Encrustation and trace element composition of <i>Neogloboquadrina dutertrei</i> assessed from single chamber analyses – implications for paleotemperature estimates

Abstract

Abstract. Crust formation is a common phenomenon in planktonic foraminifera. Because of their different formation mechanism and hence composition, crusts affect the overall test composition and therefore complicate the use of crustbearing foraminifera in paleoceanography. Such species are often used to estimate subsurface paleotemperatures, and although the influence of encrustation on the trace element/Ca ratio is recognised, it has not been systematically explored between and within tests. Here we use laser ablation ICP-MS to assess the variability in trace element composition of the crust of Neogloboquadrina dutertrei within individual chambers, as well as the effect of compositional heterogeneity of the crust on whole test chemistry. Compositionally, the outer crust differs from inner layer by lower Mg/Ca and Mn/Ca, but is indistinguishable in Sr/Ca. Crust thickness decreases towards the younger chambers, and it may be entirely absent from the last chamber. In contrast to Mn/Ca and Sr/Ca, crustal Mg/Ca ratios show a tendency towards higher values on the younger chambers. These patterns in crust thickness and in crust Mg/Ca indicate that temperature is not the dominant factor controlling crust composition. Temperature estimates based on N. dutertrei, and presumably other crust-forming species too, are therefore biased towards too low values. Through comparison of modern and glacial tests, we show that this bias is not constant and that changes in crust thickness and/or in Mg/Ca values can spuriously suggest temperature changes.

Environmental controls on the <i>Emiliania huxleyi</i> calcite mass

“…Coccolith calcite plates of coccolithophores are formed in the upper photic zone and are eventually exported to the sea floor via macroaggregates and fecal pellets (Honjo, 1975;Young, 1994: Fischer andKarakas, 2009). Such particles contain high amounts of coccoliths and can reach sinking rates of up to several hundred meters per day (Ploug et al, 2008), allowing comparison between the coccoliths retrieved in the surface sediments and the properties of the surface waters just above them.…”

“…The sedimentary data that we generated is then directly comparable with preindustrial surface ocean physicochemical properties. For example, samples with available 14 C and/or 210 Pb data (i.e., 1413-2, 1414-2, 1415-1, 1417-1, CD154-01-01K, CD154-02-03K, CD154-03-05K, CD154-05-07K, CD154-10-10K, and MD02-2594) are proven to have modern-to late-Holocene ages (Martinez-Mendez et al, 2010;Jonkers et al, 2012;Mollenhauer et al, 2004). In addition, the basic evidence that the remaining samples from the wider South Atlantic region are at least of Holocene age (and not older) comes from nearby 14 C-and/or 210 Pb-dated core tops (Mollenhauer, 2002;Mollenhauer et al, 2003Mollenhauer et al, , 2004Mollenhauer et al, , 2006Mollenhauer et al, , 2007, and from a number of investigated sediment cores from the entire study region, all yielding Holocene ages at the top (e.g., various articles in .…”

“…In order to investigate the controlling factors of coccolithophore calcification, research has centered on their variability in mass and size (Beaufort and Heussner, 1999;Young and Ziveri, 2000) in different types of experimental and field observational settings. Several environmental M. T. Horigome et al: Environmental controls on the Emiliania huxleyi calcite mass parameters have been examined (Broerse et al, 2000;Beaufort et al, 2008;Henderiks et al, 2012), such as light (Paasche, 2001), nutrient availability Båtvik et al, 1997;Paasche, 1998;Müller et al, 2012), calcification temperature (Bollmann et al, 2002;Ziveri et al, 2004;Boeckel et al, 2006), salinity (Bollmann and Herrle, 2007;Bollmann et al, 2009;Fielding et al, 2009), and carbonate chemistry (Iglesias-Rodriguez et al, 2008;Langer et al, 2009;de Bodt et al, 2010;Müller et al, 2010;Barcelos e Ramos et al, 2010;Beaufort et al, 2011;Bach et al, 2012).…”

“…However, complementary evidence points to a nonuniform response of calcification to high CO 2 (cf. Langer et al, 2006;Iglesias-Rodriguez et al, 2008;Riebesell et al, 2008;Doney et al, 2009), casting doubts on the notion that [CO 2− 3 ] is the prime (and sole) controlling factor of (bio)calcification. In order to advance our understanding of the role played by different physicochemical properties of seawater on coccolithophore calcification, we examined a widely distributed suite of surface sediment samples taken along oceanic transects characterized by steep surface ocean environmental gradients, such as the South Atlantic and southwestern Indian oceans, the Agulhas System, and the subantarctic sector of the Southern Ocean.…”

“…Hence, the new surface sediment data set presented here has the potential to elucidate the influence of multiple environmental parameters at the ocean surface (temperature,salinity,nutrients,pH,, and pCO 2 ) on the coccolith (Langer et al, 2006;Iglesias-Rodriguez et al, 2008;Riebesell et al, 2008;Bach et al, 2012;Müller et al, 2012). Although surface sediments may constrain variations in the individual environmental parameters less precisely than culture studies they allow evaluating the combined effect of a full suite of environmental property gradients on the (E. huxleyi) coccolith mass variations.…”