July 2002 – June 2022
A twenty-year span of satellite data reveals a gradual transition in sea surface color towards green.
The traditionally deep-blue ocean is exhibiting a subtle shift towards a greener hue. While this may appear less urgent compared to phenomena like unprecedentedly warm sea surface temperatures, the change in ocean color serves as an indicator of the underlying ecosystem. Phytoplankton communities, which are microscopic organisms capable of photosynthesis, populate the near-surface waters and are integral to both the marine food chain and the carbon cycle. The alteration in ocean color affirms a pattern anticipated as a consequence of climate change and signifies adjustments in the ecosystems of the global ocean, which constitutes 70 percent of Earth’s surface.
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Core Discoveries from Recent Studies
A team of researchers spearheaded by B. B. Cael, a lead scientist at the U.K.’s National Oceanography Centre, disclosed that 56 percent of the global ocean surface has experienced a notable color change over the past two decades. Utilizing color data from the MODIS (Moderate Resolution Imaging Spectroradiometer) instrument on NASA’s Aqua satellite, the researchers ascertained that this transformation largely stems from the sea becoming increasingly green.
The above map illuminates the regions where ocean surface color underwent changes between 2002 and 2022. Darker shades of green denote more substantial alterations (higher signal-to-noise ratio). Cael indicated that these locations reflect areas where alterations in ocean ecosystems have been detectable over the last 20 years. The study primarily concentrated on tropical and subtropical areas, deliberately omitting higher latitudes, which are dark for a portion of the year, and coastal waters, which exhibit inherently high data noise levels.
The Implications of Chlorophyll Variability
Black dots displayed on the map mark the zones, comprising 12 percent of the ocean surface, where chlorophyll concentrations also shifted during the research period. Historically, chlorophyll has been the default metric for remote sensing scientists to evaluate phytoplankton presence and productivity. Nevertheless, these estimates commonly rely on a limited set of colors in the visible light spectrum. The figures illustrated in green encompass the full range of visible colors, providing a more comprehensive view of the ecosystem.
An Exceptional Window into Oceanic Trends
Longitudinal data sets from a single sensor are somewhat uncommon in the realm of remote sensing. As NASA’s Aqua satellite marked its 20th anniversary in orbit—surpassing its initial design lifespan of 6 years—Cael pondered the potential for discovering long-term patterns in the amassed data. He considered the possibility of overlooked insights in the collected ocean color information. “We are underutilizing the available data,” Cael noted.
By employing an expansive approach to data analysis, the team confirmed an ocean color change that had been projected by climate models. Remarkably, this shift was expected to require 30-40 years of satellite-based chlorophyll data for detection, due to the inherent variability in chlorophyll levels relative to climate change trends. The novel method, incorporating the entire visible spectrum, validated the trend within two decades.
Potential Causes and Future Outlook
While it is currently challenging to pinpoint the exact ecological factors driving these new color shades, the researchers suggest that the changes could be attributed to differing plankton communities, an increase in detrital particles, or other marine organisms such as zooplankton. Cael stated that it is improbable that the color changes are caused by materials like plastics or other pollutants, as these substances are not sufficiently prevalent on a large scale.
Cael further elaborated that surface waters have grown more stratified in the past 20 years due to absorption of excess heat from global warming. Consequently, these waters are less likely to blend with deeper, nutrient-rich layers, thereby favoring plankton adapted to nutrient-scarce conditions. The areas where ocean color has shifted align well with regions where ocean stratification has increased, although no correlation with sea surface temperature changes has been observed.
Further insights into Earth’s marine ecosystems are anticipated with the launch of NASA’s PACE (Plankton, Aerosol, Cloud, ocean Ecosystem) satellite, slated for 2024. The upcoming data, featuring finer color resolution, will permit researchers to glean more nuanced information concerning ocean ecology, including phytoplankton species diversity and growth rates.
References
“Abrupt shifts in 21st-century plankton communities” by B. B. Cael, Stephanie Dutkiewicz, and Stephanie Henson, published in Science Advances on October 29, 2021. DOI: 10.1126/sciadv.abf8593
“Global climate-change trends detected in indicators of ocean ecology” by B. B. Cael, Kelsey Bisson, Emmanuel Boss, Stephanie Dutkiewicz, and Stephanie Henson, published in Nature on July 12, 2023. DOI: 10.1038/s41586-023-06321-z
“Detection of anthropogenic climate change in satellite records of ocean chlorophyll and productivity” by S. A. Henson, J. L. Sarmiento, J. P. Dunne, L. Bopp, I. Lima, S. C. Doney, J. John, and C. Beaulieu, published in Biogeosciences on February 15, 2010. DOI: 10.5194/bg-7-621-2010
“Increasing ocean stratification over the past half-century” by Guancheng Li, Lijing Cheng, Jiang Zhu, Kevin E. Trenberth, Michael E. Mann, and John P. Abraham, published in Nature Climate Change on September 28, 2020. DOI: 10.1038/s41558-020-00918-2
Frequently Asked Questions (FAQs) about Oceanic Color Shift
What is the main finding of the 20-year study led by B. B. Cael?
