The color of the ocean has been undergoing significant changes over the past two decades, and a recent study suggests that human-caused climate change is likely responsible for this transformation. A team of researchers, led by scientists from the National Oceanography Center in the UK and the Massachusetts Institute of Technology in the US, conducted the study and made these findings public.
According to the researchers, more than 56% of the world’s oceans have experienced a change in color that cannot be explained by natural fluctuations. In particular, tropical oceans near the equator have become greener over the past 20 years, indicating changes in their ecosystems. The study, which was published in the journal Nature, explains that the color of the ocean is influenced by the substances present in its upper layers. For example, a deep blue color indicates a lack of life, while a green color signifies the presence of ecosystems supported by phytoplankton—microscopic plant-like organisms containing chlorophyll. Phytoplankton form the foundation of the ocean’s food chain, supporting larger organisms such as krill, fish, seabirds, and marine mammals.
The study’s co-author, Stephanie Dutkiewicz, a senior research scientist at MIT, states that the exact nature of these ecosystem changes remains unclear. While certain regions may experience a decrease in phytoplankton, others may see an increase, and it is likely that all parts of the ocean will witness changes in the types of phytoplankton present. Any alteration in the phytoplankton population can disrupt the delicate balance of ocean ecosystems and impact the food chain. Dutkiewicz emphasizes that these imbalances will exacerbate over time if ocean temperatures continue to rise. Additionally, the ocean’s capacity to sequester carbon will be affected since different types of plankton absorb varying amounts of carbon.
Although the researchers are still working to fully comprehend the implications of these changes, they assert that the transformations are undeniably driven by human-induced climate change. To monitor the alterations in ocean color, the scientists employed data from the Aqua satellite, which has been observing such changes for over two decades. This satellite can detect differences in color that are imperceptible to the human eye. Analyzing data from 2002 to 2022, the researchers used climate change models to simulate the impact on the oceans both with and without additional greenhouse gas emissions.
Prior research focused on changes in the greenness of the ocean – from the verdant chlorophyll in its plankton – to learn about trends in the changing climate. But Cael’s team pored over 20 years of observations by Nasa’s Modis-Aqua satellite, an exhaustive data repository, and looked for patterns of change in the ocean’s hue through a fuller colour spectrum including red and blue.
Plankton of different sizes scatter light differently, and plankton with different pigments absorb light differently. Examining changes in colour can give scientists a clearer picture of changes in plankton populations around the globe. Phytoplankton is crucial to ocean ecosystems because it is at the base of most of its food chains.
When comparing these changes in colour with those hypothesised from a computer model simulating what the oceans would look like if human-caused global heating had never taken place, the change was clear.
“We do have changes in the colour that are significantly emerging in almost all of the ocean of the tropics or subtropics,” said Cael.
The observed color changes closely aligned with the predictions made by Dutkiewicz regarding the effects of greenhouse gas emissions on ocean color. Her simulations had indicated that approximately 50% of the world’s oceans would undergo such color changes. Although Dutkiewicz was not surprised by these results, she described them as sobering, serving as yet another wake-up call regarding the significant impact of human-induced climate change on the Earth’s systems.
Dutkiewicz acknowledges that it is challenging to determine whether these color changes would be visible to the naked eye if the process continues. She suggests that if certain regions reach a tipping point, the changes might become noticeable, although it would require close observation over an extended period to discern the alterations. In future research, Dutkiewicz plans to further investigate the color changes in different oceanic regions and explore potential underlying causes.
In conclusion, recent research indicates that the color of the ocean has undergone remarkable transformations over the past two decades, largely due to human-induced climate change. These changes reflect shifts in marine ecosystems, particularly in tropical ocean regions. The color of the ocean is influenced by the presence of phytoplankton, which serve as the basis of the marine food web. Disruptions in these ecosystems can have far-reaching consequences, affecting the balance of oceanic life and the ocean’s ability to absorb carbon. The study’s findings emphasize the urgent need to address climate change and its impact on our planet’s delicate systems.
