Publications by authors named "Appy Sluijs"

33 Publications

Eutrophication and Deoxygenation Forcing of Marginal Marine Organic Carbon Burial During the PETM.

Paleoceanogr Paleoclimatol 2022 Mar 3;37(3):e2021PA004232. Epub 2022 Mar 3.

Department of Earth Sciences Faculty of Geosciences Utrecht University Utrecht The Netherlands.

The Paleocene-Eocene Thermal Maximum (PETM) is recognized globally by a negative excursion in stable carbon isotope ratios (δC) in sedimentary records, termed the carbon isotope excursion (CIE). Based on the CIE, the cause, duration, and mechanisms of recovery of the event have been assessed. Here, we focus on the role of increased organic carbon burial on continental margins as a key driver of CO drawdown and global exogenic δC during the recovery phase. Using new and previously published sediment proxy data, we show evidence for widespread enhanced primary production, low oxygen waters, and high organic carbon (C) burial in marginal and restricted environments throughout the δC excursion. With a new biogeochemical box model for deep and marginal environments, we show that increased phosphorus availability and water column stratification on continental margins can explain the increased C burial during the PETM. Deoxygenation and recycling of phosphorus relative to C were relatively mild, compared to modern day anoxic marine systems. Our model reproduces the conditions reconstructed by field data, resulting in a burial of 6,000 Pg across the PETM, in excess of late Paleocene burial, and ∼3,300 Pg C for the critical first 40 kyr of the recovery, primarily located on continental margins. This value is consistent with prior data and model estimates (∼2,000-3,000 Pg C). To reproduce global exogenic δC patterns, this C burial implies an injection of 5,000-10,000 Pg C during the first ∼100-150 kyr of the PETM, depending on the source's δC (-11‰ to -55‰).
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http://dx.doi.org/10.1029/2021PA004232DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC9310739PMC
March 2022

Limited Lateral Transport Bias During Export of Sea Surface Temperature Proxy Carriers in the Mediterranean Sea.

Geophys Res Lett 2022 Feb 23;49(4):e2021GL096859. Epub 2022 Feb 23.

Department of Earth Sciences Utrecht University Utrecht The Netherlands.

Some lipid-biomarker-based sea surface temperature (SST) proxies applied in the modern Mediterranean Sea exhibit large offsets from expected values, generating uncertainties in climate reconstructions. Lateral transport of proxy carriers along ocean currents prior to burial can contribute to this offset between reconstructed and expected SSTs. We perform virtual particle tracking experiments to simulate transport prior to and during sinking and derive a quantitative estimate of transport bias for alkenones and glycerol dibiphytanyl glycerol tetraethers (GDGTs), which form the basis of the U and TEX paleothermometers, respectively. We use a simple 30-day surface advection scenario and sinking speeds appropriate for the export of various proxy carriers (6, 12, 25, 50, 100, 250, 500, and 1000 md). For the assessed scenarios, lateral transport bias is generally small (always <0.85°C) within the Mediterranean Sea and does not substantially contribute to uncertainties in U - or TEX-based SSTs.
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http://dx.doi.org/10.1029/2021GL096859DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC9286692PMC
February 2022

Detrital Carbonate Minerals in Earth's Element Cycles.

Global Biogeochem Cycles 2022 May 17;36(5):e2021GB007231. Epub 2022 May 17.

Department of Earth Sciences Utrecht University Utrecht The Netherlands.

We investigate if the commonly neglected riverine detrital carbonate fluxes might reconciliate several chemical mass balances of the global ocean. Particulate inorganic carbon (PIC) concentrations in riverine suspended sediments, that is, carbon contained by these detrital carbonate minerals, were quantified at the basin and global scale. Our approach is based on globally representative data sets of riverine suspended sediment composition, catchment properties, and a two-step regression procedure. The present-day global riverine PIC flux is estimated at 3.1 ± 0.3 Tmol C/y (13% of total inorganic carbon export and 4% of total carbon export) with a flux-weighted mean concentration of 0.26 ± 0.03 wt%. The flux prior to damming was 4.1 ± 0.5 Tmol C/y. PIC fluxes are concentrated in limestone-rich, rather dry and mountainous catchments of large rivers near Arabia, South East Asia, and Europe with 2.2 Tmol C/y (67.6%) discharged between 15°N and 45°N. Greenlandic and Antarctic meltwater discharge and ice-rafting additionally contribute 0.8 ± 0.3 Tmol C/y. This amount of detrital carbonate minerals annually discharged into the ocean implies a significant contribution of calcium (∼4.75 Tmol Ca/y) and alkalinity fluxes (∼10 Tmol (eq)/y) to marine mass balances and moderate inputs of strontium (∼5 Gmol Sr/y) based on undisturbed riverine and cryospheric inputs and a dolomite/calcite ratio of 0.1. Magnesium fluxes (∼0.25 Tmol Mg/y), mostly hosted by less-soluble dolomite, are rather negligible. These unaccounted fluxes help in elucidating respective marine mass balances and potentially alter conclusions based on these budgets.
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http://dx.doi.org/10.1029/2021GB007231DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC9285522PMC
May 2022

Intraspecific variation in multiple trait responses of Alexandrium ostenfeldii towards elevated pCO.

Harmful Algae 2021 01 15;101:101970. Epub 2021 Jan 15.

Department of Aquatic Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Droevendaalsesteeg 10, 6708 PB Wageningen, Netherlands.

