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1. The Link Between Southern Portuguese Climate and the East Atlantic Mode from Highly Resolved Speleothem Records

   Chormann, A. ; Wanamaker, A.D. ; Gillikin, D.P. ; Asmerom, Y. ; Polyak, V. ; Denniston, R. ; Thatcher, D. ; Ummenhofer, C. ; Regala, F.T. ( April 2022 , PAGES Open Science Meeting 2022, Virtual)

   Climate in the Iberian Peninsula is impacted by both internal and external climate modes, which are expected to shift in position and intensity due to anthropogenic climate change. Examples of such modes include the North Atlantic Oscillation (NAO) and the East Atlantic mode (EA). Changes in the behavior in these regional climate modes could significantly alter water availability in the Iberian Peninsula, a region identified by model projections as particularly sensitive to future warming scenarios. There has been extensive research and paleoclimate reconstructions of the NAO and its impacts on Iberian climate. However, to date few paleoclimate records have been developed to evaluate the behavior of the EA over the late Holocene and into the present. The development of highly resolved regional paleoclimate records from Iberia is critical for improving the predictive capability of regional climate models under future warming scenarios and to determine the extent to which different teleconnection patterns are influencing climate. Here we present a near annually resolved stable carbon isotope (δ13C) and oxygen (δ18O) isotope time-series from three stalagmites from the Algarve region of southern Portugal from two caves within 2.3 km of each other. The southern coast of Portugal offers an ideal location to studymore »the behavior of the EA due to the modulation of storm tracks coming across the North Atlantic Ocean into Iberia associated with the EA. U/Th dating indicates that our composite record spans the last millennia continuously through 2018 CE. Two stalagmites (GIA-19-1 and C-18-1) stopped growing around 1600 CE, during a dry interval, and sample GIA-19-2 grew continuously since the 15th century. GIA-19-2, with sub-annual resolution, is compared to modern instrumental records to evaluate the influence of specific environmental controls, including temperature and precipitation amounts. Isotope data from all three stalagmites exhibit substantial multidecadal variability indicating relatively wet and dry intervals. Based on our initial results, it is likely that both temperature and precipitation amount effects are the dominant controls on isotopic variability in these stalagmites. Comparison of the GIA-19-2 oxygen isotope time-series with the instrumental index (1950 to present) and reconstructed index (1650 CE to present) of the EA mode shows strong coherence with both index records. Hence, multidecadal variability observed in our stalagmite isotope time series may provide insight into the historical behavior of the EA mode and its resulting impacts on southern Portuguese climate.« less
2. The Link Between Southern Portuguese Climate and the East Atlantic Mode from Highly Resolved Speleothem Records

   Chormann, A. ( January 2022 , PAGES Open Science Meeting)

   Climate in the Iberian Peninsula is impacted by both internal and external climate modes, which are expected to shift in position and intensity due to anthropogenic climate change. Examples of such modes include the North Atlantic Oscillation (NAO) and the East Atlantic mode (EA). Changes in the behavior in these regional climate modes could significantly alter water availability in the Iberian Peninsula, a region identified by model projections as particularly sensitive to future warming scenarios. There has been extensive research and paleoclimate reconstructions of the NAO and its impacts on Iberian climate. However, to date few paleoclimate records have been developed to evaluate the behavior of the EA over the late Holocene and into the present. The development of highly resolved regional paleoclimate records from Iberia is critical for improving the predictive capability of regional climate models under future warming scenarios and to determine the extent to which different teleconnection patterns are influencing climate. Here we present a near annually resolved stable carbon isotope (δ13C) and oxygen (δ18O) isotope time-series from three stalagmites from the Algarve region of southern Portugal from two caves within 2.3 km of each other. The southern coast of Portugal offers an ideal location to studymore »the behavior of the EA due to the modulation of storm tracks coming across the North Atlantic Ocean into Iberia associated with the EA. U/Th dating indicates that our composite record spans the last millennia continuously through 2018 CE. Two stalagmites (GIA-19-1 and C-18-1) stopped growing around 1600 CE, during a dry interval, and sample GIA-19-2 grew continuously since the 15th century. GIA-19-2, with sub-annual resolution, is compared to modern instrumental records to evaluate the influence of specific environmental controls, including temperature and precipitation amounts. Isotope data from all three stalagmites exhibit substantial multidecadal variability indicating relatively wet and dry intervals. Based on our initial results, it is likely that both temperature and precipitation amount effects are the dominant controls on isotopic variability in these stalagmites. Comparison of the GIA-19-2 oxygen isotope time-series with the instrumental index (1950 to present) and reconstructed index (1650 CE to present) of the EA mode shows strong coherence with both index records. Hence, multidecadal variability observed in our stalagmite isotope time series may provide insight into the historical behavior of the EA mode and its resulting impacts on southern Portuguese climate.« less
3. Drip water δ18O variability in the northeastern Yucatán Peninsula, Mexico: implications for tropical cyclone detection and rainfall reconstruction from speleothems.

   https://doi.org/https://doi.org/10.1016/j.gca.2020.07.008  

   Lases-Hernandez F., Medina-Elizalde M. ( July 2020 , Geochimica et cosmochimica acta)

