How is global warming changing the color of the oceans?

A 20-year series of satellite data obtained with the MODIS-Aqua sensor provides compelling evidence that global warming is having a significant impact on changes in the color of ocean waters. Significant increases in temperatures and increased carbon dioxide concentrations are contributing to the expansion of phytoplankton populations. Such population growth affects the color changes in the oceans observed from satellites. The results highlight the profound impact of climate change on marine ecosystems, with far-reaching implications for biodiversity and global fisheries.

Survey methodology

The study , published in the journal Nature, was conducted by an international team of researchers that included experts from the Massachusetts Institute of Technology (MIT), the University of Southampton and a number of other research institutions. This interdisciplinary collaboration has allowed the knowledge and resources of various research centers to be combined, resulting in comprehensive results.

The researchers analyzed data collected by the MODIS satellite aboard the Aqua satellite over the past two decades. The satellite, equipped with advanced sensors, recorded the so-called “”Fusion”. remote-sensing reflectance (R_rs), which is an indicator of the health of ocean surface ecosystems. The analysis included several bands of light waves, from blue to red, providing a multifaceted picture of changes in ocean color. The data analysis process included detailed processing of raw satellite data, atmospheric correction and sensor calibration. The researchers then used advanced statistical models to identify long-term trends in light reflectivity. The focus was on identifying subtle changes in different wave bands, which allowed the precise identification of changes in the structure of marine ecosystems.

Survey results

An analysis of satellite data showed that 56 percent of. of the global ocean surface records significant changes in reflectivity (R_rs), which indicates the evolution of the structure of surface ecosystems. The most pronounced changes were observed at latitudes below 40°, corresponding to tropical and subtropical zones. The discovery represents a significant change from previous studies, which postulated the need for more than 30 years of data to detect climate trends affecting phytoplankton. By using new methodological approaches, it has become possible to observe these changes after only 20 years of research. Although the change in color of ocean waters is not noticeable to the naked eye, satellite remote sensing techniques make it possible to precisely map and document these changes.

Greening oceans

Phytoplankton (microscopic organisms), form the basis of the aquatic food web, being a key source of food for small fish, zooplankton and crustaceans such as krill. These, in turn, are eaten by larger pelagic species like tuna and whales. Without phytoplankton, the oceanic food chain would collapse. Phytoplankton also play an important role in the carbon cycle, absorbing carbon dioxide from the atmosphere through photosynthesis and storing it in their bodies. When phytoplankton die and decompose, some of this carbon sinks to the ocean floor, carrying about ten gigatons of carbon from the atmosphere to the depths each year.

Phytoplankton includes at least a hundred thousand different species, varying in color, size, composition and function. Although most are harmless, the sudden growth of some species, caused by temperature changes or nutrient influx, can lead to harmful algal blooms. These, in turn, can poison or suffocate fish and even cause respiratory failure and other diseases in humans. Warmer ocean waters favor the growth of phytoplankton, extending their reproductive periods and increasing their abundance. Rising temperatures also affect other aspects of the marine ecosystem, such as the distribution of fish species. In search of optimal thermal conditions, fish migrate, further disrupting the balance of ecosystems.

Carbon dioxide as a catalyst

In addition to warmer waters, increased atmospheric carbon dioxide concentrations are also affecting changes in phytoplankton populations. Phytoplankton use carbon dioxide in the process of photosynthesis, which means that higher concentrations of_CO2 favor their growth. This relationship could lead to an increase in biological activity in the oceans, and thus to further changes in their color. High concentrations of carbon dioxide also affect ocean acidification, which has further negative effects on marine organisms such as corals and crustaceans, which are sensitive to changes in water pH.

Global warming and global implications

Changes in the color of the oceans could have significant consequences for the global climate system. These changes directly affect the process of absorption of solar radiation by the oceans, which has far-reaching effects on global weather patterns and climate. The increase in phytoplankton populations, responsible for changing the color of the waters, also affects changes in the albedo of the ocean surface, i.e. its ability to reflect sunlight back into the atmosphere. Such changes can radically affect oceanic and atmospheric circulation, which is sometimes crucial to the Earth’s climate balance. In addition to climate aspects, these changes also have potential impacts on public health and ocean-related economic sectors such as fisheries and tourism.

Photo. main: NASA/The Aqua Satellite, Courtesy Of NASA/Goddard Space Flight Center/Jeff Schmaltz/The MODIS Land Rapid Response Team