Geochemical provenance analysis of fine-grained sediment of sediment core AND1-1

Bulk chemical fine-grained sediment compositions from southern Victoria Land glacimarine sediments provide significant constraints on the reconstruction of sediment provenance models in the McMurdo Sound during Late Cenozoic time. High-resolution (~ 1 ka) geochemical data were obtained with a non-destructive AVAATECH XRF Core Scanner (XRF-CS) on the 1285 m long ANDRILL McMurdo Ice Shelf Project (MIS) sediment core AND-1B. This data set is complemented by high-precision chemical analyses (XRF and ICP-OES) on discrete samples. Statistical analyses reveal three geochemical facies which are interpreted to represent the following sources for the sediments recovered in the AND-1B core: 1) local McMurdo Volcanic Group (MVG) rocks, 2) Transantarctic Mountain rocks west of Ross Island (W TAM), and 3) Transantarctic Mountain rocks from more southerly areas (S TAM). Data indicate in combination with other sediment facies analyses (McKay et al., 2009, doi:10.1130/B26540.1) and provenance scenarios (Talarico and Sandroni, 2009, doi:10.1016/j.gloplacha.2009.04.007) that diamictites at the drill site are largely dominated by local sources (MVG) and are interpreted to indicate cold polar conditions with dry-based ice. MVG is interpreted to indicate cold polar condition with dry-based ice. A mixture of MVG and W TAM is interpreted to represent polar conditions and the S TAM facies is interpreted to represent open-marine conditions. Down-core variations in geochemical facies in the AND-1B core are interpreted to represent five major paleoclimate phases over the past 14 Ma. Cold polar conditions with major MVG influence occur below 1045 mbsf and above 120 mbsf. A section of warmer climate conditions with extensive peaks of S TAM influence characterizes the rest of the core, which is interrupted by a section from 525 to 855 mbsf of alternating influences of MVG and W TAM.

Biogeochemistry of the Eastern Weddell Gyre

The Southern Ocean (SO) plays a key role in modulating atmospheric CO2 via physical and biological processes. However, over much of the SO, biological activity is iron-limited. New in situ data from the Antarctic zone south of Africa in a region centered at -20°E - 25°E reveal a previously overlooked region of high primary production, comparable in size to the northwest African upwelling region. Here, sea ice together with enclosed icebergs is channeled by prevailing winds to the eastern boundary of the Weddell Gyre, where a sharp transition to warmer waters causes melting. This cumulative melting provides a steady source of iron, fuelling an intense phytoplankton bloom that is not fully captured by monthly satellite production estimates. These findings imply that future changes in sea-ice cover and dynamics could have a significant effect on carbon sequestration in the SO.

Geochemistry and stratigraphy on sediment cores from Leg198 and Leg 208

The first complete cyclic sedimentary successions for the early Paleogene from drilling multiple holes have been retrieved during two ODP expeditions: Leg 198 (Shatsky Rise, NW Pacific Ocean) and Leg 208 (Walvis Ridge, SE Atlantic Ocean). These new records allow us to construct a comprehensive astronomically calibrated stratigraphic framework with an unprecedented accuracy for both the Atlantic and the Pacific Oceans covering the entire Paleocene epoch based on the identification of the stable long-eccentricity cycle (405-kyr). High resolution X-ray fluorescence (XRF) core scanner and non-destructive core logging data from Sites 1209 through1211 (Leg 198) and Sites 1262, 1267 (Leg 208) are the basis for such a robust chronostratigraphy. Former investigated marine (ODP Sites 1001 and 1051) and land-based (e.g., Zumaia) sections have been integrated as well. The high-fidelity chronology is the prerequisite for deciphering mechanisms in relation to prominent transient climatic events as well as completely new insights into Greenhouse climate variability in the early Paleogene. We demonstrate that the Paleocene epoch covers 24 long eccentricity cycles. We also show that no definite absolute age datums for the K/Pg boundary or the Paleocene - Eocene Thermal Maximum (PETM) can be provided by now, because of still existing uncertainties in orbital solutions and radiometric dating. However, we provide two options for tuning of the Paleocene which are only offset by 405-kyr. Our orbitally calibrated integrated Leg 208 magnetostratigraphy is used to revise the Geomagnetic Polarity Time Scale (GPTS) for Chron C29 to C25. We established a high-resolution calcareous nannofossil biostratigraphy for the South Atlantic which allows a much more detailed relative scaling of stages with biozones. The re-evaluation of the South Atlantic spreading rate model features higher frequent oscillations in spreading rates for magnetochron C28r, C27n, and C26n.

Investigations on a sediment core from the Indian Ocean

The Multi-Sensor Core Logger (MSCL) enables non-destructive, quasi-continuous measuroments of physical properties, reducing the time needed for discrete sample analysis. Density, compressional wave velocity (Vp), and magnetic susceptibility are measured on water-saturated sediment cores. Rapid variations in the lithology can thus be more easily recognized. The advantages of MSCL measurements over traditional sedimentological investigation methods are illustrated using several examples. Density-Vp relationships provide detailed lithological information prior to splitting the sediment cores. In terrigenous sediments, density increases with Vp, whereas in biogenic sediments it decreases. In biogenic sediments in the South Atlantic, low densities and high Vp are associated with high opal content. In biogenic sediments in the Peru Basin, density increases with carbonate content. Carbonate, which is very important for deep-sea environmental protection and for paleoclimatic studies, can be determined quantitatively from MSCL measurements in this area. In terrigenous sediments in the Bengal Fan, the acoustic impedance (the product of density and Vp) increases with grain size. There, the grain-size distribution can be rapidly derived from the acoustic impedance. Moreover, in hemipelagic sediments in the Bengal Fan, it is possible to correlate variations in magnetic susceptibility with cyclic changes in the earth's orbital parameters - an important prerequisite for detailed stratigraphic studies.

