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The pathways of recently ventilated North Atlantic Deep Water (NADW) are part of the lower limb of the Atlantic Meridional Overturning Circulation (AMOC). In the South Atlantic these pathways have been the subject of discussion for years, mostly due to the lack of observations. Knowledge of the pathways of the AMOC in the South Atlantic is a first order prerequisite for understanding the fluxes of climatically important properties. In this paper, historical and new observations, including hydrographic and oxygen sections, Argo data, and chlorofluorocarbons (CFCs), are examined together with two different analyzes of the Ocean general circulation model For the Earth Simulator (OFES) to trace the pathway of the recently ventilated NADW through the South Atlantic. CLIVAR-era CFCs, oxygen and salinity clearly show that the strongest NADW pathway in the South Atlantic is along the western boundary (similar to the North Atlantic). In addition to the western boundary pathway, tracers show an eastward spreading of NADW between ~17 and 25°S. Analyzed together with the results of earlier studies, the observations and model output presented here indicate that after crossing the equator, the Deep Western Boundary Current (DWBC) transports water with the characteristics of NADW and a total volume transport of approximately 14 Sv (1 Sv=10 6 m 3 s − 1 ). It crosses 5°S as a narrow western boundary current and becomes dominated by eddies further south. When this very energetic eddying flow reaches the Vitória-Trindade Ridge (~20°S), the flow follows two different pathways. The main portion of the NADW flow continues along the continental shelf of South America in the form of a strong reformed DWBC, while a smaller portion, about 22% of the initial transport, flows towards the interior of the basin. [ABSTRACT FROM AUTHOR]

The sparse nature of observational records across the mid- to high latitudes of the Southern Hemisphere limits the ability to place late-twentieth-century environmental changes in the context of long-term (multidecadal and centennial) variability. Historical records from subantarctic islands offer considerable potential for developing highly resolved records of change. In 1905, a whaling and meteorological station was established at Grytviken on subantarctic South Georgia in the South Atlantic (54°S, 36°W), providing near-continuous daily observations through to present day. This paper reports a new, daily observational record of temperature and precipitation from Grytviken, which is compared to regional datasets and historical reanalysis. The authors find a shift toward increasingly warmer daytime extremes commencing from the mid-twentieth century and accompanied by warmer nighttime temperatures, with an average rate of temperature rise of 0.13°C decade-1 over the period 1907-2016 (p < 0.0001). Analysis of these data and reanalysis products suggest a change of pervasive synoptic conditions across the mid- to high latitudes since the mid-twentieth century, characterized by stronger westerly airflow and associated warm föhn winds across South Georgia. This rapid rate of warming and associated declining habitat suitability has important negative implications for biodiversity, including the survival of key marine biota in the region. [ABSTRACT FROM AUTHOR]

Abstract: South Atlantic Anomaly (SAA) affects the astronomical satellites and other spacecraft that orbit the Earth at several hundred kilometers altitude; these orbits take satellites through the anomaly periodically, exposing them to several minutes of strong radiation. The SAA-related frequency shift of Jason-1 DORIS oscillator is well known and the corresponding studies were published in the past. Recent analyses indicate that SPOT-5 DORIS oscillator is probably also affected, even if with lower influence. The first goal of this study is to obtain some evidence of the SAA effect on the SPOT-5 DORIS oscillator; this was carried out by analyzing frequency estimates and post-fit residuals. Furthermore, geographical grid maps are presented, displaying the estimated oscillator frequency drift and its time derivative. The second goal of the paper is to present an empirical DORIS observation corrective model, based on the application of the frequency drift derived from the previously created grid map. Analyses of the post-fit residuals, zenithal tropospheric delay and station height bias confirm that the application of the data corrective model strongly reduces the SAA bias. Despite the fact that the data corrective model significantly improves the solution and compensates most of the data corruption, the total elimination of SAA-related bias was not achieved. The last part of the paper is analyzing the long term changes of the SAA effect on the SPOT-5 DORIS observations. The results confirm that the SAA effect was significantly rising during the period 2008.0–2012.0 and that during these 4years it has doubled in size. [Copyright &y& Elsevier]

ABSTRACT This paper examines the distributions of anomalies of sea surface temperature ( SST) and of the moisture sources in the South Atlantic Ocean during extreme dry events in southeastern Brazil in the austral autumn, winter and spring for the period 1982-2009. The extreme dry events were identified based on a combination in which consecutive dry days and variable percentiles were considered in five homogeneous regions in terms of precipitation in southeastern Brazil, as defined through cluster analysis. Composites of anomalies of SST and moisture sources for the dry events selected for the different homogeneous regions show specific characteristics for each region, but some similarities were apparent for the southern and northern parts of southeast Brazil. During spring in all regions, and during autumn and winter in the southern regions, a tripole pattern of SST anomalies was found (negative, positive and negative), together with an anomalous anticyclonic circulation in the Atlantic Ocean transporting moisture to southern Brazil associated with positive SST anomalies. A decrease in the climatological moisture sources in the south of Brazil then ensues, and dry conditions prevail in the regions of interest. In winter and autumn in the northern regions, the same tripole pattern of SST anomalies was also found, but shifted northwards. An anomalous cyclone is associated with the negative SST anomalies, and the climatological moisture sources to the northeast of Brazil reduce their contribution to the region of interest, where negative precipitation anomalies are registered. It seems that the events selected show the results of reductions both in terms of the availability of moisture and in atmospheric instability. [ABSTRACT FROM AUTHOR]

To date, a number of studies have focused on the influence of sea surface temperature (SST) on global and regional rainfall variability, with the majority of these focusing on certain ocean basins - eg, the Pacific, North Atlantic and Indian Ocean. In contrast, relatively less work has been done on the influence of the central South Atlantic, particularly in relation to rainfall over southern Africa. Previous work by the authors, using reanalysis data and general circulation model (GCM) experiments, has suggested that cold SST anomalies in the central southern Atlantic Ocean are linked to an increase in rainfall extremes across southern Africa. In this paper we present results from idealized regional climate model (RCM) experiments forced with both positive and negative SST anomalies in the southern Atlantic Ocean. These experiments reveal an unexpected response of rainfall over southern Africa. In particular, it was found that SST anomalies of opposite sign can cause similar rainfall responses in the model experiments, with isolated increases in rainfall over central southern Africa as well as a large region of drying over the Mozambique Channel. The purpose of this paper is to highlight this finding and explore explanations for the behaviour of the climate model. It is suggested that the observed changes in rainfall might result from the redistribution of energy (associated with upper-level changes to Rossby waves) or, of more concern, model error, and therefore the paper concludes that the results of idealized regional climate models forced with SST anomalies should be viewed cautiously. [ABSTRACT FROM AUTHOR]

This paper focuses on the South Atlantic Oceanic World, and the pivotal place of the Island of St. Helena within that world, as both a context and a conceptual tool for thinking about race-making and race-mixing in South Africa. Drawing on various historical ‘snapshots’ from documentary and archival sources on St. Helena, as well as from exploratory fieldwork in South Africa, St. Helena, an Atlantic World of flux and fluidity, is invoked as a contrast to an Apartheid world that insists upon fixity. These contrasting worlds are the context for thinking about the racial identifications made by St. Helenian immigrants, and their descendants in South Africa. Following Robert Young the paper is interested in ‘counter-active’ constructions of race, which means that the context of race-mixing that this paper invokes is simultaneously a context for race-making. [ABSTRACT FROM AUTHOR]

