Millennial-scale oscillations in the Kuroshio–Oyashio boundary during MIS 19 based on the radiolarian record from the Chiba composite section, central Japan

Marine isotope stage (MIS) 19 is considered to be the best orbital analog for the present interglacial. Consequently, clarifying the climatic features of this period can provide us with insights regarding a natural baseline for assessing future climate changes. A high-resolution radiolarian record from 800 to 750 ka (MIS 20 to MIS 18) was examined from the Chiba composite section (CbCS) of the Kokumoto Formation, including the Global Boundary Stratotype Section and Point for the lower–middle Pleistocene boundary on the Boso Peninsula on the Pacific side of central Japan. Millennial-scale oscillations in the Kuroshio warm and Oyashio cold currents were revealed by the Tr index, which is estimated using a simple equation based on radiolarian assemblages. The estimated Tr values ranged between 0.1 and 0.8 for MIS 18 through MIS 19, with minimum and maximum values corresponding to values observed off present day Aomori (41°N) and the Boso Peninsula (35°N), respectively. The observed patterns tended to be synchronous with the total radiolarian abundance associated with their production. Multiple maxima in radiolarian abundance occurred during periods of the Oyashio expanded mode before 785 ka and during periods of Kuroshio extension after 785 ka in MIS 19. Such increases in radiolarian abundance with the Kuroshio extension during MIS 19 are likely related to improvements in nutrient and photic environments with the development of a two-layer structure along the Kuroshio–Oyashio boundary zone. A similar pattern of millennial-scale climatic changes was also recognized in a precipitation record from the Sulmona Basin in central Italy, suggesting a close relationship with the CbCS record as a result of a large-scale climate system similar to the Arctic Oscillation in the northern hemisphere.

Drivers of East Asian millennial-scale climate over the past 400,000 years

The history of abrupt climate change in East Asia is often discussed from hydroclimate proxies that record the isotopic composition of rainfall. However, the underlying mechanisms remain obscure because water-isotope proxies respond to a wide variety of environmental variables. Here, we investigated millennial-scale climate variability in East Asia over the past 400,000 years using paired foraminiferal oxygen isotope and Mg/Ca records from the East Asian continental margin, thereby resolving variance into temperature and rainfall components. We found that the temperature and rainfall variabilities are largely asynchronous, with times when the global climate shifts from interglacial to glacial periods being the notable exception. These findings highlight the importance of both mean global state and magnitude of North Atlantic variability in determining the East Asian climate. Without a strong North Atlantic forcing, the regional feedback system might generate asynchronous temperature and rainfall variations, which is the background climate feature in East Asia.

Mid-Late Holocene Sub-Millennial Scale Inverse Trends of South Asian Summer and Winter Monsoons in Sri Lanka

The South Asian Monsoon (SAM) brings precipitation crucial for agriculture across the densely populated region of South Asia. Identifying the key long-term drivers of the SAM is essential to improve the predictability of future monsoonal trends in the context of current global climate scenarios and increasingly frequent drought and flooding events in this part of the world. Here, we reconstruct ∼6000 years of climatic and environmental history of the South Asian summer monsoon-fed Bolgoda South Lake and the Horton Plains, and the winter monsoon-fed Panama lagoon, in Sri Lanka to better understand monsoonal operation over this island and its connection to broader climate systems. Multiple proxies (diagnostic biomarkers, hydrogen and carbon isotopes of individual n-alkane, grain size, and Zr/Rb elemental ratio) indicate a sub-millennial scale decreasing trend of summer monsoon rainfall in the wet zone of Sri Lanka alongside an increasing trend of winter monsoon rainfall in the dry zone during the last ∼6000 years. We also observed multi-centennial scale arid events in the Bolgoda South Lake and Horton Plains records at ∼3,500 and ∼1,000 cal years BP. Inverse monsoonal behavior during the mid- and late Holocene seems to be led by the southward migration of the mean latitudinal position of ITCZ, induced by varying solar energy distribution between the Northern and Southern hemispheres due to Earth’s processional cycle. Our observations are broadly supported by existing paleoclimatic records from the Indian sub-continent, but abrupt arid phases are asynchronous in the regional records. In addition, these short-term arid conditions do not show systematic correlations with the different modes of climate variables known to have teleconnections with the Indian Ocean monsoon.

The Earth's climate lagged, recurrent and non-linear solar and lunar multi-millennial scale responses: An oceanic hypothesis, evidence, verifications and forecasts

This work provides a hypothesis of the links between the multi-millennia scale recurrent solar and tidal influences and Earth's climate lagged responses, associated with the oceanic transport mechanisms with a variable modulation. As a part of this hypothesis, empirical and simple, non-linear lagged models are proposed for five of the most representative Earth's climate variables (a continental tropical temperature, an Antarctic temperature [at James Ross Island], the Greenland temperature, the global temperature and the southeast asian monsoon) with multi-millennia records to account for the lagged responses to solar forcing. The proposed models implicitely include a well-known oceanic heat transport mechanism: the Ocean Conveyor Belt. This oceanic mechanism appears to generate a climate modulation through the intensity of the ocean/atmosphere circulation, and a heat and mass transport, with a consequent climate lag of several thousands of years. Tidal forcing is also considered for global temperature modelling and forecast. The consequent millennia-scale global forecasts, after being integrated/verified with an accumulated ocean travelled distance from the tropical East Pacific, and with a double evaluation of the tidal influences based on similarities and on the NASA’s solar system astronomical dynamics, indicates a cooling for the next century, and gentle oscillations over the next millennia. Our preliminary results that strongly suggest that millennial scale changes in solar activity induce circulation and thermal global impacts, also suggest that the Younger Dryas event, may be influenced by the lagged outcomes of solar driven changes in the tropical Pacific, and by tidal influences. The detected Earth's climate delayed responses, that have been working in the past and present climates, and will be working in the future climates, must be, as soon as possible, independently verified and theoretically sustained, before to be fully included in a multi-scale climate models as a scientific theory. A final example for the global temperature record over the last 170 years demonstrates with experimental results for the twenty first century evolution the convenience of a multi-scale climate modelling with contrasting lower values compared with the IPCC global temperature scenarios.