Dissolved oceanic CO concentrations are rising as result of increasing atmospheric partial pressure of CO (pCO), which has large consequences for phytoplankton. To test how higher CO availability affects different traits of the toxic dinoflagellate Alexandrium ostenfeldii, we exposed three strains of the same population to 400 and 1,000 µatm CO, and measured traits including growth rate, cell volume, elemental composition, C fractionation, toxin content, and volatile organic compounds (VOCs). Strains largely increased their growth rates and particulate organic carbon and nitrogen production with higher pCO and showed significant changes in their VOC profile. One strain showed a significant decrease in both PSP and cyclic imine content and thereby in cellular toxicity. Fractionation against C increased in response to elevated pCO, which may point towards enhanced CO acquisition and/or a downscaling of the carbon concentrating mechanisms. Besides consistent responses in some traits, other traits showed large variation in both direction and strength of responses towards elevated pCO. The observed intraspecific variation in phenotypic plasticity of important functional traits within the same population may help A. ostenfeldii to negate the effects of immediate environmental fluctuations and allow populations to adapt more quickly to changing environments.
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http://dx.doi.org/10.1016/j.hal.2020.101970DOI Listing
January 2021

A Warm, Stratified, and Restricted Labrador Sea Across the Middle Eocene and Its Climatic Optimum.

Paleoceanogr Paleoclimatol 2020 Oct 9;35(10):e2020PA003932. Epub 2020 Oct 9.

Department of Earth Sciences, Faculty of Geoscience Utrecht University Utrecht The Netherlands.

Several studies indicate that North Atlantic Deep Water (NADW) formation might have initiated during the globally warm Eocene (56-34 Ma). However, constraints on Eocene surface ocean conditions in source regions presently conducive to deep water formation are sparse. Here we test whether ocean conditions of the middle Eocene Labrador Sea might have allowed for deep water formation by applying (organic) geochemical and palynological techniques, on sediments from Ocean Drilling Program (ODP) Site 647. We reconstruct a long-term sea surface temperature (SST) drop from ~30°C to ~27°C between 41.5 to 38.5 Ma, based on TEX. Superimposed on this trend, we record ~2°C warming in SST associated with the Middle Eocene Climatic Optimum (MECO; ~40 Ma), which is the northernmost MECO record as yet, and another, likely regional, warming phase at ~41.1 Ma, associated with low-latitude planktic foraminifera and dinoflagellate cyst incursions. Dinoflagellate cyst assemblages together with planktonic foraminiferal stable oxygen isotope ratios overall indicate low surface water salinities and strong stratification. Benthic foraminifer stable carbon and oxygen isotope ratios differ from global deep ocean values by 1-2‰ and 2-4‰, respectively, indicating geographic basin isolation. Our multiproxy reconstructions depict a consistent picture of relatively warm and fresh but also highly variable surface ocean conditions in the middle Eocene Labrador Sea. These conditions were unlikely conducive to deep water formation. This implies either NADW did not yet form during the middle Eocene or it formed in a different source region and subsequently bypassed the southern Labrador Sea.
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http://dx.doi.org/10.1029/2020PA003932DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7590098PMC
October 2020

Millennial-Scale Climate Variability and Dinoflagellate-Cyst-Based Seasonality Changes Over the Last ~150 kyrs at "Shackleton Site" U1385.

Paleoceanogr Paleoclimatol 2019 Jul 16;34(7):1139-1156. Epub 2019 Jul 16.

Marine Palynology and Paleoceanography, Laboratory of Palaeobotany and Palynology, Department of Earth Sciences, Faculty of Geosciences Utrecht University Utrecht The Netherlands.

During the last glacial period, climate conditions in the North Atlantic region were determined by the alternation of relatively warm interstadials and relatively cool stadials, with superimposed rapid warming (Dansgaard-Oeschger) and cooling (Heinrich) events. So far little is known about the impact of these rapid climate shifts on the seasonal variations in sea surface temperature (SST) within the North Atlantic region. Here, we present a high-resolution seasonal SST record for the past 152 kyrs derived from Integrated Ocean Drilling Program "Shackleton" Site U1385, offshore Portugal. Assemblage counts of dinoflagellates cysts (dinocysts) in combination with a modern analog technique (MAT), and regression analyses were used for the reconstructions. We compare our records with previously published SST records from the same location obtained from the application of MAT on planktonic foraminifera. Our dinocyst-based reconstructions confirm the impression of the Greenland stadials and interstadials offshore the Portuguese margin and indicate increased seasonal contrast of temperature during the cold periods of the glacial cycle (average 9.0 °C, maximum 12.2 °C) with respect to present day (5.1 °C), due to strong winter cooling by up to 8.3 °C. Our seasonal temperature reconstructions are in line with previously published data, which showed increased seasonality due to strong winter cooling during the Younger Dryas and the Last Glacial Maximum over the European continent and North Atlantic region. In addition, we show that over longer time scales, increased seasonal contrasts of temperature remained characteristic of the colder phases of the glacial cycle.
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http://dx.doi.org/10.1029/2018PA003497DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6774308PMC
July 2019

Estimating regional flood discharge during Palaeocene-Eocene global warming.

Sci Rep 2018 09 6;8(1):13391. Epub 2018 Sep 6.

Department of Earth Sciences, University of Geneva, Rue des Maraîchers 13, 1205, Geneva, Switzerland.

Among the most urgent challenges in future climate change scenarios is accurately predicting the magnitude to which precipitation extremes will intensify. Analogous changes have been reported for an episode of millennial-scale 5 °C warming, termed the Palaeocene-Eocene Thermal Maximum (PETM; 56 Ma), providing independent constraints on hydrological response to global warming. However, quantifying hydrologic extremes during geologic global warming analogs has proven difficult. Here we show that water discharge increased by at least 1.35 and potentially up to 14 times during the early phase of the PETM in northern Spain. We base these estimates on analyses of channel dimensions, sediment grain size, and palaeochannel gradients across the early PETM, which is regionally marked by an abrupt transition from overbank palaeosol deposits to conglomeratic fluvial sequences. We infer that extreme floods and channel mobility quickly denuded surrounding soil-mantled landscapes, plausibly enhanced by regional vegetation decline, and exported enormous quantities of terrigenous material towards the ocean. These results support hypotheses that extreme rainfall events and associated risks of flooding increase with global warming at similar, but potentially at much higher, magnitudes than currently predicted.
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http://dx.doi.org/10.1038/s41598-018-31076-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6127139PMC
September 2018

Middle Eocene greenhouse warming facilitated by diminished weathering feedback.

