On Internal Tides Driving Residual Currents and Upwelling on an Island

Tides oscillate the world’s oceans, and because warmer lighter water sits on cooler dense water, wave energy travels along this interface. This process, called internal tides, creates waves which propagate in the ocean interior and are quite common in the ocean. When these waves encounter a coastline or island they function similarly to waves on a beach: they can turn, change shape, break, or reflect. These changes to the waves can create currents, often quite strong, and pull deeper cooler water into the shallow coastal areas. We performed a modeling study to determine which factors are most important in creating strong currents from these internal tides across a range of possible conditions on islands worldwide. The results show that the internal tides create complex currents and bring cooler dense water into the shallow regions under most conditions. The factor that creates potentially the best conditions for organisms living on the ocean floor is gradual ocean floor slopes (compared to steeper). The results for this condition had strong currents, increased deep ocean waters, and cooler temperatures in the shallow coastal areas which may buffer effects from future ocean warming.