The Cariaco Basin lies off the north central coast of

Venezuela Venezuela (; ), officially the Bolivarian Republic of Venezuela ( es, link=no, República Bolivariana de Venezuela), is a country on the northern coast of South America, consisting of a continental landmass and many islands and islets in th ...

and forms the Gulf of Cariaco. It is bounded on the east by

Margarita Island Margarita Island (, ) is the largest island in the States of Venezuela, Venezuelan state of Nueva Esparta, situated off the northeastern coast of the country, in the Caribbean Sea. The capital city of Nueva Esparta, La Asunción, is located on t ...

, Cubagua Island, and the

Araya Peninsula The Araya Peninsula is a peninsula on the Caribbean Sea, located in Sucre State, northern Venezuela. The peninsula is part of the eastern Serranía del Litoral mountain range, in the Venezuelan Coastal Ranges System of the northern Andes. It ext ...

; on the north by Tortuga Island and the Tortuga Banks; on the west by Cape Codera and the rocks known as Farallón Centinela; and on the south by the coast of Venezuela.

Description

The Cariaco Basin is an east-west trending

pull-apart basin In geology, a basin is a region where subsidence generates accommodation space for the deposition of sediments. A pull-apart basin is a structural basin where two overlapping (en echelon) strike-slip faults or a fault bend creates an area of crus ...

located on the continental shelf off the eastern coast of

. It is a deep depression composed of two sub-basins, the eastern basin and the western basin, each of about depth, separated by a saddle of approximately water-depth. To the south, the basin confines with the wide (~50 km) Unare Platform. It is connected to the open Caribbean Sea through two shallow (around ) channels, to the north the (Tortuga Channel) and to the west the (Centinela Channel). Water circulation inside the basin is restricted, which, combined with the high annual primary productivity of the region (~500 gCm⁻²yr⁻¹), causes the basin to be permanently

anoxic The term anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts: * Anoxic waters, sea water, fresh water or groundwater that are depleted of diss ...

, below ~250 m. This naturally occurring anoxic basin allows for sediments to be deposited without

bioturbation Bioturbation is defined as the reworking of soils and sediments by animals or plants. It includes burrowing, ingestion, and defecation of sediment grains. Bioturbating activities have a profound effect on the environment and are thought to be a ...

, forming

varve A varve is an annual layer of sediment or sedimentary rock. The word 'varve' derives from the Swedish word ''varv'' whose meanings and connotations include 'revolution', 'in layers', and 'circle'. The term first appeared as ''Hvarfig lera'' (va ...

s of alternating light and dark color, which correspond to the dry or rainy season. Its unique geography and undisturbed sediment record provides an excellent history of tropical climate change and is particularly sensitive to shifts in the

Intertropical Convergence Zone The Intertropical Convergence Zone (ITCZ ), known by sailors as the doldrums or the calms because of its monotonous windless weather, is the area where the northeast and the southeast trade winds converge. It encircles Earth near the thermal ...

(ITCZ) and has been the subject of extensive paleoclimatological research, amongst other sedimentological studies, geochemical studies, with alkenones, Mg/Ca, and micropaleontological, with

foraminifera Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly ...

, pollen and spores,

dinocyst Dinocysts or dinoflagellate cysts are typically 15 to 100 µm in diameter and produced by around 15–20% of living dinoflagellates as a dormant, zygotic stage of their lifecycle, which can accumulate in the sediments as microfossils. Organic- ...

s and

coccolith Coccoliths are individual plates or scales of calcium carbonate formed by coccolithophores (single-celled phytoplankton such as '' Emiliania huxleyi'') and cover the cell surface arranged in the form of a spherical shell, called a ''coccosphere' ...

Anoxic basin

Because of its anoxia, the Cariaco Basin has also a unique chemistry. Bacteria inhabit both the oxic and anoxic portions of the water column, with a maximum around the interface where oxygen disappears. This 'interface' oscillates between 200 and 300 meters. As such unique location, the Cariaco Basin has been the site of a variety of studies since the mid-1950s. Since 1995, an international (

and

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

) program has expanded the research in the basin. The CARIACO (Carbon Retention in a Colored Ocean

) program consists of a

time series In mathematics, a time series is a series of data points indexed (or listed or graphed) in time order. Most commonly, a time series is a sequence taken at successive equally spaced points in time. Thus it is a sequence of discrete-time data. Ex ...

station in the eastern deep of the basin which is visited on a monthly basis to collect hydrographic, nutrient and primary productivity measurements. A suite of other measurements, including a sediment trap mooring, microbiological studies and current measurements are also conducted at this site. The work that has resulted from the CARIACO ocean time series program has demonstrated that this anoxic basin is quite dynamic and has helped understand the paleoclimatic record stored in the basin's sediments.

Ecology

The Cariaco Basin is an example of upwelling zone ecosystems. The seasonal upwelling cycle and sea surface temperature changes are linked to the intensity of the

trade winds The trade winds or easterlies are the permanent east-to-west prevailing winds that flow in the Earth's equatorial region. The trade winds blow mainly from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisp ...

, and cause events of high primary production that support a very high biomass of plankton, fish, and marine birds and mammals. The seasonal productivity drives the abundance of

sardines "Sardine" and "pilchard" are common names for various species of small, oily forage fish in the herring family Clupeidae. The term "sardine" was first used in English during the early 15th century, a folk etymology says it comes from the Ital ...

and attract

dolphin A dolphin is an aquatic mammal within the infraorder Cetacea. Dolphin species belong to the families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins), Iniidae (the New World river dolphins), Pontoporiidae (the b ...

s. The waters are also home to several species of

whale Whales are a widely distributed and diverse group of fully aquatic placental marine mammals. As an informal and colloquial grouping, they correspond to large members of the infraorder Cetacea, i.e. all cetaceans apart from dolphins and ...

s (such as

rorqual Rorquals () are the largest group of baleen whales, which comprise the family Balaenopteridae, containing ten extant species in three genera. They include the largest animal that has ever lived, the blue whale, which can reach , and the fin wha ...

s and humpback), and

orca The orca or killer whale (''Orcinus orca'') is a toothed whale belonging to the oceanic dolphin family, of which it is the largest member. It is the only extant species in the genus '' Orcinus'' and is recognizable by its black-and-white ...

s.Bolaños-Jiménez J.. Fertl D.. Iñiguez M.. 2009
Killer whale (Orcinus orca) occurrence in Venezuelan waters, 1982-2008
. Latin American Journal of Aquatic Mammals (LAJAM). 7(1-2). . pp.75-79. The

ResearchGate ResearchGate is a European commercial social networking site for scientists and researchers to share papers, ask and answer questions, and find collaborators. According to a 2014 study by ''Nature'' and a 2016 article in ''Times Higher Education'' ...

. Retrieved on April 16, 2017

References

{{Sedimentary basins of Venezuela Sedimentary basins of Venezuela Pull-apart basins Anoxic waters

Description

Anoxic basin

Ecology

See also

References