The Mesa Verde Loess

Data on the abundance and distribution of organic carbon and carbonates in the recent bottom sediments of the Kerch Strait were analyzed. It was shown that the content of organic carbon in the bottom sediments of the navigable part of the strait adjacent to the Kerch Peninsula is currently 1.5–2.0 times higher than the values obtained in the 1970s and organic carbon contents in the modern bottom sediments from the part of the strait adjacent to the Taman Peninsula. This is explained by the spatial distribution of the grain-size composition of bottom sediments in the strait and changes in the sedimentation conditions due to anthropogenic activities. As possible environmental consequences of such changes, we discussed the formation of hypoxia zones and increasing risk of asphyxiation phenomena in the strait.

The determination of carbon concentrations in marine sediments and particulate matter is hindered by the difficulty in analytically partitioning the total carbon between organic carbon and carbonate carbon phases. Attempts to “selectively” remove organic carbon by burning the sample at 500°C, or carbonate carbon by acidifying with HCl, usually affect the carbon of the remaining phase as well.A new approach permits direct measurement of both organic and carbonate carbon in a single sediment sample. The carbonate carbon concentration is determined from the CO2 evolved during phosphoric acid treatment. Subsequently, a concentrated dichromate/sulfuric acid solution is added to the remaining sediment‐acid mixture, and the CO2 liberated from the oxidation of organic carbon is measured. Total carbon is calculated as the sum of organic and carbonate carbon. A LECO carbon analyzer is modified so that the amount of CO2 evolved can be measured by the instrument’s thermal conductivity detector. In addition, total carbon content is determined on another subsample using the LECO dry combustion furnace. This provides a check on the values determined by the H3PO4/dichromate technique. Any other commercially available instrument relying on combustion furnace and thermal conductivity or infrared absorption for CO2 detection could be converted in an analogous manner.

An eolian deposit–buried soil sequence in an alpine soil on the northern Tibetan Plateau: Implications for climate change and carbon sequestration

Abstract. Knowledge on past variability of sedimentary organic carbon in the Arctic Ocean is important to assess natural carbon cycling and transport processes related to global climate changes. However, the late Pleistocene oceanographic history of the Arctic is still poorly understood. In the present study we show sedimentary records of total organic carbon (TOC), CaCO3, benthic foraminiferal δ18O and the coarse grain size fraction from a piston core recovered from the northern Northwind Ridge in the far western Arctic Ocean, a region potentially sensitively responding to past variability in surface current regimes and sedimentary processes such as coastal erosion. An age model based on oxygen stratigraphy, radiocarbon dating and lithological constraints suggests that the piston core records paleoenvironmental changes of the last 155 kyr. TOC shows orbital-scale increases and decreases that can be respectively correlated to the waxing and waning of large ice sheets dominating the Eurasian Arctic, suggesting advection of fine suspended matter derived from glacial erosion to the Northwind Ridge by eastward flowing intermediate water and/or surface water and sea ice during cold episodes of the last two glacial-interglacial cycles. At millennial scales, increases in TOC might correlate to a suite of Dansgaard-Oeschger Stadials between 120 and 45 ka before present (BP) indicating a possible response to abrupt northern hemispheric temperature changes. Between 70 and 45 ka BP, closures and openings of the Bering Strait could have additionally influenced TOC variability. CaCO3 content tends to anti-correlate with TOC on both orbital and millennial time scales, which we interpret in terms of enhanced sediment advection from the carbonate-rich Canadian Arctic via an extended Beaufort Gyre during warm periods of the last two glacial-interglacial cycles and increased organic carbon advection from the Siberian Arctic during cold periods when the Beaufort Gyre contracted. We propose that this pattern may be related to orbital- and millennial-scale variations of dominant atmospheric surface pressure systems expressed in mode shifts of the Arctic Oscillation.

