Monsoon Extremes Threaten Bay of Bengal’s Marine Life, New Research Warns

In the warm, restless waters of the Bay of Bengal, where the summer monsoon breathes life into one of the world’s richest marine ecosystems, a silent drama has been unfolding for thousands of years. Now, new research led by a team of scientists—including professors from Rutgers University—has revealed a troubling twist: the very force that nurtures the region’s ocean life is becoming dangerously unpredictable, threatening the foundation of food security for millions.

Published recently in Nature Geoscience, the study dives deep into the relationship between India’s summer monsoon and the ocean’s ability to sustain marine life. Conducted by researchers from Rutgers, the University of Arizona, and partners from India, China, and Europe, the investigation peels back layers of Earth’s climatic history, exposing stark warnings for the future.

The Bay of Bengal: A Crucible of Life

Though the Bay of Bengal covers less than 1% of the world’s ocean surface, its significance is immense. These waters fuel nearly 8% of global fishery production, feeding countless communities along the densely populated coasts of India, Bangladesh, Myanmar, and beyond. Here, seafood is not just an industry—it is a lifeline, a source of daily sustenance and economic stability.

“Millions of people living along the Bay of Bengal rely on the sea for protein, particularly from fisheries,” explained Yair Rosenthal, a Distinguished Professor at Rutgers University and one of the study’s key authors. “The productivity of these waters—the ability of the ocean to support plankton growth—is the foundation of the marine food web. If ocean productivity declines, it will powerfully affect the ecosystem, ultimately reducing fish stocks and threatening food security for coastal communities.”

At the heart of this intricate web is plankton: tiny, drifting organisms that flourish near the ocean’s surface. These microorganisms form the first critical link in the marine food chain, supporting everything from small fish to apex predators. And what fuels plankton? Nutrients—vital elements delivered by the dynamic mixing of ocean waters, driven in large part by the monsoon’s seasonal pulse.

A Climate History Etched in Shells

To uncover how the Indian summer monsoon has shaped the Bay of Bengal’s biological health over millennia, researchers turned to a remarkable natural archive: the fossilized shells of foraminifera. These microscopic plankton, encased in calcium carbonate shells, accumulate on the seafloor and preserve chemical signatures of the oceans they inhabited.

“By analyzing their chemistry and tracking the abundance of certain types that thrive in productive waters, we reconstructed long-term changes in rainfall, ocean temperatures, and marine life in the Bay of Bengal,” said Kaustubh Thirumalai, a geoscientist at the University of Arizona and the lead author of the study.

The team retrieved sediment cores from the ocean floor aboard the research vessel JOIDES Resolution, a floating scientific laboratory. Using these ancient shells, they crafted an environmental timeline stretching back 22,000 years, spanning dramatic climatic events such as the last glacial maximum and the warming epoch of the early Holocene.

What emerged from the data was a sobering revelation: periods of both extreme monsoon strength and extreme weakness were catastrophic for ocean productivity.

Too Much or Too Little: A Delicate Balance Disrupted

The Bay of Bengal thrives on a delicate interplay of forces. During a “normal” monsoon, heavy rains and river runoff deliver freshwater to the bay, while robust winds churn the ocean, drawing nutrient-rich waters upward. This balance fosters ideal conditions for plankton blooms and the vibrant ecosystems they support.

But when the monsoon tips too far in either direction, chaos ensues.

During episodes of a severely weakened monsoon, such as the Heinrich Stadial 1 (around 17,500 to 15,500 years ago), diminished rainfall and weaker winds stifled ocean circulation. Without strong mixing, nutrients failed to reach the surface, causing plankton populations to collapse—and along with them, the entire marine food web.

Conversely, during periods of hyperactive monsoon, such as the early Holocene (10,500 to 9,500 years ago), an overwhelming flood of freshwater created a different problem. The lighter freshwater formed a “cap” over the denser, saltier ocean water, acting like a lid that trapped nutrients below and again starved the surface waters of life-sustaining elements.

“In both cases, whether the monsoon was too strong or too weak, marine productivity was cut nearly in half,” Thirumalai explained. “This kind of disruption reverberates all the way through the ecosystem—from the smallest microorganisms to the fish people depend on.”

A Warming World Mirrors the Past

The past, it seems, is prologue. When the researchers compared their ancient records with modern observations and future climate projections, they found troubling similarities. Today, rising global temperatures are supercharging the hydrological cycle, making the Indian monsoon more volatile. Models suggest heavier rainfall, stronger freshwater runoff, and warmer surface waters in the coming decades—conditions that echo the very scenarios that previously devastated marine productivity.

What’s worse, future wind patterns may be insufficient to break through the thickening freshwater lid and restore the critical mixing of ocean layers. The Bay of Bengal, already vulnerable, could find its primary source of biological wealth strangled.

“Both extremes threaten marine resource availability,” Thirumalai said. “And what we’re seeing today looks eerily like the conditions that led to sharp declines in the past.”

Ripples Through Communities and Economies

The implications extend far beyond the scientific community. Coastal societies from India’s eastern seaboard to the low-lying shores of Bangladesh depend intimately on the bay’s bounty. Fisheries underpin local economies, sustain cultural practices, and nourish millions.

A decline in marine productivity could spell disaster for food security, with cascading effects on health, employment, and even migration. As fish stocks dwindle, competition for resources could intensify, exacerbating social and political tensions in a region already vulnerable to climate-driven challenges such as sea-level rise and cyclonic storms.

“The relationship between monsoons and ocean biology we have uncovered in the Bay of Bengal gives us real-world evidence of how marine ecosystems have reacted to warming and monsoon shifts—and may do so in the future,” said Rosenthal. “These insights can help refine projections and inform sustainable management of fisheries and coastal resources as the impacts of climate change accelerate.”

Charting a Path Forward

Understanding the ancient dance between the monsoon and marine life offers not just a warning but a guide. By anticipating how ecosystems might respond to future changes, policymakers, conservationists, and fishery managers can begin to adapt strategies to preserve livelihoods and food supplies.

Efforts might include diversifying food sources, investing in sustainable aquaculture, protecting critical habitats, and crafting adaptive management plans that can respond to rapid environmental shifts. Above all, this research underscores the need for urgent climate action—reducing greenhouse gas emissions to temper the extreme weather patterns already emerging.

The story of the Bay of Bengal, captured in tiny shells buried beneath layers of sediment, is a testament to the planet’s profound interconnectedness. The monsoon’s breath sustains life from microscopic plankton to bustling coastal cities. But as that breath grows more erratic in a warming world, so too does the fate of millions who depend on the ocean’s invisible rhythms.

The past speaks. It tells us that resilience is possible but fragile. In the timeless tug-of-war between climate and life, foresight, science, and stewardship will be our greatest allies.

Reference: Extreme Indian summer monsoon states stifled Bay of Bengal productivity across the last deglaciation, Nature Geoscience (2025). DOI: 10.1038/s41561-025-01684-6