Nat Commun 2018 07 23;9(1):2877. Epub 2018 Jul 23.

Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Utrecht, 3584 CB, The Netherlands.

The Middle Eocene Climatic Optimum (MECO) represents a ~500-kyr period of global warming ~40 million years ago and is associated with a rise in atmospheric CO concentrations, but the cause of this CO rise remains enigmatic. Here we show, based on osmium isotope ratios (Os/Os) of marine sediments and published records of the carbonate compensation depth (CCD), that the continental silicate weathering response to the inferred CO rise and warming was strongly diminished during the MECO-in contrast to expectations from the silicate weathering thermostat hypothesis. We surmise that global early and middle Eocene warmth gradually diminished the weatherability of continental rocks and hence the strength of the silicate weathering feedback, allowing for the prolonged accumulation of volcanic CO in the oceans and atmosphere during the MECO. These results are supported by carbon cycle modeling simulations, which highlight the fundamental importance of a variable weathering feedback strength in climate and carbon cycle interactions in Earth's history.
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http://dx.doi.org/10.1038/s41467-018-05104-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6056486PMC
July 2018

Synchronous tropical and polar temperature evolution in the Eocene.

Nature 2018 07 2;559(7714):382-386. Epub 2018 Jul 2.

Department of Earth Sciences, Faculty of Geoscience, Utrecht University, Utrecht, The Netherlands.

Palaeoclimate reconstructions of periods with warm climates and high atmospheric CO concentrations are crucial for developing better projections of future climate change. Deep-ocean and high-latitude palaeotemperature proxies demonstrate that the Eocene epoch (56 to 34 million years ago) encompasses the warmest interval of the past 66 million years, followed by cooling towards the eventual establishment of ice caps on Antarctica. Eocene polar warmth is well established, so the main obstacle in quantifying the evolution of key climate parameters, such as global average temperature change and its polar amplification, is the lack of continuous high-quality tropical temperature reconstructions. Here we present a continuous Eocene equatorial sea surface temperature record, based on biomarker palaeothermometry applied on Atlantic Ocean sediments. We combine this record with the sparse existing data to construct a 26-million-year multi-proxy, multi-site stack of Eocene tropical climate evolution. We find that tropical and deep-ocean temperatures changed in parallel, under the influence of both long-term climate trends and short-lived events. This is consistent with the hypothesis that greenhouse gas forcing, rather than changes in ocean circulation, was the main driver of Eocene climate. Moreover, we observe a strong linear relationship between tropical and deep-ocean temperatures, which implies a constant polar amplification factor throughout the generally ice-free Eocene. Quantitative comparison with fully coupled climate model simulations indicates that global average temperatures were about 29, 26, 23 and 19 degrees Celsius in the early, early middle, late middle and late Eocene, respectively, compared to the preindustrial temperature of 14.4 degrees Celsius. Finally, combining proxy- and model-based temperature estimates with available CO reconstructions yields estimates of an Eocene Earth system sensitivity of 0.9 to 2.3 kelvin per watt per square metre at 68 per cent probability, consistent with the high end of previous estimates.
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http://dx.doi.org/10.1038/s41586-018-0272-2DOI Listing
July 2018

Extreme warmth and heat-stressed plankton in the tropics during the Paleocene-Eocene Thermal Maximum.

Sci Adv 2017 Mar 3;3(3):e1600891. Epub 2017 Mar 3.

Marine Palynology and Paleoceanography, Laboratory of Palaeobotany and Palynology, Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Heidelberglaan 2, 3584CS Utrecht, Netherlands.

Global ocean temperatures rapidly warmed by ~5°C during the Paleocene-Eocene Thermal Maximum (PETM; ~56 million years ago). Extratropical sea surface temperatures (SSTs) met or exceeded modern subtropical values. With these warm extratropical temperatures, climate models predict tropical SSTs >35°C-near upper physiological temperature limits for many organisms. However, few data are available to test these projected extreme tropical temperatures or their potential lethality. We identify the PETM in a shallow marine sedimentary section deposited in Nigeria. On the basis of planktonic foraminiferal Mg/Ca and oxygen isotope ratios and the molecular proxy [Formula: see text], latest Paleocene equatorial SSTs were ~33°C, and [Formula: see text] indicates that SSTs rose to >36°C during the PETM. This confirms model predictions on the magnitude of polar amplification and refutes the tropical thermostat theory. We attribute a massive drop in dinoflagellate abundance and diversity at peak warmth to thermal stress, showing that the base of tropical food webs is vulnerable to rapid warming.
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http://dx.doi.org/10.1126/sciadv.1600891DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5336354PMC
March 2017

CO-dependent carbon isotope fractionation in dinoflagellates relates to their inorganic carbon fluxes.

J Exp Mar Biol Ecol 2016 Aug;481:9-14

Marine Biogeosciences, Alfred Wegener Institute, Helmholtz Centre for Polar- and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany.

