Physical-Biological variability and covariability in the Algero-Provençal Basin by means of multisensor satellite and in situ data
Author(s)
Olita, Antonio
Date Issued
February 12, 2009
Type
Doctoral Thesis
Abstract
The climate change has been proved to influence marine ecosystems either in their physics and biology. The Mediterranean sea, because of its characteristics, is particularly sensitive to c1imatic changes and more in general to the variability of the physical forcings, as shown by several authors. In this scenario, the study of the relationships between hydrodynamics, phytoplankton distribution and primary production, becomes particularly important in order to better understand the ecological effects of eventual hydrodynamic shifts induced by climate change. The aim of the present thesis is the study of the spatial and temporal variability of the algal biomass and primary production in the Algero-Provençal Basin (Western mediterranean), as well as the study of their relationships with hydrodynamical processes. We approached the problem by analysing several remotely sensed and in situ datasets covering multiple temporal and spatial scales, from meso-scale to basin-scale. The seasonal and interannual variability of the chlorophyll fields has been studied by analyzing the Seawifs monthly dataset, while the AVISO/CLS and the Pathfinder AVHRR datasets have been used to analyze respectively Sea Level Anomalies (SLA) and Sea Surface Temperature (SST) over the decade 1997-2007. The main sesonal and interannual patterns of physical and biological fields have been identified through EOF decomposition and wavelet analysis, while the covariability has been studied trough Singular Value Decomposition (SVD). The seasonal variability of the algal biomass is composed by two annual cycles, timewise and spacewise shifted. The analysis also showed a significant interannual variability, and the footprint of an anomalous event, the summer 2003 heatwave, has been identified either in physical and biological fields. Significant correlations have been found between physical and biological fields permitting to perform a simple zonation of the domain, as function of the different bio-physical coupling. Three main zones have been therefore identified, north central and south. The central zone shows the lower trophic level and, at the same time, the strongest coupling between SLA and the algal biomass. The primary production (PP) has been estimated, for the same decade, by using a satellite based model. The model makes use of remotely sensed Photosyntetically Available Radiation (PAR), SST and chlorophyll, in order to estimate the PP integrated over the euphotic layer. The basin averaged annual primary production, for the period 1998-2006, is 142 gCrn-2year-1, in good agreement with previous findings, with a pronounced interannual variability and no evident trends. We identified the signature of the 2003 European heatwave, which determined a marked decrease of PP in summer 2003. To better understand the relationships we hypothesized between mesoscale eddies and chlorophyll, a set of hydrological and fluorometric data, collected during two oceanographic cruises, conducted in 2001 and 2002 in the Sardinian Sea (in front of the western Sardinia coast) , has been analysed. The analysis proved that the mesoscale eddies have a dominant role in modulating and redistributing the algal biomass, confirming the assumptions and the hypothesis performed in the basin scale study. The analysis of in situ data shows that the anticyclonic eddies infer in the concentration and distribution of the chlorophyll through several mechanisms, as function of their position (coastal or open-sea), size, relation with the continental shelf and depending on their reciprocal interaction.
Additional information
Dottorato di ricerca in Ecologia e gestione delle risorse biologiche
File(s)![Thumbnail Image]()
Name
aolita_tesid.pdf
Size
3.01 MB
Format
Adobe PDF
Checksum (MD5)
f97e60aff02534a1e737ee5e6ef3cbe8