Fixed nitrogen cycling and nitrous oxide production in the Arctic Ocean:
shelf transformation processes and implications for Arctic biogeochemistry
Sofia Muller (UOC)

Long-term study of the MHWs in the Mediterranean Sea and the Red Sea:
an assessment of their trends, drivers, and their early indicators
Manal Hamdeno ELAWADY (GHER)

Marine heatwaves (MHWs) are intensifying under climate change and are a major driver of ocean variability and ecosystem stress. This thesis analyzes MHW dynamics in the Mediterranean Sea and the Red Sea (1982-2024), showing increasing frequency, duration, and intensity, with strong regional contrasts linked to basin structure. Our results show that MHWs are driven by the interaction between long-term warming, atmospheric forcing, and oceanic processes, and extend below the surface, creating subsurface heat storage and ocean memory. Their impacts include enhanced stratification, reduced nutrient supply, decreased productivity, and direct thermal stress on marine organisms. In addition, compound events and interactions with atmospheric heatwaves amplify their intensity and persistence, and interactions with Medicanes show a two-way of impacts, highlighting that MHWs are complex, vertically structured, and coupled ocean-atmosphere extremes.

Mapping benthic traits over the northwestern shelf of the Black Sea: a trait-based modelling approach
Severine Chevalier (MAST)

The biological communities found at the bottom of the sea, the macrobenthos, play a critical role in marine ecosystems by influencing biogeochemical cycles and ecosystem functioning. Therefore, the macrobenthos is a primary target for biodiversity conservation. Despite the availability of databases compiling millions of species records, benthic biodiversity remains poorly mapped at a larger scale, which hinders the establishment of Marine Protected Areas. This PhD thesis addresses this critical gap by developing predictive modelling tools capable of mapping macrobenthos characteristics at the shelf scale. This study takes a functional approach to biodiversity, defining living communities by their traits (e.g. mobility, burrow type). The methodology was developed for the northwestern shelf of the Black Sea. Trait distribution models were developed to link benthic traits and their “niche” (the environmental conditions to which they are suited) and to predict their spatial distribution using maps of environmental conditions provided by an ocean model. These maps of benthic traits can serve as ecological indicators for assessing ecosystem health and can be useful for conservation policy.