The East Asian winter monsoon (EAWM) exhibits significant variability on intraseasonal, interannual, and interdecadal time scales and the variability can be extended to Holocene centennial and millennial scales. Previous Holocene EAWM proxy data records, which were mostly located in Central, Eastern and Southern China, did not show a consistent Holocene EAWM history. Therefore, it is difficult to provide insights into mechanisms of the long-term winter monsoon variability on the basis of the records. Eolian sediments at the southern edge of the Gobi Desert, Western China, are sensitive to the EAWM changes and less affected by the East Asian summer monsoon due to an obstruction of the Qinghai–Tibet Plateau. This paper presents a comparison between a well-dated Holocene EAWM record and coupled climate model simulations, so as to explore physical processes and influencing factors of the Holocene EAWM. Sediment samples from two Holocene eolian sedimentary sections [Huangyanghe (a) and Huangyanghe (b)] were acquired at the southern edge of the Gobi Desert. Chronologies were established based on twenty bulk organic matter AMS 14C ages and five pollen concentrates AMS 14C ages. Proxy data, including grain-size, total organic carbon, magnetic susceptibility and carbonate content were obtained from the two eolian sections. The grain-size standard deviation model was applied to determine components sensitive to variability of the Holocene EAWM. After a comparison of environmentally-sensitive grain-size components and proxy data, the 20–200 μm component at the Huangyanghe (a) and the 20–159 μm component at the Huangyanghe (b) section were selected as indicators of the Holocene EAWM, which show a strong early Holocene winter monsoon and a decline of the winter monsoon since the mid-Holocene. We also present equilibrium and transient simulations of the climate evolution for the Holocene using a state-of-art coupled climate model: the Community Climate System Model version 3 (CCSM3). Indices for the Holocene EAWM were calculated and are consistent with the reconstructed Holocene EAWM intensity. The simulations indicate that orbital forcing effects on the land-sea temperature and sea level pressure contrast can account for the observed EAWM trends. Other forcings that were present in the early Holocene, including the remnant Laurentide ice sheet and meltwater forcing in the North Atlantic, were not responsible for the Holocene trends.

Loess is [almost totally formed by] the accumulation of dust

Vertical sections through the Gastrioceras subcrenatum marine-band and associated shales exposed at three different localities on the North Crop of the South Wales Coalfield have been studied palaeontologically and geochemically. On the basis of quantitative palaeontology four palaeoecological phases are distinguished which are related to marine transgression and regression. Lingula can be divided into two types: those associated with goniatites and bivalves are considered to be marine, and the other type, without goniatites or bivalves, brackish. Differences in the chemical composition of the shales, after correcting for detrital quartz, can be correlated with the palaeoecological phases. Offshore sediments are characterized by higher amounts of organic carbon, carbonate, sulphur, phosphorus and uranium, together with smaller amounts of quartz. Most of the uranium is contained in organic material and collophane, while thorium occurs mainly in the clay fraction. Boron exibits a poor correlation with the palaeosalinities based on palaeontological criteria. The reasons for this are discussed. The amounts of detrital quartz, organic carbon, and the ratios of quartz to carbon, thorium to uranium, and sodium to potassium are shown to provide useful indicators of relative sedimentation rates. The quantitative distribution and type of fauna is mainly controlled by the sedimentation rate. Marine bivalve populations, like their modern representatives, exhibit a close relationship to the organic carbon content of the associated bottom sediments. While absolute values of redox potential during deposition of the shales cannot be determined, present variations in the ferric to ferrous iron and thorium to uranium ratios give some indication of relative differences. The depositional and post-depositional geochemical evolution of the shales has been controlled to a large extent by their organic carbon content.

