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

Abstract

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 .

The Roles of Wind and Sea Ice in Driving the Deglacial Change in the Southern Ocean Upwelling: A Modeling Study

“…The simulated equatorward extension of denser ocean surface water during the LGM agrees with past studies [12,38]. The simulation showed that the LGM deep ocean was extensively stratified (Figure 7a) and colder and saltier (Figure 7b) than during the O_H and agreed with previous studies [12,28,[91][92][93].…”

“…Modeling results employing an idealized wind forcing have shown that an increase or poleward shift or both in zonal wind stress forcing increases the SO upwelling [3]. Paleo records [9,14] and subsequent studies [6,[24][25][26][27][28] have suggested that wind stress forcing and air-sea gas exchange may account for the increase in SO upwelling and changes in atmospheric CO 2 concentrations. However, wind-driven enhancement in the Antarctic Circumpolar Current's baroclinicity would allow for southward eddy transport (eddy saturation) [29][30][31][32].…”

A deep Tasman outflow of Pacific waters during the last glacial period

“…A recent study proposed an increased presence of Tasman AAIW over the Challenger Plateau in the eastern Tasman Sea (west of New Zealand) during the LGM 67 . Nevertheless, previous work from the main AAIW formation region in the Southeast Pacific 68,69 , as well as in areas influenced by Tasman AAIW (i.e., eastern Tasman Sea and Bay of Plenty) 66,67,70 (Fig. 1a), are inconsistent with a deepening of Tasman AAIW to reach water depths of ~1500-1700 m during the LGM.…”

Isotopic Characterization of Water Masses in the Southeast Pacific Region: Paleoceanographic Implications

“…The study of past water masses geometry and chemistry in the SEP, relies on downcore stable isotope records from calcifers collected from the shelf and slope of the western continental margin of South America. These allow the reconstructions of density, ventilation, oxygen, and nutrient contents in the water column on various time scales (e.g., Haddam et al., 2018, 2020; Martínez‐Fontaine et al., 2019; Martínez‐Méndez et al., 2013a; Mohtadi et al., 2008; Nürnberg et al., 2015; Siani et al., 2013).…”