29 results on '"Rick Hennekam"'
Search Results
2. Intercomparison of XRF Core Scanning Results From Seven Labs and Approaches to Practical Calibration
- Author
-
Ann G. Dunlea, Richard W. Murray, Ryuji Tada, Carlos A. Alvarez‐Zarikian, Chloe H. Anderson, Adrian Gilli, Liviu Giosan, Thomas Gorgas, Rick Hennekam, Tomohisa Irino, Masafumi Murayama, Larry C. Peterson, Gert‐Jan Reichart, Arisa Seki, Hongbo Zheng, and Martin Ziegler
- Subjects
XRF scanning ,quantitative XRF ,paleoceanography ,sedimentary geochemistry ,XRF calibration ,XRF intercomparison ,Geophysics. Cosmic physics ,QC801-809 ,Geology ,QE1-996.5 - Abstract
Abstract X‐ray fluorescence (XRF) scanning of marine sediment has the potential to yield near‐continuous and high‐resolution records of elemental abundances, which are often interpreted as proxies for paleoceanographic processes over different time scales. However, many other variables also affect scanning XRF measurements and convolute the quantitative calibrations of element abundances and comparisons of data from different labs. Extensive interlab comparisons of XRF scanning results and calibrations are essential to resolve ambiguities and to understand the best way to interpret the data produced. For this study, we sent a set of seven marine sediment sections (1.5 m each) to be scanned by seven XRF facilities around the world to compare the outcomes amidst a myriad of factors influencing the results. Results of raw element counts per second (cps) were different between labs, but element ratios were more comparable. Four of the labs also scanned a set of homogenized sediment pellets with compositions determined by inductively coupled plasma‐optical emission spectrometry (ICP‐OES) and ICP‐mass spectrometry (MS) to convert the raw XRF element cps to concentrations in two ways: a linear calibration and a log‐ratio calibration. Although both calibration curves are well fit, the results show that the log‐ratio calibrated data are significantly more comparable between labs than the linearly calibrated data. Smaller‐scale (higher‐resolution) features are often not reproducible between the different scans and should be interpreted with caution. Along with guidance on practical calibrations, our study recommends best practices to increase the quality of information that can be derived from scanning XRF to benefit the field of paleoceanography.
- Published
- 2020
- Full Text
- View/download PDF
3. Alkenone Distributions and Hydrogen Isotope Ratios Show Changes in Haptophyte Species and Source Water in the Holocene Baltic Sea
- Author
-
Gabriella M. Weiss, Barbara Massalska, Rick Hennekam, Gert‐Jan Reichart, Jaap S. Sinninghe Damsté, Stefan Schouten, and Marcel T. J. van derMeer
- Subjects
hydrogen isotopes ,alkenones ,haptophytes ,Baltic Sea ,Geophysics. Cosmic physics ,QC801-809 ,Geology ,QE1-996.5 - Abstract
Abstract The Baltic Sea, a dynamic, marginal marine basin, experienced a number of large changes in salinity during the Holocene as a result of fluctuations in global and local sea level related to melting of glacial ice sheets and subsequent isostatic rebound. These changes likely had pronounced effects on the species composition of haptophytes, a common phytoplankton group found in the Baltic Sea. This dynamic environment provides the ideal setting to study how species change impacts distribution and hydrogen isotope ratios of long‐chain alkenones (δ2HC37), haptophyte‐specific biomarkers. Here we analyzed the aforementioned parameters in Holocene sediments covering the contrasting hydrological phases of the Baltic Sea. Alkenone distributions changed with different Baltic Sea salinity phases, suggesting that species shifts coincide with salinity change. δ2HC37 values show two major shifts: one in the middle of the freshwater Ancylus Lake phase (10.6 to 7.7 ka) and a second at the transition from the brackish Littorina Sea phase (7.2 to 3 ka) into the fresher Modern Baltic (3 ka to the present). The first shift represents a significant enrichment of 50‰, which cannot be explained by salinity or species changes only. At this time, the isotopically depleted ice sheets had melted, and only the relatively enriched freshwater source remained. The second shift, coincident with a change in distribution, is likely caused by a change in species composition alone. These findings show that hydrogen isotope ratios of long‐chain alkenones, combined with their relative distribution, can be used to reconstruct changes in source water.
