By Frankie Pavia
We’ve just completed our first full station and are remarkably pleased with the results. We collected 8 seawater samples to measure helium isotopes; 20 to measure thorium and protactinium isotopes; 7 in-situ pump filters to measure particulate thorium and protactinium isotopes; 6 manganese oxides cartridges that were attached to the pumps to measure actinium and radium isotopes; and 1 box core of the ocean floor to measure sedimentary thorium and protactinium isotopes. I was going to make this paragraph into the Twelve Days of Christmas song, but 7 pumps-a-pumping doesn’t really roll off the tongue that well.
What all this means is that the first station was a smashing success for us. The only thing that didn’t quite go as planned was the nine-meter-long gravity corer coming up empty. We suspect it may have been due to the corer not being able to penetrate the hard carbonate layer we saw–about 15 centimeters thick in our box core. Nonetheless, we are delighted.
We were especially pleased that our in-situ pumps worked. We arrived on the cruise with the knowledge that the pumps would be there, but figured that somebody would be an expert on how to program them, maintain them and operate them. The pumps are essentially motors hung on a line deep in the water, drawing thousands of liters water through a filter, catching the ocean’s suspended particles.
After a week of poring over the manual, we were finally ready to deploy the pumps. It would take them 2.5 hours to descend to 3600 meters water depth, 6 hours of pumping, and 2.5 hours for the deepest pump to return. A convenient time to have them pump is overnight. Sleep is hard to come by while on station, so six hours of pumps pumping away at depth is a great excuse to scuttle off to bed.
We were pretty nervous as to whether they would actually work. We had invested a lot of time and energy getting them up and running. What a bummer it’d be if they spent six hours in the deep ocean not doing anything because I had accidentally programmed them to pump at the wrong time, or something. Our test run the previous day had been a bit spotty, too. The flow rate of the pumps had been something like 3 times lower than it should have been.
We woke up at 4 a.m. the next day to wait for the pumps to arrive back on deck, driven by caffeine and nervous energy. Christmas had been two days previous. On Christmas Eve the crew put on a terrific party in the hangar, and the pumps had been decorated with big red ribbons. We were about to find out whether the pumps were a present we actually wanted, or if they were one of those fancy battery-powered toys you get with a list of parts that has three missing and ends up never working.
All the pumps have names. We were able to name the four new pumps after ourselves, while the other four pumps already names. Claudia, Bernhard, Sebastian, Frankie, Laura, Frauke, Jimmy and Hulda. They all seemed to have a little personality too – especially the old ones, Laura, Frauke, Jimmy, and Hulda. Parts of Laura were backwards, Hulda’s screws refused to come loose, Jimmy’s pump head had missing pieces.
Claudia was the first to arrive at the surface. Immediately upon getting her out of the water, we put a shower cap over the filter holder to protect the filter from contamination by atmospheric aerosols and any dust floating around the hangar. We pumped the remaining water from the bottom through the filter, removed the filter holder and brought it to the lab. We carefully unscrewed the top, opened it up, and…
The filter was covered in particles! One by one, the pumps came up with filters that were coated by an even distribution of particles. Everything worked perfectly. Even Laura, Hulda, and Jimmy, though they were stubborn above water, did everything they were supposed to do once they were submerged.
We plan to measure protactinium and thorium isotopes on the particles to learn about the kinetics of particle movement in the ocean – sinking rates, absorption coefficients for trace metals, and export fluxes. Particles are the vectors that move elements out of the surface ocean, so studying their characteristics will be crucial for understanding how things like carbon and iron are pumped and exported to the deep.
Functional pumps meant that it was a happy Christmas for us. The next full station starts this afternoon. We’ll spend 42 hours sitting in one place, measuring dissolved, particulate, and sediment samples. Yesterday we had to change all the batteries on the pumps. Each pump requires 24 D batteries per deployment, and uses them all. So for every cast of 8 pumps, we use 192 D batteries. We’ll send the pumps out tonight and retrieve them at 4 a.m. again tomorrow morning.
We’re hoping these pumps are gifts that keep on giving.
Yesterday morning the Gould returned to Palmer Station, which means that it’s time for Jamie and I to take off. I’m looking forward to getting home and working through all the data we’ve collected (and who wouldn’t want to spend Christmas sick in the Drake Passage?), but sad to be leaving at an ecologically interesting point in the season. After a particularly windy spring we’ve had a week of calm conditions. As expected this resulted in a huge increase in primary production. The water at our regular sampling stations has turned green almost overnight. In an ideal world we would have seen those conditions two weeks ago, at the height of our sampling, but there’s no predicting the timing of these events! Consistent with what we’ve seen in the minor blooms all season this major bloom is composed mostly of Chaeotoceros. Instead of short chains however, we’ve got dense chains of many tens of cells. If these calm conditions persist a little longer it bodes well for the krill (and everything else) this season. To keep track of what the Palmer LTER group is up to for the remainder of the season you can check out Nicole Couto’s blog here.
All in all it was an extremely busy and productive early season. Many thanks to everyone at Palmer Station for making it happen!
By Frankie Pavia
Six days after we were supposed to have departed, the UltraPac scientists and ship’s crew remain stranded at port aboard the FS Sonne. Containers with the last of our missing science gear are on a truck driving up from San Antonio, Chile, where the port felt comfortable unloading our acids and radioisotopes. The Sonne’s spare parts are being unloaded from a ship across the harbor that I can see from my cabin’s windows. With an abundance of time and a dearth of work, we have begun to devise ways of doing science before we can actually do science at sea.
