| 1. |
- Emile-Geay, J., et al.
(författare)
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Data Descriptor: A global multiproxy database for temperature reconstructions of the Common Era
- 2017
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Ingår i: Scientific Data. - : Springer Science and Business Media LLC. - 2052-4463. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- Reproducible climate reconstructions of the Common Era (1 CE to present) are key to placing industrial-era warming into the context of natural climatic variability. Here we present a community-sourced database of temperature-sensitive proxy records from the PAGES2k initiative. The database gathers 692 records from 648 locations, including all continental regions and major ocean basins. The records are from trees, ice, sediment, corals, speleothems, documentary evidence, and other archives. They range in length from 50 to 2000 years, with a median of 547 years, while temporal resolution ranges from biweekly to centennial. Nearly half of the proxy time series are significantly correlated with HadCRUT4.2 surface temperature over the period 1850-2014. Global temperature composites show a remarkable degree of coherence between high-and low-resolution archives, with broadly similar patterns across archive types, terrestrial versus marine locations, and screening criteria. The database is suited to investigations of global and regional temperature variability over the Common Era, and is shared in the Linked Paleo Data (LiPD) format, including serializations in Matlab, R and Python. Since the pioneering work of D'Arrigo and Jacoby1-3, as well as Mann et al. 4,5, temperature reconstructions of the Common Era have become a key component of climate assessments6-9. Such reconstructions depend strongly on the composition of the underlying network of climate proxies10, and it is therefore critical for the climate community to have access to a community-vetted, quality-controlled database of temperature-sensitive records stored in a self-describing format. The Past Global Changes (PAGES) 2k consortium, a self-organized, international group of experts, recently assembled such a database, and used it to reconstruct surface temperature over continental-scale regions11 (hereafter, ` PAGES2k-2013'). This data descriptor presents version 2.0.0 of the PAGES2k proxy temperature database (Data Citation 1). It augments the PAGES2k-2013 collection of terrestrial records with marine records assembled by the Ocean2k working group at centennial12 and annual13 time scales. In addition to these previously published data compilations, this version includes substantially more records, extensive new metadata, and validation. Furthermore, the selection criteria for records included in this version are applied more uniformly and transparently across regions, resulting in a more cohesive data product. This data descriptor describes the contents of the database, the criteria for inclusion, and quantifies the relation of each record with instrumental temperature. In addition, the paleotemperature time series are summarized as composites to highlight the most salient decadal-to centennial-scale behaviour of the dataset and check mutual consistency between paleoclimate archives. We provide extensive Matlab code to probe the database-processing, filtering and aggregating it in various ways to investigate temperature variability over the Common Era. The unique approach to data stewardship and code-sharing employed here is designed to enable an unprecedented scale of investigation of the temperature history of the Common Era, by the scientific community and citizen-scientists alike.
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| 2. |
- Ni, S., et al.
(författare)
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Holocene Hydrographic Variations From the Baltic-North Sea Transitional Area (IODP Site M0059)
- 2020
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Ingår i: Paleoceanography and Paleoclimatology. - 2572-4517. ; 35:2
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Tidskriftsartikel (refereegranskat)abstract
- Deoxygenation affects many continental shelf seas across the world today and results in increasing areas of hypoxia (dissolved oxygen concentration ([O2]) <1.4 ml/L). The Baltic Sea is increasingly affected by deoxygenation. Deoxygenation correlates with other environmental variables such as changing water temperature and salinity and is directly linked to ongoing global climate change. To place the ongoing environmental changes into a larger context and to further understand the complex Baltic Sea history and its impact on North Atlantic climate, we investigated a high accumulation-rate brackish-marine sediment core from the Little Belt (Site M0059), Danish Straits, NW Europe, retrieved during the Integrated Ocean Drilling Program (IODP) Expedition 347. We combined benthic foraminiferal geochemistry, faunal assemblages, and pore water stable isotopes to reconstruct seawater conditions (e.g., oxygenation, temperature, and salinity) over the past 7.7 thousand years (ka). Bottom water salinity in the Little Belt reconstructed from modeled pore water oxygen isotope data increased between 7.7 and 7.5 ka BP as a consequence of the transition from freshwater to brackish-marine conditions. Salinity decreased gradually (from 30 to 24) from 4.1 to ~2.5 ka BP. By using the trace elemental composition (Mg/Ca, Mn/Ca, and Ba/Ca) and stable carbon and oxygen isotopes of foraminiferal species Elphidium selseyensis and E. clavatum, we identified that generally warming and hypoxia occurred between about 7.5 and 3.3 ka BP, approximately coinciding in time with the Holocene Thermal Maximum (HTM). These changes of bottom water conditions were coupled to the North Atlantic Oscillation (NAO) and relative sea level change.