- Published
- 2020
- Full Text
- View/download PDF
4. Author Correction: Organic carbon burial in Mediterranean sapropels intensified during Green Sahara Periods since 3.2 Myr ago
- Author
-
Katharine M. Grant, Udara Amarathunga, Jessica D. Amies, Pengxiang Hu, Yao Qian, Tiah Penny, Laura Rodriguez-Sanz, Xiang Zhao, David Heslop, Diederik Liebrand, Rick Hennekam, Thomas Westerhold, Stewart Gilmore, Lucas J. Lourens, Andrew P. Roberts, and Eelco J. Rohling
- Subjects
Geology ,QE1-996.5 ,Environmental sciences ,GE1-350 - Published
- 2022
- Full Text
- View/download PDF
5. Precessional pacing of early Proterozoic redox cycles
- Author
-
Margriet L. Lantink, Wytze K. Lenstra, Joshua H.F.L. Davies, Rick Hennekam, David McB. Martin, Paul R.D. Mason, Gert-Jan Reichart, Caroline P. Slomp, Frederik J. Hilgen, Stratigraphy and paleontology, Geochemistry, Petrology, and Stratigraphy & paleontology
- Subjects
Geophysics ,oceanic redox cycles ,Space and Planetary Science ,Geochemistry and Petrology ,Ecological Microbiology ,Earth and Planetary Sciences (miscellaneous) ,banded iron formations ,Great Oxidation Event ,Milankovitch climate forcing - Abstract
Regularly alternating reduction-oxidation (redox) patterns attributed to variations in the Earth's orbit and axis (Milankovitch cycles) are widely recorded in marine sediment successions of the Phanerozoic and attest to a dynamic history of biospheric oxygen in response to astronomically forced climate change. To date, however, such astronomical redox control remains elusive for much older, Precambrian intervals of the geological record that were characterized by a globally anoxic and iron-rich ocean, i.e., prior to Earth's atmospheric oxygenation (ca. 2.4–2.2 billion years ago). Here we report a detailed cyclostratigraphic and geochemical investigation of marine-sedimentary redox cycles identified in the ca. 2.46 billion-year-old Joffre Member of the Brockman Iron Formation, NW Australia, suggesting the imprint of Earth's climatic precession cycle. Around the base and top of regularly intercalated mudrock layers, we identify sharp enrichments in redox sensitive elements (Fe, S, Ca, P) that appear to represent chemical reaction fronts formed during nonsteady state diagenesis. Using a reactive transport model, we find that the formation of characteristic double S peaks required periods of increased organic matter deposition, coupled to strongly declining Fe2+ concentrations in the overlying water column. This combination, in turn, implies a periodic deepening of the iron chemocline due to enhanced oxygenic photosynthesis in marine surface waters, and is interpreted as the result of precession-induced changes in monsoonal intensity that drove variations in runoff and associated nutrient delivery. Our study results point to a dynamic redox evolution of Precambrian oceanic margin environments in response to Milankovitch forcing, and offer a temporal framework to investigate linkages between biological activity and the early build-up of oxygen in Earth's ocean-atmosphere system.
- Published
- 2023
6. A 5-million-year record of (de)oxygenation and associated changes in basin restriction in the Mediterranean Sea
- Author
-
Isabel van der Hoeven, Katharine Grant, Eelco Rohling, Diederik Liebrand, Lucas Lourens, Gert-Jan Reichart, and Rick Hennekam
- Abstract
Restricted basins are susceptible to develop anoxia because these land-locked basins can trap nutrients and the water column can easily become stratified. The Mediterranean basin has a limited connection to the open ocean and became increasingly restricted over time, making it suitable to study effect of basin configuration on anoxia development. Enhanced runoff, related to increased North-African monsoon intensity, regularly resulted in increased productivity and/or deep-water anoxia and deposition of organic-rich sediments, the so-called sapropels. Most depositional models for sapropel formation focus on the most recent sapropels (e.g. S1 and S5), outcrop samples or individual Pliocene sapropels from ODP leg 160. Until recently, continuous and high-resolution records were lacking, whereas such records can provide important constraints on the relationship between sapropel deposition and its environmental driving forces, such as climate and basin configuration. Here we present newly acquired XRF-scanning data of redox-sensitive trace elements and estimates for total organic carbon (TOC) from a 5 Myr record of the Eastern Mediterranean Sea (ODP Site 967), where reoccurring sapropels are recorded from 3.2 Ma onwards. Based on our geochemical proxies, we reconstruct (de)oxygenation and associated basin restriction over the last 5 Myr. This record allows us to elucidate which primary processes drove sapropel formation in this basin and whether these processes changed over time. We show that the first preserved Pliocene sapropels (~3.2-3.0 Ma) are highly enriched in redox-sensitive trace elements and have TOC values up to 25%, and likely formed in a much more open (i.e. with increased water renewal) depositional environment. Such a model of Mediterranean sapropel deposition differs significantly from that of the more recent sapropels, which are deposited in a much more restricted environment. Hence, the depositional model for recent sapropel formation cannot be directly extrapolated to these older sapropel deposits.
- Published
- 2023
- Full Text
- View/download PDF
7. Reply on RC2
- Author
-
Rick Hennekam
- Published
- 2022
- Full Text
- View/download PDF
8. Co-variation systematics of uranium and molybdenum isotopes reveal pathways for descent into euxinia in Mediterranean sapropels
- Author
-
Chun Fung Chiu, Tim C. Sweere, Matthew O. Clarkson, Gregory F. de Souza, Rick Hennekam, and Derek Vance
- Subjects
molybdenum isotopes ,Geophysics ,sapropels ,Space and Planetary Science ,Geochemistry and Petrology ,redox ,Eastern Mediterranean ,Earth and Planetary Sciences (miscellaneous) ,uranium isotopes - Abstract
The elemental concentrations and isotope compositions of molybdenum (Mo) and uranium (U) are commonly used for the reconstruction of past global and local redox conditions, and recent studies using both elements have revealed the potential of their paired application. However, such studies have generally focused either on modern marine sediments or on relatively low-resolution reconstructions of deep-time paleo-redox conditions. Here, we present high-resolution profiles (every 0.2-0.3 kyr) of Mo and U elemental and isotope compositions for anoxic organic-rich sediments of Eastern Mediterranean sapropels S5 and S7. The new Mo-U data reveal the processes leading to descent into basinal euxinia in more precise and systematic detail than lower resolution datasets focused on either Mo or U only. During the intensification from anoxic non-sulfidic to persistently euxinic conditions, δ98Mo and δ238U covariation systematics exhibit two stages. We identify the Mo-U isotope signature of the early transition from anoxic non-sulfidic to mildly euxinic conditions in the first stage, characterized by a rise in U isotope ratios (from −0.3‰ to +0.2‰ ±0.05‰) controlled by the depth within the sediment of the uranium reduction-accumulation front. As the water column turns persistently euxinic, δ98Mo values approach the seawater value for both sapropels, but δ238U evolves to different final values in the two sapropels. We interpret these differences as reflecting different redox potentials and/or different degrees of restriction of these two sapropel events, and the more gradual response of U sequestration to redox variation in comparison with threshold behavior of Mo. The findings presented here show temporal patterns in δ98Mo and δ238U on relatively short timescales that suggest the combined use of these proxies at high resolution allows detailed reconstruction of local redox and hydrographic conditions., Earth and Planetary Science Letters, 585, ISSN:0012-821X, ISSN:1385-013X
