The shifting colours of the Arabian Gulf are more than a visual spectacle — they are warning signals of profound ecological change. Ocean colour reflects the delicate balance between sunlight, plankton, sediments, and nutrients, yet rising sea surface temperatures are disrupting this equilibrium. The unusual phytoplankton blooms are transforming the Gulf into a hotspot of environmental stress, intensifying concerns for marine ecosystems and coastal communities.
The Arabian Sea hosts one of the world’s largest oxygen minimum zones, spanning nearly 3.9 million km², underscoring the vulnerability of the region to further decline. This article explores the drivers behind these changes in ocean colour and examines their far-reaching impacts on the Arabian Gulf.
Figure1: Phytoplankton bloom in Lake St. Clair captured by Landsat 8
Why Ocean Colour Matters
Ocean colour is more than what meets the eye. It is an important indicator of numerous parameters such as marine productivity, climate signals, and ecosystem health. The colour of the water is determined by the interaction of sunlight with the particles present in seawater, such as chlorophyll in plankton and sediments. Because of their small size, different types of plankton drift around in the ocean due to wind and ocean currents.
Role of Phytoplankton and Pigments
The pigment chlorophyll-a give the green colour to plankton. Phytoplankton are the most common type of plankton which are microscopic algae that are autotrophic (self-feeding) algae. Phytoplankton are known to transfer carbon dioxide from atmosphere to oceans acting as a carbon sink and is a major contributor to decreasing the effects of global warming. A phytoplankton bloom attracts all sorts of species to feed on them such as whales, shrimps, and other invertebrates and vertebrates.
Drivers of Ocean Colour Change in the Arabian Gulf
Recent changes in the Arabian/Persian Gulf waters are driven by a wide range of factors. The rising sea surface temperatures linked to climate change are altering seasonal cycles and encouraging blooms at unusual times. The nutrient runoff from agriculture and urban wastewater adds nitrates and phosphorus, acting as fertilizers that accelerate phytoplankton growth. Together, these drivers increase the frequency and intensity of blooms, some of which are harmful.
Plankton
Plankton are responsible for 45% of global annual primary production and are usually at the bottom of the food chain (Brierley AS et. al, 2017). Primary production causes a huge change in the ocean colour, which can usually be seen from satellite view. Either due to seasonal, nutrient availability, or more sunlight, the abundance of phytoplankton can increase and cause a bloom. There are several reasons for the drivers of phytoplankton bloom, especially in the Arabian Gulf in recent days.
Climate Change
The changing colours of the Arabian Gulf are not just signals of crisis — they are calls to action. By recognizing ocean colour as a frontline indicator of climate change, we empower ourselves to respond with urgency and innovation. Communities, scientists, and policymakers can work together to monitor blooms, reduce nutrient runoff, and champion circular solutions that restore balance to our seas. Every effort — from local cleanups to global climate commitments — contributes to protecting the Gulf’s fragile ecosystems and the livelihoods that depend on them.
The green glow seen from space reminds us that the ocean is alive, responsive, and vulnerable. But it also reminds us that human choices shape its future. By acting collectively and sustainably, we can turn warning signals into opportunities for resilience, ensuring that the Gulf’s waters remain not a symbol of decline, but of renewal and hope.
Due to recent climate change, the Gulf nations are experiencing rising sea surface temperatures that are encouraging phytoplankton bloom and productivity at unusual times and disrupting traditional seasonal cycles. Warm waters stratify the ocean, and this essentially reduces vertical ocean mixing, thus limiting the nutrient replenishment from deeper layers. This phenomenon can create conditions in which certain species, such as Noctiluca scintillans, can dominate and become invasive and form blooms.
The semi-enclosed geography of the Arabian Gulf makes it vulnerable to circulation restrictions and more shallow depth thus easily warmed from global warming. As a result, the region is experiencing frequent and longer blooms where many of them are harmful which can essentially destabilize the food web.
Nutrient runoff
Large-scale development on the coastal sides of the land involves agriculture and urban wastewater, which contain nutrients such as nitrates and phosphorus. These nutrients can increase the growth rate of phytoplankton as they act like fertilizers. This increases the frequency of algal blooms, some of which are harmful to marine and terrestrial species. During the past few decades, these shifts in ocean colour in the Gulf have greater variability more than ever.
Ecological Consequences
Dead zones
Phytoplankton blooms alter oxygen dynamics. In the Arabian Gulf, mixotrophic species such as Noctiluca scintillans consume oxygen while producing waste that fuels bacterial decomposition. This process depletes oxygen, creating hypoxic “dead zones” where marine life cannot survive. At the same time, the carbon cycle is disrupted: instead of sinking carbon to the deep ocean, blooms recycle it at the surface, weakening the ocean’s role as a climate buffer.
