Dynamic storage of glacial CO2 in the Atlantic Ocean revealed by boron [CO32-] and pH records

• Published in: Earth and Planetary Science Letters
• Main Authors: Chalk, T. B., Foster, G. L., Wilson, P. A.
• Format: Text
• Language: English
• Published: Elsevier Science Bv
• Subjects: envir; geo; Antarctic; Mid-Atlantic Ridge; Antarc*; NADW; North Atlantic Deep Water; North Atlantic
• Online Access: https://doi.org/10.1016/j.epsl.2018.12.022; https://archimer.ifremer.fr/doc/00496/60812/64631.pdf; https://archimer.ifremer.fr/doc/00496/60812/64632.pdf; https://archimer.ifremer.fr/doc/00496/60812/

The origin and carbon content of the deep water mass that fills the North Atlantic Basin, either Antarctic Bottom Water (AABW) or North Atlantic Deep Water (NADW) is suggested to influence the partitioning of CO2 between the ocean and atmosphere on glacial-interglacial timescales. Fluctuations in the strength of Atlantic meridional overturning circulation (AMOC) have also been shown to play a key role in global and regional climate change on timescales from annual to millennial. The North Atlantic is an important and well-studied ocean basin but many proxy records tracing ocean circulation in this region over the last glacial cycle are challenging to interpret. Here we present new B/Ca-[CO32-] and boron isotope-pH data from sites spanning the North Atlantic Ocean from 2200 to 3900 m and covering the last 130 kyr from both sides of the Mid-Atlantic Ridge. These data allow us to explore the potential of the boron-based proxies as tracers of ocean water masses to ultimately identify the changing nature of Atlantic circulation over the last 130 kyr. This possibility arises because the B/Ca and boron isotope proxies are directly and quantitatively linked to the ocean carbonate system acting as semi-conservative tracers in the modern ocean. Yet the utility of this approach has yet to be demonstrated on glacial-interglacial timescales when various processes may alter the state of the deep ocean carbonate system. We demonstrate that the deep (similar to 3400 m) North Atlantic Ocean exhibits considerable variability in terms of its carbonate chemistry through the entirety of the last glacial cycle. Our new data confirm that the last interglacial marine isotope stage (MIS) 5e has a similar deep-water geometry to the Holocene, in terms of the carbonate system. In combination with benthic foraminiferal delta C-13 and a consideration of the [CO32-] of contemporaneous southern sourced water, we infer that AABW influences the eastern abyssal North Atlantic throughout the whole of the last glacial (MIS2 through 4) whereas, only ...