- Published
- 2022
9. Accurately calibrated XRF-CS record of Ti/Al reveals Early Pleistocene aridity/humidity variability over North Africa and its close relationship to low-latitude insolation
- Author
-
Rick Hennekam, Katharine M. Grant, Eelco J. Rohling, Rik Tjallingii, David Heslop, Andrew P. Roberts, Lucas J. Lourens, and Gert-Jan Reichart
- Abstract
In eastern Mediterranean Sea sediments, the titanium to aluminum ratio (Ti/Al) captures relative variability in eolian to riverine derived material, and predominantly integrates climate signals over the Saharan and Sahel regions. Long Ti/Al time series can, therefore, provide valuable records of North African humidity/aridity changes. X-ray fluorescence core scanning (XRF-CS) can generate near-continuous Ti/Al records with relatively modest effort and in an acceptable amount of time, provided that accurate Ti/Al values are acquired. Calibration of the raw XRF-CS data to those of established analytical methods is an important pathway to obtain this required accuracy. We assess how to obtain reliable XRF-CS Ti/Al calibration by using different sets of calibration reference samples for a long sediment record from ODP Site 967 (eastern Mediterranean). The accuracy of reference concentrations and the number of reference samples are important components for reliable calibration. The acquired continuous Ti/Al record allows detailed time-series analysis over the past 3 Ma. A near-direct control of low-latitude insolation on the timing and amplitude of North African aridity/humidity is observed from 3 to ~1.2 Ma. It is evident from our Ti/Al record that the most arid North African intervals (i.e., with longest period and highest amplitude) occur after the mid-Pleistocene transition (MPT; ~1.2–0.7 Ma). Concurrently, correlation between North African aridity/humidity (Ti/Al) and higher latitude climate signals (ice-volume variability) increases around the MPT. These findings support the growing consensus that African climate became more sensitive to remote high-latitude climate when a threshold ice volume was reached during the MPT.
- Published
- 2022
- Full Text
- View/download PDF
10. Supplementary material to 'Accurately calibrated XRF-CS record of Ti/Al reveals Early Pleistocene aridity/humidity variability over North Africa and its close relationship to low-latitude insolation'
- Author
-
Rick Hennekam, Katharine M. Grant, Eelco J. Rohling, Rik Tjallingii, David Heslop, Andrew P. Roberts, Lucas J. Lourens, and Gert-Jan Reichart
- Published
- 2022
- Full Text
- View/download PDF
11. Assessing Atmospheric and Oceanic Teleconnections between the Eastern and Western Mediterranean Over the Past 8,000 Years
- Author
-
Sandrine Le Houedec, Diederik Liebrand, Rick Hennekam, and Meryem Mojtahid
- Subjects
History ,Polymers and Plastics ,Business and International Management ,Industrial and Manufacturing Engineering - Published
- 2022
- Full Text
- View/download PDF
12. Slackwater sediments refine the timing of Late Holocene Icelandic canyon-carving floods and confirm they were smaller than reported
- Author
-
Jostein Bakke, Kathryn Adamson, Rick Hennekam, Willem G.M. van der Bilt, Timothy Lane, Sarah M P Berben, and Iestyn D. Barr
- Subjects
Canyon ,Paleontology ,geography ,Carving ,geography.geographical_feature_category ,language ,Icelandic ,language.human_language ,Geology ,Holocene - Abstract
Catastrophic floods have formed deep bedrock canyons on Earth, but the relationship between discharge and erosion remains contested. This hinders efforts to use geological evidence of these cataclysmic events to constrain their magnitude – a prerequisite for impact assessments. This study combines evidence from slackwater sediments with topographic models and hydraulic simulations to constrain the Late Holocene flood history of the Jökulsá á Fjöllum river in northern Iceland. We date floods to 3.5, 1.5 and 1.35 cal. ka BP and confirm that discharge peaks during these events were much smaller than previously reported. In light of recent cosmogenic evidence that nearby knickpoints retreated over 2 km during these floods, our results strengthen simulations and observations indicating that the extent of bedrock erosion is not necessarily controlled by discharge. These findings support a growing consensus that the magnitude of canyon-carving floods is much smaller than typically assumed.
- Published
- 2021
- Full Text
- View/download PDF
13. Late Holocene canyon-carving floods in northern Iceland were smaller than previously reported
- Author
-
Timothy Lane, Willem G M van der Bilt, Rick Hennekam, Sarah M P Berben, Jostein Bakke, Iestyn D. Barr, and Kathryn Adamson
- Subjects
Canyon ,geography ,GE ,Carving ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Flood myth ,Bedrock ,Magnitude (mathematics) ,Geological evidence ,010502 geochemistry & geophysics ,01 natural sciences ,Erosion ,QE ,General Earth and Planetary Sciences ,Physical geography ,Geology ,Holocene ,0105 earth and related environmental sciences ,General Environmental Science - Abstract
Catastrophic floods have formed deep bedrock canyons on Earth, but the relationship between peak discharge and bedrock erosion is not clearly understood. This hinders efforts to use geological evidence of these cataclysmic events to constrain their magnitude – a prerequisite for impact assessments. Here, we combine proxy evidence from slackwater sediments with topographic models and hydraulic simulations to constrain the Late Holocene flood history of the Jökulsá á Fjöllum river in northern Iceland. We date floods to 3.5, 1.5 and 1.35 thousand years ago and confirm that flow peaks during these events were at most a third of previous estimates. Nevertheless, exposure ages suggests that nearby knickpoints retreated by more than 2 km during these floods. These findings support a growing consensus that the extent of bedrock erosion is not necessarily controlled by discharge and that canyon-carving floods may be smaller than typically assumed.