Figure 2: Dead corals and lack of fish in the ocean due to oxygen starvation
Carbon Cycle
Normally, phytoplankton blooms help regulate climate by capturing carbon dioxide, converting it into organic matter, and sending it to the deep ocean when they die or are consumed. This “biological pump” locks carbon away for centuries, slowing global warming.
However, massive blooms of mixotrophic plankton like Noctiluca scintillans disrupt this process. Because they both photosynthesize and feed on other plankton, they generate large amounts of waste and dissolved organic matter that remain near the surface. Instead of sinking, this material is rapidly decomposed by bacteria, which consume oxygen and release carbon dioxide back into the atmosphere. The result is less carbon stored in the deep ocean and more carbon recycled at the surface, weakening the ocean’s role as a climate buffer and intensifying warming while expanding hypoxic “dead zones.”
Livelihoods and Fisheries
Harmful algal blooms and hypoxia-suffering zones can affect fish stocks in fisheries if they reach them. Coastal population depend on fisheries for food and income. Coastal communities are vulnerable to the reduction in fish stocks, as economic gains can rapidly decrease, and there are chances of people catching diseases from fish stocks suffering from hypoxia, as dead or decomposing fish increase.
Monitoring and Research
Research says that there might be something beyond natural seasonal and yearly changes in the ocean colour, and more related to the warming of ocean temperatures due to global warming than we think. Copernicus revealed that oceans globally are experiencing unprecedented warming and temperature records breaking barriers every day (BBC, 2024). Monitoring ocean colour is not just about aesthetics — it is a frontline indicator of climate change, ecosystem health, and human livelihoods in the GCC nations.
Case Study
On Feb 15, 2025, a satellite view from the PACE platform was captured showing very high chlorophyll a concentrations in the Gulf of Oman and Arabian Sea. The Gulf region is usually inhabited by dinoflagellate plankton, especially Noctiluca scintillans. The massive blooms have raised concerns about how the phytoplankton can decrease oxygen concentration in the water and cause dead zones. Many studies have highlighted how the Arabian Sea is one of the largest regions for oxygen minimum zones in the world, and worsened by the case of bigger Noctiluca scintillans blooms.
Figure 3: Chlorophyll a concentration in the Arabian Sea (Image courtesy – PACE platform)
Recent satellite images from NASA have captured massive phytoplankton blooms in the Gulf of Oman as well, painting the waters in swirling shades of green. While visually striking, these blooms signal deeper ecological stress. The culprit is also Noctiluca scintillans. Unlike traditional diatoms that support healthy food webs, Noctiluca blooms deplete oxygen, disrupt carbon cycling, and destabilize marine ecosystems.
The Gulf of Oman, a strategic waterway linking the Arabian Sea to the Persian Gulf, is particularly vulnerable. Seasonal monsoon winds drive nutrient upwelling, fueling blooms that are now larger and more frequent than in past decades. NASA’s PACE and Landsat satellites have revealed how these blooms stretch across hundreds of kilometers, reshaping the region’s ecology.
Figure 4: Phytoplankton bloom in the Gulf of Oman
What looks like a beautiful green glow from space is, in reality, a warning sign — a reminder that ocean colour is more than aesthetics. It is a vital indicator of ecosystem health, climate signals, and the resilience of communities that depend on the sea.
Conclusion
The changing colours of the Arabian Gulf are not just signals of crisis — they are an urgent call to action. By recognizing ocean colour as a frontline indicator of climate change, we empower ourselves to respond with urgency and innovation. Communities, scientists, and policymakers can work together to monitor blooms, reduce nutrient runoff, and champion circular solutions that restore balance to our seas. Every effort — from local cleanups to global climate commitments — contributes to protecting the Arabian Gulf’s fragile ecosystems and the livelihoods that depend on them.
The green glow seen from space reminds us that the ocean is alive, responsive, and vulnerable. But it also reminds us that human choices shape its future. By acting collectively and sustainably, we can turn warning signals into opportunities for resilience, ensuring that the Arabian Gulf’s waters remain not a symbol of decline, but of renewal and hope.
References
- Algae Bloom in Lake St. Clair – NASA
- Brierley AS. Plankton. Curr Biol. 2017 Jun 5;27(11):R478-R483. doi: 10.1016/j.cub.2017.02.045. PMID: 28586683.
- High Chlorophyll a Concentrations in the Gulf of Oman and Arabian Sea | NASA Earthdata
- Why the world’s oceans are changing colour
- The Ocean’s Green Glow Is a Warning Sign
- : dead zones | DEADLINE – for ocean’s life
