ABSTRACT
The polar oceans play a vital role in regulating atmospheric CO2 concentrations (pCO2) during the Pleistocene glacial cycles. However, despite being the largest modern reservoir of respired carbon, the impact of the subarctic Pacific remains poorly understood due to limited records. Here, we present high-resolution, 230Th-normalized export productivity records from the subarctic northwestern Pacific covering the last five glacial cycles. Our records display pronounced, glacial-interglacial cyclicity superimposed with precessional-driven variability, with warm interglacial climate and high boreal summer insolation providing favorable conditions to sustain upwelling of nutrient-rich subsurface waters and hence increased export productivity. Our transient model simulations consistently show that ice sheets and to a lesser degree, precession are the main drivers that control the strength and latitudinal position of the westerlies. Enhanced upwelling of nutrient/carbon-rich water caused by the intensification and poleward migration of the northern westerlies during warmer climate intervals would have led to the release of previously sequestered CO2 from the subarctic Pacific to the atmosphere. Our results also highlight the significant role of the subarctic Pacific in modulating pCO2 changes during the Pleistocene climate cycles, especially on precession timescale ( ~ 20 kyr).
ABSTRACT
The evolution and driving mechanism of the South Asian summer monsoon (SASM) are still poorly understood. We here present a 12-Myr long SASM record by analyzing the strontium and neodymium isotopic composition of detrital components at IODP Exp. 359 Site U1467 from the northern Indian Ocean. The provenance investigation demonstrates that more dust enriched in εNd from northeastern Africa and the Arabian Peninsula was transported to the study site by monsoonal and Shamal winds during the summer monsoon season. A two-step weakening of the SASM wind since ~12 Ma is proposed based on the εNd record. This observational phenomenon is supported by climate modeling results, demonstrating that the SASM evolution was mainly controlled by variations in the gradient between the Mascarene High and the Indian Low, associated with meridional shifts of the Hadley Cell and the Intertropical Convergence Zone, which were caused by interhemispheric ice-sheet growth since the Middle Miocene.
ABSTRACT
This data article describes data of magnetic stratigraphy and anisotropy of isothermal remanent magnetization (AIRM) from "Magnetic properties of early Pliocene sediments from IODP Site U1467 (Maldives platform) reveal changes in the monsoon system" [1]. Acquisition of isothermal magnetization on pilot samples and anisotropy of isothermal remanent magnetization are reported as raw data; magnetostratigraphic data are reported as characteristic magnetization (ChRM).
ABSTRACT
The Yellow River (or Huanghe and also known as China's Sorrow in ancient times), with the highest sediment load in the world, provides a key link between continental erosion and sediment accumulation in the western Pacific Ocean. However, the exact age of its influence on the marginal sea is highly controversial and uncertain. Here we present high-resolution records of clay minerals and lanthanum to samarium (La/Sm) ratio spanning the past ~1 million years (Myr) from the Bohai and Yellow Seas, the potential sedimentary sinks of the Yellow River. Our results show a climate-driven provenance shift from small, proximal mountain rivers-dominance to the Yellow River-dominance at ~880 ka, a time period consistent with the Mid-Pleistocene orbital shift from 41-kyr to 100-kyr cyclicity. We compare the age of this provenance shift with the available age data for Yellow River headwater integration into the marginal seas and suggest that the persistent influence of the Yellow River on the Chinese marginal seas must have occurred at least ~880 ka ago. To our knowledge, this study provides the first offshore evidence on the drainage history of the Yellow River within an accurate chronology framework.
ABSTRACT
The South Asian Monson (SAM) is one of the most intense climatic elements yet its initiation and variations are not well established. Dating the deposits of SAM wind-driven currents in IODP cores from the Maldives yields an age of 12. 9 Ma indicating an abrupt SAM onset, over a short period of 300 kyrs. This coincided with the Indian Ocean Oxygen Minimum Zone expansion as revealed by geochemical tracers and the onset of upwelling reflected by the sediment's content of particulate organic matter. A weaker 'proto-monsoon' existed between 12.9 and 25 Ma, as mirrored by the sedimentary signature of dust influx. Abrupt SAM initiation favors a strong influence of climate in addition to the tectonic control, and we propose that the post Miocene Climate Optimum cooling, together with increased continentalization and establishment of the bipolar ocean circulation, i.e. the beginning of the modern world, shifted the monsoon over a threshold towards the modern system.
ABSTRACT
The chemical composition of some glass samples in Jin and Yuan Dynasty were analyzed by EDXRF, to discuss the technological character of these glass samples. The result shows that the chemical composition of these glass samples is very complex. According to the chemical composition, these glass samples include K2-O-CaO-SiO2, Na2O-CaO-SiO2 and K2O-CaO-PbO-SiO2 glass, and a crystal SiO2 sample which was once considered a glass sample. The reason for the color of all blue glass samples is the existence of CuO, but not CoO.
ABSTRACT
A Liuli ring was nondestructively analyzed by EDXRF probe, to discuss the characteristic of chemical composition and the producing place of this Liuli ring. The result reveals that the chemical composition of this Liuli ring belongs to PbO-BaO-SiO2 system, which is similar to Chinese special ancient PbO-BaO-SiO2 glass dating from Chunqiu to East Han state. So, it was concluded that this Liuli ring was used Chinese special technology and formula, and was made in China. But on the appearance, this Liuli ring is not like a mature glass, but a faience or frit which is the compound of glass and crystal substance.
ABSTRACT
Liangzhu Culture is an important late neolithic culture of China, but there are different opinions on the function of some potteries of Liangzhu Culture, for example vat and Ding. In the present paper, for discussing the function of these potteries, the content of Cl, Ca and P of some shard samples of vat and Ding from Liangzhu site were analyzed by using EDXRF line scanning technology. The results show that the content of element Cl in the outside and inside parts of the bottom of vat sample is not different from that of other contemporaneous archaic potteries, and that the distribution of element Cl in the outside part of the bottom of vat sample is the same as that in the inside part of the bottom, so it is concluded that the function of vat from Liangzhu Culture is not related to the production or storage of salt, but with regard to the true function of this pottery more works remain to be done. The analytical results also show that the content of two elements, Ca and P, in the bottom of the other pottery, Ding, is obviously higher than that in vat and other contemporaneous archaic potteries, and that the content of two elements, Ca and P, in the outside part of the bottom of Ding sample is higher than that in the inside part of the bottom. So it is concluded that Ding from Liangzhu Culture is a kind of cooking ware and its main function is meal cooking.
