Rare earth elements in bottom sediments and Fe-Mn nodules of the Black Sea

Distributions of rare earth element contents in surface layer bottom sediments, in vertical sediment section, and in Fe-Mn nodules of the Black Sea have been studied. An inverse relationship of rare earth element contents and CaCO3 contents has been found in the studied sediments. Fe-Mn nodules of the Black Sea do not concentrate rare earth elements, and their rare earth element composition differs from one of host sediments. It is concluded that rare earth elements are bound with clay minerals of bottom sediments.

Concentration of the rare-earth elements in metalliferous sediments from DSDP Leg 92 holes

DSDP Leg 92 drilled at four sites along an east-west transect at 19°S on the western flank of the East Pacific Rise (EPR), in an area where sediments are essentially a mixture of hydrothermal and biogenic components, with only a minimal contribution of clastic material. Rare-earth element (REE) data on the metalliferous (non-carbonate) fraction of samples ranging in age from ~2 to ~27 Ma indicate the existence of two distinct groups of patterns corresponding to two broad age groups, one <=8 Ma, the other >=10 Ma. Within each group, REE patterns have characteristics which are near-uniform, despite large variations in total REE abundances. Sediments of the younger group are enriched in light REE (LREE) relative to deep bottom waters influenced by the hydrothermal plume extending west from the EPR at 19°S. Sediments of the older groups show further relative LREE enrichment and/or heavy REE (HREE) depletion. Surficial sediments deposited beneath the lysocline have high Sum REE concentrations resulting from slow accumulation rates, and patterns resembling older sediments due to early diagenetic effects. A correlation between the mass accumulation rates (MAR) of Sum REE and Fe + Mn suggests that ferromanganese particulate matter supplied by the hydrothermal plume scavenges REE; during this process the LREE are preferentially removed from plume seawater. The MAR of Fe + Mn shows a general decrease with age above basement, whereas Sum REE concentrations in the metalliferous component increase with age above basement. This supports the Ruhlin and Owen model wherein limited scavenging of REE, due to rapid burial of sediment near the palaeo-axis, leads to low concentrations (but high MAR-values) for the REE. Following deposition and burial of the hydrothermal component, further relative flattening of the REE pattern takes place, probably the result of diagenetic reactions over several million years. Phase partitioning data indicate that the proportion of REE residing in more poorly crystalline phases tends to increase with age (from ~45% to 90% of Sum REE). This suggests that as initial ferromanganese precipitates undergo diagenetic recrystallization, REE are transferred to the poorly crystalline phases, and/or are scavenged from pore waters by these phases. Because of the various modifications to REE patterns apparently produced both in the water column and post-depositional settings, the REE patterns of metalliferous sediments will not reflect fine-scale REE variations in associated oceanic water masses.

Rare earth elements from the Atlantic Sector

We present a Rare Earth Elements (REE) record at decadal resolution determined in the EPICA ice core drilled in Dronning Maud Land (EDML) in the Atlantic Sector of the East Antarctic Plateau, covering the transition from the last glacial age (LGA) to the early Holocene (26 600-7500 yr BP). Additionally, samples from potential source areas (PSAs) for Antarctic dust were analysed for their REE characteristics. The dust provenance is discussed by comparing the REE fingerprints in the ice core and the PSAs samples. We find a shift in REE composition at 15 200 yr BP in the ice core samples. Before 15 200 yr BP, the dust composition is very uniform and its provenance was likely to be dominated by a South American source. After 15 200 yr BP, multiple sources such as Australia and New Zealand become relatively more important, albeit South America is possibly still an important dust supplier. A similar change in the dust characteristics was observed in the EPICA Dome C ice core at around ~15 000 yr BP. A return to more glacial dust characteristics between ~8300 and ~7500 yr BP, as observed in the EPICA Dome C core, could not be observed in the EDML core. Consequently, the dust provenance at the two sites must have been different at that time.