We spent a total of a day and a half getting all of our instruments ready for installing on the reef. That might sound like a long time, but when you think about what it takes to prepare all these things it makes a lot more sense!
We have five different sites around Palmyra where we'll be putting instruments; together, they'll let us get a sense of the overall circulation changes around the island during the course of the El Nino (or at least, of the winter). At each of those spots, we'll be putting in:
- A "CTD", or Conductivity-Temperature-Depth sensor. This measures the pressure, which can be translated into water depth; the conductivity of the water, which is convertible to the salinity; and the temperature of the surrounding water.
- An "ADCP", or Acoustic Doppler Current Profiler. This instrument sends out regular acoustic "pings" like the sonars you see in movies about submarines. Those pings reflect off plankton, dirt, or other debris in the water and return to the instrument; then the change in the frequency of the ping once it gets back to where it started tells you how fast the current is flowing.
The CTD and ADCPs are attached to each other with clamps, then mounted on metal bars and weighed down with 60 pounds of zinc. Then just to make sure they won't go anywhere, they get staked to the reef! The entire setup looks like this:
Then the other thing we are measuring is the isotopic composition of water: both seawater and rainwater. These measurements are really important, because they tell us the relationship of temperature and salinity changes to changes in water composition... which is what the corals we're using to reconstruct El Nino actually 'care' about. To make it simpler: if you think of the seawater around the reef as a big bucket that's affected by
- rain coming in
- water evaporating from the surface
- ocean currents bringing water with different amounts of oxygen isotopes
(credit for background image: Widlansky et al. 2014)
what we're trying to do is measure how important each of those things are during El Nino events. The data we're collecting will be analyzed on its own, then also incorporated into our new, 'isotope-enabled' version of an ocean model (the Regional Ocean Modeling System, or ROMS) so we can get a complete picture of circulation around all of Palmyra, not just the few spots we'll be able to collect data.
In theory it should be really cool! Now to get started on those measurements...
Short post today, but I just wanted to update and say that we made it
safely to Palmyra! We got in yesterday morning, and have been busy
getting all of our instruments ready ever since (see next post for
more).
The trip to Palmyra is just a few hours from
Hawaii. To get there, the only way is either by having your own boat or
by taking the plane chartered by the Palmyra Atoll Research Consortium,
or PARC. PARC is a sort of 'club' that universities join, and by paying
their PARC fee they get a certain number of seats on the plane every
year. I'm not too clear on all the details, since Mark has been nice
enough to deal with all of that for us, but I do know that the plane to
Palmyra is easily the nicest flight I've ever been on. It's a Gulfstream
II:
I found out later that the
reason why they charter such a nice jet is so that the plane can make it
from Hawaii to Palmyra and back without needing to be refueled (and
therefore the Palmyra staff doesn't have to maintain giant airplane fuel
tanks). But this is one of the types of planes used by the super-rich,
as we found out by reading all the onboard magazines. Most flights you
get Skymall: this time we got to read about luxury resorts, investment
real estate, and the best private planes to buy. (According to the
magazine, it was the Gulfstream.)
That meant we had excellent views of the atoll when it first came into view!
It
was pretty amazing to actually see this island I've been starting at
for so long on Google Earth in person. Then the only thing left was to
get used to being quite literally in the middle of the Pacific Ocean!
Today our small team of scientists from the University of Hawaii heads out to one of the most unique destinations in the world: Palmyra Atoll. Palmyra is a tiny string of islands surrounding a lagoon, and has less than 5 square miles of land surface. It's also incredibly remote: 1000 miles south of Hawaii, or almost a 3 hour plane ride.
Haven't heard of Palmyra before? That's probably because no one lives there, at least not all the time - Palmyra is a "US Affiliated Pacific Island" managed by The Nature Conservancy, and is 'inhabited' by a rotating crew of TNC staff, US Fish and Wildlife Service personnel, and visiting scientists.
Even though Palmyra has never been permanently settled by humans, it has a very cool history: it's named for an American sailing ship, the USS Palmyra, which ran aground there in 1802. Throughout the 1800s it was annexed a variety of times: by the US government, by the Kingdom of Hawaii, then by the US again (when the US took over Hawaii - for a while there Palmyra was actually part of Hawaii!). Then in the early 1900s it was bought by a wealthy judge, and has been privately owned ever since... with the exception of a few years during World War II when it was used as a naval base by the US. The Nature Conservancy bought Palmyra in 2000 and sold part of it to the Fish and Wildlife service, and now it's maintained as a wildlife refuge.
Palmyra has an amazing variety of marine life, and one of the healthiest coral reef ecosystems in the world. It's common to see all sorts of sharks, rays, whales, and (it seems like) any other tropical fish you can think of - this makes it a very valuable destination for marine ecologists, who can actually study the ecosystem there without worrying about all the ways people have screwed it up! But none of that is the reason why we're headed out there. No, we are a physical oceanography team, and we'll be deploying instruments on Palmyra's reefs to measure the temperature, salinity, and currents around the island - and the isotopic composition (relative amounts of oxygen-18 and oxygen-16) of the sea and rain waters as well.
Why are we doing this? Well, to explain that I need to explain something else: El Nino. Not this one:
This one:
That last picture is a satellite image of sea surface temperature (SST) anomalies during the last really big El Nino event, in 1997-98.
El Nino events (and their sisters the La Ninas) happen when the trade winds that blow from east to west along the equator become either much weaker or much stronger than normal. When that happens, all the warm water that sits along the equator either 'sloshes' over to the east (El Nino) or gets pushed over into the west (La Nina). They both have dramatic impacts around the world, on weather, fisheries, and many other things: so we'd like to have an idea of how often they happen and how strong they tend to be, not to mention figuring out how they might change in the future! But the problem is that we've only been observing the oceans in enough detail for about 30 years, and El Nino/La Ninas only happen every 3-4 years, and that adds up to not enough events to get a good sense of what 'normal' is like.
One way we can get around this problem is using paleoclimate data to reconstruct what past El Nino/La Nina events were like. Paleoclimate data is basically any naturally occurring object that is sensitive to climate and accumulates fast enough to record changes in climate. On land, people use tree rings, ice cores and other things... but in the tropical oceans, coral reefs are the name of the game. Corals grow very quickly, like trees, and changes in the seawater around them affect the proportion of isotopes of oxygen that get incorporated into their skeletons. Islands in the central Pacific, like Palmyra and its neighbor Christmas Island, are excellent sites for collecting coral data since they're right where we expect the biggest effects of El Nino to be. But we still don't have good measurements of exactly how you translate between isotopes of oxygen in corals and what a particular set of El Nino events looked like, since there aren't very many measurements from right next to the reefs during their entire 'life cycle'. I've been working on using model simulations to understand the physics of how you go from El Nino to coral isotopes, but of course having more data would always be helpful.
Cue the 2014 El Nino! ...hopefully... Earlier this year, it looked like we might be in for the biggest El Nino since the one that inspired the Chris Farley video above. So my collaborators (Kim Cobb, Mark Merrifield, and Brian Powell) and I put in for a small grant to actually go down and put instruments near the reefs at Palmyra so we could watch how the event affected conditions near the shore! In a companion grant, Kim is also collaborating with coral ecologists to look at the impacts of this El Nino on coral ecology. She has a blog here:
Since we received our funding, the El Nino forecast got downgraded a bit, and it looks like any event we get won't be nearly as big as the 1997-98 one. But regardless of how big this El Nino turns out to be, the data we gather in the next week or so will be critical for understanding how these events are recorded by corals.