A thorough analysis of the stability of a coupled version of an interhemispheric three-box model of thermohaline circulation (THC) is presented. This study follows a similarly structured analysis of an uncoupled version of the same model presented in Part I of this paper. The model consists of a northern high-latitude box, a tropical box, and a southern high-latitude box, which can be thought of as corresponding to the northern, tropical, and southern Atlantic Ocean, respectively. This paper examines how the strength of THC changes when the system undergoes forcings representing global warming conditions. Since a coupled model is used, a direct representation of the radiative forcing is possible because the main atmospheric physical processes responsible for freshwater and heat fluxes are formulated separately. Each perturbation to the initial equilibrium is characterized by the total radiative forcing realized, by the rate of increase, and by the north–south asymmetry. Although only weakly asymmetric or symmetric radiative forcings are representative of physically reasonable conditions, general asymmetric forcings are considered in order to get a more complete picture of the mathematical properties of the system. The choice of suitably defined metrics makes it possible to determine the boundary dividing the set of radiative forcing scenarios that lead the system to equilibria characterized by a THC pattern similar to the present one, from those that drive the system to equilibria where the THC is reversed. This paper also considers different choices for the atmospheric transport parameterizations and for the ratio between the high-latitude and tropical radiative forcing. It is generally found that fast forcings are more effective than slow forcings in disrupting the present THC pattern, forcings that are stronger in the northern box are also more effective in destabilizing the system, and very slow forcings do not destabilize the system whatever their asymmetry, unless the radiative forcings are very asymmetric and the atmospheric transport is a relatively weak function of the meridional temperature gradient. In this latter case some relevant hysteresis graphs of the system are presented. The changes in the strength of the THC are primarily forced by changes in the latent heat transport in the hemisphere because of its sensitivity to temperature, which arises from the Clausius–Clapeyron relation. [ABSTRACT FROM AUTHOR]

The identification and mitigation of adverse effects of the bycatch of tuna longline fishery have been mainly developed and implemented for seabirds, sharks and turtles and, the knowledge on teleost bycatch for this fishery, remains very poor. This paper contributes to a comprehensive assessment of life history traits and fishery attributes of target and bycatch species caught by the tuna longline fishery in the South Atlantic and Indian Oceans. Data was compiled on seven life history traits and three fishery attributes for 33 and 27 teleost stocks caught by longliners in South Atlantic and Indian Oceans, respectively. In addition, each species was assigned into four categories describing the fate of the catch: target species for commercial use, bycatch species kept for consumption, bycatch species kept for commercial use and discarded bycatch. Life history traits and fishery attributes did not differ between oceans. However, non-target but commercialized species were smaller in the Atlantic Ocean. Teleosts caught by the tuna longline fishery was segregated into three main groups: (1) the fast growing species represented mainly by dolphinfishes ( Coryphaena hippurus and C. equisellis ), skipjack tuna ( Katsuwonus pelamis ), kawakawa ( Euthynnus affinis ), bullet tuna ( Auxis rochei ), snoek ( Thyrsites atun ) and blackfin tuna ( Thunnus atlanticus ) ; (2) target tunas and most other bycatch species which were part of an intermediate group and (3) billfishes including swordfish representing the large and slow growing species with moderate to high market values and unknown or highly uncertain stock status. Investment in some key life history traits (such as growth coefficient) and the development of quantitative or semi-quantitative approaches (stock assessment and Ecological Risk Assessment) should be priorized as precautionary management measures for these species. [ABSTRACT FROM AUTHOR]

The Great Shearwater, Ardenna gravis, breeds on islands in the South Atlantic Ocean from September to May and migrates to the North Atlantic during the non-breeding season. The species is known to range widely from its breeding islands and it occurs in the south west Indian Ocean from September to May. There are reports of single birds in the eastern Pacific from Chile, California and Alaska, and ten or more records of single or sometimes two birds from Australian waters and the south-west Pacific. This paper documents an irruption of at least 50 birds into Australian and New Zealand waters in late March and early April 2011. Possible causes for the irruption are considered, with an oil spill near the breeding islands in mid-March identified as a likely trigger. [ABSTRACT FROM AUTHOR]

Barrier layers are generated when the surface mixed layer is shallower than the layer where temperature is well mixed, in geographical regions where salinity plays a key role in setting up upper-ocean density stratification. In the tropical oceans, thick barrier layers are also found in a latitude range where spiraling trajectories from surface in situ drifters suggest the presence of predominantly cyclonic submesoscale-like vortices. The authors explore these dynamical processes and their interplay in the present paper, focusing on the tropical South Atlantic Ocean and using a high-resolution modeling approach. The objective is threefold: to investigate the mean dynamics contributing to barrier-layer formation in this region, to study the distribution and seasonality of submesoscale features, and to verify whether and how the submesoscale impacts barrier-layer thickness. The model used is the Regional Ocean Modeling System (ROMS) in its Adaptive Grid Refinement in Fortran (AGRIF) online-nested configuration with a horizontal resolution ranging between 9 and 1 km. The simulated circulation is first described in terms of mean and submesoscale dynamics, and the associated seasonal cycle. Mechanisms for barrier-layer formation are then investigated. The results confirm previous hypotheses by Mignot et al. on the relevance of enhanced winter mixing deepening the isothermal layer, whereas the salinity stratification is sustained by advection of surface fresh waters and subsurface salinity maxima. Finally, submesoscale effects on barrier-layer thickness are studied, quantifying their contribution to vertical fluxes of temperature and salinity. Submesoscale vortices associated with salinity fronts are found to have a significant effect, producing thicker barrier layers (by ~20%-35%) and a shallower mixed layer because of their restratifying effect on salinity. [ABSTRACT FROM AUTHOR]

Abstract: Risk-based inspection is nowadays the predominant approach to structural integrity assurance in complex engineering systems, such as those designed for and operated in deepwater environments. One of the major tasks in risk-based planning is risk ranking of the components comprising an engineering system. In this paper, a mathematical model based on data envelopment analysis is developed for this purpose, whereby two types of weights are employed: subjective judgmental weights which are provided as input, and objective which constitute the output of the model. The use of the mathematical model is illustrated in a real world system of subsea flexible pipes, which operational in the south Atlantic Shelf off the Southeast Coast of Brazil. [Copyright &y& Elsevier]

Abstract: The geodynamic processes that control the opening of the central segment of the South Atlantic Ocean (between the Walvis Ridge and the Ascension FZ) are debated. In this paper, we discuss the timing of the sedimentary and tectonic evolution of the Early Cretaceous rift by drawing eight paleogeographic and geodynamic maps from the Berriasian to the Middle–Late Aptian, based on a biostratigraphic (ostracodes and pollen) chart recalibrated on absolute ages (chemostratigraphy, interstratified volcanics, Re–Os dating of the organic matter). The central segment of the South Atlantic is composed of two domains, with a two phases evolution of the pre-drift (“rifting”) times: a rift phase characterized by tilted blocks and growth strata, followed by a sag basin. The southern domain includes the Namibe, Santos and Campos Basins. The northern domain extends from the Espirito Santo and North Kwanza Basins, in the south, to the Sergipe–Alagoas and North Gabon Basins to the north. Extension started in the northern domain during the Late Berriasian (Congo–Camamu Basin to the Sergipe–Alagoas–North Gabon Basins) and migrated southward. At that time, the southern domain was not a subsiding domain (emplacement of the Parana–Etendeka Trapp). Extension started in this southern domain during the Early Barremian. The rift phase is shorter in the south (5–6Ma, Barremian to base Aptian) than in the north (19 to 20Myr, Upper Berriasian to base Aptian). The sag phase is of Middle to Late Aptian age. In the northern domain, this transition corresponds to a hiatus of Early to Middle Aptian age. From the Late Berriasian to base Aptian, the northern domain evolves from a deep lake with lateral highs to a shallower organic-rich one with no more highs. The lake migrates southward in two steps, until the Valanginian at the border between the northern and southern domains, until the Early Barremian, north of Walvis Ridge. [Copyright &y& Elsevier]

Abstract: In this paper we present a paleoceanographic reconstruction of the southwestern South Atlantic for the past 13kyr based on faunal and isotopic analysis of planktonic foraminifera from a high-resolution core retrieved at the South Brazil Bight continental slope. Our record indicates that oceanographic changes in the southwestern South Atlantic during the onset of the Holocene were comparable in strength to those that occurred during the Younger Dryas. Full interglacial conditions started abruptly after 8.2kyrBP with a sharp change in faunal composition and surface hydrography (SST and SSS). Part of the observed events may be explained in terms of changes in thermohaline circulation while the other part suggests a dominant role of winds. Our data indicate that during the Early Holocene upwelling was significantly strengthened in the South Brazil Bight promoting high productivity and preventing the establishment of the typically interglacial menardiiform species. In general terms, oceanographic changes recorded by core KF02 occurred in synchrony with Antarctica's climate. [Copyright &y& Elsevier]

