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WonderBiogeochemical transport fact

Dust from the Sahara crosses the Atlantic and falls on the Amazon, bringing phosphorus that helps replace nutrients washed out of the rainforest's soils by rain.

Saharan dust

ClimateNatureScience

The story behind the card

Studies suggest that more than half of the dust reaching the Amazon comes from one place: the Bodélé Depression in Chad, the dry bed of a much larger ancient lake. Its surface is made largely of diatoms, the fossil shells of tiny algae, and strong winds lift them high into the air. Summer winds carry the dust west over the Atlantic; plumes take about five to seven days to reach the Caribbean. Most Amazon soils are old and heavily washed out, and short of phosphorus, a nutrient that limits how fast trees grow. Dust supplies only part of the phosphorus that falls on the basin, but the amount is comparable to what the forest loses each year to rain and rivers, so without it the soils would slowly run down.

Türkçe oku
Sahra'dan kalkan toz Atlas Okyanusu'nu aşıp Amazon'a düşer. Taşıdığı fosfor, yağışların ormanın toprağından yıkayıp götürdüğü besinlerin bir kısmını yerine koyar.

Araştırmalara göre Amazon'a ulaşan tozun yarıdan fazlası tek bir yerden gelir: Çad'daki Bodélé Çukuru, yani çok daha büyük eski bir gölün kurumuş tabanı. Çukurun yüzeyi büyük ölçüde diyatomlardan, yani mikroskobik alglerin fosil kabuklarından oluşur ve güçlü rüzgârlar bunları havanın yükseklerine taşır. Yaz rüzgârları tozu batıya, Atlas Okyanusu'nun üzerine sürükler; toz bulutlarının Karayipler'e varması beş ila yedi gün sürer. Amazon topraklarının çoğu çok yaşlıdır, yağmurla iyice yıkanmıştır ve ağaçların büyümesini sınırlayan fosfor bakımından yoksuldur. Havza üzerine düşen fosforun yalnızca bir kısmı tozdan gelir, ama bu miktar ormanın her yıl yağmur ve nehirlerle kaybettiğine yakındır. Toz olmasa, toprak yavaş yavaş tükenirdi.

Sources and further reading

Background reading: Saharan dust
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