- Published
- 2021
- Full Text
- View/download PDF
14. Milankovitch climate control on redox cyclicity at the onset of the Great Oxidation Event
- Author
-
Joshua Davies, Paul R.D. Mason, Maria Ovtcharova, Rick Hennekam, Wytze Lenstra, Frederik J Hilgen, David Martin, Caroline P. Slomp, Margriet L. Lantink, and Gert-Jan Reichart
- Subjects
Paleontology ,Milankovitch cycles ,Chemistry ,Great Oxygenation Event ,Redox - Published
- 2021
- Full Text
- View/download PDF
15. Controls of redox-dependent P cycling on the Namibian margin in past and present
- Author
-
Tim C. Sweere, Rick Hennekam, Peter Kraal, Gert-Jan Reichart, Zeynep Erdem, and Kristin Anna Ungerhofer
- Subjects
Chemistry ,Margin (machine learning) ,Environmental chemistry ,Cycling ,Redox - Published
- 2021
- Full Text
- View/download PDF
16. Occurrence of anaerobic ammonium oxidation (anammox) in the eastern Mediterranean Sea over the last 56 kyr
- Author
-
Marcel T J van der Meer, Zoë Rebecca van Kemenade, Jaap S. Sinninghe Damsté, Laura Villanueva, Rick Hennekam, Darci Rush, and Ellen C. Hopmans
- Subjects
Eastern mediterranean ,Anammox ,Environmental chemistry ,Anaerobic ammonium oxidation ,Environmental science - Published
- 2021
- Full Text
- View/download PDF
17. Multi-proxy reconstruction of marine inorganic carbon chemistry in the Benguela Upwelling System during the last 25 ka
- Author
-
Zeynep Erdem, Szabina Karancz, Bas van der Wagt, Lennart Jan de Nooijer, Rick Hennekam, Gert-Jan Reichart, Stefan Schouten, and Negar Haghipour
- Subjects
Oceanography ,Total inorganic carbon ,Upwelling ,Multi proxy - Published
- 2021
- Full Text
- View/download PDF
18. Intercomparison of XRF Core Scanning Results From Seven Labs and Approaches to Practical Calibration
- Author
-
Martin Ziegler, Larry C. Peterson, Chloe H Anderson, Masafumi Murayama, Adrian Gilli, Rick Hennekam, Richard W Murray, Arisa Seki, Gert-Jan Reichart, T J Gorgas, Ryuji Tada, Ann G Dunlea, Tomohisa Irino, Carlos A. Alvarez-Zarikian, Hongbo Zheng, and Liviu Giosan
- Subjects
sedimentary geochemistry ,010504 meteorology & atmospheric sciences ,Calibration (statistics) ,quantitative XRF ,XRF calibration ,010502 geochemistry & geophysics ,01 natural sciences ,Core (optical fiber) ,XRF scanning ,Geophysics ,Geochemistry and Petrology ,XRF intercomparison ,paleoceanography ,14. Life underwater ,Geology ,0105 earth and related environmental sciences ,Remote sensing - Abstract
X-ray fluorescence (XRF) scanning of marine sediment has the potential to yield near-continuous and high-resolution records of elemental abundances, which are often interpreted as proxies for paleoceanographic processes over different time scales. However, many other variables also affect scanning XRF measurements and convolute the quantitative calibrations of element abundances and comparisons of data from different labs. Extensive interlab comparisons of XRF scanning results and calibrations are essential to resolve ambiguities and to understand the best way to interpret the data produced. For this study, we sent a set of seven marine sediment sections (1.5 m each) to be scanned by seven XRF facilities around the world to compare the outcomes amidst a myriad of factors influencing the results. Results of raw element counts per second (cps) were different between labs, but element ratios were more comparable. Four of the labs also scanned a set of homogenized sediment pellets with compositions determined by inductively coupled plasma-optical emission spectrometry (ICP-OES) and ICP-mass spectrometry (MS) to convert the raw XRF element cps to concentrations in two ways: a linear calibration and a log-ratio calibration. Although both calibration curves are well fit, the results show that the log-ratio calibrated data are significantly more comparable between labs than the linearly calibrated data. Smaller-scale (higher-resolution) features are often not reproducible between the different scans and should be interpreted with caution. Along with guidance on practical calibrations, our study recommends best practices to increase the quality of information that can be derived from scanning XRF to benefit the field of paleoceanography.
