ATMOSPHERIC POLLEN CONTENT OFF WEST-AFRICA

The annual variability of the marine atmosphere pollen load off West A frica was investigated by analyzing pollen samples collected on ship-b orne filters, in terms of pollen percentage, concentration and influx. The samples were collected over one week periods during each of seven months in 1982. During all seasons, the pollen abundance of Mediterra nean taxa decreases southward, that of Guinean and Sahelo-Sudanian tax a decreases northward, while that of the less abundant, specifically S aharan taxa is maximum off the Sahara in the median section of the jou rneys. For all filters except one, the concentration in the clear atmo sphere as well as the influx involves freshly emitted pollen and depen ds upon biological and physical factors: season and amount of pollen e mission, distance from source-area, and wind direction and strength. F resh pollen is diluted in the atmosphere when winds are strong. For tw elve discrete taxa, the percentage, concentration and influx are gener ally well correlated. In one filter, for December, the discrepancy of a high concentration and a strong wind is accounted for by pollen prev iously deposited on the Saharan ground surface being brought into resu spension by dust storms. These data suggest that pollen deposited on t he sea floor off northwest Africa originated predominantly as freshly emitted, rather than as material resuspended within mineral dust.