Mehdi Gholamalifad, Bonyad Ahmadi, Parisa Nouri,
Volume 9, Issue 4 (11-2020)
Abstract
Primary production is a key indicator in the evalution of aquatic ecosystems that can directly affect carbon sequestration. Due to climate change and environmental dynamics, this component has changed spatially and temporally in different ecosystems. Therefore, to understand and monitor these changes, the most important influential parameters include; sea surface temperature, chlorophyll-a and algal bloom on this component and their changes were analyzed based on the time series. Images related to Chl-a, SST and NPP from January 2003 to December 2018 were used by MODIS sensor and VGPM model to estimate NPP in the study area. Aftar pre-processing and extracting the time series algorithm, the trend of variation was determined using the mann-kendall and theil-sen procedure. Then, using enhancing false color composite, algal blooms in the Persian Gulf and the sea of Oman were identified and the amount of chl-a concentration in the algal bloom area and outside the area was determined. The results of trend analysis with theil-sen procedure showed that the rate of change for chl-a is decreasing in all regions except the fifth region. The highest amount was observed in the fifth region (-0.19), which corresponded to the rate of NPP. The results also show that the highest amount of NPP in the first region in March and the lowest in June and July (540 and 690 gC/m2/day), which corresponds to the amount of chl-a concentration. Despite the apparent correlation, there is no cause-and-effect relationship between SST and chl-a as well as chl-a and NPP. In this way, factors other than chl-a can be considered for algal bloom and NPP.
Maryam Karimian, Omid Beyraghdar, Reza Modarres, Saeid Pourmanafi,
Volume 11, Issue 3 (8-2022)
Abstract
Chl a is the main pigment of phytoplankton, which is an indicator of phytoplankton biomass and reflects the primary production in the marine environment. In this study, level 3 (4 km) data of Chl a concentration of Persian Gulf and Oman Sea for the period of 2003- 2018 were used. The data was converted to raster format in ArcGIS10.5 environment and then the numerical values of each pixel were extracted in R (version 4.0.2). Missing data were observed in Chl a data, to solve this problem, DINEOF algorithm was applied and non-parametric Mann-Kendall and Sen’s Stimulator tests were used to analyze Chl a concentration trends. The results showed that the maximum concentration of Chl a is in September (0.09 to 18.75 mg / m3) and October (0.23 to 18.03 mg / m3) and the minimum concentration of Chl a in May (0.22 to 5.74 mg / m3) and June (0.20 to 5.12 mg / m3). The trend of Chl a concentration variability over the study period was negative in most areas and not significant. These analyses provide an overall description of Chl a concentration variability in the Persian Gulf and Oman Sea based on satellite observations; however, further investigations based on in situ observations are needed to achieve better understanding of the patterns of of Chl a concentration alterations.
Shahnaz Kaleji, Mohammad Akbarinasab, Abbas Einali,
Volume 12, Issue 4 (12-2023)
Abstract
This study investigated the Caspian Sea surface temperature fronts from 2015 until 2019 using satellite images (MODIS). The sea surface temperature front, a narrow-width area with a high-temperature gradient, plays a crucial role in various biological, chemical, physical, and agricultural parameters and climate change issues. Detecting sea surface temperature fronts also helps understand other phenomena such as upwelling, eddy, and biological accumulation. The Canny algorithm was used in the MATLAB environment for detecting the fronts, and the results were compared spatially and temporarily. It was observed that the fronts in the north of the Caspian Sea are permanent from September until November and March until May, while they are impermanent and dashed at other times of the year. In the east of the south Caspian Sea, the only detected fronts in March repeat annually, whereas in the west of the south Caspian Sea, fronts were detected in all months except for August, consistently over the five years. The pattern of temperature fronts in the east and west of the Middle Caspian Sea differs. The fronts are clustered in winter but become coherent and clear in summer. Additionally, the southern Caspian Sea temperature fronts are less abundant in the pre-summer period than in other periods. The Caspian Sea surface temperature fronts were mostly detected in the location of internal waves, steep areas near the coast, and eddies.
