Role of atmospheric input on the stoichiometry and degradability of dissolved organic matter in the Mediterranean Sea

Role of atmospheric input on the stoichiometry and degradability of dissolved organic matter in the Mediterranean Sea

Recently, it has become increasingly apparent that atmospheric transport plays an important role in the supply of mineral and organic material to the surface ocean. This atmospheric input is especially important in semi-enclosed seas, such as the Mediterranean Sea, which is close to pollution sources in Northern Europe and subjected to influx of Saharan dust.

In the ocean, carbon export to depth (and therefore, its long term storage with presumed consequences on climate) occurs both through particle sedimentation and through the transfer of dissolved organic matter (DOM) via diffusion or convection. Such export of DOM can reach up to 50% of total C export in the Mediterranean Sea. The fate of surface DOM, mineralized or exported, depends to a high extent on its biodegradability, particularly its C:N:P stoichiometry. Factors controlling the stoichiometry and degradability of the organic matter remain largely unknown.

The aim of this PhD thesis is to assess the contribution of atmospheric input to the C:N:P stoichiometry of surface DOM in the Mediterranean Sea. This assessment is carried out on two main mechanisms: a "direct" effect, through the input of new OM to the existing pool, and an "indirect" effect, through the stimulation of bacterial activity. To address this issue we will combine an observation approach (atmospheric and marine monitoring) and an experimental approach (laboratory experiments under controlled conditions aiming to determine the biogeochemical transformations of the DOM marine pool under the effect of an atmospheric input). The data obtained from both approaches will be used to force the ECO3M model in order to better understand the relationship between atmospheric input and the cycle of dissolved organic matter across the Mediterranean basin.