Take It to Print

by Stacy Carolin
We have a paper out (!) And all that text will likely cause a little headache, so I’ve condensed it down to the important talking points –in common tongue-- to bring to the dinner table tonight: 

Link to Science paper

The author examining a fallen stalagmite. Credit:  Syria Lejau

Background:
The new published record was created from stalagmites collected in Gunung Mulu National Park on the island of Borneo, which sits on the equator in the western Pacific. Variability in the isotopic chemistry of the rainwater over our site is directly related to variability in the rainfall amount in the region (see lab-colleague Jessica Moerman's recent study in EPSL). Stalagmites form from rainwater that drips through soil and limestone into cave chambers, and the isotopic chemistry in the rainwater is captured and maintained in the calcite formations over tens of thousands of years. The four stalagmites used in this study grew during most of earth's last ice age (100,000 years ago to 15,000 years ago), and reveal how rainfall amount over Borneo changed (or did not change) in response to various atmospheric and oceanic changes, both global and local, during this period.

Points (1)-(5) on published

Figure 2 --click for larger

(1) Ice-age-cycle global temperature and CO2 variations did not greatly influence rainfall amount over Borneo -- Like the Chinese stalagmite records, the 100,000-year-long Borneo record does not have a "sawtooth" shape famously characteristic in the global temperature, atmospheric CO2, and sea level records spanning several ice age cycles. We conclude then that on these multi-thousand-year timescales, those variables are not directly influencing rainfall amounts over Borneo.

(2) Abrupt sea level drop / sunda shelf exposure did not cause a synchronous shift toward dry (or wet) conditions in Borneo -- Sunda Shelf emergence (shallow continental shelf connecting Borneo to Southeast Asia) has been implicated in shaping western tropical Pacific rainfall amount in previous studies, but we find little correlation between the Borneo records and an index of Sunda Shelf exposure over the last 100,000 years. For example, significant variations in the Borneo records during the earlier glacial interval (90,000-70,000 years ago) bear little resemblance to reconstructed sea level changes, most notably ~76,000-71,000 years ago, when a 60 meter drop in sea level almost doubled the size of the exposed shelf without any corresponding shift in rainfall amount.

(3) Rainfall variability over Borneo closely followed solar radiation cycles over the equator (seasonal solar energy flux increase = rainfall amount increase, and vice versa) -- The Borneo records suggest that solar precessional cycles (meaning change in solar energy flux over the equator due to cyclical change in the orientation of earth's tilted axis) may be the dominant source of Borneo rainfall amount variability on thousand-year timescales. For example, today the tilted axis points the northern hemisphere toward the sun (northern hemisphere summer) when the earth is furthest from the sun in its elliptical orbit, while 12,000 years ago the tilted axis pointed the southern hemisphere toward the sun (northern hemisphere winter) when the earth was furthest from the sun in its elliptical orbit. These cyclical changes on thousand-year timescales vary the seasonal amount of solar energy over Borneo, which the records suggest in turn do drive changes in the amount of rainfall over Borneo.

(4) The Borneo record’s lack of many abrupt climate shifts that are present in almost all northern hemisphere records implies a selective response of Borneo rainfall to high-latitude abrupt climate change forcing -- The dominant paradigm to explain the famous global millennial-scale climate shifts first discovered in the Greenland ice cores is that they are driven from the North Atlantic region, either from weakening of the Atlantic ocean circulation or from a dramatic albedo change due to sea ice cover, which in turn shifts the northern hemisphere to cooler/drier conditions and makes the southern hemisphere warmer/wetter. The absence of several of these abrupt climate change signals in the Borneo record represents a clear challenge to our understanding of how the tropical Pacific is involved in the mechanism(s) that forced abrupt climate change during earth’s last glacial state.

(5) The largest millennial-scale anomaly in the 100,000-year Borneo record is coincident with the Toba super eruption -- The Toba eruption was the largest volcanic eruption in the past 2.5 million years and climate responses to the eruption are uncertain. Many anthropologists believe that the volcanic winter following the super-eruption decimated most “modern human” populations at that time, and caused a bottleneck in human evolution. The abrupt shift toward dry conditions over Borneo (within age error of the volcanic eruption) that then lasted for a millennium is interestingly mirrored in the Chinese stalagmite record. Further studies are needed to determine if these events are at all related.

Thanks to Kim, Jess, Jessica, Syria, Jenny, and all the rest for helping put this beast together, from field to print! What an experience!

Manus is for [Cloud] Lovers

by Jess Conroy

We’re back from our latest trek to the ends of the earth. In pursuit of the rain once again, we headed out to the far western Pacific a couple weeks ago, to the remote island of Manus, off the coast of Papua New Guinea.  This time, we also brought our Picarro instrument along for the ride!

Manus Island, the perfect place to study tropical rainfall!

