The continental shelf of Brazil is the seabed and subsoil underlying its jurisdictional waters, where the country has sovereign rights over natural resources as a party to the United Nations Convention on the Law of the Sea (UNCLOS). An area of 3.5 million square kilometers as far as from baselines along the coast is internationally recognized as such. From 2004 to 2018 Brazil submitted a series of extended continental shelf proposals beyond the 200 nautical mile line to the Commission on the Limits of the Continental Shelf (CLCS). The proposed extended shelf measures 2,094,656.59 km². A final understanding has yet to be reached with the CLCS, and therefore the outer limits of the extended shelf are still not final and binding. The Brazilian Navy includes the continental shelf in its concept of a "Blue Amazon".
The concept of a continental shelf was introduced to Brazilian law in 1950, although lacking a clear limit. In the beginning of the following decade, it was the point of contention in the "Lobster War" with France. The 1970 extension of the territorial sea to 200 nautical miles from the coast subsumed the shelf's distinct existence, as the territorial sea includes the seabed and subsoil. When the UNCLOS came into force in 1994, the territorial sea was reduced and the shelf's outer limit now matched that of the exclusive economic zone (EEZ). Offshore oil drilling began in the continental shelf over this period and since then it provides most of Brazil's fossil fuel production.
In order to substantiate its proposals of a continental shelf beyond the 200-nautical mile line, since the late 1980s the Brazilian Navy, Petrobras and the country's scientific community joined in the Brazilian Continental Shelf Survey Plan (LEPLAC) to retrieve hundreds of thousands of kilometers of geological profiles in the area. In 2007 the CLCS only accepted part of the Brazilian proposal and a new cycle of surveys began in response. Economic interest in the region grew after the discovery of fossil fuel deposits in the pre-salt layer of underwater sedimentary basins, thanks to which Brazil became the world's 8th largest crude oil and lease condensate producer in 2023. Revised proposals are larger and in 2018 covered the mineral-rich Rio Grande Rise.
Geologically, Brazil's legal continental shelf mostly corresponds to a divergent continental margin formed by the split between South America and Africa, with a well-defined shelf, slope and rise. It is at its widest off the Northern coast, where the Amazon River forms one of the world's largest submarine fans. The margin narrows through the Northeast and widens again south of the Abrolhos Bank. The São Paulo Plateau, which is the largest marginal plateau in the Brazilian coast, contains its two richest oil basins (Campos and Santos). Beyond fossil fuels, the continental margin also has mineral reserves of coal, gas hydrates, aggregates, heavy mineral sands, phosphorite, evaporites, sulphur, cobalt-rich ferromanganese crusts, polymetallic sulfides and polymetallic nodules, which are almost entirely untouched by undersea mining.
Geomorphology
From the Brazilian coast until the abyssal plains of the South Atlantic lies a portion of the South American continental margin, which is the transition between continental and oceanic crusts. When comparing terminology between maritime law and geography, this continental margin, which comprises a continental shelf, continental slope and continental rise, is the closest geological counterpart to a "continental shelf" as defined in the UNCLOS. The legal shelf is the entire natural projection of a coastal state into the seafloor and not just its geomorphological shelf.
Most of the Brazilian continental margin is a classical divergent margin formed by the breakup of the supercontinent of Gondwana and its South American and African plates. This kind of margin possesses a large continental shelf and a steep but stable incline at its slope, where accumulated sediments form the continental rise, which gently slides down with decreasing thickness until the abyssal plains. Several tectonic and sedimentary processes mean these three strips are not always neatly visible, and not all of the Brazilian continental margin is the divergent South Atlantic: the far north is in the divergent Central Atlantic, and part of the equatorial region is a transform margin, in which two plates slide against each other.
20.5% of the exclusive economic zone (EEZ)'s seafloor is at depths of up to 200 m, which may be considered part of the continental shelf. Deep-sea features cover the rest: the continental slope (13.3%), terraces (1.7%), submarine canyons (1.4%), the continental rise (40%), abyssal plains (29.6%), submarine fans (4.9%), seamounts (2.2%), guyots (1.4%), ridges (1.2%) and spreading ridges (1.4%). These percentages add up to more than 100%, as some features occupy the same spaces.
Submarine features
Following the Brazilian coast from the north, the first major feature is the Amazon Fan. Outflow from the river forms the thickest sediment beds and the widest geomorphological shelf (up to 300 km) and margin (750 km) in the entire coast. Bathymetry follows a gradient all the way to depths of 4.800 m in the Demerara Abyssal Plain. To the east lie the Maranhão Seamounts and the North Brazilian and Fernando de Noronha ridges, formed parallel to the coast by the Equatorial Atlantic's transform margin. The Fernando de Noronha Chain breaks the surface in two regions, Rocas Atoll and the Fernando de Noronha Archipelago. The North Brazilian chain is a barrier to sediment deposition and thus shortens the width of the continental margin and its resulting legal claims. The Saint Peter and Saint Paul Archipelago is geologically distinct: an emerged portion of the Mid-Atlantic Ridge, composed of mantle rocks exposed to the surface when tectonic forces opened faults in the oceanic crust.
