Molecular fossils from phytoplankton reveal secular
 P
 <scp>co</scp>
 2
 trend over the Phanerozoic

Witkowski, Caitlyn; Weijers, Johan W. H.; Blais, Brian S.; Schouten, Stefan; Damsté, Jaap S. Sinninghe

doi:10.1126/sciadv.aat4556

Cited by 118 publications

(143 citation statements)

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“…When evaluating past events based on bulk δ 13 C values, the incorporation of chemoautotrophically produced carbon must thus be considered. This also further supports claims that calculations of pCO 2 based on differences between δ 13 C of organic and inorganic carbon should not rely on bulk organic carbon that includes bacterial contributions, but instead use compound specific δ 13 C values derived from algae, consistent with previous investigations (Pancost et al, ; Pancost et al, ; reviewed by Witkowski et al, ). By extension, a deviation from the relationship between δ 13 C bulk OM and δ 13 C phytane could be an indicator for the chemoautotrophic contribution to sedimentary OM.…”

Section: Discussionsupporting

confidence: 86%

Dark carbon fixation in the Arabian Sea oxygen minimum zone contributes to sedimentary organic carbon (SOM)

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Mayser

et al. 2019

Global Biogeochemical Cycles

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In response to rising CO2 concentrations and increasing global sea surface temperatures, oxygen minimum zones (OMZ), or “dead zones”, are expected to expand. OMZs are fueled by high primary productivity, resulting in enhanced biological oxygen demand at depth, subsequent oxygen depletion, and attenuation of remineralization. This results in the deposition of organic carbon‐rich sediments. Carbon drawdown is estimated by biogeochemical models; however, a major process is ignored: carbon fixation in the mid‐ and lower water column. Here, we show that chemoautotrophic carbon fixation is important in the Arabian Sea OMZ; and manifests in a 13C‐depleted signature of sedimentary organic carbon. We determined the δ13C values of Corg deposited in close spatial proximity but over a steep bottom‐water oxygen gradient, and the δ13C composition of biomarkers of chemoautotrophic bacteria capable of anaerobic ammonia oxidation (anammox). Isotope mixing models show that detritus from anammox bacteria or other chemoautotrophs likely forms a substantial part of the organic matter deposited within the Arabian Sea OMZ (~17%), implying that the contribution of chemoautotrophs to settling organic matter is exported to the sediment. This has implications for the evaluation of past, and future, OMZs: biogeochemical models that operate on the assumption that all sinking organic matter is photosynthetically derived, without new addition of carbon, could significantly underestimate the extent of remineralization. Oxygen demand in oxygen minimum zones could thus be higher than projections suggest, leading to a more intense expansion of OMZs than expected.

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Section: Discussionsupporting

confidence: 86%

Dark carbon fixation in the Arabian Sea oxygen minimum zone contributes to sedimentary organic carbon (SOM)

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Mayser

et al. 2019

Global Biogeochemical Cycles

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“…Macroecological pattern may change through time due to evolution. And long-term evolution -macroevolution -is influenced by abiotic and biotic drivers that have given two evolutionary models: Red Queen (Van Valen, 1973) and Court Jester (Barnosky, 2001) Ziegler (1988) and Blakey (2008). hypotheses. The former states that biotic interactions drive evolutionary changes, whereas the latter asserts that changes in physical environments initiate evolutionary changes.…”

Section: Discussionmentioning

confidence: 99%

“…For nannofossil accumulation rates and pCO 2 values (parts per million and micro-atmospheres; Foster et al, 2017, Witkowski et al, 2018) (Figs. 2, S1-S2, S4), a LOESS smoothed curve was computed in order to capture long-term variations and overlook short-term shifts that are more likely controlled by the number of studied sites, sampling resolution and nannofossil preservation or, alternatively, by local environmental conditions.…”

Section: Trend Smoothingmentioning

confidence: 99%

Updated Supplementary material

Suchéras-Marx¹

2019

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The rise of calcareous nannoplankton in Mesozoic oceans has deeply impacted ocean chemistry and contributed to shaping modern oceans. Nevertheless, the calcareous nannoplankton colonization of past marine environments remains poorly understood. Based on an extensive compilation of published and unpublished data, we show that their accumulation rates in sediments increased from the Early Jurassic ( ∼ 200 Ma) to the Early Cretaceous (∼ 120 Ma), although these algae diversified up to the end of the Mesozoic (66 Ma). After the middle Eocene (∼ 45 Ma), a decoupling occurred between accumulation rates, diversity and coccolith size. The time series analyzed points toward a threephase evolutionary dynamic. An invasion phase of the openocean realms was followed by a specialization phase occurring along with taxonomic diversification, ended by an establishment phase where a few small-sized species dominated. The current hegemony of calcareous nannoplankton in the world ocean results from a long-term and complex evolutionary history shaped by ecological interactions and abiotic forcing.Published by Copernicus Publications on behalf of the European Geosciences Union.

