Unit:
Κατεύθυνση Φυσική ΩκεανογραφίαLibrary of the School of Science
Author:
Kournopoulou Antonia
Supervisors info:
Διονύσιος Ε. Ραΐτσος, Αναπληρωτής Καθηγητής, Τμήμα Βιολογίας, ΕΚΠΑ
Στέλλα Ψαρρά, Διευθύντρια Ερευνών, Ινστιτούτο Ωκεανογραφίας, ΕΛΚΕΘΕ
Κωνσταντίνος Καράντζαλος, Καθηγητής, Σχολή Αγρονόμων & Τοπογράφων Μηχανικών - Μηχανικών Γεωπληροφορικής, ΕΜΠ
Original Title:
Επίδραση της κατακόρυφης ανάμειξης στον χρόνο φυτοπλαγκτονικών ανθίσεων από τηλεπισκοπικά δεδομένα στην Ανατολική Μεσόγειο
Translated title:
Impact of Vertical Mixing on Remotely-sensed Phytoplankton Phenology in the Rhodes Gyre (Eastern Mediterranean)
Summary:
Understanding marine ecosystem responses to increasing temperatures is crucial, especially in rapidly warming regions like the Mediterranean Sea. Phytoplankton are key indicators of ecosystem shifts, forming the foundation of the marine food web, playing a significant role in carbon cycling and marine productivity. The Rhodes Gyre, an 'oasis' within the oligotrophic Levantine Basin (Eastern Mediterranean), is known for its higher primary productivity and as a major formation area of Levantine Intermediate Water—an important feature of the Mediterranean's circulation. However, previous studies on phytoplankton dynamics have been constrained by sparse in situ data and the surface-only coverage of satellite observations, limiting insights into long-term subsurface changes. Here, we use a Global 3D Multiobservational dataset, which combines satellite and Argo-derived in situ observations to provide depth-resolved biological information, enabling the estimation of ecological indicators across temporal, spatial, and vertical scales over a 23-year period (1998–2020). Our findings reveal a rise in surface temperatures after 2009, likely linked to broader oceanic warming, accompanied by evident declines in Chlorophyll-a (Chl-a, an index of phytoplankton biomass) and Particulate Organic Carbon. The warmer recent period (2009-2020) has intensified stratification, contributing to a shallower Mixed Layer Depth (MLD). We show that higher concentrations of Chl-a now occur below the MLD during summer, suggesting nutrient entrapment in subsurface layers, that coincides with an increase in oligotrophy in the mixing zone (from the surface to MLD). Phytoplankton phenology indicators show a shortening of the blooming period by approximately five weeks in the upper 150 meters and ten weeks in the mixing zone, probably related to a weakening of vertical mixing. In addition to warming, an apparent reduction in wind speed may have also contributed to the increased stratification. Our results highlight the Rhodes Gyre's increasing vulnerability to climate-driven changes and the utility of long-term 3D observational data in revealing ecosystem responses often overlooked by satellite-derived datasets. Furthermore, integrating ecological indicators and multiobservational datasets enhances our understanding of the links between phytoplankton biomass and higher trophic levels, supporting water quality management.
Main subject category:
Science
Keywords:
phytoplankton, phenology, remote sensing, Eastern Mediterranean Sea, climate change
File:
File access is restricted until 2027-12-20.
Kournopoulou_Thesis_2024.pdf
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File access is restricted until 2027-12-20.
