Greenland Climate of the Past & Present

Last summer, several IGERT fellows had the serendipitous and rare opportunity to witness a warming climate’s effect on Greenland first-hand. Julia Bradley-Cook was stationed in Kangerlussuaq collecting data on carbon cycling in soil when the bridge over the Watson river collapsed from anomalously high flows of meltwater (see http://dartmouthigert.wordpress.com/2012/07/11/glacial-melt-threatens-town-water-supply and http://dartmouthigert.wordpress.com/2012/07/11/update-the-river-powers-on). Days later, the 3rd cohort of Dartmouth IGERT students flew up to Summit Camp, Greenland’s highest point, and observed features of the ice sheet-wide surface melt. Fellow Kaitlin Keegan, Thayer Professor Mary Albert, and their collaborators study the frequency of such melt events; their work at the North Greenland Eemian Ice Drilling (NEEM) sight has suggested that such an event last transpired in 1889 and, therefore, is unprecedented in the satellite record. (See http://dartmouthigert.wordpress.com/2012/07/21/new-summit-melt-layer).

A new Nature publication on Greenland climate authored by the NEEM community, which includes Albert and Keegan, prompted an entry on the scientific blog site RealClimate.org. RealClimate was started and is maintained by “working climate scientists” who “aim to provide a quick response to developing stories and provide the context sometimes missing in mainstream commentary.” Check out the discussion on Greenland’s 2012 summer conditions, how they compare to those 125,000 years ago, and what we can learn about past temperatures and sea level rise from an ice core! I was particularly excited about the conclusion of the entry since author Dr. Steig mentioned the significance of a new ice core from West Antarctica. I just returned from a field season on Roosevelt Island assisting with the drilling of this core, which will help scientists understand the sensitivity of the Ross Ice Shelf and, thus, of the West Antarctic ice sheet to changes in climate. http://www.realclimate.org/index.php/archives/2013/01/the-greenland-melt/

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The Promised Phosphorus Blog

I’ve been promising a blog post about phosphorus in Taylor Valley, so here goes.  At this point in the season, we’re a little frantic processing samples, packaging up boxes of soil and rock to send home, returning all of our gear, and cleaning the lab.  But I’ll find the time to write this post, since it’s something I’m invested in.

So why are we interested in phosphorus in the first place?  Phosphorus is a limiting nutrient in many ecosystems, but the Taylor Valley lake basins are some of the most phosphorus deficient systems in the world.  Understanding how phosphorus enters the Taylor Valley system and becomes available to organisms is thus critical to understanding the controls on life in this extreme environment.

In addition to general phosphorus deficiency throughout most of the valley, there is also an interesting and well-established phosphorus gradient up the valley.  Down in the lowest-elevation Fryxell basin, there is a relative abundance of phosphorus compared to the higher elevation Hoare and Bonney basins.  Why does this gradient exist?  Multiple ideas have been proposed: perhaps it is due differences in climate, age of the soils, or till type from which the soil has formed.  This last explanation – that the composition of the till determines the amount of phosphorus available – is one that seems to fit best with the data.  And it is this claim that I hope to address with the samples that I have collected this season.

Even within the Fryxell basin there are different colors of till. How do different till types impact the soil geochemistry?

If the till type results in such a strong phosphorus gradient, then the till in the Fryxell basin must be significantly different from the till covering the rest of the valley.  Indeed, the Ross Sea till that covers the Fryxell basin contains kenyte, an unusual phosphorus-rich volcanic rock originating from Mt. Erebus, the volcano that dominates Ross Island.  The Taylor till found throughout the rest of the valley, on the other hand, contains no kenyte. Is Mt. Erebus responsible for providing the Fryxell basin with its higher levels of phosphorus?  Using the rock and soil samples I’ve collected, we hope to use isotopic signatures to differentiate apatite (the most common phosphorus-bearing mineral) that stems directly from Mt. Erebus from apatite stemming from other rock types.

A kenyte boulder found near Lake Fryxell. The boulder likely comes from Mt. Erebus, on Ross Island.

