Subsurface North Atlantic warming as a trigger of rapid cooling events: evidence from the early Pleistocene (MIS 31–19)

Subsurface water column dynamics in the subpolar North Atlantic were reconstructed in order to improve the understanding of the cause of abrupt ice-rafted detritus (IRD) events during cold periods of the early Pleistocene. We used paired Mg / Ca and δ 18 O measurements of Neogloboquadrina pachyderma...

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Bibliographic Details
Published in:Climate of the Past
Main Authors: I. Hernández-Almeida, F.-J. Sierro, I. Cacho, J.-A. Flores
Format: Article in Journal/Newspaper
Language:English
Published: Copernicus Publications 2015
Subjects:
Environmental pollution
TD172-193.5
Environmental protection
TD169-171.8
Environmental sciences
GE1-350
Ice Shelves
Neogloboquadrina pachyderma
North Atlantic
Planktonic foraminifera
Online Access:https://doi.org/10.5194/cp-11-687-2015
https://doaj.org/article/a291dcf2661b45beb6e10b4fdd50c21b
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Summary:Subsurface water column dynamics in the subpolar North Atlantic were reconstructed in order to improve the understanding of the cause of abrupt ice-rafted detritus (IRD) events during cold periods of the early Pleistocene. We used paired Mg / Ca and δ 18 O measurements of Neogloboquadrina pachyderma (sinistral – sin.), deep-dwelling planktonic foraminifera, to estimate the subsurface temperatures and seawater δ 18 O from a sediment core from Gardar Drift, in the subpolar North Atlantic. Carbon isotopes of benthic and planktonic foraminifera from the same site provide information about the ventilation and water column nutrient gradient. Mg / Ca-based temperatures and seawater δ 18 O suggest increased subsurface temperatures and salinities during ice-rafting, likely due to northward subsurface transport of subtropical waters during periods of weaker Atlantic Meridional Overturning Circulation (AMOC). Planktonic carbon isotopes support this suggestion, showing coincident increased subsurface ventilation during deposition of IRD. Subsurface accumulation of warm waters would have resulted in basal warming and break-up of ice-shelves, leading to massive iceberg discharges in the North Atlantic. The release of heat stored at the subsurface to the atmosphere would have helped to restart the AMOC. This mechanism is in agreement with modelling and proxy studies that observe a subsurface warming in the North Atlantic in response to AMOC slowdown during Marine Isotope Stage (MIS) 3.

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