- Published
- 2020
19. Assessment and integration of bulk and component‐specific methods for identifying mineral magnetic assemblages in environmental magnetism
- Author
-
Jinhua Li, Katharine M. Grant, Xiang Zhao, Rick Hennekam, Pengxiang Hu, Eelco J. Rohling, Yao Qian, Andrew P. Roberts, David Heslop, and Yan Liu
- Subjects
Geophysics ,Mineral ,010504 meteorology & atmospheric sciences ,Environmental magnetism ,Space and Planetary Science ,Geochemistry and Petrology ,Earth science ,Component (UML) ,Earth and Planetary Sciences (miscellaneous) ,010502 geochemistry & geophysics ,01 natural sciences ,Geology ,0105 earth and related environmental sciences - Abstract
Magnetic parameters are used extensively to interpret magnetic mineral assemblage variations in environmental studies. Conventional room temperature measurements of bulk magnetic parameters, like the anhysteretic remanent magnetization (ARM) and the ratio of the susceptibility of ARM to magnetic susceptibility (χ), can reflect, respectively, magnetic mineral concentration and/or particle size variations in sediments, although they are not necessarily well suited for identifying magnetic components within individual magnetic mineral assemblages. More advanced techniques, such as first‐order reversal curve (FORC) diagrams and low‐temperature (LT) magnetic measurements, can enable detailed discrimination of magnetic assemblages. Here, we integrate conventional bulk magnetic measurements alongside FORC diagrams, LT measurements, and X‐ray fluorescence core‐scan data, transmission electron microscope observations, and principal component analysis of FORC diagrams to identify and quantify magnetic mineral assemblages in eastern Mediterranean sediments. The studied sediments were selected because they contain complexly varying mixtures of detrital, biogenic, and diagenetically altered magnetic mineral assemblages that were deposited under varying oxic (organic‐poor marls) to anoxic (organic‐rich sapropels) conditions. Conventional bulk magnetic parameters provide continuous records of environmental magnetic variations, while more time‐consuming LT and FORC measurements on selected samples provide direct ground‐truthing of mineral magnetic assemblages that enables calculation of magnetization contributions of different end members. Thus, a combination of conventional bulk parameters and advanced magnetic techniques can provide detailed records from which the meaning of environmental magnetic signals can be unlocked.
- Published
- 2020
20. Late Holocene glacier and climate reconstruction from proglacial records in Vatnsdalur, northern Iceland
- Author
-
Timothy Lane, Iestyn D. Barr, Rick Hennekam, Willem G M van der Bilt, Konstantin Nebel, Kathryn Adamson, and Jason R. Kirby
- Subjects
geography ,geography.geographical_feature_category ,Glacier ,Physical geography ,Geology ,Holocene - Abstract
The Arctic region is experiencing surface air temperature increase of twice the global average. To better understand Holocene Arctic climate variability, there is the need for continuous, high-resolution palaeoclimate archives. Sediment cores from proglacial lakes can provide such climate archives, and have the potential to record past environmental change in detail. Vatnsdalur, a valley in northern Iceland, hosts small, climatically sensitive cirque glaciers that became independent from the Iceland Ice Sheet after its retreat following the Last Glacial Maximum (c. 15 ka BP). Importantly, this region is located at the confluence of warm water and air masses from the south and cold polar water and air masses from the north, making it highly sensitive to North Atlantic and Arctic climate change. However, at present the region is highly understudied, lacking any high-resolution climate reconstructions. To address this, we combine geomorphological mapping with the first high-resolution analysis of proglacial lake sediments, to thoroughly examine northern Iceland Late Holocene environmental change.Field mapping supplemented by high-resolution drone data was used to characterise catchment geomorphology, including seven Holocene moraines. A sediment core (SKD-P1-18) from proglacial lake Skeiðsvatn, Vatnsdalur, was analysed for sedimentological (dry bulk density, loss-on-ignition, grain size), geophysical (magnetic susceptibility) and geochemical (X-ray fluorescence core scan, 2 mm resolution) parameters. We identify three main sedimentary facies from these analyses, indicating variations in glacial input and catchment environmental conditions. Radiocarbon dating of lake macrofossils, supplemented by tephrochronology, provides a chronological framework. Catchment point samples, also analysed using the above analytical techniques, were used for sediment fingerprinting to disentangle non-glacial from glacial end-members.Our results indicate the disappearance and reformation of small, climatically sensitive cirque glaciers in Vatnsdalur during the Holocene. We interpret the data to show an abrupt return to a glaciated catchment. Our results fill a geographical gap of high-resolution proglacial sediment studies in the Arctic-North Atlantic region.
- Published
- 2020
- Full Text
- View/download PDF
21. Alkenone Distributions and Hydrogen Isotope Ratios Show Changes in Haptophyte Species and Source Water in the Holocene Baltic Sea
- Author
-
Stefan Schouten, Barbara Massalska, Rick Hennekam, Jaap S. Sinninghe Damsté, Gabriella M. Weiss, Gert-Jan Reichart, Marcel T J van der Meer, Leerstoel Aken, and non-UU output of UU-AW members
- Subjects
Alkenone ,Baltic Sea ,010504 meteorology & atmospheric sciences ,010502 geochemistry & geophysics ,01 natural sciences ,Geochemistry and Petrology ,alkenones ,skin and connective tissue diseases ,Sea level ,Holocene ,0105 earth and related environmental sciences ,geography ,geography.geographical_feature_category ,biology ,Brackish water ,fungi ,Littorina ,Post-glacial rebound ,biology.organism_classification ,hydrogen isotopes ,Salinity ,Geophysics ,Oceanography ,haptophytes ,sense organs ,Ice sheet ,Geology - Abstract
The Baltic Sea, a dynamic, marginal marine basin, experienced a number of large changes in salinity during the Holocene as a result of fluctuations in global and local sea level related to melting of glacial ice sheets and subsequent isostatic rebound. These changes likely had pronounced effects on the species composition of haptophytes, a common phytoplankton group found in the Baltic Sea. This dynamic environment provides the ideal setting to study how species change impacts distribution and hydrogen isotope ratios of long‐chain alkenones (δ2HC37), haptophyte‐specific biomarkers. Here we analyzed the aforementioned parameters in Holocene sediments covering the contrasting hydrological phases of the Baltic Sea. Alkenone distributions changed with different Baltic Sea salinity phases, suggesting that species shifts coincide with salinity change. δ2HC37 values show two major shifts: one in the middle of the freshwater Ancylus Lake phase (10.6 to 7.7 ka) and a second at the transition from the brackish Littorina Sea phase (7.2 to 3 ka) into the fresher Modern Baltic (3 ka to the present). The first shift represents a significant enrichment of 50‰, which cannot be explained by salinity or species changes only. At this time, the isotopically depleted ice sheets had melted, and only the relatively enriched freshwater source remained. The second shift, coincident with a change in distribution, is likely caused by a change in species composition alone. These findings show that hydrogen isotope ratios of long‐chain alkenones, combined with their relative distribution, can be used to reconstruct changes in source water.
