Rapid shifts in circulation and biogeochemistry of the Southern Ocean during deglacial carbon cycle events

Abstract

The Southern Ocean plays a crucial role in regulating atmospheric CO2 on centennial to millennial time scales. However, observations of sufficient resolution to explore this have been lacking. Here, we report high-resolution, multiproxy records based on precisely dated deep-sea corals from the Southern Ocean. Paired deep (∆14C and δ11B) and surface (δ15N) proxy data point to enhanced upwelling coupled with reduced efficiency of the biological pump at 14.6 and 11.7 thousand years (ka) ago, which would have facilitated rapid carbon release to the atmosphere. Transient periods of unusually well-ventilated waters in the deep Southern Ocean occurred at 16.3 and 12.8 ka ago. Contemporaneous atmospheric carbon records indicate that these Southern Ocean ventilation events are also important in releasing respired carbon from the deep ocean to the atmosphere. Our results thus highlight two distinct modes of Southern Ocean circulation and biogeochemistry associated with centennial-scale atmospheric CO2 jumps during the last deglaciation.

Productivity and Dissolved Oxygen Controls on the Southern Ocean Deep‐Sea Benthos During the Antarctic Cold Reversal

“… Chemistry of fossil Southern Ocean cold‐water corals from the last deglacial. (a) Benthic to contemporary atmosphere 14 C age offset (B‐atmosphere) recorded in corals south of Tasmania (Hines et al., 2015) and (b) and (c) Drake Passage corals used in this study (Burke & Robinson, 2012; Chen et al., 2015; Li et al., 2020). For clarity radiocarbon error ellipses are not shown.…”

Radiocarbon as a Dating Tool and Tracer in Paleoceanography

“…Although evidence for marine radiocarbon ventilation pulses coinciding with each of these CO 2 jumps is hard to identify in the bulk of the available marine radiocarbon data (mostly foraminifer‐based; see Figure 13), some tentative evidence for an association between ocean ventilation and centennial atmospheric CO 2 (and atmospheric Δ 14 C) jumps does exist. This is shown in Figure 15d, where rather subtle pulses in radiocarbon ventilation are apparent at ∼12, 15, and 16 ka BP in collected coral‐based data from both the Drake Passage in the Southern Ocean (in particular <1 km water depth) (Burke & Robinson, 2012; Chen et al., 2015; Li et al., 2020), and the Galapagos Plateau (∼600 m water depth) (Chen et al., 2020). These regions are plausibly linked hydrographically by the influence of southern sourced intermediate‐depth mode water.…”

“…(c) Atmospheric δ 13 CO 2 , based on: compiled measurements from a suite of Antarctic ice cores (Schmitt et al., 2012) (light blue filled circles and cubic spline); and based on measurements in Taylor Glacier ice (Bauska et al., 2016) (black filled squares and line). (d) Coral radiocarbon ventilation (B‐Atm) data: from the Drake Passage (filled blue circles are data >1,500 m water depth; orange filled circles are data <1,500 m water depth; solid and dashed red lines show cubic spline through all data, with 95% confidence range; Burke & Robinson, 2012; Chen et al., 2015; Li et al., 2020); from 627 m water depth off Galapagos (black filled circles and line, Chen et al., 2020). (e) Foraminifer‐based B‐Atm data from 1,000 m (filled gray circles and line) and 3,400 m (filled blue circles and line), on the Brazil Margin (Skinner et al., 2021).…”

“…Despite the plausibility of an ocean ventilation role in at least some of the deglacial centennial CO 2 jumps (Bauska et al., 2016, 2021), and the emerging support for this role from some observations (Figure 15; Chen et al., 2015, 2020; Li et al., 2020; Rae et al., 2018), other explanations for these rapid carbon cycle perturbations have also been advanced. It has been proposed for example, that the atmospheric CO 2 pulse at ∼14.8 ka BP may have resulted from northern hemisphere permafrost thawing, possibly as a knock‐on effect of abrupt AMOC intensification and North Atlantic warming (Köhler et al., 2014).…”

“…(Key et al, 2004) (bottom panels). Sections are based on zonally averaged global interpolations, after Skinner et al (2017), incorporating more recent data (Chen et al, 2020;Dai et al, 2021;Gottschalk et al, 2020;Hines et al, 2019;Li et al, 2020;Ronge et al, 2019;Shao et al, 2019;Skinner et al, 2021;…”