Understanding the 30‐year Barbados desert dust record

Abstract

[1] Atmospheric mineral aerosols influence climate and biogeochemistry, and thus understanding the impact of humans on mineral aerosols is important. Our longest continuous record of in situ atmospheric desert dust measurements comes from Barbados, which shows fluctuations of a factor of 4 in surface mass concentrations between the 1960s and the 1980s [Prospero and Nees, 1986]. Understanding fluctuations this large should help us understand how natural and anthropogenic factors change mineral aerosol sources, transport, distributions, and deposition, although we are limited in our ability to interpret the results as there is a quantitative record only at one location. We test the hypothesis that dry topographic lows (and not disturbed sources such as cultivated areas or new desert regions) are the sources of desert dust, using a hierarchy of models as well meteorological data sets to look at decadal scale changes in the North Atlantic desert dust. We find that the inclusion of a disturbed source improves our simulations in many (but not all) comparisons. Unfortunately, we are severely limited by the accuracy of the available data sets and models in making definitive statements about the role of disturbed sources or anthropogenic activity in changing the atmospheric desert dust cycle. Processes that might change the size or intensity of desert dust sources in North Africa (such as new sources due to desertification or land use) may be difficult to distinguish from topographic low sources in models due to their similar geographical locations and impact on atmospheric aerosol distributions.

A review of natural aerosol interactions and feedbacks within the Earth system

“…This long-term record has been shown to have a significant correlation with drought occurrence in the Soudano-Sahel region and with dust-event frequency from Mali visibility records (Mbourou et al, 1997). However, global models have struggled to replicate the observed dust record, and the relative contributions of changes in source strength and transport efficiency are unclear (Mahowald et al, 2002).…”

“…The combined role of climate and human intervention in controlling dust emissions makes predictions of future dust emissions unclear. Studies of the effects of anthropogenic climate change on dust loadings (neglecting land use changes) give a wide range of results from large increases (e.g., Woodward et al, 2005, find a factor of 3 increase in 2100) to large decreases (e.g., Luo, 2003, andMahowald et al, 2006, find a 60% decrease under double CO 2 concentration), to moderate (∼10 to −20%) increases/decreases (e.g. Tegen et al, 2004).…”

“…In marine regions, station observations have established links between DMS, aerosol, temperature and cloudiness (e.g., Ayers and Gras, 1991;Ayers et al, 1997;Boers et al, 1994) although the lack of supporting measurements of ocean biological and physical state highlights the difficulty of comprehensive measurements in all environments. Although the number of long term dust records is small, we have learned a great deal about climate impacts by combining observations with climate data and global models (e.g., Prospero and Lamb, 2002;Mahowald et al, 2002).…”

“…The terrestrial biosphere is a major source of primary aerosol and aerosol precursor gases that form secondary organic aerosol (SOA), and the net primary productivity of plants can be influenced by the effect of aerosol on diffuse radiation (Gu et al, 2003;Mercado et al, 2009). A large fraction of atmospheric dust is natural and such emissions may have large increases (Woodward et al, 2005) or decreases (Mahowald et al, 2003(Mahowald et al, , 2006 in a future climate, responding strongly to simulated vegetation changes. The oceans emit aerosol precursor gases such as dimethylsulphide (DMS) and primary sea spray particles, and marine biota are supplied with nutrients from aerosol deposition, particularly dust, which can impact the carbon cycle.…”

Global trends in visibility: implications for dust sources

“…Attempts to determine the impacts N. M. Mahowald et al: Global trends in visibility: implications for dust sources of global scale anthropogenic land use on dust emissions are hampered by the similarity in the spatial distribution of land use derived dust and natural dust for some sources (e.g. Mahowald et al, 2002Mahowald et al, , 2004Luo et al, 2003). Results of modeling simulations suggest that humans have either increased or decreased dust since preindustrial times, depending on the relative importance of human land use, carbon dioxide fertilization and climate change in driving dust .…”