- Published
- 2020
- Full Text
- View/download PDF
22. Timing and stepwise transitions of the African Humid Period from geochemical proxies in the Nile deep-sea fan sediments
- Author
-
Edouard Bard, Rick Hennekam, Delphine Bosch, Sébastien Pivot, Ioanna Bouloubassi, Emmanuelle Ducassou, Nina Davtian, Marie Revel, Sébastien Migeon, Guillemette Ménot, Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement [Lyon] (LGL-TPE), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-École normale supérieure - Lyon (ENS Lyon), Centre européen de recherche et d'enseignement des géosciences de l'environnement (CEREGE), Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Collège de France (CdF (institution))-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Cycles biogéochimiques marins : processus et perturbations (CYBIOM), Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN), Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU), Royal Netherlands Institute for Sea Research (NIOZ), Géosciences Montpellier, Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Université des Antilles (UA)-Centre National de la Recherche Scientifique (CNRS), UMR 5805 Environnements et Paléoenvironnements Océaniques et Continentaux (EPOC), Observatoire aquitain des sciences de l'univers (OASU), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École pratique des hautes études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Chaire Evolution du climat et de l'océan, Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Collège de France (CdF (institution))-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Collège de France (CdF (institution))-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Collège de France (CdF)-Institut national des sciences de l'Univers (INSU - CNRS)-Aix Marseille Université (AMU)-Institut National de la Recherche Agronomique (INRA), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Université des Antilles (UA), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École pratique des hautes études (EPHE)-Centre National de la Recherche Scientifique (CNRS), Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement (LGL-TPE), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Centre National de la Recherche Scientifique (CNRS), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Environnements et Paléoenvironnements OCéaniques (EPOC), Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École Pratique des Hautes Études (EPHE), and Collège de France - Chaire Evolution du climat et de l'océan
- Subjects
010506 paleontology ,Archeology ,010504 meteorology & atmospheric sciences ,Clastic εNd ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,01 natural sciences ,Deep sea ,Precipitation ,Younger Dryas ,Nile river ,Ecology, Evolution, Behavior and Systematics ,0105 earth and related environmental sciences ,Global and Planetary Change ,Terrigenous sediment ,Geology ,Arid ,African Humid Period ,13. Climate action ,[SDU]Sciences of the Universe [physics] ,[SDE]Environmental Sciences ,Erosion ,Period (geology) ,Sedimentary rock ,GDGT-indices ,Physical geography - Abstract
International audience; Large fluvial systems, such as the Nile River, allow a basin-scale integrated view of climatological and environmental changes. In this study, we reconstructed the Nile discharge history for the last 20 ka using molecular ratios of glycerol dialkyl glycerol tetraethers (GDGTs) and neodymium (Nd) radiogenic isotopes. By characterizing both the organic and inorganic fractions, we assessed the relevance of the GDGT-based proxies in deltaic environments as tracers of terrigenous origin. A large increase in Nile discharge is documented from 14.8 to 8.4 ka BP reflecting enhanced physical erosion and transport processes from the Ethiopian Traps. We confirmed the primary control of insolation on precipitation on North East Africa through the last 20 ka. The centennial time resolution reached on the sedimentary sequence revealed a step-wise onset and termination of the African Humid Period (AHP) starting at 14.8 ka and ending at 8.4 ka BP, respectively. Our centennial-millennial records allowed furthermore pinpointing the abrupt periods of arid conditions corresponding to the Younger Dryas. These data illustrate the linkage between low and high latitude hydrological variability.
- Published
- 2020
- Full Text
- View/download PDF
23. Downward particle fluxes of biogenic matter and Saharan dust across the equatorial North Atlantic
- Author
-
Rick Hennekam, Jan-Berend W Stuut, Michèlle van der Does, Stefan Schouten, Geert-Jan A Brummer, Dirk Jong, Laura F Korte, Catarina Guerreiro, Johannes A van Hateren, Chris I Munday, and Earth and Climate
- Subjects
Atmospheric Science ,010504 meteorology & atmospheric sciences ,Biogenic silica ,Seasonality ,Mineral dust ,010502 geochemistry & geophysics ,medicine.disease ,01 natural sciences ,Deep sea ,lcsh:QC1-999 ,Deposition (geology) ,lcsh:Chemistry ,Oceanography ,lcsh:QD1-999 ,13. Climate action ,Sediment trap ,medicine ,Spatial variability ,SDG 14 - Life Below Water ,Transect ,lcsh:Physics ,Geology ,0105 earth and related environmental sciences - Abstract
Massive amounts of Saharan dust are blown from the coast of northern Africa across the Atlantic Ocean towards the Americas each year. This dust has, depending on its chemistry, direct and indirect effects on global climate which include reflection and absorption of solar radiation as well as transport and deposition of nutrients and metals fertilizing both ocean and land. To determine the temporal and spatial variability of Saharan dust transport and deposition and their marine environmental effects across the equatorial North Atlantic Ocean, we have set up a monitoring experiment using deep-ocean sediment traps as well as land-based dust collectors. The sediment traps were deployed at five ocean sites along a transatlantic transect between north-west Africa and the Caribbean along 12° N, in a downwind extension of the land-based dust collectors placed at 19° N on the Mauritanian coast in Iouîk. In this paper, we lay out the setup of the monitoring experiment and present the particle fluxes from sediment trap sampling over 24 continuous and synchronized intervals from October 2012 through to November 2013. We establish the temporal distribution of the particle fluxes deposited in the Atlantic and compare chemical compositions with the land-based dust collectors propagating to the downwind sediment trap sites, and with satellite observations of Saharan dust outbreaks. First-year results show that the total mass fluxes in the ocean are highest at the sampling sites in the east and west, closest to the African continent and the Caribbean, respectively. Element ratios reveal that the lithogenic particles deposited nearest to Africa are most similar in composition to the Saharan dust collected in Iouîk. Downwind increasing Al, Fe and K contents suggest a downwind change in the mineralogical composition of Saharan dust and indicate an increasing contribution of clay minerals towards the west. In the westernmost Atlantic Ocean, admixture of re-suspended clay-sized sediments advected towards the deep sediment trap cannot be excluded. Seasonality is most prominent near both continents but generally weak, with mass fluxes dominated by calcium carbonate and clear seasonal maxima of biogenic silica towards the west. The monitoring experiment is now extended, with autonomous dust sampling buoys for better quantification of Saharan dust transport and deposition from source to sink and their impact on fertilization and carbon export to the deep ocean.
