Quantitative reconstruction of Holocene precipitation changes in southern Patagonia

Holocene variations in annual precipitation (P_ann) were reconstructed from pollen data from southern Argentinian Patagonia using a transfer function developed based on a weighted-averaging partial least squares (WA-PLS) regression. The pollen–climate calibration model consisted of 112 surface soil samples and 59 pollen types from the main vegetation units, and modern precipitation values obtained from a global climate database. The performance (r² = 0.517; RMSEP = 126 mm) of the model was comparable or slightly lower than in other comparable pollen–climate models. Fossil pollen data were obtained from a sediment core from Cerro Frias site (50°24'S, 72°42'W) located at the forest-steppe ecotone. Reconstructed P_ann values of about 200 mm suggest dry conditions during the Pleistocene–Holocene transition (12,500–10,500 cal yr BP). P_ann values were about 300–350 mm from 10,500 to 8000 cal yr BP and increased to 400–500 mm between 8000 and 1000 cal yr BP. An abrupt decrease in P_ann at about 1000 cal yr BP was associated with a Nothofagus decline. The reconstructed P_ann suggests a weakening and southward shift of the westerlies during the early Holocene and intensification, with no major latitudinal shifts, during the mid-Holocene at high latitudes in southern Patagonia.     

A systems approach to assess climate change mitigation options in landscapes of the United States forest sector

Background

United States forests can contribute to national strategies for greenhouse gas reductions. The objective of this work was to evaluate forest sector climate change mitigation scenarios from 2018 to 2050 by applying a systems-based approach that accounts for net emissions across four interdependent components: (1) forest ecosystem, (2) land-use change, (3) harvested wood products, and (4) substitution benefits from using wood products and bioenergy. We assessed a range of land management and harvested wood product scenarios for two case studies in the U.S: coastal South Carolina and Northern Wisconsin. We integrated forest inventory and remotely-sensed disturbance data within a modelling framework consisting of a growth-and-yield driven ecosystem carbon model; a harvested wood products model that estimates emissions from commodity production, use and post-consumer treatment; and displacement factors to estimate avoided fossil fuel emissions. We estimated biophysical mitigation potential by comparing net emissions from land management and harvested wood products scenarios with a baseline (‘business as usual’) scenario.

Results

Baseline scenario results showed that the strength of the ecosystem carbon sink has been decreasing in the two sites due to age-related productivity declines and deforestation. Mitigation activities have the potential to lessen or delay the further reduction in the carbon sink. Results of the mitigation analysis indicated that scenarios reducing net forest area loss were most effective in South Carolina, while extending harvest rotations and increasing longer-lived wood products were most effective in Wisconsin. Scenarios aimed at increasing bioenergy use either increased or reduced net emissions within the 32-year analysis timeframe.

Conclusions

It is critical to apply a systems approach to comprehensively assess net emissions from forest sector climate change mitigation scenarios. Although some scenarios produced a benefit by displacing emissions from fossil fuel energy or by substituting wood products for other materials, these benefits can be outweighed by increased carbon emissions in the forest or product systems. Maintaining forests as forests, extending rotations, and shifting commodities to longer-lived products had the strongest mitigation benefits over several decades. Carbon cycle impacts of bioenergy depend on timeframe, feedstocks, and alternative uses of biomass, and cannot be assumed carbon neutral.

     

Temperature profiles in the earth of importance to deep electrical conductivity models

Deep in the Earth, the electrical conductivity of geological material is extremely dependent on temperature. The knowledge of temperature is thus essential for any interpretation of magnetotelluric data in projecting lithospheric structural models. The measured values of the terrestrial heat flow, radiogenic heat production and thermal conductivity of rocks allow the extrapolation of surface observations to a greater depth and the calculation of the temperature field within the lithosphere. Various methods of deep temperature calculations are presented and discussed. Characteristic geotherms are proposed for major tectonic provinces of Europe and it is shown that the existing temperatures on the crust-upper mantle boundary may vary in a broad interval of 350–1,000°C. The present work is completed with a survey of the temperature dependence of electrical conductivity for selected crustal and upper mantle rocks within the interval 200–1,000°C. It is shown how the knowledge of the temperature field can be used in the evaluation of the deep electrical conductivity pattern by converting the conductivity-versustemperature data into the conductivity-versus-depth data.     

The nautiloid Family Eothinoceratidae from the Floian of the Central Andean Basin (NW Argentina and South Bolivia)

A single confidently dated species of cephalopod is so far known in the Tremadocian of the southern Central Andean Basin (NW Argentina and southern Bolivia). This species belongs to the Eothinoceratidae and has a strong affinity mainly with Avalonia. During the Floian, a notable increase in diversity took place, with the appearance of a variety of families represented by several genera, in particular, within the Family Eothinoceratidae. In addition to the previously described species from southern Bolivia, we evaluate the other records of that family from the Central Andean Basin, and propose the following new taxa: Saloceras sikus sp. nov., Saloceras quena sp. nov., Mutveiceras gen. nov., and Mutveiceras cienagaensis sp. nov. We also describe Margaritoceras diploide, Margaritoceras sp., and Mutveiceras sp. From a palaeogeographic perspective, the cephalopod fauna shows affinities mainly with those of England, Wales, and the Montagne Noire (cold water Gondwana and peri‐Gondwana). As with other cephalopod faunas of mid to high palaeolatitudes, eothinoceratids occur along with other cephalopods forming assemblages of low morphological diversity. We interpret the forms described here as demersal with a subvertical poise, but capable of making rapid buoyancy changes, living in a wide spectrum of shallow offshore to shoreface settings. Copyright © 2014 John Wiley & Sons, Ltd.     

