Deep North Atlantic Last Glacial Maximum Salinity Reconstruction

Abstract:

We reconstruct deep water mass salinities and distributions in the western North Atlantic during the Last Glacial Maximum (LGM, 19-26 ka), a period when atmospheric CO₂ was significantly lower than it is today. A reversal in the LGM Atlantic meridional bottom water salinity gradient has been hypothesized for several LGM water mass reconstructions. Such a reversal has the potential to influence climate, ocean circulation, and atmospheric CO₂ by increasing the thermal energy and carbon storage capacity of the deep ocean.

To test this hypothesis, we reconstructed LGM bottom water salinity based on sedimentary pore water chloride profiles in a north-south transect of piston cores collected from the deep western North Atlantic. We used two methods to determine porewater chloride: one based on density and the other on AgNO₃ titration. The density-based method yielded up to four times higher precision paleosalinities than the titration-based method. LGM bottom water salinity in the deep western North Atlantic determined from the density-based method is 3.07 – 3.65 ± 0.05 % higher than modern values. This increase: (i) is consistent with the 3.5 % global average salinity change expected from eustatic sea level rise, (ii) confirms a northward expansion of southern sourced deep water, (iii) is consistent with shoaling of northern sourced deep water, and (iv) supports the argument that the Atlantic’s north-south deep water salinity gradient was reversed during the LGM.