Carbon isotope fractionation (ε) between the inorganic carbon source and organic matter has been proposed to be a function of CO. To understand the CO-dependency of ε and species-specific differences therein, inorganic carbon fluxes in the four dinoflagellate species and have been measured by means of membrane-inlet mass spectrometry. In-vivo assays were carried out at different CO concentrations, representing a range of CO from 180 to 1200 μatm. The relative bicarbonate contribution (i.e. the ratio of bicarbonate uptake to total inorganic carbon uptake) and leakage (i.e. the ratio of CO efflux to total inorganic carbon uptake) varied from 0.2 to 0.5 and 0.4 to 0.7, respectively, and differed significantly between species. These ratios were fed into a single-compartment model, and ε values were calculated and compared to carbon isotope fractionation measured under the same conditions. For all investigated species, modeled and measured ε values were comparable () and/or showed similar trends with CO (). Offsets are attributed to biases in inorganic flux measurements, an overestimated fractionation factor for the CO-fixing enzyme RubisCO, or the fact that intracellular inorganic carbon fluxes were not taken into account in the model. This study demonstrates that CO-dependency in ε can largely be explained by the inorganic carbon fluxes of the individual dinoflagellates.
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http://dx.doi.org/10.1016/j.jembe.2016.04.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5268352PMC
August 2016

Thermogenic methane release as a cause for the long duration of the PETM.

Proc Natl Acad Sci U S A 2016 10 10;113(43):12059-12064. Epub 2016 Oct 10.

Marine Palynology and Paleoceanography, Laboratory of Palaeobotany and Palynology, Department of Earth Sciences, Faculty of Geosciences, Utrecht University, 3584CS Utrecht, The Netherlands.

The Paleocene-Eocene Thermal Maximum (PETM) (∼56 Ma) was a ∼170,000-y (∼170-kyr) period of global warming associated with rapid and massive injections of C-depleted carbon into the ocean-atmosphere system, reflected in sedimentary components as a negative carbon isotope excursion (CIE). Carbon cycle modeling has indicated that the shape and magnitude of this CIE are generally explained by a large and rapid initial pulse, followed by ∼50 kyr of C-depleted carbon injection. Suggested sources include submarine methane hydrates, terrigenous organic matter, and thermogenic methane and CO from hydrothermal vent complexes. Here, we test for the contribution of carbon release associated with volcanic intrusions in the North Atlantic Igneous Province. We use dinoflagellate cyst and stable carbon isotope stratigraphy to date the active phase of a hydrothermal vent system and find it to postdate massive carbon release at the onset of the PETM. Crucially, however, it correlates to the period within the PETM of longer-term C-depleted carbon release. This finding represents actual proof of PETM carbon release from a particular reservoir. Based on carbon cycle box model [i.e., Long-Term Ocean-Atmosphere-Sediment Carbon Cycle Reservoir (LOSCAR) model] experiments, we show that 4-12 pulses of carbon input from vent systems over 60 kyr with a total mass of 1,500 Pg of C, consistent with the vent literature, match the shape of the CIE and pattern of deep ocean carbonate dissolution as recorded in sediment records. We therefore conclude that CH from the Norwegian Sea vent complexes was likely the main source of carbon during the PETM, following its dramatic onset.
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http://dx.doi.org/10.1073/pnas.1603348113DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5087067PMC
October 2016

Stable carbon isotope analyses of nanogram quantities of particulate organic carbon (pollen) with laser ablation nano combustion gas chromatography/isotope ratio mass spectrometry.

Rapid Commun Mass Spectrom 2017 Jan;31(1):47-58

Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Heidelberglaan 2, 3584 CS Utrecht, The Netherlands.

Rationale: Analyses of stable carbon isotope ratios (δ C values) of organic and inorganic matter remains have been instrumental for much of our understanding of present and past environmental and biological processes. Until recently, the analytical window of such analyses has been limited to samples containing at least several μg of carbon.

Methods: Here we present a setup combining laser ablation, nano combustion gas chromatography and isotope ratio mass spectrometry (LA/nC/GC/IRMS). A deep UV (193 nm) laser is used for optimal fragmentation of organic matter with minimum fractionation effects and an exceptionally small ablation chamber and combustion oven are used to reduce the minimum sample mass requirement compared with previous studies.

Results: Analyses of the international IAEA CH-7 polyethylene standard show optimal accuracy, and precision better than 0.5‰, when measuring at least 42 ng C. Application to untreated modern Eucalyptus globulus (C plant) and Zea mays (C plant) pollen grains shows a ~ 16‰ offset between these species. Within each single Z. mays pollen grain, replicate analyses show almost identical δ C values.

Conclusions: Isotopic offsets between individual pollen grains exceed analytical uncertainties, therefore probably reflecting interspecimen variability of ~0.5-0.9‰. These promising results set the stage for investigating both δ C values and natural carbon isotopic variability between single specimens of a single population of all kinds of organic particles yielding tens of nanograms of carbon. © 2016 The Authors. Rapid Communications in Mass Spectrometry Published by John Wiley & Sons Ltd.
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http://dx.doi.org/10.1002/rcm.7769DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5132107PMC
January 2017

Combined Effects of Ocean Acidification and Light or Nitrogen Availabilities on 13C Fractionation in Marine Dinoflagellates.

PLoS One 2016 6;11(5):e0154370. Epub 2016 May 6.

Department of Aquatic Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, The Netherlands.

Along with increasing oceanic CO2 concentrations, enhanced stratification constrains phytoplankton to shallower upper mixed layers with altered light regimes and nutrient concentrations. Here, we investigate the effects of elevated pCO2 in combination with light or nitrogen-limitation on 13C fractionation (εp) in four dinoflagellate species. We cultured Gonyaulax spinifera and Protoceratium reticulatum in dilute batches under low-light ('LL') and high-light ('HL') conditions, and grew Alexandrium fundyense and Scrippsiella trochoidea in nitrogen-limited continuous cultures ('LN') and nitrogen-replete batches ('HN'). The observed CO2-dependency of εp remained unaffected by the availability of light for both G. spinifera and P. reticulatum, though at HL εp was consistently lower by about 2.7‰ over the tested CO2 range for P. reticulatum. This may reflect increased uptake of (13C-enriched) bicarbonate fueled by increased ATP production under HL conditions. The observed CO2-dependency of εp disappeared under LN conditions in both A. fundyense and S. trochoidea. The generally higher εp under LN may be associated with lower organic carbon production rates and/or higher ATP:NADPH ratios. CO2-dependent εp under non-limiting conditions has been observed in several dinoflagellate species, showing potential for a new CO2-proxy. Our results however demonstrate that light- and nitrogen-limitation also affect εp, thereby illustrating the need to carefully consider prevailing environmental conditions.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0154370PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4859495PMC
July 2017

Lessons on Climate Sensitivity From Past Climate Changes.

