Pierrick Penven

Institute of Research for Development | IRD · Laboratoire d'Oceanographie Physique et Spatiale

This study aims to characterize how eddies shape the biogeochemistry of the Mozambique Channel using a physical-biogeochemical model that realistically simulates its interannual dynamics. The 20-year-long numerical simulation provides a comprehensive dataset for robust statistical analysis of thousands of mesoscale features using an eddy detection...

The shallow-water shrimp fishery is an important social and economic sector in Mozambique. However, catches of shrimps have been declining over the last decades, presumably due to poor recruitment. Climate change has been proposed as a potential cause of increased mesoscale eddy activity over the Mozambique Channel, which may have played a role in...

A regional ocean model was used to study the influence of the Madagascar Ridge on the circulation and eddy variability in the Agulhas Current system. In the control experiment, the model was run with a realistic bathymetry, whereas in the idealized run the bathymetry was modified by flattening Madagascar Ridge. When the Ridge was suppressed, no obv...

Western boundaries have been suggested as mesoscale eddy graveyards, using a diagnostic of the eddy kinetic energy (EKE) flux divergence based on sea surface height (η). The graveyard's paradigm relies on the approximation of geostrophy—required by the use of η—and other approximations that support long baroclinic Rossby waves as the dominant contr...

Western boundaries have been suggested as mesoscale eddy graveyards, using a diagnostic of the eddy kinetic energy (EKE) flux divergence based on sea surface height (η). The graveyard’s paradigm relies on the approximation of geostrophy — required by the use of η — and other approximations that support long baroclinic Rossby waves as the dominant c...

Equatorward decrease of mesoscale eddy abundance, and meridional variations of their mean properties in the tropical South‐East Atlantic Ocean have been investigated on the basis of horizontal length‐scales of geostrophic flows, and theories of two‐dimensional geostrophic turbulence on a β‐plane. Meridional variations of satellite‐derived altimetri...

Introduction Ocean fronts are moving ephemeral biological hotspots forming at the interface of cooler and warmer waters. In the open ocean, this is where marine organisms, ranging from plankton to mesopelagic fish up to megafauna, gather and where most fishing activities concentrate. Fronts are critical ecosystems so that understanding their spatio...

Output from a high-resolution ocean model, a wind reanalysis and a particle tracking tool are used to improve our understanding of the shelf circulation in an embayment off South Africa's east coast, known as the KwaZulu-Natal Bight. This region spans across roughly 140 km of coastline and is located between 29°S and 30°S. It is influenced by the s...

An investigation into the ocean response to a protracted (>48 h) strong south-westerly wind event averaging 9.6 m/s on the eastern Agulhas Bank, South Africa, using in situ instrument data from Algoa Bay and a high resolution (dx ∼1 km) ROMS ocean model, is presented. A coastal trapped wave (CTW) was shown to be associated with the event, the peak...

Western boundary currents are hotspots of mesoscale variability and eddy-topography interactions, which channel energy toward smaller scales and eventually down to dissipation. Here, we assess the main mesoscale eddies energy sinks in the Agulhas Current region from a regional numerical simulation. We derive an eddy kinetic energy (EKE) budget in t...

The East Madagascar Current (EMC) is one of the western boundary currents of the South Indian Ocean. As such, it plays an important role in the climate system by transporting water and heat toward the pole and recirculating to the large‐scale Indian Ocean through retroflection modes of its southern extension. Five cruise data sets and remote sensin...

Oceanic currents can profoundly reshape the seafloor and even modify the characteristics of turbidite systems. Multiple erosional and depositional features directly formed by bottom currents (i.e. contourites), as well as by the interaction between bottom currents and turbidity currents or turbidite systems (i.e. mixed turbidite-contourite systems)...

There is a general need for a broader base of information on the finer detail of ocean processes in the Eastern Agulhas Bank region. In this thesis, the Regional Ocean Modelling System (ROMS) was applied to resolve high resolution (~1km) bay and shelf scale ocean processes along the south eastern coastline of South Africa using an offline multi-nes...

