Physical variability of chlorophyll-a of the Galician Upwelling System and different responses under the effect of climate change with model NEMO-MEDUSA.
Supervisor: Bieito Fernandez (NOCs)
The present study assesses the physical variability of chlorophyll-a in the Galician Upwelling System, a critical component of Eastern Boundary Upwelling Systems (EBUS), focusing on key oceanographic variables such as sea surface temperature (SST), salinity, dissolved inorganic nitrogen (DIN), mixed layer depth (MLD), and chlorophyll-a concentrations. Understanding these dynamics is essential due to the Galician Upwelling System’s significant role in regional and global marine productivity, which is highly sensitive to changes in environmental conditions. Our aim is to better understand the current state and future projections of upwelling dynamics in this region. To achieve this, we employed a combination of outputs from the NEMO-MEDUSA model, which provides high-resolution simulations of oceanographic processes, and observed data. The analysis reveals significant changes in these parameters, particularly around 2010, where a notable decline in chlorophyll-a concentrations coincides with decreased salinity and a shallower MLD, suggesting a reduction in nutrient availability likely driven by increased freshwater input and altered ocean circulation patterns. Our results show that this decline in primary productivity is consistent with broader trends observed in other EBUS, such as the California Current and Canary Upwelling Systems, where climate-induced shifts in upwelling intensity are reshaping ecosystem dynamics. The observed cooling along the northern coast during early spring further indicates increased stratification, potentially suppressing vertical mixing and nutrient supply to surface waters, thereby impacting phytoplankton growth. The comparison between observed data and model outputs highlights that while the NEMO-MEDUSA model accurately captures broad seasonal trends in SST and MLD, it tends to underestimate chlorophyll-a concentrations, particularly during peak upwelling seasons. This discrepancy suggests that further refinement of the model is needed to enhance its accuracy in simulating vertical mixing and nutrient dynamics, which are crucial for reliable projections of future changes in marine productivity within the Galician Upwelling System.