Intermediate water links to Deep Western Boundary Current variability in the subtropical NW Atlantic during marine isotope stages 5 and 4

Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 22 (2007): PA3209, doi:10.1029/2006PA001409.Records from Ocean Drilling Program Sites 1057 and 1059 (2584 m and 2985 m water depth, respectively) have been used to reconstruct the behavior of the Deep Western Boundary Current (DWBC) on the Blake Outer Ridge (BOR) from 130 to 60 kyr B.P. (marine isotope stage (MIS) 5 and the 5/4 transition). Site 1057 lies within Labrador Sea Water (LSW) but close to the present-day boundary with Lower North Atlantic Deep Water (LNADW), while Site 1059 lies within LNADW. High-resolution sortable silt mean (inline equation) grain size and benthic δ 13C records were obtained, and changes in the DWBC intensity and spatial variability were inferred. Comparisons are made with similar proxy records generated for the Holocene from equivalent depth cores on the BOR. During MIS 5e, inline equation evidence at Site 1057 suggests slower relative flow speeds consistent with a weakening and a possible shoaling of the LSW-sourced shallower limb of the DWBC that occupies these depths today. In contrast, the paleocurrent record from the deeper site suggests that the fast flowing deep core of the DWBC was located close to its modern depth below 3500 m. During this interval the benthic δ 13C suggests little chemical stratification of the water column and the presence of a near-uniform LNADW-dominated water mass. After ∼111 kyr B.P. the inline equation record at Site 1057 increases to reach values similar to Site 1059 for the rest of MIS 5. The strengthening of flow speeds at the shallow site may correspond to the initiation of Glacial North Atlantic Intermediate Water formation also suggested by a divergence in the benthic δ 13C records with Site 1057 values increasing to ∼1.2‰. Coupled suborbital oscillations in DWBC flow variability and paleohydrography persisted throughout MIS 5. Comparison of these data with planktonic δ 18O records from the sites and alkenone-derived sea surface temperature (SST) estimates from the nearby Bermuda Rise suggest a hitherto unrecognized degree of linkage between oscillations in subtropical North Atlantic SST and DWBC flow.This work was funded by the United Kingdom Natural Environment Research Council and supported by the NERC Radiocarbon Laboratory

Lateral podzolization in a sandstone catchment.

A sandstone catchment of the cool, perhumid Black Forest, Germany, was studied with respect to podzolization processes on a landscape scale. Soil mapping along a steep slope (25%) revealed Spodosols with thick E-horizons combined with thin spodic horizons in the upper catchment area. Lowermost parts of the landscape showed thinnest E- and thickest Bhs-horizons. This catenary trend was quantified by a non-linear increase of the “illuviation–eluviation ratio of podzolization” (IERpodzol). Soil texture, pedogenic oxides (Feo, Fed, Alo, Mnd), pH (CaCl2), Corg, and mineralogical composition of the clay and medium sand fraction were determined in six representative pedons. Chemical analysis matched morphology in that very low contents and mass densities of Feo, Fed, Alo, and Mnd were found in upslope soils. The distal pedons were 2–5-fold higher in these elements. The catenary trends corresponded to a downslope increase in pH as well as organic carbon in mineral soils. Mineralogical analysis showed a decrease in feldspar weathering and an increase in hydroxy-interlayered vermiculites towards the downslope soils. The morphological, chemical, and mineralogical results led to the conclusion of a process sequence of (i) an upslope mobilization and depletion of iron, manganese and aluminum (“E-Spodosols”), (ii) a lateral translocation (≈30% of catchment discharge occurred as interflow), and (iii) a downslope immobilization resulting in a (relative or absolute) accumulation of the translocated soil compounds (“Bs-Spodosols”). The immobilization probably was controlled by an admixture of Fe- and base-richer rocks into the parent material downslope. The concept of lateral podzolization developed in a granite landscape was confirmed in the sandstone area studied

Combining quantitative (palaeo-)pedological, palaeo-environmental studies and modelling: an important step on the way to predict soil reactions to environmental change

A study on a Holocene soil chronosequence in S-Norway is used to test the capability of the model SoilGen to model the development of soils with clay illuviation. SoilGen models soil formation as a function of the soil forming factors. Thus, the latter had to be reconstructed for the time span of soil development. The factors ‘relief’ and ‘parent material’ were obtained by field and laboratory analyses, the factor ‘time’ was derived from existing sea level curves, and the factors climate and organisms were obtained from literature and from a recent palaeo-environmental study. The chronosequence has been established on loamy marine sediments, and shows Albeluvisol development with time. Clay illuviation starts within 1650 years. The characteristic albeluvic tongues start to form after 4600 to 6200 years. They develop preferably along cracks. Albeluvic material falls into the cracks, leading to the development of albeluvic tongues, which become deeper and wider with time. Development of pH, CEC and clay content with time as measured in the investigated pedons is compared with the model results in order to check, to which degree model results agree with observed results