The dominance of wet trace element deposition to the tropical North Atlantic Ocean over dry input is proven by analysis results of rain samples from shipboard sampling. Concentrations of Al, Ca, Cd, Co, Cu, Fe, Mg, Mn, Na, Ni, Pb, Tl and Zn were measured in 9 rain samples from the equatorial Atlantic Ocean and 4 rain samples from the South Atlantic Ocean. The results include some of the first data for trace metal concentrations in South Atlantic precipitation. Elemental concentrations from seawater samples taken in parallel are introduced to allow for an estimation of recycling rates of seasalt components. This revealed a net trace metal flux from the atmosphere into the ocean in the vicinity of the ITCZ (Intertropical convergence zone). Recycling rates of Al, Cd, Co, Cu, Fe, Mn, Ni, Pb and Zn ranged from a minimum of 7 x 10-4% (Co) to a maximum of 75% (Al). Higher values were found in the Southwest Atlantic. Trace metal concentrations in Southwestern Atlantic precipitation also seem to be connected to anthropogenic sources, as implied by enrichment factors relative to the earth crust. Data on trace metal flux by wet deposition are given on an annual scale for the ITCZ, further allowing for an estimation of elemental residence times in surface seawater.
Table: Trace metal concentrations (µg/l) in precipitation from remote regions of the Atlantic Ocean - comparison with literature data
|
North Atlantic
Lim and Jickells
1990
|
Bermudas
Church et al.
1984
|
North Atlantic
Church et al.
1990
|
this work
1990
|
Al
|
1.14 - 35.2
|
-
|
8.1 - 110
|
1.30 - 131
|
Cd
|
0.009 - 0.18
|
0.034 - 0.155
|
0.003 - 1.8
|
0.016 - 0.196
|
Co
|
-
|
-
|
-
|
0.71 - 1.72
|
Cu
|
0.03 - 0.36
|
0.23 - 0.53
|
0.1 - 1.2
|
0.070 - 0.91
|
Fe
|
0.18 - 133
|
0.99 - 7.86
|
1.5 - 85
|
1.70 - 63.5
|
Mn
|
0.06 - 5.25
|
0.06 - 0.51
|
0.4 - 4.1
|
0.11 - 3.43
|
Ni
|
-
|
0.023 - 0.32
|
7.9
|
0.63-1.42
|
Pb
|
0.050 - 0.83
|
0.48 - 1.34
|
0.02 - 3.1
|
0.091 - 1.03
|
Tl
|
-
|
-
|
-
|
< 0.002 - 0.0028
|
Zn
|
0.09 - 2.21
|
0.82 - 3.49
|
0.3 - 5.0
|
0.359 - 3.93
|
|
