Late Pleistocene glacial–interglacial shell-size–isotope variability in planktonic foraminifera as a function of local hydrography

Abstract

Abstract. So-called "vital effects" are a collective term for a suite of physiologically and metabolically induced variability in oxygen (δ18O) and carbon (δ13C) isotope ratios of planktonic foraminifer shells that hamper precise quantitative reconstruction of past ocean parameters. Correction for potential isotopic offsets from equilibrium or the expected value is paramount, as too is the ability to define a comparable life stage for each species that allows for direct comparison. Past research has focused upon finding a specific size range for individual species in lieu of other identifiable features, thus allowing ocean parameters from a particular constant (i.e. a specific depth or season) to be reconstructed. Single-shell isotope analysis of fossil shells from a mid-latitude North Atlantic Ocean piston core covering Termination III (200 to 250 ka) highlight the advantage of using a dynamic size range, i.e. utilising measurements from multiple narrow sieve size fractions spanning a large range of total body sizes, in studies of palaeoclimate. Using this methodology, we show that isotopic offsets between specimens in successive size fractions of Globorotalia inflata and Globorotalia truncatulinoides are not constant over time, contrary to previous findings. For δ18O in smaller-sized globorotalids (212–250 μm) it is suggested that the offset from other size fractions may reflect a shallower habitat in an early ontogenetic stage. A reduction in the difference between small and large specimens of G. inflata between insolation minima and maxima is interpreted to relate to a prolonged period of reduced water column stratification. For the shallow-dwelling species Globigerina bulloides, no size–isotope difference between size fractions is observed, and the variability in the oxygen isotopic values is shown to correlate well with the seasonal insolation patterns. As such, patterns in oxygen isotope variability of fossil populations may be used to reconstruct past seasonality changes.

Productivity Evolution in the South Brazilian Bight During the Last 40,000 Years

“…The preference for nutrient‐enriched and highly productive environments represents the most important aspect particularly determining the distribution of these nonsymbiont‐bearing species (Oda & Yamasaki, ; Schiebel & Hemleben, ; Souto et al, ). Being primarily herbivorous, they proliferate when nutrients are introduced in the euphotic zone (e.g., upwelling regions), favoring primary production (e.g., phytoplankton blooms) (Metcalfe et al, ; Ortiz et al, ; Schiebel & Hemleben, ). For this reason, both species are considered indicative of upwelling systems (Naidu et al, ; Peeters et al, ; Souto et al, ) and have been widely applied as proxies of marine productivity in paleoceanographic reconstructions (Lessa et al, ; Ortiz et al, ; Portilho‐Ramos et al, ).…”

Oxygen Isotope Variability of Planktonic Foraminifera Provide Clues to Past Upper Ocean Seasonal Variability

“…Between 728‐ and 828‐cm core T90‐9p was sliced into 1‐cm samples at ~4‐cm intervals; this section of T90‐9P (Feldmeijer et al, ; Lototskaya et al, ; Lototskaya & Ganssen, ; Metcalfe et al, ; van Kreveld et al, ) covers the transition from MIS 8 and MIS 7 (Figures and ). The age depth relationship (Table ) is that of Feldmeijer et al (), with the downcore record of G. inflata tuned to the “planktonic foraminifera” depth‐derived δ 18 O stack of Huybers (Huybers, ) to both avoid circular reasoning and preclude the evaluation of orbital parameters (Huybers, ; Huybers & Wunsch, ).…”

“…Raw single‐specimen oxygen isotope values. (a) Age versus oxygen isotope (δ 18 O) values of Globorotalia inflata (Feldmeijer et al, ; Metcalfe et al, ) with the record selected as a tuning target, the planktonic stack of Huybers (), plotted alongside. (b) Marine isotope stages (MIS) of the core interval analyzed for single specimens of (c) G. bulloides (Metcalfe et al, ) and (d) N. pachyderma (this paper).…”

“…Also shown is the relative monthly insolation at 45°N during the corresponding time period; note that the rise in insolation is not immediately mirrored in the water column (a and b). Insert, map of North Atlantic with location of core T90‐9P indicated (Metcalfe et al, ). Arrows represent the location and direction of surface water masses, and the color represents the relative temperature from warm (red) to cold (blue).…”

Moving beyond the age-depth model paradigm in deep sea palaeoclimate archives: dual radiocarbon and stable isotope analysis on single foraminifera

“…Additional whole tests were analysed using a GasBench II preparation device coupled to a continuous flow Thermo Delta+ mass spectrometer at the Department of Earth Sciences, Vrije Universiteit Amsterdam. For these measurements, the external precision (1σ) of international standards was better than 0.12 ‰ for both δ 18 O and δ 13 C Metcalfe et al, 2015). All IRMS measurements are reported in per mil (‰) against the Vienna Peedee Belemnite (V-PDB) scale.…”