A Synthesis of Deglacial Deep‐Sea Radiocarbon Records and Their (In)Consistency With Modern Ocean Ventilation

Abstract

We present a synthesis of 1,361 deep‐sea radiocarbon data spanning the past 40 kyr and computed (for 14C‐dated records) from the same calibration to atmospheric 14C. The most notable feature in our compilation is a long‐term Δ14C decline in deep oceanic basins over the past 25 kyr. The Δ14C decline mirrors the drop in reconstructed atmospheric Δ14C, suggesting that it may reflect a decrease in global 14C inventory rather than a redistribution of 14C among different reservoirs. Motivated by this observation, we explore the extent to which the deep water Δ14C data jointly require changes in basin‐scale ventilation during the last deglaciation, based on the fit of a 16‐box model of modern ocean ventilation to the deep water Δ14C records. We find that the fit residuals can largely be explained by data uncertainties and that the surface water Δ14C values producing the fit are within the bounds provided by contemporaneous values of atmospheric and deep water Δ14C. On the other hand, some of the surface Δ14C values in the northern North Atlantic and the Southern Ocean deviate from the values expected from atmospheric 14CO2 and CO2 concentrations during the Heinrich Stadial 1 and the Bølling‐Allerød. The possibility that deep water Δ14C records reflect some combination of changes in deep circulation and surface water reservoir ages cannot be ruled out and will need to be investigated with a more complete model.

Radiocarbon Evidence for the Contribution of the Southern Indian Ocean to the Evolution of Atmospheric CO2 Over the Last 32,000 Years

“…The transient ΔΔ 14 C/Δδ 13 C‐signal between ~21 and ~17.5 ka coincided with the pattern of deep water rejuvenation observed in the downstream southwest Pacific (Ronge et al, ) and upstream South Atlantic (Skinner et al, ). Some authors, however, suggested that the observed decline in global oceanic Δ 14 C mirrors the atmospheric pattern and is rather a sign of a decreased global 14 C inventory, instead of a redistribution and aging of different carbon inventories (Zhao et al, ). It was shown that many deep water records parallel atmospheric Δ 14 C, with a somewhat higher deep water‐to‐atmosphere offset during the glacial compared to the deglacial and Holocene (Zhao et al, ).…”

“…https://doi.org/10.1029/2019PA003733 coral records from the Atlantic and the Pacific Oceans point to increased aging of deep glacial water masses (below~2,000-m water depth) or to increased deglacial ocean-atmosphere interaction, via the Southern Ocean (Burke & Robinson, 2012;Burke et al, 2015;Cook & Keigwin, 2015;Ronge et al, 2016;Sikes et al, 2016;Sikes et al, 2000;Skinner et al, 2010;Skinner et al, 2015). On the other hand, several other studies fail to record any significant aging of glacial deep waters (e.g., Broecker et al, 2004/Broecker et al, 2008Broecker & Clark, 2010;Lund et al, 2011;Zhao et al, 2018). These discrepancies further stress the importance of research in this field, highlighting the importance of our new South Indian Ocean data.…”

Ventilation of Northern and Southern Sources of Aged Carbon in the Eastern Equatorial Pacific During the Younger Dryas Rise in Atmospheric CO2

“…Occurrences of old glacial deep waters are also observed in the South Atlantic and North Atlantic (Skinner & Shackleton, ; Skinner et al, , ), with moderately aged deep water in the Drake Passage (Burke & Robinson, ; Chen et al, ). Although the magnitude of the 14 C anomaly in the deep ocean is not consistent at all sites, glacial water mass ventilation ages are consistently older at depth in the deep Atlantic, the Southern Ocean, and the deep North Pacific relative to today (e.g., Zhao et al, ), supporting the presence of a deep ocean glacial carbon reservoir responsible for the drawdown of atmospheric CO 2 .…”

Anomalous > 2000‐Year‐Old Surface Ocean Radiocarbon Age as Evidence for Deglacial Geologic Carbon Release

“…However, despite the close similarity in Gulf and Undercurrent benthic foraminifera 14 C, there are large differences in planktic foraminifera 14 C (Figure 3). While Undercurrent planktic foraminifera 14 C ages are slightly older relative to the atmosphere during the deglaciation, they are (for the most part) younger than the benthic foraminifera; observations consistent with essentially the entire catalog of published foraminifera 14 C measurements (Zhao et al, 2018). This contrasts with the Gulf of California planktic foraminifera, which have 14 C ages that are as old or older than the benthics, producing several benthic-planktic 14 C age reversals.…”