Climate Change Alters Ocean Colour | 17 Jul 2023

Source: DTE

Why in News?

Recently, a new study reveals that 56% of the world's oceans have experienced a change in colour due to climate change.

• Tropical waters, particularly the southern Indian Ocean, have turned green, indicating an increase in phytoplankton and marine life.

What are the Key Highlights of the Study?

• Long-Term Trends and Data Analysis:
  • Aqua Satellite Data:
    • Researchers analyzed data from the Moderate Resolution Imaging Spectroradiometer (MODIS) on the Aqua satellite (NASA’s Earth Science satellite mission), monitoring ocean colour for two decades (2002-2022).
    • MODIS takes measurements in seven visible wavelengths (Light of different wavelengths produces different perceptions of colour).
  • Subtle Colour Changes:
    • Human eyes cannot detect subtle colour changes in the oceans, which may contain a mix of wavelengths ranging from blue to green and even red.
  • Green Waters and Phytoplankton:
    • The study finds that green-coloured water indicates the presence of phytoplankton, essential microscopic plant-like organisms.
      • Phytoplankton serve as the base of the marine food web, similar to plants on land, and play a crucial role in supporting marine life.
    • The colour of the ocean affects the amount of carbon dioxide absorbed by the oceans, with current estimates indicating that oceans absorb 25% of global CO2 emissions.
  • Role of Climate Change:
    • By comparing annual variations in ocean colour over the two decades, the study identified climate change as the primary factor behind the observed changes.
    • Using a model, researchers simulated two scenarios—one considering greenhouse gas emissions and the other without them.
    • The scenario accounting for greenhouse gas emissions predicted that colour changes could occur in approximately 50% of the world's surface oceans, aligning with satellite observations indicating a 56% shift to green or blue waters.
  • Implications for Marine Life and Conservation:
    • Impact on Organisms:
      • The green hue comes from chlorophyll, a pigment that helps phytoplankton make food. A change in colour due to an increase or decline in the population will impact organisms that feed on plankton.
    • Carbon Sequestration:
      • Different types of plankton have varying abilities to absorb carbon, potentially influencing the ocean's capacity for carbon uptake.
  • Regional Variability and the Need for Further Study:
    • The southern Indian Ocean exhibits significant changes in colour, while waters near India do not follow the same trend, potentially due to natural variability.
• Recommendations:
  • Researchers emphasize the need for individuals and policymakers to recognize the significance of these changes and take appropriate action to protect marine ecosystems.
  • Ongoing monitoring and further research are crucial to understanding regional variations and the full extent of climate change's impact on ocean colour.