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

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 cy...

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Bibliographic Details
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
Description
Summary: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.

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