Vertical distribution of planktic foraminifera through an oxygen minimum zone: how assemblages and test morphology reflect oxygen concentrations

Abstract

Abstract. Oxygen-depleted regions of the global ocean are rapidly expanding, with important implications for global biogeochemical cycles. However, our ability to make projections about the future of oxygen in the ocean is limited by a lack of empirical data with which to test and constrain the behavior of global climatic and oceanographic models. We use depth-stratified plankton tows to demonstrate that some species of planktic foraminifera are adapted to life in the heart of the pelagic oxygen minimum zone (OMZ). In particular, we identify two species, Globorotaloides hexagonus and Hastigerina parapelagica, living within the eastern tropical North Pacific OMZ. The tests of the former are preserved in marine sediments and could be used to trace the extent and intensity of low-oxygen pelagic habitats in the fossil record. Additional morphometric analyses of G. hexagonus show that tests found in the lowest oxygen environments are larger, more porous, less dense, and have more chambers in the final whorl. The association of this species with the OMZ and the apparent plasticity of its test in response to ambient oxygenation invites the use of G. hexagonus tests in sediment cores as potential proxies for both the presence and intensity of overlying OMZs.

Intermediate water circulation drives distribution of Pliocene Oxygen Minimum Zones

“…Here we present the distribution of Globorotaloides hexagonus , a deep-dwelling, OMZ-associated planktic foraminifera 37 , as a proxy for pelagic OMZs. Globorotaloides hexagonus has been found at a range of depths (~50–1000 m) and productivity regimes and is consistently associated with sub-thermocline low-oxygen waters (Fig.…”

“…Globorotaloides hexagonus has been found at a range of depths (~50–1000 m) and productivity regimes and is consistently associated with sub-thermocline low-oxygen waters (Fig. 2a ) 37 – 40 . By leveraging extensive databases of the distribution of planktic foraminifera in modern and mid-Pliocene oceans 41 – 43 , Species Distribution Models (SDM), and a biogeochemically enabled global climate simulation resembling Pliocene conditions 25 , 44 , 45 , we provide both data-based and model-based constraints on pelagic OMZs in the Pliocene and investigate the dominant drivers of changed OMZ distributions.…”

Late Neogene evolution of modern deep-dwelling plankton

“…The observed evolutionary patterns in planktonic foraminifera and coccolithophores can be explained by the development of environmental conditions favourable to deep living plankton with cooling. For the deep-dwelling planktonic foraminifera, survival requires the availability of food at depth, and with the exception of few species adapted to oxygen minimum zones (Davis et al, 2021), the absence of severe oxygen depletion. In the published literature there is a general tendency for planktonic foraminiferal δ 18 O values to be tightly grouped during times of warm climate, becoming more spread-out during cooling episodes, for instance the transition from midto late Cretaceous (Ando et al, 2010) and early to middle Eocene (John et al, 2013).…”

Contrasting vertical distributions of recent planktic foraminifera off Indonesia during the southeast monsoon: implications for paleoceanographic reconstructions

“…Subsequent assemblage studies have attempted to improve the accuracy of past sea surface temperature (SST) reconstruction via the transfer function approach (e.g., Ortiz and Mix, 1997). Although seawater temperature has a large influence on the global distribution of planktic foraminifera (Kucera, 2007(Kucera, , 2009, other parameters such as salinity, oxygen content, food availability, turbidity, and upwelling intensity can also exert a strong control on the abundance, community structure, and vertical distribution of planktic foraminifera at regional scales (Anderson et al, 1979;Davis et al, 2021;Field, 2004;Lessa et al, 2020;Rebotim et al, 2017;Schiebel and Hemleben, 2017;Tolderlund et al, 1971).…”