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ICESCAPE analyzes chlorophyll in algae: “The most important measurements of the whole cruise”

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try of tiny plastic test tubes full of seawater samplesEditor’s Note: Haley Smith Kingsland is an Earth systems master’s student at Stanford University specializing in science communication. For five weeks she’s in the land of no sunsets participating in ICESCAPE, a NASA-sponsored research cruise to investigate the effects of climate change on the Chukchi and Bering seas. This is her third blog post for Scientific American.

I kneel under a gurgling protein experiment and swing open the mini-fridge. Out thumps a clear plastic bag wrapped around a seawater filter pump. I grapple behind it for the rectangular Styrofoam tray in which twenty-seven tiny plastic test tubes rest, each encapsulating a thin, nickel-sized filter floating in five milliliters of acetone. Twenty-four hours ago, my teammates used tweezers to attach these filters to funnels through which they poured seawater sampled from various ocean depths. Without using their fingers, they carefully folded the filters in half to retain the phytoplankton they trapped, placed them in individual test tubes pre-labeled with black Sharpie ink, and added acetone to pull pigments from the phytoplankton while refrigerated.

Yesterday, these one-celled algae were floating in the surface ocean absorbing sunlight. Phytoplankton are the base of the Arctic food web and fuel shrimp-like copepods, seabirds and whales. Today, I’ll measure the green pigment inside them that aids photosynthesis, chlorophyll-a, as an indicator of phytoplankton concentration at a set of ocean depths. "You’re making the most important measurements of the whole cruise," Rick Reynolds of the Scripps Institution of Oceanography reminds me.

I press the glowing red button on the fluorometer, a machine about half the size of a 1980s television set that quantifies fluorescence, or the amount of red light a sample emits when exposed to blue light. As it warms up and the acetone in the test tubes cools down, I transcribe their labels into my logbook: 304A, 304B, 304C…312A, 312B, 312C. Each number corresponds to a unique ocean depth; each letter to a triplicate, or one of three copies filtered from the same water source but through a different funnel. I pick up the first between my thumb and index finger, gently rotate it 180 degrees over and over, unscrew its ridged white cap and gingerly pour the liquid into the first of 27 disposable glass culture tubes that I’ve already arranged in a blue lattice frame.

One by one, I insert these cylindrical vials, rounded at the bottom and open on top, into a special slot over which I pop aHaley Smith Kingsland running samples black cover attached to a knotted metal cable. Ding. The screen flashes three significant figures. They often jump, especially when the Healy is ice-breaking and the fluorometer is jiggling on plywood. "Eventually you just have to choose a number," says my professor and the ship’s chief scientist Kevin Arrigo. Sometimes we compete for whose eyeballing best matches the chlorophyll reading—translucent acetone is 0-200, semi-green 200-400, green 400-550, and bright green OVER with dashed lines and frantic beeping. I won’t tell you about the extra steps I dread for these saturated samples that require dilution, except that my method involves three mini-Finntips and a pipette for which I’ve mastered a precise squeeze and click.

When I’ve run all triplicates, I squirt each culture tube with three dribbles of hydrochloric acid from a baby dropper. HCl converts the chlorophyll to its degraded form—phaeopigments. One by one, I reinsert each culture tube. The difference between this phaeopigment reading and the higher initial reading in which both phaeopigments and chlorophyll fluoresce is the chlorophyll fluorescence, a number that implies the amount of algae originally living in each water sample.

I stand in front of the fluorometer a few hours each morning, a couple at night, and even more when conducting rapid-fire transects. Four weeks, 111 stations, 2,802 samples, 5,658 readings. I wish I could tell you about the acetone blank, the outliers, the ceiling frames with cableways, and the ice cores that add variation to my routine. The fume hood, where fire-hazardous acetone empties rest before disposal. The Kimwipes with which I massage the culture tubes so my fingerprints don’t affect the initial reading, and the waxy Parafilm I stick over their open tops in order to shake them after acidification. The graphs Kevin generates of the overall chlorophyll distribution at each station, in which my painstaking measurements transform into downward slopes and chlorophyll maximums. Glass clinking, breakout dancing and equally intricate processes unraveling all around me as scientists split shifts. All this to better understand single cells of thousands and thousands of shapes that drift atop the sea for just two to three days before dying.

Images: Samples in the refrigerator, courtesy of Haley Smith Kingsland; Kingsland running samples, courtesy of Luke Trusel





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  1. 1. quincykim 9:46 pm 07/14/2010

    "Today, I’ll measure the green pigment inside them that aids photosynthesis, chlorophyll-a, as an indicator of phytoplankton concentration at a set of ocean depths."

    "The difference between this phaeopigment reading and the higher initial reading in which both phaeopigments and chlorophyll fluoresce is the chlorophyll fluorescence, a number that implies the amount of algae originally living in each water sample."

    I understand that this is a blog done by someone who’s performing these tasks all the time, but as a reader I needed to see the above information early on, so I’d know what all that lab procedure detail was for. I still don’t know if more phytoplankton is better, or if that’s situational by location or season, etc. A couple of sentences up front would serve to rope me in a bit more. I’m glad I read the whole thing, though.

    Link to this

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