   This study examines the oxygen isotopic composition (δ18O values) of drip water, rainfall, and groundwater in the Río Secreto Cave system, located in the Yucatán Peninsula, Mexico. The main motivation of this study was to determine the implications of drip water hydrology for the reconstruction of rainfall and for the detection of droughts and tropical cyclones from stalagmite δ18O records. Monitoring of environmental and isotopic conditions was conducted for two years, from June 2017 to April 2019. This study provides the first instrumental evidence of an “amount effect” on interannual timescales in the Yucatán Peninsula. Observed bi-weekly to interannual variability in drip water δ18O values can be explained for individual drips by different integrations of rainfall amount in the time domain. Drip sites within two chambers (stations A and B) integrate 4 to 15 months of rainfall accumulation. Within a third chamber (station LF) one drip site reflects the annual rainfall isotopic cycle with a positive offset and another, the largest rainfall events. During epikarst infiltration, the integration of rainfall amount by drip water reservoirs determines the degree to which they "dilute" a tropical cyclone (TC) isotopic signature. TCs can be detected particularly when: (1) the water volume of themore »reservoir is low, such as during a persistent drought, and; (2) TCs have a sufficiently distinct isotopic signal relative to that of the reservoir prior to the event. TC isotopic signals can "filter through" the system on time scales shorter than the integration time of the reservoir, on the order of a week, in most of the reservoirs examined. In Río Secreto Cave reconstructing precipitation amount and detecting the TC isotopic signatures from stalagmite δ18O are possible, but not in all cases. Our analysis shows that stalagmite δ18O records are more likely to underestimate the magnitude of annual-scale droughts following normal hydroclimate conditions and more likely to record TCs during multiyear droughts than during normal or wet periods. Drip water monitoring results suggest that available stalagmite δ18O records from the Maya lowlands might be underestimating the intensity of paleo-drought events, such as the Terminal Classic droughts associated with the disintegration of the Maya civilization. This study complements the results from Lases-Hernandez et al. (2019) comparing two different sampling protocols and highlights the importance of conducting multiyear monitoring of drip water and rainfall in order to interpret stalagmite δ18O as a paleoclimate proxy.« less
4. Streamflow Variability Indicated by False Rings in Bald Cypress (Taxodium distichum (L.) Rich.)

   https://doi.org/10.3390/f11101100  

   Therrell, Matthew D. ; Elliott, Emily A. ; Meko, Matthew D. ; Bregy, Joshua C. ; Tucker, Clay S. ; Harley, Grant L. ; Maxwell, Justin T. ; Tootle, Glenn A. ( October 2020 , Forests)

   Despite growing in wet lowland and riparian settings, Taxodium distichum (L.) Rich. (bald cypress) has a strong response to hydroclimate variability, and tree ring chronologies derived from bald cypress have been used extensively to reconstruct drought, precipitation and streamflow. Previous studies have also demonstrated that false rings in bald cypress appear to be the result of variations in water availability during the growing season. In this study 28 trees from two sites located adjacent to the Choctawhatchee River in Northwestern Florida, USA were used to develop a false ring record extending from 1881 to 2014. Twenty false ring events were recorded during the available instrumental era (1931–2014). This record was compared with daily and monthly streamflow data from a nearby gage. All 20 of the false-ring events recorded during the instrumental period occurred during years in which greatly increased streamflow occurred late in the growing season. Many of these wet events appear to be the result of rainfall resulting from landfalling tropical cyclones. We also found that the intra-annual position of false rings within growth rings reflects streamflow variability and combining the false-ring record with tree ring width chronologies improves the estimation of overall summer streamflow by 14%. Future workmore »using these and other quantitative approaches for the identification and measurement of false ring variables in tree rings may improve tree-ring reconstructions of streamflow and potentially the record of tropical cyclone rainfall events.« less
5. Evaluating southern Portuguese hydroclimate from highly resolved speleothem records

   Chormann, A.G. ; Wanamaker, A.D. ; Gillikin, D.P. ; Asmerom, Y. ; Polyak, V. ; Denniston, R.F. ; Thatcher, D.L. ; Ummenhofer, C.C. ; Regala., F.T. ( October 2021 , American Geophysical Union, Fall Meeting 2021 (New Orleans, LA))

   Anthropogenic climate change is expected to alter global hydrological regimes in the near future, resulting in significant changes to water availability. However, the magnitude of such changes will vary regionally. The Iberian Peninsula, and specifically Portugal, has been identified by climate model projections as an area where climate change will increase drought frequency and severity. Climate in the Iberian Peninsula is impacted by both internal and external climate modes, potentially producing different precipitation patterns within a small geographic region. Thus, the development of regional highly resolved paleoclimate records from Portugal is critical for improving the predictive capability of regional climate models under future warming scenarios and to determine the extent to which different teleconnection patterns are influencing hydroclimate. Here we present a near annually resolved stable carbon isotope (δ13C) and oxygen (δ18O) isotope time-series from three stalagmites from the Algarve region of southern Portugal from two caves within 2.3 km of each other. U/Th dating indicates that our composite record spans the last millennia continuously through 2019 CE. Two stalagmites (GIA-19-1 and C-18-1) stopped growing around 1550 CE, during a dry interval, and sample GIA-19-2 grew continuously since the 17th century. GIA-19-2, with sub-annual resolution, is compared to modern instrumentalmore »records to evaluate the influence of specific environmental controls, including temperature and precipitation amounts. Isotope data from all three stalagmites exhibit substantial multidecadal variability indicating relatively wet and dry intervals. Based on our initial results, it is likely that both temperature and precipitation amount effects are the dominant controls on isotopic variability in these stalagmites. Comparison of the GIA-19-2 oxygen isotope time-series with the instrumental record and reconstructed index of the East Atlantic (EA) pattern (1650 CE to present) shows strong coherence with a reconstructed EA index (1650-2018 CE) and an instrumental EA index (1950 to present). Hence, variability in Southern Portuguese hydroclimate associated with the EA mode should also be considered by policy makers planners as they prepare for future warming and associated water stresses.« less