Lateral and Seasonal Trends of Saharan Dust Deposition along a Transect over the Atlantic Ocean

Abstract:

Every year, an estimated 140 million tons of Saharan dust are deposited in the Atlantic Ocean, which can have several direct and indirect effects on global and regional climate. For example, dust can scatter and absorb incoming and reflected solar radiation, transport nutrients and pathogens, and act as mineral ballast particles in the ocean. In order to constrain the relations between atmospheric dust and climate, submarine sediment traps at five stations along a transect across the Atlantic Ocean at 12°N were deployed, at 1200m and 3500m water depth. Samples of seven of these sediment traps, that sampled from October 2012 to November 2013, have been analyzed on particle size and dust flux.

The size of the dust particles is important because it can have an effect on the positive or negative radiation balance in the atmosphere. Small particles in the high atmosphere can reflect incoming radiation and therefore potentially have a cooling effect on climate. Large particles in the lower atmosphere have the opposite effect by absorbing reflected radiation from the Earth’s surface. Mineral dust also affects carbon export to the deep ocean by providing mineral ballast for organic particles, and the size of the dust particles directly relates to the downward transport velocity.

Here I will present the measured grain-size distributions of first-year samples from seven sediment traps recovered from the 12°N-latitude transect as well as dust flux data. The data show seasonal variations, with finer grained dust particles during winter and spring, and coarser grained particles during summer and fall. Also a fining trend of the grain sizes of the dust particles from source (Africa) to sink (Caribbean) is observed, which is expected due to intuitive relationships between size and transport distance. The observed size of the dust particles at large distances from their source is much larger than previously assumed and applied in climate models.

See: www.nioz.nl/dust