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| 3. |
- Sheldon, C. M., et al.
(författare)
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Variable influx of West Greenland Current water into the Labrador Current through the last 7200 years : a multiproxy record from Trinity Bay (NE Newfoundland)
- 2015
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Ingår i: arktos. - : Springer Science and Business Media LLC. - 2364-9453 .- 2364-9461. ; 1:8
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Tidskriftsartikel (refereegranskat)abstract
- A multiproxy study of marine sediment gravity core AI07-06G from Trinity Bay, Newfoundland, recorded changes in the strength of the Labrador Current (LC) during the Holocene. From ca. 7.2–5.7 cal kyr BP, Trinity Bay’s seafloor was influenced by cooled Atlantic water derived from the West Greenland Current (WGC) Davis Strait branch, merging into the relatively cold LC. This Atlantic water influence gradually decreased after ca. 5.7 cal kyr BP, reaching a minimum at ca. 4.9 cal kyr BP. In contrast, surface temperatures were relatively low due to cold surface water dominated by sea ice and meltwater carried south by the LC. Icebergs from outlet glaciers around Baffin Bay were abundant in the LC prior to ca. 5.5 cal kyr BP. From ca. 4.9–2.9 cal kyr BP, bottom waters became slightly colder and salinity decreased, as increased mixing of the water column brought less saline surface waters towards the seafloor. This may be explained by a weaker North Atlantic subpolar gyre, transporting less Atlantic water from the WGC to the (outer) LC. Arctic meltwater transport was reduced as glacial melting decreased at the end of the Holocene Thermal Optimum. At ca. 2.9 cal kyr BP, bottom waters returned to colder, more stable conditions, indicating a slight decrease in bottom-water ventilation. After ca. 2.1 cal kyr BP, surface water temperatures dropped and sea ice flux increased. The seafloor of Trinity Bay saw warmer conditions, consistent with a stronger subpolar gyre and increased influx of Atlantic-sourced water.
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| 4. |
- Kotthoff, U., et al.
(författare)
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Reconstructing Holocene temperature and salinity variations in the western Baltic Sea region: a multi-proxy comparison from the Little Belt (IODP Expedition 347, Site M0059)
- 2017
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 14, s. 5607-5632
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Tidskriftsartikel (refereegranskat)abstract
- Sediment records recovered from the Baltic Sea during Integrated Ocean Drilling Program Expedition 347 provide a unique opportunity to study paleoenvironmental and climate change in central and northern Europe. Such studies contribute to a better understanding of how environmental parameters change in continental shelf seas and enclosed basins. Here we present a multi-proxy-based reconstruction of paleotemperature (both marine and terrestrial), paleosalinity, and paleoecosystem changes from the Little Belt (Site M0059) over the past ∼ 8000 years and evaluate the applicability of inorganic- and organic-based proxies in this particular setting. All salinity proxies (diatoms, aquatic palynomorphs, ostracods, diol index) show that lacustrine conditions occurred in the Little Belt until ∼ 7400 cal yr BP. A connection to the Kattegat at this time can thus be excluded, but a direct connection to the Baltic Proper may have existed. The transition to the brackish–marine conditions of the Littorina Sea stage (more saline and warmer) occurred within ∼ 200 years when the connection to the Kattegat became established after ∼ 7400 cal yr BP. The different salinity proxies used here generally show similar trends in relative changes in salinity, but often do not allow quantitative estimates of salinity. The reconstruction of water temperatures is associated with particularly large uncertainties and variations in absolute values by up to 8 °C for bottom waters and up to 16 °C for surface waters. Concerning the reconstruction of temperature using foraminiferal Mg / Ca ratios, contamination by authigenic coatings in the deeper intervals may have led to an overestimation of temperatures. Differences in results based on the lipid paleothermometers (long chain diol index and TEXL86) can partly be explained by the application of modern-day proxy calibrations to intervals that experienced significant changes in depositional settings: in the case of our study, the change from freshwater to marine conditions. Our study shows that particular caution has to be taken when applying and interpreting proxies in coastal environments and marginal seas, where water mass conditions can experience more rapid and larger changes than in open ocean settings. Approaches using a multitude of independent proxies may thus allow a more robust paleoenvironmental assessment.
