Every summer, the Southern Ocean surrounding Antarctica turns a bright shade of green. Vast phytoplankton spread across the water’s surface, forming the basis of one of the most important marine food webs on Earth. These blooms also help pull carbon dioxide out of the atmosphere. Scientists have long explained seasonal growth through sunlight, wind patterns, and ocean circulation. New research points to another, less obvious but deeper effect. Earthquakes that occur beneath the ocean floor may shape the amount of life that appears at the surface months later.
Earthquakes beneath the ocean floor may be feeding Antarctic life
A study titled “Net primary production in the Southern Ocean affected by seismically modulated hydrothermal iron” Satellite data was analyzed in conjunction with seismic records from the Southern Ocean. They focused on earthquakes of magnitude 5 or higher that occurred in the months before the summer growing peak. The pattern they found was consistent. Years of high seismic activity were followed by denser and more widespread phytoplankton blooms. In years with mild earthquakes, the flowers were noticeably smaller.The size of these flowers varied dramatically. In summer, the green belt sometimes covered an area the size of a large U.S. state. In others, it has been reduced to a fraction of its size. The strongest relationship between these fluctuations was not with weather or sunlight, but with the level of seismic activity beneath the ocean floor.
hydrothermal vent Acts as a hidden source of nutrients
The connection lies in hydrothermal vents. These are natural openings in the ocean floor that allow seawater to circulate through hot rocks deep within the Earth’s crust. When water is heated, minerals and metals, including iron, melt before returning to the ocean. Although iron is deficient in most areas of the Southern Ocean, iron is essential for phytoplankton growth.Under normal conditions, much of this iron remains deep within. Mixing occurs slowly and often not enough reaches the surface. Earthquakes seem to change that balance. As the Earth’s crust changes, hydrothermal systems can become temporarily active. These shocks release pulses of iron-rich fluid into the surrounding waters.
Nutrients move upward faster than expected
One of the most surprising findings from the study was how quickly these nutrients reach the surface. Traditional thinking was that iron released at depth would take decades to rise to thousands of feet. New analysis suggests that could happen within weeks or months.This process is uneven and sudden. It resembles a disturbance stirring up long-sedimented layers rather than a steady flow. When iron enters the upper water, phytoplankton react immediately. Growth is accelerated and flowers bloom over a wide area.
Southern Ocean ecosystems respond strongly to iron
The Southern Ocean is known for its high nutritional value and low chlorophyll content. Although other nutrients and sunlight are often available, phytoplankton growth remains limited by iron. When that constraint is lifted, even for a short time, the ecosystem responds.Larger flowers support more zooplankton, which in turn becomes food for fish and higher predators. The effects ripple upward through the food chain. At the same time, increased phytoplankton activity strengthens the ocean’s ability to absorb carbon dioxide through photosynthesis.
Carbon intake may increase during active periods
As phytoplankton grow, they take in carbon dioxide from the air and surface water. Some of that carbon eventually sinks into deeper layers when organisms die or are consumed. This process forms part of the biological carbon pump, an important mechanism that regulates Earth’s climate.The extent to which earthquake-induced nutrient inputs contribute to the global carbon cycle remains unclear. The Southern Ocean covers a vast area, and even small changes there can have large effects. The researchers caution that although this mechanism is temporary and not constant, the effects during the active phase can be significant.
What is missing from many climate models?
Most climate and ocean models focus on continuous forces such as winds, ocean currents, and seasonal mixing. Earthquakes do not easily fit into those frameworks. They are unpredictable, short-lived, and unevenly distributed. However, this study suggests that they can cause large biological responses.Other parts of the world also have hydrothermal systems. It is still unclear whether similar effects occur elsewhere, largely because deep-sea regions are difficult to monitor. Improved sensors and longer satellite records could help fill these gaps. For now, the discovery adds a new layer to the way scientists understand the ocean. Beneath the gentle surface patterns tracked year after year, deeper processes are at work. Some of them arrive without warning, leaving subtle traces and silently forming life high above the ocean floor.