Magazine article Oceanus

Specks in the Spectrometer

Magazine article Oceanus

Specks in the Spectrometer

Article excerpt

A symphony is playing in the Plasma Mass Spectometry Facility at Woods Hole Oceanographic Institution (WHOI). Tired but attentive, oceanographers attune their ears to the subtle hiss of inert gases moving through the plumbing, the percussive beat of printers churning out new numbers, and, at front and center, the whine of mass spectrometers measuring streams of atomic ions. After enough time, they can discern shrill from dull, repetitive from intermittent, rapid from slow, and hear patterns in the noise.

For researchers like me, using the Inductively Coupled Plasma Mass Spectrometer, or ICPMS, is a rite of passage. It's an intermediary zone between the gritty realities of field work, where we collect samples that go into the ICPMS, and the rarefied realms of new insights that emerge from the torrent of data coming out of the ICPMS. It's also a fascinating rite of passage for the samples themselves, which undergo a brief (about six minutes) but transformative journey inside.

Let me give you a tour-from the perspectives of both scientists and molecules.

The Great Calcite Belt

A few years ago, I was invited to participate in an expedition aboard the research vessel Roger Revelle to the Southern Ocean, where WHOI marine chemist Phoebe Lam and colleagues were investigating a phenomenon known as the Great Calcite Belt.

It appears in satellite images as a vast milky-white band in the ocean encircling Antarctica. Its color comes from the rich concentrations of the mineral calcite in the waters near the surface.

Scientists hypothesize that these high calcite concentrations are produced by massive blooms of algae spanning the Southern Ocean. These algae are called coccolithophores, each one just a thousandth of an inch in diameter. Under the microscope, they appear as spheres covered in plates of the mineral calcite.

Like all algae, coccolithophores are photosynthetic: They use solar energy to make their own food by transforming carbon dioxide (C02) in seawater into complex organic molecules: amino acids, sugars, etc. When they bloom in the austral spring, coccolithophores create the oceanic equivalent of the Great Plains or the Serengeti, providing sustenance for the greater marine food web.

Coccolithophores become part of the marine food web, and when they are eaten, digested, and expelled, some fraction of the organic material they originally produced decomposes back into C02. But the rest remains intact in particles that sink into the deep sea.

Sinking organic carbon plays a critical role in determining Earth's global climate. C02 is a heat-trapping greenhouse gas. The deeper organic carbon sinks into the ocean, the farther it is from the surface ocean and atmosphere. Even if the carbon eventually is converted back to C02 at a depth of 3,000 feet, it would take much longer for it to rise back to the surface than C02 only 30 feet deep. And if the carbon settles in sediments on the seafloor, it can be sequestered from the atmosphere for millions of years.

Long voyages to the Southern Ocean

Lam's research group at WHOI, along with collaborators in oceanographic institutions in Maine, Bermuda, and the United Kingdom, have wondered about how tiny coccolithphores in regions like the Great Calcite Belt fit into the big picture-the planetary carbon cycle that, in turn, regulates Earth's climate. They posited that the relatively heavy calcite plates from algal detritus may stick to organic carbon, dragging it more quickly and efficiently down into the deep sea.

These Great Calcite Belt scientists aimed to follow the path of organic carbon coming from these unique algal communities. To start, they visited the Southern Ocean during the austral summer (our Northern Hemisphere winter)-the warmest, calmest, and safest time to visit the most turbulent region of the world's oceans.

During ten weeks at sea, we rode through 20-foot swells, skirted around several icebergs, and worked through a few storm systems. …

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