OSL signal resetting in young deposits determined with a pulsed photon‐stimulated luminescence (PPSL) unit

Optical Stimulated Luminescence (OSL) is a technique that can be used for dating geological materials deposited within the last half‐million years, including sediments transported by air, water or gravity, as well as rocks heated at high temperatures. Recently, several studies have shown that OSL can also provide information on sediment transport. The pulsed photon‐stimulated luminescence (PPSL) unit (also known as a portable OSL reader) developed by the Scottish Universities Environmental Research Centre is an instrument designed to read luminescence signals from bulk (untreated) sediment samples comprising poly‐mineral and poly‐grain fractions. In this contribution, we evaluate the potential of the PPSL unit to assess the degree of OSL signal resetting in 27 young deposits (<2 ka) transported by different geomorphic agents in volcanic, coastal and fluvial depositional settings located in Mexico. Our results are in agreement with previous findings that used the Risø TL/OSL reader, confirming that sediments transported by debrisflows contain the highest inherited luminesce signals. Infrared stimulation (IRSL) values in volcanic ash, lavas, and sand beach and dune deposits exhibit low scatter. However, with blue stimulation (BLSL) these samples reveal a large degree of scattering, attributed to charge transfer in the case of the coastal deposits and to the low sensitivity of quartz in the case of volcanic material. The luminescence signals of fluvial sediments exhibit a highly scattered distribution in both IRSL and BLSL. We conclude that the use of a PPSL unit is a simple approach to assess the degree of OSL signal resetting in deposits sourced from different geological environments. This research contributes to previous studies that have investigated new applications of the PPSL unit to assist in OSL dating of geological materials.     

The Late Cretaceous Klepa basalts in Macedonia (FYROM)—Constraints on the final stage of Tethys closure in the Balkans

The waning stage(s) of the Tethyan ocean(s) in the Balkans are not well understood. Controversy centres on the origin and life‐span of the Cretaceous Sava Zone, which is allegedly a remnant of the last oceanic domain in the Balkan Peninsula, defining the youngest suture between Eurasia‐ and Adria‐derived plates. In order to investigate to what extent Late‐Cretaceous volcanism within the Sava Zone is consistent with this model we present new age data together with trace‐element and Sr–Nd–Pb isotope data for the Klepa basaltic lavas from the central Balkan Peninsula. Our new geochemical data show marked differences between the Cretaceous Klepa basalts (Sava Zone) and the rocks of other volcanic sequences from the Jurassic ophiolites of the Balkans. The Klepa basalts mostly have Sr–Nd–Pb isotopic and trace‐element signatures that resemble enriched within‐plate basalts substantially different from Jurassic ophiolite basalts with MORB, BAB and IAV affinities. Trace‐element modelling of the Klepa rocks indicates 2%–20% polybaric melting of a relatively homogeneously metasomatised mantle source that ranges in composition from garnet lherzolite to ilmenite+apatite bearing spinel–amphibole lherzolite. Thus, the residual mineralogy is characteristic of a continental rather than oceanic lithospheric mantle source, suggesting an intracontinental within‐plate origin for the Klepa basalts. Two alternative geodynamic models are internally consistent with our new findings: (1) if the Sava Zone represents remnants of the youngest Neotethyan Ocean, magmatism along this zone would be situated within the forearc region and triggered by ridge subduction; (2) if the Sava Zone delimits a diffuse tectonic boundary between Adria and Europe which had already collided in the Late Jurassic, the Klepa basalts together with a number of other magmatic centres represent volcanism related to transtensional tectonics.     

Importance of mixotrophic nanoplankton in Aysén Fjord (Southern Chile) during austral winter

Mixotrophy, the combination of autotrophic and heterotrophic nutrition in the same organism, is widespread in planktonic algae. Several reports from temperate and high-latitude fjords in Scandinavia suggest the occurrence of a niche in late summer and autumn during post-bloom conditions in which mixotrophic algae can become important grazers in pelagic ecosystems, accessing the nutrients bound in their prey to overcome nutrient limitation. Here, we experimentally determined the trophic modes and bacterivory rates for the nanoplankton community (2–20 μm) in Aysén Fjord located in the Chilean Northern Patagonia during two contrasting seasons: winter and spring. While mixotrophic nanoplankton was virtually absent from the system in spring, in winter at occasions it even constituted the dominant trophic group of the nanoplankton with abundances of >900 cells mL^?1. This indicates a second niche for mixotrophs in winter, when mixotrophy allows overcoming light limitation.     

