Modern and late pleistocene B/Ca ratios of the benthic foraminifer Planulina wuellerstorfidetermined with laser ablation ICP-MS
Journal
Geology
Journal Volume
39
Journal Issue
11
Pages
1039-1042
Date Issued
2011
Author(s)
Abstract
Incorporation of boron into foraminiferal shells is thought to be primarily governed by the carbonate chemistry of the ambient seawater, suggesting that it can be reconstructed from B/Ca ratios. To this end, B/Ca ratios of the benthic foraminifer Planulina wuellerstorfifrom South Atlantic core top samples have been analyzed using laser ablation-inductively coupled plasma-mass spectroscopy (LA-ICP-MS) to provide additional information on intratest trace element heterogeneity. Results show that boron is heterogeneously distributed within and between shells, with content variations of approximately ±43% displayed within a single shell. B/Ca is higher in the youngest chambers, opposite to the observed between-chamber variability of Mg/Ca. This may be explained by ontogenetic changes of physiological processes that increase the pH of the calcifying fluid and thus the borate concentration while decreasing Mg/Ca to promote calcification. Despite this heterogeneity, mean B/Ca ratios are positively correlated with the deepwater calcite saturation state (Δ[CO32-]), in line with previous studies. We apply this empirical relationship to reconstruct Δ[CO32-] for the late Pleistocene to Holocene using samples from a depth transect in the equatorial Atlantic. Reconstructed Δ[CO32-] values confirm previous studies suggesting that CaCO3-oversaturated North Atlantic Deep Water was reduced during glacial periods, whereas CaCO3-undersaturated Antarctic Bottom Water expanded vertically and propagated northwards. In summary, our data demonstrate that bulk B/Ca in P. wuellerstorfireliably reflects variations in Δ[CO32-], despite the strong physiological control of boron incorporation. © 2011 Geological Society of America.
SDGs
Other Subjects
Antarctic Bottom Water; Benthic foraminifera; Content variation; Core-top samples; Deepwater; Foraminiferal shells; Glacial period; Holocenes; In-line; La-ICP-MS; Laser-ablation-ICP-MS; Late Pleistocene; North Atlantic Deep Water; Ontogenetic changes; Physiological control; Physiological process; Saturation state; South Atlantic; Biomineralization; Calcium carbonate; Carbonate minerals; Inductively coupled plasma; Laser ablation; Mass spectrometers; Mass spectrometry; Physiology; Seawater; Boron; ablation; benthic foraminifera; boron; calcification; calcium; concentration (composition); deep water; magnesium; ontogeny; paleoceanography; Pleistocene; Pleistocene-Holocene boundary; saturation; Atlantic Ocean; Atlantic Ocean (North); Foraminifera; Planulina
Type
journal article