A data–model approach to interpreting speleothem oxygen isotope records from monsoon regions

Abstract. Reconstruction of past changes in monsoon climate from speleothem oxygen isotope (δ18O) records is complex because δ18O signals can be influenced by multiple factors including changes in precipitation, precipitation recycling over land, temperature at the moisture source, and changes in the moisture source region and transport pathway. Here, we analyse >150 speleothem records of the Speleothem Isotopes Synthesis and AnaLysis (SISAL) database to produce composite regional trends in δ18O in monsoon regions; compositing minimises the influence of site-specific karst and cave processes that can influence individual site records. We compare speleothem δ18O observations with isotope-enabled climate model simulations to investigate the specific climatic factors causing these regional trends. We focus on differences in δ18O signals between the mid-Holocene, the peak of the Last Interglacial (Marine Isotope Stage 5e) and the Last Glacial Maximum as well as on δ18O evolution through the Holocene. Differences in speleothem δ18O between the mid-Holocene and the Last Interglacial in the East Asian and Indian monsoons are small, despite the larger summer insolation values during the Last Interglacial. Last Glacial Maximum δ18O values are significantly less negative than interglacial values. Comparison with simulated glacial–interglacial δ18O shows that changes are principally driven by global shifts in temperature and regional precipitation. Holocene speleothem δ18O records show distinct and coherent regional trends. Trends are similar to summer insolation in India, China and southwestern South America, but they are different in the Indonesian–Australian region. Redundancy analysis shows that 37 % of Holocene variability can be accounted for by latitude and longitude, supporting the differentiation of records into individual monsoon regions. Regression analysis of simulated precipitation δ18O and climate variables show significant relationships between global Holocene monsoon δ18O trends and changes in precipitation, atmospheric circulation and (to a lesser extent) source area temperature, whereas precipitation recycling is non-significant. However, there are differences in regional-scale mechanisms: there are clear relationships between changes in precipitation and δ18O for India, southwestern South America and the Indonesian–Australian regions but not for the East Asian monsoon. Changes in atmospheric circulation contribute to δ18O trends in the East Asian, Indian and Indonesian–Australian monsoons, and a weak source area temperature effect is observed over southern and central America and Asia. Precipitation recycling is influential in southwestern South America and southern Africa. Overall, our analyses show that it is possible to differentiate the impacts of specific climatic mechanisms influencing precipitation δ18O and use this analysis to interpret changes in speleothem δ18O.

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A data-model approach to interpreting speleothem oxygen isotope records from monsoon regions on orbital timescales

10.5194/cp-2020-78 ◽

2020 ◽

Author(s):

Sarah E. Parker ◽

Sandy P. Harrison ◽

Laia Comas-Bru ◽

Nikita Kaushal ◽

Allegra N. LeGrande ◽

...

Keyword(s):

South America ◽

Oxygen Isotope ◽

Atmospheric Circulation ◽

Last Glacial Maximum ◽

East Asian ◽

Source Area ◽

Last Interglacial ◽

Regional Trends ◽

Precipitation Recycling ◽

Precipitation Δ18o

Abstract. Reconstruction of past changes in monsoon climate from speleothem oxygen isotope (δ18O) records is complex because δ18O signals can be influenced by multiple factors including changes in precipitation, precipitation recycling over land, temperature at the moisture source and changes in the moisture source region and transport pathway. Here, we analyse > 150 speleothem records from version 2 of the Speleothem Isotopes Synthesis and Analysis (SISAL) database to produce composite regional trends in δ18O in monsoon regions; compositing minimises the influence of site-specific karst and cave processes that can influence individual site records. We compare speleothem δ18O observations with isotope-enabled climate model simulations to investigate the specific climatic factors causing these regional trends. We focus on differences in δ18O signals between interglacial (mid-Holocene and Last Interglacial) and glacial (Last Glacial Maximum) states, and on δ18O evolution through the Holocene. Differences in speleothem δ18O between the mid-Holocene and Last Interglacial in the East Asian and Indian monsoons are small, despite the larger summer insolation values during the Last Interglacial. Last Glacial Maximum δ18O values are significantly less negative than interglacial values. Comparison with simulated glacial-interglacial δ18O shows that changes are principally driven by global shifts in temperature and regional precipitation. Holocene speleothem δ18O records show distinct and coherent regional trends. Trends are similar to summer insolation in India, China and southwestern South America, but different in the Indonesian-Australian region. Redundancy analysis shows that 37 % of Holocene variability can be accounted for by latitude and longitude, supporting the differentiation of records into individual monsoon regions. Regression analysis of simulated precipitation δ18O and climate variables show that global Holocene monsoon δ18O trends are driven by changes in precipitation, atmospheric circulation and (to a lesser extent) source area temperature, whilst precipitation recycling is non-significant. However, there are differences in regional scale mechanisms; there are clear relationships between changes in precipitation and in δ18O for India, southwestern South America and the Indonesian-Australian regions, but not for the East Asian monsoon. Changes in atmospheric circulation contributes to δ18O trends in the East Asian, Indian and Indonesian-Australian monsoons, and a weak source area temperature effect is observed over southern and central America and Asia. Precipitation recycling is influential in southwestern South America and southern Africa. Overall, our analyses show that it is possible to differentiate the impacts of specific climatic mechanisms influencing precipitation δ18O and use this analysis to interpret changes in speleothem δ18O.

