500186 - Environmental Change (Tree Dating)

Archives:

Trees:

The Basics:

The process of datin tree rings is called Dendrochronology, basically counting the number of rings present in the tree.The proxies of this arhcive are as followed:

• Tree Ring width
• δ18O and δ13C

Proxies are sources of climate information from natural archives such as tree rings, ice cores, corals, lake and ocean sediments, tree pollen. 

Tree ring formations:

New cells are added to the outside perimeter of the trees trunk each year, when in temperate zones the cells that grow in spring are larger than those forming in the winter periods where ther is often little/no growth. This lack of growth leads to a distinctive line between each years ring width. However in th tropics, there is mininal seasonal variation in regards to growth, so it is unlikely tree rings will be visible.

Tree rings grow wider when conditions are more favourable towards growth, and vice versa, grwoing narrower when conditions are unfavourable. For some trees the key control is temperatur and for others moisture availability.

Dendroclimatology - By counting tree rings, it is possible to provide a very precise and accurate chronology, assuming one ring is formed every year.

Ring width can be a very useful and perhaps essential palaeoclimate proxy. Other properties of the annual rings, such as maximum latewood density (e.g. Liang et al., 2016) have been shown to be better proxies than simple ring width. δ18O and δ13C of tree-ring cellulose can also be used. Xu et al. (2011) found there is a strong relationship between δ18O tree-ring cellulose and times of drought. 

Limitations of dendroclimatology:

Trees are not found everywhere on Earth, severly limitiing sampling sites. There are multiple factors that can affect tree ring growth besides just…