We are not only interested in how apatite gets into the Taylor Valley system; we are also curious about its fate.  How do microorganisms interact with the apatite in the soil?  Are microorganisms responsible for releasing phosphorus from the apatite?  As a start, we’ve set up a little experiment (involving soil sausages) that will stay out in the field until next season.  The sausages are tubes full of soil, apatite grains, and glass beads (used as controls), cleverly held together with red clips.  The semi-permeable tubing we used will allow the environment to interact with what’s inside the sausages while keeping everything nicely contained for retrieval next year.  When we collect the apatite grains next year, we hope to be able to see evidence of how the grains have been altered by microorganisms.  We’ll look for organisms on the grains themselves, as well as signs that the microbes have been eating away at the mineral.

Ross and I put together the apatite soil incubations.

On Friday, Eric and I went out to F6 camp to bury the sausages.  We picked a location near Von Guerard stream – a wet soil but a stable location.  We buried the soil incubations five centimeters below the surface, marking them with tags and recording the exact location.  Next year we’ll return to dig them up.  I hope both that they are intact, and that they give us more insight into the ways in which phosphorus moves throughout the Taylor Valley system.

An apatite soil incubation buried in the ground.

Next step?  Packaging up my samples to be shipped back to Dartmouth, and figuring out how to process them once we’re all back in Hanover.

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Nematodes, Rotifers, and Tardigrades (Oh My!)

While I’ve been spending the past few days rinsing dishes, measuring soil pH, and rinsing more dishes, my lab mates have been glued to the microscopes, counting nematodes, rotifers, and tardigrades (oh my!).  As I mentioned in my previous post, the Soils Team of the Dry Valleys LTER is interested in the invertebrate diversity and productivity in varying soil types.  Collecting these data requires a lot of counting; my lab mates may be going slightly crazy after spending so many days staring through a microscope, clicking their counters.

Martijn and Ashley have been tied to the microscopes all day!

For me, since I don’t actually have to count the samples, it has been exciting to get to know the different characters of the Dry Valleys soils.  The nematodes are the major players: Scottnema lindsayae, Eudorylaimus, and Plectus.  Of the three nematode genera, Scottnema (named after explorer Robert F. Scott) is the most abundant in typical Dry Valley soil.  Scottnema, unlike the other two genera, is endemic to the Dry Valleys, meaning that it is found nowhere else in the world.

Scottnema is the most abundant land animal on the Antarctic continent!

In more moist soils, along stream banks and next to ponds, Eudorylaimus and Plectus are abundant.  Rotifers and tardigrades are not as plentiful as the nematodes, and are quite exciting to spot in the scope.  Tardigrades, affectionately known as water bears, are especially cute.

So what are my lab mates looking for through the microscope?  Nematodes are identified by size, the morphology of the mouth region and tail, and the general shape of the body.  For instance, Eudorylaimus is much bigger than the other two genera, while Scottnema is distinguished by a crown-like mouth region.

Eudorylaimus is much larger than Scottnema.

After they identify the genera, the next step is to identify the type of individual: live or dead, male or female, juvenile or adult.  In a split second, a click is made and the tally of individuals goes up.  (As I type this, I’m listening to a pleasant background clicking noise of Sabrina counting a sample.)  So far the record is 1423 nematodes in one sample – and that’s just from 100 grams of soil!

Ashley uses a counter to keep track of the genus, gender, and life stage of each individual.

These little critters, so abundant in a seemingly lifeless environment, are incredibly tough.  They have to be, to survive some of the harshest conditions on the planet.  Not only do these microscopic organisms have to survive extreme cold, but they also have to contend with extreme aridity.  Indeed, some of the most closely related species to the Dry Valleys nematodes are found in hot deserts, where they use the same coping strategy to deal with the lack of water: anhydrobiosis.  In an anhydrobiotic state, a nematode’s entire metabolic system has shut down; the organism can wait indefinitely for more favorable environmental conditions.  Without such an effective strategy for dealing with the lack of liquid water, these organisms would be unable to survive in the Dry Valleys.

As the Wormherders continue to count the samples, I’ll be sure to post pictures of any interesting finds!  Many thanks to Ashley Shaw and Dr. Martijn Vandegehuchte (both from Colorado State University) for sharing their nematode knowledge and helping me to take the photos!

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