The origins of the glacial-interglacial timescale changes in atmospheric carbon dioxide observed in ice cores spanning the last million years is a decades long debate in the earth and ocean sciences. Reconstructions of nutrient drawdown in the Southern Ocean have figured prominently in most data driven explanations for ocean uptake of carbon dioxide during ice ages. Amongst these reconstructions, diatom-bound nitrogen isotope records of nutrient drawdown in the surface ocean are both abundant and considered robust. Groundtruthing of the diatom nitrogen isotope proxy is ongoing.