Synchronous deglacial thermocline and deep-water ventilation in the eastern equatorial Pacific

Umling, Natalie; Thunell, Robert C.

doi:10.1038/ncomms14203

Cited by 34 publications

(78 citation statements)

References 65 publications

(178 reference statements)

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“…Taken together, the Cd W ‐δ 13 C results of remineralization and mixing suggest both an expansion of deepwater masses to water depths of ~2.7 km along with increased remineralization at midwater depths. These results support the findings of 14 C‐derived records of ventilation, which indicate a reduction of EEP middepth ventilation during the LGM (de la Fuente et al, ; Umling & Thunell, ). Furthermore, this combination of findings provides some support for the conceptual premise that a shoaling of the isopycnal separating the upper and lower branches of SOOC under increased Antarctic sea ice extent would have allowed respired carbon to accumulate and radiocarbon to decay in middepth waters (Burke et al, ; Ferrari et al, ).…”

Section: Discussionsupporting

confidence: 89%

“…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, ).…”

Section: Discussionmentioning

confidence: 99%

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

Umling

Thunell

Bizimis

2018

Paleoceanog and Paleoclimatol

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Published estimates of the radiocarbon content of middepth waters suggest a decrease in ventilation in multiple locations during the last glacial maximum (LGM; 24.0–18.1 ka). Reduced glacial ventilation would have allowed respired carbon to accumulate in those waters. A subsequent deglacial release of this respired carbon reservoir to the atmosphere could then account for the observed increases in atmospheric CO2 and decline in atmospheric radiocarbon content. However, age model error and a release of 14C‐depleted mantle carbon have also been cited as possible explanations for the observed middepth radiocarbon depletions, calling into question the deep ocean's role in storing respired carbon during the LGM. Joint measurements of benthic foraminiferal carbon isotope values (δ13C) and cadmium/calcium (Cd/Ca) ratios provide a method for isolating the air‐sea component of a water mass from changes in remineralization. Here we use benthic foraminiferal δ13C and Cd/Ca records from the eastern equatorial Pacific to constrain changes in remineralization and water‐mass mixing over the last glacial‐interglacial transition. These records are complemented with elemental measurements of the authigenic coatings of foraminifera to monitor postdepositional changes in bottom water properties. Our results suggest an increase of deep waters at midwater depths consistent with a shoaling of the boundary between the upper and lower branches of Southern Ocean overturning circulation. Additionally, our records demonstrate increased organic matter remineralization in middepth waters during the LGM, suggesting that respired carbon did accumulate in middepth waters under periods of reduced ventilation.

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Section: Discussionsupporting

confidence: 89%

Section: Discussionmentioning

confidence: 99%

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

Umling

Thunell

Bizimis

2018

Paleoceanog and Paleoclimatol

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“…So far only two cores have been studied in the SEP using 14 C to interpret ventilation changes (Figure ): core SO161‐22SL (from now on 22SL, ~1,000 m, ~36°S; De Pol‐Holz et al, ) and core MD07‐3088 (~1,500 m, ~46°S; Siani et al, ). Based on carbon isotope data and tephrochronology estimates of R S , Siani et al () inferred enhanced upwelling in the Pacific area of the SO during the last deglaciation and found 14 C‐depleted waters during the LGM (~350‰ Δ 14 C lower than the contemporary atmosphere) in line with a large number of deep cores in the Pacific Ocean (De la Fuente et al, ; Galbraith et al, ; Keigwin & Lehman, ; Rae et al, ; Ronge et al, ; Sikes et al, ; Skinner et al, ; Umling & Thunell, ).…”

Section: Introductionmentioning

confidence: 99%

“…Evidence of the deep ocean as the source of the atmospheric 14 C decline has been found in marine sediment cores throughout the oceans. Widespread evidence of moderately 14 C‐depleted deep waters (>2,000‐m depth) during the late glacial period (25–10 ka BP) has been found in the North Pacific (NP; Galbraith et al, ; Rae et al, ), South West Pacific (SWP; Ronge et al, ; Sikes et al, ), Equatorial East Pacific (EEP; De la Fuente et al, ; Keigwin & Lehman, ; Umling & Thunell, ), and Southern Ocean (SO; Burke & Robinson, ; Chen et al, ; Skinner et al, ). These records are consistent with the hypothesis of an isolated deep ocean reservoir during the Last Glacial Maximum (LGM) associated with increased sea ice extent around Antarctica (Adkins, ; Ferrari et al, ; Keeling & Stephens, ; Stephens & Keeling, ; Watson & Naveira Garabato, ).…”

