Abstract
Within the world’s oceans, regionally distinct ecological niches develop due to differences in water temperature, nutrients, food availability, predation and light intensity. This results in differences in the vertical dispersion of planktonic foraminifera on the global scale. Understanding the controls on these modern-day distributions is important when using these organisms for paleoceanographic reconstructions. As such, this study constrains modern depth habitats for the northern equatorial Indian Ocean, for 14 planktonic foraminiferal species (G. ruber, G. elongatus, G. pyramidalis, G. rubescens, T. sacculifer, G. siphonifera, G. glutinata, N. dutertrei, G. bulloides, G. ungulata, P. obliquiloculata, G. menardii, G. hexagonus, G. scitula) using stable isotopic signatures (δ18O and δ13C) and Mg/Ca ratios. We evaluate two aspects of inferred depth habitats: (1) the significance of the apparent calcification depth (ACD) calculation method/equations and (2) regional species-specific ACD controls. Through a comparison with five global, (sub)tropical studies we found the choice of applied equation and δ18Osw significant and an important consideration when comparing with the published literature. The ACDs of the surface mixed layer and thermocline species show a tight clustering between 73–109 m water depth coinciding with the deep chlorophyll maximum (DCM). Furthermore, the ACDs for the sub-thermocline species are positioned relative to secondary peaks in the local primary production. We surmise that food source plays a key role in the relative living depths for the majority of the investigated planktonic foraminifera within this oligotrophic environment of the Maldives and elsewhere in the tropical oceans.
Highlights
Planktonic foraminifera are protozoans widely used in paleoceanographic and paleoclimatic studies to interpret and track past marine conditions [1]
The sedimentary record is an accumulation of foraminiferal tests, which can be from different seasons and represent different stages of their ontogeny as foraminifera migrate through the water column throughout their life cycles recording different geochemical signatures [1]
The δ13C values of three surface dwelling species (G. glutinata (w/b), G. bulloides and G. rubescens (p)) are depleted, whereas symbiont enrichment is evident in the five symbiont-bearing species (G. ruber (w), G. pyramidalis, Fig 6
Summary
Planktonic foraminifera are protozoans widely used in paleoceanographic and paleoclimatic studies to interpret and track past marine conditions [1]. Accurately constraining regional estimates is important as this bears significance when selecting suitable species for paleoceanographic reconstructions and for interpreting the oceans past vertical thermal structure [4,5,6,7,8,9]. There are various direct (e.g. concentration profiles calculated from multinet plankton tows, opening-closing nets and sediment traps) and indirect (e.g. test/shell geochemical signatures) methods which can be used to denote foraminifera ALDs and ACDs, respectively. The species-specific size ranges selected for measurement are, important to take into consideration when conducting such geochemical analyses
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
