Fast Holocene slip and localized strain along the Liquiñe-Ofqui strike-slip fault system, Chile

In active tectonic settings dominated by strike-slip kinematics, slip partitioning across subparallel faults is a common feature; therefore, assessing the degree of partitioning and strain localization is paramount for seismic hazard assessments. Here, we estimate a slip rate of 18.8 ± 2.0 mm/year over the past 9.0 ± 0.1 ka for a single strand of the Liquiñe-Ofqui Fault System, which straddles the Main Cordillera in Southern Chile. This Holocene rate accounts for ~ 82% of the trench-parallel component of oblique plate convergence and is similar to million-year estimates integrated over the entire fault system. Our results imply that strain localizes on a single fault at millennial time scale but over longer time scales strain localization is not sustained. The fast millennial slip rate in the absence of historical Mw > 6.5 earthquakes along the Liquiñe-Ofqui Fault System implies either a component of aseismic slip or Mw ~ 7 earthquakes involving multi-trace ruptures and > 150-year repeat times. Our results have implications for the understanding of strike-slip fault system dynamics within volcanic arcs and seismic hazard assessments.

Characterization of the resilience and variability of vegetation during the Holocene using a large database of pollen data

<p>Global climatic changes which are expected in the 21<sup>st</sup> century are likely to create unparalleled disturbances on vegetation. In addition, human activities also increase the risk of fire disturbances and insect epidemies. We investigate the resilience of different biomes by examining their behaviour during the Holocene using a taxonomically harmonized and temporally standardized global fossil pollen datasets,synthesized from 2821 palynological records from the Neotoma Paleoecology Database and additional literature. Specifically, we study the composition variability on millennial time-scale and timescale-dependant scaling of variability from centennial to multi-millennial timescales. A principal component analysis was performed in order to characterize the principal modes of variability of the pollen assemblages. We find coherent regional signals of vegetation variability and scaling of variability from the pollen assemblages, indicating significant millennial scale variability which can be related to vegetation taxa and climates. Particularly, we observe more stability in North America and Northern Europe in areas dominated by boreal forest and deciduous forests. This may be linked to the greater stability of forest ecosystems and also a more stable climate over these areas which may be the result of stabilizing feedbacks. We find that diversity plays a key role in vegetation composition and that more diverse regions allow for greater variability. </p><p> </p><div> <div> </div> </div>

Latitudinal effect of vegetation on erosion rates identified along western South America

Vegetation influences erosion by stabilizing hillslopes and accelerating weathering, thereby providing a link between the biosphere and Earth’s surface. Previous studies investigating vegetation effects on erosion have proved challenging owing to poorly understood interactions between vegetation and other factors, such as precipitation and surface processes. We address these complexities along 3500 kilometers of the extreme climate and vegetation gradient of the Andean Western Cordillera (6°S to 36°S latitude) using 86 cosmogenic radionuclide–derived, millennial time scale erosion rates and multivariate statistics. We identify a bidirectional response to vegetation’s influence on erosion whereby correlations between vegetation cover and erosion range from negative (dry, sparsely vegetated settings) to positive (wetter, more vegetated settings). These observations result from competing interactions between precipitation and vegetation on erosion in each setting.

Millennial-scale Holocene hydrological changes in the northeast Atlantic: New insights from ‘La Grande Vasière’ mid-shelf mud belt

A mid- to late-Holocene paleohydrological reconstruction from the northeast Atlantic is proposed through the study of a high-resolution sedimentary record from the northern continental shelf of the Bay of Biscay (BoB). Three foraminiferal species dominate the assemblages with Rosalina globularis showing an overall decrease in absolute and relative abundances from ~7 to 0.4 cal. ka BP, whereas the opposite trend is observed for Cibicides refulgens and Lobatula. These long-term patterns are interpreted as a response to the overall cooling trend and/or the progressive deepening of the water column because of the relative sea-level (RSL) rise. Foraminiferal δ18O and grain-size analyses show a significant shift around 3.5–2.5 cal. ka BP toward a heavier isotopic signature and finer sediments. We mainly link this change to enhanced contribution of continental freshwaters and fine sediments after the near-stabilization of the RSL rise. By reducing coastal accommodation spaces, this led to a better channelization of river outflows and probably to the formation of the modern winter thermohaline front. Superimposed on these long-term patterns, our data highlight strong millennial-scale variability (1250-year peak). Such cyclicity is consistent with several records tracing changes in rainfall and storminess regimes in northern Europe, and the dynamics of the subpolar gyre (SPG). We suggest a millennial time-scale control of a NAO-like (North Atlantic Oscillation) climatic process modulating continental humidity (and the associated river discharges) and SPG dynamics through wind stress. Spectral analyses reveal an additional 500-year frequency peak implying a possible solar forcing.

Easy Volcanic Aerosol (EVA v1.0): An idealized forcing generator for climate simulations

The Easy Volcanic Aerosol (EVA) forcing generator produces stratospheric aerosol optical properties as a function of time, latitude, height and wavelength for a given input list of volcanic eruption attributes. EVA is based on a parameterized three-box model of stratospheric transport, and simple scaling relationships used to derive mid-visible (550 nm) aerosol optical depth and aerosol effective radius from stratospheric sulfate mass. Pre-calculated look up tables computed from Mie theory are used to produce wavelength dependent aerosol extinction, single scattering albedo and scattering asymmetry factor values. The structural form of EVA, and the tuning of its parameters, are chosen to produce best agreement with the satellite-based reconstruction of stratospheric aerosol properties following the 1991 Pinatubo eruption, and with prior millennial-time scale forcing reconstructions including the 1815 eruption of Tambora. EVA can be used to produce volcanic forcing for climate models which is based on recent observations and physical understanding, but internally self-consistent over any time-scale of choice. In addition, EVA is constructed so as to allow for easy modification of different aspects of aerosol properties, in order to be used in model experiments to help advance understanding of what aspects of the volcanic aerosol are important for the climate system.

Early land use and centennial scale changes in lake-water organic carbon prior to contemporary monitoring

Organic carbon concentrations have increased in surface waters across parts of Europe and North America during the past decades, but the main drivers causing this phenomenon are still debated. A lack of observations beyond the last few decades inhibits a better mechanistic understanding of this process and thus a reliable prediction of future changes. Here we present past lake-water organic carbon trends inferred from sediment records across central Sweden that allow us to assess the observed increase on a centennial to millennial time scale. Our data show the recent increase in lake-water carbon but also that this increase was preceded by a landscape-wide, long-term decrease beginning already A.D. 1450–1600. Geochemical and biological proxies reveal that these dynamics coincided with an intensification of human catchment disturbance that decreased over the past century. Catchment disturbance was driven by the expansion and later cessation of widespread summer forest grazing and farming across central Scandinavia. Our findings demonstrate that early land use strongly affected past organic carbon dynamics and suggest that the influence of historical landscape utilization on contemporary changes in lake-water carbon levels has thus far been underestimated. We propose that past changes in land use are also a strong contributing factor in ongoing organic carbon trends in other regions that underwent similar comprehensive changes due to early cultivation and grazing over centuries to millennia.