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

Online Access: Get full text
doi: 10.1016/j.epsl.2018.12.022
Author(s): Chalk, Thomas B.; Foster, Gavin L.; Wilson, Paul A.
Author Affiliation(s): Primary:
University of Southampton, School of Ocean and Earth Science, National Oceanography Centre Southampton, Southampton, United Kingdom
Woods Hole Oceanographic Institution, United States
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, Vol.510, p.1-11. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. Includes appendix. 51 refs.; illus., incl. sect., sketch map
Summary: 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-[CO2-3] 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 (∼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 δ13C and a consideration of the [CO2-3] 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 in the coldest stages (MIS2 and MIS4) of the last glacial cycle was AABW an important contributor to our deep sites in both North Atlantic basins. Taken together, our carbonate system depth profiles reveal a pattern of changing stratification within the North Atlantic that bears strong similarities to the atmospheric CO2 record, evidencing the important role played by ocean water mass geometry and the deep ocean carbonate system in driving changes in atmospheric CO2 on these timescales.
Year of Publication: 2019
Research Program: IODP Integrated Ocean Drilling Program
ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 24 Surficial Geology, Quaternary Geology; Alkaline earth metals; Antarctic Bottom Water; Atlantic Meridional Overturning Circulation; Atlantic Ocean; B-11/B-10; B/Ca; Benthic taxa; Boron; Calcium; Carbon dioxide; Carbonates; Caribbean Sea; Cenozoic; Colombian Basin; Expedition 303; Expedition 306; Expeditions 303/306; Foraminifera; Glacial-interglacial cycles; IODP Site U1308; IODP Site U1313; Integrated Ocean Drilling Program; Isotope ratios; Isotopes; Leg 162; Leg 165; Metals; Microfossils; Mid-Atlantic Ridge; North Atlantic; North Atlantic Deep Water; Northeast Atlantic; ODP Site 980; ODP Site 999; Ocean Drilling Program; Ocean circulation; PH; Quaternary; Rockall Bank; Stable isotopes; Storage; Stratification; Tracers; Upper Quaternary
Coordinates: N552906 N552906 W0144208 W0144208
N124437 N124437 W0784422 W0784422
N410000 N410000 W0325700 W0325700
N495300 N495300 W0241400 W0241400
Record ID: 2019055640
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands