Acoustic propagation in the Brazil current system off the Southeastern coast

The Brazil Current (BC) is perhaps the less studied subtropical boundary current of the world ocean. Within this region, the BC develops vigorous meanders and rings. A combination of numerical simulations and observational studies are important tools to unravel these phenomena. Direct current measurements are rare and usually too short to depict the mean, long term circulation patterns. Similarly, quasi-synoptic hydrographic data in the region is sparse. Acoustic waves are an efficient tool for covering large regions of the water column in a synoptic way. Acoustic tomography can be therefore useful to better predict through inversion for the effective sound speed field and its assimilation to a circulation model the oceanographic fields of interest (temperature, salinity, density). Such information is particularly important for initialization and data assimilation to regional models for which small and meso-scale processes are of fundamental interest. In this paper, a preliminary study of acoustic propagation modeling through two vertical sections off the Brazilian southeastern coast is presented. Actual hydrographic data from DEPROAS 2003 sea trial serve to construct the physical parameters that characterize these sections

First observational evidence of a North Madagascar Undercurrent

<i>In situ</i> observations reveal a southeastward-directed North Madagascar Undercurrent (NMUC) below and opposite to the equatorward-directed North Madagascar Current (NMC) off Cape Amber, at the northern tip of Madagascar. Results show an undercurrent hugging the continental slope with its core at 460 m depth and velocities over 0.7 m s-1. Its volume transport is estimated to be 3.1–3.8 Sv, depending on the velocity extrapolation methods used to fill in the data gaps near the slope (no-slip and full-slip, respectively). The thermohaline characteristics show a saltier and warmer NMUC, compared to the surrounding offshore waters, transporting mainly South Indian Central Water. Also, strong horizontal gradients of density are found in the NMUC domain. An inshore cell of coastal downwelling due to Ekman Transport toward the coast is identified, which can explain, at least in part, the strong baroclinic pressure gradients as well as the NMUC development and possible persistence

COBRA Master Class: Providing deep-sea expedition leadership training to accelerate early career advancement

Leading deep-sea research expeditions requires a breadth of training and experience, and the opportunities for Early Career Researchers (ECRs) to obtain focused mentorship on expedition leadership are scarce. To address the need for leadership training in deep-sea expeditionary science, the Crustal Ocean Biosphere Research Accelerator (COBRA) launched a 14-week virtual Master Class with both synchronous and asynchronous components to empower students with the skills and tools to successfully design, propose, and execute deep-sea oceanographic field research. The Master Class offered customized and distributed training approaches and created an open-access syllabus with resources, including reading material, lectures, and on-line resources freely-available on the Master Class website (cobra.pubpub.org). All students were Early Career Researchers (ECRs, defined here as advanced graduate students, postdoctoral scientists, early career faculty, or individuals with substantial industry, government, or NGO experience) and designated throughout as COBRA Fellows. Fellows engaged in topics related to choosing the appropriate deep-sea research asset for their Capstone “dream cruise” project, learning about funding sources and how to tailor proposals to meet those source requirements, and working through an essential checklist of pre-expedition planning and operations. The Master Class covered leading an expedition at sea, at-sea operations, and ship-board etiquette, and the strengths and challenges of telepresence. It also included post-expedition training on data management strategies and report preparation and outputs. Throughout the Master Class, Fellows also discussed education and outreach, international ocean law and policy, and the importance and challenges of team science. Fellows further learned about how to develop concepts respectfully with regard to geographic and cultural considerations of their intended study sites. An assessment of initial outcomes from the first iteration of the COBRA Master Class reinforces the need for such training and shows great promise with one-quarter of the Fellows having submitted a research proposal to national funding agencies within six months of the end of the class. As deep-sea research continues to accelerate in scope and speed, providing equitable access to expedition training is a top priority to enable the next generation of deep-sea science leadership

An observational study of the western boundary currents in the Indian and South Atlantic Oceans

