- Jim Hench
- Stanford University
Having been surfing since I was little, it’s probably not an entire coincidence that I’m a physical oceanographer. My main research interest is in shallow-water circulation, which is often characterized by unsteadiness, strong advective accelerations, stratification, and frictional boundary layers that occupy much or all of the water column. I am also interested in interdisciplinary problems that have a significant physical component, such as our work with sponges on this Aquarius mission.
Saturation diving out of Aquarius gives us dramatically extended bottom times, and thus provides the unique opportunity to set up extensive intricate instrumentation on specific organisms, and parts of the reef. These types of measurements would not be possible using traditional “over-the-side” oceanographic methods or using unmanned ocean observatories, and thus open new views of the ocean. During our mission we will study the effects of sponge pumping on the nutrient budget of the reef. Our early measurements of sponge excurrents indicated that for some species in the Florida Keys, excurrent jets exceed 25 centimeters per second. Thus it appears likely that the water flowing near the bottom of some tropical reefs, such as Conch Reef, may be significantly affected by sponge activity. To further explore this effect, we will be deploying a set of acoustic Doppler current meters above individual sponges to continuously measure their pumping flowrates, and the currents and scalar structure around them. Data from these instruments will be sent by cable to Aquarius to be recorded. Streaming these data into Aquarius is a physical oceanographer’s dream (nearly unlimited electrical power and computer storage, and, where else can you Matlab underwater?) Even better for the sponge work, is the unique capability to collect excurrent and ambient water samples around the clock (9 km offshore) using saturation diving and a hookah rig. Combining these two capabilities we plan to look at the effects that environmental conditions have on sponge pumping rates, water chemistry transformations, and how sponges modify currents over the reef.
