by As ocean waves rise and fall, they exert forces on the seabed below and generate seismic waves. These seismic waves are so powerful and widespread that they show up as a steady thump on seismographs, the same tools used to monitor and study earthquakes.
That wave signal has been rising in recent years, indicating stormy seas and higher ocean swells.
In a new study in the journal Nature Communications, colleagues and I tracked that increase around the world over the past four decades. These global data, along with other ocean, satellite and regional seismic studies, show a multi-year increase in wave energy coinciding with increasing storminess due to global warming.
What does seismology have to do with ocean waves
Global seismographic networks are best known for monitoring and studying earthquakes and allowing scientists to create images of the planet’s interior.
These highly sensitive instruments continuously record a huge variety of natural and man-made seismic phenomena, including volcanic eruptions, nuclear and other explosions, meteor strikes, landslides and glacial tremors. They also capture continuous seismic signals from wind, water and human activity. For example, seismographic networks observed the global silence in human-caused seismic noise when lockdown measures were instituted around the world during the coronavirus pandemic.
However, the most prevalent background seismic signal around the world is the relentless thump created by stormy ocean waves known as global microseism.
Two types of seismic signals
Ocean waves generate microwave signals in two different ways.
The more energetic of the two, called the secondary microseism, throbs at a period of about eight to 14 seconds. As sets of waves travel across the oceans in different directions, they interfere with each other, creating pressure variations on the sea floor. However, transverse waves are not always present, so in this sense, it is an imperfect proxy for overall ocean wave activity.
The second way ocean waves generate global seismic signals is through the primary microseismic process. These signals are caused by ocean waves traveling directly pushing and pulling on the seabed. Since water movements within waves drop off rapidly with depth, this occurs in regions where the water depth is less than about 1,000 feet (about 300 meters). The primary microseism signal appears in seismic data as a steady hum with a period between 14 and 20 seconds.
What the trembling planet tells us
In our study, we estimated and analyzed historical primary microseismic intensity back to the late 1980s at 52 seismograph sites around the world with a long history of continuous recording.
We found that 41 (79%) of these stations showed very significant progressive increases in energy in recent years.
The results show that the average ocean wave energy has increased by 0.27% per year since the end of the 20th century. Since 2000, however, that global average increase in rate has increased by 0.35% per year.
We found the largest overall microseismic energy in the highly turbulent regions of the Southern Ocean near the Antarctic peninsula. But these results show that North Atlantic waves have strengthened to the fastest in recent years compared to historical levels. That’s consistent with recent research that suggests North Atlantic storm intensity and coastal hazards are increasing. One record example was storm Ciaran, which hit Europe with powerful waves and hurricane force winds in November 2023.
The multidecadal microclimate record also shows the seasonal oscillation of strong winter storms between the Northern and Southern Hemispheres. It shows the wave dampening effects of Antarctic sea ice growth and shrinkage, as well as the multi-year highs and lows of the El Niño and La Niña cycles and their long-range effects on ocean waves and storms.
Together, these and other recent seismic studies complement the findings from climate and ocean research showing that storms and waves are intensifying as the climate worsens.
Coastal warning
About 90% of the excess heat associated with greenhouse gas emissions from increasing human activities in recent years has been absorbed by the oceans. That extra energy can translate into more damaging waves and more powerful storms.
Our findings offer another warning for coastal communities, where rising ocean wave heights can affect coastlines, damage infrastructure and erode land. The consequences of increasing wave energy are exacerbated by continued sea level rise due to climate change and subsidence. And they highlight the importance of mitigating climate change and building resilience in coastal infrastructure and environmental protection strategies.
This article is republished from The Conversation, a non-profit, independent news organization that brings you reliable facts and analysis to help you make sense of our complex world. The Conversation has a variety of free newsletters.
Written by: Richard Aster, Colorado State University.
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Richard Aster receives funding from the US National Science Foundation.