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| 5. |
- van Wirdum, Falkje, et al.
(författare)
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Middle to late holocene variations in salinity and primary productivity in the central Baltic Sea : A multiproxy study from the landsort deep
- 2019
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Ingår i: Frontiers in Marine Science. - : Frontiers Media S.A.. - 2296-7745. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- Anthropogenic forcing has led to an increased extent of hypoxic bottom areas in the Baltic Sea during recent decades. The Baltic Sea ecosystem is naturally prone to the development of hypoxic conditions due to its geographical, hydrographical, geological, and climate features. Besides the current spreading of hypoxia, the Baltic Sea has experienced two extensive periods of hypoxic conditions during the Holocene, caused by changing climate conditions during the Holocene Thermal Maximum (HTM; 8–4.8 cal ka BP) and the Medieval Climate Anomaly (MCA; 1–0.7 cal ka BP). We studied the variations in surface and bottom water salinity and primary productivity and their relative importance for the development and termination of hypoxia by using microfossil and geochemical data from a sediment core retrieved from the Landsort Deep during IODP Expedition 347 (Site M0063). Our findings demonstrate that increased salinity was of major importance for the development of hypoxic conditions during the HTM. In contrast, we could not clearly relate the termination of this hypoxic period to salinity changes. The reconstructed high primary productivity associated with the hypoxic period during the MCA is not accompanied by considerable increases in salinity. Our proxies for salinity show a decreasing trend before, during and after the MCA. Therefore, we suggest that this period of hypoxia is primarily driven by increasing temperatures due to the warmer climate. These results highlight the importance of natural climate driven changes in salinity and primary productivity for the development of hypoxia during a warming climate.
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| 6. |
- Möller, Per, et al.
(författare)
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Data set on sedimentology, palaeoecology and chronology of Middle to Late Pleistocene deposits on the Taimyr Peninsula, Arctic Russia
- 2019
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Ingår i: Data in Brief. - : Elsevier. - 2352-3409. ; 25, s. 1-35
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Tidskriftsartikel (refereegranskat)abstract
- This Data in Brief paper contains data (including images) from Quaternary sedimentary successions investigated along the Bol'shaya Balakhnya River and the Luktakh-Upper Taimyra-Logata river system on southern Taimyr Peninsula, NW Siberia (Russia). Marine foraminifera and mollusc fauna composition, extracted from sediment samples, is presented. The chronology (time of deposition) of the sediment successions is reconstructed from three dating methods; (i) radiocarbon dating of organic detritus (from lacustrine/fluvial sediment) and molluscs (marine sediment) as finite ages (usually <42 000 years) or as non-finite ages (>42 000-48 000 years) on samples/sediments beyond the radiocarbon dating limit; (ii) Electron Spin Resonance (ESR) dating on marine molluscs (up to ages >400 000 years); (iii) Optically Stimulated Luminescence (OSL) dating, usually effective up to 100-150 0000 years. Terrestrial Cosmogenic Nuclide (TCN) exposure dating has been applied to boulders resting on top of moraine ridges (Ice Marginal Zones). See (Moller et al., 2019) (doi.org/10.1016/j.earscirev.2019.04.004) for interpretation and discussion of all data. (c) 2019 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
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| 7. |
- Möller, Per, et al.
