Vanishing coccolith vital effects with alleviated carbon limitation

Hermoso, Michaël; Chan, Isani; McClelland, H. L. O.; Heureux, Ana; Rickaby, Rosalind E. M.

doi:10.5194/bg-13-301-2016

Cited by 45 publications

(62 citation statements)

References 58 publications

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“…Noncoccolith particles, such as discoasters (star-shaped or rosette calcareous nannoliths particularly prone to diagenetic alteration) and foraminiferal fragments, were retained in the coarse fractions (8-20 μm) preceding the 5-8-μm and 3-5-μm microfraction steps. The so-called micarbs corresponding to undetermined micrometric crystals (53) In the present study, we used a paleo-DIC equation derived from recent coccolithophore culture work with a geological perspective (19,20). This proxy relies on the interspecies δ 13 C compositions (Δ 13 C large-small ) of coccoliths of distinct sizes recently formalized in ref.…”

Section: Methodsmentioning

confidence: 99%

“…1; see SI Materials and Methods), accounting for local seawater δ 18 O values (6,22) (Figs. S1 and S2) and the vital effect (19,20) (Fig. S3).…”

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confidence: 96%

“…In sequences postdating the Late Miocene, large isotope vital effects have been reported in coccoliths (21). This was attributed to the consequence of relatively low pCO 2 concentrations, as DIC/CO 2 aq limitation is thought to be the main cause of the vital effects in these biominerals (20,21,(23)(24)(25)(26)(27). In contrast, studies of laboratory cultures and downcore sediments indicate that the vital effect in coccoliths (regardless of taxonomy) was limited and invariant when pCO 2 concentrations in the atmosphere were above ∼500 ppm, as was the case during the time period investigated (28, 29) (see SI Materials and Methods for further explanations on the relation…”

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confidence: 99%

“…Their excellent preservation, even in warm and high pCO 2 settings (18), may overcome methodological caveats associated with the absence or frequent recrystallization of foraminiferal shells (1,2,17). Recent culture and sedimentary studies have produced new coccolith-based proxies that make it possible to exploit this underexplored paleoclimatic archive (SI Materials and Methods) (19)(20)(21). In the present study, we used the established temperature dependence of oxygen isotope ratios of coccolith calcite gathered in size-restricted microfractions to calculate SSTs (Eq.…”

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confidence: 99%

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Equatorial heat accumulation as a long-term trigger of permanent Antarctic ice sheets during the Cenozoic

Tremblin

Hermoso

Minoletti

2016

Proc. Natl. Acad. Sci. U.S.A.

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Growth of the first permanent Antarctic ice sheets at the Eocene−Oligocene Transition (EOT), ∼33.7 million years ago, indicates a major climate shift within long-term Cenozoic cooling. The driving mechanisms that set the stage for this glaciation event are not well constrained, however, owing to large uncertainties in temperature reconstructions during the Eocene, especially at lower latitudes. To address this deficiency, we used recent developments in coccolith biogeochemistry to reconstruct equatorial Atlantic sea surface temperature (SST) and atmospheric pCO 2 values from pelagic sequences preceding and spanning the EOT. We found significantly more variability in equatorial SSTs than previously reported, with pronounced cooling from the Early to Middle Eocene and subsequent warming during the Late Eocene. Thus, we show that the Antarctic glaciation at the Eocene−Oligocene boundary was preceded by a period of heat accumulation in the low latitudes, likely focused in a progressively contracting South Atlantic gyre, which contributed to cooling high-latitude austral regions. This prominent redistribution of heat corresponds to the emplacement of a strong meridional temperature gradient that typifies icehouse climate conditions. Our equatorial coccolith-derived geochemical record thus highlights an important period of global climatic and oceanic upheaval, which began 4 million years before the EOT and, superimposed on a longterm pCO 2 decline, drove the Earth system toward a glacial tipping point in the Cenozoic. . These records exhibit rather conflicting proxy data for the TDP and overall long-term cooling for the Atlantic sites 925 and 929. There is, however, no clear and significant cooling trend from the Early to Middle Eocene that indicates the termination of the Early Eocene Climatic Optimum (Fig. 1A). Furthermore, recent quality-checked SSTs for ODP 925 and 929 sites using the Ring Index indicate relatively similar temperatures between the Late Eocene and the Early Oligocene (5). In contrast, high-latitude sites are consistent in demonstrating appreciable cooling of austral subpolar regions during much of the Eocene (3,4,(6)(7)(8). This apparent lack of substantial temperature change in the intertropical belt during the Eocene and across the EOT remains an enigmatic feature that complicates our understanding of the interplay between seawater temperatures at a global scale, pCO 2 , and changes in global ocean circulations in the context of new Southern Ocean gateways (9-14). The paucity of low-latitude data, especially in the Pacific Ocean, prevents the reconstruction of the latitudinal temperature gradient, much needed for the successful modeling of processes that drove the greenhouse to icehouse transition (10, 15, 16).As an alternative to the relatively poor preservation of the foraminifera and issues with the calibration of organic-based proxies (1, 5, 17), this study exploits the coccoliths as a source of paleoclimatic information. Coccolithophores, single-celled phytoplankton algae, are a key componen...

