Reconstruction of hydrographic changes in the southern Norwegian Sea during the past 135 kyr and the impact of different foraminiferal Mg/Ca cleaning protocols
Journal
Geochemistry, Geophysics, Geosystems
Journal Volume
17
Journal Issue
8
Pages
3420-3436
Date Issued
2016
Author(s)
Abstract
The shallow subsurface hydrography in the southern Norwegian Sea during the past 135,000 years was investigated using parallel measurements of Mg/Ca and δ18O in shells of the planktic foraminiferal species Neogloboquadrina pachyderma. Two cleaning methods were applied prior to Mg/Ca analysis, “Mg cleaning” and “full cleaning” methods. Different results were obtained, which are most likely due to a more efficient removal of Mn-contaminant coatings of the shells, when the “full cleaning” procedure was applied. We further combined Mg/Ca and B/Ca from the “full cleaning” method with δ18O values to constrain the calcification temperature and seawater-δ18O (δ18Osw) in the past. During Heinrich Stadial (HS)1 (∼18.5–15 ka) N. pachyderma constituted >80% of the planktic foraminiferal population, δ18Osw decreased by ∼1.5‰, and shallow subsurface temperature increased by ∼1.5–3°C, suggesting strong stratification in the upper water column and a possible subsurface inflow of Atlantic water below a well-developed halocline during the calcification seasons of N. pachyderma. Similar decreases in δ18Osw are also recorded for other Heinrich stadials (HS2, 3, 4, 6, and 11). Our temperature estimates confirm previous observations of the delay of the last interglacial “Eemian” warm peak in the eastern Nordic Seas compared to the North Atlantic, and a late warming coinciding with the summer insolation minimum at 60°N. In addition, relatively high values of δ18Osw during the early Eemian suggest a shallow subsurface inflow of Atlantic water below a thin layer of Arctic surface water. © 2016. American Geophysical Union. All Rights Reserved.
Subjects
Mg/Ca; N. pachyderma; the last glacial; the last interglacial; the Nordic Seas
Other Subjects
Biomineralization; Bone; Hydrographic surveys; Mooring; Stripping (removal); Surface waters; Calcification temperature; Cleaning protocols; Hydrographic changes; Last glacial; Last interglacial; N. pachyderma; Nordic seas; Strong stratification; Decontamination; calcification; calcium; Eemian; environmental change; hydrographic survey; interglacial; Last Glacial; magnesium; paleoceanography; paleotemperature; planktonic foraminifera; reconstruction; stratification; water column; Arctic Ocean; Atlantic Ocean; Atlantic Ocean (North); Norwegian Sea; Neogloboquadrina pachyderma
Type
journal article