Analysis of mixed layer depth and a primary production variable - chlorophyll-a - in Maltese territorial waters

Abstract

The global ocean is a complex system comprising of a number of variables that differ in type as well as quantity across the world. Two of these variables are mixed layer depth and chlorophyll-a. These rather unique and important ocean variables affect multiple atmosphere-ocean processes, including primary production and oceanographic variability. The main focus of this research project is to study the regional trends of the two ocean parameters within the 12 nautical mile extent of Maltese territorial waters, how they vary over a longer period of time and see if there is any statistically significant correlation present that would represent a certain relationship. The chlorophyll-a and mixed layer depth data for 2000 to 2019 were extracted as NetCDF files from Copernicus Marine website, downloaded for processing and clipped to a required extent – 12 nautical miles around the Maltese Islands. The numerical values for both variables were organised in Excel, followed by a visual analysis via graphs, as well as statistical analysis. Results show that all seasonal chlorophyll-a trends, positive and negative, are significant, meaning that clear yearly and seasonal trends can be recognised since the year 2000 until present. Moreover, findings also show that the highest chlorophyll-a concentrations are generally found in the second depth level (75 metres) and that the surface chlorophyll-a concentration trend is significantly decreasing over the extent of all seasons for the whole duration of the dataset. When it comes to the statistical correlation of the two ocean variables, it was found that only one strong significant relationship was present between summer mixed layer depths and surface chlorophyll-a. Seasonal mixed layer depth analysis also showed that summer depths are significantly decreasing, which implies that the mixed layer in the Maltese territorial waters undergo seasonal shoaling in summer months