Decoding Our Changing Ocean

Mysterious Turquoise Waters in Scotland

During the summer of 2021, beachgoers and sailors in Scottish waters witnessed a remarkable phenomenon: the ocean turned a vibrant turquoise color not once, but twice in different locations ² .

The OSR7 investigation revealed this stunning visual display was caused by unusual blooms of coccolithophores—a type of marine plankton that influences the carbon cycle by capturing and storing atmospheric carbon ² .

Scientists determined that specific weather conditions triggered these unusual events:

• Coldest April in 30 years in the Clyde Sea restricted the regular spring bloom
• Subsequent stormy, wet weather in May added nutrients to the waters
• Summer arrived with increased sunlight and warmer temperatures

These conditions combined to create the perfect environment for coccolithophores to flourish in unprecedented numbers ² .

Storm Blas and Mediterranean Upwelling

In November 2021, an intense and prolonged cyclone named Storm Blas affected the Balearic Islands in the Mediterranean Sea, causing dramatic oceanographic changes ² .

The storm triggered intense upwelling—a process where deep, cold water rises to the surface—along the northwestern coasts of Mallorca and Ibiza. This resulted in surface temperatures up to 6°C colder than usual for three consecutive days ² .

While this might seem like a refreshing change in a warming world, such rapid, extreme temperature shifts can have devastating consequences for marine life adapted to specific thermal conditions.

The event also caused a reversal of the regional current system, demonstrating how extreme weather events can disrupt fundamental ocean processes ³ . Despite these local cooling effects, the Mediterranean, like other ocean basins, continues to experience long-term warming trends with significant impacts on marine ecosystems.

Marine Heatwaves and Cold Spells

The OSR7 documents concerning trends in extreme temperature events across the global ocean. Marine heatwaves—prolonged periods of anomalously high ocean temperatures—have become more frequent and intense in recent decades ² .

According to the report, the ocean has experienced approximately one additional heatwave event every five to ten years, while marine cold spells (periods of unusually low temperatures) have become less frequent, with one fewer event every five years ² .

These trends matter because extreme temperature events can have devastating impacts on marine ecosystems. Marine heatwaves have been linked to coral bleaching, species migrations, changes in fishery productivity, and alterations to marine food webs. The report notes that in 2023 alone, 22% of the global ocean surface experienced at least one severe to extreme marine heatwave event .

Circulation Changes and Ecological Shifts

The report also examines changes in global ocean circulation patterns, including the Atlantic Meridional Overturning Circulation (AMOC)—a critical system of currents that redistributes heat around the planet ² .

The OSR7 found a surprising discrepancy between observational data and model results regarding inter-basin transports around the Southern Ocean, which will inform future improvements in ocean and climate monitoring ² .

Additionally, the report documents a record low heat exchange across the Greenland-Scotland Ridge between 2017-2019, decreasing by 4-9% compared to the 1993-2020 average ² . This system plays a key role in shaping Arctic climate patterns and is linked to the broader AMOC system.

Changes in these circulation patterns can have far-reaching effects on regional climates, nutrient distribution, and consequently, biological communities throughout the ocean.

Methodology: A Multi-Tool Approach

Coastal upwelling—the process by which deep, nutrient-rich water rises to the surface—plays a crucial role in supporting productive marine ecosystems. To better monitor this important phenomenon, scientists developed an innovative method that combines multiple data sources ² .

The researchers focused on two test regions: the northwestern Iberian Peninsula and the Bay of Biscay ³ .

Experimental Procedure:

1. High-Frequency Radar (HFR) Deployment: Specialized radar systems were used to measure surface currents with high precision in coastal areas ² .
2. Multi-Platform Data Collection: Researchers integrated data from autonomous platforms, moored buoys, research expeditions, and satellite observations ³ .
3. Indicator Development: Scientists created a new coastal upwelling index that incorporates information on ocean currents, wind patterns, sea level pressure, and sea surface temperature ² .
4. Validation: The team compared results from their new method with traditional monitoring approaches and existing ocean reanalysis data to verify accuracy ³ .

Results and Analysis: Mapping Ocean Fertilization

The new monitoring method proved highly effective at categorizing upwelling events and producing high-resolution 2D maps of these processes ² .

The research confirmed that upwelling connects offshore waters with coastal ecosystems, bringing cold, nutrient-rich waters to the surface that "fertilize" coastal areas and support productive fishing grounds ² .

The study also demonstrated that Storm Blas—mentioned earlier—triggered dramatic upwelling around the Balearic Islands, causing surface temperatures up to 6°C colder than usual and reversing regional current systems ³ .

This finding highlights how extreme weather events can significantly impact coastal processes with potential consequences for fisheries, aquaculture, and coastal communities.

This innovative approach to monitoring upwelling represents a significant advancement in our ability to track important ocean processes. The method can be applied to any coastal area of the global ocean, making it a valuable tool for managing marine resources, protecting ecosystems, and supporting the sustainable development of coastal economies ² .