Links between eastern equatorial Pacific stratification and atmospheric CO₂ rise during the last deglaciation

Abstract

It is difficult to untangle the mixed influences of high-and low-latitude climate forcing in the eastern equatorial Pacific (EEP). Here we test the hypothesis that the Southern Ocean drove change in the EEP via subsurface intermediate waters during the last deglaciation. We use the δ 18 O signature of benthic foraminifera to reconstruct water density changes during the last 25 kyr at three intermediate water depths (370 m, 600 m, and 1000 m) in the EEP. Carbonate δ 18 O records a combined signature of temperature and salinity and is therefore more closely related to density than temperature or salinity alone. We find that benthic foraminiferal δ 18 O values decreased first in the subsurface, simultaneously with rising temperatures over Antarctica, and propagated up to the surface within~3 kyr. The early subsurface response initiated a rapid decrease in density stratification over the upper water column as indicated by reduced δ 18 O gradients between surface and intermediate depths. Stratification of the upper water column remained low through the termination, with stratification minima reached during Heinrich Stadial 1 and the Younger Dryas (YD), synchronous with the two-part deglacial rise in atmospheric CO 2 . Centennial-scale shifts toward heavier δ 18 O signatures at 370 and 600 m during the YD indicate short-lived shifts in the Subantarctic Mode Water/Antarctic Intermediate Water boundary to shallower intermediate depths. We suggest that decreased density gradients during the deglaciation accelerated vertical mixing across the EEP, and potentially the entire South Pacific subtropical gyre, which enhanced CO 2 delivery from depth to the surface ocean and atmosphere.

Alternating Influence of Northern Versus Southern‐Sourced Water Masses on the Equatorial Pacific Subthermocline During the Past 240 ka

“…A δ 13 C study on thermocline‐dwelling Neogloboquadrina dutertrei demonstrates that the onset of deglacial δ 13 C minima events in the EEP occur simultaneously with the initiation of Southern Ocean warming (Spero & Lea, ). This is in harmony with a stable isotope study from the EEP showing an increased inflow of SOIW at the onset of the termination (Bova et al, ; Pena et al, , ). The intensified SOIW ventilation expanded further north into the ETNP, where δ 13 C records and ε Nd signatures show comparable values to Southern Ocean signatures within the last deglaciation (Basak et al, ; Leduc et al, ).…”

Deepwater Expansion and Enhanced Remineralization in the Eastern Equatorial Pacific During the Last Glacial Maximum

“…During the formation of AAIW in the Southern Ocean, the high‐Cd w deepwater signature likely becomes entrained in intermediate waters, which are then propagated northward to low latitudes. This link between AAIW and low‐latitude surface waters has been previously observed (Anderson et al, ; Bova et al, ; Spero & Lea, ). Similarly, AAIW was marked by reduced ventilation during the LGM (Burke & Robinson, ; Sikes et al, , ; Skinner et al, ) and may have contributed to the radiocarbon depletions documented for shallow waters in the EEP (Umling & Thunell, ).…”

Deep‐Sea Oxygen Depletion and Ocean Carbon Sequestration During the Last Ice Age

“…Based on the dissimilar patterns between the shallowest core (VM21‐30) and each of the other cores (Figure b), we infer that the boundary between water masses with greater DO concentrations during the LGP and those with lower DO levels was situated between the depths of VM21‐30 and VM19‐27 (617 and 1,373 m, respectively), consistent with the LGP oxygen distribution inferred using other proxies (Galbraith & Jaccard, ; Jaccard et al, ; Jaccard & Galbraith, ). Greater water column density stratification above 1,000 m (Bova et al, ) during the LGP likely influenced the evolving pattern of DO distribution (Sigman et al, ), although other factors may have contributed as well.…”