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Paleohydrology

crooked pond lake level
Ground Penetrating Radar image and stratigraphic diagram of Crooked Pond. The sedimentary record within this New England pond suggests there were several millennial-scale "low stands," or dry intervals, during the Holocene. Enlarge »
tree rings
Sub-decadal variability in oxygen isotope data from a fossil tree specimen indicates rapid changes in the hydrologic regime. Enlarge »
new long pond
Evidence of the "8.2 ka event" in New Long Pond, MA. Enlarge »
danube delta
Coring flood deposits in the Danube Delta, Romania. Enlarge »

The complex and multivariate nature of climate requires that analyses of past climate change consider not only temperature variations, but also changes in moisture balance. Sub-millennial-scale Holocene climate variation may be best characterized by hydrologic variability. 'Spatial fingerprints' of paleohydrologic change (e.g., regional contrasts in the direction and magnitude of moisture balance) may be studied in order to better understand how North Atlantic circulation patterns, the rapid collapse of the Laurentide Ice Sheet, and other factors have caused sub-orbital climate variability during the Holocene.

Centennial to Millennial-Scale Change in New England Lakes
Small lakes without surface inlets or outlets can provide a record of past water table fluctuations (lake level) within their sediment record. Using geophysical sub-bottom imaging tools (e.g. ground penetrating radar and Chirp sonar) we are mapping the sedimentary record of lakes throughout the northeastern U.S. Targeted coring allows for the recovery of key stratigraphic intervals for sedimentological analysis, dating, and interpretation. Future work includes extending this analysis to lakes across eastern North America and Europe. Analysis of sites across the east-west moisture-balance gradient of North America and Europe will allow the examination of the full character and impacts of late-Quaternary climate variation on a continental spatial scale.

Annual to Decadal-Scale Records of Hydrologic Change
Understanding the causes of short-term climate variability is critically important if we are to be able to predict future changes and possibly mitigate their impacts; it is environmental change on these timescales that may pose the greatest challenge to society. To study climate on the annual and sub-decadal level, we are developing records using tree rings and varved sediments in New England. Many cedar bogs in the previously glaciated northeast U.S. formed in the early Holocene, and the wood preserved within these sediments contains an as of yet unexploited annual record of climatic variability. Preliminary oxygen isotope data from fossil cedars show significant sub-decadal variability likely related to changes in hydrologic regime. Further development of these records will provide an unprecedented description of paleoclimatic variability for the northeastern United States. Similarly, sediments recently recovered from Pout Pond, NH contain varves extending back ~14,000 years. Coupling isotopic and other sedimentological proxy records of environmental change from Pout Pond with cedar tree ring records will provide critical insight into the nature of late Quaternary hydrological variability in New England at an unprecedented temporal scale.

Abrupt Climate Change
Changes on the terrestrial landscape can cause alterations of the climate system. For example, glacial meltwater pulses into the North Atlantic Ocean are often postulated to have altered thermohaline circulation by shutting down North Atlantic Deep Water (NADW) formation and initiating abrupt climate-cooling events like the Younger Dryas (YD) and the “8.2 ka event”. In order to understand the influence of glacial meltwater pulses on millennial-scale climate change, it is critical to constrain the timing, magnitude, and location of meltwater release.

To address this issue, we are currently analyzing the terrestrial and near-shore evidence of meltwater drainage in eastern North America. New evidence indicates that the Hudson Valley was the conduit for catastrophic drainage of meltwater (>1012 m3) from Glacial Lake Iroquois (and other large glacial lakes at the southern margin of the Laurentide Ice Sheet) between 13.1 and 13.5 ka. The timing of this catastrophic draining event down the Hudson Valley is consistent with the onset of the Inter-Allerod cool period, possibly indicating a direct link between meltwater flux through the Hudson Valley and centennial to millennial-scale changes in ocean circulation and climate.

Extreme Fluvial Floods
Sediments deposited in settings with continuous accumulation, such as floodplain lakes or prodeltas, offer records of extreme hydrologic variability at potentially high temporal resolution. Recently recovered cores from the Danube floodplain and delta reveal a record of large flood events over the last 1000 years. These sediments will allow us to quantify and reconstruct the evolution of the Danube delta in the late Holocene, and explore links between shoreline evolution, discharge, sea-level variability, and climate.

For more information please contact:

Jeff Donnelly (jdonnelly@whoi.edu)

Bryan Shuman (http://www.geog.umn.edu/Faculty/Shuman.htm)

Liviu Giosan (lgiosan@whoi.edu)

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