Jake Zaragoza

2011 JISAO Summer Research Internship

Reconstructing past tropical climates

Jake Zaragoza
Jake Zaragoza

I am a chemistry undergraduate from Gonzaga University, and I had the awesome opportunity of being a “Husky” for the summer as a Joint Institute for the Study of the Atmosphere and Ocean (JISAO) intern. I was chosen to work under the mentorship of Dr. Julian Sachs and his graduate student Nemiah Ladd at the UW School of Oceanography. Where do Dr. Sachs’ interests lie? He is interested in reconstructing the past climate of the tropics and particularly in monitoring the past shifts of theintertropical convergence zone (ITCZ). But how does one monitor past climate? A relatively new method is to infer past rainfall variations by utilizing deuterium to hydrogen ratios (D/H) of lipid biomarkers, which just happen to reflect the D/H of their source water.

Analyzing D/H of lipid biomarkers is the easy part, most of the time, it is the preparative work that proves to be the most time consuming and difficult. This is where I came in. I basically spent my summer contributing to the big picture paleoclimate reconstructions by helping to purify one compound of interest, taraxerol, from another compound, β-sitosterol. Taraxerol is produced by many plants, but on the island of Kosrae, FSM, it can be traced to the Rhizophera mangrove tree. However, in order to get reliable D/H measurements of taraxerol it must be purified from β-sitosterol, as both compounds just happen to have similar retention times on gas chromatographs.

My project was partitioned into 3 major goals: help develop a reverse phase-high performance liquid chromatography-mass spectrometry (RP-HPLC-MS) purification method to separate taraxerol from β-sitosterol and utilize a gas chromatograph-mass spectrometer (GC-MS) to confirm separation; evaluate the method for recovery and reproducibility using a gas chromatograph-flame ionization detector (GC-FID), and for isotopic fractionation (the unequal isotopic composition of a chromatogram peak) using a gas chromatograph-isotope ratio mass spectrometer (GC-irms); and to apply the method to samples collected along a salinity gradient, checking for effects on taraxerol’s abundance from salinity.

Of course, RP-HPLC-MS, GC-MS, GC-FID, and GC-irms were all relatively new to me, so I got a crash course in instrument use and terminology during the first few weeks, but by the end of the summer I was an “expert” with most of the fancy equipment. In addition to instrument analysis, I also got to experience instrument failures and how work can almost come to a grinding halt when something does break down (i.e. I never used the GC-irms and ended up having to cut that portion of my project due to the instrument being down all summer). Luckily, the Sachs lab manager, Dr. Joshua Gregerson, was quite patient with me and I ended up learning much about the inner workings of the machinery I was using.

Fortunately, instrument failures were not a common occurrence and I was able to finish up the project with the exception of the isotope ratio measurements. In fact, much of the work I did involved quite a bit of “bench chemistry.” After sterol-alcohol samples would run through the HPLC, they would get collected into 6 X 30 ml fractions with either taraxerol or a standard in its own vial. Then I would evaporate the solvents in the 30 ml fractions with a TurboVap before transferring each fraction to its own 2 ml vial. After more evaporation of the 2 ml vials, I would take only the vial with the compound of interest and dissolve it in toluene. Then I would do another transfer, this time to a 200 μl gas chromatograph (GC) insert, followed by more evaporation. The next step was to acetylate the compound of interest by adding 25 μl of pyridine and 25 μl of acetic anhydride and heating to 70 degrees Celsius for half an hour. But, in order to prevent contamination I would need to clean a 50 μl syringe which was a tedious process in itself. After acetylation was complete, I would evaporate once more, add an internal standard, and FINALLY run the sample on the GC-MS or GC-FID. Hence, yes I did get to play with some fancy machinery but there were quite a few in between steps that usually kept me pretty busy all summer.

However, all work and no play would drive anyone insane. In my time away from the lab, I spent a lot of time exploring the UW campus and frequently hitting up the gym or taking a jog along the Burke-Gilman Trail. Also, I explored much of Seattle during the weekends, going to the downtown area a few times, taking a trip to Mt. Rainer one week-end courtesy of JISAO Director Tom Ackerman, exploring different restaurants and café’s with the other interns, and even going to a Sounders game! Yep, my first time to Seattle was definitely a memorable one.

All in all, this summer was an amazing experience. I had the privilege of doing research in a field related to what I have always had interest in, I learned so much about paleoclimate reconstructions and instrument analysis, and I got to experience the city of Seattle. Before this summer I knew I wanted to get a Ph.D. in some field of atmospheric science, and although nothing has changed, my drive to do so has only gotten stronger. I would like to thank JISAO and everyone involved in putting the program together, the entire Sachs lab for being so welcoming and helpful this summer, and Dr. Melamed for fueling my interests.