Clay mineralogy and multi-element chemistry of surface sediments on the Aiberian-Arctic Shelf

Clay mineral and bulk chemical (Si, Al, K, Mg, Sr, La, Ce, Nd) analyses of terrigenous surface sediments on the Siberian-Arctic shelf indicate that there are five regions with distinct, or endmember, sedimentary compositions. The formation of these geochemical endmembers is controlled by sediment provenance and grain size sorting. (1) The shale endmember (Al, K and REE rich sediment) is eroded from fine-grained marine sedimentary rocks of the Verkhoyansk Mountains and Kolyma-Omolon superterrain, and discharged to the shelf by the Lena, Yana, Indigirka and Kolyma Rivers. (2) The basalt endmember (Mg rich) originates from NE Siberia's Okhotsk-Chukotsk volcanic belt and Bering Strait inflow, and is prevalent in Chukchi Sea Sediments. Concentrations of the volcanically derived clay mineral smectite are elevated in Chukchi fine-fraction sediments, corroborating the conclusion that Chukchi sediments are volcanic in origin. (3) The mature sandstone endmember (Si rich) is found proximal to Wrangel Island and sections of the Chukchi Sea's Siberian coast and is derived from the sedimentary Chukotka terrain that comprises these landmasses. (4) The immature sandstone endmember (Sr rich) is abundant in the New Siberian Island region and reflects inputs from sedimentary rocks that comprise the islands. (5) The immature sandstone endmember is also prevalent in the western Laptev Sea, where it is eroded from sedimentary deposits blanketing the Siberian platform that are compositionally similar to those on the New Siberian Islands. Western Laptev can be distinguished from New Siberian Island region sediments by their comparatively elevated smectite concentrations and the presence of the basalt endmember, which indicate Siberian platform flood basalts are also a source of western Laptev sediments. In certain locations grain size sorting noticeably affects shelf sediment chemistry. (1) Erosion of fines by currents and sediment ice rafting contributes to the formation of the coarse-grained sandstone endmembers. (2) Bathymetrically controlled grain size sorting, in which fines preferentially accumulate offshore in deeper, less energetic water, helps distribute the fine-grained shale and basalt endmembers. An important implication of these results is that the observed sedimentary geochemical endmembers provide new markers of sediment provenance, which can be used to track sediment transport, ice-rafted debris dispersal or the movement of particle-reactive contaminants.

Interstitial water d13C and sediment geochemistry of ODP Leg 166 sites

A review of interstitial water samples collected from Sites 1003-1007 of the Bahamas Transect along with a shore-based analysis of oxygen and carbon isotopes, minor and trace elements, and sediment chemistry are presented. Results indicate that the pore-fluid profiles in the upper 100 meters below seafloor (mbsf) are marked by shifts between 20 and 40 mbsf that are thought to be caused by changes in sediment reactivity, sedimentation rates, and the influence of strong bottom currents that have been active since the late Pliocene. Pore-fluid profiles in the lower Pliocene-Miocene sequences are dominated by diffusion and do not show significant evidence of subsurface advective flow. Deeper interstitial waters are believed to be the in situ fluids that have evolved through interaction with sediments and diffusion. Pore-fluid chemistry is strongly influenced by carbonate recrystallization processes. Increases in pore-fluid Cl- and Na+ with depth are interpreted to result mainly from carbonate remineralization reactions that are most active near the platform margin. A lateral gradient in detrital clay content observed along the transect, leads to an overall lower carbonate reactivity, and enhances preservation of metastable aragonite further away from the platform margin. Later stage burial diagenesis occurs at slow rates and is limited by the supply of reactive elements through diffusion.

Geochemistry of continental slope and deep sea basin sediments off Uruguay

Pore water and solid phase from surface sediments of the continental slope off Uruguay and from the Argentine Basin (southwestern Atlantic) were investigated geochemically to ascribe characteristic early diagenetic reactions of iron and manganese. Solid-phase iron speciation was determined by extractions as well as by Mössbauer spectroscopy. Both methods showed good agreement (<6% deviation) for total-Fe speciation. The proportion of easy reducible iron oxyhydroxide relative to total-Fe oxides decreased from the continental slope to the deep sea which is attributed to an increase in crystallinity during transport as well as to a general decrease of iron mobilization. The product of iron reoxidation is Fe oxyhydroxide which made up less than 5% of total Fe. In addition to this fraction, a proportion of smectite bound iron was found to be redox reactive. This fraction made up to 10% of total Fe in sediments of the Argentine Basin and was quantitatively extracted by 1 N HCl. The redox reactive Fe(+II) fraction of smectite was almost completely reoxidized within 24 h under air atmosphere and may therefore considerably contribute to iron redox cycling if bioturbation occurs. In the case of the slope sediments we found concurrent iron and manganese release to pore water. It is not clear whether this is caused by dissimilatory iron and manganese reduction at the same depth or dissimilatory iron reduction alone inducing Mn(+IV) reduction by (abiotic) reaction with released Fe2+. The Argentine Basin sediment showed a significant manganese solid-phase enrichment above the denitrification depth despite the absence of a distinct pore-water gradient of Mn. This implies a recent termination of manganese mobilization and thus a non-steady-state situation with respect to sedimentation or to organic carbon burial rate.

Spatiotemporal monitoring of water quality in coral reefs of Tayrona National Natural Park, Colombian Caribbean, 2011-2013

Tayrona National Natural Park (TNNP; 11°17' - 11°22' N and 73°53' - 74°12' W) is a hotspot of coral reef biodiversity in the Colombian Caribbean, located between the city of Santa Marta (>455,000 inhabitants) and several smaller river mouths (Rio Piedras, Mendihuaca, Guachaca). The region experiences a strong seasonal variation in physical parameters (temperature, salinity, wind, and water currents) due to alternating dry seasons with coastal upwelling and rainy seasons. Here, a range of water quality parameters relevant for coral reef functioning is provided. Water quality was measured directly above local coral reefs (~10 m water depth) by a monthly monitoring for up to 25 months in the four TNNP bays (Chengue, Gayraca, Neguanje, and Cinto) and at sites with different degree of exposition to winds, waves and water currents (exposed vs. sheltered sites) within each bay. The water quality parameters include: inorganic nutrient (nitrate, nitrite and soluble reactive phosphorus), chlorophyll a, particulate organic carbon and nitrogen concentrations (with a replication of n=3) as well as oxygen availability, biological oxygen demand, seawater pH, and water clarity (with a replication of n=4). This is by far the most comprehensive coral reefs water quality dataset for the region. A detailed description of the methods can be found within the referenced publications.

(Table 1) Permanent currents in the Campeche Bank area based on data of 24-hour stations

Data of twenty buoy stations were used to compile a new chart of permanent currents in the surface layer (10 m depth) for the region of the Yucatan shelf (Campeche Bank). It was found that vertical variations in direction of the currents are insignificant within the shallow plateau of the banks.