Day 28 – Some Shorter Dives
Breakfast
- Egg sandwiches
- Blueberry pancakes
- Yogurt with blackberries
- Sausage, bacon and spam
- Fresh fruit
Lunch
- Bratwurst
- Lentil soup
- Sauerkraut
- Salad bar
Dinner
- Grilled NY Steak
- Angel hair pasta
- Veggie marinara
- Peas and carrots
- Salad bar
- Chocolate ice cream
Weather
Low winds, seas 6-10 ft.
Position
S 44° 17.57′ by E 147° 22.67′
Recently, we’ve been doing a series of shorter dives, mostly due to shortened weather windows available to us. It has become apparent, especially over these last few dives where we dove to significantly below 2400 meters, that there is a distinct line where our target, D. dianthus, stops appearing. On a previous cruise, this depth limit of 2400 meters was seen up at the New England Seamounts, and it was hoped that this was just due to the bathymetry and current patterns in the North Atlantic; also, this depth was not explored as thoroughly as it was on this cruise. However, over this cruise, we have seen many, many prime places for dianthus to grow, and instead we see these faces either empty or populated by other life.
In some ways, this is similar to the treeline on mountains, except in the coral’s case it’s a global phenomenon – the same cutoff of 2400 meters is found in the North Atlantic and the Southern Ocean! That’s pretty incredible – what could bring about such an abrupt cutoff like that? It could be temperature, or perhaps a pressure change that causes it. Regardless, it’s been frustrating for us, because to fully investigate ocean circulation, we needed to get some samples from around 3500 meters – I guess that’s not going to happen.
It’s always frustrating in science when something doesn’t work out the way it should – in the lab, this is often the case. There are always unexpected problems you have to work around, but this is part of what makes laboratory research so interesting and challenging. But in the field, it seems to be a different beast entirely. Indeed, how can we even begin to answer a question if the samples aren’t there? Disappointment in science happens in every field, whether it be finding out a synthetic route is unavailable or a purification technique is flawed, or in this case finding out that our most powerful tracer of ocean mixing at the Last Glacial Maximum cannot tell us what we need to know, because it doesn’t grow deep enough. What is most frustrating here is the amount of time and energy it takes to conduct field work, especially in oceanography. At $50,000 dollars a day, this research is not cheap. To be sure, we will have the most complete set of corals from depths of 2400 meters all the way up to 6 or 700 meters – but to find that the biggest question we came out here to answer is currently unanswerable is definitely a let down.
However, there are many other things we can look at with our sample set, even though there will be no complete picture of the ocean – through our solitary corals at least - at the Last Glacial Maximum without usable samples from 3500 meters. For example, we can investigate the role of Antarctic Intermediate water in many systems, from heat transport to its role in the glacial ocean. This is actually a very big issue: no one knows right now if there was any intermediate water in the glacial ocean, and the boundary between North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW) is currently thought to reside at around 2,000 meters. Since our histogram goes down to 2400 meters, we should be able to say something about intermediate water at this boundary, provided we have corals from the Last Glacial Maximum. Heat transport is also a major function of the oceans – it will be great if we can say something about the Antarctic Intermediate Water’s role in heat transport.
I’m sure our data set will get us other very interesting data about this area and the global ocean cycle, however – so not all is lost! In other news, we’ve been working on doing some hydrocast CTDs – in which we collect water samples at different depths – in order to measure trace metals in seawater. Seth set up a makeshift clean lab, with some plastic sheeting and a filter and fan (see pictures below). The concept is that the seawater samples will not get exposed to any metal particles from the air or other sources. When working with trace metals, even a small exposure could lead to a large error in data, because the concentrations are so small. In a trace metal lab, the environment is high-pressure and everything is plastic and teflon so there is no possible contamination. Many times, the teflon used for bottles is washed and cleaned thoroughly before use to get rid of any traces of metal particles. Seth is working with iron isotopes, and the Southern Ocean is one of a few regions where iron is deficient in the ocean; iron is an essential metal to life, and is found in many proteins, so the iron in seawater is directly tied to the amount of photosynthetic bacteria it can support. In fact, one of the solutions to the growing concentration of atmospheric CO2 that has been passed around involves dumping mass quantities of iron into iron-deficient ocean zones, like the Southern Ocean, in an attempt to sequester CO2 in the form of organic matter. Although it has been tested successfully on a small scale, we really have no idea what this might do on a larger scale.
In other news, we’re currently in the middle of our last Jason dive of the cruise; after this, we’ll do some CTD work and then head in to port. We exlpored this 200-meter high sheer cliff, which has been truly fascinating, with tons of carnivorous anenomes and corals covering the face, and some very interesting basalt crystal formations. The fossil collection has been quite good, so hopefully we’ll round out the cruise with some good samples from this dive. Stay tuned for more updates as the trip comes to a close!
January 14th, 2009 at 11:50 am
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