Not everyone would be excited about blue and gray dots hopping horizontally across a graph, but Laurie Juranek is. It means the amount of oxygen in the water sampled over the past 24 hours is abnormally high. The blue dots are Juranek’s data and the gray dots are from the oxygen sensor attached to the ship. Normally these points would hover around 1 on the vertical axis. (The graph plots “measured oxygen” against “expected oxygen”, showing the ratio between the two. A ratio of 1 means they are the same.) But today Juranek notices the plotted points are around 1.75. This means there is much more oxygen than expected. And that could mean there’s a lot of life in the water around us.
Finding where life has been in the Arctic for the OSU team is a little like doing CSI. They go through an area picking up clues about what happened in the water. In this case, they don’t know who did it, but they know what was done – oxygen was left in the water and primary productivity is high.
Oxygen saturation plotted on the Sikuliaq’s course from Seward to Nome to the present day.
Juranek measures dissolved gases in the seawater. She uses a method called Equilibrator Inlet Mass Spectrometry to collect ocean water, separate the gases from that water, and see what those gases are. Essentially that process involves:
- Water filtered in from the front of the ship and brought up through tubes into lab sinks is circulated in a bucket at her lab station.
- This water is sucked up through a membrane.
- Gases from the water are separated across this membrane.
- A tiny capillary tube placed in the little space just ahead of the membrane “sniffs” the gas coming through the membrane.
- The gas then passes through the capillary into the attached mass spectrometer.
- A mass spectrometer is an instrument that measures the mass of gases. In this case, Juranek is looking for the masses 28, 32, and 40 – which indicate nitrogen, oxygen, and argon gas respectively.
Juranek’s lab setup
The capillary tube
The bucket where the surface seawater is held.
The mass spectrometer
From Anal. Chem. 2009, 81, 1855-1864, Figure 1. The large seawater reservoir (A) sits in a sink. After going through an inline coarse filter (500μm pore size), seawater flows into the inner reservoir (B) at a rate of 3-5 L min-1(large arrow). Most of the water running into B overflows into A, which is used as a water bath thermostatted to the temperature of ambient seawater. A small fraction (100 mL min-1) of the high flow rate is pulled with a gear pump through a filter sleeve (C), with 100 and 5μm pore size on the outside and inside, respectively. From the gear pump, the seawater flows through the equilibrator (D). The equilibrator sits in reservoir A to keep its temperature identical to that of the incoming seawater. A capillary, attached to the headspace of the equilibrator, leads to a multiport Valco valve. This valve alternates between admitting gas from the equilibrator and ambient air to the quadrupole mass spectrometer. An optode (not shown) in container B measures total oxygen saturation. Also not shown is a water flow meter located downstream of the equilibrator and thermocouples monitoring tem- peratures throughout the system.
Only a handful of labs are doing the types of measurements Juranek does. This is partially because only in the past couple decades have people started taking mass spectrometers out to sea. And the ones that were taken out previously were much bulkier and more inconvenient than the one Juranek has. She’s used hers for six years, and has gained a reputation as a kind of oxygen queen. She has measured oxygen on the research vessels Healy, Marcus G. Langseth, Ronald H. Brown, and most recently the Sikuliaq.
Measuring oxygen is like watching the ocean breathe because the ocean essentially takes up CO2 and lets out O2 – our own human breathing in reverse.
Juranek also looks at the ratio of oxygen to argon. Argon is a twin sister to oxygen, but it’s not affected by biology. Juranek doesn’t only want to know if there’s oxygen in the water; she wants to know why. Argon allows her to do just that. If there’s a lot of oxygen in the water, it could be because the water is very cold (cold water can hold more gas) – this would be a physical cause. Or high oxygen levels could be because a lot of tiny microscopic photosynthesizers have been busy converting CO2 into O2 – this would be a biological cause. Argon can tell us whether high oxygen levels are from a physical or biological cause because argon is not affected by photosynthesizers.
Of course, Juranek doesn’t operate in a vacuum. Colleagues from the Hales and Goñi labs collect their own data that can be compared to Juranek’s results. (More about how they do their work in later blogs.) Thanks to her Equilibrator Inlet Mass Spectrometry setup and the corresponding measurements from the Hales and Goñi labs last year, Juranek discovered a region of high productivity between Barrow and Wainwright in the Chukchi Sea. The amounts of productivity noticed today are much higher than those found last year. Why and how are still unanswered, but we’re hoping to find out.