Early Holocene greening of the Sahara requires Mediterranean winter rainfall.

The greening of the Sahara, associated with the African Humid Period (AHP) between ca. 14,500 and 5,000 y ago, is arguably the largest climate-induced environmental change in the Holocene; it is usually explained by the strengthening and northward expansion of the African monsoon in response to orbital forcing. However, the strengthened monsoon in Early to Middle Holocene climate model simulations cannot sustain vegetation in the Sahara or account for the increased humidity in the Mediterranean region. Here, we present an 18,500-y pollen and leaf-wax δD record from Lake Tislit (32° N) in Morocco, which provides quantitative reconstruction of winter and summer precipitation in northern Africa. The record from Lake Tislit shows that the northern Sahara and the Mediterranean region were wetter in the AHP because of increased winter precipitation and were not influenced by the monsoon. The increased seasonal contrast of insolation led to an intensification and southward shift of the Mediterranean winter precipitation system in addition to the intensified summer monsoon. Therefore, a winter rainfall zone must have met and possibly overlapped the monsoonal zone in the Sahara. Using a mechanistic vegetation model in Early Holocene conditions, we show that this seasonal distribution of rainfall is more efficient than the increased monsoon alone in generating a green Sahara vegetation cover, in agreement with observed vegetation. This conceptual framework should be taken into consideration in Earth system paleoclimate simulations used to explore the mechanisms of African climatic and environmental sensitivity.

Bioaccumulation of heavy metals in Donax obesulus from the Lambayeque littoral, Peru / Bioacumulación de metales pesados en Donax obesulus del litoral de Lambayeque, Perú / Bioacumulação de metais pesados ​​em Donax obesulus da costa de Lambayeque, Peru

Donax obesulus is a bivalve widely mined and consumed by the local coastal population of the Lambayeque region, Peru. The coastal-marine environment where Donax obesulus lives present anthropogenic disturbances, including pollutants such as heavy metals (cadmium, copper, and lead). The objectives of this investigation were to quantify and evaluate the concentrations of copper, lead, and cadmium in edible tissues of Donax obesulus. Donax obesulus samples were collected from three beaches on the Lambayeque coast (from south to north: Lagunas, San José, and El Gigante) between May and July 2013. The samples were subjected to a toxicological test by inductively coupled plasma optical emission spectrometry (OES) (ICP). The results showed that copper presented a clear cumulative trend in Donax obesulus with the highest concentration at San José beach in July (10.1 µg g-1). In contrast, the concentrations of lead (> 0.3 µg g-1) and cadmium (> 0.2 µg g-1) were meager in all the sampling areas throughout the time the investigation covered. Bioaccumulation of copper, lead, and cadmium founded in Donax obesulus might vulnerate the food safety of its consumers.

Donax obesulus es un bivalvo ampliamente extraído y consumido por la población local del litoral de la región Lambayeque, Perú. El ambiente costero-marino donde habita D. obesulus se encuentra alterado a causa de las actividades agrícola-industriales, pobre tratamiento de aguas servidas, entre otros. Esto permite la presencia de contaminantes como metales pesados (cadmio, cobre y plomo). Los objetivos de esta investigación fueron cuantificar y evaluar las concentraciones de cobre, plomo y cadmio en tejidos comestibles de D. obesulus. Se recolectaron muestras de D. obesulus en tres playas del litoral de Lambayeque (de sur a norte: Lagunas, San José y El Gigante) entre los meses de mayo y julio del 2013. Las muestras se sometieron a un ensayo toxicológico por espectrometría de emisión óptica (OES) de plasma acoplado inductivamente (ICP). Los resultados demostraron que el cobre presentó una clara tendencia acumulativa en D. obesulus con mayor concentración en la playa San José en julio (10,1 µg g-1). En contraste, las concentraciones de plomo (>0,3 µg g-1) y cadmio (>0,2 µg g-1) fueron exiguas en todas las áreas de muestreo durante todo el tiempo que abarcó la investigación. Estos resultados podrían sugerir que la bioacumulación de cobre, plomo y cadmio en D. obesulus implicaría la seguridad alimentaria de sus consumidores.

Donax obesulus é um bivalve amplamente minerado e consumido pela população costeira local da região de Lambayeque, Peru. O ambiente marinho-costeiro em que D. obesulus vive é alterado devido a atividades agroindustriais, tratamento inadequado de águas residuais, entre outros. Isso permite a presença de contaminantes como metais pesados ​​(cádmio, cobre e chumbo). Os objetivos desta pesquisa foram quantificar e avaliar as concentrações de cobre, chumbo e cádmio nos tecidos comestíveis de D. obesulus. Amostras de D. obesulus foram coletadas em três praias da costa de Lambayeque (de sul a norte: Lagunas, San José e El Gigante) entre os meses de maio e julho de 2013. As amostras foram submetidas a um teste toxicológico por espectrometria de emissão. Ótica de plasma indutivamente acoplada (OES) (ICP). Os resultados mostraram que o cobre apresentou uma clara tendência cumulativa em D. obesulus com maior concentração na praia de San José em julho (10,1 µg g-1). Por outro lado, as concentrações de chumbo (> 0,3 µg g-1) e cádmio (> 0,2 µg g-1) foram escassas em todas as áreas de amostragem durante todo o período da investigação. Esses resultados podem sugerir que a bioacumulação de cobre, chumbo e cádmio em D. obesulus implicaria na segurança alimentar de seus consumidores.