3-D circulation, impact of the terrestrial loading and atmospheric conditions on seasonal and climatic time scales in Eastern Mediterranean Gulfs: a case study in Kalloni Gulf, Lesvos island, Greece

Abstract

PREFACE: In order to investigate the various issues raised in the present study, a number of objectives were defined and approached in different chapters. The framework starts with a synoptic scale approach studying the in situ data, continues raising the scale to seasonal study and in the last chapter the study focuses in larger scale with the study of the response of the ecosystem to climate change. The climate trends for the study area established, and a water budget model applied aiming to highlight the impact of the climate trends to the ecosystem of the Kalloni gulf. The 1st Chapter is focusing on the Aegean Sea where the study area is located. The climate trends and the climate indices that already had been established in the global bibliography for the Aegean were presented; while the impacts that already are visible in the Aegean regions, especially along the coast, are reported. In addition the circulation of the Aegean Sea is presented from various papers that had been carried out for the basin. In Chapter 2 an overview that focuses on the Mediterranean coastal lagoons was made. The characteristic of the coastal lagoons as well as their role and their importance as ecosystems were analyzed. The anthropogenic pressure as a major factor in the sensitivity of the marine ecosystem was approached. The unique functioning of the lagoons was reviewed; while the hot spot of the response of the marine ecosystem to the climate change was analyzed according to exits studies. Finally the state of the art – the knowledge for the study area was conducted in a detailed overview from the first study in 1980 until nowadays. Chapter 3 refers to the aims and the objectives of the present framework; while some general information about the strategy that was followed for the conducting of the research is given. Chapter 4 is targeted to the observational methodology that was followed. At the begging the characteristics of the study area (Kalloni Gulf) are given analytically. Thereafter the field work and the data processing as well as the method that was used for the first analyzes are discussed.5th Chapter continues with the observational approach, emerging the seasonal fluctuations and provides the description of the ecosystem. Climatological data was compiled while time series for the wind forcing was studied further. The chemical parameters were analyzed and valuable information for the ecosystem was revealed. The physical parameters studied in detailed, aims to understand and emerge the hydrodynamic structure of the gulf with the observational method. Finally two different patterns were emerged, showing the 2D circulation pattern of the gulf. In Chapter 6 the numerical approach established, pointing to reveal whatever was overlooked with the first method. Although the observational method gives valuable results for the hydrodynamic structure of the gulf, basic characteristics led to the question ‘’if in reality the circulation isn’t 2D but 3D’’ and to the possibility to have been overlooked with the specific approach. The 3D hydrodynamic Princeton Ocean Model (POM) applied for the Kalloni gulf and the entire methodology is explained in the present chapter. Chapter 7, refers to the thermohaline structure of the Kalloni Gulf and the seasonal variability as it arises from the model. Although it isn’t possible to make a detailed validation, an analytical comparison between the results from the observational method and the computed results from the model along the same axis is performed. The 3D circulation pattern emerged and the previous assumption from chapter 5 is rebutted, while the 3D circulation pattern of the gulf is established. In Chapter 8, the horizontal variability of the circulation in the Kalloni Gulf is studied. The 3D circulation is analyzed and verified from the kinetic energy. The existence of boundary currents in the gulf emerged for first time. A water budget computed for the basin and the residence time is calculated monthly. In the Chapter 10, an attempt was made to reach the study one step ahead. To combine all the information that was revealed from the framework until now and considering the strong presence of boundary currents, was judged crucial to study further the sensitivity of the general circulation of the gulf, to the surface and the lateral water fluxes. Thus, three sensitivity tracer experiments were developed.

Προκειμένου να διερευνηθούν τα διάφορα ζητήματα που τέθηκαν στην παρούσα μελέτη, ορίστηκαν και προσεγγίστηκαν ορισμένοι στόχοι σε διαφορετικά κεφάλαια. Η έρευνα αρχικά εστιάζει σε μια προσέγγιση συνοπτικής κλίμακας μελετώντας τα in-situ δεδομένα, συνεχίζει ανεβάζοντας την κλίμακα σε εποχιακή μελέτη και στο τελευταίο κεφάλαιο η μελέτη εστιάζει σε μεγαλύτερη κλίμακα με τη μελέτη της απόκρισης του οικοσυστήματος στην κλιματική αλλαγή. Καθιερώθηκαν οι κλιματικές τάσεις για την περιοχή μελέτης και εφαρμόστηκε ένα μοντέλο ισοζύγιο νερού σε επίπεδο λεκάνης απορροής με στόχο να αναδείξει την επίδραση των κλιματικών τάσεων στο οικοσύστημα του κόλπου της Καλλονής.