Why here, of all places?  To complement our rain and seawater collections on Christmas Island and in the Galápagos, we wanted to collect waters from a site bathed in the tepid waters of the West Pacific Warm Pool. I can testify that it was far more delightful to dip my toes in Manus seawater, compared to the chilly waters off the Galápagos!

Grabbing a water sample from a coastal lagoon.

Additionally, to understand the convective clouds that so often drape across the Manus sky, the US Department of Energy and the Australian Bureau of Meteorology have parked loads of fancy instruments here. So, coupled with water vapor isotope measurements from our Picarro, we will be able to place our precipitation isotope measurements in a very rich atmospheric context.

Team Manus: David Noone, me, and Jessica Moerman
standing proudly at the site with our automated rain collector!

What exactly are we looking for? Once again, we are trying to dissect the relationship between stable isotopes in water molecules and climate. In warm, wet, tropical places like Manus, there are usually fewer heavy oxygen and hydrogen isotopes in the rain. And, with more rain, there are fewer and fewer of the heavy isotopes. This important relationship, dubbed the ‘amount effect,’ is used by many paleoclimatologists, along with measurements of fossil water archived in things like speleothems and sediments, to estimate how wet or dry it was many decades, centuries, and even millennia before we started measuring precipitation rates.

Saying goodbye to the Manus weather observers, who will
continue to take our water samples for the next few years.

But, the question we are asking now is, why does this relationship exist? Interestingly, the mechanism for this relationship that I learned in my graduate classes back in the day is only really part of the story (we think). For example, it was once thought that since tropical rain is so intense, all the heavy isotopes rain out initially, making the subsequent precipitation lighter and lighter isotopically. But in the last few years, many new insights about the physics of the ‘amount effect’ suggest other causes of this relationship, like the evaporation of rain beneath the clouds, and the recycling of vapor with very low isotope values from the evaporated rain back into the rain clouds. But these insights come from models, not observations. So, our hope and goal is that, equipped with mountains of atmospheric data from Manus--like cloud base height, 3 different kinds of radar, temperature and humidity profiles through the atmosphere, and rain drop size distributions, for starters, we can start to understand this relationship between precipitation isotopes and rain amount, ultimately improving our interpretation of all those records of past rainfall from paleoclimate records.
 

Students bring energy efficiency message to the Hill

On May 6, I accompanied the winning team from my class' Carbon Reduction Challenge to Washington DC to boast of their accomplishments to staffers on Capitol Hill, and to learn more about the current status, and future prospects, of energy/climate legislation on the Hill. Team "Lumber Jills" included four young women (Mary Farrell, Rebecca Harris, Olivia Myers, and Priscilla Tong) who averted over 190,000lbs !! of CO2 emissions over the 8-week Challenge this spring. By comparison, our flights to DC emitted ~1500lbs of CO2, as calculated here. They worked with a RBC Bearings, Inc plant in Hartsville, SC to significantly reduce wood pallet waste (we're talking ~20 tons of wood waste per month!) It's a fine example of new win-win partnerships that can emerge between higher education and corporations - saving companies money and providing real-world training for the next generation of energy stewards.

 Here's what the students had to say:

Winners Olivia Myers and Rebecca Harris pose with
Kim Cobb, in front of the Capitol building between
office visits.

Once it was announced that our group had won the Carbon Reduction Challenge, I was excited about the trip to DC. I was excited about flying. I was excited about meeting with legislators. I was excited to possibly change some attitudes regarding energy efficiency. After arriving at Dr. Cobb's parents’ house in DC, we had a delicious dinner and enjoyed the entertaining and stimulating conversation with her parents, who are both professors at George Mason University. Later that evening, Dr. Cobb rapidly educated us on “asks” (What do you want from the lawmaker?) and helped us create “leaves” (a 1-pager containing our main points, key graphics, and contact info - see below) and generally prepared us for the next day. I went to bed with my head spinning.

When we first arrived to Capitol Hill at 8:00am, I was in awe of the majestic architecture of the Supreme Court, the Library of Congress, and the Capitol building. That day, we would meet with people who had influence over the major decisions made in this country.

Even though our first meeting, with a staffer for Congressman Lewis (D-GA) was supposed to be “friendly,” Rebecca and I were extremely nervous. Once we sat down, however, we surprised ourselves by coherently explaining our project and delivering our main points:  that energy efficiency should be key component of energy-related legislation, and that the economic gains that it affords make it attractive to lawmakers across the ideological spectrum. The legislative aides seemed to really care about what we were saying. The day went by in a blur, and we grew more confident in delivering our message with each meeting.  As we boarded the plane back to Atlanta, we were tremendously satisfied with our time on the Hill. While I am not planning on going into politics anytime soon, I truly appreciate how much of an impact just one person can have on the process.