The continental shelf measures 170 km in width at the Parnaíba River's delta, narrows to 50 km in the east, at the coast of Ceará, and even more until Cape São Roque, no Rio Grande do Norte. The Northeast has the narrowest stretches of continental margin (100 km) and geomorphological shelf (30–50 km), down to a mere 8 km of shelf off the coast in Recife. From the 10th to the 16th parallel south, this is owed to the influence of the São Francisco Craton. The continental rise descends until the Brazil abyssal plain, with several features perpendicular to the coast, from north to south: the Rio Grande do Norte, Paraíba, Pernambuco and Bahia seamounts and the Ferraz Ridge. The continental margin widens again from Abrolhos Bank, which the Besnard Bank connects to the Vitória-Trindade Ridge, a sequence of about 30 seamounts extending 950 km to east and peaking at their eastern end in the islands of Trindade and Martim Vaz.
Further south, the continental margin exceeds 500 km in width. The Campos, Santos and Paraná sedimentary basins comprise the São Paulo Plateau, the largest marginal plateau in the Brazilian coast, which is placed between the continental slope and rise. Its outer limits meet the Jean Charcot Seamounts and the São Paulo Channel. The Vema Channel and the Rio Grande Rise (RGR) define the Brazil Abyssal Plain's southern limit, separating it from the Argentine Abyssal Plain. The RGR spans the 28th to the 34th parallel south, in a total area of 500 thousand km2, emerging from a seabed 5,000 m below sea level to 650 m at its highest. Its origin and evolution are controversial. It is aligned to the Paraná and Etendeka Traps and the Walvis, Gough and Tristan da Cunha ridges. In the past, some portions were above sea level.
The southern continental margin, from the São Paulo Plateau to the Uruguayan maritime boundary, contains the Santa Catarina Plateau, the Rio Grande Terrace, the Pelotas Basin and the Rio Grande Fan.
Legal definition
The continental shelf was introduced in Brazilian law by decree in 1950: "the submarine shelf, in the part which corresponds to Brazil's continental and insular territory is integrated to that same territory, under exclusive jurisdiction and domain of the federal government". This legislation did not define the shelf's limits; its international precedent, Harry S. Truman's 1945 unilateral declaration of a continental shelf for the United States, went as far as a maximum depth of a . The Brazilian decree made no change to the continental shelf, which extended at the time to from the coast.Decree n. 28,840, 8 November 1950. .
The 1958 Convention on the Continental Shelf, signed as a result of the 1st United Nations Convention on the Law of the Sea, consolidated the concept within international law. This agreement outlined a continental shelf as far as a depth of 200 m or wherever there were exploitable resources. "The coastal State exercises over the continental shelf sovereign rights for the purpose of exploring it and exploiting its natural resources", including its sedentary organisms. France was interested in fishing lobsters in Brazil's continental shelf and questioned the animal's classification as a sedentary species, though neither government had signed the convention. In 1963 both sides moved warships to the Brazilian Northeastern coast in what would be called the "Lobster War". Tensions calmed in the following year, domestic interest on the sea increased and the debate on lobster classification would contribute to later developments in international law.
In June 1968 a new decree established a similar definition to the convention's (200 meters in depth or wherever natural resources were exploitable, in either case outside the territorial sea). The hybrid criterion of depth and exploitability was criticized as too ambiguous since the past decade. This definition did not last; in August, another decree revoked the former and determined that the shelf's limits would follow "treaties or international conventions ratified by Brazil". As the country was not a party to the Convention on the Continental Shelf, the limit was left undefined.Decree n. 62,837, 6 June 1968. .Decree n. 63,164, 26 August 1968. . The 1970 extension of the territorial sea to from the shore absorbed the continental shelf as a distinct area, although it was still mentioned as federal property in the Constitution. The territorial sea includes the seabed and subsoil.
The 3rd UN Convention on the Law of the Sea, concluded in 1982, produced the United Nations Convention on the Law of the Sea (UNCLOS), which Brazil ratified. Adjustments to national law to comply with the UNCLOS revoked the 1970 decree and established a 12-mile territorial sea, 200-mile EEZ and a continental shelf "throughout the natural prolongation of its land territory to the outer edge of the continental margin, or to a distance of 200 nautical miles from the baselines from which the breadth of the territorial sea is measured". In effect, the shelf's outer margin remained at 200 nautical miles from coast, the same outer boundary used by the EEZ, but with a possible extended continental shelf to be recognized in the future beyond this line.
Following article 77 of the UNCLOS, "the coastal State exercises over the continental shelf sovereign rights for the purpose of exploring it and exploiting its natural resources". "If the coastal State does not explore the continental shelf or exploit its natural resources, no one may undertake these activities without the express consent of the coastal State", and these rights "do not depend on occupation, effective or notional, or on any express proclamation". International scientific research and submarine cable laying in this area are conditioned on the Brazilian government's consent., cap. I, p. 20-21.
Extended shelf