Browsing by Author "Kaufman, DS"

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    A global database of holocene paleotemperature records
    (Springer Nature Limited, 2020-04-14) Kaufman, DS; McKay, N; Rouston, C; Erb, M; Davis, B; Heiri, O; Jaccard, SL; Tierney, J; Dätwyler, C; Axford, Y; Brussel, T; Cartapanis, O; Chase, BM; Dawson, A; de Vernal, A; Engels, S; Jonkers, L; Marsicek, J; Moffa-Sánchez, P; Morrill, C; Oris, A; Rehfeld, K; Saunders, KM; Sommer, PS; Thomas, E; Tonello, M; Tóth, M; Vachula, R; Andreev, A; Bertrand, S; Biskaborn, B; Bringué, M; Brooks, S; Caniupán, M; Chevalier, M; Cwynar, L; Emile-Geay, J; Fegyveresi, J; Feurdean, A; Finsinger, W; Fortin, MC; Foster, L; Fox, M; Gajewski, K; Grosjean, M; Hausmann, S; Heinrichs, M; Holmes, N; Ilyashuk, B; Ilyashuk, E; Juggins, S; Khider, D; Koinig, K; Langdon, P; Larocque-Tobler, I; Li, JY; Lotter, A; Luoto, T; Mackay, A; Magyari, E; Malevich, S; Mark, B; Massaferro, J; Montade, V; Nazarova, L; Novenko, E; Pařil, P; Pearson, E; Peros, M; Peinitz, R; Płóciennik, M; Porinchu, D; Potito, A; Rees, ABH; Reinemann, S; Roberts, SJ; Rolland, N; Salonen, S; Self, A; Seppä, H; Shala, S; St-Jacques, JM; Stenni, B; Syrykh, L; Tarrats, P; Taylor, K; van den Bos, V; Velle, G; Wahl, E; Walker, I; Wilmshurst, J; Zhang, E; Zhilich, S
    A comprehensive database of paleoclimate records is needed to place recent warming into the longer-term context of natural climate variability. We present a global compilation of quality-controlled, published, temperature-sensitive proxy records extending back 12,000 years through the Holocene. Data were compiled from 679 sites where time series cover at least 4000 years, are resolved at sub-millennial scale (median spacing of 400 years or finer) and have at least one age control point every 3000 years, with cut-off values slackened in data-sparse regions. The data derive from lake sediment (51%), marine sediment (31%), peat (11%), glacier ice (3%), and other natural archives. The database contains 1319 records, including 157 from the Southern Hemisphere. The multi-proxy database comprises paleotemperature time series based on ecological assemblages, as well as biophysical and geochemical indicators that reflect mean annual or seasonal temperatures, as encoded in the database. This database can be used to reconstruct the spatiotemporal evolution of Holocene temperature at global to regional scales, and is publicly available in Linked Paleo Data (LiPD) format. © 2020 The Authors
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    Identifying outliers and assessing the accuracy of amino acid racemization measurements for geochronology: I. age calibration curves
    (Elsevier, 2008-11) Kosnik, MA; Kaufman, DS; Hua, Q
    Numerical ages derived from amino acid racemization (AAR) geochronology are typically based on calibration curves that relate the extent of AAR to the age of independently dated specimens. Here, we compare options for developing calibration curves and quantifying age uncertainties using AAR data from 481 late Holocene shells, and AMS 14C analyses of 36 shells of four molluscan taxa (Ethalia, Natica, Tellina, and Turbo) collected from shallow sediment cores from a back-reef lagoon of the central Great Barrier Reef. The four taxa differed substantially in the quality of their geochronogical results. Explicitly including data from specimens alive at the time of collection improves calibration curves, but weighting numerical ages based on their uncertainty has no effect. Calibration curve statistics do not adequately assess calibration uncertainty. The relation between ages inferred from different amino acids is recommended for identifying aberrant specimens and quantifying the uncertainty of inferred ages. For this study, the AAR ages based on two amino acids (aspartic acid and glutamic acid) exceed 200 yr or 20% of their mean inferred age in 15% of the specimens. Once these were removed, the mean age error (1σ) for individual specimens based on two amino acids analyzed in duplicate subsamples ranged from 53 to 142 yr for Tellina and Turbo, respectively, or about a 30% age error for these relatively young shells. This compares favorably with analytical errors estimated at 50 yr or 5%. The presence of notable outliers undetectable using data from single amino acids emphasizes the importance of analyzing multiple amino acids. © 2008, Elsevier Ltd.