-Olivia Myers (3rd year biology major)

Our adventure in DC proved to be very exciting indeed. What was most interesting was the way in which the talks with legislative staffers unfolded. The quality of the exchange always depended on the way we framed our “ask” and the response from the staffer as they summarized his/her Congressman’s position on energy legislation. We mostly visited with the offices of Republican Congressmen and Senators, but we met with people from both sides of the aisle. It was very interesting to see how they differently they approached our suggestions to focus on efficiency as a way to be green and cost-effective. The staffers offered a spectrum of viewpoints and approaches to governance, illustrating the divisions in government that are celebrated in this country as bringing about a balanced solution.

One example of compromise in the presence of division is the process of “marking up” the 2013 Farm Bill that includes legislation on biofuels and bioenergy, slated to occur that week. As part of that process, Senators Franken (D-MN) and Harkin (D-IA) introduced the “Rural Energy Investment Act” that allocates funding to a host of initiatives aimed at encouraging agricultural energy technologies, including advanced biofuels, biogas, biomass, and renewable energies. One staffer joked that the Farm Bill was rapidly becoming an energy bill. Dr. Cobb, Olivia, and I had a very interesting conversation about the evolution of energy-related provisions in the Farm Bill, including past subsidies for corn-based ethanol, and their ultimate effects on climate change. It’s just another example of how energy and climate policy make their way into many different types of legislation.

Later, Olivia and I got a chance to reflect over the day, our conversations with legislative staffers of different parties, the conversations within our own group, as well as our personal viewpoints. We both agreed that this experience allowed us to more greatly appreciate the complexities lawmakers work through during the legislative process. Compromise has always been a tenant of our government, and we see now that it is necessary in order to honor the nation’s diverse viewpoints and frameworks. The day also allowed us to be privy to the core beliefs that guide individual lawmakers. While scientific facts may suggest one course of action, lawmakers have to balance science with other goals when approaching climate and energy legislation. Even though it was frustrating and sometimes maddening when staffers did not agree with us and seemed to ignore the facts, I gained respect for the value they place in best representing the interests of their constituents.

-Rebecca Harris (2nd year public policy major)

A handout illustrating the Lumber Jills
winning strategy for CO2 reduction.

A handout illustrating some of the climate and
energy initiatives at Georgia Tech.

Quick and Dirty Dating

So many untouched cores of coral!

by Pamela Grothe

Week 1: Scripps

I started my two-week jaunt to California last week at Chris Charles’ lab at Scripps Institution of Oceanography, Kim’s alma mater.  After several expeditions in the field, Kim has collected quite a collection of fossil coral from the Line Islands (and in particular from Palmyra), all of which have not been dated or geochemically analyzed. Since Scripps is just down the road from UC Irvine, we figured it would be a great opportunity to inventory the collection that exists there and take samples from them to date in addition to my samples from Christmas Island. Unfortunately, half the collection was off-site in storage bays located in rattlesnake habitat, so I was only able to inventory half the existing collection. That just means I will have to return another day to inventory the rest! In all, I found 48 cores that have not been analyzed yet that I measured, photographed, categorized, and sampled.

Week 2: UC Irvine

Doing what I do best, exploring the area on a 10 mile trail
run in Crystal Cove State Park on Easter Sunday.
I haven't seen hills like this since I left Boulder!

After enjoying my time in beautiful La Jolla, I bummed a ride up to Irvine on Friday afternoon from the guy who works at the Cal Tech Marine Lab, where I’m staying. It just so happened that he was in the area picking up sea urchins and saved me the headache of public transportation to head up the coast! With Kim’s connections at Cal Tech, I was able to stay at their Marine Lab right on the water in Corona Del Mar! The accommodations are far from luxurious but you can’t beat cheap oceanfront lodging.

I spent Saturday in the lab washing and drying the samples I grabbed at Scripps, and then took Easter Sunday to myself to explore the area and get caught up on some homework since I’m missing two weeks of classes.

And so the dating process begins! Carbon-14 is a radioactive element that decays with a known half-life of 5,730 years. Corals take up carbon from the water while it’s living, including stable 12C and radioactive 14C. Once it dies, 14C begins to decay while the stable 12C remains constant, thus changing the 14C to 12C ratio. By comparing the measured 14C/12C ratio with the 14C/12C ratio of the atmosphere an age can be calculated.  This is the radiocarbon age, which is not the true age because the 14C/12C ratio of the atmosphere has not been constant through the past. Luckily the experts have worked this out and we can just apply a calibration curve to our data (in my case a curve that also takes into account the reservoir age of the water in which the corals grew) and we get a true calendar age!

The AMS. Much bigger than our mas spec!