(författare)
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Glacial and palaeo-environmental history of the Cape Chelyuskin area, Arctic Russia
- 2008
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Ingår i: Polar Research. - : Norwegian Polar Institute. - 0800-0395 .- 1751-8369. ; 27:2, s. 222-248
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Tidskriftsartikel (refereegranskat)abstract
- Quaternary glacial stratigraphy and relative sea-level changes reveal at least two glacial expansions over the Chelyuskin Peninsula, bordering the Kara Sea at about 77°N in the Russian Arctic, as indicated from tills interbedded with marine sediments, exposed in stratigraphic superposition, and from raised beach sequences mapped to altitudes of at least up to ca. 80 m a.s.l. Chronological control is provided by accelerator mass spectrometry 14C dating, electron-spin resonance and optically stimulated luminescence geochronology. Major glaciations, followed by deglaciation and marine inundation, occurred during marine oxygen isotope stages 6–5e (MIS 6–5e) and stages MIS 5d–5c. These glacial sediments overlie marine sediments of Pliocene age, which are draped by fluvial sediment of a pre-Saalian age, thereby forming palaeovalley/basin fills in the post-Cretaceous topography. Till fabrics and glacial Tectonics record expansions of local ice caps exclusively, suggesting wet-based ice cap advance, followed by cold-based regional ice-sheet expansion. Local ice caps over highland sites along the perimeter of the shallow Kara Sea, including the Byrranga Mountains and the Severnaya Zemlya archipelago, appear to have repeatedly fostered initiation of a large Kara Sea ice sheet, with the exception of the Last Glacial Maximum (MIS 2), when Kara Sea ice neither impacted the Chelyuskin Peninsula nor Severnaya Zemlya, and barely touched the northern coastal areas of the Taymyr Peninsula.
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| 8. |
- Möller, Per, et al.
(författare)
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Glacial history and palaeo-environmental change of southern Taimyr Peninsula, Arctic Russia, during the Middle and Late Pleistocene
- 2019
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Ingår i: Earth-Science Reviews. - : Elsevier. - 0012-8252 .- 1872-6828. ; 196
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Forskningsöversikt (refereegranskat)abstract
- We here reconstruct a glacial and climate history of arctic NW Siberia for the last similar to 600,000 years, based on the stratigraphy and chronology of 35 studied river sections on the southern Taimyr Peninsula. From this strati graphic mosaic we have identified four glacial events, marked by tills/glaciotectonics, which are intercalated with mainly marine sediments deposited in proglacial settings during transitions from glacial conditions into subsequent interglacials/interstadials. The traces of early shelf-based Kara Sea Ice Sheet (KSIS) glaciations in marine isotope stages (MIS) 12-14 and 8 are sparsely preserved, but these ice advances are suggested to have terminated far south into the central Siberian uplands, as also was the case with the younger Taz glaciation (MIS 6). The inception phase of the latter glaciation was complex, with ice advancing into a proglacial marine basin both from the south (Putorana - Anabar uplands) and the north. The deglaciation leading into the Karginsky interglacial (MIS 5e) was marked by the development of the southerrunost ice-marginal zones (IMZs) on the Taimyr lowlands - the Urdakh and Sampesa IMZs. The most recent (late Pleistocene) glacial cycle is recorded by three successively smaller KSIS advances from the Kara Sea shelf onto Taimyr, of which only the first, during Early Zyryanka (MIS 5d), reached south of the Byrranga Mountains, with its maximum extent marked by the Jangoda - Syntabul - Severokokorsky IMZ. Retreat of the ice margin during MIS 5c-b was accompanied by deposition of glaciomarine sediment in the proglacial basin and deposition of large successions of delta sediments in the foothills of the Byrranga Motmtains, reaching a >= 100 m above present sea level. The region north of the Byrranga Mountains was subjected to two subsequent KSIS glaciations, during MIS 4 and MIS 2, while the area south of the Byrranga Mountains transitioned to a terrestrial environment from the Middle into the Lower Zyryanka, as evidenced by deposition of fluvial, aeolian and ice-complex (Yedoma) sediments.
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| 9. |
- Ni, S., et al.