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    Identifying outliers and assessing the accuracy of amino acid racernization measurements for geochronology: II. data screening
    (Elsevier, 2008-11) Kosnik, MA; Kaufman, DS
    Amino acid racemization (AAR) is a cost-effective method for dating the large numbers of specimens required for time-averaging studies. Because the aim of time-averaging studies is to determine the structure of the age distribution, any data screening must be done cautiously and systematically. Methods to quantitatively assess the quality of AAR data and to identify aberrant specimens are under-developed. Here we examine a variety of screening criteria for identifying outliers and determining the suitability of specimens for numerical dating including: high serine concentrations (modern contamination), covariance of aspartic acid (Asp) and glutamic acid (Glu) concentrations (diagenetic influences), replication of measurements (specimen heterogeneity), and the relation between Asp and Glu d/l values (internal consistency). This study is based on AAR analyses of 481 late Holocene shells of four molluscan taxa (Ethalia, Natica, Tellina, and Turbo) collected from shallow sediment cores from the central Great Barrier Reef. Different outliers are flagged by the different screening criteria, and 6% of specimens were found to be unsuitable for time-averaging analyses based on screening the raw AAR data. We recommend a hybrid approach for identifying outliers and specimens for numerical dating. © 2008, Elsevier Ltd.
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    One fossil record, multiple time resolutions: disparate time-averaging of echinoids and mollusks on a Holocene carbonate platform
    (Geological Society of America, 2017-11-11) Kowalewski, M; Casebolt, S; Hua, Q; Whitacre, KE; Kaufman, DS; Kosnik, MA
    Our quantitative understanding of the temporal resolution of the fossil record is largely based on numerical dating of Holocene bivalves. However, for paleontologically important taxa with less-robust skeletons, no quantitative estimate of time-averaging exists. Here, we compare time-averaging in sympatric accumulations of the echinoid Leodia sexiesperforata and the bivalve Tucetona pectinata on a shallow carbonate platform of San Salvador Island, Bahamas. Using graphite-target and carbonate-target accelerator mass spectrometry (AMS) radiocarbon methods, we dated 30 echinoid tests and 30 mollusk valves collected from surficial sediments at a single site. All echinoid tests yielded post-bomb (taking into account radiocarbon from nuclear weapons testing) ages, and the estimated time-averaging (interquartile age range) is at most 2 yr. In contrast, sympatric mollusk valves spanned 4000 yr with an estimated time-averaging of 1830 yr. This three-orders-of-magnitude difference in the extent of time-averaging quantifies the taphonomic expectation that echinoid tests should degrade more rapidly and experience less time-averaging when compared to more durable mollusk shells. When preserved, fossil echinoids are likely to indicate a more finely resolved fossil record than skeletally robust organisms such as mollusks, and may provide a fundamentally distinct class of paleontological data, potentially adequate for investigating biological and physical processes that operate at subdecadal time scales. Immensely disparate time-averaging of sympatric mollusks and echinoids indicates that, at broader phylogenetic scales, differences in intrinsic skeletal durability may be the main determinant of the temporal resolution of fossil assemblages. Copyright © 2017 Geological Society of America
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    Radiocarbon dating of individual foram tests show that alleged Lessepsian species are of Holocene age
    (European Geosciences Union (EGU), 2021-04) Albano, PG; Sabbatini, A; Lattanzio, J; Steger, J; Szidat, S; Hua, Q; Kaufman, DS; Zuschin, M; Negri, A
    The Lessepsian invasion – the largest marine biological invasion – followed the opening of the Suez Canal in 1869 (81 years BP). Shortly afterwards, tropical species also distributed in the Red Sea appeared on Mediterranean shores: it was the dawn of what would become the invasion of several hundred tropical species. The time of the Suez Canal opening coincided with an acceleration in natural history exploration and description, but the eastern sectors of the Mediterranean Sea lagged behind and were thoroughly explored only in the second half of the 20th century. Many parts are still insufficiently studied today. Baseline information on pre-Lessepsian ecosystem states is thus scarce. This knowledge gap has rarely been considered by invasion scientists: every new finding of species belonging to tropical clades has been assumed to be a Lessepsian invader. We here question this assumption by radiocarbon dating seven individual tests of miliolids – imperforated calcareous foraminifera – belonging to five alleged non-indigenous species. Tests were found in two sediment cores collected at 30 and 40 m