Curr Clim Change Rep 2016 20;2(4):148-158. Epub 2016 Oct 20.

24Department of Earth Sciences, Utrecht University, PO Box 80.021, 3508 TA Utrecht, The Netherlands.

Over the last decade, our understanding of climate sensitivity has improved considerably. The climate system shows variability on many timescales, is subject to non-stationary forcing and it is most likely out of equilibrium with the changes in the radiative forcing. Slow and fast feedbacks complicate the interpretation of geological records as feedback strengths vary over time. In the geological past, the forcing timescales were different than at present, suggesting that the response may have behaved differently. Do these insights constrain the climate sensitivity relevant for the present day? In this paper, we review the progress made in theoretical understanding of climate sensitivity and on the estimation of climate sensitivity from proxy records. Particular focus lies on the background state dependence of feedback processes and on the impact of tipping points on the climate system. We suggest how to further use palaeo data to advance our understanding of the currently ongoing climate change.
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http://dx.doi.org/10.1007/s40641-016-0049-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6979625PMC
October 2016

A Paleolatitude Calculator for Paleoclimate Studies.

PLoS One 2015 10;10(6):e0126946. Epub 2015 Jun 10.

Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands; Royal Netherlands Institute for Sea Research (NIOZ), Den Burg, The Netherlands.

Realistic appraisal of paleoclimatic information obtained from a particular location requires accurate knowledge of its paleolatitude defined relative to the Earth's spin-axis. This is crucial to, among others, correctly assess the amount of solar energy received at a location at the moment of sediment deposition. The paleolatitude of an arbitrary location can in principle be reconstructed from tectonic plate reconstructions that (1) restore the relative motions between plates based on (marine) magnetic anomalies, and (2) reconstruct all plates relative to the spin axis using a paleomagnetic reference frame based on a global apparent polar wander path. Whereas many studies do employ high-quality relative plate reconstructions, the necessity of using a paleomagnetic reference frame for climate studies rather than a mantle reference frame appears under-appreciated. In this paper, we briefly summarize the theory of plate tectonic reconstructions and their reference frames tailored towards applications of paleoclimate reconstruction, and show that using a mantle reference frame, which defines plate positions relative to the mantle, instead of a paleomagnetic reference frame may introduce errors in paleolatitude of more than 15° (>1500 km). This is because mantle reference frames cannot constrain, or are specifically corrected for the effects of true polar wander. We used the latest, state-of-the-art plate reconstructions to build a global plate circuit, and developed an online, user-friendly paleolatitude calculator for the last 200 million years by placing this plate circuit in three widely used global apparent polar wander paths. As a novelty, this calculator adds error bars to paleolatitude estimates that can be incorporated in climate modeling. The calculator is available at www.paleolatitude.org. We illustrate the use of the paleolatitude calculator by showing how an apparent wide spread in Eocene sea surface temperatures of southern high latitudes may be in part explained by a much wider paleolatitudinal distribution of sites than previously assumed.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0126946PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4462584PMC
March 2016

Rapid short-term cooling following the Chicxulub impact at the Cretaceous-Paleogene boundary.

Proc Natl Acad Sci U S A 2014 May 12;111(21):7537-41. Epub 2014 May 12.

Marine Palynology, Department of Earth Sciences, Faculty of Geosciences, Laboratory of Palaeobotany and Palynology, Utrecht University, 3584 CD, Utrecht, The Netherlands;

The mass extinction at the Cretaceous-Paleogene boundary, ∼ 66 Ma, is thought to be caused by the impact of an asteroid at Chicxulub, present-day Mexico. Although the precise mechanisms that led to this mass extinction remain enigmatic, most postulated scenarios involve a short-lived global cooling, a so-called "impact winter" phase. Here we document a major decline in sea surface temperature during the first months to decades following the impact event, using TEX86 paleothermometry of sediments from the Brazos River section, Texas. We interpret this cold spell to reflect, to our knowledge, the first direct evidence for the effects of the formation of dust and aerosols by the impact and their injection in the stratosphere, blocking incoming solar radiation. This impact winter was likely a major driver of mass extinction because of the resulting global decimation of marine and continental photosynthesis.
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http://dx.doi.org/10.1073/pnas.1319253111DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4040585PMC
May 2014

Pronounced zonal heterogeneity in Eocene southern high-latitude sea surface temperatures.

Proc Natl Acad Sci U S A 2014 May 21;111(18):6582-7. Epub 2014 Apr 21.

Department of Geology and Geophysics, Yale University, New Haven, CT 06520.

