183 research outputs found
Paleomagnetism of Quaternary sediments from Lomonosov Ridge and Yermak Plateau: implications for age models in the Arctic Ocean
No full textInclination patterns of natural remanent magnetization (NRM) in Quaternary sediment cores from the Arctic Ocean have been widely used for stratigraphic correlation and the construction of age models, however, shallow and negative NRM inclinations in sediments deposited during the Brunhes Chron in the Arctic Ocean appear to have a partly diagenetic origin. Rock magnetic and mineralogical studies demonstrate the presence of titanomagnetite and titanomaghemite. Thermal demagnetization of the NRM indicates that shallow and negative inclination components are largely “unblocked” below ?300 °C, consistent with a titanomaghemite remanence carrier. Following earlier studies on the Mendeleev–Alpha Ridge, shallow and negative NRM inclination intervals in cores from the Lomonosov Ridge and Yermak Plateau are attributed to partial self-reversed chemical remanent magnetization (CRM) carried by titanomaghemite formed during seafloor oxidation of host (detrital) titanomagnetite grains. Distortion of paleomagnetic records due to seafloor maghemitization appears to be especially important in the perennially ice covered western (Mendeleev–Alpha Ridge) and central Arctic Ocean (Lomonosov Ridge) and, to a lesser extent, near the ice edge (Yermak Plateau). On the Yermak Plateau, magnetic grain size parameters mimic the global benthic oxygen isotope record back to at least marine isotope stage 6, implying that magnetic grain size is sensitive to glacial–interglacial changes in bottom-current velocity and/or detrital provenance
Dating late Quaternary planktonic foraminifer Neogloboquadrina pachyderma from the Arctic Ocean using amino acid racemization
No full textThe long-term rate of racemization for amino acids preserved in planktonic foraminifera was determined by using independently dated sediment cores from the Arctic Ocean. The racemization rates for aspartic acid (Asp) and glutamic acid (Glu) in the common taxon, Neogloboquadrina pachyderma, were calibrated for the last 150 ka using 14C ages and the emerging Quaternary chronostratigraphy of Arctic Ocean sediments. An analysis of errors indicates realistic age uncertainties of about ±12% for Asp and ±17% for Glu. Fifty individual tests are sufficient to analyze multiple subsamples, identify outliers, and derive robust sample mean values. The new age equation can be applied to verify and refine age models for sediment cores elsewhere in the Arctic Ocean, a critical region for understanding the dynamics of global climate change
Plio-Pleistocene sedimentary record from the Northwind Ridge: new insights into paleoclimatic evolution of the western Arctic Ocean for the last 5 Ma
No full textSediment core HLY0503-03JPC from the top of the Northwind Ridge provides the first confirmed Plio-Pleistocene record from the western Arctic Ocean, with calcareous microfossils uniquely preserved to ca. 5 Ma. Results are compared to nearby core P1-93AR-P23 from the ridge slope, which was previously used to reconstruct early Quaternary sea-ice conditions in the region (Polyak et al. in Quat Sci Rev 79:145–156, 2013), and is now re-dated to at least the late Pliocene. Ages were estimated primarily from strontium isotope stratigraphy on benthic foraminifers. Based on multiple physical, paleomagnetic, elemental geochemical, and paleobiological (foraminifers) proxies, we identify three major stratigraphic divisions (Units 1, 2a, and 2b) roughly representing upper to middle (“glacial”) Quaternary, lower Quaternary to Pliocene, and lower Pliocene to possibly upper Miocene (undated). Benthic foraminiferal assemblages were utilized to evaluate paleo-sea-ice conditions, while other proxies were used to interpret paleocirculation and sediment transport processes. Early Quaternary and older sediments indicate diminutive effect from glaciations, reduced sea-ice conditions, and a periodic strong current impact on the ridge top, possibly due to an enhanced Atlantic water flow. Ages derived from the first foraminiferal tests appearing at ca. 5 Ma likely indicate a redeposition pulse that we attribute to the onset of Pacific water throughflow via the Bering Strait. A large hiatus above this level in JPC3 spans most of the Pliocene. The Unit 2a/1 boundary, estimated to ca. 0.8 Ma, is marked by an abrupt faunal and sedimentary change, which is consistent with the major climatic shift that occurred during this time (Mid-Pleistocene Transition). Unit 1 exhibits a strong control from glacial cyclicity, with a progressive expansion of the Laurentide Ice Sheet primarily affecting the study region, and mostly perennial sea-ice conditions. Overall results suggest that the Pliocene and early Pleistocene may provide relevant paleoclimatic analogs for the rapidly changing Arctic environments of today
Study of Core 92AR-P25 from the Northwind Ridge, Central Arctic Ocean
No full textThe Arctic Ocean is presently the least understood ocean in the world. The
perennial sea ice that covers most of the Arctic has hindered exploration and
interpretation of this last remaining portion of the Earth’s surface. The geologic history of this ocean is not fully understood and needs to be studied in greater detail. The stratigraphic record in the Arctic is a topic of much debate, specifically when discussing
ages and sedimentation rates. Various ways of age dating has shed new light on ages and
sedimentation rates of the established stratigraphy. Proxies such as microfossils and isotope evidence are giving us new insights to the paleoceanography of the Arctic Ocean basin. Core 92AR-P25 from the Northwind Ridge shows correlation with the