depth off Ashqelon, on the Mediterranean Israeli shelf. We dated one Cribromiliolinella milletti (core at 40 m, 20 cm sediment depth), three Nodophthalmidium antillarum (core at 40 m, 35 cm sediment depth), one Miliolinella cf. fichteliana (core at 30 m, 110 cm sediment depth), one Articulina alticostata (core at 40 m, 35 cm sediment depth) and one Spiroloculina antillarum (core at 30 m, 110 cm sediment depth). All foraminiferal tests proved to be of Holocene age, with a median calibrated age spanning between 749 and 8285 years BP. Only one test of N. antillarum showed a 2-sigma error overlapping the time of the opening of the Suez Canal, but with a median age of 1123 years BP. Additionally, a thorough literature search resulted in a further record of S. antillarum in a core interval dated 1820–2064 years BP in Turkey. Therefore, these foraminiferal species are not introduced, but native species. They are all circumtropical or Indo-Pacific and in the Mediterranean distributed mostly in the eastern sectors (only S. antillarum occurs also in the Adriatic Sea). Two hypotheses can explain our results: these species are Tethyan relicts that survived the Messinian salinity crisis (5.97–5.33 Ma) and the glacial periods of the Pleistocene in the Eastern Mediterranean, which may have never desiccated completely during the Messinian crisis and which may have worked as a warm-water refugium in the Pleistocene; or they entered the Mediterranean Sea from the Red Sea more recently but before the opening of the Suez Canal, for example during the Last Interglacial (MIS5e) high-stand (125,000 years BP) when the flooded Isthmus of Suez enabled exchanges between the Mediterranean and the Indo-Pacific fauna. The recognition that some alleged Lessepsian invaders are in fact native species influences our understanding of the invasion process, its rates and environmental correlates. © Author(s) 2021
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    Radiocarbon-calibrated amino acid racemization ages from Holocene sand dollars (Peronella peronii)
    (Elsevier, 2017-04) Kosnik, MA; Hua, Q; Kaufman, DS; Kowalewski, M; Whitacre, KE
    Amino acid racemization (AAR) is widely used as a cost-effective method to date molluscs in time-averaging and taphonomic studies, but it has not been attempted for echinoderms despite their paleobiological importance and distinct biomineralization. Here we demonstrate the applicability of AAR geochronology for dating Holocene Peronella peronii (Echinodermata: Echinoidea) collected from Sydney Harbour (Australia). Using standard HPLC methods we determined the extent of AAR in 74 Peronella tests and performed replicate analyses on 23 tests. Replicate analyses from the outer edge of 23 tests spanning the observed range of D/L values yielded median coefficients of variation <4% for Asp, Glu, and Phe D/L values, which is comparable to the analytical precision. Correlations between THAA D/L values across 178 independently prepared subsamples of 74 individuals are also very high (Spearman ρ ≥ 0.95) for these three amino acids. The ages of 20 individuals spanning the observed range of D/L values were determined using 14C analyses, and Bayesian model averaging was used to determine the best AAR age model. Only three models fit to Glu D/L contributed to the final averaged age model. Modeled ages ranged from 14 to 5496 years, and the median 95% confidence interval for the 54 AAR ages was ±29% of the modelled age. In comparison, the median 2σ confidence interval for nine graphite target 14C ages was ±8% of the median age estimate and the median 2σ confidence interval for 20 carbonate target 14C ages was ±26% of the median age estimate. Overall Peronella yield high-quality D/L values and appear to be a good target for AAR geochronology. ©2016 Elsevier B.V
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    Radiocarbon-calibrated multiple amino acid geochronology of holocene molluscs from Bramble and Rib Reefs (Great Barrier Reef, Australia)
    (Elsevier Ireland Ltd, 2013-04-01) Kosnik, MA; Kaufman, DS; Hua, Q
    Calibrated amino acid racemisation methods allow paleobiologists to quantify the age distributions of fossil assemblages. Focussing on 110 Scissulina dispar and 110 Liloa sp. specimens collected from Bramble and Rib Reefs (central Great Barrier Reef, Australia), we create calibration curves for seven amino acids for each taxon. Using these curves we calculate seven quasi-independent age estimates for each specimen. We evaluate each calibration curve for consistency and use the weighted mean and uncertainty of the quasi-independent ages as the specimen age for geochronological analyses. We extend the "Y" criterion for screening specimens and describing the precision of an AAR dataset from two amino acids to any number of amino acids. Using weighted mean ages and Y < 0.2 we demonstrate that the top 1.4 m of Bramble and Rib Reefs preserve remarkably well-mixed shell assemblages spanning from living to similar to 3400 years old with median ages of 373 and 326 years old, respectively. © 2013, Elsevier Ltd.
