 The primary research question of Orcas is how the Southern Ocean is exchanging carbon dioxide with the atmosphere. And we're specifically interested in how the combined influences of biological productivity and physical and dynamical processes in the ocean are influencing that exchange. Our current understanding of the processes responsible for that uptake are not very good. And one of the reasons for that is because the Southern Ocean is so hard to reach and has not been studied in as much depth as other regions of the world. But it actually plays a really important role in absorbing a significant fraction of what we're emitting. We're measuring oxygen because of what it can tell us about the carbon system in the ocean and the air sea exchange of carbon dioxide. By themselves, the variations in oxygen we expect will be very small. And they're so small in fact that we can only assess them by measuring changes in the ratio between oxygen and the other major atmospheric component, nitrogen. And we refer to this quantity as the O2-N2 ratio. The Southern Ocean is a very unique place on the planet. It's the one place on the planet where the ocean can circumnavigate the globe unimpeded by continental landmass. And as a result of that unique physical setting, there's a unique current and circulation associated with that current. There's the Antarctic circumpolar current that wraps around Antarctica. And associated with that current is a meridional overturning circulation. That's a circulation that brings water from the north at depth to the surface where it can be exposed to the atmosphere and then subsequently subducted back into the ocean interior. I've been to the Southern Ocean twice before. It's a very beautiful but austere place. We often experience rough seas and high wind conditions. And those same winds are fundamental in driving the Antarctic circumpolar current. And that current plays a fundamental role in determining the uptake of heat and carbon dioxide by the Southern Ocean from the atmosphere. So ocean biology actually play a leading-order role in determining the flux of CO2 from the atmosphere to the ocean. In the surface ocean there are algae phytoplankton that photosynthesize. And that is a process that converts carbon dioxide into organic material. And that organic material has the capacity to sink. Sinking of that organic material is something we call the biological pump. It's essentially a mechanism to transport carbon dioxide from the surface ocean directly into the ocean interior. Modeling of the Southern Ocean is challenging for two primary reasons. First, the oceanography of the region is fairly complicated. The Southern Ocean is a place where mesoscale eddies play a leading-order role in the circulation dynamics. And that's fairly unique. So the physics is the first challenge. The second challenge is to understand the role of biology. And while we have, in a sense, exact mathematical descriptions of ocean circulation, we don't have a comparable set of equations governing the biology. So to model biology we're forced to make approximations. And it's really the degree to which those approximations are sufficient, sufficiently accurate, that determines the quality of our model solutions. We'll be conducting flights of several types. And one of those will be profiling from almost as high as the aircraft can go to very near the surface. The plane will just do that up and down for about seven or eight hours and then come back to Plintoranus. On the subset of the flights we'll be overflying a research ship that's operating off the Antarctic Peninsula, as well as some of the research stations. The ship and the station have been measuring oxygen and carbon dioxide for a long time, but with the aircraft we can connect those measurements to the larger-scale patterns in the atmosphere. The aircraft is being supported by the National Science Foundation. We have a large science team that includes Scripps Institution of Oceanography, the University of Michigan, the University of Colorado at Boulder, as well as the Jet Propulsion Laboratory in Pasadena. And NASA is also contributing support for a remote sensing instrument on the plane. It's important if we want to be able to predict how much warmer it might get or decide how much fossil fuel to burn today if we want to keep to a certain temperature change to be able to predict how the Southern Ocean will absorb CO2 in the future.