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Free-drifting icebergs as proliferating dispersion sites of iron
enrichment, organic carbon production and export in
the Southern Ocean

Reports from the field
Written by Alison Kelley

March 02-08 | March 09-15 | March 16-22 | March 23-31 | Early April | Mid-April

Week of 16-22 March 2009

C18a iceberg

On a rare clear day, the immensity of C18A fills the view from the bridge.
This iceberg is 6 kilometers wide by 32 kilometers long!

Mike Lewis

Mike Lewis, our Marine Technician, enjoys a moment of peace while he awaits the CTD rosette's return
from its journey to 500 meters below the sea surface. (Image by Alison Kelley.)

This week's theme is "You asked for it? You got it!"

It's been quite a contrast this week, as we transitioned from equipment testing and surface mapping to full-scale sampling mode. Not only were we able to complete multiple CTD casts, both in the near-field and in the far-field, but we also began two seawater enrichment experiments (SEE) Learn more about our experiments in our 2nd post. This kept all of us in the phytoplankton, trace metal, and microbes science groups hopping at quite a pace. Fog blanketed the waters around C18a for much of the week, and finding the right mix of weather to deploy the ROV or the UAV (more on equipment) proved tricky at best, and at times, simply frustrating. The symmetry between the wind waves, and water that yields safe work conditions for the crew on deck and minimizes potential damage to our sampling equipment at risk is an easier balance to strike for the CTD rosette and the Niskin bottles.

Hai Lin and Ben Twining with first sample

The Iron Men, Hai Lin and Dr. Ben Twining, clutch their prized first sample
from the trace metal Niskin Sampler. Smiles all around! (Image by Vivian Peng.)

Dr. Cole Hexel making preparations

The calm before the storm... Dr. Cole Hexel prepares for the deluge of water he’ll receive from the red-tether ROV. Working with Dr. Tim Shaw and Scott Kindleberger, this group needs very large volumes to capture the miniscule amounts (trace levels) of chemicals they seek. (Image by Vivian Peng.)

Scott Kindleberger working

Scott Kindleberger tends the red tether on the ROV, which pumps the large volume water samples
that the Shaw group needs to quantify trace elements. (Image by Alison Kelley.)

When the Murray Field Team wasn't processing CTD samples – concentrating them for DNA, measuring leucine and ectoenzyme activity, preparing slides for cell counts – we were working with the Phyto Phanatics and the Iron Men, sub-sampling our SEEx samples. We had set up two experiments – one with water we collected near the iceberg, the other with water we collected far from the iceberg – so we sub-sampled every day to check for any effects we might have induced with the various additions of iron, carbon, and combinations of the two.

bottles

The ethereal experimental world we've created for our experiment simulates the quality of light that penetrates
the sea where our target organisms, bacteria and phytoplankton, live. (Image by Diane "PD" Chakos.)

Dr. Cole Hexel preparing sample bottles

Dr. Cole Hexel prepares sample bottles for the various analyses that he, Scott Kindleberger, and Dr. Tim Shaw will conduct. Their research focuses on the source of trace elements in the water near the iceberg. Are these elements pre-existing, recent inputs from the iceberg, or perhaps from some other process? (Image by Alison Kelley.)

Vivian Peng inside the clean bubble

Happy St. Patty's Day! Inside the Clean bubble, Vivian Peng exposes her wee bit 'o' Irish,
while the hurried process of sub-sampling the SEEx moves forward.

Vivian and Alison collect a sample

Let the work begin! Vivian Peng and Alison Kelley collect the first
of many samples yet to come from the CTD. (Image by Alison Murray.)

From a distance, the face of C18a appears static and unchanging, yet each aspect lends a different perspective that hints at its history. Its cracks, fissures, caves, smudges, smears, and channels weave a story of its passage, and the traces of those who may have called it home for a while (such as birds and algae). We had a moment of excitement when she calved one afternoon. Those on deck rushed inside and dogged the doors behind them. It was a poignant reminder that even when the sun is high, the seas are flat, and the winds are a mere breeze upon one's brow that life amidst the ice can change at any moment.

The crew exhaled, assessed conditions, and operations continued. After all, there was work to do.

C18a in the sun

The sun makes a brief appearance to kiss the edge of C18a. (Image by Alison Murray.)