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    Sediment accumulation, stratigraphic order, and the extent of time-averaging in lagoonal sediments: a comparison of 210Pb and 14C/amino acid racemization chronologies
    (Springer Link, 2014-11-15) Kosnik, MA; Hua, Q; Kaufman, DS; Zawadzki, A
    Carbon-14 calibrated amino acid racemization (14C/AAR) data and lead-210 (210Pb) data are used to examine sediment accumulation rates, stratigraphic order, and the extent of time-averaging in sediments collected from the One Tree Reef lagoon (southern Great Barrier Reef, Australia). The top meter of lagoonal sediment preserves a stratigraphically ordered deposit spanning the last 600 yrs. Despite different assumptions, the 210Pb and 14C/AAR chronologies are remarkably similar indicating consistency in sedimentary processes across sediment grain sizes spanning more than three orders of magnitude (0.1–10 mm). Estimates of long-term sediment accumulation rates range from 2.2 to 1.2 mm yr−1. Molluscan time-averaging in the taphonomically active zone is 19 yrs, whereas below the depth of final burial (~15 cm), it is ~110 yrs/5 cm layer. While not a high-resolution paleontological record, this reef lagoon sediment is suitable for paleoecological studies spanning the period of Western colonization and development. This sedimentary deposit, and others like it, should be useful, albeit not ideal, for quantifying anthropogenic impacts on coral reef systems.© 2014, The Author(s).
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    Sediment mixing and stratigraphic disorder revealed by the age-structure of Tellina shells in Great Barrier Reef sediment
    (Geological Society of America, 2007-09) Kosnik, MA; Hua, Q; Jacobsen, GE; Kaufman, DS; Wust, RAJ
    Radiocarbon-calibrated amino acid racemization ages of 250 individually dated Tellina shells from two sediment cores are used to quantify molluscan time averaging with increasing burial depth in the shallow-water carbonate lagoon of Rib Reef, central Great Barrier Reef, Australia. The top 20 cm of sediment contain a distinct, essentially modern assemblage with a median age of only 5 yr. Sediment between 20 and 125 cm are age-homogeneous and significantly older than the surface sediment (median age 189 yr). Shell age distributions within layers indicate that the top 125 cm of lagoonal sediment is thoroughly mixed on a subcentennial scale. Shell size is an important correlate of shell half-life and an important determinant of the inferred age of sedimentary layers. These results illustrate the importance of bioturbation in these environments, indicate that age estimates in this depositional setting are sensitive to specimen choice, and document a size-dependent bias in death assemblage formation. © 2007, Geological Society of America
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    Taphonomic bias and time-averaging in tropical molluscan death assemblages: differential shelf half-lives in Great Barrier Reef sediments
    (The Paleontological Society, 2009-11) Kosnik, MA; Hua, Q; Kaufman, DS; Wust, RA
    Radiocarbon-calibrated amino acid racemization ages of 428 individually dated shells representing four molluscan taxa are used to quantify time-averaging and shell half-lives with increasing burial depth in the shallow-water carbonate lagoon of Rib Reef, central Great Barrier Reef, Australia. The top 20 cm of sediment contains a distinct, essentially modern assemblage. Shells recovered at depths from 25 to 125 cm are age-homogeneous and significantly older than the surface layer. Taxon age distributions within sedimentary layers indicate that the top 125 cm of lagoonal sediment is thoroughly mixed on a sub-century scale. The age distributions and shell half-lives of four taxa (Ethalia, Natica, Tellina, and Turbo) are found to be largely distinct. Shell half-lives do not coincide with any single morphological characteristic thought to infer greater durability, but they are strongly related to a combined durability score based on shell density, thickness, and shape. These results illustrate the importance of bioturbation in tropical sedimentary environments, indicate that age estimates in this depositional setting are sensitive to taxon choice, and quantify a taxon-dependent bias in shell longevity and death assemblage formation. © 2009, The Paleontological Society