In this thesis we have investigated different aspects of the WBCs in the Indian and South Atlantic Oceans, based on observational data sampled both in situ and from satellites. In October 2010 an array of five moorings were deployed off eastern Madagascar, nominally at 23S, as part of the “INdian-ATlantic EXchange in present and past climate” (INATEX) observational program. The instruments remained in the water for about 2.5 years, until March 2013. Based on the INATEX data, we study the East Madagascar Current (EMC) in terms of its observed velocities, estimated volume transport and variability. The EMC is dominated by a nearly bi-monthly (45–85 days) period band. Satellite data show that such variability is explained by westward-propagating eddies impinging on the EMC. Anticyclonic eddies strengthen the flow while cyclonic eddies attenuate the EMC transport. Besides the surface patterns of the western boundary currents, the presence of an undercurrent flowing in opposite direction and beneath the surface cur rent is a recurring feature observed in different WBC systems. This thesis is also dedicated to the study of this counter flow, observed below the EMC: the equatorward East Madagascar Undercurrent (EMUC). Also supported by data from the INATEX moorings, we show that the EMUC is hugging the continental slope, with a core at a depth of 1200 m. Its mean equatorward volume transport amounts to nearly 10% of the mean transport estimated for the surface poleward EMC. On approaching Madagascar, the bifurcation of the SEC also generates the equatorward directed North Madagascar Current (NMC). We here provide the first evidence of the existence of a poleward counter current below the NMC, which we named North Madagascar Undercurrent (NMUC). Two interocean teleconnections, which take place downstream and upstream of the EMC system, are also investigated in this study. First, we explore the connection between the WBCs in the Indian and South Atlantic Oceans. The EMC, as well as the flow in the Mozambique Channel, are sources for the Agulhas Current (AC). In turn, the AC flows downstream until the southern tip of Africa, where part of the water transported by this current turns back into a loop to the Indian Ocean, generating an important feature known as Agulhas Retroflection. Anticyclonic eddies are created and are released into the Atlantic Ocean by this retroflection process, establishing the so-called Agulhas Leakage. We reveal that this mechanism of retroflection also represents a pulse of energy that crosses the Atlantic, imposing a nearly trimonthly period of variability on the Brazil Current, at the Santos Basin. Second, we focus on the teleconnection between Pacific and Indian Oceans by means of both Indonesian Throughflow and South Indian tropical gyre. The first represents the waters passing through the Indonesian islands, while the latter is a clockwise gyre near the equatorial region. The SEC, which is the northern branch of the subtropical gyre, can also be interpreted as the southern branch of the tropical gyre, and it has an important role in redistributing waters from the Indonesian Throughflow into the Indian Ocean. We show that the tropical gyre has a marked seasonal cycle. An analysis of major forcing mechanisms suggests the interaction of basin-scale wind stress curl, local-scale wind stress forcing, remote forcing driven by the Indonesian Throughflow, as well as westward-propagating Rossby waves

The East Madagascar Current: Volume Transport and Variability Based on Long-Term Observations

This study provides a long-term description of the poleward East Madagascar Current (EMC) in terms of its observed velocities, estimated volume transport, and variability based on both ~2.5 yr of continuous in situ measurements and ~21 yr of satellite altimeter data. An array of five moorings was deployed at 23°S off eastern Madagascar as part of the Indian–Atlantic Exchange in present and past climate (INATEX) observational program. On average, the EMC has a horizontal scale of about 60–100 km and is found from the surface to about 1000-m depth. Its time-averaged core is positioned at the surface, at approximately 20 km from the coast, with velocity of 79 (±21) cm s-1. The EMC mean volume transport is estimated to be 18.3 (±8.4) Sverdrups (Sv; 1 Sv = 106 m3 s-1). During the strongest events, maximum velocities and transport reach up to 170 cm s-1 and 50 Sv, respectively. A good agreement is found between the in situ transport estimated over the first 8 m of water column [0.32 (±0.13) Sv] with the altimetry-derived volume transport [0.28 (±0.09) Sv]. Results from wavelet analysis display a dominant nearly bimonthly (45–85 days) frequency band of transport variability, which explains about 41% of the transport variance. Altimeter data suggest that this band of variability is induced by the arrival of westward-propagating sea level anomalies, which in turn are likely represented by mesoscale cyclonic and anticyclonic eddies. Annual averages of the altimeter-derived surface transport suggest that interannual variabilities also play a role in the EMC system

Water mass, front and meanders of the Brazil Current seen through acoustics: a preliminary study

The Brazil Current (BC) is perhaps the least studied subtropical boundary current of the world's oceans. Within this region, the BC develops vigorous meanders and rings. A combination of numerical simulations and observational studies are important tools for unravelling these phenomena. Direct current measurements are rare and usually too short to depict the mean, long term circulation patterns. Similarly, quasi-synoptic hydrographic data in the region is sparse. Acoustic waves are an efficient tool for covering large regions of the water column in a synoptic way. Acoustic tomography can, therefore, be useful to better predict, through inversion for the effective sound speed field and its assimilation to a circulation model, the oceanographic fields of interest (temperature, salinity, density). Such information is particularly important for initialization and data assimilation to regional models for which small and meso-scale processes are of fundamental interest. In this paper, a preliminary study of acoustic propagation modelling through one vertical section off the Brazilian southeastern coast is presented. The acoustic rays are trapped in a minimum sound speed channel bounded by Antarctic Intermediate Water and Upper Circumpolar Deep Water. Between this so-created deep channel and the shel break, one interesting region from the acoustic viewpoint is identified. Notable variations in the transmission loss field are found in this region when the Brazil Current front is moving. In addition, the results show the baroclinic currents more sensitive to salinity variations than sound speed structure, as well as acoustic propagation

The Report of Growth of the Main Tree Species in the Kyushu University Forests in the Miyazaki district.