- Published
- 2017
- Full Text
- View/download PDF
24. Integral view of Holocene precipitation and vegetation changes in the Nile catchment area as inferred from its delta sediments
- Author
-
Timme H. Donders, Rick Hennekam, Gert J. de Lange, and Karin Zwiep
- Subjects
Hydrology ,Delta ,Archeology ,Global and Planetary Change ,geography ,geography.geographical_feature_category ,biology ,viruses ,Drainage basin ,virus diseases ,Sediment ,Geology ,Sahara pump theory ,Vegetation ,biology.organism_classification ,humanities ,nervous system diseases ,Erosion ,Physical geography ,Ecology, Evolution, Behavior and Systematics ,Holocene ,Globigerinoides - Abstract
We compare geochemical and pollen data of several well-dated, high-resolution cores to provide an integral Holocene overview of Nile outflow, sedimentation, and vegetation in and around the Nile delta. We show that the focus point of the Nile plume varied considerably, as indicated by planktonic foraminifer Globigerinoides ruber oxygen isotopes tracing Nile discharge differences in an east-west delta transect At 13-11.5 cal kyr BP, Nile discharge was low and runoff was predominantly directed to the western part of the delta. Sediment arriving in the delta during that period was dominated by Ethiopian Highland (similar to Blue Nile) material, shown by high Ti/Al values of the bulk sediment, indicating dry conditions in the source area of the Blue Nile. Nile discharge increased from similar to 11.5 cal kyr BP, and was high across the whole delta from similar to 10-6.5 cal kyr BP. During this time, the Ti/Al values decreased within most Nile-delta sediments, suggesting that the relative contribution of Blue-Nile sediment decreased. This was likely due to an increased vegetation cover causing diminished erosion in the Ethiopian Highlands. Nile discharge gradually decreased from similar to 6.5 cal kyr BP to present. This decrease was more abrupt in the Western Province of the delta and became more gradual towards the east as the shrinking Nile runoff was directed there. The gradual decrease in precipitation in the Nile catchment area seems not to be matched by a gradual response in vegetation growing around the river plain in the lower Nile catchment. Our findings suggest a nonlinear response of northeast African vegetation to precipitation from the middle to late Holocene. (C) 2015 Elsevier Ltd. All rights reserved.
- Published
- 2015
- Full Text
- View/download PDF
25. Compositional changes of present-day transatlantic Saharan dust deposition
- Author
-
Stefan Schouten, Geert-Jan A Brummer, Jan-Berend W Stuut, Catarina Guerreiro, Johannes A van Hateren, Chris I Munday, Laura F Korte, Rick Hennekam, Michèlle van der Does, and Dirk Jong
- Subjects
13. Climate action ,0211 other engineering and technologies ,Environmental science ,02 engineering and technology ,Present day ,Mineral dust ,021001 nanoscience & nanotechnology ,0210 nano-technology ,Atmospheric sciences ,Deposition (chemistry) ,021101 geological & geomatics engineering - Abstract
Massive amounts of Saharan dust are blown from the African coast across the Atlantic Ocean towards the Americas each year. This dust has, depending on its chemistry, direct and indirect effects on global climate including reflection and absorption of solar radiation as well as transport and deposition of nutrients and metals fertilizing both ocean and land. To determine the temporal and spatial variability of Saharan dust transport and deposition and their marine environmental effects across the equatorial North Atlantic Ocean, we have set up a monitoring experiment using deep-ocean sediment traps as well as land-based dust collectors. The sediment traps were deployed at five ocean sites along a transatlantic transect between northwest Africa and the Caribbean along 12⁰ N, in a down-wind extension of the land-based dust collectors placed at 19⁰ N on the Mauritanian coast in Iwik. In this paper, we lay out the setup of the monitoring experiment and present the particle fluxes from sediment trap sampling over 24 continuous and synchronised intervals from October 2012 through to November 2013. We establish the temporal distribution of the particle fluxes deposited in the Atlantic and compare chemical compositions with the land-based dust collectors propagating to the down-wind sediment trap sites, and with satellite observations of Saharan dust outbreaks. First-year results show that the total mass fluxes in the ocean are highest at the sampling sites in the east and west, closest to the African continent and the Caribbean, respectively. Element ratios reveal that the lithogenic particles deposited nearest to Africa are most similar in composition to the Saharan dust collected in Iwik. Down-wind increasing Al, Fe and K contents suggest a downwind change in the mineralogical composition of Saharan dust and indicate an increasing contribution of clay minerals towards the west. In the westernmost Atlantic, admixture of re-suspended clay-sized sediments advected towards the deep sediment trap cannot be excluded. Seasonality is most prominent near both continents but generally weak, with mass fluxes dominated by calcium carbonate and clear seasonal maxima of biogenic silica towards the west. The monitoring experiment is now extended with autonomous dust sampling buoys for better quantification Saharan dust transport and deposition from source to sink and its impact on fertilization and carbon export to the deep ocean.