Physics, geochemistry and bulk sedimentology on cores from the Peru Basin

Empirical relationships between physical properties determined non-destructively by core logging devices and calibrated by carbonate and opal measurements determined on discrete samples allow extraction of carbonate and opal records from the non-destructive measurements in biogenic settings. Contents of detrital material can be calculated as a residual. For carbonate and opal the correlation coefficients (r) are 0.954 and ?0.916 for sediment density, ?0.816 and 0.845 for compressional-wave velocity, 0.908 and ?0.942 for acoustic impedance, and 0.886 and ?0.865 for sediment color (lightness). Carbonate contents increase in concert with increasing density and acoustic impedance, decreasing velocity and lighter sediment color. The opposite is true for opal. The advantages of deriving the sediment composition quantitatively from core logging are: (i) sampling resolution is increased significantly, (ii) non-destructive data can be gathered rapidly, and (iii) laboratory work on discrete samples can be reduced. Applied to paleoceanographic problems, this method offers the opportunity of precise stratigraphic correlations and of studying processes related to biogenic sedimentation in more detail. Density is most promising because it is most strongly affected by changes in composition.

Age model and color measurements of sediment cores from the eastern equatorial Pacific

High-resolution records of glacial-interglacial variations in biogenic carbonate, opal, and detritus (derived from non-destructive core log measurements of density, P-wave velocity and color; r >= 0.9) from 15 sediment sites in the eastern equatorial (sampling resolution is ~1 kyr) clear response to eccentricity and precession forcing. For the Peru Basin, we generate a high-resolution (21 kyr increment) orbitally-based chronology for the last 1.3 Ma. Spectral analysis indicates that the 100 kyr cycle became dominant at roughly 1.2 Ma, 200-300 kyr earlier than reported for other paleoclimatic records. The response to orbital forcing is weaker since the Mid-Brunhes Dissolution Event (at 400 ka). A west-east reconstruction of biogenic sedimentation in the Peru Basin (four cores; 91-85°W) distinguishes equatorial and coastal upwelling systems in the western and eastern sites, respectively. A north-south reconstruction perpendicular to the equatorial upwelling system (11 cores, 11°N-°3S) shows high carbonate contents (>= 50%) between 6°N and 4°S and highly variable opal contents between 2°N and 4°S. Carbonate cycles B-6, B-8, B-10, B-12, B-14, M-2, and M-6 are well developed with B-10 (430 ka) as the most prominent cycle. Carbonate highs during glacials and glacial-interglacial transitions extended up to 400 km north and south compared to interglacial or interglacial^glacial carbonate lows. Our reconstruction thus favors glacial-interglacial expansion and contraction of the equatorial upwelling system rather than shifting north or south. Elevated accumulation rates are documented near the equator from 6°N to 4°S and from 2°N to 4°S for carbonate and opal, respectively. Accumulation rates are higher during glacials and glacial-interglacial transitions in all cores, whereas increased dissolution is concentrated on Peru Basin sediments close to the carbonate compensation depth and occurred during interglacials or interglacial-glacial transitions.

Sedimentology on cores from the Peru Basin

We investigated surficial sediments for physico-chemical composition from numerous sites of seven study areas in the manganese nodule field of the northern Peru Basin as part of a deep-sea environmental study. Major results from this study are strong variability with respect to water depth, productivity in surface waters, locality, bottom water flow, and seafloor topography. Sediment sites are located mostly in 3900 to 4300 m water depth between the lysocline and the carbonate compensation depth (CCD). Large fluctuations in carbonate content (0% to 80%) determine sediment density and compressional-wave velocity, and, by dilution, contents of opal and non-biogenic material. Mass accumulation rates of biogenic components as well as geochemical proxies (barium and phosphorus) distinguish areas of higher productivity in the northwest near equatorial upwelling and in the northeast close to coastal upwelling, from areas of lower productivity in the west and south. Comparisons between the central Peru Basin area (Discol) and western Peru Basin area (Sediperu) reveals, for the Sediperu area, a shallower CCD, more carbonate but less opal, organic carbon, and non-biogenic material in sediments at the same water depth as well as larger down-core fluctuations of organic carbon and MnO2. Bottom water flow in the abyssal hill topography causes winnowing of material from summits of seamounts and ridges, where organic carbon preservation is poor, to basins where organic carbon preservation is better. Down-core measurements in box cores indicate a three-fold division in the upper 50 cm of the sediment column. An uppermost semi-liquid top layer is dark brown, 5-15 cm thick and contains most of the ferro-manganese nodules. A 5-15 cm thick transition zone of light sediment color has increasing shear strength, lowest opal contents and compressional-wave velocities, but highest carbonate contents and sediment densities. The lowermost layer contains stiffer light gray sediments.