Upper ocean variability off NE Greenland (79°N) since the last glacial maximum reconstructed from stable isotopes in planktic foraminifer morphotypes

• Published in: Quaternary Science Reviews
• Main Authors: Spielhagen, Robert F., Mackensen, Andreas
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2021
• Subjects: Greenland; Neogloboquadrina pachyderma; Sea ice
• Online Access: https://oceanrep.geomar.de/id/eprint/53563/; https://oceanrep.geomar.de/id/eprint/53563/1/Spielhagen_Mackensen_QSR_accepted.pdf; https://oceanrep.geomar.de/id/eprint/53563/2/Spielhagen%26Mackensen.pdf; https://doi.org/10.1016/j.quascirev.2021.107070

Highlights • Neogloboquadrina pachyderma morphotypes can have different isotope compositions. • Isotopic offsets between morphotypes depend on environmental background conditions. • Thin-shelled Neogloboquadrina pachyderma are good recorders of near-surface salinity. • A strong freshwater event off NE Greenland at 12.7 ka may be related to deglaciation. Abstract We report on stable oxygen and carbon isotope data obtained on two different morphotypes of polar planktic foraminifers, i.e., fully encrusted and minor encrusted Neogloboquadrina pachyderma, from a sediment core taken on the NE Greenland continental margin. These morphotypes are supposed to live at different water depths of the upper water column in the area which today is strongly stratified, with a low-saline, cold-water layer at the surface. The paired isotopic data sets inform on temporal variations of past water salinity and temperature in the preferred water depth ranges of the investigated morphotypes and allow conclusions on the stratification of the upper water column. The radiocarbon-dated sediment core covers the time interval from 21 to 4 cal-ka, but the early part of the deglacial interval (18.5–12.7 cal-ka) is not represented, probably due to intense erosion by bottom currents. In sediments from the late last glacial maximum, oxygen isotope differences between thin-shelled and thick-shelled N. pachyderma are low and point at a weaker stratification with less freshwater than today near the surface. The carbon isotopes indicate a dense, perennial sea ice cover, very limited bioproduction, and the presence of a subsurface Atlantic Water layer. In the late deglaciation until ∼10.3 cal-ka, the stable isotope values of both analyzed morphotypes are considerably lower, with significantly stronger amplitudes in the record of thin-shelled specimens than later on. The high-amplitude record stems from a laminated sediment sequence whose older part was deposited within just a few decades. The data are evidence of a strong freshwater event in the ...