- Published
- 2016
- Full Text
- View/download PDF
26. Supplementary material to 'Compositional changes of present-day transatlantic Saharan dust deposition'
- Author
-
Laura F. Korte, Geert-Jan Brummer, Michèlle van der Does, Catarina V. Guerreiro, Rick Hennekam, Johannes A. van Hateren, Dirk Jong, Chris I. Munday, Stefan Schouten, and Jan-Berend W. Stuut
- Published
- 2016
- Full Text
- View/download PDF
27. X-ray fluorescence core scanning of wet marine sediments: methods to improve quality and reproducibility of high-resolution paleoenvironmental records
- Author
-
Rick Hennekam and Gert J. de Lange
- Subjects
Reproducibility ,Absorption of water ,Materials science ,Resolution (mass spectrometry) ,Mineralogy ,X-ray fluorescence ,Ocean Engineering ,Sedimentary rock ,Inductively coupled plasma ,Water content ,FOIL method - Abstract
X-ray fluorescence (XRF) core-scanning is a convenient non-destructive tool to rapidly assess elemental variations in unprocessed sediments. However, substantial analytical deviations may occur in such data due to physical sedimentary properties. The consequences of these artifacts on element intensities are important for paleoclimatic studies, but as yet have not been adequately studied for high resolution (≤ 1-cm interval) records. We have done a high resolution comparison between results from XRF scanning and from two more conventional methods: XRF with beads and inductively coupled plasma optical emission spectrometry (ICP-OES), both on discrete samples. Our XRF scan data concord reasonably well with those from the conventional methods for most elements. In several discrete intervals large deviations occur that could have been attributed to major paleoceanographic events. However, these deviations appear to be mainly related to water content and distribution. We show that the variability in the water film thickness underneath the plastic foil is highly variable, causing significant apparent variability in all elements from Al to Fe. The unverified use of these elements in ratios can thus lead to deviations in the paleoenvironmental interpretation. Erroneous element (ratio) variability can, however, be recognized and corrected using conventional analytical data of a few discrete samples. The antipathetic behavior of Ca to K or Ti, and their similar behavior to water absorption, leaves their ratios relatively unaffected at variable water film thicknesses. Hence, Ca/K and Ca/Ti ratios are recommended for a preliminary down-core overview of sedimentary variability and for stratigraphic correlations between unprocessed marine cores.
- Published
- 2012
- Full Text
- View/download PDF
28. Differences between the last two glacial maxima and implications for ice-sheet, δ18O, and sea-level reconstructions
- Author
-
Eelco J. Rohling, Gavin L. Foster, Gianluca Marino, Katharine M. Grant, Andrew P. Roberts, Rick Hennekam, Jimin Yu, Jody M. Webster, Felicity Williams, Gert J. de Lange, Fiona D. Hibbert, Yusuke Yokoyama, Marine geochemistry, Geochemistry, and General geochemistry
- Subjects
010506 paleontology ,Archeology ,010504 meteorology & atmospheric sciences ,Evolution ,Arctic ice shelf ,01 natural sciences ,Last Interglacial ,Behavior and Systematics ,Ice volume ,Penultimate Glacial Maximum ,Ice age ,Deglaciation ,Cryosphere ,Sea level ,Glacial period ,Ecology, Evolution, Behavior and Systematics ,0105 earth and related environmental sciences ,geography ,δO ,Global and Planetary Change ,geography.geographical_feature_category ,Last Glacial Maximum ,Ecology ,Geology ,Post-glacial rebound ,Arctic ice pack ,Ice-sheet model ,Archaeology ,13. Climate action ,Climatology ,Ice sheet ,Glacioisostatic adjustment - Abstract
Studies of past glacial cycles yield critical information about climate and sea-level (ice-volume) variability, including the sensitivity of climate to radiative change, and impacts of crustal rebound on sea-level reconstructions for past interglacials. Here we identify significant differences between the last and penultimate glacial maxima (LGM and PGM) in terms of global volume and distribution of land ice, despite similar temperatures and radiative forcing. Our analysis challenges conventional views of relationships between global ice volume, sea level, seawater oxygen isotope values, and deep-sea temperature, and supports the potential presence of large floating Arctic ice shelves during the PGM. The existence of different glacial ‘modes’ calls for focussed research on the complex processes behind ice-age development. We present a glacioisostatic assessment to demonstrate how a different PGM ice-sheet configuration might affect sea-level estimates for the last interglacial. Results suggest that this may alter existing last interglacial sea-level estimates, which often use an LGM-like ice configuration, by several metres (likely upward).
- Published
- 2017
29. Baltic sea alkenones: Novel insights into distribution changes and hydrogen isotope ratios during the Holocene
- Author
-
Stefan Schouten, G. J. Reichart, J.S. Sinninghe Damsté, Rick Hennekam, M.T.J. van der Meer, Gabriella M. Weiss, and B. Massalska
- Subjects
Oceanography ,Baltic sea ,Distribution (number theory) ,Hydrogen isotope ,Geology ,Holocene
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.