It is a beautiful day. If you weren’t looking toward the 20+ ships and couple of rigs a kilometer away, it would seem like another hot, sticky summer day on the Gulf of Mexico.
I worked in the Gulf in the mid-1990s on the NOAA Ship Chapman and the late-1990s on the R/V Pelican. I remember long stretches of calm days, blue water (not a deep blue, but a light blue), and marine life: dolphins, whales, tuna, and more. I have seen all these things in within 1500 meters of the wellhead over the past three days. The release of millions of gallons of oil is an environmental disaster, and the problem is still with us. But even so, the Gulf of Mexico is still beautiful.
We are continuing our acoustic monitoring in the area around the wellhead. We have made 20+ passes over the wellhead in the past two days. From our cursory examination of the data and from the acoustic experts onshore, there has been very little change in conditions. There are acoustic returns in the water column – likely from methane gas – but the magnitude has not increased. The wellhead area is closed now for the static kill and it will be interesting to see what the acoustic data shows when we get back into the 500 meter zone.
Last evening, we started our water sampling effort. We cannot work inside the 1500 meter zone at night and we have used this time to acoustically map much of the area between 1500 and 3000 meters. Our plan last night was to go back to two areas of acoustic returns outside the wellhead, remap these areas, and collect water samples.
We are interpreting these areas as natural seeps – areas where hydrogen sulfide, methane and other hydrocarbon-rich fluid ‘seep’ into the ocean. We ‘see’ seeps as areas of acoustic returns that extend into the water column from the bottom. Some of these areas are persistence; identifiable every time we cross over them, while others are intermittent; they are sometimes there and sometimes not.
We made two conductivity, temperature depth casts (CTD), one to 1000 meters and the other to 1400 meters. A CDT instrument measures the temperature, conductivity, and depth through the water column. Conductivity is converted to salinity – how salty the ocean is. Temperature and salinity are basic oceanographic variables that say a lot about the source of water sampled.
We also have a dissolved oxygen and a color dissolved organic matter sensor. Obviously, the dissolved oxygen sensor measures oxygen in the water. The color dissolved organic matter sensor provides a measure of how much oil there is in the water. Two of the features that have been described for subsurface oil are an increase in colored dissolved organic matter (dissolved oil) and a decrease in dissolved oxygen; the argument being that bacteria are using oxygen to break down the oil.
Water bottles on the CTD can be used to collect water from specific depths. If we see a layer of water with increased color dissolved organic matter and decreased oxygen, we can close a bottle, bring the water to the surface and prepare the water for chemical analyses. The measurement of dissolved oxygen uses a Winkler titration and these can be preformed on the ship. The measurement of oil requires a gas chromatograph, which we do not have onboard. The water is poured into specially prepared bottles, put into a big walk-in refrigerator and then transported to shore in a small boat for analysis.
The first CTD cast was made over an area of blue water; no acoustic evidence of seeps. Unfortunately, we had problems with the winch and the CTD was not deployed all the way to the bottom. We did, however, collect water as the CTD was brought back to the surface. Once the CTD was on deck, the water chemistry team descended on it, and collected the water from the bottles for the dissolved oxygen analysis and oil analysis.
The second cast was made over an area of a seep. The presence of the seep was confirmed using acoustics and then the ship tried to sit right on top of the location for the 2.5 hour CTD cast – it takes a long time to lower a CTD a mile and then bring it back. The ship drifted in and out of the seep, but we did get the CTD through the acoustic signature of the seep. Once on deck, the chemists descended again, and oxygen and hydrocarbon samples were taken.
We then moved to other seep location and conducted more acoustic surveys to pinpoint the location for CTD sampling tonight. The sun came up just as we were completing our acoustic survey, and we returned to the wellhead site. Since then, we have been circling all day monitoring the perimeter for evidence of leaks from the well (we have not detected any). We are also waiting for our chance to survey over the wellhead to evaluate the success of the kill operation.
