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To achieve a sufficient understanding of the spatial dynamics of terrestrial climate variability, new proxies and networks of data that cover thousands of years and run up to the present day are needed. Here we show the first Gram-negative bacterial 3-hydroxy fatty acid (3-OH-FA) based temperature and hydrological records from any paleoclimate archive globally. The data, covering the last 9 ka before present (BP), are generated from an individual stalagmite, collected from Heshang Cave, located on a tributary of the Yangtze River, central China (30°27′N, 110°25′E; 294 m). Our results indicate a clear early-to-middle Holocene Climatic Optimum (8.0–6.0 ka BP) followed by a long-term monotonic cooling and increasing variability over the last 0.9 ka BP. The hydrological record shows two relatively long wet periods (8.8–5.9 ka BP and 3.0–0 ka BP) and one relatively dry period (5.9–3.0 ka BP) in central China. We show that 3-OH-FA biomarkers hold promise as independent tools for paleoclimate reconstruction, with the potential to deconvolve temperature and hydrological signals from an individual stalagmite. [ABSTRACT FROM AUTHOR]

• Warm-dry and cold-wet hydroclimate modes were showed according to 18,000-year temperature and DWT changes in Dajiuhu Basin. • Peatland ecology sensitively responded to palaeo-hydroclimatic changes. • More bulliform phytoliths induced by exaggerated plant leaf water loss occurred during warm-dry mid-Holocene. • Plant water regulation, climate, and irradiance showed a synchronous ~1000-yr cycle. Peatland ecosystem processes are strongly influenced by hydrology linked to climate change. However, how transpiration, as major water loss pathway in closed peatland, responds to climate change and then regulates ecosystem water balance that remains poorly understood. Here, we reported an 18,000-year fossil phytolith record from an herbaceous community-dominated mountain peatland in central China to reconstruct climate changes and vegetation evolution and reveal the interactions between regional climate changes and peatland ecosystem. The abundance of bulliform phytoliths—a silicified type of cells that regulate the movements of plant leaves to reduce light exposure and transpiration rate—shows close correlations with the Holocene climate variations with higher bulliform abundance in response to warm-dry climate (11,500–9600 cal yr BP; 7500–3000 cal yr BP) and lower values associated with cold-wet climate (13,000–11,500 cal yr BP; 3000 cal yr BP-present). Spectral analysis reveals that bulliform abundance and reconstructed climate vary with a major ~1000-year periodicity during the Holocene, suggesting a possible causal relationship to solar activity. A high bulliform abundance and warm-dry climate correspond with enhanced solar activity, and vice versa. We interpret that the resultant leaf water deficit resulted from greater light interception, high temperature and drought promoted the production of bulliform cells to fold leaf for water conservation, which is an effective protective mechanism of peatland grasses from the environmental stress. These results expand our understanding of how grass-dominated peatland plant water regulation recorded by bulliform phytoliths responds to solar radiation and local hydroclimate during geological period. [ABSTRACT FROM AUTHOR]

Stalagmites have become a key archive in Quaternary palaeoclimatic reconstruction due to their ability to yield continuous and undisturbed records, precise and absolute chronologies, and their global terrestrial distribution. Oxygen isotopes are effectively the master proxy for speleothem analysis, but inherently encode a mix of climatic signals. Thus it is tricky to deconvolve the temperature and precipitation signal from speleothems. Bacterial derived 3-hydroxy fatty acids (3-OH-FAs) have potential as independent temperature and pH proxies. By applying the 3-OH-FA based temperature proxy RAN15 and the pH proxy RIAN to the HS4 stalagmite from central China, we recently reconstruct Holocene temperature and hydrological changes, respectively. Now we address the issue of how terrestrial carbon storage feeds back on warm climate states, which is critical for improving global warming projections. Soils may act as a positive feedback on climate if warming increases soil carbon decomposition rates. Conversely, if increases in net primary production (NPP) exceed increases in decomposition, the climate feedback will be negative. Here we present new constraints on the response of terrestrial carbon cycle feedbacks, especially soil respiration, during earlier warm episodes of the early Holocene Climate Optimum (HCO) and Medieval Warm Period (MWP), which have hitherto been poorly constrained due to a lack of proxies (and thus available data). We utilize the first palaeoclimatic application of compound-specific δ13C measurements on n-fatty acid biomarkers extracted from a stalagmite. We resolve a proportional increase in C3 plants in the catchment area during these warmer/wetter intervals. Moreover, we find that heterotrophic soil respiration was highly substrate selective, indicating that NPP outpaced decomposition and the catchment behaved as a carbon sink. Thus, we provide the first palaeoclimate evidence that subtropical mineral soils in warmer/wetter climates can act as a negative climate feedback. [ABSTRACT FROM AUTHOR]