A new study led by B. B. Cael from the UK's National Oceanography Centre has revealed a significant shift in the colour of the world's oceans, with far-reaching implications for marine ecosystems and the global carbon cycle.
The research, which analysed 20 years of data from Nasa's Aqua satellite, found that 56 per cent of the global sea surface has undergone a noticeable change in colour since 2002, primarily turning greener.
This colour change, while subtle to the human eye, provides crucial insights into the health and composition of ocean ecosystems.
The greening trend is particularly pronounced in tropical and subtropical regions, indicating potential alterations in phytoplankton communities - microscopic organisms that form the foundation of the marine food web and play a vital role in carbon sequestration.
The study utilised data from the MODIS instrument aboard the Aqua satellite, which has been monitoring ocean colour for two decades. By analyzing the full spectrum of visible light reflected from the ocean surface, researchers were able to detect changes that traditional chlorophyll measurements might have missed.
Cael emphasised that these colour shifts likely signify broader changes in ocean ecosystems, potentially including different assemblages of plankton, increased detrital particles, or changes in zooplankton populations. The research team ruled out widespread pollution or plastics as the cause, noting that these are not prevalent enough to account for the observed changes.
One key factor identified in the study is increased ocean stratification due to climate change. As surface waters warm and become less prone to mixing with deeper, nutrient-rich layers, it creates conditions that favour certain types of plankton adapted to nutrient-poor environments.
The findings align with climate model predictions but have been detected much earlier than anticipated. This early confirmation of the trend underscores the rapid pace of climate-induced changes in our oceans and the need for continued monitoring and research.
Looking ahead, Nasa's upcoming PACE satellite mission, set to launch in 2024, promises to provide even more detailed observations of ocean colour, potentially offering further insights into phytoplankton diversity and growth rates.
As our understanding of these changes deepens, it becomes increasingly clear that the shifting colours of our oceans are a visible manifestation of the profound impacts of climate change on Earth's most vital ecosystems.
