Varve dating method
The alternating layers of dark and light count the years like tree rings.The sedimentation or annual varve thickness is relatively uniform, typically 1.2 mm per yr for present conditions in Lake Suigetsu which is located near the coast of the Sea of Japan.Also, lakes that are thermally stratified, separated into a warm upper layer and a cool bottom layer, for long periods of time can lead to the cool lower layer becoming anoxic (lacking oxygen).This can prevent the organisms that can mix the sediment from becoming established (O’Sullivan, 1983).With varved sediments this can be observed, since the annual layers are visible, instead of assumed. Imprecise time measurements are often the limiting factor in paleoecological studies. The advantage varved sediments have over other sediments is the ability to determine precise temporal changes, sometimes down to the season. pollen, diatoms, charcoal, etc.) deposited in chronological order.
Varves don’t form in all lakes, in fact they are found in very few.The main factor controlling varve formation is climate variability; there must be large seasonal differences in both temperature and precipitation.This sets up the succession of biotic life and the physical and chemical structure of the lake necessary to form the contrasting layers.Each spring, tiny plants bloom in Lake Suigetsu, a small body of water in Japan.When these one-cell algae die, they drift down, shrouding the lake floor with a thin, white layer.