Speleothem d¹⁸O records have extensively been used to study Asian monsoon changes. However, less attention has been paid to the spatial distribution of speleothem d¹⁸O values. Despite some caveats, we advocate an approach to reconstruct spatial and temporal transects (“maps”) of speleothem d¹⁸O, thus time series of precipitation d¹⁸O distribution over the region. We obtained three speleothem d¹⁸O records from caves along a SW-NE transect from coastal Myanmar to southwestern China. All the three records cover the whole or a major portion of the past 40,000 years, particularly the last glacial maximum and present day. The comparisons between the records show a broadly decreasing trend in speleothem d¹⁸O values along the transect, consistent with an overall continental rainout effect of water isotopes when surface moisture is transported further inland. A much larger d¹⁸O gradient however exists during the last glacial maximum than in the late Holocene. A stronger water isotope fractionation during the glacial period is likely caused by a larger temperature gradient and suppressed plant transpiration along the transport pathway. Caution therefore is needed when interpreting the speleothem d¹⁸O records from a monsoon downwind region.

Since the late 19th century, it has been understood that lakes of the western United States reached their high stands after the last maximum of mountain glaciers (e.g., Russell, 1889). This interpretation is consistent with absolute age data obtained since the mid-20th century (e.g., Broecker and Orr, 1958). More recent studies of the last three decades show evidence to support lake high stands occurred during the last deglacial interval (~18 to 12 ka), with Heinrich Stadial 1 (~18 to 15 ka) encompassing a window when nearly all lakes had reached their maximum sizes (Munroe and Laabs, 2013). Efforts to understand the mechanisms that enhanced regional wetness depend strongly on age determinations for lake high stands. However, significant intra- and inter-lake basin disagreements on high stand age permit different interpretations of the climate dynamics that led to greater regional wetness. Our extensive stratigraphic, geomorphic, and geochronologic data from the Mono Basin leads us to suggest that the deglacial high stand of Mono Lake occurred in a very brief interval at about 16 ka. The time spanning the lake rise to its high stand cannot be exactly determined with the available data because the age constraints at hand across a 45 m elevational range are overlapping (16.07 ± 0.08 a to 15.94 ± 0.05 a). These observations require that the rise was sudden and achieved in less than 300 years. The timing of this sudden rise of the level of Mono Lake correlates with changes in tropical climate proxy records that are interpreted to reflect an abrupt southward diversion of the tropical rain belt. The correlation between tropical rainfall records and Mono Lake level is consistent with the hypothesis that changes in the position of the tropical rain belt result in modifications to the hydroclimate of the western US.

In the Fiji Islands, late Holocene environmental change is generally better understood for coastal and lowland situations than for the interior uplands of high volcanic islands. Lake Tagimaucia, a montane volcanic crater lake on Taveuni Island, is Fiji’s only high-elevation lake. It therefore potentially represents a very important site for preserving an environmental record in the highlands through the late Holocene. Physiographic factors expected to promote fast sedimentation rates are the large annual rainfall (>9000 mm), frequent passage of intense tropical cyclones, young geomorphology with erodible volcanic soils, steep catchment slopes, and rapid organic productivity in the surrounding cloud forest. The lake’s remote location means that its catchment is unlikely to have been anthropogenically affected during early human occupation in Fiji after 3000 BP. At present, however, it is not known whether Lake Tagimaucia’s deposits are able to provide a detailed, interpretable, environmental archive through the late Holocene. How fast is sedimentation occurring? Can any disturbances be identified, such as fire events, strong episodes of ENSO-driven drought or exceptional storms? Is there any evidence of the posited significant regional climatic shift called the ‘AD 1300 event’? Results are presented from the analysis of a shallow lake core, charcoal fragments, age-dating, stable isotopes δ¹³C and δ¹⁵N, and observed sedimentary anomalies. Possible influences of volcanic activity, catchment fire and the growth of unusual floating lake islands of sedge peat are discussed.