Kazuho Horiuchi

A global multiproxy database for temperature reconstructions of the Common Era

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.

Cosmic ray event of A.D. 774–775 shown in quasi‐annual 10Be data from the Antarctic Dome Fuji ice core

14C content in tree rings and 10Be concentration records in polar ice core provide information about past cosmic ray intensities. The A.D. 774–775 cosmic ray event has been identified by 14C measurement in several tree rings from all over the world. Although the quasi-decadal 10Be Dome Fuji data in the Antarctic ice core also shows a sharp peak around A.D. 775, annual 10Be variations in the Dome Fuji core or in other cores have not been revealed. We have measured quasi-annual 10Be concentrations from approximately A.D. 763–794 in the Dome Fuji ice core, and detected a clear increase (~80% above the baseline) in 10Be concentration around A.D. 775. However, an accurate height of this increase is not straightforwardly estimated due to the background variation in 10Be concentration. The 10Be increase can be due to the same cosmic ray event as shown in the 14C content in A.D. 774–775.

State dependence of climatic instability over the past 720,000 years from Antarctic ice cores and climate modeling

Global cooling in intermediate glacial climate with northern ice sheets preconditions climatic instability with bipolar seesaw. Climatic variabilities on millennial and longer time scales with a bipolar seesaw pattern have been documented in paleoclimatic records, but their frequencies, relationships with mean climatic state, and mechanisms remain unclear. Understanding the processes and sensitivities that underlie these changes will underpin better understanding of the climate system and projections of its future change. We investigate the long-term characteristics of climatic variability using a new ice-core record from Dome Fuji, East Antarctica, combined with an existing long record from the Dome C ice core. Antarctic warming events over the past 720,000 years are most frequent when the Antarctic temperature is slightly below average on orbital time scales, equivalent to an intermediate climate during glacial periods, whereas interglacial and fully glaciated climates are unfavourable for a millennial-scale bipolar seesaw. Numerical experiments using a fully coupled atmosphere-ocean general circulation model with freshwater hosing in the northern North Atlantic showed that climate becomes most unstable in intermediate glacial conditions associated with large changes in sea ice and the Atlantic Meridional Overturning Circulation. Model sensitivity experiments suggest that the prerequisite for the most frequent climate instability with bipolar seesaw pattern during the late Pleistocene era is associated with reduced atmospheric CO2 concentration via global cooling and sea ice formation in the North Atlantic, in addition to extended Northern Hemisphere ice sheets.

Radiocarbon Analysis of Tree Rings from a 15.5-cal kyr BP Pyroclastically Buried Forest: A Pilot Study

We have determined the radiocarbon ages for 40-yr-interval tree rings in 2 fossil trees of the Towada Hachinohe buried forest, northeastern Honshu Island, Japan. The 14C ages range from 13.0 to 13.3 kyr BP (about 15.5 cal kyr BP). The weighted average of the 14C age of the outermost 5 rings is 13,133 33 BP, which can be calibrated to 15,36315,679 cal BP by using the IntCal04 standard curve (Reimer et al. 2004). ?he estimated ?14C values range between 265 and 300 and show approximately sinusoidal fluctuation of an indicated ~200-yr cycle, perhaps reflecting contemporary solar activity change. Comparison between the tree 14C profile and the Cariaco Basin 14C record provides further information on the accurate date of the Towada Hachinohe buried forest and the eruption that produced it. 14C analysis of tree rings from the buried forest may contribute to the construction of a better 14C calibration curve and the elucidation of solar activity change during the last glacial period, as well as possible global and regional impacts of the huge eruption from Towada Volcano.

