Tropical monsoons are key mechanisms for transfer of heat and moisture to higher latitudes. Here we present a high-resolution, terrestrial proxy summer monsoon record for the southeast Asian monsoon, from a rapidly accumulating Holocene loess/soil sequence in the western Chinese Loess Plateau. We use magnetic and clastic grain size proxies to make quantitative estimates of Holocene rainfall and identify variations in winter monsoon intensity. Our record reveals cyclical millennial and multimillennial rainfall changes. As with the northwest African/southwest Asian monsoon records, a short arid interval at - 12.5 to 11.5 ka BP (the Younger Dryas) and subsequent summer monsoon intensification are recorded. However, at 6 ka BP, the southeast Asian summer monsoon weakened, when the northwest African/ southwest Asian monsoons strengthened, and then, from - 5 ka BP, intensified, when northwest Africa/ southwest Asia became dry. These antiphase monsoonal relationships may reflect competition between sea surface temperature changes and solar forcing. The intensity of the southeast Asian winter monsoon intensified from - 9 ka BP onwards, varying in its phase relationships with summer monsoon intensity. After - 2.25 ka BP, extreme climatic instability is indicated by both climate proxies.
High-resolution optically stimulated luminescence (OSL) dating of a terraced loess section in the western margins of the Chinese Loess Plateau provides evidence of continuous and varying accumulation of dust throughout the Holocene. From 12030 to 2500 years ago, the sediment-accumulation rate was approxi mately 0.2 mm/year. After this time, it increased to approximately 0.8 mm/year, during a historically docu mented period of agricultural expansion in adjacent areas. From 680 years ago, a further increase in accumu lation rate, to approximately 3.4 mm/year, is evident. Particle-size analysis indicates that this increase in accumulation rate was associated with anthropogenic addition of sandy sediment, probably for soil improve ment. The OSL dating also identifies the period when the terrace was first cut for agricultural use, between 2500 and 2070 years ago.
An integrated biomagnetostratigraphic study of the latest Early Triassic to the upper parts of the Middle Triassic, at Milne Edwardsfjellet in central Spitsbergen, Svalbard, allows a detailed correlation of Boreal and Tethyan biostratigraphies. The biostratigraphy consists of ammonoid and palynomorph zonations, supported by conodonts, through some 234 m of succession in two adjacent sections. The magnetostratigraphy consists of 10 substantive normal—reverse polarity chrons, defined by sampling at 150 stratigraphic levels. The magnetization is carried by magnetite and an unidentified magnetic sulphide, and is difficult to fully separate from a strong present‐day‐like magnetization. The biomagnetostratigraphy from the late Olenekian (Vendomdalen Member) is supplemented by data from nearby Vikinghøgda. The early and middle Anisian has a high sedimentation rate, comprising over half the ca. 140‐m thickness of the Botneheia Formation, whereas the late Anisian and lower Ladinian is condensed into about 20 m. The two latest Boreal Ladinian ammonoid zones are absent as a result of erosional truncation below the Tschermakfjellet Formation. Correlation with Tethyan biomagnetostratigraphies shows the traditional base of the Boreal Anisian (base of the Grambergia taimyrensis Zone) precedes the base of the Anisian (using definitions based on the Dęsli Caira section in Romania). The Boreal upper Anisian Gymnotoceras rotelliforme and Frechites nevadanus ammonoid zones correlate with most of the Tethyan Pelsonian and Illyrian substages. The base Ladinian defined in the Tethyan global boundary stratotype and point (GSSP) is closely equivalent to the traditional base of the Boreal Ladinian at the Intornites oleshkoi Zone. The latest Olenekian—early Anisian magnetic polarity time scale is refined using the Spitsbergen data.
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