This paper examines the factors governing rainfall variability in western equatorial Africa (WEA) during the April-June rainy season. In three of the five regions examined some degree of large-scale forcing is indicated, particularly in the region along the Atlantic coast. Interannual variability in this coastal sector also demonstrates a strong link to changes in local sea surface temperatures (SSTs) and the South Atlantic subtropical high. To examine potential causal mechanisms, various atmospheric parameters are evaluated for wet and dry composites. The results suggest that the intensity of the zonal circulation in the global tropics is a crucial control on rainfall variability over WEA. A La Niña (El Niño)-like signal in both SSTs and zonal circulation over the Pacific is apparent in association with the wet (dry) conditions in the western sector. However, remote forcing from the Pacific modulates the circulation over Africa indirectly by way of synchronous changes in the entire Indian or Atlantic Ocean. Anomalies in the local zonal winds are similar in all three regions: the wet (dry) composite is associated with an intensification (weakening) of the upper-tropospheric easterlies and low-level westerlies, but a weakening (intensification) of the midlevel easterlies. This work also suggests that, in most cases, the relationship between local SSTs and rainfall reflects a common remote forcing by the large-scale atmosphere-ocean system. This forcing is manifested via changes in the zonal circulation. Thus, the statistical associations between rainfall and SSTs do not indicate direct forcing by local SSTs. One point of evidence for this conclusion is the stronger association with atmospheric parameters than with SSTs. [ABSTRACT FROM AUTHOR]

Fisheries-related mortality of globally threatened albatrosses and petrels in the Falkland Islands is largely attributed to collisions with warp cables on stern trawlers. Following the introduction Tori lines, also known as bird-scaring lines, in 2004, incidental mortality has been substantially reduced. However, there is still a requirement for further development and optimisation of mitigation methods. In this paper, we present results of sea trials to compare the efficacy of a modified Tori line design with the initial (2004) design. The modified design resulted in 28 and 33% fewer warp contacts than the 2004 design for all species, and high-risk species (black-browed albatross and giant petrels), respectively. Surprisingly, these differences were not found to be statistically significant. However, the modified design was more effective at reducing interactions with the Tori lines themselves. The modified design provided better coverage and protection of the warps, particularly in crosswinds, and was safer for the crew to use. Our study highlights the importance of continued research and development in the field of bycatch mitigation and has relevance for trawl fisheries globally. [ABSTRACT FROM AUTHOR]

A series of recent papers showed that sea surface temperature (SST) anomalies in the south equatorial tropical Atlantic modulate the interannual variability of the African and Indian monsoon rainfall. Physically this teleconnection can be explained by a simple Gill-Matsuno mechanism. In this work, the output from five different models chosen within the CMIP3 (Coupled Model Intercomparison Project version 3) ensemble of coupled general circulation models (CGCMs) are analyzed to investigate how state-of-the-art CGCMs represent the impact of the South Tropical Atlantic (STA) SSTs on the Indian and African region. Using a correlation-regression technique, it is found that four out of the five models display a teleconnection between STA and Indian region which is generally weaker than in the observations but in agreement in the rainfall field pattern. This teleconnection is also noticeable in the ensemble mean of the five models. Over Africa, however, the significant changes in rainfall displayed in the observation are properly caught by only one of the CGCMs. Additionally, none of the models reproduces the symmetric upper-level wind response around the Equator seen over the Indian Ocean in the observations and all have significant biases also in the surface pressure field response to the tropical Atlantic SSTs. Nonetheless the STA response, particularly over the southern hemisphere, is indicative of the Gill-Matsuno-type mechanism identified in previous studies using idealized experiments with atmospheric GCMs and observational data. With a suite of atmospheric-only GCM integrations it is shown that the differences in amplitude and pattern are not only due to the strong biases and reduced variabilities of the CGCMs over the tropical Atlantic but they are also caused by the different physical parameterizations used in models. [ABSTRACT FROM AUTHOR]

A large fraction of the atmospheric aerosol load reaching the free troposphere is frequently located above low clouds. Most commonly observed aerosols above clouds are carbonaceous particles generally associated with biomass burning and boreal forest fires, and mineral aerosols originating in arid and semiarid regions and transported across large distances, often above clouds. Because these aerosols absorb solar radiation, their role in the radiative transfer balance of the earth-atmosphere system is especially important. The generally negative (cooling) top-of-the-atmosphere direct effect of absorbing aerosols may turn into warming when the light-absorbing particles are located above clouds. The actual effect depends on the aerosol load and the single scattering albedo, and on the geometric cloud fraction. In spite of its potential significance, the role of aerosols above clouds is not adequately accounted for in the assessment of aerosol radiative forcing effects due to the lack of measurements. This paper discusses the basis of a simple technique that uses near-UV observations to simultaneously derive the optical depth of both the aerosol layer and the underlying cloud for overcast conditions. The two-parameter retrieval method described here makes use of the UV aerosol index and reflectance measurements at 388 nm. A detailed sensitivity analysis indicates that the measured radiances depend mainly on the aerosol absorption exponent and aerosol-cloud separation. The technique was applied to above-cloud aerosol events over the southern Atlantic Ocean, yielding realistic results as indicated by indirect evaluation methods. An error analysis indicates that for typical overcast cloudy conditions and aerosol loads, the aerosol optical depth can be retrieved with an accuracy of approximately 54%% whereas the cloud optical depth can be derived within 17%% of the true value. [ABSTRACT FROM AUTHOR]

This paper is concerned with expressions of Argentine territorial nationalism with a specific focus on the Malvinas/Falklands dispute. notion of banal nationalism has been widely applied as a means to understanding the ways in which national identities are learnt and reproduced by the populace, through a multitude of ‘mundane’ representations. More recently thesis has been critiqued () for its rigidity and inability to take account of the different ways these nationalisms are produced and received () within and outside of the nation-state. We build on these interventions by arguing that research into territorial nationalism should not ignore the wider temporal, spatial, political and everyday contexts in which such discourses emerge and are consumed. To illustrate this diversity we contend that territorial nationalism and, more specifically, the attention placed on the Malvinas dispute by the Argentine government has varied in its intensity, depending on wider political events and agendas in the South West Atlantic and Latin American regions. Secondly, through the use of interview extracts from a pilot study conducted with 20 young people in Buenos Aires, we suggest that Argentine territorial nationalism is not received uniformly across the nation-state and, rather, should be explored in its everyday contexts. These contexts take into consideration things like respondent’s geographical location, personal/familial relationships and generation, amongst other variables, in order to more sensitively appreciate Argentine territorial nationalism’s multifarious reception. [Copyright &y& Elsevier]

Using observational data and outputs from an ocean general circulation model, the growth and decay of the South Atlantic subtropical dipole (SASD) are studied. The SASD is the most dominant mode of interannual variability in the South Atlantic Ocean, and its sea surface temperature (SST) anomaly shows a dipole pattern that is oriented in the northeast-southwest direction. The positive (negative) pole develops because the warming of the mixed layer by the contribution from the climatological shortwave radiation is enhanced (suppressed) when the mixed layer is thinner (thicker) than normal. The mixed layer depth anomaly over the positive (negative) pole is due to the suppressed (enhanced) latent heat flux loss associated with the southward migration and strengthening of the subtropical high. During the decay phase, since the temperature difference between the mixed layer and the entrained water becomes anomalously large (small) as a result of the positive (negative) mixed layer temperature anomaly, the cooling of the mixed layer by the entrainment is enhanced (reduced). In addition, the cooling of the mixed layer by the contribution from the climatological latent heat flux is enhanced (suppressed) by the same thinner (thicker) mixed layer. This paper demonstrates the importance of taking into account the interannual variations of the mixed layer depth in discussing the growth and decay of SST anomalies associated with the SASD. [ABSTRACT FROM AUTHOR]

