Southern Ocean Iron Experiment (SOFeX) Cruise
January 5 - February 26, 2002
Logbook
Skip to Log Entry from the R/V Melville
February 5, 2002: Day 32
R/V Revelle:
Ship: @ 2/5/02 08:08Z,-66 22.4, -172 03.3
So. Patch In Drifter @ 2/5/02 01:41Z,-66 13.9746, -172 8.1492
So. Patch Out Drifter, passed over to MELVILLE
No. Patch In Drifter @ 2/3/02 18:00Z,-54 9.3, -169 37.62
No. Patch Out Drifter @ 2/3/02 18:00Z,-55 23.22, -172 37.32
R/V Revelle Log Entry: Hi, were headed north! Ginger, Steve and Craig are mighty happy about that.So are the cooks. So is the Captain. Hmmm, I have to admit that even Ive got "barn fever". Only Dick Barber seems sorry to go.
We finished adding our fourth and final batch of iron to the patch at 1600 and then stood by while MELVILLE prepared a sediment trap to float over to us for deployment in the North Patch. We took advantage of the time to perform a final cast in the patch. While people are happy to go, they were mighty eager to get that water. The patch has really taken off, and this is their last chance for a sample.
MELVILLE reports chlorophyll values that are at least 10 times the initial values.We can now see nitrate drawdown in the patch each time we cross it. And carbon dioxide concentrations are really starting to drop. Pete reports that light attenuation in the patch is much higher than when we arrived, due to the increased phytoplankton population. The attenuation is 3-fold greater. The deep chlorophyll fluorescence maximum, that we found below the mixed layer, has now disappeared under the patch. It is still present outside the patch at control stations - are plankton living below the mixed layer of the patch now light limited?
But after watching MELVILLE pitching in the swell, Im glad to be heading north.Were launching the SeaSoar now for a last pass through the patch as we head north. Erich Scholz last chance to wind the SeaSoar winch amidst the icebergs.After that, we reel it up and head for the North Patch as fast as REVELLE will go.And no time too soon - food supplies are dwindling and the troops are getting restless.Well thats all for now.
- Ken J.
R/V Melville:
Position: 66 degrees, 17 minutes South, 172 degrees, 3 minutes West
R/V Melville Log Entry: At the Southern Patch in day 12 of this enrichment study, we are seeing consumption of macronutrients silicate and nitrate, drawdowns in carbon dioxide, although overcast for what seems like forever, the waters appear a different color, but are they really? When you look into a newborns eyes, are they blue or brown.or green? Perhaps it is too early to see with our eyes, but we really do see a difference in all our underway-measured parameters, chlorophyll, FRRF (see the pablum story), flow cytometry (the hose story), nitrate, silicate, pCO2, etc Even the 20-micron filters are slowing down. The water clarity has changed and the euphotic zone has crept closer to the surface as a result. Since there is more light absorbed in the mixed layer and we believe we can detect a small increase in water temperature. This is less than one tenth of a degree, but it looks convincing.
All these observations are evidence that indicates the wheels of the food web are turning more quickly, that the system is now functioning in a healthy and productive way. But how can we tell whether the "biological pump" (the actions of the food web that result in the flux of carbon from the surface layers to the deeper waters) has been stimulated, or are the products of photosynthesis just being recycled in the surface layer? Is the pump just spinning its wheels or is carbon being exported? Why is this important? Because if carbon is being exported as a result of iron enrichment, then iron may have played an important role in glacial/interglacial transitions, global warming and atmospheric carbon dioxide. So, getting the motor running is one thing, but getting the car to go somewhere is quite another and it is the latter that is important for carbon transport and climate change.
So, how do you tell if carbon is going anywhere. One might think that this would be easy, but it is in fact one of the most challenging aspects of this program. The most basic approach we take is to deploy sediment traps, we call them particle interceptor traps, or PITS both inside and outside the patch. The idea is that the PITS collect particles sinking from the surface and we can compare this flux both inside and outside the patch. In rough seas, suspended from a floating array, however, these PITS may get jerked around quite a bit and they may not quantitatively collect particles.
Another approach is to do a census of all the carbon in the system and then see if we see a change inside vs. outside. This is the carbon budget approach. OK you might say, send out the census takers and count em all up. This means you have to go to every single home in every single city and count every single carbon atom.For big carbon reservoirs small changes can mean big fluxes. The challenge is to measure these reservoirs with great enough accuracy that small differences can be seen. The pools we are measuring (cities we are visiting) are the total inorganic pool (this is like LA, New York, New Delhi, Amsterdam, Paris, London, and Beijing combined), dissolved organic matter (Chicago), particulate organic matter (San Francisco), and carbon dioxide gas (Reno). If we add all these up and we see there are fewer atoms inside than outside, then the difference is a flux...the census bureau may call this migration. This requires accurate counts in all cities, a very difficult task.
Alternatively, one can measure a proxy for carbon flux. What is that? It is something that moves like carbon but is not carbon. Here we assume that dissolved carbon does not move, it stays in solution and mixes around without sinking. It is only carbon in particles that can sink. This is like assuming that all the carbon atoms in the world need to go through the port city of San Francisco before they can emigrate to the nether world. As you might expect carbon people are well traveled and San Francisco is a very dynamic city with residence times of its population being quite short. Once carbon is a particle, it does not hang around. It either sinks out or it redissolves.