(författare)
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Early diagenesis of foraminiferal calcite under anoxic conditions : A case study from the Landsort Deep, Baltic Sea (IODP Site M0063)
- 2020
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Ingår i: Chemical Geology. - : Elsevier BV. - 0009-2541. ; 558
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Tidskriftsartikel (refereegranskat)abstract
- The chemical composition of foraminiferal calcite is widely used for studying past environmental conditions and biogeochemistry. However, high rates of microbial organic matter degradation and abundant dissolved metal sources in sediments and pore waters may impede the application of foraminifera-based proxies due to formation of secondary carbonates or other authigenic minerals on and/or inside of foraminiferal tests. Secondary carbonate precipitation severely alters the bulk foraminiferal geochemistry and can be difficult to eliminate through standard foraminiferal trace element cleaning procedures. We present results showing the mineral composition and formation sequence of diagenetic coatings on foraminiferal tests formed under extreme anoxic conditions in the Baltic Sea's deepest basin (the Landsort Deep, IODP Exp. 347, Site M0063). Our study focuses primarily on the diagenetic carbonates present on and in the tests of the low-oxygen tolerant benthic foraminiferal species Elphidium selseyensis and Elphidium clavatum. We applied various geochemical and imaging methods to ascertain the diagenesis processes and the authigenic mineral formation sequence on foraminifera. The authigenic carbonates were enriched in Mn, Mg, Fe and Ba, depending on the environmental redox conditions when the authigenic carbonates were precipitated. Concentrations of redox-sensitive elements such as Mn and Fe were particularly elevated in bottom waters and sedimentary pore waters under oxygen-depleted conditions in the Landsort Deep, resulting in formation of carbonates with highly elevated Mn and Fe contents. In addition to Mn- and Fe carbonates, several other types of authigenic minerals also formed on and in the foraminiferal chambers, including authigenic calcite, and non-carbonate accessory minerals. The formation sequence reveals the redox sensitivities of different elements and the preferential sequence of oxidants used by the microbes during organic matter oxidation and secondary redox reactions. This study provides a case study of extreme early diagenesis of foraminiferal calcite and may serve as a valuable guide when interpreting foraminiferal trace element records from low oxygen environments.
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| 10. |
- Ni, S., et al.
(författare)
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Last interglacial seasonal hydroclimate in the North Sea–Baltic Sea region
- 2023
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Ingår i: Quaternary Science Reviews. - 0277-3791 .- 1873-457X. ; 312
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Tidskriftsartikel (refereegranskat)abstract
- The Last Interglacial (LIG) experienced substantial changes in seasonal insolation compared with the present day, which may have affected the hydrography and water-mass exchange in the North Sea and Baltic Sea region. Here we investigate the effects of solar radiation and greenhouse gas (GHG) forcing on the regional climate by analyzing model simulations of the LIG (127 ka BP), pre-industrial (PI, 1850 CE), and present-day (PD, 1990 CE) climates. We also interpret the reconstructed seasonal bottom water conditions using benthic foraminifera and geochemistry data. Our simulations reveal that during the LIG, the Baltic Sea region (including the Kattegat and the Danish Straits) experienced more saline and colder bottom waters than those in the PD, in agreement with the reconstruction data. This can be attributed to lower GHG levels and enhanced water exchange of cooler, saline North Sea water into the Baltic Sea during the LIG. The thermocline was stronger during the summer months in the LIG, mainly due to the higher sea surface temperature (SST) compared to that of the PD resulting from increased summer insolation. Further, the temperature anomalies (LIG–PD) show significant inverse correlations with the precipitation–minus–evaporation (P–E) at the Baltic Sea entrance. However, the P–E balance appears to have had minimal impact on salinity changes in the North Sea, the Baltic Proper, and the open sea area. Our findings indicate that monthly surface and bottom water salinity anomalies of LIG-PI exhibit strong positive correlations with the North Atlantic Oscillation (NAO) anomalies in the Baltic entrance region. During the LIG, a more positive phase of the NAO index in autumn played a crucial role in wind-driven major inflows and led to more intensive water exchange in the North Sea–Baltic Sea region compared to the late Holocene.
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