Pleistocene sediment offloading and the global sulfur cycle

Marković, Stefan; Paytan, Adina; Wortmann, Ulrich G.

doi:10.5194/bg-12-3043-2015

Cited by 29 publications

(17 citation statements)

References 103 publications

(158 reference statements)

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“…For our "Low O 2 " scenario, the posterior probability distribution for the global rate of organic carbon burial (J bur oc ) suggests a mid-Proterozoic rate of ~0.5−2.5 Tmol C year −1 , with a median of 1.10 +0.93 −0.64 Tmol C year −1 (1σ) and a 95% credible interval of 0.20−3.41 Tmol C year −1 (Figure 2a blue). These fluxes are well below estimates of marine organic carbon burial for the modern (10.5−13.3 Tmol C year −1 ) (Berner, 1982;Burdige, 2005 (Figure 2b blue), within a factor of 2 of the "near-modern" (Quaternary average) ocean value of 1.2−1.6 Tmol S year −1 (Berner & Berner, 2012;Markovic, Paytan, & Wortmann, 2015). Taken together, we estimate a combined rate of O 2 production of about 3.51 Tmol O 2 year −1 , roughly 25% of the present value (J O2 in Figure 2c).…”

Section: Limited O 2 Production In Proterozoic Oceansmentioning

confidence: 55%

“…TA B L E 1 Parameter ranges used in our Monte Carlo analysis with a 95% credible interval of 0.81−1.63 Tmol S year −1(Figure 2bblue), within a factor of 2 of the "near-modern" (Quaternary average) ocean value of 1.2−1.6 Tmol S year −1(Berner & Berner, 2012;Markovic, Paytan, & Wortmann, 2015). For our "Low O 2 " scenario, the posterior probability distribution for the global rate of organic carbon burial (J bur oc ) suggests a mid-Proterozoic rate of ~0.5−2.5 Tmol C year −1 , with a median of 1.10 +0.93 −0.64 Tmol C year −1 (1σ) and a 95% credible interval of 0.20−3.41 Tmol C year −1(Figure 2ablue).…”

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confidence: 96%

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A sluggish mid‐Proterozoic biosphere and its effect on Earth's redox balance

2018

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The possibility of low but nontrivial atmospheric oxygen (O 2 ) levels during the mid‐Proterozoic (between 1.8 and 0.8 billion years ago, Ga) has important ramifications for understanding Earth's O 2 cycle, the evolution of complex life and evolving climate stability. However, the regulatory mechanisms and redox fluxes required to stabilize these O 2 levels in the face of continued biological oxygen production remain uncertain. Here, we develop a biogeochemical model of the C‐N‐P‐O 2 ‐S cycles and use it to constrain global redox balance in the mid‐Proterozoic ocean–atmosphere system. By employing a Monte Carlo approach bounded by observations from the geologic record, we infer that the rate of net biospheric O 2 production was Tmol year −1 (1σ), or ~25% of today's value, owing largely to phosphorus scarcity in the ocean interior. Pyrite burial in marine sediments would have represented a comparable or more significant O 2 source than organic carbon burial, implying a potentially important role for Earth's sulphur cycle in balancing the oxygen cycle and regulating atmospheric O 2 levels. Our statistical approach provides a uniquely comprehensive view of Earth system biogeochemistry and global O 2 cycling during mid‐Proterozoic time and implicates severe P biolimitation as the backdrop for Precambrian geochemical and biological evolution.

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Section: Limited O 2 Production In Proterozoic Oceansmentioning

confidence: 55%

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confidence: 96%

A sluggish mid‐Proterozoic biosphere and its effect on Earth's redox balance

2018

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“…Multiple lines of evidence based on geochemistry, sedimentology and modelling suggest that the rate of silicate weathering, which adds alkalinity to the ocean, accelerated around 1.5 Myr ago as the North American Precambrian basement shed regolith and experienced more intense subglacial erosion 39 . At the same time the first large amplitude sea level cycles accelerated erosion of shelf sediments 40 . Estimates of alkalinity from carbon system proxies are subject to multiple uncertainties.…”

Section: Resultsmentioning

confidence: 99%

Decrease in coccolithophore calcification and CO2 since the middle Miocene

et al. 2016

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Marine algae are instrumental in carbon cycling and atmospheric carbon dioxide (CO2) regulation. One group, coccolithophores, uses carbon to photosynthesize and to calcify, covering their cells with chalk platelets (coccoliths). How ocean acidification influences coccolithophore calcification is strongly debated, and the effects of carbonate chemistry changes in the geological past are poorly understood. This paper relates degree of coccolith calcification to cellular calcification, and presents the first records of size-normalized coccolith thickness spanning the last 14 Myr from tropical oceans. Degree of calcification was highest in the low-pH, high-CO2 Miocene ocean, but decreased significantly between 6 and 4 Myr ago. Based on this and concurrent trends in a new alkenone ɛp record, we propose that decreasing CO2 partly drove the observed trend via reduced cellular bicarbonate allocation to calcification. This trend reversed in the late Pleistocene despite low CO2, suggesting an additional regulator of calcification such as alkalinity.

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“…Sample residues were scanned using a scanning electron microscope with energy‐dispersive spectrometry, and barite typically consisted of more than 95% of the sample. Based on crystal morphology and sulfur isotope ratios, no diagenetic barite was present in this core [ Markovic et al , ]. Values of weight percent barite were determined based on the fraction of barite recovered from the initial dry sediment used (Table S1 in the supporting information).…”

Section: Methodsmentioning

confidence: 99%

Export production fluctuations in the eastern equatorial Pacific during the Pliocene‐Pleistocene: Reconstruction using barite accumulation rates

Ravelo

Liu

et al. 2015

Paleoceanography

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Export production is an important component of the carbon cycle, modulating the climate system by transferring CO2 from the atmosphere to the deep ocean via the biological pump. Here we use barite accumulation rates to reconstruct export production in the eastern equatorial Pacific over the past 4.3 Ma. We find that export production fluctuated considerably on multiple time scales. Export production was on average higher (51 g C m−2 yr−1) during the Pliocene than the Pleistocene (40 g C m−2 yr−1), decreasing between 3 and 1 Ma (from more than 60 to 20 g C m−2 yr−1) followed by an increase over the last million years. These trends likely reflect basin‐scale changes in nutrient inventory and ocean circulation. Our record reveals decoupling between export production and temperatures on these long (million years) time scale. On orbital time scales, export production was generally higher during cold periods (glacial maxima) between 4.3 and 1.1 Ma. This could be due to stronger wind stress and higher upwelling rates during glacial periods. A shift in the timing of maximum export production to deglaciations is seen in the last ~1.1 million years. Results from this study suggest that, in the eastern equatorial Pacific, mechanisms that affect nutrient supply and/or ecosystem structure and in turn carbon export on orbital time scales differ from those operating on longer time scales and that processes linking export production and climate‐modulated oceanic conditions changed about 1.1 million years ago. These observations should be accounted for in climate models to ensure better predictions of future climate change.

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Pleistocene sediment offloading and the global sulfur cycle

Cited by 29 publications

References 103 publications

A sluggish mid‐Proterozoic biosphere and its effect on Earth's redox balance

A sluggish mid‐Proterozoic biosphere and its effect on Earth's redox balance

Decrease in coccolithophore calcification and CO2 since the middle Miocene

Export production fluctuations in the eastern equatorial Pacific during the Pliocene‐Pleistocene: Reconstruction using barite accumulation rates

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