CO2 storage and release in the deep Southern Ocean on millennial to centennial timescales

Abstract

The cause of atmospheric CO 2 change during the recent ice ages remains a first order question in climate science. Most mechanisms have invoked carbon exchange with the deep ocean, due to its large size and relatively rapid exchange time with the atmosphere 1 . The Southern Ocean is thought to play a key role in this exchange, as much of the deep ocean is ventilated to the atmosphere in this region 2 . However reconstructing changes in deep Southern Ocean carbon storage is challenging, so few direct tests of this hypothesis exist. Here we present new deep-sea coral boron isotope data that track the pH -and thus CO 2 chemistry -of the deep Southern Ocean over the last 40,000 years. At sites closest to the Antarctic continental margin, and most influenced by the deep Southern waters that form the ocean's lower overturning cell, we find a close relationship between ocean pH and atmospheric CO 2 : during intervals of low CO 2 ocean pH is low, reflecting enhanced ocean carbon storage; during intervals of rising CO 2 ocean pH rises, reflecting loss of carbon from the ocean to the atmosphere. Correspondingly, at shallower sites we find rapid (millennial to centennial-scale) pH decreases during abrupt CO 2 rise, reflecting the rapid transfer of carbon from the deep to the upper

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

“…Therefore, we argue that upwelling of radiocarbon depleted, low δ 13 C deep waters is a likely driver of upper South Indian Ocean 14 C and 13 C during the deglacial transition. This interpretation is in line with δ 11 B reconstructions from coral dredges in the Drake Passage (Rae et al, ) that highlight a drop in UCDW pH, interrupting the long‐term pH increase —indicative for a simultaneous injection of old and CO 2 ‐rich waters— during the same time interval (Figure ). Steepening pycnoclines also indicate the onset of stratification breakdown in the transient model simulation (Figure ).…”

“…( a) Splice of atmospheric CO 2 records (red; Köhler et al, ) and atmospheric Δ 14 C values (black; SHCal13; Reimer et al, ). (b) Deep‐sea coral (dredges; Drake Passage) δ 11 B‐data (Rae et al, ). (c) Intermediate water ΔΔ 14 C off Oman (Bryan et al, ).…”

Rapid Loss of CO2 From the South Pacific Ocean During the Last Glacial Termination

“…Support for a Southern Ocean link is provided by concurrent changes in Southern Ocean pH (Figure ; Rae et al, ). In the absence of competing effects, an increase in CO 2 content of seawater results in a decrease in pH.…”

“…In the absence of competing effects, an increase in CO 2 content of seawater results in a decrease in pH. The existence of a strong horizontal pH gradient in the Drake Passage during the LGM suggests relative carbon enrichment of deeper Pacific water, while the breakdown of that gradient during deglaciation suggests ventilation—a transfer of carbon from the deep ocean to the upper ocean (Rae et al, ). The deglacial rise in pH of the Southern Ocean “lower cell” is matched by the [CO 3 2− ] and δ 13 C rise at South Pacific site 125 (Figure ), pointing to deglacial ventilation of the South Pacific via the Southern Ocean.…”

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

“…Mean Gulf circulation is: in at depth (dashed arrows) and out at the surface (solid arrows) (Lavín & Marinone, 2003). Hence a widespread interpretation of these anomalously old 14 C ages/low Δ 14 C values is that they originate from the deglacial release of carbon sequestered in the deep sea during the last glaciation (Burke & Robinson, 2012;Marchitto et al, 2007;Rae et al, 2018), rather than from addition of geologic carbon. Diamonds indicate the location of California Undercurrent (red) and Gulf of California (white) site LPAZ-21P.…”