We first discussed how to optimize our sample depth selections. In the first three stations, the deep waters will be downwind of the East Pacific Rise, one of the fastest spreading mid-ocean ridges in the world. At ridge axes, water that has percolated through the ocean crust and weathered mantle-derived rocks is erupted back out by volcanism and hydrothermal vents. This ‘plume water’ bears a distinct signature of the Earth’s mantle – high in rare noble gases like 3He, biologically critical trace metals like iron and manganese, and small particles that are reactive sites for removing other elements like phosphorous, magnesium, and most importantly (for me!), protactinium and thorium.
When this plume water enters the ocean, it is very hot and less dense than the surrounding waters. It rises until it attains a state of neutral buoyancy – when its density is the same as ambient seawater. Then it simply moves and acts like any other water – in currents and eddies. But since it bears distinct chemical signatures, chemical oceanographers can find easily find it – after they’ve measured something in it.
But we want to know where it is before we sample it. We want to understand the processes going on inside the plume. What kind of particles are there? How fast do they remove trace metals from the ocean? How much iron enters the ocean from submarine volcanism? If we are to answer these questions, we must first be able to sample exactly within the plume waters – which means we must know where they are before we deploy our bottles.
Luckily, past cruises from the World Ocean Circulation Experiment (WOCE) have measured helium isotopes and density in the Pacific before. As a result, we know roughly what density surface is associated with the neutrally-buoyant plume waters. When we sample, we will send down a line with a CTD sensor to measure temperature, salinity, and pressure, from which we can calculate density. That line will have our bottles on it. We can instantaneously calculate the density of the waters we are sampling, find the depth of the density surface we know is associated with plume waters, then tell our bottles to open and sample at that depth. Problem solved!
We also set up an imaging system to take pictures of the particle filters we bring back. At seven depths of each station, we will deploy in-situ pumps that filter thousands of liters of seawater through a filter at a given depth. We then haul the pumps back to the surface, remove the filters, and analyze them.
We would like to photograph the filters before we analyze them so we can visually assess how much material there is on each filter, to confirm the results from our chemistry. To do this accurately, we must photograph every filter from the same angle, with the same lighting, with the same shutter speed. We went to a hardware store in town yesterday and bought some supplies, not knowing if the imagined setup would actually work.
It worked! We turned a lamp with a flexible stand for adjusting light height into a camera holder, decapitating the lamp portion and replacing it with a tripod holding the camera. Then we installed software allowing the camera to be controlled from a phone, so we could take pictures and adjust shutter speed remotely. We bought a clip-on lamp that will be attached to the camera holder for constant lighting (this one used for its true purpose!).
We are finally scheduled to receive our last missing container and depart port late tonight, around 22:00. While the delay has been frustrating, I suppose it hasn’t been all bad. We were scheduled to leave December 17, the day before the new Star Wars movie came out. Six extra days in port meant we were able to go into town to watch it. It was our last little leisure activity on land. Now it’s time for the ocean.
By Frankie Pavia
Still stuck in Antofagasta, the scientists are becomingly increasingly antsy. Every day we are stuck at the port is a day of sampling we won’t be able to do at sea. Every time we want to take a sample from the bottom of the ocean, at around 5,000 meters depth (16,404 feet), it will take us four hours to lower the line, several hours to do sampling (fill bottles, pumps, etc), and four hours to pull it back up. There are several of these casts at each of eight stations. Every hour we have at sea is precious for returning valuable samples.
What am I doing here, anyway? I am an oceanographer and an isotope geochemist. Originally, I only planned to measure naturally occurring radionuclides thorium and protactinium dissolved in seawater and stuck onto ocean particles. But slowly, more scientists found out there was a chance to get seawater from this part of the ocean and asked us to take samples for them.
The South Pacific Gyre is the most oligotrophic (nutrient-poor) region in the ocean. This makes it largely barren of life and matter—the waters are the clearest in the ocean. The sediments accumulate below the water at rates as low as 0.1 millimeter per thousand years. So, 10 centimeters of seafloor are equivalent to one million years of material deposition in the South Pacific.
The scarcity of particles and lack of eukaryotic life are two major reasons the South Pacific is fascinating to a chemical oceanographer.
Surface biology and dust deposition are the two main factors regulating the flux of particles through the ocean interior. Being so far from land and upwind of major dust sources, almost no atmospheric material makes its way to the South Pacific. Since there is no dust, and no eukaryotes, the particles must largely be made up of tiny bacteria, of which there are millions in each milliliter of seawater.
Much of what we are setting out to do is simply the chemical characterization of the region. We are exploring the ocean using chemistry. We can’t see the scarce sinking particles, but trusty old thorium and protactinium can. They are extremely insoluble. Every time they encounter a particle, they stick to it. We exploit this simple characteristic to provide rare accounts of rates in the ocean. Just by measuring protactinium and thorium, we can calculate how fast particles are sinking through the water, how much dust is entering the water column, how fast different elements are being removed from the water at the seafloor, and more. It’s almost incomprehensible that two obscure elements can teach us so much.
These isotopes are the oceanographer’s equivalent to the Hubble telescope.
They help us see where we cannot. We measure thorium and protactinium to tell us input and removal rates. We measure helium isotopes to trace hydrothermal plumes in the deep ocean. We measure radium and actinium isotopes to determine the mixing rates of waters in the deep ocean. None of these processes are discernable by eye, yet all are crucial for understanding the chemical and physical state of the entire ocean.
So we continue to wait to make our measurements and do our science until we can depart. The void is filled by lighthearted scientific arguments, whether or not we could make a jetpack for one of the massive hordes of dead jellyfish floating around the boat. The idea is that you could throw a bit of dry ice underneath the jellyfish, which would then sublimate, expand, and rise out of the water, taking the jellyfish with it.
Ultimately, no one ever tried it. Who wants to do an experiment where you can just see the answer with your own eyes?