Paleoclimate studies suggest that increased global warmth during the Eocene epoch was greatly amplified at high latitudes, a state that climate models cannot fully reproduce. However, proxy estimates of Eocene near-Antarctic sea surface temperatures (SSTs) have produced widely divergent results at similar latitudes, with SSTs above 20 °C in the southwest Pacific contrasting with SSTs between 5 and 15 °C in the South Atlantic. Validation of this zonal temperature difference has been impeded by uncertainties inherent to the individual paleotemperature proxies applied at these sites. Here, we present multiproxy data from Seymour Island, near the Antarctic Peninsula, that provides well-constrained evidence for annual SSTs of 10-17 °C (1σ SD) during the middle and late Eocene. Comparison of the same paleotemperature proxy at Seymour Island and at the East Tasman Plateau indicate the presence of a large and consistent middle-to-late Eocene SST gradient of ∼7 °C between these two sites located at similar paleolatitudes. Intermediate-complexity climate model simulations suggest that enhanced oceanic heat transport in the South Pacific, driven by deep-water formation in the Ross Sea, was largely responsible for the observed SST gradient. These results indicate that very warm SSTs, in excess of 18 °C, did not extend uniformly across the Eocene southern high latitudes, and suggest that thermohaline circulation may partially control the distribution of high-latitude ocean temperatures in greenhouse climates. The pronounced zonal SST heterogeneity evident in the Eocene cautions against inferring past meridional temperature gradients using spatially limited data within given latitudinal bands.
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http://dx.doi.org/10.1073/pnas.1321441111DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4020054PMC
May 2014

Plate tectonic controls on atmospheric CO2 levels since the Triassic.

Proc Natl Acad Sci U S A 2014 Mar 10;111(12):4380-5. Epub 2014 Mar 10.

Department of Earth Sciences, Utrecht University, 3584 CD, Utrecht, The Netherlands.

Climate trends on timescales of 10s to 100s of millions of years are controlled by changes in solar luminosity, continent distribution, and atmosphere composition. Plate tectonics affect geography, but also atmosphere composition through volcanic degassing of CO2 at subduction zones and midocean ridges. So far, such degassing estimates were based on reconstructions of ocean floor production for the last 150 My and indirectly, through sea level inversion before 150 My. Here we quantitatively estimate CO2 degassing by reconstructing lithosphere subduction evolution, using recent advances in combining global plate reconstructions and present-day structure of the mantle. First, we estimate that since the Triassic (250-200 My) until the present, the total paleosubduction-zone length reached up to ∼200% of the present-day value. Comparing our subduction-zone lengths with previously reconstructed ocean-crust production rates over the past 140 My suggests average global subduction rates have been constant, ∼6 cm/y: Higher ocean-crust production is associated with longer total subduction length. We compute a strontium isotope record based on subduction-zone length, which agrees well with geological records supporting the validity of our approach: The total subduction-zone length is proportional to the summed arc and ridge volcanic CO2 production and thereby to global volcanic degassing at plate boundaries. We therefore use our degassing curve as input for the GEOCARBSULF model to estimate atmospheric CO2 levels since the Triassic. Our calculated CO2 levels for the mid Mesozoic differ from previous modeling results and are more consistent with available proxy data.
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http://dx.doi.org/10.1073/pnas.1315657111DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3970481PMC
March 2014

Onset of carbon isotope excursion at the Paleocene-Eocene thermal maximum took millennia, not 13 years.

Proc Natl Acad Sci U S A 2014 Mar 26;111(12):E1062-3. Epub 2014 Feb 26.

Department of Oceanography, School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, HI 96822.

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http://dx.doi.org/10.1073/pnas.1321177111DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3970517PMC
March 2014

Ocean acidification reduces growth and calcification in a marine dinoflagellate.

PLoS One 2013 11;8(6):e65987. Epub 2013 Jun 11.

Marine Biogeosciences, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany.

Ocean acidification is considered a major threat to marine ecosystems and may particularly affect calcifying organisms such as corals, foraminifera and coccolithophores. Here we investigate the impact of elevated pCO2 and lowered pH on growth and calcification in the common calcareous dinoflagellate Thoracosphaera heimii. We observe a substantial reduction in growth rate, calcification and cyst stability of T. heimii under elevated pCO2. Furthermore, transcriptomic analyses reveal CO2 sensitive regulation of many genes, particularly those being associated to inorganic carbon acquisition and calcification. Stable carbon isotope fractionation for organic carbon production increased with increasing pCO2 whereas it decreased for calcification, which suggests interdependence between both processes. We also found a strong effect of pCO2 on the stable oxygen isotopic composition of calcite, in line with earlier observations concerning another T. heimii strain. The observed changes in stable oxygen and carbon isotope composition of T. heimii cysts may provide an ideal tool for reconstructing past seawater carbonate chemistry, and ultimately past pCO2. Although the function of calcification in T. heimii remains unresolved, this trait likely plays an important role in the ecological and evolutionary success of this species. Acting on calcification as well as growth, ocean acidification may therefore impose a great threat for T. heimii.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0065987PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3679017PMC
January 2014

Eocene cooling linked to early flow across the Tasmanian Gateway.

Proc Natl Acad Sci U S A 2013 Jun 29;110(24):9645-50. Epub 2013 May 29.

Department of Earth Sciences, Faculty of Geosciences, Utrecht University, 3584 CD Utrecht, The Netherlands.

The warmest global temperatures of the past 85 million years occurred during a prolonged greenhouse episode known as the Early Eocene Climatic Optimum (52-50 Ma). The Early Eocene Climatic Optimum terminated with a long-term cooling trend that culminated in continental-scale glaciation of Antarctica from 34 Ma onward. Whereas early studies attributed the Eocene transition from greenhouse to icehouse climates to the tectonic opening of Southern Ocean gateways, more recent investigations invoked a dominant role of declining atmospheric greenhouse gas concentrations (e.g., CO2). However, the scarcity of field data has prevented empirical evaluation of these hypotheses. We present marine microfossil and organic geochemical records spanning the early-to-middle Eocene transition from the Wilkes Land Margin, East Antarctica. Dinoflagellate biogeography and sea surface temperature paleothermometry reveal that the earliest throughflow of a westbound Antarctic Counter Current began ~49-50 Ma through a southern opening of the Tasmanian Gateway. This early opening occurs in conjunction with the simultaneous onset of regional surface water and continental cooling (2-4 °C), evidenced by biomarker- and pollen-based paleothermometry. We interpret that the westbound flowing current flow across the Tasmanian Gateway resulted in cooling of Antarctic surface waters and coasts, which was conveyed to global intermediate waters through invigorated deep convection in southern high latitudes. Although atmospheric CO2 forcing alone would provide a more uniform middle Eocene cooling, the opening of the Tasmanian Gateway better explains Southern Ocean surface water and global deep ocean cooling in the apparent absence of (sub-) equatorial cooling.
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http://dx.doi.org/10.1073/pnas.1220872110DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3683727PMC
June 2013

Reorganization of Southern Ocean plankton ecosystem at the onset of Antarctic glaciation.

