Physical Oceanography in Paradise

by Sam Stevenson

As Kim has described in her earlier posts, our team has a dual mission: at Christmas Island, to document the impacts of the El Nino event on coral reef health; and at Palmyra Atoll a bit further north, to look at the physical changes taking place around the atoll during the course of the event. Here is a map showing both, with Hawaii included for context:

The physical-oceanographic (PO) side of the proposal is very closely related to the work I'm doing under an NSF postdoc fellowship: modeling how El Nino and La Nina events create changes in the oxygen isotopic ratio in seawater near tropical Pacific reefs. This is really important since when you try to reconstruct past climate variability, you're assuming a relationship between the thing you're measuring (coral oxygen isotopes) and the thing you want to reconstruct (El Nino/La Nina). So I'm working on trying to understand that relationship as well as possible - we started out simply using the new version of an ocean model we've developed, but when the 2014 El Nino was looking like it might be 'The Next Big One' it seemed like a great opportunity to get out in the field and collect some data as well. And even now that the likely size of the El Nino is smaller, from my perspective it is still a great opportunity, since we'll just be able to assess what small El Ninos, rather than big ones, do to isotope changes near the reefs.

The PO project would not have been possible without Mark Merrifield, who made all the Palmyra logistics happen and supplied his amazing team of dive technicians to do the installation of instruments on the reef. We'll be measuring temperature, salinity, and the speed of currents in several spots around the island. Then the other set of data we'll be collecting is the isotopic ratio of oxygen in both rainwater and seawater at Palmyra. Taken together, this will give us an idea of pretty much everything that can affect isotopes in seawater near these reefs.

Now, normally the work that I do takes place on a computer screen, so I was already pretty excited about going to collect "real" data. And I have to say, if you have to pick a single place to do fieldwork, Palmyra is a pretty excellent choice! Unlike Christmas, no one actually lives on Palmyra - it's a wildlife refuge and the only people there are scientific researchers and support staff from the Nature Conservancy (TNC) and the Fish and Wildlife Service. So it's an extremely pristine environment, and everything is designed to make the research experience as easy as possible. Of course, the fact that no one lives there means it's a lot harder to get to than Christmas... the only flights in and out are on a jet chartered by TNC, that comes once every week to week and a half (and sometimes not at all, if you're unlucky with the weather).

When we were at Palmyra, most of the time the population of the entire atoll was only 15, which gives things a bit of a "summer camp-like" vibe. You stay in small cabins, have assigned chores, and eat communally at set times: then there are scheduled activities every week like "science night", when the visiting researchers give brief talks on why they're there for the other scientists and the staff. And because it's such an isolated environment, the snorkeling you can do in your spare time is some of the most incredible I've ever seen:

(this photo credit goes to David Slater, our amazing dive tech/photographer!)

Our little expedition achieved its goals without too many issues, aside from having to revisit a couple of sites during more favorable weather conditions. We visited five different sites around Palmyra: one each on the northern, northwestern, western, and southern sites plus one inside the channel that connects the lagoon inside the atoll to the open ocean. In each location, we installed a specially designed mount which holds a CTD (conductivity/temperature/depth) sensor which measures temperature and salinity, and an ADCP (acoustic Doppler current profiler) to measure current speeds. The whole thing is weighted down by 60 pounds of lead, and looks like this:

(pic also from Dave Slater, this time with my GoPro)

The two divers are Carly and Christina, who did all the prep work and testing at UH. They did a fantastic job! They also did the transporting of the CTD and current meters down to the ocean floor by 'lift bags' (yellow bag you see above, it is quite buoyant and helps you deal with carrying lots and lots of lead underwater), and staking everything down into the reef with long metal poles. All the techs will be returning to Palmyra in March to retrieve the instruments and put new ones down, and I am eagerly awaiting all the data that's hopefully being collected as we speak.

Back on land, we also set up a program to collect samples of rain and seawater at regular intervals, to be analyzed by Kim's lab for their oxygen isotopic composition. I installed a rain collection system prepared by Kim's student Jessica Moerman, right next to the rain gauge that was already in the main camp area:

Our collector is the one on the left, and the on-site staff were nice enough to agree to empty it every day and collect a sample for us along with recording the amount of rainfall. And being the amazingly nice people that they are, they also agreed to collect samples of seawater every week. This doesn't sound like it would be all that difficult on the face of it, but there aren't exactly very many trails around Palmyra... and the ones that do exist are so overgrown that you don't even recognize them at first. Things just want to grow in the tropics!

Anyway, the point is that doing seawater sample collection requires that you wade across the reef flats on the north shore of the island to get to breaking waves, which is a bit of a process. 

(see the breakers way off in the distance?)

