Dates
In the Greenland oxygen isotope record, the Older Dryas appears as a downward peak establishing a small, low-intensity gap between the Bølling and the Allerød. This configuration presents a difficulty in estimating its time, as it is more of a point than a segment. But which point, and how long a segment should be assigned? The segment is small enough to escape the resolution of most C-14 series; i.e., the points are not close enough together to find it.
One approach to the problem assigns a point and then picks an arbitrary segment. You might read that the Older Dryas is "centered" near 14,100 BP or is 100 to 150 years in duration "at" 14,250 BP.
A second approach finds C-14 or other dates as close to the end of the Bølling and the beginning of the Allerød as possible and selects end points based on them. This type of date is of the form, for example, 14,000-13,700 BP.
The best approach attempts to include the Older Dryas in a sequence of points as close together as possible (high resolution), or within a known event. For example, pollen from the island of Hokkaidō in Japan records a Larix pollen peak and matching sphagnum decline at 14,600-13700 BP. In the White Sea a cooling occurred at 14,700-13,400/13,000, which resulted in a readvance of the glacier in the initial Allerød. In Canada, the Shulie Lake phase (a readvance) is dated to 14,000-13,500 BP. On the other hand, varve chronology in southern Sweden indicates a range of 14,050-13,900 there.
Capturing the Older Dryas through high resolution dating continues to be of concern to researchers in climatology.
Read more about this topic: Older Dryas
Famous quotes containing the word dates:
“Dates are stupidly annoying—what we want is not dates but taste;Myet we are uncomfortable without them.”
—Henry Brooks Adams (1838–1918)
“What is most interesting and valuable in it, however, is not the materials for the history of Pontiac, or Braddock, or the Northwest, which it furnishes; not the annals of the country, but the natural facts, or perennials, which are ever without date. When out of history the truth shall be extracted, it will have shed its dates like withered leaves.”
—Henry David Thoreau (1817–1862)
“We do NOT know the past in chronological sequence. It may be convenient to lay it out anesthetized on the table with dates pasted on here and there, but what we know we know by ripples and spirals eddying out from us and from our own time.”
—Ezra Pound (1885–1972)