Science 2013 Apr;340(6130):341-4

Department of Earth Sciences, Laboratory of Palaeobotany and Palynology, Faculty of Geosciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, Netherlands.

The circum-Antarctic Southern Ocean is an important region for global marine food webs and carbon cycling because of sea-ice formation and its unique plankton ecosystem. However, the mechanisms underlying the installation of this distinct ecosystem and the geological timing of its development remain unknown. Here, we show, on the basis of fossil marine dinoflagellate cyst records, that a major restructuring of the Southern Ocean plankton ecosystem occurred abruptly and concomitant with the first major Antarctic glaciation in the earliest Oligocene (~33.6 million years ago). This turnover marks a regime shift in zooplankton-phytoplankton interactions and community structure, which indicates the appearance of eutrophic and seasonally productive environments on the Antarctic margin. We conclude that earliest Oligocene cooling, ice-sheet expansion, and subsequent sea-ice formation were important drivers of biotic evolution in the Southern Ocean.
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http://dx.doi.org/10.1126/science.1223646DOI Listing
April 2013

A Cenozoic record of the equatorial Pacific carbonate compensation depth.

Nature 2012 Aug;488(7413):609-14

Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, Waterfront Campus, European Way, Southampton SO14 3ZH, UK.

Atmospheric carbon dioxide concentrations and climate are regulated on geological timescales by the balance between carbon input from volcanic and metamorphic outgassing and its removal by weathering feedbacks; these feedbacks involve the erosion of silicate rocks and organic-carbon-bearing rocks. The integrated effect of these processes is reflected in the calcium carbonate compensation depth, which is the oceanic depth at which calcium carbonate is dissolved. Here we present a carbonate accumulation record that covers the past 53 million years from a depth transect in the equatorial Pacific Ocean. The carbonate compensation depth tracks long-term ocean cooling, deepening from 3.0-3.5 kilometres during the early Cenozoic (approximately 55 million years ago) to 4.6 kilometres at present, consistent with an overall Cenozoic increase in weathering. We find large superimposed fluctuations in carbonate compensation depth during the middle and late Eocene. Using Earth system models, we identify changes in weathering and the mode of organic-carbon delivery as two key processes to explain these large-scale Eocene fluctuations of the carbonate compensation depth.
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http://dx.doi.org/10.1038/nature11360DOI Listing
August 2012

The geological record of ocean acidification.

Science 2012 Mar;335(6072):1058-63

Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964, USA.

Ocean acidification may have severe consequences for marine ecosystems; however, assessing its future impact is difficult because laboratory experiments and field observations are limited by their reduced ecologic complexity and sample period, respectively. In contrast, the geological record contains long-term evidence for a variety of global environmental perturbations, including ocean acidification plus their associated biotic responses. We review events exhibiting evidence for elevated atmospheric CO(2), global warming, and ocean acidification over the past ~300 million years of Earth's history, some with contemporaneous extinction or evolutionary turnover among marine calcifiers. Although similarities exist, no past event perfectly parallels future projections in terms of disrupting the balance of ocean carbonate chemistry-a consequence of the unprecedented rapidity of CO(2) release currently taking place.
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http://dx.doi.org/10.1126/science.1208277DOI Listing
March 2012

Transient Middle Eocene atmospheric CO₂ and temperature variations.

Science 2010 Nov;330(6005):819-21

Biomarine Sciences, Institute of Environmental Biology, Faculty of Science, Laboratory of Palaeobotany and Palynology, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, Netherlands.

The long-term warmth of the Eocene (~56 to 34 million years ago) is commonly associated with elevated partial pressure of atmospheric carbon dioxide (pCO(2)). However, a direct relationship between the two has not been established for short-term climate perturbations. We reconstructed changes in both pCO(2) and temperature over an episode of transient global warming called the Middle Eocene Climatic Optimum (MECO; ~40 million years ago). Organic molecular paleothermometry indicates a warming of southwest Pacific sea surface temperatures (SSTs) by 3° to 6°C. Reconstructions of pCO(2) indicate a concomitant increase by a factor of 2 to 3. The marked consistency between SST and pCO(2) trends during the MECO suggests that elevated pCO(2) played a major role in global warming during the MECO.
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http://dx.doi.org/10.1126/science.1193654DOI Listing
November 2010

Early Palaeogene temperature evolution of the southwest Pacific Ocean.

Nature 2009 Oct;461(7265):776-9

Palaeoecology, Institute of Environmental Biology, Faculty of Science, Laboratory of Palaeobotany and Palynology, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, The Netherlands.