The interocean exchange of water from the South Atlantic with the Pacific and Indian Oceans is examined using the output from the ocean general circulation model for the Earth Simulator (OFES) during the period 1980-2006. The main objective of this paper is to investigate the role of the interocean exchanges in the variability of the Atlantic meridional overturning circulation (AMOC) and its associated meridional heat transport (MHT) in the South Atlantic. The meridional heat transport from OFES shows a similar response to AMOC variations to that derived from observations: a 1 Sv (1 Sv ≡ 106 m3 s−1) increase in the AMOC strength would cause a 0.054 ± 0.003 PW increase in MHT at approximately 34°S. The main feature in the AMOC and MHT across 34°S is their increasing trends during the period 1980-93. Separating the transports into boundary currents and ocean interior regions indicates that the increase in transport comes from the ocean interior region, suggesting that it is important to monitor the ocean interior region to capture changes in the AMOC and MHT on decadal to longer time scales. The linear increase in the MHT from 1980 to 1993 is due to the increase in advective heat converged into the South Atlantic from the Pacific and Indian Oceans. Of the total increase in the heat convergence, about two-thirds is contributed by the Indian Ocean through the Agulhas Current system, suggesting that the warm-water route from the Indian Ocean plays a more important role in the northward-flowing water in the upper branch of the AMOC at 34°S during the study period. [ABSTRACT FROM AUTHOR]

The wavenumber spectra of wind kinetic energy over the ocean from Quick Scatterometer (QuikSCAT) observations have revealed complex spatial variability in the wavelength range of 1000-3000 km, with spectral slopes varying from −1.6 to −2.9. Here the authors performed a spectral analysis of QuikSCAT winds over the global ocean and found that (i) the spectral slopes become steeper toward the Poles in the Pacific and in the South Atlantic, and the slopes exhibit minimal longitudinal dependence in the South Pacific; (ii) the steepest slopes are in the tropical Indian Ocean and the shallowest slopes are in the tropical Pacific and Atlantic; and (iii) the spectra are steeper in winter than summer in most regions of the midlatitude Northern Hemisphere. The new findings reported in the paper provide a test bed for theoretical studies and atmospheric general circulation models. [ABSTRACT FROM AUTHOR]

This paper demonstrates a causal link between the air--sea phenomenon referred to as the South Atlantic Ocean (SAO) dipole (SAOD) and the interannual variability of precipitation over West Africa during the boreal summer monsoon rainy season in which most of the annual rainfall is recorded using an array of observational datasets. Analyses show that positive precipitation anomalies exceeding 40 mm month−−1 over most locations at the Guinea Coast are associated with the positive phase of the SAOD, which is characterized by warm sea surface temperature anomalies (SSTAs) in the northeastern part of the SAO or the northeast pole (NEP)--that is, the Atlantic Niño sector--and cool SSTA in the southwestern part [[southwest pole (SWP)]] off the Argentina--Uruguay--Brazil coast. On the other hand, interannual variability in the Sahel is closely connected to the West African summer monsoon and the Atlantic Niño. The results of this study reveal that the well-known influence of the Atlantic Niño on Guinea Coast precipitation in the literature represents only a component of the ocean--atmosphere interactions in the SAO causing the precipitation anomalies. Indeed, correlation and composite analyses using Guinea Coast precipitation indices consistently yield significant links to both the NEP and SWP centers of action. The hypothesized physical mechanism through which the SAOD-type SST gradients could induce Guinea Coast precipitation anomalies is the Lindzen--Nigam process. During the positive phase of the SAOD, the imprint of SST gradients gives rise to divergence over the SWP linked to convergence and vigorous upward motion over the NEP thereby leading to enhancement of precipitation over the Guinea Coast. [ABSTRACT FROM AUTHOR]

Abstract: The DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) data are processed in the framework of the International DORIS Service (IDS) at several analysis centers. Each analysis center follows its own processing strategy and models. This manuscript presents the results of the processing based on a development version 5.0 of the Bernese GPS Software at the Geodetic Observatory Pecný analysis center (GOP). The complete period 1993.0–2009.0 was processed applying the free-network approach in order to estimate main parameters namely station and polar motion coordinates. A significant improvement has been achieved in the estimated station coordinates and polar parameters by processing the data from the satellites equipped with the second generation of the DORIS receiver, SPOT-5 and Envisat, launched in 2002. The RMS of polar coordinates in 2003.0–2008.0 shows a decreasing trend over the entire analyzed time period. The transformation parameters between the DORIS solution and ITRF2005 were subjected to a spectral analysis, confirming the domination of the annual and semiannual periodicity. The behavior of the terrestrial reference frame scale is quite stable with a few exceptions. The analysis of a major scale shift at the end of 2004 revealed SPOT-5 and Envisat satellites as the source of the problem. However, the termination of the TOPEX/Poseidon DORIS data processing at the end of 2004 did not influence significantly the overall scale level. Another objective of the paper is a detailed analysis of relations between the value of the observation residuals and the length of the observation Doppler count interval. A simple empirical model considering the observation noise as a sum of the constant and time-dependent terms is propounded and discussed. The estimated troposphere total zenith delays are compared to the corresponding values derived from GNSS (IGS PPP products) and the source of the differences as well as their systematic behavior and dependence on several factors are discussed. A significant DORIS–GNSS bias was detected when processing SPOT-5 data for the South American stations Santiago, Cachoeira Paulista and Arequipa. The location of these stations is close to the South Atlantic Anomaly (SAA). An important effect of SAA on the DORIS observation noise is well known from Jason-1 data, but it has not been detected for any other satellite yet. Additional tests of the estimated station coordinates and the beacon frequency offsets, based on single-satellite solutions, confirm the possible relation between the SPOT-5 bias and the SAA. [Copyright &y& Elsevier]

Dechlorane Plus (DP), a highly chlorinated flame retardant, was investigated in marine boundary layer air and surface seawater from East Greenland Sea and in the Northern and Southern Atlantic toward Antarctica. The concentrations of DP ranged from 0.05 to 4.2 pg m-3 in the atmosphere and from

The Brazil-Malvinas Confluence (BMC) region constitutes one of the most important ocean features in the South Atlantic Ocean basin. Understanding the BMC upper ocean temperature variability could represent one of the key factors to understanding its connection to local and global ocean circulation. Some important local and remote ocean processes are related to the annual and interannual variability of its thermal/salt front position. This paper investigates the upper ocean variability in the BMC region under the influence of an El Niño/Southern Oscillation-type wind stress field using an oceanic general circulation model (Modular Ocean Model version 4.0). The results revealed the occurrence of positive anomalies, with values ranging from 0.5°C to 1.0°C (centered at 40.5°S and 55.0°W), near the BMC region associated with upper ocean velocity anomalies during the peak of the ocean kinetic energy phase. This mechanism was a response of a volume transport balance between the Brazil Current (BC) and the Malvinas Current (MC), the latter being accelerated by the Antarctic Circumpolar Current (ACC). The occurrence of positive anomalies was always associated with an enhanced BC meridional surface volume transport, together with a decrease of the ACC zonal volume transport, vertically integrated across the Drake Passage, and a correspondent decrease in the upper layer MC volume transport. It was possible to see negative upper layer temperature anomaly predominance just before the peak ocean kinetic energy month and positive anomaly predominance immediately following this month. The occurrence of upper layer temperature anomalies in the BMC region was not restricted to just the peak ocean kinetic energy month since they occurred throughout the perturbed experiment integration time. [ABSTRACT FROM AUTHOR]

Abstract: In the case of the International Space Station (ISS), the attitude of which is usually stabilized in the local vertical reference frame (airplane-like attitude), the anisotropies in the radiation field, such as the effect of the Earth''s shadow, the angular dependence of the geomagnetic transmission factors and the East–West asymmetry in the South Atlantic Anomaly (SAA), cannot be ignored. One-dimensional telescopes used for dosimetry have strong directional sensitivity and therefore they might either under- or overestimate the dose equivalent. The application of 3D telescopes with three, mutually orthogonal axes improves significantly the measuring precision of the instrument. The present paper addresses the expected responses of 1D and 3D telescopes for anisotropic radiation in low Earth orbit on board the ISS. Calculations were performed to estimate the differences between the obtained LET-spectra of the untrapped particles as well as the absorbed dose values. The directionality of trapped protons in the SAA was addressed as well. [Copyright &y& Elsevier]

