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Abstract. Oxygen-depleted regions of the global ocean are rapidly expanding, withimportant implications for global biogeochemical cycles. However, ourability to make projections about the future of oxygen in the ocean islimited by a lack of empirical data with which to test and constrain thebehavior of global climatic and oceanographic models. We usedepth-stratified plankton tows to demonstrate that some species of plankticforaminifera are adapted to life in the heart of the pelagic oxygen minimumzone (OMZ). In particular, we identify two species, Globorotaloides hexagonus and Hastigerina parapelagica, living within theeastern tropical North Pacific OMZ. The tests of the former are preserved inmarine sediments and could be used to trace the extent and intensity oflow-oxygen pelagic habitats in the fossil record. Additional morphometricanalyses of G. hexagonus show that tests found in the lowest oxygen environments arelarger, more porous, less dense, and have more chambers in the final whorl.The association of this species with the OMZ and the apparent plasticity ofits test in response to ambient oxygenation invites the use of G. hexagonus tests insediment cores as potential proxies for both the presence and intensity ofoverlying OMZs.