Precessional control on ocean productivity in the Western Pacific Warm Pool for the last 400 kyr: Insight from biogenic magnetite

The Western Pacific Warm Pool plays a significant role in large-scale atmospheric circulation and global hydrology. We conducted an environmental magnetic study of two late Pleistocene sediment cores from the western equatorial Pacific Ocean offshore of New Guinea in order to better constrain climatic and oceanographic variability, particularly spatiotemporal ocean productivity variations. Magnetic property measurements and transmission electron microscopy reveal that the magnetic mineral assemblages in the studied sediments are a mixture of biogenic and terrigenous magnetite. Variations in the acid soluble sediment component, interpreted as carbonate content, and the proportion of biogenic to terrigenous magnetite estimated from the ratio of anhysteretic to saturation remanent magnetizations are in-phase with northern hemisphere summer insolation variations. We interpret that ocean productivity increased during insolation maxima, which induced higher populations of magnetotactic bacteria through a larger nutrient supply to the seafloor. This interpretation assumes that magnetotactic bacterial populations are greatest in sediments just below the seafloor. Precessional frequencies in magnetic mineral concentration variations are suppressed after correction for carbonate dilution, whereas cyclic changes with a ∼100 kyr periodicity remain in carbonate-free magnetic concentration variations. Glacial/interglacial changes in bottom water currents may have influenced transportation and deposition of magnetic minerals. We demonstrate the usefulness of magnetic proxies for paleoceanographic studies, particularly of biogenic magnetite proxies for estimating paleoproductivity variations. This article is protected by copyright. All rights reserved.

14C Dating of Holocene Soils from an Island in Lake Pumoyum Co (Southeastern Tibetan Plateau)

Soil samples from an 85-cm-long continuous section (PY608ES) were collected from an island in Lake Pumoyum Co (southeastern Tibetan Plateau, ~5020 m asl) in August 2006. To estimate past environmental conditions of Lake Pumoyum Co during the Holocene, we analyzed radiocarbon ages, stable carbon isotope compositions, and total organic carbon/total nitrogen (TOC/TN) atomic ratios of the soil samples. The 14C measurements were performed with the Tandetron accelerator mass spectrometry system at the Center for Chronological Research, Nagoya University. The 14C concentration in the surface layer (101 pMC; 5-10 cm soil depth) was nearly modern. A 14C chronology of the sequence indicated that continuous soil development began on the island in Lake Pumoyum Co at ~5800 cal BP (at 63 cm soil depth, the top of a gravel layer). These results may reflect a decrease in the lake level in the middle Holocene. The age of the obvious lithologic boundary (~5800 cal BP) corresponds to the end of Holocene climate optimum.

Data Descriptor: A global multiproxy database for temperature reconstructions of the Common Era

PAGES, a core project of Future Earth, is supported by the U.S. and Swiss National Science Foundations. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Some of this work was conducted as part of the North America 2k Working Group supported by the John Wesley Powell Center for Analysis and Synthesis, funded by the U.S. Geological Survey. B. Bauer, W. Gross, and E. Gille (NOAA National Centers for Environmental Information) are gratefully acknowledged for helping assemble the data citations and creating the NCEI versions of the PAGES 2k data records. We thank all the investigators whose commitment to data sharing enables the open science ethos embodied by this project.

Characterization and 10Be content of iron carbonate concretions for genetic aspects – Weathering, desert varnish or burning: Rim effects in iron carbonate concretions

The research investigated three iron carbonate (siderite) sedimentary concretions from Nagykovácsi, Úri and Délegyháza, Hungary. To identify possible source rocks and effects of the glaze-like exposed surface of the concretions, we carried on comparative petrological, mineralogical, geochemical and isotopic studies. The samples were microbially mediated siderite concretions with embedded metamorphous and igneous mineral clasts, and had specific rim belts characterized by semi-concentric outer Fe-oxide layers, fluffy pyrite-rich outer belts and siderite inner parts. We investigated the cross section of the Fe-carbonate concretions by independent methodologies in order to identify their rim effects. Their surficial oxide layers showed evidence of degassing of the exposed surface caused most probably by elevated temperatures. The inner rim pyrite belt in the concretions excluded the possibility of a prolonged wet surface environment. Microtextural and mineralogical features did not support desert varnish formation. 10Be nuclide values of the Nagykovácsi and Uri concretions were far above the level of terrestrial in-situ cosmogenic nuclides, but they were consistent with the lowest levels for meteorites. Though the data were not conclusive to confirm any kind of known origin, they are contradictary, and open possibilities for a scenario of terrestrial meteorite origin.