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Section: Methodsmentioning

confidence: 99%

“…1; see SI Materials and Methods), accounting for local seawater δ 18 O values (6,22) (Figs. S1 and S2) and the vital effect (19,20) (Fig. S3).…”

mentioning

confidence: 96%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Equatorial heat accumulation as a long-term trigger of permanent Antarctic ice sheets during the Cenozoic

Tremblin

Hermoso

Minoletti

2016

Proc. Natl. Acad. Sci. U.S.A.

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“…However, there have been relatively few studies of carbon isotopes in coccolith calcite6, and fewer still where experiments have been carried out in vivo under closely monitored conditions6789. Although so-called vital effects are known to vary with growth rate4, and CO 2 availability7, the reasons for these isotopic departures from equilibrium remain poorly understood.…”

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The origin of carbon isotope vital effects in coccolith calcite

et al. 2017

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Calcite microfossils are widely used to study climate and oceanography in Earth's geological past. Coccoliths, readily preserved calcite plates produced by a group of single-celled surface-ocean dwelling algae called coccolithophores, have formed a significant fraction of marine sediments since the Late Triassic. However, unlike the shells of foraminifera, their zooplankton counterparts, coccoliths remain underused in palaeo-reconstructions. Precipitated in an intracellular chemical and isotopic microenvironment, coccolith calcite exhibits large and enigmatic departures from the isotopic composition of abiogenic calcite, known as vital effects. Here we show that the calcification to carbon fixation ratio determines whether coccolith calcite is isotopically heavier or lighter than abiogenic calcite, and that the size of the deviation is determined by the degree of carbon utilization. We discuss the theoretical potential for, and current limitations of, coccolith-based CO2 paleobarometry, that may eventually facilitate use of the ubiquitous and geologically extensive sedimentary archive.

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The history of calcite diagenesis and origin of exceptionally negative oxygen isotope values in chalks of the Niobrara Formation, Denver Basin, USA

Simon

Budd

Snell

2023

The Depositional Record

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The Niobrara Formation of north‐east Colorado, USA, has anomalously negative δ18O values compared to all other Cretaceous chalks. These unique δ18O values have been attributed to elevated heat flow and/or freshening of the Cretaceous Western Interior Seaway. This work utilises clumped isotopes of calcite (Δ47), peak burial temperatures estimated from pyrolysis data, and strontium and neodymium isotopes of carbonate to re‐evaluate the origin of the calcite's 18O‐depletion. Peak temperatures indicate lateral variability in geothermal gradients of ca 20°C/km at the tens of kilometre scale, and corroborate prior studies proposing locally elevated palaeotemperatures. Greater insight is provided by numerical models of calcite recrystallisation and oxygen isotope evolution that are constrained by measured Δ47‐derived temperatures, calcite δ18O values and inferences from the 87Sr/86Sr and εNd values. The models indicate that (1) sea water in the seaway had normal marine δ18O values of −1 (VSMOW) except on the eastern margin of the basin where some freshwater dilution yielded −2 to −3‰ (VSMOW) water, and (2) the main driver of the anonymously negative calcite δ18O values was a semi‐open hydrologic system that provided a few percent by pore volume of meteoric groundwater derived from post‐Laramide recharge into the basin. Minor contributions were a Laramide‐aged heat pulse related to the underlying Colorado Mineral Belt, the thermal insulating effects of now eroded coals, and a small flux of compaction‐driven Cretaceous sea water evolved by smectite dehydration. However, those three factors alone were insufficient drivers of the calcites' 18O depletion. High burial temperatures are interpreted to have caused clumped isotope reordering in at least one well, but those temperatures cannot yield the observed calcite δ18O values. The study illustrates the unique attributes of the Niobrara's diagenetic system that results in its anomalous δ18O values, and reaffirms the value of clumped isotopes in unravelling the diagenetic history of chalk systems.

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Vanishing coccolith vital effects with alleviated carbon limitation

Cited by 45 publications

References 58 publications

Equatorial heat accumulation as a long-term trigger of permanent Antarctic ice sheets during the Cenozoic

Equatorial heat accumulation as a long-term trigger of permanent Antarctic ice sheets during the Cenozoic

The origin of carbon isotope vital effects in coccolith calcite

The history of calcite diagenesis and origin of exceptionally negative oxygen isotope values in chalks of the Niobrara Formation, Denver Basin, USA

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