Testing the accuracy of quartz OSL dating using a known-age Eemian site on the river Sula, northern Russia

Quartz optically stimulated luminescence (OSL) forms the basis for the chronology of Weichselian ice advances in Arctic Eurasia developed over the last few years. There is almost no age control on this chronology before 40 ka, except for some marine sediments correlated with marine isotope stage (MIS) 5e on the basis of their palaeofauna. Results from more southern latitudes have shown that dose estimates based on quartz OSL and the single aliquot regenerative (SAR) dose procedure may underestimate the age of MIS 5e deposits. Here we use the same method to date well-described marine sediments, thought to have been deposited during the very beginning of the Eemian interglacial at 130 ka, and exposed in two sections on the river Sula in northern Russia. Various quality-control checks are used to show that the OSL behaviour is satisfactory; the mean of 16 ages is 112±2 ka (σ=9 ka). This represents an underestimate of 14% compared to the expected age, a discrepancy similar to that reported elsewhere. In contrast to SAR, the single aliquot regeneration and added (SARA) dose procedure corrects for any change in sensitivity during the first OSL measurement. The SARA results are shown to be 10% older than those from SAR, confirming the geological age estimate and suggesting that SAR ages may underestimate older ages (larger doses), despite their good performance in the younger age range.     

Was southern Sweden ice free at 19–25 ka, or were the post LGM glacifluvial sediments incompletely bleached?

Glacifluvial deposits along an ice-marginal zone in Småland, southern Sweden, have been dated using post-IR blue OSL. To test for incomplete bleaching, we adopted two strategies: analysis of modern analogues and small-aliquot dose distributions. Samples of modern fluvial sediments show no significant incomplete bleaching; they yield equivalent doses of only 0.5–2 Gy (0.25–4% of our glacifluvial sediment doses). Small-aliquot dose distributions do not provide any evidence for incomplete bleaching.

The sediments are believed to have been deposited during deglaciation and appear to fall into two age groups: 19–25 ka (mainly sandur sediments) and 33–73 ka (mainly deltaic sediments). Compared to the expected ages (13–15 ka), even the younger glacifluvial OSL ages appear up to 10 000 years (25 Gy) too old. The ages are nevertheless stratigraphically consistent and correspond between sites; we deduce that the 19–25 ka ages are true deposition ages. For glacifluvial sedimentation to take place on the South Swedish Upland at this time either a very early deglaciation is required, or alternatively ice-free conditions just prior to the LGM. The deltaic sediments (33–73 ka) were most likely not significantly bleached during deposition and thus they date events prior to the latest ice advance.     

A test case for anomalous fading correction in IRSL dating

Infrared-stimulated luminescence (IRSL) dating of feldspars has the potential to date deposits beyond the age range of quartz optical (OSL) dating. Successful application of feldspar IRSL dating is, however, often precluded due to anomalous-fading, the tunnelling of electrons from one defect site to another. In this paper we test procedures proposed for anomalous-fading correction by comparing feldspar IRSL and quartz OSL dating results on a suite of samples from continental deposits from the southeastern Netherlands. We find that even after anomalous-fading correction IRSL ages underestimate the burial age of the deposits and argue that this may be a consequence of a dependency of anomalous fading rate on the dose rate and on the absorbed dose.     

Coastal management challenges from a community perspective: The problem of ‘stealth privatization’ in a Canadian fishery

Intertidal clam fisheries seem ideal candidates for the devolution of management authority from government to local stakeholders. In St. Mary's Bay, Nova Scotia, a private firm recently applied for a 10-year renewal of a large (1,627 ha) lease for quahog clam aquaculture. This case study examines the challenges of implementing community-based natural resource management (CBNRM) in rural fisheries within a broad integrated coastal management (ICM) institutional environment that favours corporate stakeholders. The challenges facing clam harvesters in rural Digby Neck, Nova Scotia arise from poor communication and coordination within government and between government and communities, as well as higher-level policy conflicts. The most important challenge arises from ‘stealth privatization’ of clam beaches. A single firm was granted rights of first refusal to depurate all clams harvested from closed (polluted) beaches in the region, resulting in the de facto privatization of all (polluted and unpolluted) clam beaches. Experiences in other parts of Canada suggest there may be community-based governance approaches that avoid the pitfalls associated with corporate management of clam beaches. New thinking is required about how to moderate the ‘privatization paradigm’ so prevalent within senior levels of government in order to ensure environmental and social sustainability in rural fishing communities.     