まえがき　I 調査の目的 II 調査の方法　III 調査対象樹種および本数　IV　供試材採取地の環境および調査結果について　V　むすび　参考文献The results of the surveys regarding the growths of the main tree species in the Kyushu University Forests in Miyazaki District and vicinity are shown in Fig. 16 \u22Comparative Table of Total Volume\u22 and Fig. 17 \u22Comparative Table of Volume Growth.\u22 As seen in the tables, SUGI (Cryptomeria Japonica D. Don,) is the most vigorousin growth, followed by AKA MATSU (Pinus densiflora Sieb. et Zucc.) and MOMI.(Abies firma Sieb. et Zucc.) SUGI occupies relatively small area per tree and is the most promising in the stand growth, and MATSU and MOMI are also promising species of good growth if the location is properly selected. With respect to MOMI, however, it has a drawback in that it takes long in growing the seedling. Therefore, at the present stage, it is necessary to study into rapid methods of growing the seedling. KIHADA (Phellodendendron amurense Lupr.) is a promising species inthat both wood and bark are utilized, but the other species do not appear to be promising. Though not included in this survey, the growth of HINOKI (Chamaecyparis obtusa Sieb. et Zucc) was good in the forests planted with HINOKI of 25 years of age or younger. In view of the elevation and other conditions of the Kyushu University Forests in Miyazaki District, HINOKI seems to be a very promising species for planting

Seasonal atmospheric and oceanographic factors influencing poleward mangrove expansion in the southeastern American coast

Mangrove ecosystems are distributed worldwide, along tropical and subtropical coastlines. For a long time, mangrove biogeographers have been challenged by the question: why is mangrove distribution restricted to its current latitudinal limits? The Araranguá estuary in Brazil is located ~75 km beyond the eastern South America mangrove limit. Despite its geomorphology apparently being suitable for mangrove colonization, mangroves have been reported absent from this estuary. In this work, we analyze key environmental variables (such as the longest available observational in-situ records of air temperature) and provide an assessment of other environmental players (such as the adjacent ocean circulation and upwelling system) to better understand which factors could be determinant in the species range limits in eastern South America. Our results and assessment suggest that, depending on the season, multiple factors could combine to prevent a poleward dispersion of mangrove species. These are mainly the northward-directed longshore drift which dominates throughout the year and the high occurrence of chilling events during winter, although seasonal upwelling of cold waters in spring and summer could also influence the propagules’ viability

On the double sampling Method

An array of five moorings was deployed at 23°S off eastern Madagascar and maintained for about 2.5 years as part of the “INdian-ATlantic EXchange in present and past climate” (INATEX) experiment. The observations reveal a recurrent equatorward undercurrent (during 692 of 888 days), the East Madagascar Undercurrent (EMUC), flowing below the poleward surface East Madagascar Current (EMC). The average core of the undercurrent was found near the continental slope, at a depth of 1260 m and at an approximate distance of 29 km from the coast, with mean velocities of 6.4 (±4.8) cm s-1. Maximum speeds reach 20 cm s-1. The mean equatorward volume transport is estimated to be 1.33 (±1.41) Sv with maxima up to 6 Sv. The baroclinic/barotropic partitioning of the geostrophic flow shows a persistent equatorward baroclinic velocity in the undercurrent core, which is sometimes inhibited by a stronger poleward barotropic contribution. The wavelet spectrum analysis of the transport time series displays two dominant frequency bands: (i) nearly bi-monthly (46–79 days), previously observed in the surface EMC, and attributed to the forcing of barotropic waves generated in the Mascarene Basin; and (ii) nearly semi-annual (132–187 days), which seems to be related to the semi-annual cycle in the equatorial winds near the Indian Ocean eastern boundary. A historical dataset of temperature–salinity Argo profiles was used to investigate the spatial variability of the thermohaline properties at intermediate levels. Lastly, Argo-derived velocities suggest an undercurrent flowing upstream until approximately 17°S