Sea Surface Temperature Variability in Izmir Bay, Aegean Sea: Marine Heat Waves, Cold Spells, and Fish Mass Mortality Events
Ocean Science Journal, vol.61, no.3, 2026 (SCI-Expanded, Scopus)
- Publication Type: Article / Article
- Volume: 61 Issue: 3
- Publication Date: 2026
- Doi Number: 10.1007/s12601-026-00306-5
- Journal Name: Ocean Science Journal
- Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus, BIOSIS, Geobase, INSPEC, Zoological Record, Natural Science Collection (ProQuest), Biological Science Database (ProQuest), Earth, Atmospheric, & Aquatic Science Collection (ProQuest)
- Keywords: Aegean sea, Fish mass mortality events, Izmir Bay, Marine cold spells, Marine heat waves, Sea surface temperature, Trends
- Dokuz Eylül University Affiliated: Yes
Abstract
Izmir Bay, a densely populated semi-enclosed basin in the Aegean Sea, remains poorly studied in terms of long-term variability in sea surface temperature (SST), marine heat waves (MHWs), and cold spells (MCSs). A fish mass mortality event in summer 2024 further underscores the need to characterize SST extremes and their potential links to such events. This study addressed this gap by analyzing daily SST data from 1982 to 2025 to examine long-term variability and trends in SST, MHWs, and MCSs, exploring the influence of the Atlantic Multidecadal Oscillation (AMO) and the North Atlantic Oscillation (NAO) on SST variability using wavelet coherence analysis, and examining MHW characteristics during the fish mass mortality event. Izmir Bay exhibited a warming trend of 0.038 °C/yr during 1982–2025, with stronger warming in the outer bay and higher seasonal trends in summer (0.049 °C/yr) and autumn (0.040 °C/yr). Pettitt's test identified a significant change point in May 2007, with an approximately 1 °C increase in mean SST between the two periods, reflecting the progressive warming of the bay. Wavelet analysis revealed a concurrent weakening of AMO–SST coherence at multiannual scales around this change point. At the annual scale, both the AMO and NAO exhibited significant coherence with SST. MHW days and frequency exhibited significant positive annual trends, while MCSs displayed significant negative trends in Izmir Bay. The year 2024 was marked by the highest MHW activity during the study period, with elevated mean and maximum intensity and the highest number of MHW days. The eastern inner bay experienced prolonged and intensified MHW activity in 2024, exceeding long-term averages in duration and intensity both prior to and during the fish mass mortality period, suggesting MHWs as a possible contributing driver of the mortality event in the most affected area. The findings provide a valuable baseline for ecological and fisheries studies, regional climate assessments, and evidence-based coastal and marine resource management in this sensitive semi-enclosed basin.