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Chinese loess and the evolution of the east Asian monsoon

Progress in Physical Geography Earth and Environment ◽

10.1177/030913330002400104 ◽

2000 ◽

Vol 24 (1) ◽

pp. 75-96 ◽

Cited By ~ 27

Author(s):

Chun Chang Huang ◽

Jiangli Pang ◽

Jingpo Zhao

Keyword(s):

Climatic Change ◽

Atmospheric Circulation ◽

Asian Monsoon ◽

East Asian Monsoon ◽

East Asian ◽

The Tibetan Plateau ◽

Glacial Cycle ◽

Last Interglacial ◽

Chinese Loess ◽

Climatic Variations

The history of the east Asian monsoon has been reconstructed from proxy records from the aeolian loess-palaeosol sequence in the Loess Plateau. It has been suggested that the monsoonal atmospheric circulation was initiated abruptly at 2.6 M yr BP. From about 1.2 M yrBP, the climate was characterized by contrasts between dry-cold periods brought on by the northwesterly monsoon and humid-warm periods brought about by the southeasterly monsoon. The periodic changes related to the earth’s orbital cycles have been clearly identified. Since about 0.6 M yr BP, the monsoonal climatic variations have become extremely pronounced and these correlate well with the marine isotope stages. The three-step shift in the east Asian monsoon towards greater variation seems to have been caused by the accelerated uplifting of the Tibetan Plateau. Climatic change during the last interglacial-glacial cycle recorded in the loess seems to match the SPECMAP δ18O record exactly. Six episodes of extremely strong dustfall events (brought on by the strengthened northwesterly monsoon winds) have been identified during the last glaciation. The ages of these episodes seem to match the Heinrich events in the North Atlantic and the Dansgaard-Oeschger events in Greenland. It is therefore suggested that the atmospheric circulation in east Asia is very sensitive to climatic change in high latitudes and has been responsive to global climatic change over the last 2.6 M yr. Millennial-scale climatic variations have also been identified in the Holocene loess. The article concludes by suggesting areas of research that might be undertaken in order to improve our understanding of the Chinese loess and of the evolution of the east Asian monsoon.

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Atmospheric Controls on Seasonal and Interannual Variations in the Precipitation Isotope in the East Asian Monsoon Region

Journal of Climate ◽

10.1175/jcli-d-15-0363.1 ◽

2016 ◽

Vol 29 (4) ◽

pp. 1339-1352 ◽

Cited By ~ 50

Author(s):

Zhongyin Cai ◽

Lide Tian

Keyword(s):

Atmospheric Circulation ◽

Asian Monsoon ◽

East Asian Monsoon ◽

East Asian ◽

Walker Circulation ◽

Condensation Temperature ◽

Interannual Variations ◽

Atmospheric Circulation Patterns ◽

Circulation Patterns ◽

Precipitation Δ18o

ABSTRACT Understanding variations in isotopic composition of precipitation from monsoon regions is crucial for its utilization in paleoclimate studies. This study explores the relationship between precipitation δ18O data for the East Asian monsoon (EAM) region archived in Global Network for Isotopes in Precipitation (GNIP) and the cloud data archived in ISCCP and their linkage with large-scale atmospheric circulation patterns. Results show that precipitation δ18O are significantly and positively correlated with cloud-top pressure (CTP) on both local and regional scales. Mechanically speaking, the stronger the monsoon convection precipitation, the higher the cloud and the lower the condensation temperature and thus the lower the precipitation δ18O. This result implies that the sharp drop in precipitation δ18O in the early summer in monsoonal Asia is related to the atmospheric circulation pattern rather than the different moisture sources, as was previously assumed. This result helps explain the processes leading to the observed “amount effect.” A comparison of atmospheric circulation patterns with precipitation δ18O on an interannual scale shows that the positive CTP anomalies in the central Indo-Pacific within the weak Walker circulation (El Niño) can be associated with positive δ18O anomalies, while negative CTP anomalies in the central Indo-Pacific within the strong Walker circulation (La Niña) can be linked to negative δ18O anomalies. This result further confirms the aforementioned conclusion. This is important for understanding paleoclimatic change in monsoonal Asia, as interannual variations in stable isotopes in that region have received less attention in the past.

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