Lacustrine sediment archives preserve continuous records of changes in basin-to regional-scale processes that reflect broader variability in climatic conditions. Here, we present a 1500-year sediment record of effective moisture (precipitation/evaporation; P/E) from glacially-formed Pope Lake in central Wisconsin that spans much of the Common Era (CE; i.e., the last 2 kyr), including the Current Warm Period (CWP; last 150 years), Medieval Climate Anomaly (MCA; ca. 950-1250 CE), and Little Ice Age (LIA; ca. 1400-1700 CE). A suite of sediment proxies constrained by 14C and 210Pb ages were analyzed at decadal resolution to investigate Common Era changes in Upper Midwest effective moisture in response to temperature and synoptic scale atmospheric variability. Lake water isotopes reconstructed using authigenic carbonate oxygen isotopes (518Ocal) from Pope Lake covary with results from other Midwestern closed-basin lakes, indicating that P/E was a significant control on the isotopic composition of lake water. Relatively lower 518Ocal values during the MCA suggest that the moisture availability was greater during the MCA than LIA, despite increased air temperatures. This is supported by low carbon/nitrogen (C/N) ratios and low terrestrial lithic contributions that reflect increased lake levels during the MCA. Reversals of these trends were observed during the cooler LIA. Comparisons of the Pope Lake record to synoptic scale forcings, such as the Pacific North American (PNA) pattern, suggest that shifts in regional P/E were consistent with high amplitude PNA-like variability that likely affected the source and seasonality of precipitation. The general warm/wet and cool/dry relationships respectively noted during the MCA and LIA underscore how global temperature anomalies may alter the balance of effective moisture in the Upper Midwest in relatively short succession. The Pope Lake sediment record presented here is an important step toward reconstructing the region's hydroclimatic history and may inform expectations of near-future climate variability in a region with few Late Holocene records of comparable length or resolution.

Tropical hydroclimate variability during the Middle and Late Holocene was investigated using geochemical indicators of local-scale precipitation and evaporation preserved in sediment cores from two sites in the Mexican Yucatan Peninsula. Scanning X-Ray fluorescence spectroscopy data show generally decreasing precipitation trends during the Early and Middle Holocene. During the transition between the Middle and Late Holocene, geochemical evidence of reduced watershed erosion and increased evaporation indicate that a centennial-scale drying event impacted the region between 4.3 and 4.0 ka (kilo-anum; thousand years before present). These findings suggest that the 4.2 ka drying event, which has been previously recorded in Europe, Asia, and North and South America, also impacted the northern Neotropics. A comparison between our data and existing regional hydroclimate records suggests that dry conditions during the 4.2 ka event were coherent across western Central America. The timing of these regionally dry conditions coincided with a reduction in zonal sea surface temperature gradients in the tropical Pacific Ocean and a consequent mean-state increase in the frequency of El Nino o events, suggesting that linkages between Pacific Ocean-atmosphere dynamics played a significant role in the regional drying that occurred during that time. These data provide new support for a Central American expression of the 4.2 ka event, evidence for which is currently rare.

Variability in the source and seasonality of precipitation in the midcontinental United States during the Holocene was investigated using isotopic and sedimentological data from Martin Lake, northeastern Indiana, USA. Between 7100 and 4000 years before present (yr BP; present = 1950 CE), high S 18 O cal and S 13 C cal values with low variability indicate that moisture was predominantly derived from subtropical, southerly sources and delivered primarily during the warm season. Mean state shifts toward lower S 18 O cal and S 13 C cal occurred at ca. 4000 and 2550 yr BP, respectively, indicating an increase in northerly-sourced cold-season precipitation during the Late Holocene (i.e., the past 4200 years) and a subsequent reduction in warm season duration after 2550 yr BP. Record low %lithics from ca. 5000 to 4000 yr BP indicates major reductions in warm-season rain storms, consistent with regional evidence of drought at this time. An increase in the amplitude of centennial-scale variability in S 18 O cal , S 13 C cal , and %lithics after 1900 yr BP indicates greater precipitation source variability during the Common Era. During this interval, precipitation fluctuated between southerly-sourced, convective rainstorms when the Northern Hemisphere (NH) was warm (e.g., during the Medieval Climate Anomaly; 700-1000 - 1000 yr BP) and northerly-sourced rain and snow when the NH was cool (e.g., during the Little Ice Age; 150-550 - 550 yr BP). These trends, especially the change at ca. 4000 yr BP, are consistent with other North American paleoclimate records that collectively suggest a continental-scale shift in precipitation seasonality during the Middle to Late Holocene transition as the tropical Pacific Ocean transitioned from La Nina-like a-like conditions to a more El Nino-like o-like mean state. Concurrent NH cooling and persistent El Nino-like o-like conditions during the Late Holocene would have favored a southerly polar front jet stream with enhanced ridge and trough atmospheric circulation over North America - conditions resembling the positive mode of the Pacific-North American teleconnection (PNA). This would have increased interactions between high-latitude and subtropical airmasses over the midcontinent, increasing the proportion of northerly precipitation with low S 18 O delivered during the cold season (i.e., snowfall) and during extended periods with +PNA-like atmospheric circulation (e.g., the Little Ice Age).

