HR: 0800h
AN: GC31A-0110    [Abstracts]
TI: Effects of Holocene Climate Variability on Lago Paixban, a Perennial Wetland in Peten, Guatemala
AU: * Wahl, D
EM: dwahl@usgs.gov
AF: U.S.G.S., 345 Middlefield Rd. MS-975, Menlo Park, CA 94025, United States
AB: This paper presents the results of analyses carried out on a 6-m long sediment core from Lago Paixban, a perennial wetland in northern Peten, Guatemala. Pollen, δ¹³C_org, magnetic susceptibility, and LOI have been used to track the vegetation and hydrology of this karstic basin from 10,000 cal yr B.P. to present. Lack of fossil preservation in the basal sediments indicates relatively dry conditions leading into the early Holocene, followed by increased humidity and the presence of a shallow marsh by ~9,000 cal yr B.P. An approximately 3-cm thick band of calcite was deposited around 8,200 cal yr B.P., representing a distinct hydrological shift likely associated with the North Atlantic 8.2 ka event. Increased humidity in the early Holocene led to the formation of an open-water lake in the basin by 7,500 cal yr B.P., which persisted for around 2,000 years. At 5,500 cal yr B.P. lake levels dropped dramatically, marked by an abrupt transition to a 1-m thick peat horizon dominated by wetland taxa. This shift from lake to marsh reflects the onset of regionally drier conditions in the latter part of the Holocene. Ecological changes during this late Holocene dry period suggest lowest recorded water levels from ~5,500-4,500 cal yr B.P., followed by increased water levels and the establishment of an extensive sawgrass marsh. Anthropogenic impacts are recorded as a dramatic increase of disturbance and agricultural taxa during the period of prehistoric Maya settlement in the late Holocene. This interval, from ~3,500-1,100 cal yr B.P., is marked by a 1-m thick horizon of calcareous clay marl, indicating a change in local hydrological conditions. It is difficult to determine whether hydrological changes during this `Maya Period` were primarily driven by climate or human activity. Shortly after the area was abandoned, a perennial wetland dominated by sawgrass ( Cladium jamaicense) developed and has persisted to the present.
DE: 1605 Abrupt/rapid climate change (4901, 8408)
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
SC: Global Environmental Change [GC]
MN: 2007 Fall Meeting