Latitudinal patterns of export production recorded in surface sediments of the Chilean Patagonian fjords (41–55°S) as a response to water column productivity

The Chilean Patagonian fjords region (41–56°S) is characterized by highly complex geomorphology and hydrographic conditions, and strong seasonal and latitudinal patterns in precipitation, freshwater discharge, glacier coverage, and light regime; all of these directly affect biological production in the water column. In this study, we compiled published and new information on water column properties (primary production, nutrients) and surface sediment characteristics (biogenic opal, organic carbon, molar C/N, bulk sedimentary δ¹³C_org) from the Chilean Patagonian fjords between 41°S and 55°S, describing herein the latitudinal pattern of water column productivity and its imprint in the underlying sediments. Based on information collected at 188 water column and 118 sediment sampling sites, we grouped the Chilean fjords into four main zones: Inner Sea of Chiloé (41° to ～44°S), Northern Patagonia (44° to ～47°S), Central Patagonia (48–51°S), and Southern Patagonia (Magellan Strait region between 52° and 55°S). Primary production in the Chilean Patagonian fjords was the highest in spring–summer, reflecting the seasonal pattern of water column productivity. A clear north–south latitudinal pattern in primary production was observed, with the highest average spring and summer estimates in the Inner Sea of Chiloé (2427 and 5860 mg C m^?2 d^?1) and Northern Patagonia (1667 and 2616 mg C m^?2 d^?1). This pattern was closely related to the higher availability of nutrients, greater solar radiation, and extended photoperiod during the productive season in these two zones. The lowest spring value was found in Caleta Tortel, Central Patagonia (91 mg C m^?2 d^?1), a site heavily influenced by glacier meltwater and river discharge loaded with glacial sediments. Biogenic opal, an important constituent of the Chilean fjord surface sediments (Si_OPAL ～1–13%), reproduced the general north–south pattern of primary production and was directly related to water column silicic acid concentrations. Surface sediments were also rich in organic carbon content and the highest values corresponded to locations far away from glacier influence, sites within fjords, and/or semi-enclosed and protected basins, reflecting both autochthonous (water column productivity) and allochthonous sources (contribution of terrestrial organic matter from fluvial input to the fjords). A gradient was observed from the more oceanic sites to the fjord heads (west–east) in terms of bulk sedimentary δ¹³C_org and C/N ratios; the more depleted (δ¹³C_org ?26‰) and higher C/N (23) values corresponded to areas close to rivers and glaciers. A comparison of the Chilean Patagonian fjords with other fjord systems in the world revealed high variability in primary production for all fjord systems as well as similar surface sediment geochemistry due to the mixing of marine and terrestrial organic carbon.     

A global assessment of the impact of climate change on water scarcity

This paper presents a global scale assessment of the impact of climate change on water scarcity. Patterns of climate change from 21 Global Climate Models (GCMs) under four SRES scenarios are applied to a global hydrological model to estimate water resources across 1339 watersheds. The Water Crowding Index (WCI) and the Water Stress Index (WSI) are used to calculate exposure to increases and decreases in global water scarcity due to climate change. 1.6 (WCI) and 2.4 (WSI) billion people are estimated to be currently living within watersheds exposed to water scarcity. Using the WCI, by 2050 under the A1B scenario, 0.5 to 3.1 billion people are exposed to an increase in water scarcity due to climate change (range across 21 GCMs). This represents a higher upper-estimate than previous assessments because scenarios are constructed from a wider range of GCMs. A substantial proportion of the uncertainty in the global-scale effect of climate change on water scarcity is due to uncertainty in the estimates for South Asia and East Asia. Sensitivity to the WCI and WSI thresholds that define water scarcity can be comparable to the sensitivity to climate change pattern. More of the world will see an increase in exposure to water scarcity than a decrease due to climate change but this is not consistent across all climate change patterns. Additionally, investigation of the effects of a set of prescribed global mean temperature change scenarios show rapid increases in water scarcity due to climate change across many regions of the globe, up to 2 °C, followed by stabilisation to 4 °C.