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Images: Lessons from Nature, Models, and the Past

Biogeochemist John Martin promulgated the ?iron hypothesis? in the 1990s, saying that iron in the ocean could stimulate phytoplankton blooms that would help draw carbon dioxide from the air into the ocean and lower global temperatures. (Photo courtesy of Lynn McMasters, Moss Landing Marine Laboratories)

DIGGING DOWN AND BACK IN TIME?Each year?s snowfall is stacked up and preserved atop glaciers, forming layers, almost like annual tree rings, as seen here in the receding Quelccaya Ice Cap in the Peruvian Andes Mountains. The ice traps isotopes, gas bubbles, and particles that scientists analyze for evidence of the Earth?s environment long into the past. (Lonnie G. Thompson, The Ohio State University)

THE IRON-CLIMATE CONNECTION?Climate records extracted from ice at the Vostok station in Antarctica extend back 400,000 years. They consistently link low atmospheric carbon dioxide levels (top) with low air temperatures (middle), and high levels of iron-rich dust (bottom)?and vice versa. That supports the ?iron hypothesis.?
(Figure by J.R. Petit, et al., Nature )

Researchers take water samples on an expedition to explore how phytoplankton blooms occur naturally in certain parts of the ocean.
(Photo courtesy of Stephane Blain of CNRS/universite de la Mediterranee)

A NATURAL BLOOM DOWN UNDER?Phytoplankton blooms recur naturally off tiny Kerguelen Island, between South Africa and Australia in the Southern Ocean. Greens, yellows, and reds indicate increasingly higher levels of chlorophyll in photosynthesizing phytoplankton. The blooms are fueled by iron and other nutrients brought to the surface by currents flowing across a 600-meter-deep shelf. (Map courtesy of Stephane Blain of CNRS/Universite de la Mediterranee )