Carbon storage in the mid‐depth Atlantic during millennial‐scale climate events. (3rd August 2017)

• Record Type: Journal Article
• Authors: Lacerra, Matthew; Lund, David; Yu, Jimin; Schmittner, Andreas
• Is Part Of: Paleoceanography. Volume 32:Number 8(2017)
• Page Start: 780
• Page End: 795
• Publication Date: 2017-08-03
• Subjects: carbon -- millennial‐scale -- Atlantic -- AMOC -- circulation -- boron; Paleoceanography -- Periodicals; 551.46
• DOI: 10.1002/2016PA003081
• Languages: English
• ISSNs: 0883-8305

Abstract

Abstract: Carbon isotope minima were a ubiquitous feature of the mid‐depth Atlantic during Heinrich Stadial 1 (HS1, 14.5–17.5 kyr BP) and the Younger Dryas (YD, 11.5–12.9 kyr BP), yet their cause remains unclear. Recent evidence indicates that North Atlantic processes triggered the δ 13 C anomalies, with weakening of the Atlantic Meridional Overturning Circulation (AMOC) being the most likely driver. Model simulations suggest that slowing of the AMOC increases the residence time of mid‐depth waters in the Atlantic, resulting in the accumulation of respired carbon. Here we assess ΣCO2 variability in the South Atlantic using benthic foraminiferal B/Ca, a proxy for [CO3 2− ]. Using replicated high‐resolution B/Ca records from ~2 km water depth on the Brazil Margin, we show that [CO3 2− ] decreased during HS1 and the YD, synchronous with apparent weakening of the AMOC. The [CO3 2− ] response is smaller than in the tropical North Atlantic during HS1, indicating there was a north–south gradient in the [CO3 2− ] signal similar to that for δ 13 C. The implied variability in ΣCO2 is consistent with model results, suggesting that carbon is temporarily sequestered in the mid‐depth Atlantic during millennial‐scale stadial events. Using a carbon isotope mass balance, we estimate that approximately 75% of the HS1 δ 13 C signal at the Brazil Margin was driven by accumulation of remineralized carbon, highlighting the nonconservative behavior of δ 13 C during the last deglaciation. Key Points: Mid‐depth Atlantic sequesters carbon during stadial events of the last deglaciation Carbon storage varies coherently with proxies of AMOC variability Storage and release of carbon from mid‐depths may modulate atmospheric CO2 Plain Language Summary: The rise in atmospheric CO2 between the last ice age and the current interglacial period is the most recent example of natural CO2 variability driving changes in Earth's climate. It is generally believed that atmospheric CO2 increased due to the release of carbon from the deep ocean. Here we show that the mid‐depth (1.5–2.5 km) Atlantic temporarily stored carbon during the deglaciation while atmospheric CO2 was rising. Our results suggest that the mid‐depth Atlantic was not a persistent source of carbon during the last deglaciation and that other factors must have accounted for rising atmospheric CO2 levels.