Carbonate saturation and the effect of pressure on the alkalinity of interstitial waters from the Guatemala Basin

Interstitial water samples were collected from the Guatemala Basin using an in situ sampler and by centrifuging box core sediment samples. Results from these two sampling methods for Mn, Si, PO₄ agree well. There is a systematic difference in the alkalinity values, however, which suggests that CaCO₃ (s) precipitates from the box core samples when they are brought from in situ pressure at 1 atm. Thus the alkalinity on box core samples is less than that on samples collected in situ. The magnitude of the alkalinity decrease can be calculated using basic thermodynamic principles and the observed and predicted differences agree well.Both sampling methods show a sharp drop in pH just below the sediment water interface which can be explained by the oxidation of organic matter by O₂ in the absence of CaCO₃. Alkalinity increases during the reduction of MnO₂(s) and release of Mn²⁺ to the interstitial water. The result is that interstitial waters become undersaturated with CaCO₃ immediately below the sediment/water interface and then return to or nearly to saturation at depth.     

Interstitial water chemistry in the sediments of Saanich Inlet

Measurements of nutrients and trace metals are used to examine the processes controlling their distributions in the interstitial waters of Saanich Inlet. Samples were collected using both in situ and squeezing techniques with excellent agreement. Additional measurements of porosity, organic carbon and sedimentation rate by ²¹⁰Pb are used in conjunction with the nutrient measurements to test the equation for the diagenesis of organic matter in fine-grained, organic-rich and rapidly-accumulating sediments.Organic carbon and sulfate decrease with depth in the sediment whereas ammonia and alkalinity increase. In the zone of sulfate reduction (0–20 cm) the rate constants for sulfate reduction ($\text{k}{}_{\mathrm{s}}$), ammonia production ($\text{k}{}_{\mathrm{N}}$) and organic carbon decomposition ($\text{k}{}_{\mathrm{c}}$) agree within a factor of two. Our calculations indicate, however, that this is fortuitous since the observed decrease in paniculate organic carbon is insufficient to account for the sulfate consumption. Sulfate must also be consumed by reaction with methane diffusing up from the underlying sediments. The rate constant for sulfate reduction using particulate organic carbon is lower than a modelled rate encompassing all organic species, including methane.The rate constant for ammonia production ($\text{k}{}_{\mathrm{N}}$) decreases by an order of magnitude when sulfate is completely depleted and methane production dominates.Thermodynamic calculations suggest that the interstitial waters are saturated or supersaturated with respect to all forms of iron ‘monosulfides’, apatite and rhodochrosite.     

Metal-solid interactions in the marine environment: Estimating apparent equilibrium binding constants

Surface chemistry concepts developed for heterogeneous oxide surfaces are illustrated with Cu, Cd, and Zn adsorption data on a well defined, model surface—goethite (αFeOOH)—and then applied to define the interaction or Zn with interfacial sediments from the Guatemala Basin at MANOP site H.Apparent equilibrium binding constants which describe metal associations with a surface, whose sites are composed of a spectrum of binding energies, are independent of adsorption density when sites are available in excess, but dependent on adsorption density when sites are limited. This conclusion makes it especially important to properly apply laboratory experimental results to describe adsorption processes in the natural environment. Therefore, a means for estimating the maximum adsorption density of an element on natural particles is discussed and used to estimate the quantity of Zn in interfacial sediments at MANOP site H which can be ascribed to the process of adsorption.