It has been known for centuries that oil reduces the ability for wind to create sea surface waves. Benjamin Franklin famously hid oil in the bottom of his cane, so he could shake it over a pond like a sorcerer, and stop the wind’s creation of ripples. More recently, scientists have demonstrated the mechanism that is at work – oil films reduce water’s surface tension, reducing the air-to-water flux of momentum, also known as wind stress. Studies have even shown that natural oil slicks above seafloor seeps in many parts of the world are visible from space due to their effects on sea surface roughness.
The widespread and persistent surface oil on the Gulf of Mexico caused by the 2010 oil spill provided an unprecedented opportunity last summer to explore the effect of oils on atmosphere-ocean exchanges of momentum, as well as heat and gases. I wrote a proposal with Wade McGillis (Columbia University) that was funded by the National Science Foundation. The plan was to quantify these effects using an anchored catamaran on the Alabama continental shelf, as well as large-scale mapping aboard a ship with air-sea flux measurements.
The research also has many applications related to understanding the Gulf oil spill and its consequences, because modified air-sea exchanges of heat, moisture and momentum could impact oil spill transport, atmospheric delivery of moisture to the Southeastern United States, and transfer of heat from the ocean to the atmosphere, an important factor during hurricane season. The hurricane season was quiet in the Gulf, and it is possible that the oil films left over from the spill reduced the availability of the ocean’s heat and moisture for growing tropical storms.
The mooring study was conducted from July 30 through August 10, examining the water column heat budget and air-sea heat and CO2 fluxes. The study included one hydrographic profile mooring, vessel-based measurements, and a moored catamaran with measurements of oxygen, chlorophyll, turbidity, atmosphere and water pCO2, air-sea fluxes of CO2, heat, momentum, and moisture using the gradient flux (atmospheric profile) technique (McGillis et al. 2001), and net shortwave and longwave radiation.
The oil spill was capped right before we began the field work, so — fortunately for those who live in and around the Gulf — we never got the opportunity to study how oils affected the air-sea fluxes. And there is only so much you can do with three months of post-doc funding, so deeper analysis of our field data will require additional funding. In retrospect, it was an amazing adventure and great experience for Wade, four undergraduate students, and myself, learning how to make automated field measurements of the coastal ocean heat budget.