The frequency and duration of Late-Holocene hydrologic extremes in northern Guatemala were investigated using multiple sedimentological and geochemical proxies preserved in a sediment core collected from Lake Petén Itzá. A general trend of increasing aridity in the Maya Lowlands during the past 2000 years was punctuated by several multidecadal- to centennial-scale drought events recorded in the Petén Itzá sediments. In particular, the period spanning the Maya Terminal Classic Period and the Medieval Climate Anomaly (MCA), between 800 and 1300 CE, was marked by several extreme droughts and included the driest conditions of the past 2000 years between 950 and 1100 CE. Similarities between our data and other existing regional paleoclimate records suggest regional drying events during this time may have been driven by a common mechanism. Specifically, comparisons between these records and tropical Atlantic sea surface temperatures (SSTs) suggest that the dry intervals may have been driven by a westward expansion of the North Atlantic Subtropical High pressure system. This period was unique in the general agreement between regional proxy records, which are otherwise notably heterogeneous during the Late-Holocene. During the Little Ice Age (LIA; 1400–1800 CE) mean precipitation at Petén Itzá was further reduced, and multidecadal drying events were recorded between 1500–1530, 1600–1640, and 1770–1800 CE. However, regional hydroclimatic coherency was weaker during the LIA, suggesting that additional climatic mechanisms played a more important role in local-scale hydrology during that time.

Long-term relationships between mean-state climatic conditions and flood frequencies in the mid -continental United States (US) are not well established because instrumental records of fluvial processes are limited to the current warm period (CWP; the last ca. 150 years) and continuous paleo-flood records are exceedingly rare. Here, we investigate climate-flood relationships in the midcontinental US by reconstructing flood frequencies at Half Moon Pond, a 1600-year-old oxbow lake on the lower White River, Indiana (watershed 1/4 ca, 29,000 km2). We used sediment accumulation rates and clastic fluxes constrained by high-resolution radiocarbon (14C) dating. Frequent flooding, as indicated by high sedi-mentation rates and clastic fluxes to Half Moon Pond, occurred leading up to and during the Medieval Climate Anomaly (MCA; 950-1250 CE) when paleoclimate records suggest the predominance of ocean -atmosphere mean states resembling the negative phases of the Pacific Decadal Oscillation (-PDO-like) and Pacific North American Mode (-PNA-like). Reductions in sedimentation rates and clastic fluxes, indicating reduced flooding, subsequently occurred during the transition out of the MCA and into the Little Ice Age (LIA; 1250-1830 CE) as ocean-atmosphere conditions shifted to + PDO-like and +PNA-like mean states. Sedimentation rates and clastic fluxes increased again after ca. 1800 CE, indicating increased flooding during the CWP as ocean-atmosphere conditions returned to-PDO-like and-PNA-like mean states. The White River trends were notably antiphased with sedimentation-rate-based flood frequencies for the lower Ohio River (500,000 km2 watershed) prior to 1830 CE. This antiphased relationship is consistent with flooding in moderate to small watersheds in the Midwest being sensitive to the occur-rence of rainstorm events, which were more frequent leading up to and during the MCA, and flooding in large watersheds being more sensitive to large spring melts associated with extensive snowpacks, which characterized the LIA. That both the White and Ohio rivers experienced their most frequent flooding during the CWP suggests deforestation and changing land use practices increased flooding on Mid-western watersheds across scales despite a current climatic mean state that in the past only resulted in increased flooding on moderate to small watersheds. Continued increased in midcontinental rainfall are therefore likely to enhance the occurrence of floods in Midwestern watersheds across different geographic scales.(c) 2022 Elsevier Ltd. All rights reserved.

As Earth's atmospheric temperatures and human populations increase, more people are becoming vulnerable to natural and human-induced disasters. This is particularly true in Central America, where the growing human population is experiencing climate extremes (droughts and floods), and the region is susceptible to geological hazards, such as earthquakes and volcanic eruptions, and environmental deterioration in many forms (soil erosion, lake eutrophication, heavy metal contamination, etc.). Instrumental and historical data from the region are insufficient to understand and document past hazards, a necessary first step for mitigating future risks. Long, continuous, well-resolved geological records can, however, provide a window into past climate and environmental changes that can be used to better predict future conditions in the region. The Lake Izabal Basin (LIB), in eastern Guatemala, contains the longest known continental records of tectonics, climate, and environmental change in the northern Neotropics. The basin is a pull-apart depression that developed along the North American and Caribbean plate boundary ∼ 12 Myr ago and contains > 4 km of sediment. The sedimentological archive in the LIB records the interplay among several Earth System processes. Consequently, exploration of sediments in the basin can provide key information concerning: (1) tectonic deformation and earthquake history along the plate boundary; (2) the timing and causes of volcanism from the Central American Volcanic Arc; and (3) hydroclimatic, ecologic, and geomicrobiological responses to different climate and environmental states. To evaluate the LIB as a potential site for scientific drilling, 65 scientists from 13 countries and 33 institutions met in Antigua, Guatemala, in August 2022 under the auspices of the International Continental Scientific Drilling Program (ICDP) and the US National Science Foundation (NSF). Several working groups developed scientific questions and overarching hypotheses that could be addressed by drilling the LIB and identified optimal coring sites and instrumentation needed to achieve the project goals. The group also discussed logistical challenges and outreach opportunities. The project is not only an outstanding opportunity to improve our scientific understanding of seismotectonic, volcanic, paleoclimatic, paleoecologic, and paleobiologic processes that operate in the tropics of Central America, but it is also an opportunity to improve understanding of multiple geological hazards and communicate that knowledge to help increase the resilience of at-risk Central American communities.

