Source Regions of Infragravity Waves Recorded at the Bottom of the Equatorial Atlantic Ocean, Using OBS of the PI‐LAB Experiment

Infragravity waves are generated along coasts, and some small fraction of their energy escapes to the open oceans and propagates with little attenuation. Due to the scarcity of deep‐ocean observations of these waves, the mechanism and the extent of the infragravity waves energy leakage from the coasts remains poorly understood. Understanding the generation and pathways of infragravity wave energy is important among others for understanding the breakup of ice‐shelves and the contamination of high‐resolution satellite radar altimetry measurements of sea level. We examine data from 37 differential pressure gauges of Ocean Bottom Seismometers (OBS) near the equatorial mid‐Atlantic ridge, deployed during the Passive Imaging of the Lithosphere‐Asthenosphere Boundary (PI‐LAB) experiment. We use the beamforming technique to investigate the incoming directions of infragravity waves. Next, we develop a graph‐theory‐based global back‐projection method of noise cross‐correlation function envelopes, which minimizes the effects of array geometry using an adaptive weighting scheme. This approach allows us to locate the sources of the infragravity energy. We assess our observations by comparing to a global model of infragravity wave heights. Our results reveal strong coherent energy from sources and/or reflected phases at the west coast of Africa and some sources from South America. These energy sources are in good agreement with the global infragravity wave model. In addition, we also observe infragravity waves arriving from North America during specific events that mostly occur during October–February 2016. Finally, we find indications of waves that propagate with little attenuation, long distances through sea ice, reflecting off Antarctica. Plain Language Summary Infragravity waves are oceanic surface waves with periods between 30 and 300 s and wavelengths up to tens of kilometers. They are generated along coasts; however, a small fraction of the energy escapes to the open ocean and travels with little attenuation over transoceanic distances. They play a significant role in phenomena such as seiches, coastal barrier breaching, and the break‐up of ice‐shelves. Therefore, it is important to determine their sources, how they propagate through the ocean and their interactions with the coasts. To shed light on these questions, we examine pressure data recorded at an array of ocean bottom instruments deployed beneath the equatorial Atlantic Ocean. We use array techniques to