147 
ISSN 0012-0308 
© BSH, Hamburg und Rostock 
Deutsche Hydrographische Zeitschrift 
German Journal of Hydrography 
Volume 48 (1996) Number 2 
Near-Bottom Currents and Bottom Boundary 
Layer Variability Over Manganese Nodule Fields 
in the Peru Basin, SE-Pacific 
Holger Klein 
Summary 
Near-bottom current meter data recorded between 0.6 and 500 metres above bottom (mab) at two man 
ganese nodule sites in the deep Peru Basin are discussed with respect to the vertical current structure and 
the formation and variability of the benthic boundary layer (BBL) and its sublayers. The data reveal a weak 
current regime with great spatial and temporal variability and a bottom intensification at about 30-50 mab. 
The BBL height varies according to the daily mean values of flow above the BBL, reaching maximally 150 to 
200 metres. 
Bodennähe Strömungen und Bodengrenzschichtvariabilität über Manganknollenfeldern im Peru 
Becken, SO-Pazifik (Zusammenfassung) 
Bodennähe Strommessungen (0,6 bis 500 m Bodenabstand) aus zwei Manganknollengebieten im Peru 
Becken werden bezüglich des vertikalen Stromprofils und der Bildung und Variabilität der Bodengrenz 
schicht und ihrer Unterschichten diskutiert. Die Daten zeigen ein schwaches Strömungsregime mit großer 
zeitlicher und räumlicher Variabilität und einer Bodenintensivierung der Strömung bei etwa 30 bis 50 m Bo 
denabstand. Die Höhe der Bodengrenzschicht variiert entsprechend den täglichen Mittelwerten der Strö 
mung über der Bodengrenzschicht und erreicht eine maximale Höhe von 150 bis 200 m. 
Introduction 
Since 1988, the TUSCH-group 1) , a multidiscipli 
nary association of research groups, has investi 
gated the potential impact of deep-sea manganese 
nodule mining on the abyssal ecosystem of the 
Peru Basin (Thiel and Schriever [1989], Thiel et al. 
[1994], Thiel [1995]). During the DISCOL 2 ) experi 
ment in 1989, part of the DISCOL Experimental 
Area (DBA) was disturbed using a towed plow- 
harrow in order to simulate a mining operation and 
to investigate the subsequent recolonization of local 
benthic communities (Schriever [1995]). Biological, 
geological, geochemical, and soil-mechanical inve 
stigations in the DBA and surrounding undisturbed 
areas were carried out before the disturbance, di 
rectly after the disturbance, and in subsequent 
years (Schriever et al. [1996]). 
Besides the direct disturbance of the sea bed, 
the influence of settling sediments - mobilized du 
ring mining operations - has to be considered. Mo 
bilized sediment plumes are dispersed according to 
local current strength and current variability. Rese 
dimentation of advected suspended particles may 
also affect areas beyond the mining sites proper. 
Moreover, the local current regime - together with 
bottom roughness and topography - controls the 
properties of the bottom or benthic boundary layer 
(BBL) and its variability. Knowledge about the BBL 
structure is of great significance because local che 
mistry, biology, and physics of the BBL are closely 
interwined (Berner [1976]). 
11 TUSCH = Tiefsee-Umweltschutz = deep-sea environmental protection 
21 DISCOL = Disturbance and recolonization experiment in the South Pacific