Dust deposition in the Aral Sea, MWP and LIA

Posted: May 23, 2012 by tchannon in climate, Ice ages, weather
aral-sea-fao

Aral sea. Image credit FAO

Dust deposition in the Aral Sea: implications for changes in atmospheric circulation in central Asia during the past 2000 years

Xiangtong Huanga , Hedi Oberhänsli, Hans von Suchodoletz, Philippe Sorrel

Quaternary Science Reviews, Volume 30, Issues 25–26, December 2011, Pages 3661–3674

Abstract

“We investigated mineral aerosol (dust) deposition in the Aral Sea with intention to understand the variability of dust in central Asia and its implications for atmospheric circulation change in the late Holocene. Using an 11.12-m sediment core of the lake, we calculated bulk sediment fluxes at high time-resolution and analyzed grain-size distributions of detrital sediments. A refined age-depth model was established by combined methods of radiocarbon dating and archeological evidence. Besides, a principal component analysis (PCA) of grain-size fractions and elements (Fe, Ti, K, Ca, Sr) was used to assess the potential processes controlling detrital inputs. The results

suggest that two processes are mainly relevant for the clastic input as the medium silt fractions and Ti, Fe and K are positively correlated with Component 1 (C1), and the fine size fractions (<6 µm) are positively correlated with Component 2 (C2). Taking the results of the PCA, geological backgrounds, clastic input processes into account, we propose that the medium silt fractions and, in particular, the grain-size fraction ratio (6–32 µm/2–6 µm), can serve as indicators of the variability of airborne dust in the Aral Sea region. On the contrary, the fine size fractions appear to be contributed mainly by the sheetwash processes. The bulk sediment deposition fluxes were extremely high during the Little Ice Age (LIA; AD 1400–1780), which may be related to the increased dust deposition. As indicated by the variations of grain-size ratio and Ti, the history of dust deposition in central Asia can be divided into five distinct periods, with a remarkably low deposition during AD 1–350, a moderately high value from AD 350–720, a return to relatively low level between AD 720 and AD 1400 (including the Medieval Warm Period (MWP, AD 755–1070)), an exceptionally high deposition from AD 1400 to 1940s and an abnormally low value since 1940s. The temporal variations in the dust deposition are consistent with the changes in the Siberian High (SH) and mean atmospheric temperature of the northern hemisphere during the past 2000 years, with low/high annual temperature anomalies corresponding to high/low dust supplies in the Aral Sea sediments, respectively. The variations in the fine size fraction also show a broadly similarity to a lacustrine d18O record in Turkey (Jones et al., 2006), implying that there was less moisture entering western central Asia from the Mediterranean during the LIA than during the MWP.”

I notice one of the authors: Dr. rer. nat. Hans von Suchodoletz, a professor at University of Leipzig has an interesting publication list on sediments. His personal institute page is here.

aral-sea-1

Figure 11: (manipulated to a more familiar orientation by Tim)

Grain-size records from the Aral Sea (A, D) compared to proxies for temperature change in China (B, Yang B. et al., 2002) and the Northern Hemisphere (C, Mann and Jones, 2003) and a d18O record for precipitation in the eastern Mediterranean (E, Jones et al., 2006).

Commentary

Recently there has been a flurry of publication on airborne particles ranging from chemical precusors through actual solid. Part of this story is how these affect weather processes and part about extra terrestrial origin. In this paper the focus is on a sediment core taken from the bed of the Aral sea. The region has a continental climate.

The authors note a correlation between named climatic events and dust. This suggest a wind/precipitation association.


Post by Tim Channon, co-moderator

Comments
  1. tallbloke says:

    An interesting hockey stick in the Northern hemisphere according to plot ‘C’. The blade is less than 0.5C in height, indicating a remarkably stable temperature series.

    Can we all go home now?

  2. tchannon says:

    Don’t know what to make of the scales.

  3. Roger Andrews says:

    I don’t know how it might affect the results, but the Aral Sea has shrunk by 90% since 1960, when the Soviets began to divert the rivers feeding the sea for irrigation projects.

  4. tallbloke says:

    Can’t see Mickey Mann being too happy with it for sure… 😉

    So have you seen the rest of the paper? Which elements are though to be ET?