Across the Shelf Edge: Generation and Dispersal of Harmful Algal Blooms in Northern Omani Waters

This project aims to resolve the mechanisms that cause and disperse harmful algal blooms (HABs) along the northern Omani coasts. The Sea of Oman frequently experiences HABs that can compromise food and water security in Oman and the surrounding states. Algal blooms directly affect fisheries, aquaculture, fresh-water supply from desalination plants as well as naval operations and a growing tourism industry. While the general phenology of these HABs is well studied, critical links in the local ocean dynamics that control their generation and distribution are still not understood. The most prominent circulation features within the Sea of Oman are the outflow of the Arabian Gulf Water (AGW); an energetic field of persistent mesoscale eddies; and circulation driven by seasonal wind regimes. While these dynamics are well resolved on basin scale, their coupling to shelf edge processes responsible for HAB generation is not well understood.
The main trigger for HABs is a nutrient enrichment of near surface layers by upwelling or vertical mixing, often coupled to a sharp decrease in oxygen concentrations induced by water from the oxygen minimum zone. In contrast to the pronounced summer-monsoon upwelling in the Arabian Sea, upwelling at the northern Omani shelf appears in the form of short irregular events. The main drivers for local upwelling and the exchange of water and its properties across the shelf break are not fully resolved. In particular, the relative importance of the two dominant causes of upwelling (Ekman dynamics and eddy/topography interactions) and their interactions with the AGW slope-current are not known. Cross-shelf coupling is strongly determined by processes on the sub-mesoscale with weak surface signatures preventing analysis through remote sensing. The high system complexity and the lack of adequate observations explain past difficulties in resolving cross-shelf transport and local upwelling responsible for HAB.
To address this challenge, sub-surface and sub-mesoscale observations are required across the shelf edge over periods of sufficient length to capture transient events. We propose to combine in situ data collection from stationary moored sensors with data collection from autonomous vehicles over a period of several weeks during repeated summer campaigns. We will install a network of moorings on the shelf west of Muscat and conduct regular plankton sampling. A surface (wave) glider will be operated between the moorings and across the shelf edge. A second, deep-going, sea glider will extend data collection from the shelf edge up to 60 km offshore into the Sea of Oman.
With this dataset, we aim to identify how basin scale processes interact with the steep shelf edge and the outflow from the Arabian Gulf to modulate cross shelf exchange and ageostrophic transport on the shelf. Specifically, we will assess how Ekman dynamics versus eddy-topography interactions control the intensity and extent of upwelling, the nature of upwelled water, and whether this water leads to HAB formation and how HABs are transported on-shore to the coast. Linking the new findings of this study to operational met-ocean products will improve our system understanding and provide the crucial foundation for the advancement of HAB prediction and towards adequate early warning and impact mitigation. Through the cost matching collaboration with a leading research institution from Sweden, the project will furthermore provide a novel dataset, training for two Omani research assistants on state of the art oceanographic data collection and optimized operation methods for the WaveGlider of EJAAD.

Algal bloom, coral reefs, tourism, Shelf edge dynamics