The South‐East Madagascar Bloom, one of the most compelling biogeochemical features of the Indian Ocean, occurs sporadically during austral summer in the oligotrophic waters south‐east of Madagascar, where it can cover up to 1% of the global ocean surface area. Its spatial extension and its timing are highly variable. A high‐resolution biophysical...

Evidences of sedimentation affected by oceanic circulation, such as nepheloid layers and contourites are often observed along continental slopes. However, the oceanographic processes controlling sedimentation along continental margins remain poorly understood. Multibeam bathymetry and high‐resolution seismic reflection data revealed a contourite de...

This study addresses the dynamics of the Agulhas inshore front in the submesoscale range upstream of 26° E. Submesoscale frontal eddies are observed in the vicinity of Port Elizabeth (26° E) from satellite images and in observations collected from underwater gliders. Using a submesoscale‐resolving numerical model (dx ∼ 0.75 km), we are able to simu...

We present a combined study of the geomorphology, sedimentology, and physical oceanography of the Mozambique Channel to evaluate the role of bottom currents in shaping the Mozambican continental margin and adjacent Durban basin. Analysis of 2D multichannel seismic reflection profiles and bathymetric features revealed major contourite deposits with...

The South‐East Madagascar Bloom occurs in an oligotrophic region of the southwest Indian Ocean. Phase locked to austral summer, this sporadic feature exhibits substantial temporal and spatial variability. Several studies, with different hypotheses, have focused on the initiation mechanism triggering the bloom, but none has been as yet clearly subst...

Mixed turbidite-contourite systems can be found in oceans where bottom currents and turbidity currents interact. The Zambezi turbidite system, located in the Mozambique Channel (SW Indian Ocean), is one of the largest sedimentary systems in the world in length and area of the related catchments. The oceanic circulation in the Mozambique Channel is...

Mixed turbidite-contourite systems can be found in oceans where bottom currents and turbidity currents interact. The Zambezi turbidite system, located in the Mozambique Channel (SW Indian Ocean), is one of the largest sedimentary systems in the world in length and area of the related catchments. The oceanic circulation in the Mozambique Channel is...

The Agulhas Current plays a significant role in both local and global ocean circulation and climate regulation, yet the mechanisms that determine the seasonal cycle of the current remain unclear, with discrepancies between ocean models and observations. Observations from moorings across the current and a 22-year proxy of Agulhas Current volume tran...

South Indian Ocean eddies (SIDDIES), originating from a high evaporation region in the eastern Indian Ocean, are investigated by tracking individual eddies from satellite data and co‐located Argo floats. A subsurface‐eddy identification method, based on its steric dynamic height anomaly, is devised to assign Argo profiles to surface eddies (surfSID...

A high-resolution, two-way nested Regional Ocean Modeling System, forced with monthly climatologies, has been set up for the Sofala Bank and adjacent deeper ocean of the Mozambique Channel to investigate the role of offshore mesoscale eddies on the shelf circulation, hydrographic structures and river plumes. The model is shown in comparison with av...

Cruise datasets, satellite remote sensing observations and model data analyses are combined to highlight the existence of a coastal surface poleward flow in the south-west of Madagascar: the South-west MAdagascar Coastal Current (SMACC). The SMACC is a relatively shallow (<300 m) and narrow (<100 km wide) warm and salty coastal surface current, whi...

Madagascar's southern coastal marine zone is a region of high biological productivity which supports a wide range of marine ecosystems, including fisheries. This high biological productivity is attributed to coastal upwelling. This paper provides new insights on the structure, variability and drivers of the coastal upwelling south of Madagascar. Sa...

The dynamics and seasonal variability of jet currents on the southern Benguela shelf-edge are investigated using a climatologically forced Regional Ocean Modelling System (ROMS) model. The jet is primarily forced by the intense horizontal gradients that exist across the southern Benguela shelf. These gradients are set up by nearshore cooling via th...

Coupled ocean–atmosphere simulations are carried out for the Mozambique Channel, the Agulhas Current system, and the Benguela upwelling system to assess the ocean surface current feedback to the atmosphere and its impact on the Agulhas Current (AC) retroflection and leakage. Consistent with previous studies, the authors show that the current feedba...

