Paleoclimate support for a persistent dry island effect in the Colombian Andes during the last 4700 years

We investigated middle- and late-Holocene hydroclimate patterns in the Colombian Andes using indicators of watershed erosion (lithic abundance), precipitation intensity (% silt), lake-level variability (organic carbon and nitrogen, % sand, and diatoms), and fire frequency (fossil charcoal) from a ~4700-year-long sediment archive from Laguna de Ubaque, a small sub-alpine lake on the eastern flank of the eastern Colombian Andes. Our results indicate reduced precipitation, low lake levels, and increased fire occurrence at Ubaque between 4700 and 3500 cal. yr BP (hereafter BP). Precipitation and lake levels increased abruptly while fire occurrence decreased between 3500 and 2100 BP, with the exception of a 300-year dry phase between 2800 and 2500 BP. Although wetter than the 4700–3500 BP interval, precipitation decreased, lake levels fell, and fire occurrence increased after 2100 BP, but with high-frequency variability. Comparison of the Ubaque results with other Colombian paleoclimate records (e.g. Lakes Fúquene and La Cocha) supports an antiphase pattern of precipitation between the high/interior Andes and frontal slope sites. This spatial pattern of variability is consistent with modern responses to the changes in terrestrial atmospheric convection associated with the so-called ‘dry island’ effect. Further comparison with paleoclimate records from Venezuela suggests that the millennial trend toward increasing frontal slope precipitation is consistent with orbitally induced increases in Andean atmospheric convection. Sub-orbital dry island–like hydroclimate variability suggests that other mechanisms that affect Northern Hemisphere convection may act to enhance or diminish this effect on centennial and shorter timescales

Contrasting responses of lake ecosystems to environmental disturbance: a paleoecological perspective from northern Patagonia (Argentina)

Paleoecological studies are crucial for understanding ecosystem disturbance and resilience dynamics. However, nearly all the research related to the response of aquatic communities to disturbances has been developed at short-term ecological scales. In this study, we investigate the long-term response of chironomid insects of two lakes, to volcanic and other environmental disturbances that have taken placeduring the last 200 years. The studied lakes, Lake Verde and Lake Toncek, are located in the Nahuel Huapi National Park (northern Patagonia, Argentina),under contrasting environmental settings. Our results show that the main driver of faunal changes in both lakes is volcanism. Indeed, after the impact of the 1960Puyehue/Calbuco volcanic events, the chironomid assemblage of Lake Verde recovered to initial conditions showing high resistance and a strong resilience tothe impact. In this lake, the canopy, the presence of macrophytes, and the dynamic of the watershed are important determinants of resilience providing habitats for species colonization and/or by giving refugia to the community. Contrarily, chironomid assemblages from Lake Toncek did not recover to theoriginal state after the impact of the ash. This lake is located above the tree line, and therefore it is highly probable that the lack of vegetation cover in the basinoffered no protection for the aquatic environment, leaving the ecosystem highly exposed to the effect of the volcanic ashes. Subordinate to the effects of thevolcanism, rising temperatures in the last 50 years and/or increasing human activities in the area, especially in L. Toncek, may also be responsible for the changes in chironomid assemblages.Fil: Massaferro, Julieta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Administración de Parques Nacionales; ArgentinaFil: Correa Metrio, Alex. Universidad Nacional Autónoma de México; MéxicoFil: Montes de Oca, Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Administración de Parques Nacionales; ArgentinaFil: Mauad, Melina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentin

A Progressively Wetter Early through Middle Holocene Climate in the Eastern Lowlands of Guatemala

Climate records from Central America and the Caribbean region reveal considerable spatiotemporal complexity in precipitation variability, with multiple hypotheses explaining the likely ocean-atmosphere processes influencing precipitation in the region. Here we report on findings from a 760-cm long sediment core from Lake Izabal, eastern Guatemala that affords insight on regional hydroclimate change over the last ∼9,500 years. We utilized a radiocarbon-based age-depth model integrated with lithological, XRF elemental abundances, and principal component analyses to infer changes in erosion/precipitation, lake productivity, and lake water chemistry. Abundance of elements commonly associated with terrigenous sources increase from the early to the latest mid-Holocene, from ca. 9,500 to ca. 4,800 calibrated years before present (cal yr BP), suggesting a progressive increase in erosion/precipitation. This is followed by relatively stable and high erosion/precipitation conditions until ca. 1,200 cal yr BP, with an abrupt decrease in erosion/precipitation ∼1,200 years ago. Comparison of the Izabal record with other paleoclimate records from Central America and the Caribbean region indicates substantial heterogeneity in hydroclimate, even across relatively short distances, likely due to a combination of topographic complexity and the combined influences of Atlantic and Pacific basin ocean-atmosphere dynamics. Our results suggest that the progressive increase in boreal autumn insolation throughout the middle and late Holocene may have driven an increase in Caribbean sea-surface temperatures (SST) during the late wet season, leading to increased moisture availability through enhanced evaporation and greater precipitation amounts associated with zonal convergence and orographic uplift along the eastern coast of Central America. However, other nearby records demonstrate hydroclimate changes that are at least partially at odds with the Izabal record, indicating that the modern SST relationships with atmospheric circulation, including Intertropical Convergence Zone dynamics, and precipitation alone cannot be used as a framework for explaining hydroclimate variability across Central America during the Holocene

