It is Tues. 1/17 (Guam time) and we will be arriving back in Guam early in the the morning on Sun 1/22, so this will almost certainly be my last post of the cruise. It's entirely possible I'll do another cruise before I finish my PhD, but for now there are no more planned. It's safe to say that I am ready to be back on dry land for the foreseeable future. With the exception of the almost 2 week break between cruises (which felt a lot shorter than that), I have been on a boat since 11/4, by the time I get back I will have been at sea for ~62 days (~104 days total if you include the very first cruise on the Langseth). There have been highlights and good experiences, but also a lot of boredom during the slow times, especially on the current cruise. My free time has been filled with a lot of movies and TV shows in the lounge, email/facebook/general internet time, standing on the deck at night looking at the stars or just feeling the wind and breathing the fresh air, getting some sun on the hammock during the day, working out in the gym for 2.5+ hours every other day, and reading books. The feeling of confinement gets old, and the constant motion of the ship does get annoying even though I am very accustomed to it at this point. But I have survived it just fine, and it has been valuable to learn more about the process of collecting the data that I work with and the various pieces that go into the final product.
Sonar Mapping
There hasn't been a whole lot to report on in terms of the work I've been doing on this cruise since data processing isn't particularly exciting to talk about. However, the deep-towed sidescan data looks very good and should produce a nice data set for me to work with. The deep-towed bathymetry looks okay overall, but due to the narrower swaths of data and the much higher levels of noise, it will be less useful than the sidescan. The bathymetry from the hull-mounted sonar system looks very good though and is higher resolution than what we currently have, so it will provide a nice complement to the deep-towed data. The hull-mounted sidescan data will be largely useless however, the water depths were just too much for that system to handle. I'm not entirely sure why the bathymetry turned out so much better, presumably the depth should have affected both the hull-mounted bathymetry and sidescan data. For the last 3-4 days of the cruise, we will be collecting magnetic and gravity data throughout the survey areas to provide a different perspective and complimentary data to go along with the sidescan and bathymetry. We can collect this data much quicker since we can go about 5x faster while towing the magnetometer than we could while towing the IMI-30 sonar (~10 knots vs. ~2 knots). We should be able to cover the region that took us a few weeks to map with the deep-towed sonar in a few days.
Dredging
The dredging has had pretty mediocre results overall. They have done over 30 dredges now (probably will be a little over 40 by the time we're done), almost half of them have produced little to no usable rock, and they have scooped up a fair amount of sediment as well. The rocks that they have gotten have not been particularly exciting either. The vast majority are just good ol' basalt (dark gray to black lava rock), not much variety in texture, not particularly fresh, very few crystals, and relatively few vesicles (gas bubbles). In my opinion as a non-geochemist, crystals and vesicles are really the only things that make basalt interesting to look at. I expected to find some serpentinite (essentially mantle rock [peridotite] with water incorporated into the crystal structure) as we got closer to the trench, but as far as I know they have not found any. Once they actually do chemical analyses, I'm sure they will find more variety within the samples, but from a superficial visual observation, there is very little variety. We have yet to find any rocks that are estimated at less than a few million years old (no dating has actually been performed yet). While these results may not be very exciting, the fact that the lavas all look very similar is important information in itself. In contrast, we had a huge variety of rock types and textures on the last cruise, reflecting different tectonic processes and local variations in the chemistry of the magma sources. Plus, we never had a single dredge that gave us no usable rock. It's unclear exactly why the dredging has not gone as well. Part of the problem is that the chain bag on the dredge has significantly larger gaps, and for most of the dredges they had a very flimsy net inside the chain bag, which pretty much ripped to shreds during each dredge. The current net they have been using for the last 5-6 dredges is much stronger, so that has helped them retain some of the rock that they have collected. They have also incorporated a pipe dredge (basically a heavy metal cylinder) along with the regular dredge, which is what collected the sediment and has also helped to get a few more rocks. Also, this region appears to be significantly less volcanically active overall than the NE Lau Basin, so the rocks are older and there is a thicker layer of sediment covering the rocks.
Thoughts on Marine field work vs. Terrestrial field work
While I still prefer the experience of land-based field work overall, marine geologic field work does have a few advantages. On land, I enjoy the freedom of being in a beautiful open setting rather than feeling somewhat trapped on a boat, walking around in nature, actually being able to touch the rocks and take samples with my hands, taking photos of the beautiful scenery, and the exercise of hiking around and mapping. However, the boat has the advantage of creature comforts: toilets/showers/sinks, a bed (even if it is tiny), having all of my meals cooked for me and not having to wash dishes, computer/internet access, a lounge with a TV, etc. It is enjoyable going out on deck and getting some fresh air, some sun, or looking at the stars at night, but staring out at the ocean does not quite compare to being out in the mountains and enjoying the much greater variety and beauty of the scenery. Scientifically, marine geology has the significant advantage of allowing me to study plate tectonic and subduction zone processes at a relatively large scale (10's to 100's of km), whereas it is difficult to study that large of an area on land, so you are usually forced to look at smaller-scale features and processes. You are typically limited to an area on the order of a few km for a land-based field project, since you have to map it by walking around the area rather than driving a ship over it and bouncing sound waves off of it to map. I think the work that I do with Fernando is just about perfect in terms of the scale and types of processes that I examine. At larger scales (1000's of km to global), you have to do too much generalization and assumption, and you lose a lot of the interesting detail because you simply can't take all of the small-scale variations into account. At a smaller scale (km or less), you get overly-focused on the tiny details and often lose track of how it fits into the larger picture. I think I have found an almost perfect balance in the work that I do with Fernando, which is a big reason why I chose to move on to do a PhD with him rather than transferring elsewhere to do something different. His personality and location in Hawaii were certainly factors as well. I also like the fact that I work from a truly geologic perspective (i.e. the features that are actually there on the seafloor), rather than purely geophysical (using measurements of gravity, magnetics, seismic waves, etc. to infer what might or might not be there), geochemical (using chemistry to make inferences about processes that we can't directly observe), or modeling (using complex equations and assumptions to either reconstruct past events or predict future events rather than using actual data). With that said, even though my work is from a geologic perspective, I also incorporate geophysical and geochemical observations and even a little modeling to support the geologic observations, which makes it much more robust and well-rounded. That interdisciplinary approach appeals to my personality. I've never been someone who can focus on just one thing and I've never had just one subject that I enjoyed or was really good at. I enjoy having variety in my work and I hope that my future career(s) will allow me to have some variety as well.
Well, I think that's all I have to say for now, I may add a couple photos over the next couple days, but otherwise this will be my last post for a long time. I hope you enjoyed the blog, and as always let me know if there are any questions...
