Location: Bahamas, Turks and Caicos Islands
Duration/timing: 14 days. Any time from September 2019 until summer 2020
Necessary equipment: None – all equipment will be supplied
Submerged ocean waves (known as internal tides) measuring up to 700 metres exist beneath the surface of the ocean. These massive bodies of water, driven by ocean currents, are most obvious when they meet barriers such as seamounts, mid-ocean ridges or continental shelves. When they break, they create turbulence that drives an upward flux of nutrients from the deep ocean (which is light-limited but nutrient-rich) to the photic zone above (which is nutrient-poor).
One of the best places for studying internal tides is the Atlantic coastline of the Caribbean islands, especially the southern Bahamas and the Turks and Caicos Islands. Traditionally, observing internal waves required multiple instruments, which caused problems when matching biochemical responses to the physical processes. To avoid this issue, the team will use an ocean glider to make their observations.
Two berths are required, one for a scientist and one for a glider technician. The glider will be deployed for 14 days (a spring/neap tidal cycle), and the mission could take place any time between September 2019 and summer 2020. There are a series of seamounts near the Bahamas and the Turks and Caicos Islands where tidal currents are significant, and so this region would be an ideal experiment location.
On a basic level, there are two ocean layers, one near the surface with lots of light and not enough nutrients, and another deeper layer with lots of nutrients and not enough light. Internal tides breaking over seamounts stir deep, nutrient-rich water up into the upper layers. These extra nutrients are taken up by phytoplankton, which are an important food source for fish in the upper layer. It’s important to study any mechanism that can bring water with nutrients up into the surface ocean as scientists don’t yet fully understand exactly where or how these waves function.
Training in physical, chemical and biological oceanography will be provided on board during the experiment and through the Introduction to Oceanography scuba divers course run annually at the University of East Anglia (UEA). Findings will be disseminated through high-impact peer-reviewed manuscripts and conference presentations. The glider mission will be followed in real-time through the UEA website, ueaglider.uea.ac.uk.
Dr Hall is a senior lecturer in physical oceanography at the Centre for Ocean and Atmospheric Sciences at the UEA, UK. A member of the UEA Glider Group, he has led several Seaglider missions.
“Any mechanism that can bring water up from the deep will help support productivity in the surface ocean. Internal tides do precisely this, but we don’t really know how they function. Improving our understanding of how this process impacts up the food chain will be very beneficial.”