Section: Introductionmentioning

confidence: 99%

Ventilation of the Deep Ocean Carbon Reservoir During the Last Deglaciation: Results From the Southeast Pacific

Fontaine

Pol‐Holz

Michel

et al. 2019

Paleoceanog and Paleoclimatol

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Coeval changes in atmospheric CO 2 and 14 C contents during the last deglaciation are often attributed to ocean circulation changes that released carbon stored in the deep ocean during the Last Glacial Maximum (LGM). Work is being done to generate records that allow for the identification of the exact mechanisms leading to the accumulation and release of carbon from the oceanic reservoir, but these mechanisms are still the subject of debate. Here we present foraminifera 14 C data from five cores in a transect across the Chilean continental margin between~540 and~3,100 m depth spanning the last 20,000 years. Our data reveal that during the LGM, waters at~2,000 m were 50% to 80% more depleted in Δ 14 C than waters at~1,500 m when compared to modern values, consistent with the hypothesis of a glacial deep ocean carbon reservoir that was isolated from the atmosphere. During the deglaciation, our intermediate water records reveal homogenization in the Δ 14 C values between~800 and~1,500 m from 16.5-14.5 ka cal BP to~14-12 ka cal BP, which we interpret as deeper penetration of Antarctic Intermediate Water. While many questions still remain, this process could aid the ventilation of the deep ocean at the beginning of the deglaciation, contributing to the observed~40 ppm rise in atmospheric pCO 2 .

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“…Glacial [O 2 ] decrease in the deep EEP supports higher respired DIC accumulation (Bradtmiller et al, ), although without elucidating the mechanism behind its variation. In this respect, it is now apparent that the EEP was less ventilated over the last part of the last glacial period, becoming better ventilated at the onset of the Heinrich Stadial 1 (de la Fuente et al, ; Umling & Thunell, ). This would indirectly support the idea of a more efficient biological pump during the last glacial due to a longer residence time for carbon in the deep ocean, thus reducing the leakiness of the biological pump and enhancing the deep ocean's respired carbon inventory.…”

Section: Introductionmentioning

confidence: 99%

The Evolution of Deep Ocean Chemistry and Respired Carbon in the Eastern Equatorial Pacific Over the Last Deglaciation

et al. 2017

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It has been shown that the deep Eastern Equatorial Pacific (EEP) region was poorly ventilated during the Last Glacial Maximum (LGM) relative to Holocene values. This finding suggests a more efficient biological pump, which indirectly supports the idea of increased carbon storage in the deep ocean contributing to lower atmospheric CO2 during the last glacial. However, proxies related to respired carbon are needed in order to directly test this proposition. Here we present Cibicides wuellerstorfi B/Ca ratios from Ocean Drilling Program Site 1240 measured by laser ablation inductively coupled plasma mass spectrometry (LA‐ICPMS) as a proxy for deep water carbonate saturation state (Δ[CO32−], and therefore [CO32−]), along with δ13C measurements. In addition, the U/Ca ratio in foraminiferal coatings has been analyzed as an indicator of oxygenation changes. Our results show lower [CO32−], δ13C, and [O2] values during the LGM, which would be consistent with higher respired carbon levels in the deep EEP driven, at least in part, by reduced deep water ventilation. However, the difference between LGM and Holocene [CO32−] observed at our site is relatively small, in accordance with other records from across the Pacific, suggesting that a “counteracting” mechanism, such as seafloor carbonate dissolution, also played a role. If so, this mechanism would have increased average ocean alkalinity, allowing even more atmospheric CO2 to be “sequestered” by the ocean. Therefore, the deep Pacific Ocean very likely stored a significant amount of atmospheric CO2 during the LGM, specifically due to a more efficient biological carbon pump and also an increase in average ocean alkalinity.

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Synchronous deglacial thermocline and deep-water ventilation in the eastern equatorial Pacific

Cited by 34 publications

References 65 publications

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

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

Ventilation of the Deep Ocean Carbon Reservoir During the Last Deglaciation: Results From the Southeast Pacific

The Evolution of Deep Ocean Chemistry and Respired Carbon in the Eastern Equatorial Pacific Over the Last Deglaciation

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