Satellite-observed significant decrease in Arctic phytoplankton biomass during the COVID-19 pandemic due to reduced...

Area of Science:

• Marine Ecology
• Oceanography
• Remote Sensing

Background:

• The COVID-19 pandemic lockdown drastically reduced global human activities, impacting marine ecosystems.
• Studies on the Arctic Ocean's phytoplankton biomass response to these changes were limited.
• Phytoplankton, crucial for marine food webs and carbon cycling, are sensitive indicators of environmental shifts.

Purpose of the Study:

• To develop and validate an accurate pan-Arctic ocean color model for chlorophyll-a (Chla) retrieval.
• To establish a long-term, high-resolution daily Chla dataset for the Arctic Ocean.
• To investigate the impact of COVID-19 lockdown-induced human activity changes on Arctic Chla.

Main Methods:

• Developed a novel pan-Arctic ocean color model for chlorophyll-a (Chla) concentration retrieval using optical classification.
• Applied the model to satellite ocean color imagery from 2003-2022 during the Arctic Ocean's sunshine period (April-September).
• Analyzed the correlation between reduced land-based nutrient inputs (wastewater discharge, atmospheric pollution) and Chla changes.

Main Results:

• A significant 19% decrease in regionally-averaged Arctic Ocean Chla was observed during the 2020-2021 COVID-19 lockdown compared to 2019.
• The most substantial Chla declines (31-49%) occurred in April-May 2021, with the European sector showing the longest duration of decrease.
• Reduced wastewater discharge and atmospheric PM2.5 were strongly correlated with Chla decrease (R=0.52-0.71), impacting shallow and deep seas differently.

Conclusions:

• Arctic Ocean ecosystems were significantly impacted by human activity reductions during the COVID-19 pandemic.
• Wastewater discharge reduction most affected shallow Arctic seas, while atmospheric pollution reduction impacted deep Arctic waters.
• Effective Arctic ecosystem protection requires integrating both long-term climate change and short-term human activity assessments.