The main finding is that 56 percent of the global ocean surface has experienced a significant shift in color towards green over the past two decades. This change is largely attributed to an increase in phytoplankton communities in near-surface waters.
What implications does the change in ocean color have?
The shift in ocean color is indicative of underlying changes in marine ecosystems. It confirms a pattern anticipated due to climate change and signifies alterations in the ecosystems of the global ocean, affecting both the marine food chain and the carbon cycle.
What is the significance of chlorophyll in this study?
Chlorophyll has been the traditional metric used to assess phytoplankton abundance and productivity. In this study, changes in chlorophyll levels were observed in areas covering 12 percent of the ocean’s surface. These changes were mapped to provide a more comprehensive understanding of ocean ecology.
How reliable is the data source used in the study?
The study utilizes data from the MODIS (Moderate Resolution Imaging Spectroradiometer) instrument on NASA’s Aqua satellite, which has been in orbit for 20 years. The longevity of the data set adds credibility to the study’s findings, especially considering that long-term data sets from a single sensor are relatively rare in remote sensing.
What areas were primarily focused on in this study?
The study concentrated mainly on tropical and subtropical regions. It deliberately omitted higher latitudes, which are dark for part of the year, and coastal areas, where data are naturally very noisy.
What future research is planned in this area?
NASA’s PACE (Plankton, Aerosol, Cloud, ocean Ecosystem) satellite, set to launch in 2024, is expected to provide finer color resolution data. This will enable researchers to glean more nuanced information concerning ocean ecology, such as phytoplankton species diversity and growth rates.
What are the potential causes for the ocean’s color change according to the study?
While the exact ecological factors are not definitively identified, potential causes could include differing plankton communities, an increase in detrital particles, or the presence of other marine organisms such as zooplankton. It is unlikely that materials like plastics or other pollutants are causing these changes.
How does ocean stratification relate to the findings?
Over the past 20 years, surface waters have absorbed excess heat due to climate change, becoming more stratified and less prone to mixing with nutrient-rich deeper layers. This favors phytoplankton adapted to nutrient-poor conditions and aligns well with the areas where ocean color has shifted.
Are the observed changes in ocean color correlated with sea surface temperature changes?
No, the study found that the areas where ocean color has shifted do not overlap with regions where sea surface temperature changes have been observed.
What does the study predict or indicate about the future state of marine ecosystems?
While the study does not make specific predictions, it confirms a trend in ocean color change that had been projected by climate models. This change is indicative of shifts in marine ecosystems and could have far-reaching implications for the marine food chain and carbon cycle.
More about Oceanic Color Shift
- Ocean Color and Climate Change: An Overview
- National Oceanography Centre: Research Publications
- NASA Aqua Satellite: Data and Mission Details
- Phytoplankton and Marine Ecosystems: A Primer
- MODIS Instrument: Technical Specifications and Data Availability
- NASA’s PACE Mission: Future Prospects in Ocean Monitoring
- The Role of Chlorophyll in Ocean Ecology
- Ocean Stratification and Climate Change: A Review
- Global Trends in Marine Ecosystems: Implications for Conservation
8 comments
Wow, this is some serious stuff. Had no idea the ocean color could tell us so much about whats happening beneath the surface.
never thought I’d see the day when the sea itself starts changing color. Climate change is real people, and this is solid proof.
Why aren’t we talking about this more? Seems like the kinda thing that should be all over the news. It’s not just warm weather, it’s a whole ecosystem at stake.
I’m no scientist but this article made it pretty easy to understand the complexities involved. Kudos to the researchers and the writer.
so the color change is linked to plankton? Interesting. Guess even the smallest creatures can have a big impact.
I agree with Robert. This needs to be discussed more openly and maybe then more people will realize the urgency of climate change.
Always amazed at what satellites can do. Monitoring ocean color from space? That’s next-level stuff right there.
This is really scary, to be honest. But it’s also an amazing use of tech to understand what we’ve done to the planet. Just hope it’s not too late to reverse some of this.