How can one tell if carbon-carrying particles are sinking or dissolving?
We measure primary production, this is a measure of how fast carbon is being incorporated into plants or phytoplankton. But this does not tell us how fast the fixed carbon is being removed. The proxy for carbon export that we use is actually a naturally occurring radioisotope pair. It is the ratio of the daughter isotope, Th-234 to its parent radionuclide U-238. Thorium is produced uniformly throughout the water column but it has a bad habit of sticking tightly to particles. With no particle removal there should be an equal amount of Th-234 activity and U-238 activity in the water. If there are lots of particles that are sinking out, then the particles remove Thorium and there is little Th-234 activity relative to U-238 in the water column.
Ok, ready for the analogy:
Daddy Warbucks caramel popcorn factory has been making sticky popcorn at a constant rate since 4.5 billion years BP. The carbon people in San Francisco cant get enough of it. They like to dress up in it, that is until it goes stale, then they feed it to the pigeons, or flush it down the toilet. Whatever its demise, we know the shelf life and how fast it goes bad. Stay with me here. The production rate of the Warbucks popcorn factory should equal the rate at which the inventory of popcorn goes stale plus the rate at which carbon people, dressed in popcorn, take the ferry to the nether world.So, inventory the popcorn and you can calculate emigration (carbon flux).This story demonstrates the limitation of analogy and why we need more marine radiochemists in the world.
Well check back with John and Glenn and see how things are going.
Jodi Brewster writes: Hello to all! We have spent the last week in the Southern Patch at about 66 degrees South, 172 Degrees W. We have crossed the Antarctic circle several times. Many of us haven't done that before and we are expecting some silly ritual to welcome us to the few that make up the group of people who have crossed the Circle.
After arriving here, we immediately began our station ritual: CTD casts, TM Rosette casts, net tows, thorium pumping, & Go Flo casts. Everyone has been getting used to their jobs for whichever instrument they have to deploy. I have an 8am CTD cast every morning (if the seas aren't rolling or something else is wrong). We try to have it back on ship by 9am so the first TM cast of the morning can go over-only one instrument deployed at one time. (TM stands for Trace Metal. Many experiments require that the water is free from certain metals.) We've been about 50% successful in keeping to that time schedule.
My afternoons & evenings are spent in a really cold van that sits out on the upper deck running extracted chlorophyll samples on a Turner Fluorometer. Thank goodness for space heaters! We are definitely seeing a difference between our out & in stations in chlorophyll. Two days ago, we did a transect line through the patch. That was a long day. We started at 6:30 am & did 7 stations. At each station, a TM cast, CTD cast, and Go Flo cast were done. It took all day & up to 3 am at night to get only to the middle of the patch. It was a Looooong day. We had a rhythm going, but people were starting to get tired around midnight. One last station & we called it quits. We will have two more days like that coming up again soon.
We did get to meet up with the R/V Revelle for a few days. Scientists from the Revelle could call up the Melville & discuss sampling strategies with each other. There was also a wireless network set up so the two ships could swap files from their computer to ours to help in our sampling efforts here in the southern patch. We passed off a PIT to them last night before bidding them farewell. They are heading up to the northern patch to do some sampling again before heading back to Lyttleton, NZ.
A little bit of wild life shows up now & then. Rumors have been flying about seeing humpback, minke, and fin whales. The birds are gorgeous flying about our boat. One silly bird kept flying round and around our ship for an hour. Large albatross, giant petrols, & cape petrols. We've seen more icebergs than we can count. The watch on the bridge is always to look out for "floaters", little icebergs that could really do damage to the ship.
The excitement this week was over the Super Bowl. It was weird since it was actually on Monday morning for us; we are still following New Zealand time. Everyone is excited that tomorrow is hump day, that means that the trip is half way over. We still have another week here in the southern patch before heading back to the northern one. We had a beautiful sunset last night, and there was a sighting of the green flash. The moon was colorful, since the sun doesn't go too far below the horizon. With so few clouds last night, the sky was very bright, and the moon was really orange. It has been snowing off and on. Sometimes cold & windy, sometimes sunny & "warm". A few times it has been rolling & bumpy, but today is really calm. Most people are off any sea sickness medication, even in rough weather. It just makes it hard to sleep at night when you feel like you are going to fall 3 meters out of your bed. The Melville rolls more side to side then front to back.
Food has been so/so. We still have fresh salads every meal. The cooks bake fresh bread for dinner every night. We have a never ending supply of ice cream & popsicles for snacks as well as bread for peanut butter & jelly. There is always a hot pot of water for hot chocolate, coffee or tea. We are drinking lots of real juice out of juice box containers that remind me of summer camp. The boxes came from Tahiti and New Zealand, so some of them aren't always in English. You kind of have to guess what they are according to the pictures on the front of the box or sound out the French words. Everyone here is craving Mexican food.
Ahhh, dinner time. Talk to you next week. Jodi