Browsing by Subject "Medieval Climate Anomaly"

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    Common Era Midcontinental Hydroclimate Variability Inferred from Iowan Lake Sediments, USA
    (2024-02) Goswami, Anusuya; Bird, Broxton; Filippelli, Gabriel; Jacinthe, Pierre-André
    Global climate change manifests diverse consequences across the United States, creating distinct challenges in different regions. For example: The Western United States grapples with a notable surge in wildfires and drought events, indicating reduced effective moisture. In contrast, the Eastern part faces severe and frequent flooding events, reflecting higher effective moisture conditions and suggesting an East-West dipole-like climatic pattern. While the current East-West dividing hinge-line sits at 96°W, questions linger about its persistence throughout the late Holocene or whether it has undergone changes over time. Understanding the evolution and stability of this hinge-line is crucial for predicting the impacts of ongoing global warming on various U.S. regions. To address this issue, it is essential to develop additional paleoclimate records from the U.S. Midcontinent, especially those in close proximity to the modern hydroclimate hinge-line. This research focuses on understanding the common era (CE; last 2000 years) hydroclimate variability and its driving mechanisms using lake sediment archives from two hydrologically restricted Iowan kettle lakes, West Lake Okoboji (~1800 years long) and Clear Lake (~2000 years long). The results of multiproxy sedimentological, geochemical, and isotopic analyses reveal a wetter period during the Medieval Climate Anomaly (MCA; 950-1250 CE) and a drier phase during the Little Ice Age (LIA; 1350-1850 CE), aligning with regional patterns in the upper Midwest. Comparisons with regional paleoclimate records suggest that pluvial conditions during the MCA were linked to mean state atmospheric circulation conditions resembling the negative phase of the Pacific-North American (-PNA) teleconnection pattern when Pacific Ocean-atmosphere conditions similarly resembled the negative phase of the Pacific Decadal Oscillation (-PDO). Conversely, drier conditions during the LIA occurred when +PNA-like atmospheric circulation patterns predominated under +PDO-like conditions in the North Pacific Ocean. Comparison with records near the modern hydroclimate hinge-line indicates in-phase relationships with records east of 96˚ W and anti-phased relationships with records west of 96˚ W. This supports idea of the stable hinge line position during the Common Era.
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    Ocean-atmosphere forcing of centennial hydroclimate variability in the Pacific Northwest
    (AGU, 2014-03-11) Steinman, Byron A.; Abbott, Mark B.; Mann, Michael E.; Ortiz, Joseph D.; Feng, Song; Pompeani, David P.; Stansell, Nathan D.; Anderson, Lesleigh; Finney, Bruce P.; Bird, Broxton W.; Earth Sciences, School of Science
    Reconstructing centennial timescale hydroclimate variability during the late Holocene is critically important for understanding large-scale patterns of drought and their relationship with climate dynamics. We present sediment oxygen isotope records spanning the last two millennia from 10 lakes, as well as climate model simulations, indicating that the Little Ice Age was dry relative to the Medieval Climate Anomaly in much of the Pacific Northwest of North America. This pattern is consistent with observed associations between the El Niño–Southern Oscillation (ENSO), the Northern Annular Mode, and drought as well as with proxy-based reconstructions of Pacific and Atlantic ocean-atmosphere variations over the past 1000 years. The large amplitude of centennial variability indicated by the lake data suggests that regional hydroclimate is characterized by longer-term shifts in ENSO-like dynamics and that an improved understanding of the centennial timescale relationship between external forcing and drought is necessary for projecting future hydroclimatic conditions in western North America.
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    Using sediment accumulation rates in floodplain paleochannel lakes to reconstruct climate-flood relationships on the lower Ohio River
    (Elsevier, 2022-12-15) Gibson , Derek K.; Bird, Broxton W.; Pollard, Harvie J.; Nealy, Cameron A.; Barr, Robert C.; Escobar, Jaime; Earth and Environmental Sciences, School of Science
    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.