Abstract. In order to assess seasonal and interannual variability in the export of particulate matter and its main constituents, sediment traps were deployed at five successive depths from February 2006 to March 2010 in the deepest basin of the Mediterranean (SE Ionian Sea, NESTOR site). The average total mass fluxes were 66, 58, 54, 34, and 52 mg m−2 d−1, at 700, 1200, 2000, 3200, and 4300 m, respectively. The temporal variations of the mass flux showed similar seasonal signal at all sampling depths with higher values in spring–summer and lower in autumn–winter. Changes in the main constituents of the mass flux (organic carbon, carbonates, opal, and lithogenic matter) largely followed the same temporal variability with total mass flux, revealing mechanisms of rapid vertical (top-down) transport from 700 m down to 4300 m depth. Lateral inputs at the deepest trap are probably of importance, attributed to the influence of the deep Adriatic water, characterized by relatively higher turbidity than overlying water masses. Two major processes seem to control the seasonal mass flux variability: (a) primary productivity at the euphotic zone; and (b) episodic dust input events. Primary productivity shows two maxima during late winter/early spring and late spring/summer, as witnessed by the organic carbon, carbonate, and opal fluxes in the mesopelagic and bathypelagic layers, whereas the influence of dust inputs is evidenced by enhanced lithogenic fluxes occurring during spring and summer. The interannual variability generally shows a gradual increase of fluxes during the time frame of the experiment. Both seasonal and interannual variability of mass flux are associated with variations in the intensity and position of the neighboring Pelops anticyclonic gyre, which appears to affect the upwelling of intermediate, nutrient-rich waters and subsequently the surface productivity. Combination of estimated satellite and algorithm-generated primary production data for the Ionian Sea, calculated POC fluxes out of the euphotic layer and POC fluxes measured by sediment traps at the mesopelagic and bathypelagic layers of NESTOR site during our 4 yr experiment, reveal that only a small portion of primary production (0.46%) reaches at 3200 m, corresponding to a mean annual carbon export of 1.12 g C m−2 yr−1.

Organic carbon and carbonate analysis from ODP Hole 128-798B

Organic carbon and carbonate fluxes: Links to climate change

Aeolian dune and sand sheet deposits, as well as sandy loess and loess deposits, cover extensive areas in the northwest and central European Lowlands. These sediments have received a great deal of attention during recent decades, leading to a variety of litho‐ and chronostratigraphic classifications. Although the aeolian stratigraphic record is known in great detail in most European countries, there is still discussion about the exact timing of phases of aeolian deposition, due to the fact that dates usually relate to materials reflecting phases of non‐deposition. This paper presents an overview of recent advances in luminescence dating of cold‐climate, predominantly Last Glacial (Weichselian), aeolian sand and loess deposits. These dates are compared with the results of conventional radiocarbon and AMS‐dating of palaeosols and other stratigraphic marker horizons. Although optical luminescence dating techniques, especially of the quartz fraction, appears to provide reliable ages for aeolian sediments in western Europe ranging in age from a few decades to at least 150 ka BP, there still are various uncertainties in the interpretation of luminescence ages due to methodological problems, difficulties in field extrapolation of stratigraphic relationships, and limited independent chronological control. Copyright © 2005 John Wiley & Sons, Ltd.

Total organic carbon, carbonate, alkenone, n-alkane and sea-surface temperature data determined at North Atlantic IODP Site U1313 (MIS 12-9)

Although numerous soil‐test methods for estimating extractable phosphorus (P) have been developed around the world, their results are difficult to compare because of the very different scale levels used. In the present study, the Bray–Kurtz method (Bray‐P) is used as a reference value. Two other methods [lactate‐P and sodium bicarbonate (NaHCO3)‐P] were modified to facilitate the comparison of extractable‐P determinations, mainly by adjusting the shaking time. These three methods were applied to 101 soil samples from an extensive region of Argentina with soil pH values ranging from 5.5 to 8.5. The results confirm that the Bray‐P and the two modified methods (lactate‐P and NaHCO3‐P) determine similar contents of extractable P but are not applicable to all types of soils and conditions. Equations that minimize the statistical error were selected for soil properties such as organic carbon (OC) content, pH, soluble salts, and calcium carbonate content. Correlation coefficients between Bray‐P and NaHCO3‐P increased to 0.91 and 0.95 in soils with high and low OC levels, respectively. It was also demonstrated that the lactate‐P test is not suitable for soils rich in calcium carbonate or soluble salts. These two modified methods are expected to be useful for testing P values that impact agricultural production.

Testing the potential of K-feldspar pIR-IRSL and quartz ESR for dating coastal alluvial fan complexes in arid environments

Arsenic solubilization and redistribution under anoxic conditions in three aquifer sediments from a basin-fill aquifer in Northern Utah: The role of natural organic carbon and carbonate minerals