Carbon-14 atoms are rare and so in order to measure them you need an accelerator mass spectrometer, such as the one here at UC Irvine (pictured on right). These instruments are equipped with an ion source that bombards the sample with cesium ions, which are then focused into the accelerator by magnets. In the accelerator, they collide with Argon gas that is circulating throughout in order to break up molecular ions. The filtered ions then enter the detector and are measured. Only a special few get to operate this, so for this part, my only participation was watching the experts load my sample wheel from outside the high voltage cage.

Cartoon schematic illustrating the different
components of the AMS.

But there’s a lot of prep work to get the samples ready for the AMS. Luckily for me, I’m performing the “quick and dirty” method, also known as the fast screening method, so my prep time is reduced dramatically. Normally, the samples that go into the wheel are graphitized, a process that takes the original sample and converts it into graphite (leaching with HCl to clean the sample, dissolving in phosphoric acid to convert sample to a CO2 gas, and then graphitizing the CO2 gas to graphite). However, the quick and dirty removes all those steps and just uses the powdered sample mixed with pure iron!

Of course, that being said, the process of physically handling 85 samples still took three days. The samples I collected at Scripps needed to be crushed. Iron has to be weighed out to between 5.0 and 6.5 milligrams (about half-way through I became good enough to just eye ball this saving more time). Then 0.3 milligrams of the powdered sample needs to be weighed out and mixed with iron (this you can’t eye ball because the beam current works best with 0.3 milligrams of sample so there’s not much wiggle room here). The last step is pouring this tiny amount of sample into a pin-sized hole without spilling and then pressing it to 400 psi so that it is no longer loose powder. It took a bit of muscle memory before getting the tilt and pour method down without spilling my sample everywhere! But the biggest time consuming part of all of this is cleaning every tool in-between samples, as you don’t want to contaminate your next sample. It’s crazy how mush waste I generated in just prepping my two wheels as nothing is reused in this lab because of possible contamination.

Now that the samples are prepped and ready, it’s time to let the AMS do its job and wait for the final results.

Straight forward prep work for rapid screening dating method - no wet chemistry involved here!

Hello from Southern California!

by Pamela Grothe

Not all trips in the Cobb lab are to exotic places, but we still travel to cool places nationally too, visiting other labs and collaborating with others (as Stacy and Hussein have already blogged about). I should probably introduce myself first. Hi, I’m Pamela Grothe, Kim’s newest PhD student, blogging from Southern California. I started at Georgia Tech last August and am just beginning to wrap up my second semester. A bit about myself, I’m a native Virginian, however, I’m a Coloradan at heart. I moved to Atlanta from Boulder after spending the last four years there, working as a research assistant in a NOAA lab and completing my master’s degree at CU. Everyone tells me I’m crazy for trading Boulder for Atlanta, but hey, it’s ONLY five years, right! Other than science, I love to run and race. I also love to bike and swim, hike and camp, scuba dive and kayak, and whatever else that involves the outdoors – I think that is par for course for anybody working in the earth sciences.

My Research

A ridge of fossil coral rubble  on Christmas Island

I fall on the coral side of the Cobb Lab (despite the photo of me in a caving helmet). For my research, I will be working on a new method of using hundreds of short (5-20yr-long) fossil coral segments (a.k.a. rubble) to reconstruct the El Nino-Southern Oscillation (ENSO) and tropical Pacific climate variability over the last 7,000 years in the central tropical Pacific. To date, paleo-ENSO variability has relied on exceedingly rare, decades-long fossil coral sequences, 16 of which are presented in Kim’s new Science paper spanning the last 7,000 years. However, smaller fossil coral rubble pieces are plentiful on Christmas Island (see photo at right, and which the gang graciously collected samples of last May). The plan is to use these numerous but shorter rubble pieces to produce a more statistically robust paleoclimate reconstruction – it’s all about the numbers! That’s the gist of the project, which I am only just beginning and super excited about!

Southern California

With any type of paleo-reconstruction, in order to put your record in context, you have to know how old your sample is! And that’s why I’m in California. I’m here to date the fossil coral that the group collected all across Christmas Island last May. My new approach of using hundreds of fossil coral rubble presents a unique challenge to me though. As you recall from Stacy’s dating lesson on U/Th dating, it is a quite intensive and time-consuming technique and thus very inefficient for quickly dating hundreds of sample at a time. So I’ve been in touch with collaborators Dr. John Southon and Dr. Guaciara do Santos at University of California Irvine’s Keck Accelerator Mass Spectrometry Lab, working with them on a method to quickly date lots of sample using high throughput radiocarbon dating (up to 60 per day)!

So in a nutshell, that’s who I am, what I’m working on and why I’m in California. Next up will be more details on my actual trip, which also includes a side trip to Chris Charles' lab Scripps Institution of Oceanography in La Jolla to sample fossil corals that Kim collected back in 1998!