paleomagnetic time scale and agreement with the manganese color cycles proposed by
Jakobsson et al, (2000). The correlation of the core, shows that many cores throughout
the Central Arctic Ocean can be similarly correlated, allowing us to form a
paleoceanography history of the Arctic Ocean
Quaternary foraminiferal data from western Arctic Ocean sediment cores, 2013-2016
No full textData reported for downcore distribution of foraminifers in three sediment cores distributed across the western Arctic Ocean (Northwind, Mendeleev, and Lomonosov Ridges). Data include total numbers for benthic and planktic foraminifers and identification of benthic species. The purpose of the data is to characterize stratigraphic changes in foraminiferal assemblages as proxies for sedimentary environments. This investigation provides insights into middle to late Pleistocene history of Arctic paleoceanographic and sea-ice conditions on multi-millennial time scales. Calcareous foraminiferal abundances and composition show stratigraphically consistent development, including glacial–interglacial variability and long-term evolution of foraminiferal assemblages. The long-term trend shows notably a diminishing role of phytodetritus-related species indicative of ice-margin proximity at the expense of oligotrophic species adapted to live under persistent sea ice. These changes presumably indicate an overall expansion of year-round ice cover in the Arctic during the Pleistocene. Data is reformatted from Lazar, K.M., Polyak, L., 2016. Middle to late Pleistocene benthic foraminifers in the Arctic Ocean: implications for sea-ice and circulation history. Marine Micropaleontology 126, 19-30
Quaternary foraminiferal data from western Arctic Ocean sediment cores, 2013-2016
No full textData reported for downcore distribution of foraminifers in three sediment cores distributed across the western Arctic Ocean (Northwind, Mendeleev, and Lomonosov Ridges). Data include total numbers for benthic and planktic foraminifers and identification of benthic species. The purpose of the data is to characterize stratigraphic changes in foraminiferal assemblages as proxies for sedimentary environments. This investigation provides insights into middle to late Pleistocene history of Arctic paleoceanographic and sea-ice conditions on multi-millennial time scales. Calcareous foraminiferal abundances and composition show stratigraphically consistent development, including glacial–interglacial variability and long-term evolution of foraminiferal assemblages. The long-term trend shows notably a diminishing role of phytodetritus-related species indicative of ice-margin proximity at the expense of oligotrophic species adapted to live under persistent sea ice. These changes presumably indicate an overall expansion of year-round ice cover in the Arctic during the Pleistocene. Data is reformatted from Lazar, K.M., Polyak, L., 2016. Middle to late Pleistocene benthic foraminifers in the Arctic Ocean: implications for sea-ice and circulation history. Marine Micropaleontology 126, 19-30
Correlation of sediment core characteristics from Mendeleev Ridge, Central Arctic Ocean
No full textOcean sediment cores can provide key information on timing and nature of climate events. Two ocean sediment cores from Mendeleev Ridge, Arctic Ocean, one of which has been previously studied and dated with absolute age dating techniques, are compared for various attributes, notably color, biogenic matter, bulk density, and coarse-grained content. These proxies are used to correlate the two cores and assign timing to the one for which no absolute age data exists. Timing of glacial and interglacial events and marine isotope stages (MIS) is thus assigned. Rough estimates of sedimentation rates are compared, and large differences in rates are inferred. Differences in grain size between shallow and deep cores suggests that winnowing and transport of sediment from upslope is a factor in deposition in the area
Changes in terrestrial organic matter input to the Mendeleev Ridge, western Arctic Ocean, during the Late Quaternary
No full textHydrocarbons and glycerol dialkyl glycerol tetraethers (GDGTs) were analyzed in Late Pleistocene sediments of Core HLY0503-08JPC collected at the Mendeleev Ridge during the Healy-Oden Trans Arctic Expedition 2005 (HOTRAX'05) to investigate environmental changes in the western Arctic Ocean during the last full glacial cycle, ca. 130 kyr. Variations in long-chain n-alkane and GDGT concentrations correspond to alternated color banding, brown (interglacial/interstadial) and grayish (glacial/stadial) layers. Grayish layers are characterized by abundant higher plant n-alkanes and branched GDGTs, implying larger contribution of terrestrial plant and soil organic matter (OM) in glacial environments, possibly due to the deposition of fine-grained products of glacial erosion in the Amerasian basin. Lithic n-alkanes derived from mature OM show pronounced peaks, which can be classified into six types presumably indicative of various sediment sources. Some peaks are correlated to events of iceberg discharge and freshwater outbursts from proglacial lakes of the Eurasian and, possibly, Laurentide ice sheets, suggesting that other peaks may correspond to similar events
(Table 2) Stable isotope composition of benthic foraminifera from surface sediments of the Kara Sea
No full text(Table 2) Stable isotope composition of benthic foraminifera from surface sediments of the Kara Se
(Table 4) Stable oxygen isotope composition of water samples of the Kara Sea
No full text(Table 4) Stable oxygen isotope composition of water samples of the Kara Se
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