Abstract: Coalbed methane (CBM) is a worldwide exploration target of the petroleum industry. In Brazil, the most important coal-bearing succession is associated with the Permian Rio Bonito Formation of the Paraná Basin. The gas-prone areas are located at the southeastern margin of the Paraná Basin and possibly in the offshore region of the northern part of the Pelotas Basin. Coalfields end abruptly at the present day shoreline, a result of rifting of Gondwana and the evolution of the South Atlantic Ocean. All geologic indicators suggest that in pre-rift times the coal seams extended further eastwards, probably now lying deeply buried below the sedimentary succession of the Pelotas Basin. The present paper discusses structural, stratigraphic, seismic and aeromagenetic data that support the preservation of continental crust beneath ocean sediment. If the coal beds had similar lateral extent to known onshore coals, and coal beds extended across the projected extension of the Parana basin, and there was a conservative 5m of cumulative coal thickness, then a potential methane volume can be estimated for this newly inferred resource. Average onshore coal gas content is 32scf/ton (1.00m3/ton). If this is similar in the offshore coal deposits, then the hypothetical methane volume in the offshore area could be in excess of 1.9×1012 scf (56×109 m3). Metamorphism from dikes associated with rifting are potential complicating factors in these deposits, and since no borehole reaching the deep-lying strata in the offshore area are available, this is a hypothetical gas resource with a certain level of uncertainty which should be tested in the future by drilling a deep borehole. [Copyright &y& Elsevier]

Variability in sea surface height (SSH) can be decomposed into two contributions: one from changes in mass in the water column (barotropic) and the other from purely steric changes (baroclinic). Both contributions can be determined from data recorded by a pressure sensor–equipped inverted echo sounder (PIES). PIES data from the Agulhas South Atlantic Thermohaline Experiment (ASTTEX) were used, collected in the Cape Basin off South Africa, along 1000 km of an eddy corridor where Agulhas eddies carry cores of warm, salty Indian Ocean waters into the South Atlantic. The paper presents in detail the method used to convert PIES measurements into barotropic, baroclinic, and total SSH, and discusses the error budget. The baroclinic contribution is geopotential height (reference 4500 dbar), which can be determined from the measured vertical acoustic travel time together with a lookup curve based on the regional hydrography. The main error source is scatter about this curve that depends on the extent to which water masses advecting along each geopotential streamline may derive from different ocean regions. The barotropic contribution can be determined from the bottom pressure measurements of the mass variation in the water column and has an uncertainty due to sensor calibration drift in two years corresponding to 1-cm water column height. The barotropic component accounts for 20% of the overall SSH variance and 47% during large signal intervals exceeding 15 cm. PIES data demonstrate via the two measurements that barotropic and baroclinic contributions may work independently or in concert in different mesoscale eddies. The combined structure need not be equivalent barotropic. In particular, deep barotropic eddies exhibit mesoscale spatiotemporal scales and may or may not be systematically tilted or aligned in space or time relative to baroclinic eddies. [ABSTRACT FROM AUTHOR]

Abstract: The passive margin of the South Atlantic shows typical features of a rifted volcanic continental margin, encompassing seaward dipping reflectors, continental flood basalts and high-velocity/density lower crust at the continent–ocean transition, probably emplaced during initial seafloor spreading in the Early Cretaceous. The Springbok profile offshore western South Africa is a combined transect of reflection and refraction seismic data. This paper addresses the analysis of the seismic velocity structure in combination with gravity modelling and isostatic modelling to unravel the crustal structure of the passive continental margin from different perspectives. The velocity modelling revealed a segmentation of the margin into three distinct parts of continental, transitional and oceanic crust. As observed at many volcanic margins, the lower crust is characterised by a zone of high velocities with up to 7.4 km/s. The conjunction with gravity modelling affirms the existence of this body and at the same time substantiated its high densities, found to be 3100 kg/m3. Both approaches identified the body to have a thickness of about 10 km. Yet, the gravity modelling predicted the transition between the high-density body towards less dense material farther west than initially anticipated from velocity modelling and confirmed this density gradient to be a prerequisite to reproduce the observed gravity signal. Finally, isostatic modelling was applied to predict average crustal densities if the margin was isostatically balanced. The results imply isostatic equilibrium over large parts of the profile, smaller deviations are supposed to be compensated regionally. The calculated load distribution along the profile implies that all pressures are hydrostatic beneath a depth of 45 km. [Copyright &y& Elsevier]

This paper describes a quasi-3D Bayesian inversion of oceanographic tracer data from the South Atlantic Ocean. Initially, one active neutral-density layer is considered with an upper and lower boundary. The available hydrographic data are linked to model parameters (water velocities, diffusion coefficients) via a 3D advection–diffusion equation. A robust solution to the inverse problem can be obtained by introducing prior information about parameters and modeling the observation error. This approach estimates both horizontal and vertical flow as well as diffusion coefficients. A system of alternating zonal jets is found at the depths of the North Atlantic Deep Water, consistent with direct measurements of flow and concentration maps. A uniqueness analysis of the model is performed in terms of the oxygen consumption rate. The vertical mixing coefficient bears some relation to the bottom topography even though the authors do not incorporate topography into their model. The method is extended to a multilayer model, using thermal wind relations weakly in a local fashion (as opposed to integrating the entire water column) to connect layers vertically. Results suggest that the estimated deep zonal jets extend vertically, with a clear depth-dependent structure. The vertical structure of the flow field is modified by the tracer fields relative to the a priori flow field defined by thermal wind. The velocity estimates are consistent with independent observed flow at the depths of the Antarctic Intermediate Water; at still shallower depths, above the layers considered here, the subtropical gyre is a significant feature of the horizontal flow. [ABSTRACT FROM AUTHOR]

Abstract: Pelagic longlines are widely known to interact with several species of sea turtles, and there is an increasing concern about the by-catch of turtles in commercial fisheries and its impact on their populations. However, information on sea turtle by-catch in the South Atlantic Ocean is scarce, and there are no quantitative by-catch data available on olive ridleys for the Equatorial Eastern Atlantic. In this paper we analyze data collected by observers on board an Uruguayan long-liner targeting swordfish in two areas in the Equatorial Eastern Atlantic: off the Gulf of Guinea and north of Saint Helenaa Island. Specimens of Lepidochelys olivacea and Dermochelys coriacea were hooked or entangled in 26 longline sets. All registered interactions with olive ridleys took place off the The Gulf of Guinea, with captures ranging from 1 to 3 specimens in a single set. The captured specimens, though not measured directly, appeared to be juveniles. In addition, the examination of the stomach contents of one female mako shark showed dermal scutes, vertebrae and the complete head of a sea turtle identified as L. olivacea, allowing us to estimate its curved carapace length. In contrast, adult specimens of D. coriacea were caught in the two fishing areas. The capture of 10 individuals in a single set was recorded. Due to the high rate of sea turtle by-catch observed off the The Gulf of Guinea (1.02 ind/1000 hooks) conservation programs in the area should take into consideration the possible existence of a developmental and feeding area in this zone. Accordingly, longline fisheries in this area should be monitored and mitigation measures put in place to avoid or minimize damage to the pelagic phase of African populations of sea turtles. [Copyright &y& Elsevier]

The use of documentary sources has proven useful to identify extreme climatic events and their variability during the pre-instrumental period. The aim of this paper is to describe iceberg sightings in the Western South Atlantic during the second half of the 18th century, as recorded from Spanish logbooks. A total of five sightings have been found, two corresponding to isolated bergs and three to outbreaks. The relevance of these results is twofold: they are the first documented iceberg sightings to date and, above all, they correspond to very unusual episodes, characterized by a high number of high-sized bergs and by the relatively low latitude of their location. It is suggested that they could be associated to cold episodes in Antarctica. [ABSTRACT FROM AUTHOR]

