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Scientists are looking for shells on beaches along the East Coast, from near Washington, D.C. to Orlando, Fla. These are not ordinary shells on today's beaches, but the surf line of the Pliocene, about 3 million years ago. "I wish I could take people that question the significance of sea level rise out in the field with me," says Lamont-Doherty scientist Maureen E. Raymo.

More people than ever are living and cities, a trend that Lamont-Doherty scientist Chris Small is studying via satellite images of nighttime skies lit up by artificial lighting.

By Ana Camila Gonzalez

 

“You can do math on excel?” I ask. I immediately imagine a face-palm response, but Dario, one of my advisors, is nice enough to hide it. I’ve collected tree core samples, I’ve prepared them and cross-dated them. Now what?

Oh, right. The Science.

Science! Photo: N. Pederson

 

I guess I never really understood there could be so much involved in answering a question. When I imagine the scientific method I’ve learned since the sixth grade, I somehow imagine a question that can be answered with a yes or no. If I let go of this apple, will it fall to the ground? Hypothesis: yes, it will. Experiment: yes, it does. Conclusion: yes, it will. To the credit of my high school science teachers, it’s not that they didn’t make it perfectly clear that the why and the how are just as important as the yes or the no. I just couldn’t imagine that you’d have to explain why the apple falls with four different figures: haven’t you seen an apple fall too?

Dario is helping me understand how to analyze the data from the black oak samples I have already been working with for some time now. I know these samples. Or at least I think I know these samples. I’m learning there’s more to know about them than I initially thought.

We’re analyzing the climate response, which proves to be exactly what it sounds like. We have recorded measurements of climate (precipitation records, temperature records) and a proxy for tree growth (our ring width measurements!) and by comparing those we can see how a tree population responds to a range of climactic conditions. Alright. I can do this. I’ve made graphs before.

 

“So we’re going to find correlations,” says Dario.

“Click on an empty cell.” I start to make a scatter plot; I think what we’re going to do is look at the slope of a line of best fit.

“So we’re going to see if the correlation is positive or negative?” I ask.

“Yes, but we also have to see if the correlations are significant.” Isn’t any correlation higher than a zero significant? They’re showing a relationship. 

Dario continues, “Any correlation above a 0.2 or so is significant for the hundred years of ring width and climate that you have for this analysis.” I learn how to use the =correl function to compare the populations to temperature and I have to say I’m disappointed. I thought 0.2 sounded so low, but some of my data is showing a much lower correlation, and the data that is significant only ranges from about really close to 0.2 to 0.38 or so. I wanted to see a 0.5 correlation like I did between tree samples within a species as I was cross-dating. Comparing precipitation to ring width gives me slightly higher correlations, a few in the 0.3 range, but I’m still feeling underwhelmed.

“No, but it’s still significant! It matters!” Dario tells me to make a scatter plot comparing precipitation to ring-width measurements over time at both sites. At first it looks like a ball of yarn, but as I mask the plot out I can see why those 0.3 correlations are significant. I follow each curve, visually skateboarding up and down the peaks and valleys and noticing that I’m going up and down a lot of very similar hills as I do so. What’s most rewarding is looking for years I know are drought years (1966 and 1954 were big droughts) and seeing relatively low measures of precipitation and ring width during those years. I knew while I was cross-dating that those years were important when I saw how small the rings were, but now I can prove it. Like the apple falling, I can’t just say that because I see the rings are small those were dry years. I have to compare it to precipitation records, temperature records, and, dare I say it, the Palmer Drought Severity Index (I have to admit I don’t entirely understand the mechanics behind the index, but I understand that dryness is a composite of precipitation and temperature forcings).

Dario, over multiple days, teaches me a few more nuances of Excel and helps me understand the ARSTAN program and how we use it to make our ring-width measurements more effective as proxies for tree growth. He mentions this would all be easier if I knew how to use R. I make a mental note: learning R is the next step. If I thought that was scary, now I have to put this information on a poster. That real people will see. At a real conference.

Neil shows me a few poster examples, and the message is clear. Show your data instead of describing it in words. That also means I’ll have to explain my data by actually… talking… about it. Gulp. The North East Natural History Conference is next weekend, but I feel like I’m ready. I understand the why and how after analyzing my data. At least I understand it enough to give an answer better than yes or no.

 

__________________

 

Ana Camila Gonzalez is a first-year environmental science and creative writing student at Columbia University at the Tree Ring Laboratory of Lamont-Doherty Earth Observatory. She will be blogging on the process of tree-ring analysis, from field work to scientific presentations.

