HOST 1: And Rolf is up next and he's going to tell you-- HOST 2: And he's going to talk a little bit more about this. [INAUDIBLE] [INAUDIBLE] ROLF SONNERUP: Yeah, also am-- [INAUDIBLE] [LAUGHTER] ROLF: The justifications that deal with-- We have the imprint of processes of the sea floor and we have the imprints of processes at the sea surface. So NOAA has had a tracer program-- It was one of the earliest programs started by Richard Gammon in the mid 1980s. John Bullister and David Wisegarver were very careful analytical chemists, and they made this one of the best labs in the world, and that tradition continues thanks to the efforts of Bonnie Chang. We measure tracers because we want to know how much of the ocean is actively exchanging with the atmosphere. We want to know how much it's influencing the atmosphere, and we want to know how much the atmosphere is influencing the ocean and how quickly. So tracers are critical to efforts to determine the imprint of atmosphere pertubations like anthropogenic warming, and anthropogenic CO2. You can use tracers, I'm going to show you this, to quantify ocean circulation rates, and you can use tracers to quantify turnover timescales of major biogeochemicals. Our bread and butter at PMEL has been measuring of freons or the CFCs which were introduced to the atmosphere, at least in the early 1950s. They increased in the atmosphere until they were phased out in the late 80s and the 1990s. Because the gases are now decreasing in the atmosphere, we started measuring sulfur hexafluoride on the same samples at minimal additional cost. This is a section from right down the middle of the Atlantic Ocean from near Antarctica to Iceland. This is sulfur hexafluoride in 2013. The [INAUDIBLE] tank is zero and, red is the highest concentration on this scale. In 2013, you can see that sulfur hexafluoride has flooded the main thermocline, and that means that the thermocline exchanges with the atmosphere on timescales less than about 20 years. Sulfur hexafluoride now looks like CFCs did 20 years ago. This is what CFC looks like now. You can see that CFC has penetrated quite a bit farther into the water column with North Atlantic Deep Water formation and Weddell Sea Bottom water formation. And in fact, in the South Western basin here all of the water has seen the atmosphere within the last 50 years. In the upper ocean the trends here are driven by the temperature of the water. In fact, all of these water samples are in saturation equilibrium with the atmosphere, and that means that this atmosphere tracer history is actually a history of the trace gas concentrations at the sea surface. And that means you can take a subsurface samples CFC concentration and estimate a date that that water parcel was last at the sea surface, and that's how we know how old the thermocline and these newly formed bottom waters are. That approach only works when the tracers are increasing in time or changing in time, and it works best when it's linear. There was a golden age of CFCs here in the 70s, 80s and 90s. Well, and now we're in the golden age of sulfur hexafluoride. These two complement each other in time and in space. So the combination of the two allows us to see ventilation rates at the sea surface and further into the water column using the older tracer. I did mention we do about a cruise a year. In fact Bonnie Chang and Emily Norton are about to head out for this one probably in the next couple of days. These are repeats of cruises that were done 10, 20 and sometimes 30 years ago, so we're able to see changes in the ocean's physical state. This is an example from Darryn Waugh. Some meridional north-south section from the Indian, two sections from the Pacific and from the Atlantic Ocean. What it's showing here is that comparing 1990s with 2000s data, there was an increase in ventilation in these subantarctic mode waters in the 2000s, and that ventilation South of the subantarctic front had apparently slowed down substantially. CFCs are critical to studying the ocean's impact on the global carbon cycle, because not only does the sea surface track the atmospheric CFC history, they track the atmospheric CO2 history, and that means you can kind of skip the data step. You can take a CFC concentration and relate it to the CO2 history to infer that that same water parcel had co-rated with respect to about a 70 PPM increase in CO2. The CFC number is unambiguous. It's detectable at high signals of noise where 72 PPM in pCO2 space is a very small signal relative to natural bedrock variability. So CFCs are fundamental to CO2. In fact, the anthropogenic CO2 inventory calculated by Chris Sabine for the 1990s, looks a lot like the CFC inventory. Not just because they're governed by the same processes, but because the CO2 field was calculated from the CFC field. So CFCs have always been very useful for upper ocean turnover timescales, and I want to just talk about the future for CFCs with this last slide. This is a section from along the dateline near New Zealand. From near Antarctica all the way to the equator 1996, 2009, and 2016 in the bottom. In 1996, we could see some tracer burning in newly formed Antarctic bottom waters, and you can see that that plume is gradually working its way northwards sliding along the sea floor, and that means in the next couple of decades CFCs are going to herald the arrival of anthropogenic signals that are otherwise very difficult to detect. This signal down here at the equator, it's pretty easy to find in CFCs but it's still impossible to see in CO2. And that's all I got. Thank you. [APPLAUSE] AUDIENCE: Did you see the heat basin conservance experiment in the South Atlantic? ROLF: Did you see it? AUDIENCE: Did you? ROLF: I did, yes. AUDIENCE: In SF 6. ROLF: Here it is. It's in the figure. Can I go back? HOST 3: Yeah, [INAUDIBLE] ROLF: Oh. HOST 3: Hang on. ROLF: So SF 6 had, well, it has a number of uses, but because of its-- [INAUDIBLE] it's really easy to detect with a [INAUDIBLE] capture detector. So people used to measure dissipation rate in the ocean interior by releasing it, and so we're not allowed to do that anymore 'cause it's now anthropogenic tracers, but this is the signature of an experiment that was conducted in that area. There are about five places in the world ocean where you have to look out for that signature. AUDIENCE: Now it's NSF 5 [INAUDIBLE] AUDIENCE 2: [INAUDIBLE] ROLF: [INAUDIBLE] or something. Yeah. HOST 1: All right. Thank you. [LAUGHTER] HOST 1: It's a lightning talk. ROLF: But I want to keep talking. [LAUGHTER]