Water Masses Chemical Properties in the Western Tropical Atlantic Ocean

2021 ◽  
Author(s):  
Renan Luis Evangelista Vieira ◽  
Leticia Cotrim da Cunha ◽  
Ricardo de Almeida Keim ◽  
Carlos Augusto Musetti de Assis ◽  
Jessica da Silva Nogueira ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
Nutrient Concentration ◽  
Chemical Properties ◽  
Intertropical Convergence Zone ◽  
Water Masses ◽  
Nutrient Concentrations ◽  
Convergence Zone ◽  
Tropical Atlantic ◽  
Tropical Atlantic Ocean

<p>Here we characterize the chemical properties of the water masses in the Western Tropical Atlantic Ocean according to their inorganic nutrient concentration: dissolved inorganic nitrogen (DIN), phosphate and silicate. We collected full-depth water samples from 16 oceanographic stations along the 38°W transect, from 1°S to 15°N during the PIRATA-BR XVIII cruise, in October-November 2018. In this region, the surface and subsurface circulation in the Atlantic Ocean displays complex seasonal patterns, under influence of the Intertropical Convergence Zone. The samples were collected from Niskin bottles closed in ten different depths, stored frozen, and later analysed through spectrophotometry. Besides that, the CTD-O<sub>2</sub> data provided continuous salinity, temperature, and dissolved oxygen measurements, used to identify the water masses according to their thermohaline indexes. Six water masses were identified in the region based on their neutral density limits: Tropical Surface Water (TSW, γ<sup>n</sup> < 24.448 kg m<sup>-3</sup>); South and North Atlantic Central Water (SACW and NACW, γ<sup>n</sup> 24.448 – 26.815 kg m<sup>-3</sup>); Antarctic Intermediate Water (AAIW, γ<sup>n</sup> 26.815 – 27.7153 kg m<sup>-3</sup>); North Atlantic Deep Water (NADW, γ<sup>n</sup> 27.7153 – 28.135 kg m<sup>-3</sup>); and Antarctic Bottom Water (AABW, γ<sup>n</sup> > 28.135 kg m<sup>-3</sup>).  The oligotrophic TSW is almost completely depleted in nutrients; Central Waters NACW and SACW have the following concentration ranges: DIN, 5 – 15 µmol/kg, phosphate, 0.5 – 1.0 µmol/kg, silicate, 5 – 20 µmol/kg); AAIW nutrient concentrations are DIN: 30 – 40 µmol/kg, phosphate: 1.5 – 2.5 µmol/kg, and silicate: 25 – 40 µmol/kg; NADW nutrient concentrations are DIN: 15 – 25 µmol/kg, phosphate: 1.0 – 1.5 µmol/kg) , and silicate: 20 – 45 µmol/kg; and AABW nutrient concentration ranges are: 40 – 80 µmol/kg silicate, 30 – 35 µmol/kg DIN, and 1.5 – 2.5 µmol/kg phosphate. North of 5°N up to 15°N, there is a region of lower oxygen and higher phosphate concentrations, comprising the central water and the upper AAIW layers, extending from 200 m to 800 m. This corresponds to the area under influence of the eastward flowing North Equatorial Counter Current (NECC) and North Equatorial Under Current (NEUC), which are both, in turn, influenced by the position of the Intertropical Convergence Zone (ITCZ). Further study directions include a detailed study of the multiple source waters to this central layer, associated to the regional circulation, and possible linking to the eastern tropical Atlantic oxygen minimum zone.</p>

EUREC4A-OA/ATOMIC experiment  : Themohaline and dynamical descriptions of mesoscale and submesoscale structures of the Northwest Tropical Atlantic Ocean

2021 ◽  
Author(s):  
Pierre L'Hégaret ◽  
Sabrina Speich ◽  
Yanxu Chen ◽  
Gaston Manta ◽  
Léa Olivier ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Mesoscale Eddies ◽  
Water Masses ◽  
Ocean Dynamics ◽  
Tropical Atlantic ◽  
Fine Scale ◽  
Surrounding Water ◽  
Tropical Atlantic Ocean ◽  
North Brazil ◽  
Oxygen Concentrations

<p>In January-February 2020, the EUREC4A-OA/ATOMIC experiment took place in the Northwest Tropical Atlantic Ocean with the overall objective of understanding the role of fine scale processes in the internal ocean dynamics and air-sea interaction. Four oceanographic vessels, the French Atalante, German Maria S Merian and Meteor, and the American Ron Brown, closely coordinated with air-borne observations and autonomous ocean platforms (gliders, saildrones, and drifters) to simultaneously measure the ocean and atmosphere east of the island of Barbados and the coast of Guyana in the western Tropical Atlantic. A whole battery of instruments measuring the thermohaline and dynamic characteristics of the region was launched. The fixed CTD stations, reaching great depths while measuring salinity, temperature, and oxygen concentrations, serve as a reference to calibrate and validate other devices, in particular, shallower uCTD, TSG, and MVP, acquired during ship transits, and autonomous gliders and saidrones. Combined, these datasets increase the horizontal resolution and thus the description of structures ranging from mesoscale to fine scale.</p><p>The Northwest Tropical Atlantic Ocean is a dynamical region filled with mesoscale eddies of different origins and transporting various water masses across the region. These eddies have rich and diverse characteristics ranging from shallow cyclonic and anticyclonic eddies to the deep reaching North Brazil Current (NBC) Rings. On the surface, down to 200 m depth, the signatures of shallow cyclones and anticyclones (NBC rings) were measured. The shallow mesoscale eddies, with core centered around a density of 25.5 kg m-3, advect highly saline and warm waters, with low oxygen concentrations compared to the surrounding water masses. Below, evolving at density around 26.7 kg m-3, thick anticyclones were observed, characterized by low temperature and salinity but with high values of oxygen, indicative of a South Atlantic origin. One was observed drifting slowly northward and another one at the NBC retroflection. Similarly, mesoscale cyclonic eddies were also observed both at the surface and at depth. Surface and subsurface eddies are not aligned vertically and they seem to evolve independently. </p><p>The large number and diversity (ship-mounted or autonomous) of observing platforms implemented in the project made made it possible to innovatively sample the upper-ocean frontal scales and stratification. It has been found that the interaction between the particularly fresh waters from the Amazon River, flowing northward along the shelf-break, and NBC rings create a rich variety of submesoscale fronts and a strong barrier layer, leading to interleaving. With the high vertical and horizontal resolutions, we quantify the layering and mixing processes at play.</p>

