Researchers at Khalifa University investigated how the vertical and horizontal distribution of nutrients respond seasonally to upwelling in the Arabian Gulf and the Sea of Oman.
Dr. Maryam Al Shehhi, Assistant Professor, and Kaltham Abbas Ismail, graduate student, both from the Khalifa University Department of Civil Infrastructure and Environmental Engineering, used data obtained from the World Ocean Atlas 2018 and estimates of coastal and curl-driven upwelling in both the Arabian Gulf and the Sea of Oman to determine the vertical and horizontal distribution of three important nutrients and how these nutrients respond to upwelling on a seasonal basis.
They published their results in PLoS One.
Upwelling is a process in which deep cold water rises toward the surface. It occurs in the open ocean and along coastlines as winds blowing across the ocean surface push water away. Water from beneath the surface then rises to replace the water that was pushed away. Water that rises to the surface as a result of upwelling is typically colder and rich in nutrients. These nutrients fertilize surface waters, leading to high biological productivity.
The lack of research into the nutrients found in the Arabian Gulf and their sources prompted the researchers to investigate. They analyzed the spatial and temporal variability of nitrate, phosphate and silicate in the Arabian Gulf and the Sea of Oman and considered the effect of seasonal upwelling on the distribution of nutrients.
They found that the Sea of Oman’s surface and deep waters contained 80 percent higher concentrations of nutrients than those of the Arabian Gulf. The average surface nutrient concentrations in both are higher in the winter than in the summer, except for nitrates, where a very low concentration was observed in both summer and winter in the Arabian Gulf.
“In the southern part of the Gulf, especially along the coastline of the UAE, we saw higher concentrations of phosphate,” Dr. Al Shehhi said. “These levels were consistent during both seasons but we found even higher concentrations again in the Sea of Oman. Higher concentrations in winter than in summer suggest waters rich in phosphate flow from the Sea of Oman into the Arabian Gulf during the summer months.”
This movement of phosphate from one body of water to another is an example of the horizontal distribution of nutrients responding to seasonal influences in the Arabian Gulf and the Sea of Oman. Similar to phosphate, surface silicate revealed a clear seasonal variation with higher variability in the Sea of Oman during the winter season.
The researchers identified two strong upwelling zones in the Arabian Gulf along the Iranian coasts and two in the Sea of Oman along the southeast and northwest coasts. The strongest upwelling zone was found in the Sea of Oman, supporting the evidence that this body of water contains more nutrients due to the vertical transport of the available nutrients in the deeper water. The Arabian Gulf, on the other hand, showed slight vertical variations, explained by its shallower waters and weaker upwelling.
As climate change continues to influence all natural processes on Earth, understanding the dynamics of the oceans is crucial to predicting changes.
The macro and micronutrients needed by photosynthetic organisms in the oceans exist with varying distribution. The Southern Ocean has the highest amount of macronutrients, while the Arctic Ocean contains significant amounts of micronutrients from river runoff, dust and sediments deposited in shallow coastal waters.
The Arabian Gulf, however, is under pressure, according to the researchers.
“The Arabian Gulf has a pressured marine ecosystem due to the growing population along its coast,” Dr. Al Shehhi said. “More people means more treated wastewater from residential and industrial areas is discharged into the Gulf, increasing the concentration of nutrients in seawater — a phenomenon called eutrophication.”
More nutrients sounds like a benefit to an ecosystem, but when an environment sees excessive nutrient inputs, algal blooms and hypoxic waters can kill fish and seagrass, setting off a chain reaction in the ecosystem. Large amounts of carbon dioxide from the decomposing plant matter acidifies the water, slowing the growth of fish and shellfish. Eutrophication threatens humanity too — a reduced catch for commercial and recreational fisheries means smaller harvests and more expensive seafood.
Understanding the normal nutrient dynamics in the Arabian Gulf enables us to recognize the harm in discharging wastewater into the sea. By studying the horizontal and vertical variants in nutrients, researchers can help protect marine resources.
Jade Sterling
Science Writer
9 January 2023
