Whiplash Movie Internet Archive

[Klaudia Aricas]

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Recent wildfire activity in semi-arid regions like western North America exceeds the range of historical records. High-resolution paleoclimate archives such as stalagmites could illuminate the link between hydroclimate, vegetation change, and fire activity in pre-anthropogenic climate states beyond the timescale of existing tree-ring records. Here we present an analysis of levoglucosan, a combustion-sensitive anhydrosugar, and lignin oxidation products (LOPs) in a stalagmite, reconstructing fire activity and vegetation composition in the California Coast Range across the 8.2 kyr event. Elevated levoglucosan concentrations suggest increased fire activity while altered LOP compositions indicate a shift toward more woody vegetation during the event. These changes are concurrent with increased hydroclimate volatility as shown by carbon and calcium isotope proxies. Together, these records suggest that climate whiplash (oscillations between extreme wetness and aridity) and fire activity in California, both projected to increase with anthropogenic climate change, were tightly coupled during the early Holocene.

Here we demonstrate a link between fire activity, vegetation change, and climate whiplash in California during the early Holocene. We also provide an analysis of levoglucosan and LOPs in modern dripwater and calcite to place constraints on how surface signals of fire and vegetation move through the modern cave system.

Shown are speleothem samples with ages from 8.5 to 8.3 kiloyears before present (kyrs BP) (triangles), 8.2 to 7.8 kyrs BP (squares), and 7.7 to 7.0 kyrs BP (circles). The combined modern calcite samples are shown as an open diamond. The area shaded in dark brown corresponds to lignin originating from gymnosperm woody plants, as defined by Hedges and Mann29. The orange area is associated with gymnosperm non-woody plants, the purple area corresponds to angiosperm woody samples, and the pink area is associated with angiosperm non-woody plant parts. Error bars represent the standard deviation of samples measured in duplicate. The arrows highlight the changes over time. Plant icons available from phyloPic.org60 (lower left) and freesvg.org61 (others) and are licensed under Public Domain Dedication 1.062.

The recovery of the 13C6-levoglucosan spike for all but one stalagmite sample fall within the standard deviation of the average recovery of the whole sample set (Supplementary Fig. 2). This includes the samples with the highest measured levoglucosan concentrations, indicating that there is no divergent recovery rate and that these high values are unlikely to be an analytical artefact. Theoretically, stalagmite levoglucosan concentrations could also reflect changes in subsurface seepage water flow pathways that would route water from different locations on the surface to the stalagmite. Changes in subsurface water routing would also likely bring water into contact with different mineral phases within the host rock, and thus should be recorded by stalagmite strontium isotope ratios (87Sr/86Sr) which reflect the balance of water interactions with soils and host rocks with different 87Sr/86Sr fingerprints. Although we do observe host rock and soil phases with different 87Sr/86Sr values above WMC, we do not find a shift in stalagmite 87Sr/86Sr during the 8.2 kyr event15 concurrent with the levoglucosan peak. This indicates that a sustained change in seepage water routing is very unlikely during this interval. Thus, the observed changes in levoglucosan concentrations and LOP ratios across the WMC1 record most likely reflect shifts in fire activity and vegetation community in the vicinity of the cave across the 8.2 kyr event.

Increased fire activity coincident with higher proportions of woody vegetation is also evident in Holocene charcoal and pollen records from across the Pacific Northwest31, reflecting a potential feedback of increased woody fuel driving fire dynamics or a climate driver that affects both vegetation type and fire activity. The vegetation change noted in WMC1 is broadly consistent with regional changes in vegetation as recorded by pollen from the marine sediment core ODP 1018 off the coast of Santa Cruz which indicates increased redwood and decreased herbs and chaparral species just prior to 8000 years BP32. Lake sediment records from California and southern Oregon suggest increasing fire activity under progressively more intense aridity from the early to middle Holocene33,34,35,36, with lakes in the Klamath Mountains suggesting enhanced fire activity at 8400 years BP and the growth of a chaparral understory through the mid-Holocene37. However, challenging chronologies and low sediment accumulation rates preclude investigation of fire-vegetation relationships at these sites at temporal resolution comparable to the WMC speleothem.

Tree-ring data from western North America reveal strong sensitivity of fire activity to summer temperatures and hydrological drought since the late Holocene41,42,43. In the southern Cascades43 and Sierra Nevada44, variations in fire activity have been associated with changes in the magnitude of interannual fluctuations in rainfall amount, with enhanced fire activity occurring when high interannual variations in the Palmer Drought Severity Index (PDSI) coincide with higher temperatures43. Similar relationships are evident in the early to mid-Holocene record of the Pacific Northwest, where pollen and charcoal reconstructions link increased fire activity to summer drought31,33, while lacustrine oxygen isotope records document wetter winters45.

These proxy comparisons describe a link between hydroclimate volatility, vegetation change, and fire occurrence during the 8.2 kyr event similar to that observed in modern tree-ring records that are of higher temporal resolution than the stalagmite, and in Holocene lake sediments that are of lower resolution31,33,43,44. Seasonality was enhanced in the early Holocene including during the 8.2 kyr event, with increased summer insolation leading to higher summer temperatures and vice versa36,45. Although freshwater forcing led to cooling in the North Atlantic region, modelling indicates only a small (

In order to statistically identify changes in the amplitude and frequency of proxy variability, and thus to pinpoint the potential onset and cessation of changes in hydroclimate volatility, we conducted changepoint analysis on the previously published stalagmite δ13C record13 using the changepoint package in R55. Changepoints were identified in the δ13C record as changes in mean and variance using the PELT algorithm56 and the modified Bayes Information Criterion (MBIC) penalty57. The δ13C timeseries was chosen for this analysis because of its continuity (trace element records for this stalagmite have gaps) and high resolution (the δ44Ca record is of much lower temporal resolution).

An age model was constructed for the levoglucosan and LOP samples using the Stalage algorithm in R58 and the previously collected stalagmite 230Th/U dates13. The ages of the upper and lower surfaces of the segments collected for levoglucosan and LOP analysis were modelled separately and presented as the upper and lower bounds of the sample ages.

Samples of modern calcite were scraped from the surface of artificial substrates (glass plates) that were placed in the cave underneath active drip sites. Artificial substrates were placed under drip site WMC2 in December 2015 and WMC1 in March 2016 in the upper level of the cave (see Supplementary Fig. 3). Both plates were recollected in June 2018.

The levoglucosan and LOP data generated for this study are provided in Supplementary Table 1 and are publicly archived with the National Centers for Environmental Information at -search/study/37018. Previously published proxy data are archived at -search/study/32012 and -search/study/22270.

This work was supported by funding from NSF (AGS1554998) and the National Geographic Society (NGS-39815) to J.L.O. and the Karst Waters Institute to C.B.d.W. J.H. acknowledges financial support by the Max Planck Graduate Center Mainz. We thank Mike Davies and Bruce Rogers of the Western Cave Conservancy for guidance in the field and Susan Petrie of the Peninsula Open Space Trust for cave access.

J.H., J.L.O., C.B.d.W., S.F.M.B., and T.H. designed the study. J.H. conducted the sample preparation and data analysis for levoglucosan and LOPs. C.B.d.W. and J.L.O. subsampled the stalagmite for analysis, constructed the age model, and performed the changepoint analysis on δ13C. All co-authors participated in discussions, interpretation of the data, and writing of the manuscript.

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