Why Is the Ocean Getting Greener? – Impakter

The Changing Color of the World’s Oceans: A Sign of Climate Change?

The sky and the ocean both appear blue in color, but not because either one is a reflection of the other – it’s down to how they absorb or scatter sunlight. While Earth’s atmosphere scatters the blue end of sunlight’s spectrum the most, its ocean absorbs the light at the red end and leaves the blue behind.

Both of these effects result in a blue color visible to the human eye, and not only on the ground in the ocean’s case – given that more than 70% of Earth’s surface is covered by ocean, it also appears as a “blue planet” from space.

However, according to a new study published in Nature last month, the world’s oceans overall appear to be changing color: They’re getting greener.

How Was the Color Change Detected?

The group analyzed 20 years of ocean color data collected by one of the scientific instruments onboard “Aqua” – one of NASA’s Earth Science satellites.

This instrument is known as the Moderate Resolution Imaging Spectroradiometer (MODIS), which determines ocean color by measuring light reflected off the surface of the water.

Upon analyzing MODIS’ time series dataset from 2002-2022, the group observed significant color change trends over 56% of the world’s oceans during this time – particularly in the subtropical and tropical regions.

What’s Causing the Greening?

Although the total environmental impact of human-driven climate change is still unclear, we do know it’s having a profound impact on Earth’s ecosystems – marine ecosystems included.

And as the Nature study highlights, climate change has been shown to affect surface-ocean ecosystems at specific locations, but it can be hard to monitor such changes on a global scale over long periods of time.

That’s where satellite remote sensing of ocean color comes in: Because changes in the color of the ocean can indicate changes to the life existing on its surface.

According to the group, the observed color change trends in the world’s oceans over the past couple of decades reflect relative changes in marine ecosystems – changes which they suggest could be caused by climate change.

Although they’re not sure of the exact ecological shift that’s causing the color change – and they also mention the greening could be caused by “an increase in detrital particles” – the study’s scientists suggest that the greening could also be down to the effect of climate change on phytoplankton communities.

Regardless of the cause, the group note that the observed changes will have “ecological implications.”

What Are Phytoplankton?

With a name derived from the Greek for “plant” (phyton) and “wanderer” (plankton), phytoplankton are microscopic plant-like organisms that live near the ocean’s surface and are of great ecological significance.

Not only are phytoplankton integral to the aquatic food web and marine biodiversity, but they also form a vital component of the ocean carbon cycle. They sequester enormous amounts of carbon dioxide from the atmosphere, and produce a significant portion of the oxygen that we breathe through photosynthesis, acting as a crucial part of the “ocean biological carbon pump.”

Why Do They Think Climate Change is Involved?

As the study states: “A key question is whether the identified trends are driven by climate change.”

To see how climate change might play into the color change, the group used a computer simulation to model changes in the global ocean ecosystem during the 21st century (2000-2105) under two different scenarios: One with high greenhouse gas emissions and one with emissions consistent with the levels of 1860 as a control.

“Thus, the differences between the simulations indicate anthropogenically driven climate change,” states the study.

When comparing the trends that emerged in the high emissions simulation with the real observed trends in the world’s oceans, similarities became apparent, suggesting climate change as the driving factor behind the color change.

How do they think climate change is affecting phytoplankton? The group notes that although changes in sea surface temperature (SST) do not appear related to the observed trends, changes in the structure and stratification of the ocean’s layers – factors known to change with climate and also affect phytoplankton – might be the culprits.

“Altogether, these results suggest that the effects of climate change are already being felt in surface marine microbial ecosystems,” states the study.

What’s the Significance of These Findings?

Due to the ecological importance of phytoplankton for ocean ecosystems, biodiversity and carbon storage, the observed ocean color change – possibly indicating changes in the structure and biomass of phytoplankton communities – could have implications for the marine environment.

The group behind the study note how their findings may be relevant for ocean conservation and governance, specifically pointing out how monitoring changes in surface-ocean microbial ecosystems could help inform where to establish marine protected areas (MPAs) as part of the recently adopted and historic United Nations High Seas Treaty.

They also highlight the importance of satellite data and the value of long-term missions such as NASA’s MODIS-Aqua, stating that “for future work, merged multi-satellite products, as well as work that is currently underway to improve them, are essential.”

In fact, NASA are actually advancing towards the scheduled 2024 launch of a new satellite science mission to study ocean color, biology and health called PACE (Plankton, Aerosol, Cloud, ocean Ecosystem), announcing in April this year that the spacecraft has been successfully assembled.

Furthermore, the group also call for ongoing work to delve deeper into studying such trends further to understand what kind of surface-ocean ecosystem shifts could be behind the color change, stating:

“Given the key role of plankton ecosystems in marine food webs, global biogeochemical cycles and carbon cycle–climate feedbacks, detecting change in these ecosystems is of great utility.”

SDGs, Targets, and Indicators

1. Which SDGs are addressed or connected to the issues highlighted in the article?

• SDG 14: Life Below Water

2. What specific targets under those SDGs can be identified based on the article’s content?

• Target 14.1: By 2025, prevent and significantly reduce marine pollution of all kinds, in particular from land-based activities, including marine debris and nutrient pollution.
• Target 14.2: By 2020, sustainably manage and protect marine and coastal ecosystems to avoid significant adverse impacts, including by strengthening their resilience, and take action for their restoration in order to achieve healthy and productive oceans.

3. Are there any indicators mentioned or implied in the article that can be used to measure progress towards the identified targets?

• Indicator 14.1.1: Index of coastal eutrophication and floating plastic debris density.
• Indicator 14.2.1: Proportion of national exclusive economic zones managed using ecosystem-based approaches.

The article discusses the changing color of the world’s oceans, specifically the greening trend observed over the past couple of decades. This is connected to SDG 14: Life Below Water, which aims to conserve and sustainably use the oceans, seas, and marine resources.

Based on the content of the article, two specific targets under SDG 14 can be identified:

1. Target 14.1: By 2025, prevent and significantly reduce marine pollution of all kinds, in particular from land-based activities, including marine debris and nutrient pollution.
2. Target 14.2: By 2020, sustainably manage and protect marine and coastal ecosystems to avoid significant adverse impacts, including by strengthening their resilience, and take action for their restoration in order to achieve healthy and productive oceans.

The article mentions the use of satellite data and the analysis of ocean color trends to detect changes in marine ecosystems. This implies the use of indicators to measure progress towards the identified targets. Two relevant indicators are:

• Indicator 14.1.1: Index of coastal eutrophication and floating plastic debris density. This indicator measures the level of pollution in coastal areas, including nutrient pollution and marine debris.
• Indicator 14.2.1: Proportion of national exclusive economic zones managed using ecosystem-based approaches. This indicator assesses the extent to which marine and coastal ecosystems are being sustainably managed and protected.

4. Table: SDGs, Targets, and Indicators

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Source: impakter.com

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