Dynamical interpolation of five years of TOPEX/POSEIDON altimeter data (October 1992-September 1997) is performed in the South Atlantic basin, through the use of a simple quasigeostrophic model and a simple nudging data assimilation technique. The resulting data set is analysed in order to evidence the role of mesoscale eddies on the interannual variability of the South Atlantic ocean circulations. The annual mean circulations and the eddy fields reveal some significant interannual variability in the Brazil-Malvinas confluence region and in the Aghulas Retroflection region. But this interannual variability spreads out also in large extensions of those previous regions as well as in other areas of the South Atlantic basin. In particular, significant variability shows up in the upper return branch of the subtropical gyre that is interpreted in relation with the drift of some Aghulas rings. The role of those latter rings which are crucial for the Indian-Atlantic interocean exchange processes, is further investigated in the paper, and the fate of five specific rings analysed in detail. The overall influence of topography on the circulation is clearly evidenced, especially through its interaction with eddies. [ABSTRACT FROM AUTHOR]

Mercury and many of its compounds behave exceptionally in the environment because of their volatility, capability for methylation, and subsequent biomagnification in contrast with most of the other heavy metals. Long-range atmospheric transport of elemental mercury, its transformation to more toxic methylmercury compounds, the ability of some to undergo photochemical reactions, and their bioaccumulation in the aquatic food chain have made it a subject of global research activities, even in polar regions. The first continuous high-time-resolution measurements of total gaseous mercury in the Antarctic covering a 12-month period were carried out at the German Antarctic research station Neumayer (70°39' S, 8°15' W) between January 2000 and February 2001. We recently reported that mercury depletion events (MDEs) occur in the Antarctic after polar sunrise, as was previously shown for Arctic sites. These events (MDEs) end suddenly during Antarctic summer. A possible explanation of this phenomenon is presented in this paper, showing that air masses originating from the sea-ice surface were a necessary prerequisite for the observations of depletion of atmospheric mercury at polar spring. Our extensive measurements at Neumayer of atmospheric mercury species during December 2000-February 2001 show that fast oxidation of gaseous elemental mercury leads to variable Hg[sup 0] concentrations during Antarctic summer, accompanied by elevated concentrations, up to more than 300 pg/m³, of reactive gaseous mercury. For the first time in the Southern Hemisphere, atmospheric mercury species measurements were also performed onboard of a research vessel, indicating the existence of homogeneous background concentrations over the south Atlantic Ocean. These new findings contain evidence for an enhanced oxidizing potential of the Antarctic atmosphere over the continent that needs to be considered for the interpretation of dynamic transformations of mercury during summertime. [ABSTRACT FROM AUTHOR]

The analysis of the structure and evolutionary history of the Late Miocene marine molluscs along the southwestern Atlantic littoral indicates that these faunas did not give rise to the present assemblages of the Argentinean Province of the same region, the latter being characterised by a typically transitional association (in the sense of Scarabino [(1977) Com. Soc. Malac. Urug. 4, 177–285]) that developed after Miocene times once the cold Malvinas (Falkland) Current was completely operating. The Late Miocene Valdesian and Paranaian Provinces, mainly composed of paratropical warm-water faunas, are defined in this paper. The former includes assemblages recovered from the Puerto Madryn Formation. Its southern limit is placed at 42°S, while in the north its boundary with the Paranaian Province is situated approximately between 37 and 39°S. The Paranaian Province includes assemblages belonging to the Parana´ and Camacho Formations. It extends northwards along the Uruguayan and southern Brazilian littoral, but its northern boundary still remains unknown. An incipient thermal gradient is recognised, as the temperature values for the Paranaian Province are slightly higher than those for the Valdesian Province. Taking into account that in the Valdesian Province water temperature was in fact warm, it is concluded that the cold Malvinas (Falkland) Current still had a very low activity in the area during the Late Miocene. The presence of upwelling phenomena is also suggested by the presence of widely distributed turritellid beds in the northern Patagonian region. [Copyright &y& Elsevier]

The reproduction of the brittle star Astrotoma agassizii was studied from deep waters of the South Atlantic Ocean, based on samples collected in August 2012, and May and September 2013. Ten samples from 800 to 1400 m depths off Mar del Plata Canyon were studied. The species was found to be a brooding simultaneous hermaphrodite. Hermaphroditic gonads contained testis and ovaries inside the same sacs. Both, ovary and testis contained different stages of gametogenesis development simultaneously. Gonads contained several stages of oocytes in different stages of gametogenesis. The largest oocyte recorded was 800 µm diameter. Free spermatozoa were observed in the lumen of the testis, together with spermatogenic columns. Five individuals, from a total of 30 examined, resulted brooding, and most contained mature ovotestis at the same time. Incubation occurs in five of the ten bursal sacs, containing 15–20 young juveniles each. Maximum disc diameter recorded for a brood was 1100 µm. Herein we hypothesize that Astrotoma agassizii could be continuous breeder species in the deep-sea. [ABSTRACT FROM AUTHOR]

This work describes the spatial distribution of pigments and main taxonomic groups of phytoplankton in the biogeochemical provinces of the subtropical South Atlantic Ocean, along 30°S latitude. Seawater samples (surface to 200 m depth) were collected along 120 oceanographic stations occupied in the early austral spring of 2011, during a CLIVAR Repeat Hydrography cruise. The pigments were identified and quantified by high performance liquid chromatography (HPLC), and CHEMTAX software was used to determine the relative contributions of the main taxonomic groups to total chlorophyll a (phytoplankton biomass index). Sampling stations were grouped into three provinces: Africa, Gyre, and Brazil, corresponding to the eastern, central, and western sectors of the transect, respectively. Our results showed that both vertical and horizontal distribution patterns of pigments and taxonomic groups were mainly determined by the availability of light and/or nutrients. Photosynthetic carotenoids (PSCs), associated with small flagellates (mainly haptophytes), dominated the light-limited and nutrient-enhanced deep chlorophyll maximum (DCM) layers of both the Brazil and Gyre provinces, as well as the upwelling influenced surface waters of the Africa province. The latter showed the highest chlorophyll a values ​​(>1 mg m –3 ) and abundance of dinoflagellates in the coastal region. Photoprotective carotenoids (PPCs) were predominant in the nutrient-poor and well-lit surface layers of the Brazil and Gyre provinces, associated with a low content of chlorophyll a (~0.1 mg m –3 ) and dominance of prokaryotes ( Synechoccocus and Prochloroccocus ). This study demonstrates that pigment analysis can provide a useful approach to better understand the distribution of phytoplankton communities along physical-chemical gradients in a still undersampled region of the South Atlantic Ocean. [ABSTRACT FROM AUTHOR]

Lagrangian floats and current meter measurements from two moored arrays are analyzed, in combination with altimetry data, in order to investigate the recirculation of Antarctic Intermediate Waters (AAIW), and of the Intermediate Western Boundary Current (IWBC) at the Tubarão Bight, in the vicinity of the Vitória-Trindade Ridge (VTR), Brazil. Results from a high-resolution numerical simulation provide a complementary view of the flow at intermediate and surface levels. The data depict a topographically-induced cyclonic recirculation at intermediate levels, and five Argo floats are successively trapped inside the bight for two-and-a-half years, performing a total of 10 closed clockwise gyres during this period of time. In situ measurements at the western side of the bight show an intense alongshore flow at intermediate levels, with averaged velocities at 800 m of ~30 cm/s, and peak velocities exceeding 50 cm/s, magnitudes comparable to the Brazil Current (BC) flow at surface levels. The recirculation extends from at least 1000 m deep up to 370 m, reaching sometimes depths as shallow as 150 m, but is mostly uncoupled from the surface flow during the one-and-a-half year long current meter record. Three different flow patterns are observed, and simulated, at surface levels inside the bight during the time the recirculation is well established at intermediate levels: a shallow cyclonic circulation, somewhat akin to the Vitória Eddy; a recurrent anticyclonic flow that encompasses the entire bight; and a southwestward-oriented circulation, associated with the BC being reorganized in a coherent flow after negotiating its way through the VTR channels. A significant portion (about 50% according to the model) of the inflow of intermediate waters recirculates, enhancing the flow of the IWBC within the bight, and increasing the age of AAIW that will eventually cross the VTR on its way to lower latitudes. Although the data are not conclusive about a preferential pathway of the intermediate flow across the VTR, the simulation indicates that up to 70% will exit through the main channel located between the Besnard Bank and the Vitória Seamount, while 30% will follow eastward to the south of the VTR, in a region of intense mesoscale activity, and then cross the ridge farther east. [ABSTRACT FROM AUTHOR]

