Mg/Ca ratios of Neogloboquadrina pachyderma (s) and Globigerina bulloides in Irminger Sea sediment trap time series

• Main Authors: Jonkers, Lukas, Jimenez-Amat, Patricia, Mortyn, P Graham, Brummer, Geert-Jan A
• Format: Dataset
• Language: English
• Published: PANGAEA 2013
• Subjects: DATE/TIME; Date/time end; DEPTH; water; Event label; Globigerina bulloides; Magnesium/Calcium ratio; Inductively coupled plasma - mass spectrometry (ICP-MS); IRM_1; IRM_3; IRM_4; Neogloboquadrina pachyderma; North Atlantic; Sample code/label; Trap; sediment; TRAPS; Irminger Sea
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.816232; https://doi.org/10.1594/PANGAEA.816232

iven the importance of high-latitude areas in the ocean-climate system, there is need for a paleothermometer that is reliable at low temperatures. Here we assess the applicability of the Mg/Ca-temperature proxy in colder waters (5-10 °C) by comparing for the first time the seasonal Mg/Ca and d18O cycles of N. pachyderma (s) and G. bulloides using a sediment trap time-series from the northern North Atlantic. While both species show indistinguishable seasonal d18O patterns that clearly track the near surface temperature cycle, their Mg/Ca are very different. G. bulloides Mg/Ca is high (2.0-3.1 mmol/mol), but varies in concert with the seasonal temperature cycle. The Mg/Ca of N. pachyderma (s), on the other hand, is low (1.1-1.5 mmol/mol) and shows only a very weak seasonal cycle. The d18O patterns indicate that both species calcify in the same depth zone. Consequently, depth habitat differences cannot explain the contrasting Mg/Ca patterns. The elevated Mg/Ca in pristine G. bulloides might be due to the presence of high Mg phases that are not preserved in fossil shells. The contrasting absence of a seasonal trend in the Mg/Ca of N. pachyderma (s) confirms other studies where calcification temperatures were less well constrained. The reason for this absence is not fully known, but may include species-specific vital effects. The very different seasonal patterns of both species' Mg/Ca underscore the importance of parameters other than temperature in controlling planktonic foraminiferal Mg/Ca. Our results therefore lend further caution in the interpretation of Mg/Ca-temperature reconstructions from high northern latitudes.