Relative to the present day, meridional temperature gradients in the Early Eocene age ( approximately 56-53 Myr ago) were unusually low, with slightly warmer equatorial regions but with much warmer subtropical Arctic and mid-latitude climates. By the end of the Eocene epoch ( approximately 34 Myr ago), the first major Antarctic ice sheets had appeared, suggesting that major cooling had taken place. Yet the global transition into this icehouse climate remains poorly constrained, as only a few temperature records are available portraying the Cenozoic climatic evolution of the high southern latitudes. Here we present a uniquely continuous and chronostratigraphically well-calibrated TEX(86) record of sea surface temperature (SST) from an ocean sediment core in the East Tasman Plateau (palaeolatitude approximately 65 degrees S). We show that southwest Pacific SSTs rose above present-day tropical values (to approximately 34 degrees C) during the Early Eocene age ( approximately 53 Myr ago) and had gradually decreased to about 21 degrees C by the early Late Eocene age ( approximately 36 Myr ago). Our results imply that there was almost no latitudinal SST gradient between subequatorial and subpolar regions during the Early Eocene age (55-50 Myr ago). Thereafter, the latitudinal gradient markedly increased. In theory, if Eocene cooling was largely driven by a decrease in atmospheric greenhouse gas concentration, additional processes are required to explain the relative stability of tropical SSTs given that there was more significant cooling at higher latitudes.
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http://dx.doi.org/10.1038/nature08399DOI Listing
October 2009

Environmental precursors to rapid light carbon injection at the Palaeocene/Eocene boundary.

Nature 2007 Dec;450(7173):1218-21

Palaeoecology, Institute of Environmental Biology, Utrecht University, Laboratory of Palaeobotany and Palynology, Utrecht, The Netherlands.

The start of the Palaeocene/Eocene thermal maximum--a period of exceptional global warming about 55 million years ago--is marked by a prominent negative carbon isotope excursion that reflects a massive input of 13C-depleted ('light') carbon to the ocean-atmosphere system. It is often assumed that this carbon injection initiated the rapid increase in global surface temperatures and environmental change that characterize the climate perturbation, but the exact sequence of events remains uncertain. Here we present chemical and biotic records of environmental change across the Palaeocene/Eocene boundary from two sediment sections in New Jersey that have high sediment accumulation rates. We show that the onsets of environmental change (as recorded by the abundant occurrence ('acme') of the dinoflagellate cyst Apectodinium) and of surface-ocean warming (as evidenced by the palaeothermometer TEX86) preceded the light carbon injection by several thousand years. The onset of the Apectodinium acme also precedes the carbon isotope excursion in sections from the southwest Pacific Ocean and the North Sea, indicating that the early onset of environmental change was not confined to the New Jersey shelf. The lag of approximately 3,000 years between the onset of warming in New Jersey shelf waters and the carbon isotope excursion is consistent with the hypothesis that bottom water warming caused the injection of 13C-depleted carbon by triggering the dissociation of submarine methane hydrates, but the cause of the early warming remains uncertain.
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http://dx.doi.org/10.1038/nature06400DOI Listing
December 2007

Arctic hydrology during global warming at the Palaeocene/Eocene thermal maximum.

Nature 2006 Aug;442(7103):671-5

Department of Geology and Geophysics, Yale University, PO Box 208109, New Haven, Connecticut 06520, USA.

The Palaeocene/Eocene thermal maximum represents a period of rapid, extreme global warming 55 million years ago, superimposed on an already warm world. This warming is associated with a severe shoaling of the ocean calcite compensation depth and a >2.5 per mil negative carbon isotope excursion in marine and soil carbonates. Together these observations indicate a massive release of 13C-depleted carbon and greenhouse-gas-induced warming. Recently, sediments were recovered from the central Arctic Ocean, providing the first opportunity to evaluate the environmental response at the North Pole at this time. Here we present stable hydrogen and carbon isotope measurements of terrestrial-plant- and aquatic-derived n-alkanes that record changes in hydrology, including surface water salinity and precipitation, and the global carbon cycle. Hydrogen isotope records are interpreted as documenting decreased rainout during moisture transport from lower latitudes and increased moisture delivery to the Arctic at the onset of the Palaeocene/Eocene thermal maximum, consistent with predictions of poleward storm track migrations during global warming. The terrestrial-plant carbon isotope excursion (about -4.5 to -6 per mil) is substantially larger than those of marine carbonates. Previously, this offset was explained by the physiological response of plants to increases in surface humidity. But this mechanism is not an effective explanation in this wet Arctic setting, leading us to hypothesize that the true magnitude of the excursion--and associated carbon input--was greater than originally surmised. Greater carbon release and strong hydrological cycle feedbacks may help explain the maintenance of this unprecedented warmth.
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http://dx.doi.org/10.1038/nature05043DOI Listing
August 2006

Subtropical Arctic Ocean temperatures during the Palaeocene/Eocene thermal maximum.

Nature 2006 Jun;441(7093):610-3

Palaeoecology, Institute of Environmental Biology, Utrecht University, Laboratory of Palaeobotany and Palynology, Budapestlaan 4, 3584 CD Utrecht, The Netherlands.

The Palaeocene/Eocene thermal maximum, approximately 55 million years ago, was a brief period of widespread, extreme climatic warming, that was associated with massive atmospheric greenhouse gas input. Although aspects of the resulting environmental changes are well documented at low latitudes, no data were available to quantify simultaneous changes in the Arctic region. Here we identify the Palaeocene/Eocene thermal maximum in a marine sedimentary sequence obtained during the Arctic Coring Expedition. We show that sea surface temperatures near the North Pole increased from 18 degrees C to over 23 degrees C during this event. Such warm values imply the absence of ice and thus exclude the influence of ice-albedo feedbacks on this Arctic warming. At the same time, sea level rose while anoxic and euxinic conditions developed in the ocean's bottom waters and photic zone, respectively. Increasing temperature and sea level match expectations based on palaeoclimate model simulations, but the absolute polar temperatures that we derive before, during and after the event are more than 10 degrees C warmer than those model-predicted. This suggests that higher-than-modern greenhouse gas concentrations must have operated in conjunction with other feedback mechanisms--perhaps polar stratospheric clouds or hurricane-induced ocean mixing--to amplify early Palaeogene polar temperatures.
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http://dx.doi.org/10.1038/nature04668DOI Listing
June 2006
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