Wave energy flux in the Caribbean Sea: Trends and variability

Wave Energy Flux (WEF) in the Colombian Caribbean Sea is assessed using a 60 years wave reanalysis from 1958 to 2017. Significant wave height (Hs) and mean wave energy period (Tm_1,0) are validated against in situ buoy data from the National Oceanic and Atmospheric Administration and from the Dirección General Marítima in the Central Caribbean Sea and in front of the Colombian shelf. WEF is calculated at virtual buoys allocated in the central Caribbean, at the continental shelf and around insular territories revealing a long-term decrease in magnitude with an annual rate between 0.01 and 0.2% with different regional behavior. In addition, WEF variations at interannual scale are found to be associated with ENSO phases. Wave energy power decreased from 1989 to 2017 in all analyzed locations.This work was supported by COLCIENCIAS (Departamento Administrativo de Ciencia, Tecnología e Innovación), convocatoria 727. A. Orfila would like to thank financial support from Ministerio de Ciencia, Innovación y Universidades of Spain through the MOCCA project (grant no. RTI2018-095441-B-C21).Peer reviewe

A Millennium of Anthropic and Climate Dynamics in the Lake Izabal Basin, Eastern Lowland Guatemala

Modern Precipitation Gradients Across the Maya Region in Central America Result in a Diverse Vegetational Mosaic that Varies from Scrub Forest to Rainforest. in This Region, Evidence of Past Changes in the Distribution of Vegetation Indicates Two Main Patterns: I) a Holocene Long-Term Trend towards a More Seasonal Forest, and Ii) Sharp Changes in Vegetation Cover Resulting from Human Occupation. the History of Vegetation in Moister Areas of the Maya Region, However, Has Been Mostly Extrapolated from Studies Carried Out in the Yucatan Peninsula. We Reconstructed the Paleoenvironmental and Paleoecological Dynamics of the Last ∼1300 Years in the Lake Izabal Basin, One of the Wettest Areas within the Maya Region. Palynological and Geochemical Evidences Indicate that from ∼650–1150 CE, Vegetation Assemblages Were Dominated by Disturbance Taxa, under Relatively Low Erosion in the Catchment Area. This Pattern Probably Resulted from Anthropogenic Activities during the Terminal Classic Period (800–950 CE) Combined with the Dry and More Seasonal Conditions of the Medieval Climate Anomaly. the Record from 1150 to 1400 CE Points to an Increase in Moisture Availability with a Change towards a Forested Landscape. from 1400 to 1950 CE, Geochemical Data Indicate Lower Precipitation, While the Vegetation Appears Less Fragmented and a Mature Forest Developed. Such Pattern Probably Emerged from Lower Evapotranspiration Associated with the Little Ice Age (1350–1850 CE) Favoring Vegetation Recovery. during the Last 1300 Years, Vegetation Change in the Lake Izabal Basin Parallels that of the Yucatan Peninsula, with Anthropogenic Influences and Moisture Availability Exerting First- and Second-Order Controls on Vegetation Turnover, Respectively

Ecological turnover in neotropical freshwater and terrestrial communities during episodes of abrupt climate change

The last 85,000 years were characterized by high climate and environmental variability on the Yucatan Peninsula. Heinrich stadials are examples of abrupt climate transitions that involved shifts in regional temperatures and moisture availability. Thus, they serve as natural experiments to evaluate the contrasting responses of aquatic and terrestrial ecosystems. We used ostracodes and pollen preserved in a 75.9-m-long sediment core (PI-6, similar to 85 ka) recovered from Lake Peten Itza, Guatemala, to assess the magnitude and velocity of community responses. Ostracodes are sensitive to changes in water temperature and conductivity. Vegetation responds to shifts in temperature and the ratio of evaporation to precipitation. Ostracodes display larger and more rapid community changes than does vegetation. Heinrich Stadial 5-1 (HS5-1) was cold and dry and is associated with lower ostracode and vegetation species richness and diversity. In contrast, the slightly warmer and dry conditions during HS6 and HS5a are reflected in higher ostracode species richness and diversity. Our paleoecological study revealed the greatest ecological turnover for ostracodes occurred from 62.5 to 51.0 ka; for pollen, it was at the Pleistocene/Holocene transition. Future studies should use various climate and environmental indicators from lake and marine sediment records to further explore late glacial paleoclimate causes and effects in the northern neotropics

Stable carbon isotopes (δ13C) of total organic carbon and long-chain n-alkanes as proxies for climate and environmental change in a sediment core from Lake Petén-Itzá, Guatemala

Sediment core PI-6 from Lake Petén Itzá, Guatemala, possesses an ~85-ka record of climate and environmental change from lowland Central America. Variations in sediment lithology suggest large and abrupt changes in precipitation during the last glacial and deglacial periods, and into the early Holocene. We measured stable carbon isotope ratios of total organic carbon and long-chain n-alkanes from the core, the latter representing a largely allochthonous (terrestrial) source of organic matter, to reveal past shifts in the relative proportion of C3–C4 terrestrial biomass. We sought to test whether stable carbon isotope results were consistent with other paleoclimate proxies measured in the PI-6 core, and if extraction and isotope analysis of n-alkanes is warranted. The largest δ13C variations are associated with Heinrich Events. Carbon isotope values in sediments deposited during the last glacial maximum indicate moderate precipitation with little fluctuation. The deglacial was a period of pronounced climate variability, e.g. a relatively warm and moist Bølling–Allerød, but a cool and dry Younger Dryas. Arid periods of the deglacial were inferred from samples with high δ13C values in total organic carbon, which reflect times of greater proportions of C4 plants. These inferences are supported by stable isotope measurements on ostracod shells and relative abundance of grass pollen from the same depths in core PI-6. Similar trends in carbon stable isotopes measured on bulk organic carbon and n-alkanes suggest that carbon isotope measures on bulk organic carbon in sediments from this lake are sufficient to infer past climate-driven shifts in local vegetation