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“…δ p is calculated by correcting the δ 13 C for each individual biomarker for the offset with photosynthetic biomass caused by isotopic fractionation during biosynthesis. The isotopic offset between phytol and biomass is 3.5 ± 1.3 ‰ based on the average of twenty-three species compiled in (Witkowski et al, 2018) and the isotopic offset between sterols and biomass is 4.5 ± 3.0 ‰ based on the average of eight algal species (Schouten et al, 1998). The isotopic offset for loliolide from 5 biomass, however, has not been studied.…”

Section: The ɛ P Among General Algal Biomarkersmentioning

confidence: 99%

“…In our study, we explore the relationship between Ɛ p and CO 2[aq] across several pre-established sites with different (temporally consistent) levels of PCO 2 at the warm-temperate CO 2 seep at Mikama Bay off the shore of Shikine Island, Japan. We test this relationship using general algal biomarkers, compounds which have rarely been used for Ɛ p -based PCO 2 reconstructions despite their potential utility (Freeman and Hayes, 1992;Popp et al, 1989;Witkowski et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

Validation of carbon isotope fractionation in algal lipids as a PCO2 proxy using a natural CO2 seep (Shikine Island, Japan)

Witkowski¹,

Agostini²,

Harvey³

et al. 2019

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Abstract. Carbon dioxide concentrations in the atmosphere play an integral role in many earth system dynamics, including its influence on global temperature. Long-term trends can provide insights into these dynamics though reconstructing long-term trends of atmospheric carbon dioxide (expressed in partial pressure; PCO2) remains a challenge in paleoclimatology. One promising approach for reconstructing past PCO2 utilizes isotopic fractionation associated with CO2-fixation during photosynthesis into organic matter (&#400;p). Previous studies have focused primarily on testing estimates of &#400;p derived from species-specific alkenone compounds in laboratory cultures and mesocosm experiments. Here, we analyze &#400;p derived from general algal compounds from sites at a CO2 seep near Shikine Island (Japan), a natural environment with CO2 concentrations ranging from ambient (ca. 310&#8201;&#181;atm) to elevated (ca. 770&#8201;&#181;atm). We observed strong, consistent &#948;13C shifts in several algal biomarkers from a variety of sample matrices over the steep CO2 gradient. Of the three general algal biomarkers explored here, namely loliolide, phytol, and cholesterol, &#400;p positively correlates with PCO2 in agreement with &#400;p theory and previous culture studies. PCO2 reconstructed from the &#400;p of general algal biomarkers show the same trends throughout, as well as the correct control values, but with lower absolute reconstructed values than the measured values at the elevated PCO2 sites. Our results show that naturally-occurring CO2 seeps may provide useful testing grounds for PCO2 proxies and that general algal biomarkers show promise for reconstructing past PCO2.

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Molecular fossils from phytoplankton reveal secular P co ₂ trend over the Phanerozoic

Abstract: Fossil remains from algae are used to reconstruct 500 million years of atmospheric carbon dioxide concentrations.

Cited by 118 publications

References 94 publications

Dark carbon fixation in the Arabian Sea oxygen minimum zone contributes to sedimentary organic carbon (SOM)

Dark carbon fixation in the Arabian Sea oxygen minimum zone contributes to sedimentary organic carbon (SOM)

Updated Supplementary material

Validation of carbon isotope fractionation in algal lipids as a <i>P</i>CO<sub>2</sub> proxy using a natural CO<sub>2</sub> seep (Shikine Island, Japan)

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Molecular fossils from phytoplankton reveal secular P co 2 trend over the Phanerozoic

Abstract: Fossil remains from algae are used to reconstruct 500 million years of atmospheric carbon dioxide concentrations.

Cited by 118 publications

References 94 publications

Dark carbon fixation in the Arabian Sea oxygen minimum zone contributes to sedimentary organic carbon (SOM)

Dark carbon fixation in the Arabian Sea oxygen minimum zone contributes to sedimentary organic carbon (SOM)

Updated Supplementary material

Validation of carbon isotope fractionation in algal lipids as a &lt;i&gt;P&lt;/i&gt;CO&lt;sub&gt;2&lt;/sub&gt; proxy using a natural CO&lt;sub&gt;2&lt;/sub&gt; seep (Shikine Island, Japan)

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Molecular fossils from phytoplankton reveal secular P co ₂ trend over the Phanerozoic

Validation of carbon isotope fractionation in algal lipids as a <i>P</i>CO<sub>2</sub> proxy using a natural CO<sub>2</sub> seep (Shikine Island, Japan)