Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
The sub-chronologies obtained from the two groups of higher and lower mean MXD are shown as grey and brown lines. Chronologies were smoothed using spline with 50-year frequency cutoff. Grey area show mean-tree sample depth. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)
