Anti-cyclonic eddy imprint on calcite geochemistry of several planktonic foraminiferal species in the Mozambique Channel

Abstract

Hydrographic conditions in the Mozambique Channel are dominated by the passing of large anticyclonic eddies, propagating poleward into the upstream Agulhas area. Further south, these eddies have been found to control the shedding of Agulhas rings into the Atlantic ocean, thereby playing a key role in Indo-Atlantic Ocean exchange. The element composition of several planktonic foraminifera species collected from sediment trap samples, was compared to in situ water column data from the Mozambique Channel. Single-chamber trace element composition of these foraminifera reveals a close coupling with hydrographic changes induced by anticyclonic eddies.Obtained Mg/Ca values for the surface dwelling Globigerinoides ruber as well as the thermocline dwelling Neogloboquadrina dutertrei follow temperature changes and reduced temperature stratification during eddy conditions. At greater depth, Globorotalia scitula and Pulleniatina obliquiloculata record stable temperatures and thus respond to hydrographic changes with a deepening in habitat depth. Furthermore, test Mn/Ca values indicate a close relationship between water column oxygenation and Mn incorporation in these planktonic foraminiferal species.

Neodymium isotope constraints on provenance, dispersal, and climate‐driven supply of Zambezi sediments along the Mozambique Margin during the past ∼45,000 years

“…Due to the strong and turbulent eddy‐induced currents, hemipelagic muds deposited along the Mozambique Margin may even partly originate from the volcanic lineament of the Comoros Archipelago and from rivers of NW Madagascar, which drain considerable portions of geologically younger formations. This interpretation is supported by Lagrangian back trajectories of foraminifera deposited along the Mozambique slope, which even have higher sinking rates than clay minerals [ Steinhardt et al ., ; van Sebille et al ., ]. The southward sediment transport is also recorded by radiogenic isotope signatures of the detrital fraction typical for a Mozambique Channel origin all the way down into the Agulhas Current system [ Franzese et al ., ].…”

Profiling planktonic foraminiferal crust formation

“…Regardless of the spatial resolution, profiles measured both with the LA‐Sector Field‐ICP‐MS and that measured with the LA‐Quadrupole‐ICP‐MS show similar thickness of low‐Mg and high‐Mg parts of crust or cortex and lamellar calcite. Previously measured LA‐Sector Field‐ICP‐MS profiles [ Steinhardt et al ., , Figure 4] are as representative as LA‐Quadrupole‐ICP‐MS ablation profiles. Profiles showing concentrations deviates more than twice the standard deviation from the average of the initial data set were regarded outliers and therefore discarded from the data set (28 from the 629).…”

“…The Mg/Ca ratios of single chambers used in this study were previously published [ Steinhardt et al ., ] and were determined by Laser Ablation‐Inductively Coupled Plasma‐Mass Spectrometry (LA‐ICP‐MS) at Utrecht University [ Reichart et al ., ]. The matrix matched in‐house standard showed an average relative standard deviation (SD) for Mg/Ca of 3.7%.…”

“…However, minor and trace elements are known to be distributed heterogeneously within foraminiferal tests [ Eggins et al ., ; Hathorne et al ., ; Allison and Austin , ; Sadekov et al ., ; Kunioka et al ., ; Jonkers et al ., ]. This is mainly caused by physiological (i.e., biomineralization) controls on chamber formation [ Bé , ; Hemleben et al ., ; Fairbanks et al ., ; Erez , ; De Nooijer et al ., ; Steinhardt et al ., ; Vetter et al ., ], although the absolute values may be modified by depth migration during their life cycle. Diurnal rhythms in symbiont activity potentially cause the alternating bands of high‐Mg/Ca and low‐Mg/Ca ratios found in some species [ Bemis et al ., ; Eggins et al ., ; Spero et al ., 2015].…”

“…For this purpose, we selected specimens from three planktonic foraminiferal species with contrasting life cycles, all known to form crusts or a cortex. Neogloboquadrina dutertrei is a mixed layer dweller, Pulleniatina obliquiloculata has a similar albeit somewhat deeper assumed habitat, and Globorotalia scitula is a subsurface to deep dwelling species [e.g., Bé and Hutson , ; Fairbanks et al ., ; Watkins et al ., ; Ortiz et al ., ; Mücke and Oberhänsli , ; Steinhardt et al ., ]. We compare structural differences between lamellar, crust, and cortex calcite using SEM imaging in combination with laser ablation (LA) ICP‐MS depth profiling of shell walls to investigate compositional differences within and between species and to quantify their contribution to the overall calcite composition.…”