A new study examining the impact of iron released from continental margin sediments has documented a natural limiting switch that may keep these ocean systems from developing a runaway feedback loop that could lead to unchecked hypoxic areas, or persistent 'dead zones.' The findings are particularly important, scientists say, because as the climate warms oxygen minimum zones are expected to expand in coming decades and could affect coastal fisheries as well as the global carbon cycle. But the study suggests that there may be a limit to the expansion of these OMZs....