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. 2018 Jun 19;9(1):2396.
doi: 10.1038/s41467-018-04625-7.

Enhanced ocean-atmosphere carbon partitioning via the carbonate counter pump during the last deglacial

Stéphanie Duchamp-Alphonse  1 , Giuseppe Siani  2 , Elisabeth Michel  3 , Luc Beaufort  4 , Yves Gally  4 , Samuel L Jaccard  5
Affiliations

Enhanced ocean-atmosphere carbon partitioning via the carbonate counter pump during the last deglacial

Stéphanie Duchamp-Alphonse et al. Nat Commun. .

Abstract

Several synergistic mechanisms were likely involved in the last deglacial atmospheric pCO2 rise. Leading hypotheses invoke a release of deep-ocean carbon through enhanced convection in the Southern Ocean (SO) and concomitant decreased efficiency of the global soft-tissue pump (STP). However, the temporal evolution of both the STP and the carbonate counter pump (CCP) remains unclear, thus preventing the evaluation of their contributions to the pCO2 rise. Here we present sedimentary coccolith records combined with export production reconstructions from the Subantarctic Pacific to document the leverage the SO biological carbon pump (BCP) has imposed on deglacial pCO2. Our data suggest a weakening of BCP during the phases of carbon outgassing, due in part to an increased CCP along with higher surface ocean fertility and elevated [CO2aq]. We propose that reduced BCP efficiency combined with enhanced SO ventilation played a major role in propelling the Earth out of the last ice age.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1
Location of sites and modern ocean surface temperature and phosphate concentrations. Temperature (a) and phosphate (b) concentration fields are plotted with the Ocean Data View (ODV) software with WOA09. Solid black lines represent the: Subtropical (STF), Subantarctic (SAF), Polar (PF) and Subantarctic Circumpolar Current (SACCF) Fronts. The Polar Frontal and Subantarctic Zones are the regions between the PF and SAF, and between the SAF and the STF respectively. a Solid white circles symbolize the geographic location of sediment cores MD07-3088 (46.1°S, 75.7°W, 1536 m), TN057-13-4PC (53.2°S, 5.1°E, 2850 m), and sites ODP 1233 (41.0°S, 74.4°W, 838 m) and 1238 (1.5°S, 82.5°W, 2203 m). The solid white square highlights the West Antarctic Ice Sheet Divide ice core (WDC, 79.5°S, 112.1°W, 1766 m above sea level)
Fig. 2
Fig. 2
Southern Ocean productivity and circulation patterns during the last deglaciation. a, c, d Number of Noëlaerhabdaceae, H. carteri and C. leptoporus at site MD07-3088 (/g of sediment), with an error bar of ±1%. b Number of coccoliths at site ODP 1233 (/g of sediment). e Summer sea surface temperatures (SST, °C) using the Modern Analogue Technique, . f 14C age difference between paired benthic and planktonic foraminifera (14C B-P). g Δ δ13C = δ13CG. bulloides – δ13CC. wuellerstorfi. h Opal fluxes at TN057-13-4PC. i Noëlaerhabdaceae mass (pg) at site MD07-3088 with an error bar of ±3%. j Surface ocean ΔpCO2 reconstruction for ODP 1238. LG and LGIT are for Late Glacial and Last Glacial-Interglacial Transition, respectively. Smoothed curves (thick lines of a–e, g, and i) use a three-point moving average. Yellow shading marks periods of enhanced deep-water ventilation and resumption of SO upwelling during the last deglaciation, in conjunction with higher ocean surface fertility, [CO2aq], and sometimes increased SST conditions
Fig. 3
Fig. 3
Noëlaerhabdaceae coccolith morphometrics, and their response to excepted [CO2aq] at site MD07-3088 over the last deglaciation. a–d Relationships between coccolith mass (pg) and coccolith area (a), thickness (b), as well as coccolith aspect ratio (ARL) (c) and SN thickness (d) (Methods section). e–i Coccolith morphometric changes during the deglaciation: e mass (pg), f area (μm2), g thickness (µm), h–i SN and ARL indices (Methods section). Coccolith mass show no relationship with coccolith area, but clear positive relationships with size normalized coccolith mass indices ARL and SN which indicates that the mass of coccoliths typically increases in proportion with their thickness. Therefore, changes in coccolith mass document changes in the degree of coccolith calcification (i.e. PIC/POC ratio). Obviously, the Noëlaerhabdaceae coccolith mass increases observed during enhanced SO upwelling associated with higher sea surface fertility conditions (yellow shading), document increased coccosphere calcite quota in response to SSW [CO2aq] rises during HS1 and YD
Fig. 4
Fig. 4
Subantarctic carbonate counter pump strength and biological pump efficiency coupled with circulation pattern and atmospheric pCO2 during the last deglaciation. a–c Noëlaerhabdacea, coccolith and planktonic foraminifera calcite masses (mg/g of sediment) at site MD07-3088, with errors bars of ±3% and ±20%, respectively. d Br/Ca ratio as an indicator of POC/PIC rain ratio and thus biological carbon pump efficiency (see Supplementary Fig. 3). e Δ δ13C = δ13CG. bulloides – δ13CC. wuellerstorfi. f Atmospheric pCO2 from WDC. Smoothed curves (thick lines of a–c, e and d) use three and eleven-point moving averages respectively. LG and LGIT are for Late Glacial and Last Glacial-Interglacial Transition, respectively. Yellow shading marks periods of reinvigorated SO upwelling (associated with enhanced sea surface fertility conditions and higher [CO2aq]) during the last deglaciation, in conjunction to higher CCP strength and subdued biological pump efficiency, at times of increased atmospheric pCO2
Fig. 5
Fig. 5
Influence of soft tissue and carbonate counter pumps on the CO2 partial pressure of surface waters, as a function of the POC/PIC rain ratio (1/ρ). Solid black line isocontours represent pCO2 (μatm) for constant salinity (34‰), temperature (14 °C), and depleted phosphate (0.5 µmol/kg) and silicate (3 µmol/kg) contents. The solid black arrows represent the effect of biogenic export production in the case of photosynthesis and calcification only. The dashed (or dot-dashed) black and grey arrows illustrate the influence of the biological pump (and particularly the CCP) during the HS1 relative to the ACR, i.e., when 1/ρ decreases by a factor of 1.8, assuming that 10 (or 50%) of the exported POC has been preserved within the sediment, i.e., under two probable export production conditions at site MD07-3088
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