A
peat bog in Romania provides a new insight into our knowledge of when the
Sahara began to transform from grassland into the desert we know today, and the
impact this had on dust deposition within Eastern Europe.
Using
carbon dating and chemical analysis, researchers from Northumbria University,
Newcastle have shown that significant changes in dust levels occurred in
Romania around 6,100 years ago, despite the climate in Eastern Europe being
relatively wet at this time, indicative of an extraregional source of such dust,
most likely to be from the Sahara.
This
discovery is valuable new evidence of the impact changes in the climate and
vegetation of North Africa may have on dust in Europe and may allow climate modellers
to better understand the movement of dust and the impact of desertification,
both in the past and the future.
The
research was led by Jack Longman, a Geography PhD student at Northumbria. His
resulting paper, Periodic input of dustover the Eastern Carpathians during the Holocene linked with Saharandesertification and human impact, has now been published in
the journal Climate of the Past and
is one of just 29 ‘highlight’ papers selected by the journal as
being of particular scientific interest.
Jack
said: “We know that as recently as 6,000 years ago, what is now the vast, dusty
and uninhabited Saharan desert was covered in lush grassland. However, the end
of this period has been subject to much discussion, both with regards to its
timing and its impact on the environment.
“To
investigate the impact such a large climatic and environmental shift had on
Europe, we analysed the elemental makeup of a peat bog in the Eastern
Carpathians, Romania. Such bogs form slowly over thousands of years, with each
new layer being deposited on top of the previous, trapping the chemical, and
organic signature of that precise time period within it.
“Using
carbon dating, the age of the bog was determined, allowing us to look back at
the conditions which occurred at the time each layer formed. A core of almost
10 metres of peat sediment was recovered, representing nearly 11,000 years of
deposition.”
Jack
and his team analysed peat from different periods in time, looking specifically
for higher levels of titanium, potassium and silicon – all chemical elements
associated with higher levels of dust within the peat.
In
addition, they also counted the numbers of various types of single-celled
organisms called testate amoebae, whose population changes depending on the amount
of water in the bog, giving an indication of how wet or dry the climate was
during different periods.
Combining
this information allowed the team to determine when dust from the Sahara began
to land in Romania. As Jack explains: “Between 10,800 and 6,100 years ago, the number
of testate amoeba present appears to be in sync with the amount of dust recorded,
indicating that the dust is likely to be related to local droughts and soil
erosion. However, for the past 6,100 years the number of testate amoebae
present show the bog was constantly wet, despite numerous large dust deposits
during this time.
“We
also saw that over the last 6,100 years the dust has contained higher levels of
titanium, which suggests a major shift from a local source to one which appears
Saharan in origin. The amount of dust recorded in the bog also shifts around
this time, with much more deposited in the last 6,100 years than previously.”
Between
approximately 14,000 B.C. and 4,000 B.C. the climate in the Sahara was warm and
humid due to higher levels of incoming solar radiation which modified the
location of the African monsoon – a period known as the African Humid Period.
Today,
the Sahara is the largest hot desert in the world, covering an area of 9.2
million square kilometres. Dust from the area has been deposited as far as the Caribbean
and the Amazon basin and can affect air temperatures, cause ocean cooling, and
alter rainfall amounts.
Jack
added: “Dust is one of the most important aerosols for both the climate and the
biology of an environment, and so understanding the amount of dust produced,
and the distance and direction it travels is vital to allow us to understand
its effect better.”
Working alongside Jack to
conduct the research was Senior Lecturer Dr Vasile Ersek and Professor of
Palaeoecology Ulrich Salzmann, both of Northumbria University, as well as Daniel
Veres of the Romanian Academy’s Institute of Speleology, Katalin Hubay of the Hungarian
Academy of Science and Marc Bormann, Volker Wennrich and Frank Schäbitz of the University
of Cologne.
Northumbria is a specialist in
the multidisciplinary research theme Extreme Environments. Academics working in
this area explore research questions in environments where life is under threat
from the most extreme conditions, from the ice of Antarctica to the surface of
the sun. For more about research into Extreme Environments click here.