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    The taphonomic clock in fish otoliths
    (Cambridge University Press, 2021-09-06) Agiadi, K; Azzarone, M; Hua, Q; Kaufman, DS; Thivaiou, D; Albano, PG
    Paleobiological and paleoecological interpretations rely on constraining the temporal resolution of the fossil record. The taphonomic clock, that is, a correlation between the alteration of skeletal material and its age, is an approach for quantifying time-averaging scales. We test the taphonomic clock hypothesis for marine demersal and pelagic fish otoliths from a 10–40 m depth transect on the Mediterranean siliciclastic Israeli shelf by radiocarbon dating and taphonomic scoring. Otolith ages span the last ~8000 yr, with considerable variation in median and range along the transect. Severely altered otoliths, contrary to pristine otoliths, are likely to be older than 1000 yr. For pelagic fish otoliths, at 30 m depth, taphonomic degradation correlates positively with postmortem age. In contrast, no correlation occurs for demersal fishes at 10 and 30 m depth, mostly because of the paucity of very young pristine (<150 yr) otoliths, possibly due to a drop in production over the last few centuries. Contrary to molluscan and brachiopod shells, young otoliths at these depths are little affected and do not show a broad spectrum of taphonomic damage, because those that derive from predation are excreted in calcium- and phosphate-rich feces forming an insoluble crystallic matrix that increases their preservation potential. At 40 m depth, all dated otoliths are very young but rather damaged because of locally chemically aggressive sediments, thus showing no correlation between taphonomic grade and postmortem age. Our results show that local conditions and the target species population dynamics must be considered when testing the taphonomic clock hypothesis. © The Author(s), 2021. Published by Cambridge University Press on behalf of The Paleontological Society.
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    Time-averaging and stratigraphic resolution in death assemblages and Holocene deposits: Sydney Harbour’s molluscan record
    (GeoScience World, 2016-11-01) Dominguez, JG; Kosnik, MA; Allen, AP; Hua, Q; Jacob, DE; Kaufman, DS; Whitacre, KE
    Time-averaging has evolved from an unrecognized variable in paleoecological analyses to a key concept in understanding the dynamics of sedimentary systems and the formation of fossil deposits. Here we used radiocarbon-calibrated amino acid racemization ages from 173 Fulvia tenuicostata shells collected from Sydney Harbour (NSW, Australia) to quantify time-averaging in surficial and excavated death assemblages. A novel approach to estimating the total age-estimate variability of a collection of specimens is presented that integrates the age-estimation error associated with the AAR calibration model and the effect of time-averaging variability on the age distribution. Fulvia collected from a single 1.6-m deep excavation were used to quantify changes in time-averaging with burial depth. Fulvia collected from surficial death assemblages at six sites were used to quantify spatial variation in time-averaging. The median shell age increased from ∼ 150 yr to ∼ 4230 yr and time-averaging from ∼ 40 yr to ∼ 960 yr with increased burial depth. While four sites contained surface shell assemblages with median ages of ∼ 150 yr and time-averaging of ∼ 40 yr, two sites had death assemblages with older median ages and time-averaging > 1900 yr. A decline in the abundance of Fulvia in the post-colonial period is likely responsible for the rarity of very young shells in the surface death assemblages, while local factors such as dredging and other human activities are likely responsible for the total age-estimate variability in the two highly time-averaged surface collections. These analyses provide a geochronological context for assessing ecological changes in the harbor's benthic communities since colonization and offer an important perspective on the formation of Holocene fossil deposits. © 2016 GeoScience World