{"id":145768,"date":"2014-03-14T19:07:07","date_gmt":"2014-03-14T22:07:07","guid":{"rendered":"http:\/\/revistapesquisa.fapesp.br\/?p=145768"},"modified":"2015-09-02T12:48:30","modified_gmt":"2015-09-02T15:48:30","slug":"mud-south","status":"publish","type":"post","link":"https:\/\/revistapesquisa.fapesp.br\/en\/mud-south\/","title":{"rendered":"Mud from the South"},"content":{"rendered":"
\"Mouth

DE AGOSTINI \/ N. CIRANI<\/span>Mouth of the Rio de la Plata: source of sediments for the southern and southeastern coast of BrazilDE AGOSTINI \/ N. CIRANI<\/span><\/p><\/div>\n

A gradual change in climate\u2014from dry to moist\u2014and in rainfall patterns, with more intense and frequent rains falling in the inland regions of South America during the past 6,000 years, is believed to have altered the influence and the discharge of sediments from the torrential Rio de la Plata into the Atlantic Ocean. Recent studies by oceanographers and geologists from Brazil, Germany, and Uruguay indicate that the fine grains of sand, mud, and organic material carried by the river and later caught up in ocean currents began to arrive in this era\u2014and are still arriving\u2014as far as the ocean floor near the island of S\u00e3o Sebasti\u00e3o on the coast of the state of S\u00e3o Paulo, 2,000 km from Montevideo, capital of Uruguay and one of the last cities bathed by the river before its waters mix with those of the sea.<\/p>\n

For more than ten years, the team headed by Michel Mahiques, professor at the Oceanographic Institute of the University of S\u00e3o Paulo (USP), has been analyzing samples of sediments taken from the ocean floor along the Brazilian coast and from the estuary of the Rio de la Plata in order to confirm that theory. Now the results obtained from the physical and chemical analyses of the sediments indicate the existence of two distinct regions, known as geochemical provinces: one to the south and one to the north of S\u00e3o Sebasti\u00e3o.<\/p>\n

The physical and chemical characteristics of the sediments south of S\u00e3o Sebasti\u00e3o closely resemble those recorded in the Rio de la Plata and differ from the samples obtained between the island of S\u00e3o Sebasti\u00e3o and Cabo Frio, on the coast of Rio de Janeiro State. Mahiques and his colleagues have concluded that it is likely that the Doce and Para\u00edba do Sul Rivers are the two principal sources contributing to the deposition of sediments north of S\u00e3o Sebasti\u00e3o, while the Rio de la Plata supplies sediments to the southern coast and part of Brazil\u2019s Southeast, up to S\u00e3o Sebasti\u00e3o.<\/p>\n

Even though the Rio de la Plata is situated more than a thousand kilometers from S\u00e3o Paulo, it may be important for marine management to learn about its possible influence on the S\u00e3o Paulo coast. \u201cAny environmental impact that occurs in the Rio de la Plata basin,\u201d Mahiques observes, \u201cwill certainly have an impact on S\u00e3o Paulo\u2019s coastline.\u201d He is referring to the potential for currents to carry radioactive elements of manmade origin, which have already been measured. The same reasoning is valid, he says, in the event of some event that might interfere with marine life resources in southern and southeastern Brazil.<\/p>\n

To differentiate the types of sediment detected, oceanographers and geologists employed several laboratory analyses. For example, they measured the amounts of clay, organic materials, cesium, neodymium, and lead found in the marine sediments, as well as the size of the sediments themselves. In this case, samples were collected at three sites: off the coast of Santos and adjacent cities; near the city of Cananeia on the southern coast of S\u00e3o Paulo; and along Itaja\u00ed, in the state of Santa Catarina. The sand or mud from the upper portion of the collected samples represents the most recent sediments, because they were the last to be deposited, while the material from the seabed is very old, because it arrived earlier at the sampled sites.<\/p>\n

Witnesses of the River<\/strong>
\nEach particle of sediment bears a sort of geochemical signature, as the researchers like to say. In this case, sets of matching signatures form a single group. When those groupings are laid out on a map, the two major provinces appear, divided in geographical terms along the northern coast of S\u00e3o Paulo State. The geochemical map that resulted from the assessments demonstrated the differences and, therefore, the differing origins of the sediments.<\/p>\n