The oceans play an important role in absorbing a significant fraction of the atmospheric CO 2 surplus, but there are still uncertainties concerning several open ocean regions, such as the under-sampled South Atlantic Ocean. This study assessed the net sea-air CO 2 fluxes and distribution of sea-surface CO 2 fugacity ( f C O 2 sw ) along the 35°S latitude in the South Atlantic, during 2011 spring and early summer periods. Underway CO 2 molar fraction, temperature, salinity and dissolved oxygen measurements were taken continuously from South American to South African continental shelves. Values of both satellite and discrete in situ chlorophyll-a concentration along the ship's track were used as ancillary data. Both f C O 2 sw and difference in sea-air fugacity (Δ f CO 2 ) showed high variability along the cruise track, with higher values found on the continental shelf and slope regions. All Δ f CO 2 values were negative, implying that a sinking process was occurring during the cruise period, with an average net CO 2 flux of −3.1±2.2 mmol CO 2 m −2 day −1 (using Wanninkhof, 1992 ). Physical variables were the main drivers of f C O 2 sw variability in South American continental shelf and open ocean regions, while the biological factor dominated the South African continental shelf. Algorithms for estimating f CO 2 and temperature-normalized f CO 2 were developed and applied separately to the three defined sub-regions: the South American shelf, the open ocean and the South African continental shelf, with the regional temperature-normalized f CO 2 models showing better results. [ABSTRACT FROM AUTHOR]

Chemosynthetic communities have been described from a variety of deep-sea environments across the world's oceans. They constitute very interesting biological systems in terms of their ecology, evolution and biogeography, and also given their potential as indicators of the presence and abundance of consistent hydrocarbon-based nutritional sources. Up to now such peculiar biotic assemblages have not been reported for the western South Atlantic Ocean, leaving this large region undocumented with respect to the presence, composition and history of such communities. Here we report on the presence of a chemosynthetic community off the coast of southern Brazil, in an area where high-levels of methane and the presence of gas hydrates have been detected. We performed metagenomic analyses of the microbial community present at this site, and also employed molecular approaches to identify components of its benthic fauna. We conducted phylogenetic analyses comparing the components of this assemblage to those found elsewhere in the world, which allowed a historical assessment of the structure and dynamics of these systems. Our results revealed that the microbial community at this site is quite diverse, and contains many components that are very closely related to lineages previously sampled in ecologically similar environments across the globe. Anaerobic methanotrophic (ANME) archaeal groups were found to be very abundant at this site, suggesting that methane is indeed an important source of nutrition for this community. In addition, we document the presence at this site of a vestimentiferan siboglinid polychaete and the bivalve Acharax sp., both of which are typical components of deep-sea chemosynthetic communities. The remarkable similarity in biotic composition between this area and other deep-sea communities across the world supports the interpretation that these assemblages are historically connected across the global oceans, undergoing colonization from distant sites and influenced by local ecological features that select a stereotyped suite of specifically adapted organisms. [ABSTRACT FROM AUTHOR]

Calanoid copepods constitute the most numerous organisms not only in the pelagic realm, but also in the benthic boundary layer, which gives them an important role in the turnover of organic matter in the benthopelagic habitat. During seven expeditions to the South Atlantic and Southern Ocean, the diversity and biogeography of deep-sea benthopelagic calanoid copepods were studied. The communities of calanoids living in the vicinity of the seabed were characterized by high diversity comparable to many pelagic habitats, but low abundance of individuals. Members of the taxon Clausocalanoidea dominated the communities, and within this taxon most individuals belonged to detritivore calanoids characterized by sensory setae on the second maxillae or aetideid copepods. 73% of all genera classified as obligate or predominantly benthopelagic copepods detected during these expeditions were new to science and a vast number of genera and species have been described since then. Comparing the communities of calanoid genera between different regions, the assemblages in the Southern Ocean differed significantly from the Southeast and Southwest Atlantic. A latitudinal diversity gradient could be observed, with highest numbers of genera in the Southwest Atlantic and low numbers at stations in the Southern Ocean. Reviewing the literature, endemism for benthopelagic calanoids appeared to be low on a latitudinal range caused by connectivity in benthopelagic habitats through spreading water masses. However, considering the habitats structuring the water column vertically, a high number of genera are endemic in the benthopelagial and specialized to living within the vicinity of the seabed. [ABSTRACT FROM AUTHOR]

We have measured both prokaryotic heterotrophic production (PHP) and respiration ( R ), then providing direct estimates of prokaryotic growth efficiencies (PGE), in the upper mesopelagic zone (300–600 m) of the South Atlantic and Indian Oceans. Our results show that in situ R ranged 3-fold, from 87 to 238 μmol C m −3 d −1 . In situ PHP rates were much lower but also more variable than R (ranging from 0.3 to 9.1 μmol C m −3 d −1 ). The derived in situ PGE values were on average ~1.4% (from 0.3% to 3.7%), indicating that most of the organic substrates incorporated by prokaryotes were respired instead of being used for growth. Together with the few previous studies on PGE published before for the Atlantic Ocean and Mediterranean Sea, our findings support the hypothesis that the global mesopelagic zone represents a key remineralization site for export production in the open ocean. We also found a strong correlation between R and PGE with temperature across a gradient ranging from 8.7 to 14.9 °C. The derived Q 10 value of 3.7 suggests that temperature variability in the mesopelagic zone plays a significant role in the remineralization of organic matter. [ABSTRACT FROM AUTHOR]

An analysis of the mean three-dimensional horizontal circulation in the subtropical South Atlantic based on velocity fields derived primarily from Argo data and AVISO sea surface heights, collected in the years 2000-2012, provides new insight into the zonal and meridional transports in the subtropical gyre. The velocity fields reveal the reduction of the latitudinal extent of the subtropical gyre with increasing depth that is mainly due to a southward shift of the westward flowing branch of the subtropical gyre, which is most pronounced near the western boundary. An analysis of zonal and meridional transports in the subtropical gyre in five 400m thick layers from the surface to 2000m reveals an interior pathway from the South Atlantic Current (SAC) to the Southern South Equatorial Current (SSEC) between 18°W and 1°E. At 35°S the northward transport in this longitude band ranges from 5.5Sv (1Sv=1 Sverdrup=106m3s-1) in the shallowest layer to 3.5Sv in the deepest layer, and adds up to total transport of 14.6Sv in the upper 800m. Within the uncertainty of the estimated transports, these northward transports are consistent with the east-to-west strengthening of the SSEC in 18°W and 1°E (e.g. 14.2Sv in the upper 800m). For the SAC, the change of the transport has the correct sign, but the west-to-east shrinking of the transport is larger than the northward transport, which suggests a transfer of water from the SAC to the Antarctic Circumpolar Current. With respect to the boundary currents that are part of the subtropical gyre, the southward transport of the western boundary current in the upper 2000m increases from 5.2Sv at 28°S to 44.2Sv at 33°S. This is followed by a decrease to 22.2Sv at 36°S and another increase to 38.7Sv at 39°S. Further analysis shows that the increase of the transport by 15.2Sv between 31°S and 33°S is primarily due to the small recirculation cell just east of the Brazil Current that has a northward transport of 13.1Sv at 35°S in the upper 2000m. Along the eastern boundary, the transport of the Benguela Current within the upper 1200m at 35°S is 23.9Sv, increasing by about 10Sv between 37°S and 32°S. To the east of this current, the Benguela Poleward Undercurrent can be detected in the velocity and salinity fields derived for the core of the Antarctic Intermediate Water. This current extends as far south as 30°S and potentially even to 33°S. [ABSTRACT FROM AUTHOR]

