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never exhausted in surface waters, and phytoplankton biomass is less than expected. Martin (6, 7) suggested that it is the scarcity of biologically available iron in these high-nutrient, low-chlorophyll (HNLC) regions that makes it impossible for the phytoplankton to use the excess N and P. He also recognized that atmospheric dust from land is an important source of iron for the sea and that HNLC regions receive a relatively small dust flux. Furthermore, he noted that ice core records of atmospheric CO2 and dust concentrations over the past 180,000 years are anticorrelated: when dust was high, CO2 was low. This is consistent with the notion that during the arid glacial periods, dust transport was greater, more iron was available, and the biological pump delivered more CO2 to the deep sea. This “iron hypothe
Chisholm et al. (Fri,) studied this question.