Aline Arens

Name : Aline ARENS

Title : Biogeochemical fluxes in the Mozambique Channel : connection between Sofala Bank and the Scatter Islands of the Indian Ocean

Supervisors : Pierrick Penven (director), Fanny Chenillat (ACTIMAR), Stephane Pous (LOCEAN), Fialho Nehama (ESCMC), Bernardino Malawene (CMR)

Start date : November 2024

Funding : 50% ANR (project PEPR BRIDGES AVATAR)/ 50% UBO

 

WHAT ? The Mozambique Channel, located between the southeastern coast of Africa and the island of Madagascar, plays a vital role in biogeochemical processes. The region's biogeochemistry is intricately linked to the presence of Mozambique Channel rings and eddies. In an ocean primarily characterized as oligotrophic, nutrient availability is crucial for biological production, with coastal sources being the primary contributors. These sources, including rivers like the Zambezi, Pungue, or Limpopo, transport substantial quantities of organic matter, sediments, and essential elements such as nitrogen and phosphorus, enriching the channel's waters. Coastal upwelling, exemplified by the Angoche upwelling cell (Malauene et al., 2015), also significantly contributes to coastal nutrient content. The turbulent transport of nutrient-rich coastal waters can manifest as filaments around eddies or in-between dipoles (Roberts et al., 2014; or as observed during the RESILIENCE campaign, Penven et al., 2024). Eddies are established to play a fundamental role in transporting material from the coast offshore, impacting the broader marine ecosystems. In addition recent simulation have shown that a significant amount of nutrient could originate from the northern side of the Mozambique Channel (Chenillat, 2024).

For the Scattered Islands in the Indian Ocean, including Bassas da India and Europa, the eddy transport could represent a significant additional source of nutrients compared to a more typical island mass effect. This prompts the question: What is the distribution of nutrient sources for Sofala Bank and the Mozambique coasts, and how does this impact the ecosystems of the Scattered Islands in the Indian Ocean? Understanding the biogeochemical dynamics of the Mozambique Channel is crucial for preserving the health of its marine ecosystems in the context of climate change.

 

HOW ? To achieve these goals, new coupled physics-biogeochemistry realistic eddy-resolving simulations based on CROCO-PISCES will be conducted. Previous work has demonstrated the ability of ROMS_AGRIF / CROCO to resolve the turbulent dynamics of the region (Halo et al., 2014) and PISCES for biogeochemistry (Jose et al., 2014; 2016). Recent simulations with CROCO-PISCES (Chenillat, 2024) will be further developed based on the OceanFrontChange project and RESILIENCE campaign. Special attention will be given to the typical processes of the Mozambique Channel, including eddies, tides, and rivers. Long simulations over the 2000-present period will be conducted, comparing them with available observations and using lateral boundary conditions from a basin-scale NEMO-PISCES simulation. Sensitivity studies will quantify the role of different sources, and future scenarios will be explored in collaboration with colleagues from the PEPR BRIDGES (see https://www.bridges-wio.com/fr/). Comparisons will be made with satellite observations and data from the MESOBIO and RESILIENCE campaigns, particularly addressing the island mass effect for the Scattered Islands in the Indian Ocean. The research will benefit from the expertise in CROCO-PISCES modeling in the region from the supervising team and with access to sufficient computing resources from the Jean-Zay calculator at IDRIS under the MOONRISE project (PI P. Penven).