Abstract: Deep-sea red crabs Chaceon ramosae and Chaceon notialis are commercially and ecologically important crustaceans in South Atlantic waters. With some overlapping occurring at the edge of the crabs’ distribution, the fisheries are managed separately in Brazil and Uruguay, with some differences in the regulations, although the stock is supposedly shared between the two countries. To assess genetic information on these two species, we examined the nucleotide sequence of the mitochondrial 16S rDNA and CO1 mtDNA genes in samples from the southern region. We also compared these data to sequences from other congeners. The genetic analysis revealed a clear separation between C. notialis and C. ramosae. In addition, we detected the existence of at least two different groups within the species that is currently recognized as C. notialis. This might indicate the existence of cryptic species, leading us to speculate about the presence of two different taxonomic entities, although further research is needed to resolve this issue. [Copyright &y& Elsevier]

Abstract: The exchange of heat and salt between the South Indian Ocean and South Atlantic Ocean, at the southern terminus of the Agulhas current, forms a crucial link in the global ocean circulation. It has been surmised that upstream retroflections in this current could produce temporary interruptions to the exchange, but that their impact would depend on the vertical extent of such retroflections and on their duration. The fortuitous presence at sea of a research vessel has now enabled us to investigate such an episode at subsurface levels in combination with remote sensing of the sea surface. We present here the first in situ evidence that an upstream or early retroflection can extend to a depth of well over 750m and last for 5 months. This event was likely triggered upstream by the happenstance of two Natal Pulses, large cyclonic eddies inshore of the Agulhas current. These eddies short-circuited the Agulhas with its Return current, leading to the shedding of three large Agulhas rings in quick succession. The arrival of a third cyclonic eddy when the Retroflection was still quite retracted did not lead to another ring shedding event. The resulting early retroflection may have had the effect of stalling the shedding of Agulhas rings and their motion towards the Cape Basin. However, these early retroflections are too scarce to allow generic statements on their generation or consequences, and the relation with large-scale environmental factors. It is likely that the observed withdrawal of the retroflection into the Transkei Basin is a fortuitous result of a series of contingent interactions. [Copyright &y& Elsevier]

Abstract: The properties of the meridional overturning circulation (MOC) and associated meridional heat transport (MHT) and salt fluxes are analyzed in the South Atlantic. The oceanographic data used for the study consist of Expendable bathythermograph (XBT) data collected along 27 sections at nominally 35°S for the period of time 2002–2011, and Argo profile data collected in the region. Previous estimates obtained with a shorter record are improved and extended, using new oceanographic sections and wind fields. Different wind products are analyzed to determine the uncertainty in the Ekman component of the MHT derived from their use. Results of the analysis provide a 9-year time series of MHT, and volume transport in the upper layer of the MOC. Salt fluxes at 35°S are estimated using a parameter introduced by numerical studies, the M ov that represents the salt flux and helps determine the basin scale salt feedback associated with the MOC. Volume and heat transport by the western and eastern boundary currents are estimated, and their covariablity is examined. Analysis of the data shows that the South Atlantic is responsible for a northward MHT with a mean value of 0.54±0.14PW. The MHT exhibits no significant trend from 2002 to 2011. The MOC varies from 14.4 to 22.7Sv with a mean value of 18.1±2.3Sv and the maximum overturning transport is found at a mean depth of 1250m. Statistical analysis suggests that an increase of 1Sv in the MOC leads to an increase of the MHT of 0.04±0.02PW. Estimates of the M ov from data collected from three different kinds of observations, contrary to those obtained from models, feature a positive salt advection feedback (M ov<0) suggesting that freshwater perturbations will be amplified and that the MOC is bistable. In other words, the MOC might collapse with a large enough freshwater perturbation. Observations indicate that the mean value of the Brazil Current is −8.6±4.1Sv at 24°S and −19.4±4.3Sv at 35°S, increasing towards the south. East of 3°E, the northward flowing Benguela Current and Agulhas rings have a net northward transport of 22.5±4.7Sv. No significant correlation is observed between the MOC and the Brazil Current transport, and most of the compensation derives from the eastern boundary and interior transports. Products from the Ocean general circulation model For the Earth Simulator (OFES) are used to validate methodology used to extend the XBT record, and to aid in the interpretation of the observed findings. [Copyright &y& Elsevier]

Abstract: This study provides new information about the composition, diversity and zoogeography of abyssal polychaetes in the little-studied South Eastern Atlantic (Angola Basin). During the austral winter of 2000, twenty-five box core samples (total area sampled 6m2) were taken along a 500-km transect in five work areas at depths exceeding 5000m. A total of 1047 individuals representing 86 species belonging to 32 families was collected. Well over half the polychaetes (58 species; 67%) appear to be new to science, with the highest number of new species among the Cirratulidae, Paraonidae, Phyllodocidae, Ampharetidae, Opheliidae, and Spionidae. Eight of these new species were among the 16 dominant species in the deep Angola Basin whereas, 32 species (37%) were considered to be rare with only 1–2 individuals collected. Species accumulation curves did not level off at a fixed number of species, indicating that diversity would increase with additional sampling. Polychaete community assemblages among box core samples were highly variable. Ten of the known species are biogeographically widespread outside the Angola Basin whereas five appear to be restricted to the deep Atlantic. Two species have only been recorded in the Southern Ocean, and one in the southern hemisphere. Twenty (35%) of the species considered to be new to science were also found in samples from the deep Southern Ocean, whereas eight of the known species found in the Angola Basin have not been reported from the Southern Ocean to date. Surface deposit feeders and carnivores were the dominant functional groups both in terms of number of individuals and number of species. Necessary steps to further our knowledge of the little-known abyssal ecosystem are discussed. [Copyright &y& Elsevier]

Abstract: Swarming is a fundamental part of the life of Euphausia superba, yet we still know very little about what drives the considerable variability in swarm shape, size and biomass. We examined swarms across the Scotia Sea in January and February 2003 using a Simrad EK60 (38 and 120kHz) echosounder, concurrent with net sampling. The acoustic data were analysed through applying a swarm-identification algorithm and then filtering out all non-krill targets. The area, length, height, depth, packing-concentration and inter-swarm distance of 4525 swarms was derived by this method. Hierarchical clustering revealed 2 principal swarm types, which differed in both their dimensions and packing-concentrations. Type 1 swarms were generally small (<50m long) and were not very tightly packed (<10ind.m−3), whereas type 2 swarms were an order of magnitude larger and had packing concentrations up to 10 times greater. Further sub-divisions of these types identified small and standard swarms within the type 1 group and large and superswarms within the type 2 group. A minor group (swarm type 3) was also found, containing swarms that were isolated (>100km away from the next swarm). The distribution of swarm types over the survey grid was examined with respect to a number of potential explanatory variables describing both the environment and the internal-state of krill (namely maturity, body length, body condition). Most variables were spatially averaged over scales of ∼100km and so mainly had a mesoscale perspective. The exception was the level of light (photosynthetically active radiation (PAR)) for which measurements were specific to each swarm. A binary logistic model was constructed from four variables found to have significant explanatory power (P<0.05): surface fluorescence, PAR, krill maturity and krill body length. Larger (type 2) swarms were more commonly found during nighttime or when it was overcast during the day, when surface fluorescence was low, and when the krill were small and immature. A strong pattern of diel vertical migration was not observed although the larger and denser swarms tended to occur more often at night than during the day. The vast majority of krill were contained within a minor fraction of the total number of swarms. These krill-rich swarms were more common in areas dominated by small and immature krill. We propose that, at the mesoscale level, the structure of swarms switches from being predominantly large and tightly packed to smaller and more diffuse as krill grow and mature. This pattern is further modulated according to feeding conditions and then level of light. [Copyright &y& Elsevier]