The northern Gulf of Guinea is a part of the eastern tropical Atlantic where oceanic conditions due to the presence of coastal upwelling may influence the regional climate and fisheries. The dynamics of this coastal upwelling is still poorly understood. A sensitivity experiment based on the Regional Oceanic Modeling System (ROMS) is carried out to...

A modelling approach is used to investigate the influence of the Agulhas on the southern Benguela system. Two climatological ROMS simulations are run that are identical except that in one of them the effect of the Agulhas is removed. Comparing their output allows for a clear indication of the role of the Agulhas on both the large-scale and shelf dy...

Sardinella aurita is the most abundant small pelagic fish in the northern Gulf of Guinea. Its reproduction and recruitment depend crucially on environmental conditions. We developed a biophysical model of S. aurita early life history by coupling offline an individual-based model with the regional oceanic modeling system (ROMS). We used this model t...

The Sofala Bank, a wide shelf located along the central coast of Mozambique, hosts tides with high amplitudes. The Regional Ocean Modelling System (ROMS) was used to analyse the tidal currents on the bank and to investigate their effects on the stratification and generation of tidal fronts. During spring tides, barotropic tidal currents with maximu...

S. aurita is the most abundant small pelagic fish in the northern Gulf of Guinea. Its reproduction and recruitment depend crucially on environmental conditions. We developed a biophysical model of S. aurita early life history by coupling offline an individual-based model with the regional oceanic modeling system (ROMS). We used this model to invest...

The oceanic circulation in the upper layers of the north of the Gulf of Guinea is analyzed, as inferred from in situ observations and numerical simulations. This particular region, in spite of the presence of a coastal upwelling and its impact on resources and regional climate, is still poorly documented. Cruises carried out in the framework of dif...

A regional ocean model was used to simulate the annual cycle of the upper-ocean dynamics and its influence on ocean properties in the tropical western Indian Ocean. Surface winds and heat fluxes from the National Centers for Environmental Prediction (NCEP) reanalysis forced the model (Model_NCEP) with initial and lateral boundary conditions derived...

We used a coupled physical-biogeochemical model to investigate how the strong eddy activity typical of the Mozambique Channel affects biological production. A numerical experiment was carried out, in which mesoscale dynamics were suppressed by cancelling the nonlinear terms for horizontal momentum in the Naviers-Stokes equation. Mesoscale dynamics...

The objective of this study is to document and shed light on the circulation around the Delagoa Bight region in the southern Mozambique Channel using a realistic modelling approach. A simulation including mesoscale forcings at the boundaries of our regional configuration succeeds in reproducing the general circulation in the region as well as the e...

The dynamical link between the Indian Ocean and Atlantic Meridional Overturning Circulation (AMOC) remains poorly understood. This partly arises from the complex Agulhas leakage, which occurs via rings, cyclones and non-eddy flux. Hindcast simulations suggest leakage has recently increased, but have not decomposed this signal into its constituent m...

Cyclonic eddies generated downstream of Cape Palmas and Cape Three points have been suggested to contribute to the coastal upwelling along the northern coast of the Gulf of Guinea. A numerical analysis using a high resolution model is used to investigate the mesoscale activity and the coastal upwelling generation processes. An eddy detection and tr...

In this study we used more than seventeen years of satellite altimetry observations and output from an ocean model to investigate the mesoscale eddy variability and forcing mechanisms to the south of Madagascar. Analysis of energy conversion terms in the model has shown seasonality on eddy formation, both by barotropic and baroclinic instabilities:...

The relationship between the Agulhas Current and the Agulhas leakage is not well understood. Here, this is investigated using two basin-scale and two global ocean models, of incrementally increasing resolution. The response of the Agulhas Current is evaluated under a series of sensitivity experiments, in which idealised anomalies, designed to geome...

A regional ocean model was used to study interannual variations in the Tanzanian shelf region and offshore in the tropical western Indian Ocean for the period 1980–2007. The model was forced with surface winds and heat fluxes from the National Centers for Environmental Prediction (NCEP) reanalysis, and its initial and lateral boundary conditions we...

