Less Remineralized Carbon in the Intermediate‐Depth South Atlantic During Heinrich Stadial 1

Abstract

The last deglaciation (~20-10 kyr BP) was characterized by a major shift in Earth's climate state, when the global mean surface temperature rose~4°C and the concentration of atmospheric CO 2 increased~80 ppmv. Model simulations suggest that the initial 30 ppmv rise in atmospheric CO 2 may have been driven by reduced efficiency of the biological pump or enhanced upwelling of carbon-rich waters from the abyssal ocean. Here we evaluate these hypotheses using benthic foraminiferal B/Ca (a proxy for deep water [CO 3 2− ]) from a core collected at 1,100-m water depth in the Southwest Atlantic. Our results imply that [CO 3 2− ] increased by 22 ± 2 μmol/kg early in Heinrich Stadial 1, or a decrease in ΣCO 2 of approximately 40 μmol/kg, assuming there were no significant changes in alkalinity. Our data imply that remineralized phosphate declined by approximately 0.3 μmol/kg during Heinrich Stadial 1, equivalent to 40% of the modern remineralized signal at this location. Because tracer inversion results indicate remineralized phosphate at the core site reflects the integrated effect of export production in the sub-Antarctic, our results imply that biological productivity in the Atlantic sector of the Southern Ocean was reduced early in the deglaciation, contributing to the initial rise in atmospheric CO 2 .

Deglacial Temperature and Carbonate Saturation State Variability in the Tropical Atlantic at Antarctic Intermediate Water Depths

“…The similarity of the BWT and CdW reconstructions from the Demerara Rise and Florida Margin, discussed in Section 5, supports our chronology for the Demerara Rise site between ∼9 and 14 ka, which, as noted above, is poorly constrained. Lacerra et al, 2019;Umling et al, 2019), Demerara Rise site KNR197-3-46CDH (Huang et al, 2014;Oppo et al, 2018; this study), and Florida Strait site KNR166-2-26JPC (e.g., Lynch-Stieglitz et al, 2014;Valley et al, 2017Valley et al, , 2019. Tobago Basin site M78/235-1 is shown in yellow (Poggemann et al, 2017(Poggemann et al, , 2018.…”

“…The Demerara Rise $${\Delta }\left[{\mathrm{C}\mathrm{O}}_{3}^{2-}\right]$$ began a long‐term decrease at ∼17 ka. Four factors may have contributed to the glacial‐Holocene decline: (a) decreasing “endmember” $${\Delta }\left[{\mathrm{C}\mathrm{O}}_{3}^{2-}\right]$$ values of northern surface source waters due to rising atmospheric CO 2 (Yu et al., 2008), (b) decreasing $${\Delta }\left[{\mathrm{C}\mathrm{O}}_{3}^{2-}\right]$$ of AAIW after about 16 ka (Lacerra et al., 2019), (c) an LGM‐to‐Holocene decrease in the contribution of high‐$${\Delta }\left[{\mathrm{C}\mathrm{O}}_{3}^{2-}\right]$$ northern‐sourced waters relative to low‐$${\Delta }\left[{\mathrm{C}\mathrm{O}}_{3}^{2-}\right]$$ AAIW, and (d) greater accumulation of respired material in the ocean interior along the water mass pathways to the site. CdW increased from the LGM to the Holocene, implying that at least some component of the $${\Delta }\left[{\mathrm{C}\mathrm{O}}_{3}^{2-}\right]$$ decrease was due to increasing southern waters and/or enhanced accumulation of remineralized organic matter, that is the third and/or fourth mechanisms.…”

“…Published data used in this study are available in Marchitto (2008, 2010), Huang et al (2014), Lacerra et al (2019, Oppo et al (2018), Umling et al (2019), and Valley et al (2017. Data generated for this study are available in Oppo et al (2023b).…”

“…The latter would imply a strengthening AMOC during this early-mid Holocene interval. rose at the Brazil Margin site near the beginning of HS1 (Lacerra et al, 2019), probably due to outgassing of CO 2 in the South Atlantic sector of the Southern Ocean (Yu et al, 2022). There appears to have been little change in the Demerara Rise and low CdW imply that northern source waters continued to dominate the water mass mixture at the Demerara Rise, even during early HS1.…”

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

“…The biological pump was more efficient during the last glacial period than it is todday (Martínez‐García et al, ; Studer et al, ). A deglacial decrease in the efficiency of the global biological pump could account for a portion of deglacial atmospheric CO 2 rise and also drive an increase in interior‐ocean [CO 3 2− ] (Lacerra et al, ), potentially accounting for portions of deglacial [CO 3 2− ] rise in our southwest Pacific records. A decrease in biological pump efficiency corresponds to a less complete utilization of nutrients in the surface ocean (Knox & McElroy ).…”