Report and preliminary results of RV METEOR Cruise M78/3. Sediment transport off Uruguay and Argentina: from the shelf to the deep sea ; 19.05.2009 – 06.07.2009, Montevideo (Uruguay) – Montevideo (Uruguay)

The waters off Uruguay and Northern Argentina offer the possibility to study sediment transport processes from ‘source-to-sink’ in a relatively small area. Quickly accumulated sediments are potentially unstable and might be transported downslope in canyons and/or on the open slope. Strong contour currents result in along-slope sediment transport. Within the scope of Meteor-Cruise M78/3 we investigated sediment transport and depositional patterns by means of hydroacoustic and seismic mapping as well as geological sampling with conventional coring tools and the new MARUM seafloor drill rig (MeBo). Geotechnical investigations were carried out with the aim to analyze the controlling parameters for the destabilization of the slope and the succeeding failure of a sediment body. Various types of sediment instabilities have been imaged in geophysical and core data, documenting particularly the continental slope offshore Uruguay to be locus of frequent submarine landslides. Apart from individual landslides, however, gravitational downslope sediment transport along the continental slope is restricted to the prominent Mar del Plata Canyon and smaller canyons identified in the bathymetric data. In contrast, many morphological features reveal that sediment transport is predominantly controlled by strong contour bottom currents. This suggests a significant impact of the western boundary currents on the overall architectural evolution of the margin. The investigations are related to projects of the DFG Research Center / Excellence Cluster 'The Ocean in the Earth System', University of Bremen, as well as the Excellence Cluster 'The Future Ocean', University of Kiel

Internal structure and origin of the double reefs of North Bohol and the Olango reef flat (Philippines)

Nine holes were drilled with a submersible hydraulic drill into the slopes and reef flats of the Caubyna and Calituban reefs as well as of Olango Flat. The maximum depth of core penetration was 11 m. 14C ages showed that the Caubyan and Caltituban reefs were formed within the last 6,000 years. Corals settled on a pre-existing relief prallel to the island of Bohol, building a framework for other carbonate-producing organisms. The reef flat south of Olango has a different structure. Formation took place during a Pleistocene high sea level, e.g. 125,000 years ago

A high resolution camera system (ParCa) for imaging particles in the ocean: System design and results from profiles and a three-month deployment

For direct optical measurement of abundance, concentration and size distribution of marine particles, a high-resolution camera system (ParCa) was designed to improve on similar systems used by Honjo et al. (1984), Asper (1987) and others. Imaging a probe volume of up to 37 1, smallest particles with diameters of 50 μm can be counted. The images provide information on particle size, shape and abundance either during profiling through the water column or while moored in a certain depth over time. Depth profiles were acquired between fall 1992 and late spring 1993 on R. V. Meteor cruises M22-1 and M23-3 at 6 stations in the equatorial Atlantic Ocean and off the west African shelf. The images show variable particle and aggregate concentrations through 550 m of the water column, with highest concentrations in the upper 80 m. A distinctive change in the depth of the upper chlorophyll maximum from about 75 m in the Brazil Basin to about 50 m in the Guinea Basin was measured with the attached INFLUX current meter (Krause and Ohm, 1996) and is as well represented in the particle abundances maximum of two selected profiles. In contrast, both profiles show a second particle abundance maximum between 100 and 250 m, which is not visible in the chlorophyll-α and backscatter signal of the INFLUX sensors. Total particle abundance maxima raise from 677 counts per liter in the central Brazil Basin to 991 counts in the Guinea Basin, corresponding to marine snow abundances of 57 and 127 counts per liter, respectively. In order to compare high-resolution data on particle concentration and flux through time, ParCa was also deployed on a sediment-trap mooring at 995 m depth in the Canary Basin between June and September 1994. First results show similar trends in sediment-trap derived fluxes of particulate matter from 2.8 to 67.2 mg m−2 d−1 and equivalent spherical volumes of particles with diameters \u3e0.5 mm from 0.98 to 4.13 mm3 l−1

Oxygen isotope composition of living Neogloboquadrina pachyderma (sin.) in the Arctic Ocean

Data from the Nansen Basin of the Arctic Ocean are used to investigate the habitat and conditions under which the polar planktic foraminifer Neogloboquadrina pachyderma (sin.) calcifies. The vertical distribution of δ18O values of net-sampled speciments, together with their abundances and proportion of calcification, are compared with δ18O values from both water samples and foraminiferal tests from core-top sediments. Within the Nansen Basin the average depth of habitat of N. pachyderma (sin.) changes from about 150 m in the southern part to about 80 m in the northern. The average depth of calcification, however, in both regimes varies between 100 and 200 m water depth. δ18O data from net sampled N. pachyderma (sin.) are directly reflected in the core-top sediment data, but compared to equilibrium calcite δ18O values derived from measurements of the ambient water, a consistent offset of about 1‰ over all depth intervals is observed. While in the southern part of the Nansen Basin advection through Fram Strait of planktic foraminifers from further south may play a role, the data from the northern part of the Nansen Basin give clear evidence that the observed offset in δ18O values is caused by a vital effect of N. pachyderma (sin.)

The imprint of anthropogenic CO2 in the Arctic Ocean: evidence from planktic δ13C data from watercolumn and sediment surfaces

δ13C values of N. pachyderma (sin.) from the water column and from core top sediments are compared in order to determine the 13C decrease caused by the addition of anthropogenic CO2 to the atmosphere. This effect, which is referred to as the surface ocean Suess effect, is estimated to be about −0.9‰(±0.2‰) within the Arctic Ocean halocline waters and to about −0.6‰(±0.1‰) in the Atlantic-derived waters of the southern Nansen Basin. This means that the area where the Arctic Ocean halocline waters are formed, the Arctic shelf regions, are relatively well ventilated with respect to CO2. Nevertheless, δ13C of dissolved inorganic carbon (δ13CDIC) in the Arctic Ocean halocline waters is far from isotopic equilibrium. Absolute values of δ13C of N. pachyderma (sin.) covary with the surface ocean Suess effect, and we interprete changes in both parameters as a reflection of the degree of ventilation of the waters on the shelf sea. Measurements of δ13C of N. pachyderma (sin.) in the Arctic Ocean from plankton tows reveal a “vital effect” of about −2‰, significantly different from other published values. A first-order estimate of the total anthropogenic carbon inventory shows, that despite of its permanent sea-ice cover, the Arctic Ocean, with 2% of the global ocean area, is responsible for about 4–6% of the global ocean's CO2 uptake

Colonization of artificial substrates by Foraminifera

From June 1972 to October 1974 colonization experiments were carried out off Boknis Eck (Eckernförder Bay, Western Baltic Sea) with artificial substrates (gravel, sand and clay) in 3 different water depths, 19 m (1.5 m above the bottom), 15 m (4.5 m) and 11 m (5.0 m). The first Foraminifera appeared in spring 1973. With few exceptions only Elphidium excavatum clavatwn (CUSHMAN 1930) was present. lt is assumed that E. excavatum clavatum has an especially good passive distribution capability by advection. This explains why this sub-species rapidly recolonizes the deeper areas of the Baltic after reestablishment of aerobic conditions