Late Holocene flood frequencies on the lower Ohio River were investigated using 14C-based sedimentation rates from three floodplain lakes located in Illinois (Avery Lake), Kentucky (Grassy Pond), and Indiana (Goose Pond). Changes in sediment accumulation rates were attributed to variability in the delivery of overbank sediment to each site as controlled by the frequency of Ohio River flooding. Sedimentation rates reached their lowest values in all three lakes between 400 and 1230 CE, indicating a regional reduction in flood frequencies on the lower Ohio River during a period that included the Medieval Climate Anomaly (MCA; ca. 950–1250 CE). Sedimentation rates increased after ca. 1230 CE and remained moderately high through the Little Ice Age (LIA; 1350–1820 CE) until the onset of extensive land clearance during the early 1800s CE. After 1820 CE, sedimentation rates increased further and were higher than any other time during the late Holocene. A comparison of regional paleoclimatic proxies with the above floodplain sedimentation records shows that Ohio River flooding during the late Holocene was responsive to mean-state changes in atmospheric circulation. During the MCA, when clockwise mean-state atmospheric circulation advected southerly moisture from the Gulf of Mexico into the Ohio River Valley primarily in the form of convective rainstorms, flooding on the Ohio River was least frequent. During the LIA, meridional mean-state atmospheric circulation increased the proportion of midcontinental moisture that was sourced from the northern Pacific and Arctic and delivered as snowfall, hence increasing flooding on the Ohio River. We attribute the increase in Ohio River flooding during the LIA to an increase in snowpack volume across the Ohio River Valley and the watershed-scale integration of runoff during spring snowmelt. Following Euro-American land clearance in the early 1800s, flood frequencies decoupled from this relationship and the lower Ohio River became susceptible to frequent flooding, despite a return to southerly and clockwise synoptic atmospheric conditions. These modern climate-flood dynamics are fundamentally different than those of the paleo-record and suggest that land-use changes – such as deforestation, tile draining, and landscape conversion to intensive row crop agriculture – have fundamentally altered the modern Midwestern hydrologic cycle.

Geophysical analysis of lacustrine sediment stratigraphy at Lago de Tota (Tota), Boyaca, Colombia provided evidence for significant lake-level fluctuations through the late Quaternary and produced a record that potentially spans the last 60 ka. CHIRP data collected in 2015 from this large, high-elevation lake in the Eastern Cordillera of the northern hemisphere Colombian Andes reveal a series of off-lap and on-lap sequences in the upper ~ 20 m of the lake’s sediment column that indicate large amplitude changes in lake level. Because 14C dated sediment cores are only available for the upper 3 m of the sediment column, known Holocene sedimentation rates were extrapolated in order to assign preliminary ages to the off-lap and on-lap sequence boundaries below 3 m depth. These data suggest that lake levels at Tota were lower than present during marine isotope stage (MIS) 4 between 60 and 57 ka, relatively high during MIS 3 between 57 and 29 ka, fell to their lowest levels during MIS 2 between 29 and 14 ka, and gradually rose to the modern high stand through a series of transgressions during MIS 1 and the Holocene from ~ 14 ka to the present. These fluctuations are broadly consistent with trends observed in other lake-level reconstructions from the northern (in phase) and southern (out of phase) hemisphere Andes, possibly supporting the idea that millennial-to-orbital-scale South American hydroclimate variability is linked to shifts in the mean latitude of the intertropical convergence zone due to the influence of insolation- and ocean circulation-driven hemispheric temperature gradients during glacial/stadial and interglacial/interstadial events. Although additional geochronological data will be needed to better resolve the timing of the Tota lake-level changes and their relationships with other records, these preliminary results from Tota, as well as the presence of a thick (> 300 m) sedimentary archive, indicate that this site has significant potential to produce high-resolution, quantitative, paleo-hydroclimate data spanning much of the last 1 million years. Because geophysical surveys and long paleoclimate records from northern hemisphere South America are exceedingly rare, these data provide critical insight into regional hydroclimate trends through the Late Quaternary. Additional work, such as the collection of sediment cores spanning the depth interval represented in the CHIRP data, is required, however, in order to place firmer chronological constraints on the hypothesized timing of lake-level fluctuations at Tota and to investigate their paleo-hydroclimatic implications.