SO240-FLUM: Fluidflux and Mn nodules in the equatorial eastern Pacific

Begin of project: February 1, 2015

End of project: July 31, 2017

Status of project: April 22, 2015

Low-temperature fluid circulation at seamounts and hydrothermal pits: heat flow regime, impact on biogeochemical processes, and its potential influence on the occurrence and composition of manganese nodules in the equatorial eastern Pacific

Figure 1: Planned cruise track and working area of SONNE cruise SO240

Scientific Programme

The scientific objectives of this project are:

1. What is the pattern and size of low-temperature fluid circulation systems in the working area?

It will be the task of the project to investigate the circulation pattern in terms of recharge and discharge sites based on systematic heat flow measurements. Single-channel seismics will be used to determine the sediment-basalt inter-face, a prerequisite to correctly interpret the regional heat flow. Based on the results of the heat flow measurements, the locations of sediment, nodules and pore-water sampling as well as video transects will be chosen. We have select-ed 4 different working areas (see Figure 2).

2. What is the impact of fluid circulation on element cycling and (bio)geochemical processes in the sediments overlying the permeable basaltic crust?

At recharge sites, oxic, unaltered seawater entrains the basaltic crust on basal-tic outcrops. Sediments in the immediate vicinity of a recharge site are subject to upward oxygen diffusion from the sediment-basement interface, inducing oxic conditions throughout the sediments. Increased oxygen content in pore water has implications for the microbial activity as well as the preservation of organic compounds and the mobilisation potential of elements sensitive to microbial turnover rates and redox processes (Mn, Cd, Cu, Li, V, etc. and isotopic systems of Sr, Li, O, H).

As the seawater migrates through the basaltic crust, it mines heat from the lith-osphere, starts reacting with the basaltic rocks and feeds the microbial commu-nity with oxygen and nutrients. Pore-waters at discharge sites should have de-tectable differences in composition compared to seawater (e.g. elevated Mn, Ca, Ba, B, Si) and detectable sedimentary precipitates (e.g. Mn oxides).

Nothing is known about the mobility of trace and ultra-trace metals in such fluid circulation systems. This will be one focus of biogeochemical work.

Based on this reasoning, we plan to take long sediment cores and multicorers along transects on the flanks of the seamount recharge and discharge sites.

3. What is the potential influence of fluid circulation on the occurrence and composition of manganese nodules?

Manganese nodules consist of a succession of single layers which alternately form either from oxic pore- and seawater or from suboxic pore-water. Prolonged oxic conditions at recharge sites may lead to the enrichment of iron, cobalt, zir-conium, tellurium, lead, and rare earth elements. Apart from the economic im-portance of these metals, the formation and enrichment processes under pro-longed oxic pore-water conditions in a sedimentary environment are still poorly known.

We will investigate the influence of seamounts on the occurrence and composition of Mn nodules, be it from low-temperature hydrothermal fluid flow or from the change of the hydrography around large seamounts. We will use box core sampling and video mapping of the seafloor to realise this task.

4. What will be the sediment plume dilution and dispersion during a Mn nodule mining?

At the end of SO-240 four days will be dedicated to the recovery of bottom landers and four near-bottom current moorings. The landers were deployed at the beginning of SO-239 and the recovery at the end of SO-240 should provide longer time-series measurements (ca. 10 weeks). The four current moorings were deployed in 2014 by the BGR and will be recovered during this cruise, data will be downloaded, the moorings will be maintained and re-deployed at the same positions. This work is part of the European Joint Initiative Program Oceans (JPI-O) in a possible future Mn nodule mining area (Fig. 2).

Figure 2: Working areas of SO240. The scientific program of SO240 will be realized in WA1 – WA 4, in working area 5 landers and moorings will be recovered as part of JPI-O project EcoResponse (Assessing the Ecology, Connectivity, and Resilience of Polymetallic Nodule field Systems). Bathymetric map from Rühlemann et al. (2011)

Partner:

BGR
Bundesanstalt für Geowissenschaften und Rohstoffe
Stilleweg 2
D-30655 Hannover / Germany
Internet: www.bgr.bund.de

JUB
Jacobs University Bremen
Campus Ring 8
D-28759 Bremen
Internet: www.jacobs-university.de

AWI
Alfred Wegener Institut für Polar- und Meeresforschung
Am Handelshafen 12
D-27570 Bremerhaven / Germany
Internet: www.awi.de

GeoB
Fachbereich Geowissenschaften
Universität Bremen,
Postfach 330440
D-28334 Bremen
Internet: www.geo.uni-bremen.de

IUP
Institut für Umweltphysik, Ozeanographie
Universität Bremen
PF 330440
28334 Bremen / Germany
Internet: www.ocean.uni-bremen.de

DZMB
Deutsches Zentrum für Marine Biodiversitätsforschung
Senckenberg am Meer
Südstrand 44
D-26382 Wilhelmshaven / Germany
Internet: www.senckenberg.de

Promotion / document number:

03G0240A (BMBF)