\u201cThe sources of the grains, i.e., the rocks that were worn away by rain or wind in order to create the sediments that were later carried down the river, are different,\u201d Mahiques says. To confirm the results obtained from samples of the sediments taken at the surface, the research groups consulted what are known as geological witnesses that can generate data from thousands of years ago, in this case columns of sand and mud removed from the sea floor using a metal pipe.<\/p>\n

\"\"Ana Paula Campos<\/span><\/a>\u201cYou can see a remarkable change from the deposition pattern of sediments that arrived about 2,800 years ago,\u201d Mahiques says. The analysis of the witnesses indicated that while the Rio de la Plata was discharging a heavy load of sediments along the Santa Catarina coast up until 2,800 years ago, it was only after that period that sand generated by the Paran\u00e1 River basin, in the form of sediments from basalts that are typical of that region, began to appear up near the city of Santos. \u201cBecause the Paran\u00e1 basin had begun to receive more rain, the system of marine currents had more water, which it could use to carry the sediment further north,\u201d he says. \u201cAnd so we have been able to determine the point at which the Rio de la Plata started to influence the coast of S\u00e3o Paulo.\u201d<\/p>\n

Having answered one question, others arise. If a lot of mud is exported by the Rio de la Plata to S\u00e3o Paulo in areas close to the coast, could that material not also reach the deep ocean, down to a depth of 3,000 meters? The researchers hope to find the answer in the coming years, now that they have the valuable assistance of the oceanographic research vessel Alpha-Crucis. They began to use it this year to collect sediments from areas that are deeper and lie farther off the S\u00e3o Paulo coast. (See Pesquisa FAPESP Issue No.206<\/em><\/a>).<\/p>\n

Preliminary surveys conducted by using equipment from the Alpha-Crucis identified a structure that resembles a huge slope over which mud and the sand from the flatter region, the continental shelf, could reach deeper areas. The slope would help explain why sediments have accumulated beyond the flatter regions of the S\u00e3o Paulo coastline, which are known to be poor in terms of sediments. Mud and sand have apparently slid hundreds of meters through large underground canyons, scientists believe.<\/p>\n

Projects<\/strong>
\n1.<\/strong> Halocene changes in the paleo-productivity of the southeastern continental shelf of Brazil (03\/10740-0<\/a>) Grant<\/strong> mechanism<\/strong> Regular line of Research Project Award. Coord.<\/strong> Michel Michaelovitch de Mahiques \u2013 IO\/USP: Investment<\/strong> R$321,619.03 (FAPESP).
\n2.<\/strong> Increase of the research capabilities in oceanography and related sciences in S\u00e3o Paulo State, Brazil; (10\/06147-5<\/a>) Grant<\/strong> mechanism<\/strong> Research Program on Global Climate Change Coord.<\/strong> Michel Michaelovitch de Mahiques \u2013 IO\/USP: Investment<\/strong> R$15,451,697.60 (FAPESP).<\/p>\n

Scientific Article<\/em>
\nBURONE L. et al<\/em>. A multiproxy study between the Rio de la Plata and the adjacent Southwestern Atlantic inner shelf to assess the sediment footprint of river vs. marine influence<\/a>. Continental Shelf Research<\/strong> v. 55, pp. 41-54. 2013.<\/p>\n","protected":false},"excerpt":{"rendered":"Sediments from Rio de la Plata travel as far north as S\u00e3o Sebasti\u00e3o","protected":false},"author":475,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_exactmetrics_skip_tracking":false,"_exactmetrics_sitenote_active":false,"_exactmetrics_sitenote_note":"","_exactmetrics_sitenote_category":0,"footnotes":""},"categories":[159],"tags":[252],"coauthors":[785],"class_list":["post-145768","post","type-post","status-publish","format-standard","hentry","category-science","tag-oceanography"],"acf":[],"_links":{"self":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts\/145768","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/users\/475"}],"replies":[{"embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/comments?post=145768"}],"version-history":[{"count":0,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts\/145768\/revisions"}],"wp:attachment":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/media?parent=145768"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/categories?post=145768"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/tags?post=145768"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/coauthors?post=145768"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}