Font size:
Print
Monsoon Extremes Threaten Marine Productivity
Changes in monsoon affect marine productivity in Bay of Bengal: study
Context: A recent study published in Nature Geoscience reveals that strong and weak Indian Summer Monsoons (ISM) over the last 22,000 years have significantly impacted marine productivity in the Bay of Bengal.
Key Findings of the Study
- Marine Productivity and Its Importance: Marine productivity, which is a proxy for plankton growth, is critical for the marine food web, providing the primary source of nutrition for aquatic life.
- The Bay of Bengal, despite covering less than 1% of the world’s ocean area, produces 8% of global fishery production.
- The region’s nutrient-rich waters support dense communities dependent on fisheries for food and income.
- Impact of Strong and Weak Monsoons: Both strong and weak monsoons disrupt ocean mixing, reducing the availability of nutrients for plankton, which are essential for marine life.
- Extreme monsoon conditions interfere with the vertical movement of nutrient-rich waters from the deep ocean to the surface, leading to a 50% reduction in food for marine organisms.
Methods Used
- Scientists analysed fossilised shells of foraminifera, small marine organisms that record environmental data in their calcium carbonate shells, to reconstruct long-term changes in rainfall, ocean temperatures, and marine life.
- These microfossils were retrieved from seafloor sediments aboard the JOIDES Resolution, a research ship operating under the International Ocean Discovery Program.
Historical Data
- During historical periods such as Heinrich Stadial 1 (17,500 to 15,500 years ago) and the early Holocene (10,500 to 9,500 years ago), marine productivity sharply declined when monsoons were unusually strong or weak.
- Monsoon rainfall affects river runoff into the Bay of Bengal, influencing ocean salinity and circulation. Excess freshwater on the surface hinders nutrient mixing, while weak monsoons reduce wind-driven mixing.
Implications for the Future
- Link to Climate Change: The study warns of similarities between past climate conditions and future projections. Expected increases in surface water temperatures and stronger freshwater runoff could lead to decreased marine productivity, similar to past declines.
- Weakened winds, which are projected in future climate scenarios, may fail to break ocean stratification, preventing the necessary nutrient cycling for plankton growth.
- Potential Impact on Coastal Communities: The decline in marine productivity can severely affect fish stocks, threatening food security for the millions of people who rely on fisheries along the Bay of Bengal.
- Disruptions in the marine food web due to these monsoon extremes could have profound consequences for both ecosystems and local economies.
