Arid sedimentation in the oceans and atmospheric particulate matter

Abstract

Recent studies on the continental sources of aerosol production, transport and deposition to the ocean (natural sink) allowed us to recognize the possibility of long-range high-altitude (transoceanic) transport of aerosol dust of specific composition and properties. The dust consists of fine (micro- and nanosized) particles (94%, less than 2 μm) originated in the arid (undrained) tropical and subtropical regions extending into the oceans and are similar in composition to deep-sea (pelagic) red clays. Satellite and aircraft observation data were used to track trajectories of long-range (and transoceanic) transport of dust clouds. These data were coupled with direct shipboard measurements on ice core records and data on nuclear explosions and volcanic eruptions. Several zones of arid sedimentation were identified based on climatic conditions (shortage of water), conditions of dust production, wind-blown transport at different altitudes and deposition onto the ocean surface. The main transport occurs at two altitude scales (from land to the cloud top and above) (5–7 km) where wind speed of 300 km/h will be critical for a long-range transport. Three types of transport are identified based on the particle dynamics, composition and properties: 1—local (0–10 km from the source); 2—regional (100–1000 km); 3—global (over 1000 km). The finer particles are a product of local-scale transport with a total flux of 1.6 billion t/yr, which is almost equal to the net influx of the riverine terrigenous material to the pelagic zones of the oceans (outside the marginal filters). There are four main sources of aerosol dust, which is transported and deposited over arid oceanic regions. The arid oceanic regions account for about 1/3 of the modern ocean surface. During glacial periods, the sea-level drop of 100–120 m caused a significant increase in the size of arid regions due to the exposure of the shelf areas, which is equal to the area of the African continent. This caused 3–5 times higher dust emission, a decrease in the heat flux and in the transparency of the atmosphere. Comparison of ice core records and deep drilling data provide basis for studies on the ancient arid sedimentation.