Nutrient distributions over the Southwestern South Atlantic continental shelf from Mar del Plata (Argentina) to Itajaí (Brazil): Winter–summer aspects

Nutrient distributions observed at some depths along the continental shelf from 27°05′S (Brazil) to 39°31′S (Argentina) in winter, 2003 and summer, 2004 related to salinity and dissolved oxygen (mL L⁻¹) and saturation (%) data showed remarkable influences of fresh water discharge over the coastal region and in front of the La Plata estuary. In the southern portion of the study area different processes were verified. Upwelling processes caused by ocean dynamics typical of shelf break areas, eddies related to surface dynamics and regeneration processes confirmed by the increase of nutrients and the decrease of dissolved and saturation oxygen data were verified. High silicate concentrations in the surface waters were identified related to low salinities (minimum of 21.22 in winter and 21.96 in summer), confirming the importance of freshwater inputs in this region, especially in winter. Silicate concentration range showed values between 0.00 and 83.52 μM during winter and from 0.00 to 41.16 μM during summer. Phosphate concentrations worked as a secondary trace of terrestrial input and their values varied from 0.00 to 3.30 μM in winter and from 0.03 to 2.26 μM in summer; however, in shallow waters, phosphate indicated more clearly the fresh water influence. The most important information given by nitrate concentrations was the presence of water from SACW upwelling that represents a new source of nutrients for marine primary production. Nitrate maximum values reached 41.96 μM in winter and 33.10 μM in summer. At a depth ∼800 m, high nitrate, phosphate and silicate concentrations were related to Malvinas Current Waters, Subantarctic Shallow Waters and Antarctic Atlantic Intermediate Waters (AAIW). Dissolved oxygen varied from 3.41 to 7.06 mL L⁻¹ in winter and from 2.65 to 6.85 mL L⁻¹ in summer. The percentage of dissolved oxygen saturation in the waters showed values between 48% and 113% in winter and from 46% to135% in summer. The most important primary production was verified in the summer, and situations of undersaturation were mainly observed below 50 m depth and at some points near the coast. The anti-correlation between nutrients and dissolved oxygen which showed evident undersaturation also revealed important potential sites of remineralization processes. The nutrient behaviours showed some aspects of the processes that occur over the Southwestern South Atlantic continental shelf and in their land–sea interfaces between Mar del Plata and Itajaí.     

Diatom paleoecology of the Mar Chiquita lagoon delta,Argentina

A 68 cm thick outcrop of diatomaceous sediments at the head of Mar Chiquita Lagoon on the Argentine coast near Buenos Aires provides evidence of Holocene paleoenvironmental changes related to sea level changes and freshwater input to the lagoon system. Salinity tolerances of extant diatom taxa were used for the reconstruction and multivariate analytical techniques were applied to reduce subjective interpretations of the diatom percentage data.The basal half of the record was deposited before 3000 years ago and fossil diatoms indicate generally freshwater conditions with one fluctuation in mesohalobous diatoms suggesting brackish water conditions at a depth of about 60 cm. Polyhalobous (marine) diatoms characterize the record after 3000 years ago and large numbers of epiphytic diatoms indicate salt marsh environments with episodic seawater fluctuations to supratidal levels. Freshwater diatoms returned at the top of the outcrop, presumably as a result of the restriction of the historic marine inlet to the lagoon and the effects of freshwater inflow to the basin.This is the second in a series of papers published in this issue on Paleolimnology in Southern South America. Dr. C. A. Fernández served as guest editor for these papers.     

Geochemical mobility of arsenic in the surficial waters from Argentina

The presence of arsenic (As) in surface water constitutes an important environmental risk, where mobility and adsorption processes are responsible for its behavior in the sediment–water interface. Therefore, the assessment of adsorption, mobility and water availability of arsenic in freshwater sediments, with agricultural, livestock and urban soil uses was performed. Arsenic concentrations in sediments ranged from 5.4 to 15.9 mg kg^?1 (total) and 2.8 to 6.5 mg kg^?1 (labile), and those of iron and manganese were 11,563–23,500 and 140.6–662.1 mg kg^?1, respectively. The As levels in water were significantly lower than those of sediments. Results would suggest that As co-precipitation and adsorption on Fe oxides are probably the major route of immobilization, determining its low lability. Manganese did not present an outstanding contribution to the retention, and cation-exchange capacity, pH and organic matter of sediments did not show an influence on the mobility of As.