The generally lower net primary production in HNLC zones results in lower biological draw-down of atmospheric carbon dioxide and thus these regions are generally considered a net source of carbon dioxide to the atmosphere. HNLC areas are of interest to geoengineers and some in the scientific community who believe fertilizing large patches of these waters with iron could potentially lower dissolved carbon dioxide and offset increased anthropogenic carbon emissions. Analysis of Antarctic ice core data over the last million years shows correlation between high levels of dust and low temperature, indicating that addition of diffuse iron-rich dust to the sea has been a natural amplifier of climate cooling.