One of the enduring mysteries of biological oceanography is the existence of regions with abundant nitrogen and phosphorus at the surface that remain only partially used by phytoplankton. In most parts of the ocean, phytoplankton draw these key nutrients to essentially zero and thus nitrogen and phosphorus supply limits growth at the base of the food chain. The eastern equatorial Pacific is oe such zone. It has abundant sunlight to fuel photosynthesis, yet the plankton do not consume the available nitrogen and phosphorus. One hypothesis suggests that the micronutrient Iron might be limiting growth in this region. Iron is dominantly supplied by wind-blown dust, and the equatorial Pacific has a very small dust supply. Our project set out to use a natural climate experiment from the past ice age. The atmosphere was much dustier then, so if the "Iron Hypothesis" held true we would expect to see a sign of higher nitrogen use and higher biological productivity at the last ice age. We used marine sediments that extend into the past to investigate this idea. In work at Brown, we performed geochemical analyses to fingerprint the dust content over time, we determined ages of the sediment layers, and we performed organic biomarker analyses that give an indication of past biological productivity. We were sytmied in our ultimate goal, because our collaborating laboratory was unable to provide foraminiferal-bound nitrogen isotopes that would have fully tested the hypothesis. Nevertheless, we obtained valuable records of past ocean productivity and have also provided the community with our stratigraphic infomation, deposited in an online data repository. Last Modified: 10/24/2022 Submitted by: Timothy D Herbert