The palaeoenvironmental and palaeohydrological evolution of Padul Peat Bog (Granada, Spain) over one million years, from elemental, isotopic and molecular organic geochemical proxies

The elemental (concentration of organic carbon, atomic H/C and C/N ratios), isotopic (δ¹³C values of organic matter) and molecular (predominant n-alkane chain length and carbon preference index (CPI)) organic components were measured for 600 samples taken from a 107-m long core from the Padul Basin (Andalusia, Spain). The record runs from the Lower Pleistocene (ca. 1 Ma B.P.) to the mid-Holocene (ca. 4.5 ka B.P.) with, in general, little diagenesis (removal of components). Two markedly different hydrogeological scenarios were interpreted: (1) From ca. 1 Ma to ca. 400 ka B.P. run-off recharge was significant and water depths were greater (lacustrine scenario). From ca. 400 to 4.5 ka B.P., the Padul Basin became a peat bog s.s. with the major water input coming from groundwater inflow. From ca. 400 to ca. 180 ka B.P. alternating episodes with either predominant grasses, trees or aquatic macrophytes which were linked to wet/dry phases, took place. An important deglaciation episode has been interpreted to occur between ca. 180 and 170 ka B.P. The global climatic changes occurring from ca. 170 to 25 ka B.P. were not recorded in the proxies, though they do show important variations linked to the Last Glacial Maximum and the beginning of the Holocene (ca. 25–10 ka B.P.): (2) Cold phases coexisting with dry periods produced the recession of forests and the development of grasses. After these periods, as both temperature and precipitation increased, forests expanded and the water level, linked to thaw, rose, especially at ca. 20 ka B.P. Few changes occurred during the Holocene, although there were short alternations between wet and dry episodes. Overall, the techniques applied proved to be excellent palaeoenvironmental proxies for studying the basin’s palaeoclimatological and palaeohydrological evolution.     

A matrix representation of the potential second-rank gradient tensor for local modelling

Summary. This paper introduces a new matrix computational approach to the local determination of gravity gradients, convenient for comparing with gradient signals from moving base gradiometer systems or calculating topographic effects at instrument heights. The method represents a practical alternative to the more conventional spherical harmonics formulation, primarily global in nature, and it may be considered as an extension to other previously used local representations, such as point masses. Important characteristics of the analytical development outlined herein are its conceptual simplicity and the possibility of obtaining at once, up to a certain order n , and in an arbitrary Cartesian coordinate system, the symmetric point gradient tensor of second rank.     

Letters from Carlos Ibáñez e Ibáñez de Ibero to Aimé Laussedat: new sources for the history of nineteenth century geodesy

Recently found letters written by Carlos Ibáñez e Ibáñez de Ibero (1825–1891), first president of the International Geodetic Association, to geodesist–photogrammetrist Aimé Laussedat (1819–1907) are discussed. The contents of these epistolary conversations reflect their personal preoccupation with solving the geodetic problems of the time (1857–1889) and their desire to develop and propagate geodetic knowledge across all international boundaries.     

Laminated sediments from the central Peruvian continental slope: A 500 year record of upwelling system productivity, terrestrial runoff and redox conditions

Sedimentological studies including X-ray digital analyses, mineralogy, inorganic contents, and organic geochemistry on cores of laminated sediments accumulated in the oxygen minimum zone of the central Peruvian margin reveal variable oceanographic and climate conditions during the last 500 yr. Coherent upcore variations in sedimentological and geochemical markers in box cores taken off Pisco (B0405-6) and Callao (B0405-13) indicate that variability in the climate proxies examined has regional significance. Most noteworthy is a large shift in proxies at 1820 AD, as determined by ²¹⁰Pb and ¹⁴C radiometric dating. This shift is characterized by an increase in total organic carbon (TOC) in parallel with an abrupt increase in the enrichment factor for molybdenum Mo indicating a regional intensification of redox conditions, at least at the sediment water interface. In addition there was lower terrestrial input of quartz, feldspar and clays to the margin. Based on these results, we interpret that during several centuries prior to 1820, which corresponds to the little ice age (LIA), the northern Humboldt current region was less productive and experienced higher terrestrial input related to more humid conditions on the continent. These conditions were probably caused by a southward displacement of the inter-tropical convergence zone and the subtropical high pressure cell during the LIA. Since 1870, increases in TOC and terrigenous mineral fluxes suggest an increase of wind-driven upwelling and higher productivity. These conditions continued to intensify during the late 20th century, as shown by instrumental records of wind forcing.     

Latent Compositional Factors in The Llobregat River Basin (Spain) Hydrogeochemistry

The study of hydrogeochemical data sets frequently calls for statistical dimension reducing techniques. It is well known that hydrochemical parameters are compositions and, for this type of data, the direct application of classical statistical methods based on the correlation matrix yield spurious results. But new results on compositional data analysis have identified the sampling space, the simplex, with an Euclidean space, a fact that allows us to define a simplicial factor analysis strategy, thus overcoming the problem. For illustration, we use samples from the Llobregat River and its tributaries (NE Spain). Three unobservable or latent factorial components are extracted, which are identified with pristine waters, potash-mining influence and urban sewage influence. These three factorial components or compositional factors are plotted in a factorial ternary diagram, which reflects the relative influence of each one of these factors on each observation.