INSTITUT FÜR OSTSEEFORSCHUNG WARNEMÜNDE
Trace metal (Hg, Pb, Cd, Cu, Ni, Mn, Fe, Co) distribution in Eastern-Atlantic surface waters Reflection of natural and anthropogenic sources by comparing data from 1990 and 2005 Christa Pohl
1, Ursula Hennings
1, Michiel Rutgers v. d. Loeff
2, Peter Croot
3and Gereon Budeus
21 Leibnitz-Institute for Marine Research, Seestrasse 15, D-18119 Warnemünde, Germany
2 Alfred-Wegener-Institute for Polar- and Marine Research, PO-Box 120161, D-27515 Bremerhaven, Germany
3 Leibnitz-Institute for Marine Research, Düsternbrookerweg 20, D-24105 Kiel, Germany
X
X
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30°
15°
0°
30°
15°
45°
25°
25°
Westerlies Subtropics
Westerlies North-East Tradewinds
Innertropical Convergence Innertropical Convergence Innertropical Convergence Innertropical Convergence
South-East Tradewinds Subtropics
X
X
X
30°
15°
0°
30°
15°
45°
25°
25° X
X
X X
X
X
30°
15°
0°
30°
15°
45°
25°
25°
Westerlies Subtropics
Westerlies North-East Tradewinds
Innertropical Convergence Innertropical Convergence Innertropical Convergence Innertropical Convergence
South-East Tradewinds Subtropics
Total mercury (Hgtot) concentrations were directly analysed on board by using cold vapour technique with Hg-amalgamation on a gold net and the determination by fluorescence detection.
Sampling and methods
On Polarstern cruise ANT XXIII/1 seawater surface samples were taken with the „Fish“ in the eastern Atlantic.
Objectives of the project
1. Intercalibration of several analytical methods in the framework of GEOTRACES 2. Distribution of trace elements and the comparison to a dataset from 1990
3. Mercury distribution under consideration of the main oceanic regimes, and meteorological systems, including an oceanic region which is affected by high Saharan dust deposition
For
Cd and Co
atmospheric input from African desserts can be neglected. For both elements it seems that different regional up- welling systems are responsible for the fluctuations of the surface concentrations.South North
Angola Dome ITCZ Guinea Dome
0 10 20 30 40 50 60 70
-35-30-25 -20-15-10 -5 0 5 10 15 20 25 30 35 40 45 50 Latitude
Cd pmol/kg
Cd 1990 (tot)
Cd 2005 (tot)
Cd
0 20 40 60 80 100 120 140 160
-35-30 -25-20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 50 Latitude
Co nmol/kg
Co 1990 (tot) Co 2005 (tot)
Co
Total lead (Pb)
concentrations are ranging between 5-20 pmol/kg with slightly increasing values in the Intertropical Convergenz Zone (ITCZ).In 1989 concentrations were by factor 2 higher in this region, while maximium values (factor 10-15 higher) were obtained in the North Atlantic.
This is related to anthropogenic atmospheric Pb input by the prevailing westerly wind directions from the industrialised areas of northern America.
15 years later, most of the Pb was removed from surface waters by scavening.
0 50 100 150 200 250 300
-35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 50
Latitude
Pb pmol/kg
Pb 1989 (tot) GFAAS Pb 2005 (tot) GFAAS Pb 1990 (tot) DPASV
Pb
South ITCZ North
*Pohl et al 1993:
J Mar Systems
**Helmers & R. v.
d. Loeff, 1993:
J. Geophys Res Concentrations of Pb, Cd, Cu, Ni,
Mn, Fe, Co were analysed in filtered (<0.4µm) and unfiltered samples, after liquid-liquid extraction with APDC / DDDC and enrichment with GF-AAS in the home laboratory.
Fe and Mn
data show nearly identical concentrations between 1990 and 2005. Since both elements are mainly of terrigenic origin these results are possibly due to the composition of atmospheric transported dust, from different sources. Also residence times and seasonal effects in the water column have to be taken into account.0 2 4 6 8
-35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 50 Latitude
Mn nmol/kg
Mn 1989 (tot) Mn 2005 (tot)
Mn
0 2 4 6 8 10
-35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 50 Latitude
Fe nmol/kg Fe 1990 (tot)
Fe 2005 (tot)
Fe
South ITCZ North
Ni, Cu, and Zn
concentrations are nearly identical between 1990 and 2005, with slightly increasing values in the northern hemisphere. Like Cd, increasing values were registrated in the seasonal upwelling regions of the “Guinea- & Angola Dome” during spring.0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0
-35 -30-25 -20-15 -10 -5 0 5 10 15 20 25 30 35 40 45 50 Latitude
Zn nmol/kg
Zn 1990 (tot) Zn 2005 (tot)
Zn
0,0 0,5 1,0 1,5 2,0 2,5 3,0
-35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 50 Latitude
Cu nmol/kg
Cu 1990 (tot) Cu 2005 (tot)
Cu
0 1 2 3 4 5
-35-30-25 -20-15-10 -5 0 5 10 15 20 25 30 35 40 45 50 Latitude
Ni nmol/kg
Ni 1990 (tot) Ni 2005 (tot)
Ni
South North
Angola DomeITCZGuinea Dome
From 23°N to 0°
total Hg, (Hgtot)
concentrations are well correlated to the distribution of manganese in the surface water. They are ranging between 2.0 and 4.5 pmol/L on a higher level, which is due to Sahara dust input by North-East trade winds. Southward and northward of these area Hgtot concentrations decrease to very low levels of 0.5-3.0pmol/L.
South ITCZ North
Hg and Mn 2005
0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0
-30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 50
34,0 34,5 35,0 35,5 36,0 36,5 37,0 Hg tot (pmol/l)
Mn tot (nmol/kg) Salinity