More coverage of induced-earthquake study in Geology co-authored by Lamont scientists Heather Savage and Geoff Abers.

Scientists have found evidence that wastewater injection induced a record-setting quake in Oklahoma two years ago. How big can a man-made earthquake get, and will we see more of them in the future? Lamont-Doherty scientist Geoff Abers comments.

“There are many things that could be done that are not being done,” said Lamont-Doherty scientist Mark Cane. “I have no doubts that there are at least some technical solutions to these problems.”

Lamont-Doherty researchers Robin Bell and Nick Frearson and education coordinator Margie Turrin discuss their new "IcePod," a tool able to study glacier dynamics from the wing of an airplane.

Ways to save water? "Tear out your lawn," says Lamont-Doherty climate modeler Mark Cane.

A damaging earthquake in central Oklahoma two years ago most likely resulted from the pumping of wastewater from oil production into deep wells, according to a new study coauthored by Lamont-Doherty scientists Heather Savage and Geoff Abers.

By Ana Camila Gonzalez

 

Ever since I’ve started learning to cross-date tree core samples, I’ve learned I have a type. I prefer my tree cores to be black oaks, middle-aged, with some nice big rings to show me. Alright, fine, I can deal with some smaller rings every now and then. As long as they’re some nice marker rings.

Unfortunately, the trees don’t seem to be trying to impress me.

Sensitive black oak rings, showing the 1960s drought (faint bands of wood between the two dots on the right side of this image), from eastern NY State. Image: AC Gonzalez and N. Pederson

I was told on a fifth grade field trip that you could tell the age of a tree by chopping it down and counting from the ring on the outside, which represents the current year, to the inside ring, which represents the year it started to grow. I’m coming to learn at the Tree Ring Laboratory of Lamont-Doherty Earth Observatory that there are a few problems with that statement.

Primarily, you don’t have to chop the tree down. I learned while doing fieldwork that coring a tree does not damage it at all. More importantly however, you can’t always find the exact age of a tree by simply counting the rings backwards. One has to verify the years you assigned to each ring against other samples, and, occasionally, against known climatic or ecological events. Sometimes a ring can be missing, possibly from either a very dry year or insect defoliation that causes a lack of growth on the side of the tree you’re looking at. Sometimes a ring is there, but it’s tiny; so small you need a microscope to see it: a micro ring. And this is where cross dating comes in.

A large, Y-shaped black oak in eastern NY State. Photo: N. Pederson.

 

I sit down to cross date my first batch of samples, black oaks from 2003, with rings I can see without using a microscope. I use the microscope regardless, of course, because sometimes what looks like a ring from far away can actually be a false ring: an “extra” late wood growth caused by an early freeze, early warming, or some disruption to ‘normal’  seasonal weather. The microscope helps me see whether these bands have defined edges or seem to fade, and I’ll know that only the truly defined ones are rings.

I seem to be lucky, however, as none of the Black Oaks seem to have any false rings. I’m actually eager to find some missing rings and micro rings, but I don’t find any of those either; missing rings in oak are so rare that you’ll likely be able to plant your own oak forest and watch it grow to maturity before you find one. This is so easy, I think. I feel like I have it in the bag.

I finish measuring the rings on my samples and labeling them with the years I assigned hypothetically to each ring from my cross dating. Now I’m ready to run the measurements through COFECHA, a program that gives me the correlations between individual samples and finally the correlation between all of the samples. When I first run the program with every sample, I’m told something between 0.5 and 0.6 is the expected correlation for ‘good’ black oaks (in other words, there is a 50 to 60 percent chance that given the ring-width measurements on one sample, you’d be able to predict the measurements on a second sample from the same batch). I get a 0.3 correlation. What could I have possibly done wrong?

I soon find that although Black Oaks don’t usually produce missing rings, micro rings or false rings, it is still a possibility, for reasons I didn’t understand at that time. There is also the possibility of human error resulting from mounting the samples incorrectly, missing pieces of the sample after coring and so on. (Editor’s note: one of the biggest issues dating oaks is jumping from one side of a ray to another while moving down an increment core. Sometimes the rings that are aligned across this division are not!).

———

 

What I was doing up until this point was just writing down the years where I found narrow and wider rings as marker rings and trying to find a pattern with everything I wrote down. It was helpful, but I needed to learn more about cross dating to make a few problem samples correlate with the population.

