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

Abstract

Extreme 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.

Seasonal Patterns in Phytoplankton and Zooplankton across the North of Gulf of Oman: A Numerical Study

“…By comparing the modeled time series with satellite data, it can be concluded that satellite sensors might be overestimating surface chlorophyll. The satellite observations (SeaWiFS at 24°N, 58°E from Asia-Pacific Data Research Center) from 1997 to 2013 suggested that chlorophyll-a concentration in the Gulf of Oman increased in August 2000, September 2004 and August 2008 [47]. The results showed that a significant correlation exists between inshore and offshore chlorophyll-a distribution throughout the year.…”

“…Recent studies have delved into the biological and chemical parameters of the Persian Gulf and Oman Sea, employing coupled physical-biological ROMS models and satellite data to explore various facets of marine ecology [24][25][26][27][28][29]. However, there remains a gap in our understanding of the behavior of biological parameters with seasonal changes in the Oman Sea region, especially in the context of basin hydrodynamics and atmospheric forces.…”

“…The Gulf of Oman experiences pronounced atmospheric forcing during the southwest monsoon (from late May to September) and the Northeast monsoon (from December to March). These monsoons introduce significant seasonal variability in biological productivity [25][26][27]. Such variability, driven by physical conditions like surface light, water temperature, and the depth of the upper mixed layer, can influence the cycle of plankton populations in the region [28].…”

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

“…This could be considered as a first step to better understand that the severity of MHWs is not only directly caused by their occurrence, but also by their interactions with other atmospheric conditions that may lead to other catastrophic extreme events. Therefore, for future work, we propose to investigate the combination between MHWs and other extreme events in the region such as storms, atmospheric heatwaves, low chlorophyll-a events, and extreme nutrient and oxygen depletion events which is also suggested by (Leonard et al, 2014;Le Grix et al, 2021;Hamdeno et al, 2022). Due to the rapid increase in the frequency, days, and intensity of MHW, it is also necessary to quantify their potential impacts on the overall ecological components, structures, functioning, and overall health of the Mediterranean Sea.…”

Understanding the compound marine heatwave and low-chlorophyll extremes in the western Pacific Ocean

“…Previous studies have shown that these climate modes, such as ENSO, DMI, NAO, AO, and PDO, favor or suppress the occurrence of MHW-LChl events (Le Grix et al, 2021;Hamdeno et al, 2022). To further understand the influence of large-scale modes of interannual to decadal climate variability on compound MHW-LChl events in the study region, we perform correlation and composite analysis between the total days of compound events and five different climate modes (see Section 2.1).…”