p> <div id="attachment_9878" style="width: 1034px" class="wp-caption alignnone"><img aria-describedby="caption-attachment-9878" loading="lazy" class="size-large wp-image-9878" src="" alt="Two thousand recently identified craters on the Brazilian coast release greenhouse gases" width="1024" height="574" srcset=" 1024w, 300w, 768w, 610w, 1886w" sizes="(max-width: 1024px) 100vw, 1024px" /><p id="caption-attachment-9878" class="wp-caption-text">Methane bubbles</p></div> <p><span style="font-weight: 400;">In 2016, a team from the Oceanographic Institute of the University of São Paulo (IO-USP) identified 984 craters in an area 130 kilometers long and 30 kilometers wide, spanning from the south coast of São Paulo to the north of Rio Grande do Sul. According to a study published in September 2018 in the Journal of Geochemical Exploration, some craters are still emitting methane. &#8220;It&#8217;s difficult to know which are releasing the gas and which have already stopped.</span></p> <p><span style="font-weight: 400;">The only way to find out it by using a methane sensor, which we do not have yet,&#8221; says geologist Michel Mahiques, a professor at IO-USP and coordinator of the expedition with the boat Alpha Crucis, which led to the discovery of the craters. The formations are distributed at depths varying between 300 and 700 meters. &#8220;In December 2017, we carried out more surveys in the area and found even bigger pockmarks in even deeper regions,&#8221; he adds.</span></p> <p><span style="font-weight: 400;">&#8220;The release of methane in the ocean would have been more intense in the past, mainly during the ice age when the sea levels reduced by around 120 meters and there was a reduction in the water pressure on the gas deposits on the ocean bed, facilitating the seepage,&#8221; Brazilian biologist Rodrigo Portilho-Ramos, currently a researcher at Marum, in Bremen, told Fapesp.</span></p> <p><span style="font-weight: 400;">In a study held at the Fluminense Federal University in Rio de Janeiro and USP, in collaboration with Mr. Rathburn and and other specialists from Germany and the United States, Dr. Portilho-Ramos identified a reduction in the levels of carbon in shells of fossilized organisms found in sediments of a 475-meter deep crater on the coast of Florianopolis, in comparison with samples collected in neighboring areas. The variation in carbon content is expected to be the result of an intense but not yet measured release of methane between 20,000 and 40,000 years ago, which corresponds with the last ice age, according to an article published in April 2018 in <a href="">Scientific Reports</a>.</span></p> <p><span style="font-weight: 400;">The craters on the São Paulo coast &#8211; and then others, close to the reefs of Abrolhos in the south of Bahia and north of Espirito Santo &#8211; began being identified in isolation in 2007 by researchers of the Rio Grande Federal University Foundation and were initially regarded as remains of caves.</span></p> <hr /> <div id="attachment_9879" style="width: 1034px" class="wp-caption alignnone"><img aria-describedby="caption-attachment-9879" loading="lazy" class="size-large wp-image-9879" src="" alt="Points along the Brazilian coast release greenhouse gases" width="1024" height="696" srcset=" 1024w, 300w, 768w, 610w, 1260w" sizes="(max-width: 1024px) 100vw, 1024px" /><p id="caption-attachment-9879" class="wp-caption-text">Where the Brazilian coast is deeper</p></div> <hr /> <p><span style="font-weight: 400;">In 2016, the team from USP carried out a comprehensive survey and saw that the craters were abundant and were able to release methane, but it is still unknown how many there are on the Brazilian coast, nor how many emit methane. &#8220;The seabed of the Brazilian coast is scarcely mapped by research institutes, though oil and gas companies and their service providers have lots of information, rarely released to the public as they may indicate the presence of petroleum and natural gas reserves,&#8221; says Mahiques.</span></p> <p><span style="font-weight: 400;">The release of gas on the southeastern Brazilian coast is principally caused by the rise of salt columns underneath the seabed, according to a study from the USP group published in February 2017 in scientific journal Heliyon. Owing to the internal pressure to which they are submitted, the salt columns, called diapirs, break the rock layers of the seabed, which sinks, forming the crater. This movement releases the methane trapped with organic material (the remains of animals and plants) accumulated at the bottom of the sea.</span></p> <h2>Biological diversity</h2> <p><span style="font-weight: 400;">The craters form unique environments with communities of microorganisms, mollusks and other invertebrates which are more diverse and abundant than in neighboring regions. In a 1,200-meter deep area of the Arctic Ocean, the diversity of species was 2.5 times higher in the methane-rich areas than in others, as observed by researchers from Norway and the United States in an article published in October 2007 in journal Limnology and Oceanography. In these areas, the authors of the paper found that methane is the source of life, not sunlight, which does not reach the deep sea.</span></p> <p><span style="font-weight: 400;">In her laboratory in IO-USP, biologist Vivian Pellizari cultivates bacteria and other microorganisms which produce methane from the degradation of organic material on the seabed, in an environment without oxygen. &#8220;The challenge now is to keep these cultures viable until the isolation of the micro-organisms,&#8221; says Vivian, who intends to understand the diversity of micro-organisms which produce and consume methane at the bottom of the ocean. </span></p> <p><span style="font-weight: 400;">This month, she will coordinate the São Paulo School of Advanced Science in Methane in Ilhabela, on the São Paulo coast, where the origin and transformations of methane in sea and land environments will be debated.</span></p> <p><span style="font-weight: 400;">The first underwater craters of this type were discovered off the coast of Nova Scotia, Canada at the end of the 1960s by a team from the Bedford Oceanography Institute, also in Canada. Detected by a then-novel sonar system, the craters in Nova Scotia were 150 meters wide and 10 meters deep.</span></p> <p><span style="font-weight: 400;">Then, they were identified all around the world. In 2013, researchers from New Zealand, Germany, and the United States found the largest underwater craters, 500 kilometers west of Christchurch, New Zealand. The biggest craters of this region were 11 kilometers wide and 100 meters deep, around 1 kilometer from the surface. They were probably created by the eruption of gases through sediments, but apparently, they no longer release methane.

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