First, I was told I could take a step back and get my nose off of the microscope. By holding up a problem sample to one with a good correlation, I could try and find where patterns aligned visually, and this was usually more helpful than just trying to find the patterns in a sea of numbers I had written down. Second, I was focusing too much on individual samples and not remembering that multiple cores are often taken from the same tree: before a sample can correlate well with an entire forest it is easier to make sure it correlates against the others from the same tree. Finally, I learned that some trees—the very young, the very old, and the trees that constantly get outcompeted for resources—just don’t conform: the rebels, the grumpy old men, the proud nerds. Very suppressed rings won’t correlate well with a series, and neither will very wide rings that signal a release from competition from neighboring giants.  Sometimes a 0.3 or a 0.4 correlation is the best you can get for a sample, and I had to learn how to know whether to accept that or keep trying further.

That first batch took me a week and a half to finally cross-date. You should’ve seen the look on my face when I saw my first correlation in the 0.5 range.

 

And that was just the black oak.

 

Two, twin black oak – velvet goodness! Photo: N. Pederson.

I decided to continue coming to the Tree Ring Lab over winter break, and at first it was incredibly peaceful. A few days of sanding and stabilizing some pines really put me in the Christmas spirit. And then I met Baldcypress, which made me more of a Grinch.

At first, baldcypress and I were really only going to be a one-time thing. I was only told to measure three or four batches from the 80s as a side project, but after I logged all the measurements the COFECHA results were cringe-worthy. I was told I had to try my hand at cross dating the cypress.

If I thought the black oak population had trouble samples, I reconsidered. While Quercus velutina hardly ever displays missing rings, false rings or micro rings, Taxodium distichum seems to want to flaunt them. My first batch had mostly been false rings, but I also learned what a micro ring actually looked like.

I remember staring at a set of what should have been ten rings for 20 minutes, but only seeing nine. I finally asked my advisor and then watched as Neil marked a band relatively darker than its surroundings a cell wide as a ring. If any ring could be called a marker ring, it was this one. Sometimes finding a micro ring where I knew, from the chronology, that a narrower ring should be, was actually a relief. 1966, a heavy drought year for most of the Northeastern US, quickly (and morbidly) became my favorite year.

I dealt with so many false rings that I felt like I was five and my fingers were all turning green (I’m glad no one ever showed me this; I always felt like a princess). Every time I thought a sample couldn’t have any more missing rings I found more. I started thinking everything was a micro ring.

The black oak took a week and a half. I’ve gotten through three batches of baldcypress, and I’m on my fourth: I started over winter break and it is currently spring break. Of course, I’ve been working on other things as well, including a poster presentation on my black oak samples for the Northeast Natural History Conference, but it feels as if the baldcypress just doesn’t want to leave me alone.

 

Yes, I do have a type. I like real rings, I like big rings and I like rings that conform. In the end, however, I’ve learned more from the “problem children” than the ones that worked out like I wanted them to. I might even admit that the baldcypress has been much more rewarding to work through.

Shhh, don’t tell the black oak.

________

 

Ana Camila Gonzalez is a first-year environmental science and creative writing student at Columbia University at the Tree Ring Laboratory of Lamont-Doherty Earth Observatory. She will be blogging on the process of tree-ring analysis, from field work to scientific presentations.

 

Lamont-Doherty scientists Andrew Juhl and Timothy Creyts explain what may have caused mysterious melt circles on a frozen pond in upstate New York.

A study in Geology by Lamont-Doherty scientists Heather Savage and Geoff Abers links wastewater disposal wells in Oklahoma to a series of earthquakes. In Ohio, Lamont-Doherty scientist John Armbruster made a similar connection between a spate of earthquakes and wastewater injection underground.

Scientists can now quickly assess characteristics of a landslide soon after slopes fail, based on its seismic signature. The technique is discussed in a new study in Science co-authored by Lamont-Doherty scientists Goran Ekstrom and Colin Stark.

Scientists have linked Oklahoma’s biggest recorded earthquake to the disposal of wastewater from oil production, adding to evidence that may lead to greater regulation of hydraulic fracturing for oil and gas. “There’s not a magic bullet,” said Lamont-Doherty scientist Heather Savage, co-author of a study in Geology reporting the findings. “But if we have more monitoring capabilities, we can watch these things, and catch all the precursor events.”

Feature on LDEO scientist Klaus Jacob

Eruptions that ripped apart continents in the Triassic also caused mass extinctions, says a new study co-authored by Lamont-Doherty scientists Paul Olsen and Dennis Kent.

Giant landslides have a seismic fingerprint that allows researchers to estimate their size, duration, and even how far they...

Features study by Colin Stark

Article on research by LDEO scientist Aaron Putnam in Bhutan and China

Scientists can remotely detect landslides with seismometers. The data contains critical information about the source and size of the rock falls.