Diatom-bound N isotope records over the last two glacial cycles in sediment core PS75/072-4

These data indicate tight coupling between the degree of nitrate consumption and Antarctic climate across the last two glacial cycles, with d15Ndb (and thus the degree of nitrate consumption) increasing at each major Antarctic cooling event.

Coupled with evidence from opal- and barium-based proxies for reduced export production during ice ages, the d15Ndb increases point to ice age reductions in the supply of deep ocean-sourced nitrate to the AZ surface. The two diatom assemblages and species abundance data indicate that the d15Ndb changes are not the result of changing species composition. The pennate and centric assemblage d15Ndb records indicate similar changes but with a significant decline in their difference during peak ice ages.