But the data that we end up with will be one of the best resources out there for understanding exactly what an El Nino event does to seawater isotopic composition - especially when combined with the information returned from the moored instruments. Now I just need to figure out how to thank the Nature Conservancy!

Agony, ecstasy, and irony

by Kim Cobb

You cannot make this stuff up.

Pam and I arrived the day before yesterday to find Julia Baum’s team facing more than the usual challenges on Christmas Island. They had been struggling for the past week to get tanks filled for their SCUBA-intensive research. The Baum team arrived on Christmas to learn that the main compressor on the island had failed and they were using a backup unit. Julia and I have been diving at Christmas using tanks from Dive Kiribas – ostensibly the only dive operation on the island - for over a dozen expeditions combined. Shifting to the backup unit brought two problems:  1) it stopped running on occasion, requiring several hours of repair, and 2) when it was working, the resulting tanks had toxic levels of carbon monoxide. Thankfully they were able to cherry-pick a few tanks that were under internationally-accepted limits of 10ppm, as they had brought a CO monitor. But the poor volume and quality of tanks had left both our field programs in a precarious state.

 

Compressor roulette. Are
you feeling lucky?

With creepy prescience, Julia and I had shipped a very expensive field-ready compressor down for this expedition, because we didn’t want to rely on the aging compressor at Dive Kiribati (DK). Indeed, it had actually arrived on the island the very day that the DK compressor failed for good! We patted ourselves on the back and the Baum team fired it up and happily filled their tanks for two days before it started spewing black smoke. By Day 3 it was unable to fill a tank, so the Baum team was back to an ever-dwindling supply of tanks with acceptable CO levels. Our plane touched down on Day 4 of this fiasco:  the mechanic was struggling to resurrect the DK compressor and Julia’s stalwart student, Kieran Cox, had been wrestling with the new compressor all day to diagnose and fix the problem.

The very minute I alighted at DK, at 5pm, I was whisked to the shed to discuss the decision of the moment:  whether to use epoxy to glue the engine back together after a screw had sheared off during repair. After much hemming and hawing, and with a huge amount of optimism, we decided we had no choice but to proceed. [Twitter followers will note that this is where I used the single malt scotch I had brought to wipe lubricant off the metal sealing surfaces prior to epoxy application (see photo).] Pam and I spent the evening taking

Kieran using a pipette to administer
scotch to the compressor.

1-hr shifts holding the epoxied components of our compressor together while it set (label said 4-6 hours), listening to the mechanics work on the DK compressor.

I went to bed that night positively delusional (in hindsight):  sure that by morning our compressor would be working, as well as that of Dive Kiribas. In the morning, ours was still spewing black smoke, and the DK compressor sprung a fuel leak. Of course. By noon we decided to do some water sampling and install some temperature and salinity sensors, before we exploded in frustration. We did quite a bit of free-diving, and used one remnant tank that had 2000psi to install all the sensors. When we got back, however, no compressor. In fact, they had decided to swap in another World War II vintage engine – it would be at least another full day of repairs.

The wind had gone out of my sails – Christmas had finally sucked the optimism right out of me. That is a very hard thing to do to this seasoned field guru. I went to bed that night facing the reality that we wouldn’t get any of our primary science goals done. There would be no dive tanks. I might as well get used to it. I hardly slept that night. At 6am, I leapt out of bed on a mission – I was not going to go down without a fight. Let’s just say I conveyed my extreme displeasure to the DK manager while asking her if she knew of any other compressor (dive rated or no) on the island. I told her the entire year-long project was at risk. I reminded her how much money myself, Julia, and the other PIs of the project had on the line. I began brainstorming. What about the two industrial fishing boats anchored off the pier? Maybe. What about the airport? No. Then (and I have no earthly idea why this hadn’t come up sooner), she tells me that her neighbor two doors down has a SCUBA compressor. What?!? I walk over there, and sure enough, in a back room of a compound devoted to the aquarium fish trade, there is an aging compressor – electric, thank God. The irony of the situation did not escape me. The aquarium fish trade plucks unrestricted quantities of pretty fish off the reef for sale in Honolulu and beyond. Yet they had just saved our entire science program - one dedicated to studying reef resilience to climate change and human disturbance. Unreal.

The kind man gave me the 6 tanks he had filled, and suddenly I’m planning a day of diving! And believe me, Christmas Island never looked so beautiful as it did that morning, motoring out to the reef for a day of science. I’m not entirely sure the boat even touched the water. And the reef itself never looked so beautiful. I admit to lingering for at least a half hour at each of our work sites, swimming around, taking it all in, snapping some cheesy photos with Pam. At one particularly beautiful site, our last for the day, the light was just perfect – the low angle added some reds to the reef, and the colors just shone. There was an incredibly diverse set of large colonies that piled up to form walls 6ft high on either side of white sand channels 3-4ft wide. As I made my way through the living maze, I suddenly realized that if a strong El Niño arrives this winter, it would decimate these dazzling corals. They looked healthy and strong now, but they would be no match for sustained 4-5F warming. And in the back of my brain, far removed from science and NSF and publications, I thought “Maybe it’s OK if this El Niño is weak after all.”

