Hello again, this time from the middle of the icy Bering Sea and famous home for the hit docu-drama Deadliest Catch. I’m sorry to those of you (esp. my wiggletracer bloggies and my science pals) who’ve been expecting blogs for some time now but we’re back online and here we go. We are currently experiencing some high seas and winds at 40+ knots (46 mph) and on day 16 of 26. Life at sea is unpredictable but hopefully I’ll have a chance to fill you in about the last 16 days over the next ten.
Here is the game plan. This post will give you a science overview and the following posts will hopefully include: daily life on a ship, life on a ship as experienced by the five senses, marine seismology, the equipment we use, expansion on the topics discussed in this blog, our first few weeks at sea, and the last few weeks at sea. And now, SCIENCE!
Chief scientists Ginger Barth (USGS) and Warren Wood (NRL) are conducting this cruise primarily to help delineate the U.S. extended continental shelf (ECS) in the central Bering Sea. The seismic data collected over these weeks will help determine sediment thickness, a variable put into a formula that helps determine ECS boundaries. (For more info on the ECS: http://continentalshelf.gov/) In addition to sediment thickness, this cruise also hopes to help answer other geologic and oceanographic questions about an area which little is known.
Above: From continentalshelf.gov, an image of our study area and the surrounding bathymetry. A very flat seafloor where we are.
In addition to sediment thickness, this cruise is addressing the distribution of Velocity-AMPlitude (VAMP) structures in the central Bering. VAMPs are believed to be concentrated deposits of methane hydrate.
“New analyses by the USGS show that a single large VAMP structure involves a volume of methane equivalent to that of a large conventional gas field (approx 0.6-0.9 trillion ft3).”
These hydrate deposits create a velocity anomaly in the seismic record because the methane hydrate is in a “frozen” state where the seismic energy travels through at higher velocities than the surrounding sediment. These VAMPs image in a stacked section as mushroom-top like “bumps” that occur over rises in the basement topography. We have imaged many of these mushroom-like features on our cruise so far.
The other science happening out here that I couldn’t possibly fail to mention is seismic oceanography. Active source seismologists discovered relatively recently that small impedance contrasts created by thermohaline boundaries in the ocean can be imaged with frequencies generated by standard multi-channel seismic techniques. In the last few years unprecedented images of eddies, internal waves, and fronts have been generated using this technique. This is where I play my biggest part in this cruise. My role is to deploy expendable thermo-bathygraphs (XBTs) that measure temperature with depth and process/look at the water column portion of the multi-channel seismic data for interesting oceanographic features. The Bering is oceanographically interesting for many reasons that include a dissolved silicate layer near the seafloor and a 100 m thick cold layer from seasonal ice melt near the surface. The cold layer makes for some funky ray-path physics which I hope to blog about later.
Of course, research of this magnitude is rarely simple and there is much more to tell you than I can fit in a short blog, but you get the idea. ;o)
Now, I’m headed off to bed to try and catch a few hours of sleep before I head back to the lab. Sleep will not come easy tonight with these crazy waves and 45-degree rolls – it will be more of a quest to stay in my bunk which is situated fore and aft to the vessel. This will no doubt be a topic in a future blog. =) Good night!
“A smooth sea never made a skilled mariner.” –English Proverb