scholarly journals The Predictive Skill and the Most Predictable Pattern in the Tropical Atlantic: The Effect of ENSO

2007 ◽  
Vol 135 (5) ◽  
pp. 1786-1806 ◽  
Author(s):  
Zeng-Zhen Hu ◽  
Bohua Huang
Keyword(s):  
South America ◽  
Atlantic Ocean ◽  
North Atlantic ◽  
Lead Time ◽  
Tropical Atlantic ◽  
Tropical Atlantic Ocean ◽  
Predictive Skill ◽  
Tropical North Atlantic ◽  
Predictable Pattern ◽  
Most Predictable Patterns

Abstract This work investigates the predictive skill and most predictable pattern in the NCEP Climate Forecast System (CFS) in the tropical Atlantic Ocean. The skill is measured by the sea surface temperature (SST) anomaly correlation between the predictions and the corresponding analyses, and the most predictable patterns are isolated by an empirical orthogonal function analysis with a maximized signal-to-noise ratio. On average, for predictions with initial conditions (ICs) of all months, the predictability of SST is higher in the west than in the east. The highest skill is near the tropical Brazilian coast and in the Caribbean Sea, and the lowest skill occurs in the eastern coast. Seasonally, the skill is higher for predictions with ICs in summer or autumn and lower for those with ICs in spring. The CFS poorly predicts the meridional gradient in the tropical Atlantic Ocean. The superiority of the CFS predictions to the persistence forecasts depends on IC month, region, and lead time. The CFS prediction is generally better than the corresponding persistence forecast when the lead time is longer than 3 months. The most predictable pattern of SST in March has the same sign in almost the whole tropical Atlantic. The corresponding pattern in March is dominated by the same sign for geopotential height at 200 hPa in most of the domain and by significant opposite variation for precipitation between the northwestern tropical North Atlantic and the regions from tropical South America to the southwestern tropical North Atlantic. These predictable signals mainly result from the influence of the El Niño–Southern Oscillation (ENSO). The significant values in the most predictable pattern of precipitation in the regions from tropical South America to the southwestern tropical North Atlantic in March are associated with excessive divergence (convergence) at low (high) levels over these regions in the CFS. For the CFS, the predictive skill in the tropical Atlantic Ocean is largely determined by its ability to predict ENSO. This is due to the strong connection between ENSO and the most predictable patterns in the tropical Atlantic Ocean in the model. The higher predictive skill of tropical North Atlantic SST is consistent with the ability of the CFS to predict ENSO on interseasonal time scales, particularly for the ICs in warm months from March to October. In the southeastern ocean, the systematic warm bias is a crucial factor leading to the low skill in this region.

scholarly journals Post-Bomb Radiocarbon Records of Surface Corals from the Tropical Atlantic Ocean

Radiocarbon ◽  
1996 ◽  
Vol 38 (3) ◽  
pp. 563-572 ◽  
Author(s):  
Ellen R. M. Druffel
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
Water Mass ◽  
Cape Verde ◽  
North Equatorial Current ◽  
Tropical Atlantic ◽  
Tropical Ocean ◽  
Tropical Atlantic Ocean ◽  
Renewal Rate ◽  
The North

Δ14C records are reported for post-bomb corals from three sites in the tropical Atlantic Ocean. In corals from 18°S in the Brazil Current, Δ14C values increased from ca. −58% in the early 1950s to +138% by 1974, then decreased to 110‰ by 1982. Shorter records from 8ºS off Brazil and from the Cape Verde Islands (17°N) showed initially higher Δ14C values before 1965 than those at 18ºS, but showed lower rates of increase of Δ14C during the early 1960s. There is general agreement between the coral results and Δ14C of dissolved inorganic carbon (DIC) measured in seawater previously for locations in the tropical Atlantic Ocean. Δ14C values at our tropical ocean sites increased at a slower rate than those observed previously in the temperate North Atlantic (Florida and Bermuda), owing to the latter's proximity to the bomb 14C input source in the northern, hemisphere. Model results show that from 1960–1980 the Cape Verde coral and selected DIG Δ14C values from the North Equatorial Current agree with that calculated for the North Atlantic based on an isopycnal mixing model with a constant water mass renewal rate between surface and subsurface waters. This is in contrast to Δ14C values in Bermuda corals that showed higher post-bomb values than those predicted using a constant water mass renewal rate, hence indicating that ventilation in the western north Atlantic Ocean had decreased by a factor of 3 during the 1960s and 1970s (Druffel 1989).

scholarly journals Correction to: Weakened SST variability in the tropical Atlantic Ocean since 2000

2021 ◽  
Author(s):  
Arthur Prigent ◽  
Joke F. Lübbecke ◽  
Tobias Bayr ◽  
Mojib Latif ◽  
Christian Wengel
Keyword(s):  
Atlantic Ocean ◽  
Tropical Atlantic ◽  
Tropical Atlantic Ocean ◽  
Sst Variability
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