Showing off my handiwork, having installed a temperature logger (aka yellow stick) on the reef.
Note the SCUBA tank and bubbles ascending from my regulator. Hallelujah.

What a long, strange trip it's been

by Kim Cobb

Today we are on our way to the middle of the Pacific Ocean, where we will install a large number of temperature and salinity sensors around Christmas Island (2°N, 157°W), in the hopes of capturing the dramatic environmental shifts associated with the strong El Niño event this coming winter. But will it actually materialize?

Many months have passed since my blog post about the potential for a very strong El Niño event this winter. Two months later I sealed my fate by tweeting the following:  “Going on record for a strong El Niño this winter, amplitude of 2.5+/- 0.3°C as measured by NIÑO3 SST. Anybody else in? #nogutsnoglory” In late spring, the Atmospheric and Geospace Science and Biology divisions at NSF funded myself and four other PIs to gather a suite of physical oceanographic and ecological data from Christmas and Palmyra Islands. These remote coral atolls lie near the equator in the central tropical Pacific, in the very heart of El Niño action. In doing so, NSF took a fairly big gamble that the climate models forecasting a significant El Niño for this winter were accurate. They hoped that our group would document the impacts, both physical and biological, of a large El Niño event in unprecedented detail. I refer readers to our inaugural post on the project to read about our research goals and their broader relevance.

Months of planning and many tens of thousands of dollars later, our entire science team is now deployed on the equator for the first of three large, coordinated expeditions. In our “divide and conquer” strategy, Mark Merrifield’s team is currently on Palmyra to install moored arrays of sensors that will log temperature, salinity, and currents with incredible accuracy and precision. Samantha Stevenson (a climate modeler turned field buff for the month) is setting up the seawater and rainwater collection program at Palmyra, so that we can monitor the El Niño’s effects on the atmospheric and oceanic distributions of oxygen isotopes. This isotope system forms the basis of our reconstructions of paleo-El Niño events in corals from these sites. Meteorological stations on both islands will log a suite of atmospheric variables, including winds, rainfall, and pressure. On Christmas Island, we will join Julia Baum’s team of reef ecologists in surveying up to a dozen sites that she’s been monitoring for the last 5 years. We are excited to learn their elaborate sampling protocols, even if it means signing on to their 4-dives-a-day, 9-hr boat operations. And we thought fossil coral scavenging on sun-baked beaches was hard work…

So here’s the million dollar question:  Will there be a strong El Niño event this winter? Note that most climatemodels do forecast a moderate El Niño event. But we are really banking on (quite literally) The Big One. Admittedly, much of the wind has gone out of the El Nino sails this summer, when favorable conditions in mid-June (see Figure 1) gave way to a near death experience by late July. However, a modest westerly wind burst in mid-August has breathed new life into the tropical Pacific, with a prominent depression of the thermocline making its way eastward. The only remaining hope for a strong El Niño event rests on the subsequent surface warming that will appear in the next weeks in the eastern equatorial Pacific, and a concomitant relaxation of the trade winds. Whether the trades weaken enough to sustain the depression of the thermocline and associated surface warming is unknown. I will say that the persistent warm SST anomalies near the dateline throughout the spring and summer (see Figure 1) have not helped, as they weaken the atmospheric punch of the intermittent surface warmings in the eastern equatorial Pacific. Upon waking today, however, I noted that anomalies of >1°C are now visible across a broad swathe of the eastern equatorial Pacific. So there is still a chance for a major event to take shape, but that window is rapidly closing. These next few weeks are critical.

Maps of 5-day averaged SST and wind anomalies across the equatorial Pacific, ending in the date specified. The region of westerly wind burst activity is indicated in the red box. "Favorable" winds blow from the west towards the east, and drive equatorial warming in the eastern Pacific in the next months, furthering the development of El Niño conditions. The blue 'X' marks the location of Christmas and Palmyra Islands. The top plot shows average SST and winds for the 5-day period ending on June 15, 2014, for reference. Plots from http://www.pmel.noaa.gov/tao/

For the purposes of our research at Christmas and Palmyra, the ~0.5-1°C warming that has characterized the last 6 months at these sites may have already had significant impacts on the coral reef ecosystem.  So in terms of El Niño impacts, we might be perfectly placed to capture the peak of what might be a relatively strong ‘central Pacific El Niño’. In that sense, our research would be an important contribution to ecological and climate science (and specifically, their intersection), as many models project a shift towards such events in coming decades.


Stay tuned for updates from the field over the next two weeks!