During the RESILIENCE cruise aboard the R/V Marion Dufresne II (April 19-24 May 2022), a high-resolution in situ observation campaign investigated a mesoscale dipole in the Mozambique Channel, composed of a large anticyclonic ring and a cyclonic eddy. Using an innovative adaptive sampling strategy to track its movement, we employed continuous observing systems, including a Moving Vessel Profiler and Acoustic Doppler Current Profilers, to capture high-resolution vertical sections. The results revealed a distinct dipolar structure: The 250 km-wide anticyclonic ring featured low chlorophyll and homogeneous waters, while the smaller cyclonic eddy exhibited higher chlorophyll concentrations and pronounced salinity variations. These include patches, vertically stacked layers, and filaments, reflecting a mix of contrasted water masses from the southern Mozambique Channel and the Sofala Bank. A central jet between the eddies exhibited horizontal velocities up to 130 cm s-1 , facilitating significant offshore transport exceeding 10 Sverdrups in the upper 250 m and emphasizing the dipole's role in eastward water movement. Vertical velocities, derived from the Quasi-Geostrophic Omega equation, highlighted the influence of smaller-scale structures in driving vertical motions, reaching 40 m day-1 at depth. Lagrangian particle trajectories revealed the dipole's spiraling structure and its connectivity to coastal waters. These findings show that Mozambique Eddy-Ring Dipoles efficiently transport properties from the continental shelf to the open ocean, enhancing regional ecosystem connectivity. This work provides new insights into their biogeochemical, biological and ecological significance, challenging traditional cyclonic/anticyclonic eddy paradigms, and setting the foundation for future studies on mesoscale dipoles in the region.

The oceans loom large in our imaginations as ever fascinating, ever immense, ever mysterious, and at times, inhospitable. Yet, how the oceans function and carry heat, salt, freshwater, goods, and services around the globe is a fundamental part of what makes our world go round. Here, we introduce readers to the underlying principles governing what drives ocean currents, how solar radiation is stored as heat, and how salt and other tracers are spread by the oceans across the planet. We will explore how this all takes place in a range of marine environments, such as estuaries, the deep ocean basins, the shallow continental shelf seas, and the ice-covered polar oceans. Finally, we will discuss the impact and feedback of the ocean on earth's climate.

Satellite altimetry data provide a solution to the lack of in situ tide gauge data, which are essential for comprehending various marine processes worldwide. In the present study, we seek to validate ALES-retrieved sea-level data against tide gauge observations from four ground stations on the coast of Mozambique. The approach consisted of extracting data from selected tracks of the Jason-1, Jason-2 and Jason-3 missions, and processing it to (i) remove outliers, (ii) collocate alongside tide gauge data, (iii) remove the tidal component and detrend, and (iv) perform a set of statistical analyses. Good agreement was found between the altimetry and tide gauge data in three of the four stations (Maputo, r = 0.59; Inhambane, r = 0.87; and Pemba, r = 0.75), with the exception of Beira. The annual and semi-annual cycles in the two datasets revealed that the altimetry signal is smaller in amplitude and ahead (with a few exceptions) of tide gauge by a varying number of days in each location. Both the annual and semi-annual cycles are far more comparable in Pemba, where the amplitude in particular has the same order of magnitude, followed by the Maputo station. The study concluded that the selected altimetry data for Pemba and Maputo stations are valid and can be used for coastal risk analysis and other applications. No altimetry data could be validated for Inhambane and Beira stations due to lack of consistent and sufficiently long tide gauge records. This difficulty urges the need for improved maintenance practices of ground stations located near human settlements that rely on sound information of the sea level and its variability to protect lives, infrastructure and livelihoods.

Resumo: A zona costeira é uma unidade territorial de transição entre o domínio marinho e terrestre; caracterizada pela deposição dos sedimentos que podem ser distinguidos pelo seu tamanho, forma e composição. Esses sedimentos são controlados pelos fatores hidrodinâmicos governantes no ambiente. Este trabalho objetiva-se analisar a variação da distribuição sedimentar das praias de Madal e Zalala, localizadas na Província da Zambézia, Moçambique, visando compreender o padrão de transporte de sedimentos ao longo da praia, e inferir a energia de agitação marítima típica que chega às praias com base na distribuição dos sedimentos. Foram coletadas dezoito amostras de sedimentos em ambas as praias, ao longo de três níveis definidos: Linha Alta da Maré, Zona Intermédia e Linha Baixa da Maré. As amostras foram submetidas a análises granulométricas e determinação de parâmetros estatísticos. Os sedimentos dos ambientes são maioritariamente finos a muito finos, moderadamente a bem selecionados, de assimetria variando de negativa a muito positiva e com predominância de curvas mesocúrticas a platicurticas nas linhas Alta e Baixa da Maré, e mesocurtica na Zona Intermédia da Maré. Os agentes de transporte como ondas, correntes e ventos fazem a seleção dos sedimentos ao longo das praias, destacando-se mais as ondas, que fazem a remoção das partículas mais finas durante o fluxo e refluxo da onda, em sincronismo com a variação da maré, depositando os sedimentos mais finos na Linha Alta da Maré. Palavras-chave: Praias Arenosas; Tamanho do Grão; Distribuição Sedimentar. Abstract: The coastal zone is a territorial unit of transition between the marine and terrestrial domain; characterized by deposition of sediments that can be distinguished by their size, shape and composition. These sediments are controlled by the governing hydrodynamic factors in the environment. This work analyses the sedimentary distribution variation of the beaches of Madal and Zalala, in the Zambezi Province, Mozambique,

The Zambezi River plume constitutes a sizable feature in the horizontal distribution of both surface salinity and suspended sediments, and it spreads both downstream and upstream, influencing substantially the coastal ecosystems. Here we present the results of several numerical experiments conducted using the Regional Oceanic Modeling System, to investigate the plume’s response to impulsive wind forcing. The model uses realistic geometry and bathymetry, as well as constant discharges emanated from three point sources. Different wind directions and magnitudes were explored, including a daily oscillating wind field. In the absence of wind forcing, a modest discharge generates a plume that propagates northeastwards trapped to the coast. A constant wind field can alter the plume shape to become either a “coastal current” or a “large bulge”, depending on the predominant wind direction. The “coastal current” characterized by a northeastward (downstream) spreading of the plume reaching up to 180 km was directly related to a downwelling favorable winds. While the “large bulge” characterized by an increased upstream penetration is related to upwelling-favorable winds. Diurnal breezes were effective in transforming the trajectories of surface water particles into ellipsoids, as well as promoting additional mixing of the plume and ambient waters. The realistic wind field can transport plume waters to nearly 120 km downstream, 75 km upstream, and 65 km seaward.