The objective of this study is to document the circulation in the vicinity of La Réunion and Mauritius islands, i.e. within 500 km offshore, on the intraseasonal time scale, using a high-resolution realistic modeling strategy. The simulated sea level anomalies, water mass properties and large-scale circulation compare favorably with satellite and i...

Three methods are proposed for the inclusion of inertia when deriving currents from sea surface height (SSH) in the Mozambique Channel: gradient wind, perturbation expansion and an iterative method. They are tested in a model and applied to satellite altimetry. For an eddy of 25 cm amplitude and 100 km radius, typical of Mozambique Channel rings at...

The impact of mesoscale activity on phytoplankton and nutrient distribution in the Mozambique Channel was simulated by coupling a biogeochemical model (PISCES) with a regional oceanic model (ROMS). Examples of the effects of eddies on the biogeochemistry of the Mozambique Channel are presented to illustrate the complexity of the system. In the mode...

A multidisciplinary programme, MESOBIO (Influence of mesoscale dynamics on biological productivity at multiple trophic levels in the Mozambique Channel) was undertaken in the Mozambique Channel within the framework of a scientific partnership between France and South Africa. MESOBIO focused on the signature of the highly energetic eddy dynamics in...

Analysis of satellite altimetry observations, transports estimates from a mooring array, as well as output from two different numerical ocean circulation models (ROMS and HYCOM), have been used to investigate the mesoscale eddy properties and transport variability in the Mozambique Channel. The power spectral density of model transports at 17 S ind...

Analysis of satellite altimetry observations, transports estimates from a mooring array, as well as output from 2 different numerical ocean circulation models (ROMS and HYCOM), have been used to investigate the mesoscale eddy properties and transport variability in the Mozambique Channel. The power spectral density of model transports at 17oS indic...

The impact of mesoscale activity on phytoplankton and nutrient distribution in the Mozambique Channel was simulated by coupling a biogeochemical model (PISCES) with a regional oceanic model (ROMS). Examples of the effects of eddies on the biogeochemistry of the Mozambique Channel are presented to illustrate the complexity of the system. In the mode...

Large-scale, multiyear climatic variations in the Benguela upwelling region have been observed from time to time and have been dubbed "Benguela Niños as an analogue to the Pacific event. The Benguela Nifio, like its Pacific counterpart, has a strong effect on regional fisheries and this in turn has led to an effort to forecast these events. Benguel...

Three scales of LOW variability were found to be amenable to forecasting as well as being suitable to provide information that would be of use to management response plans.u⊙ Short time scale: 7 day lead events linked to local wind variability and "HABs"⊙ Medium Time Scale: 2 month lead events linked to "ETSA" easterly equatorial winds⊙ Decadal Tim...

The Agulhas Cur rent plays a crucial role in the thermohaline circulation through its leakage into the South Atlantic. Under both past and present climates, the trade winds and westerlies could have the ability to modulate the amount of Indian - Atlantic inflow. Compelling arguments have been put forward suggesting that trade winds alone have littl...

Understanding the dynamics of the coastal oceans is important for managing coastal ecosystems, and hence for protecting lives and planning sustainable development. Among other countries in the southwest Indian Ocean, Mozambique has a greater number of environmental problems to solve. These problems include the landing of tropical cyclones1 along th...

A multidisciplinary programme, MESOBIO (Influence of mesoscale dynamics on biological productivity at multiple trophic levels in the Mozambique Channel) was undertaken in the Mozambique Channel within the framework of a scientific partnership between France and South Africa. MESOBIO focused on the signature of the highly energetic eddy dynamics in...

Sea surface temperature in the central-eastern equatorial Atlantic has a seasonal cycle far bigger than that of the Pacific, but interannual anomalies smaller than those of the Pacific. Given the amplitude of seasonal SST variability, one wonders whether the seasonal cycle in the Atlantic is so dominant that it is able to strongly influence the evo...

South of Africa, the Agulhas Current retroflects and a portion of its waters flows into the South Atlantic Ocean, typically in the form of Agulhas rings. This flux of warm and salty water from the Indian to the Atlantic Ocean (the Agulhas leakage) is now recognized as a key element in global climate. An Agulhas leakage shutdown has been associated...