Responses of Satellite Chlorophyll-a to the Extreme Sea Surface Temperatures over the Arabian and Omani Gulf

peer reviewedExtreme events such as Marine Heat Waves (MHWs) and Low Chlorophyll-a (LChl-a) in the ocean have devastating impacts on the marine environment, particularly when they occur simultaneously (i.e., the compound of MHWs and LChl-a events). In this study, we investigate the spatiotemporal variability of MHWs and LChl-a events in the Arabian and Omani Gulf. For this purpose, we used satellite-based high-resolution observations of SST (0.05° × 0.05°; from 1982 to 2020) and chlorophyll-a concentration data (0.04° × 0.04°; from 1998 to 2020). Hourly air temperature, wind, and heat flux components from the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA5) were used to explain the link between these extreme events and atmospheric forcings. Moreover, our results revealed that the annual frequency of MHW and LChl-a is related to the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). The results revealed an average SST warming trend of about 0.44 ± 0.06 °C/decade and 0.32 ± 0.04 °C/decade for the Arabian Gulf (AG) and the Gulf of Oman (OG), respectively. This warming rate was accompanied by MHW frequency and duration trends of 0.97 events/decade and 2.3 days/decade, respectively, for the entire study region from 1982 to 2020. The highest annual MHW frequencies were recorded in 2010 (6 events) and 2020 (5 events) associated with LChl-a frequency values of 4 and 2, respectively. La Niña events in 1999, 2010, 2011, and 2020 were associated with higher frequencies of MHW and LChl-a. The positive phase of IOD coincides with high MHW frequency in 2018 and 2019. The longest compound MHW and LChl-a event with a duration of 42 days was recorded in 2020 at OG. This extreme compound event was associated with wind stress reduction. Our results provide initial insights into the spatiotemporal variability of the compound MHW and LChl-a events that occurred in the AG and OG

Drivers of the 2019 Marine Heatwaves in the Mediterranean Sea

Marine heatwaves (MHWs) are prolonged discrete anomalously warm water events that last for more than five successive days and can be described by their duration, intensity, rate of evolution, and spatial coverage. These Episodes of large-scale anomalously high ocean temperatures can have many impacts on marine ecology and ecosystems and major implications for fisheries as well. As a result of the anthropogenic climate change, MHWs have been observed in many parts of the world's oceans and their intensity and frequency are expected to increase in the future. This thesis investigates the 2019 MHWs that have occurred in the Mediterranean Sea, their possible drivers, and their mechanism of formation. The MHWs that occurred in the Mediterranean Sea between June and December 2019 were defined and categorized using the daily NOAA OISST data set and based on a 30-years climatology (1982–2011) baseline. The eastern and western basins of the Mediterranean Sea have shown dissimilarities in the SST and SST anomaly distributions as well as in the characteristics of the MHW events that occurred in them during the study period. The MHWs occurred more often in the WMED than in the EMED with higher intensities while the EMED marine heatwaves were observed to have a longer duration than the WMED ones. In both basins, the MHWs characteristics were linked to the changes in the heat flux anomaly, mixed layer depth, air temperature, mean sea level pressure, and winds. The high anomalous sea surface temperature of the marine heatwaves was associated with high heat flux anomaly, shallow mixed layer, high air temperature, high-pressure system, and low wind speed

Marine heatwaves characteristics in the Mediterranean Sea: Case study the 2019 heatwave events

peer reviewedMarine Heatwaves (MHWs) are considered one of the main consequences of global warming. MHWs negatively affect ecosystems, threaten economies, and intensify storms. In this work, we investigated the main characteristics of MHWs in the Mediterranean Sea from 1982 to 2020 and examined the relationship between their frequency and teleconnection patterns (e.g., East Atlantic Pattern (EAP) and East Atlantic/Western Russian Pattern (EATL/WRUS)). We then focused on the most intense MHW events that occurred in 2019 in the western Mediterranean Sea (WMB) and eastern Mediterranean Sea (EMB) by examining the link between the SST anomaly (SSTA) and various atmospheric forcings during these events. Our results showed that MHWs were more frequent and intense in the WMB than in the EMB on temporal and spatial scales, while the duration of MHWs was longer in the EMB. The trend of MHW frequency and duration in the Mediterranean Sea between 1982 and 2020 was about 1.3 ± 0.25 events/decade and 3.6 ± 1.16 days/decade, respectively. More than half of all MHW events in the Mediterranean Sea were recorded in the last decade (2011-2020). The results also showed that the EAP plays an important role in modulating MHW frequency in the Mediterranean Sea, with a strong positive correlation of 0.74, while the EATL/WRUS was strongly negatively correlated with MHW frequency in the EMB, with a correlation of about -0.60. In 2019, six MHW events were observed in the WMB, three of which were classified as strong events (SST exceeded two times the climatological threshold), while two events were detected and classified as strong events in the EMB. In the WMB, the 2019 MHWs extended to a depth of about 20 meters into the water column, while the MHWs in the EMB extended to greater depths of over 50 meters. The strong MHW events in the WMB were associated with a large positive heat flux anomaly and a shallow mixed layer. In the EMB, the high SSTA associated with MHW events caused heat loss from the ocean to the atmosphere and was associated with a shallow mixed layer and anomalously low mean sea level pressure. Finally, a negative relationship between the SSTA and surface Chl-a concentrations was observed during the 2019 MHW events. This negative influence of MHWs on Chl-a was more pronounced in the WMB than in the EMB, suggesting that the WMB MHW events were intense enough to infer a response to chlorophyll-a concentrations

Synthesis and Bioactivity Assessment of Novel Spiro Pyrazole-Oxindole Congeners Exhibiting Potent and Selective in vitro Anticancer Effects

The present work aims to design and synthesize novel series of spiro pyrazole-3,3’-oxindoles analogues and investigate their bioactivity as antioxidant and antimicrobial agents, as well as antiproliferative potency against selected human cancerous cell lines (i.e., breast, MCF-7; colon, HCT-116 and liver, HepG-2) relative to healthy noncancerous control skin fibroblast cells (BJ-1). The mechanism of their cytotoxic activity has been also examined by immunoassaying the levels of key anti- and proapoptotic protein markers. The analytical and spectral data of the all synthesized target congeners were compatible with their structures. Synthesized compounds showed diverse moderate to powerful antimicrobial and antioxidant activities. Results of MTT assay revealed that seven synthesized compounds (i.e., 11a, 11b, 12a, 12b, 13b, 13c and 13h) particularly exhibited significant cytotoxicity against the three cancerous cell lines under investigation. Ranges of IC50 values obtained were 5.7–21.3 and 5.8–37.4 µg/mL against HCT-116 and MCF-7, respectively; which is 3.8 and 6.5-fold (based on the least IC50 values) more significant relative to the reference chemotherapeutic drug doxorubicin. In HepG-2 cells, the analogue 13h exhibited the highest cytotoxicity with IC50 value of 19.2µg/mL relative to doxorubicin (IC50 = 21.6µg/mL). The observed cytotoxicity was specific to cancerous cells, as evidenced by the minimal toxicity in the noncancerous control skin-fibroblast cells. ELISA results indicated that the observed antiproliferative effect against examined cancer cell lines is mediated via engaging the activation of apoptosis as illustrated by the significant increase in proapoptotic protein markers (p53, bax and caspase-3) and reduction in the antiapoptotic marker bcl-2. Taken together, results of the present study emphasize the potential of spiro pyrazole-oxindole analogues as valuable candidate anticancer agents against human cancer cells