LATE GLACIAL STAGE-HOLOCENE TRANSITION RECORDED IN A NORTHERN SOUTH AMERICAN STALAGMITE

A 0.50 m stalagmite collected from Cueva Zarraga in northern Venezuela (N 11°10’, W 69°37’; 960 m above sea level) preserves a growth record from ~21 to 1.5 ka BP capturing the Late Glacial (LG) to Holocene transition.  The transition is characterized by a rapid (c.a. 300 yrs) and major decrease in stalagmite stable isotopic composition.  d¹⁸O shifts from pre-Holocene average composition of –1.4 ‰ to an average composition of –3.9 ‰ and d¹³C values shift from –5.4 ‰ to –9.1 ‰.

Dry and colder conditions prevailed above Cueva Zarraga prior to the LG-Holocene transition, and C4 vegetation was more abundant.  The isotopic shift at the LG-Holocene transition records a rapid warming and increased precipitation resulting in an expansion of C3 vegetation.  Although both d¹⁸O and d¹³C values exhibit significant variability, it appears that the d¹³C record is very sensitive to moisture.  Humid conditions prevail from 10,200 to 8,200 yr BP.  At 8,200 yr BP, a major increase in d¹³C values suggest a brief period of reduced moisture until 7,800 yr BP.  d¹³C values decrease steadily and reach minimum values at about 2,000 years BP.  At 2,000 yr BP d¹³C values begin to increase and suggest reduced moisture.

Timing and nature of changes recorded by Cueva Zarraga speleothem are coincident with lake level and vegetation changes recorded at Lake Valencia, and sediment input and foraminiferal isotope changes recorded in the Cariaco basin.  The LG-Holocene shift recorded by Cueva Zarraga speleothem lags by 1,200 years those in Sajama ice core and supports the notion of asymmetry in timing of climate response between northern and southern tropics.