Paleolimnology of Lake Iznik (NW Turkey) during the past ~ 31 ka cal BP

Lake Iznik, situated in the Marmara region (NW Turkey), is an alkaline lake with about 300 km2 surface area, inserted in an area of typical Mediterranean climate. During the dry summer season, carbonates are precipitating from the water column. The endogen carbonate accumulation, e.g. aragonite, is expected to hold past climate information. A detailed understanding of the limnological system is required to differentiate site specific signals and responses to climatic forcing. Geochemical and mineralogical evidence from a continuous composite profile was documented in a decadal to centennial time scale. A novel improved age model shows that the sediment record reaches up to ~ 31.5 ka cal BP. Compositional Data (CoDa) analysis allowed the identification of three groups of elements, and particular elements with distinct geochemical behavior, which indicate specific geochemical processes. Also, CoDa analysis allowed clear geochemical characterization of litho-stratigraphic units. Grain size measurements were undertaken to determine the energy levels of the physical deposition environment. Detailed grain size analysis allowed amorphous silica to be quantified. From siliciclastic grain size analysis, the ratio coarse silt/clay was identified to be a sensitive indicator to infer changes in the depth of the water column. This ratio was a calibrated to the modern depositional regime. The endogen carbonate production proved to be a sensitive climatic indicator. Changes in carbonate concentration are timely associated to the inferred fluctuations in water column depth. The aragonite concentrations are most likely related to regional temperature, catchment hydrology and the mixing dynamics of the lake. The physical mixing dynamics of the lake is reflected in (a) behavior of elements mobile under different oxic/anoxic conditions, and (b) geochemical patterns for carbonate bound elements in hardwater lakes, and (c) stability of various minerals. This study established the current knowledge of the geochemical evolution of Lake Iznik. It further adds to the understanding of paleoclimate evolution in the Marmara region on a millennial time scale. From ~31 ka cal BP until the deglaciation at ~18 ka cal BP, Lake Iznik is characterized by low productivity and higher detrital load, in association to a low carbonate accumulation. Thicker epilimnion and lower supersaturation states are inferred in association to a deeper water column. During the last glacial, i.e. from ~ 26 ka cal BP to ~18 ka cal BP, Lake Iznik passes through prolonged stages of incomplete mixing of the water column, whereas the lake level is most likely maintained during that period. In addition, the crystal structure of carbonates reflects mineral instability. At the Last Glacial Maximum (~ 22 ka cal BP) carbonate accumulation in the lake is nearly absent. During the deglaciation, starting at ~18 ka cal BP, dynamic and pronounced lake level variations occur. A shallow water column is inferred at ~ 16.5 ka calBP, and a possible low stand is identified for the period between ~ 14 and ~ 9 ka cal BP. Generally Marine Isotope Stage (MIS) 1 is marked by increased aragonite concentrations, and enhanced chemical weathering. The terrestric organic load increases gradually, and is accompanied by lake trophic conditions. Lake Iznik climate event stratigraphy highly correlates with the regional geological record. The endogen carbonate accumulation seems to occur in phase to Northern Hemisphere climate variability, for instance warm interstadials and cold stadials are depicted. In synchrony with Dansgaard-Oeschger interstadials Iznik sediments point to a deep water column, which decreases in time. After a short time lag, geochemistry reacts with increasing aragonite concentrations. In synchrony with Heinrich stadials, the Iznik sediments underwent a short phase of magnesian calcite preservation, after that generally more elevated calcite concentrations prevail. In general the cold phases are associated to a higher input of detrital calcite, likewise during the Younger Dryas cold event (~ 12 ka cal BP). The early Holocene (from ~ 12 to ~ 9 ka cal BP) is characterized by pronounced summer stratification of the water column and higher epilimnion carbonate supersaturation. Recurrent stages of good lake mixing are accompanying a shallow water column. The middle Holocene is generally more humid, as indicated by enhanced chemical weathering and by two distinct lake level increases. The first of such increases occured at ~ 9.3 ka cal BP and is related to the reconnection of the Black Sea to Mediterranean water ways. This geological event is followed by the settlement of the first farming communities in the Iznik basin. Moreover, at circa 5 ka cal BP a change occurs in delivery of grain size proportions – in relation to what is expected according to the inferred water column depth. This is most likely resulting from anthropic land-use within the basin.Der alkalische Iznik See ist in der Marmara Region (NW-Türkei), in der ein typisches mediterranes Klima vorherrscht, gelegen. Er besitzt eine Oberfläche von ca. 300 km2. Im See selbst fallen aus der Wassersäule Karbonate hauptsächlich während des Sommers aus, wobei die hydro-geochemischen Bedingungen die Karbonatkonservierung in den Sedimenten begünstigen. Es wird erwartet, dass endogene Karbonate, besonders Aragonit, Informationen über die vergangenen klimatischen Bedingungen speichern. Die geochemische und mineralogische Zusammensetzung der Sedimente wurde für ein kontinuierliches Kompositprofil untersucht. Ein neu erstelltes Altersmodell zeigt dass dieses Kompositprofil ~31.5 ka der Klimageschichte der Marmara Region aufzeichnet. Somit ergeben die Untersuchungen eine zeitliche Auflösung von zehn bis zu hundert Jahren. Die statistische Analyse der Daten (Compositional Data Analysis, CoDa) identifiziert drei geochemische Hauptgruppen aus Elementen, die hydro-geochemisch ähnlich auf Umweltveränderungen reagieren. Entsprechend konnten die fünf lithostratigraphischen Einheiten auch eindeutig geochemisch erfasst werden und lassen sich im Kontext vergangener Klimazustände interpretieren. Die siliziklastischen Korngrößenverteilungen der Sedimente deuten das Energieniveau der Ablagerungsbedingungen der Iznik Sedimente an. Besondere Einblicke hierzu liefert das Verhältnis von Grobsilt zu Ton. Der Zusammenhang zur Wassersäulentiefe wurde anhand der rezenten Sedimentation modelliert. Somit konnten die Änderungen der Seetiefe bzw. der Seespiegel für die Vergangenheit rekonstruiert werden. Die endogene Karbonatausfällung erweist sich als äußerst klimasensitiv. Änderungen in der Karbonatakkumulation zeigen Änderungen in der Mischungsdynamik innerhalb der Wassersäule an, da der vertikale Wasseraustausch sensitiv auf Klimaveränderungen reagiert, was wiederum die Karbonatausfällung im Wasser beeinflusst. Entsprechend spiegelt sich die Dynamik der Seemischung (a) im Verhalten von redox-sensitiven Elementen (oxische versus anoxische Bedingungen), (b) in geochemischen Mustern von Elementen die sich an Karbonate binden, und (c) in der geochemischen Stabilität diverser Minerale wider. Aus den abgeleiteten Veränderungen der Seespiegelschwankungen und Mischungsdynamik im Iznik-See lassen sich Aussagen über die regionale Klimaentwicklung der Marmara Region gewinnen, da das Klima letztlich das Mischverhalten des Sees maßgebend bestimmt. Somit war der Iznik See in der Zeitspanne zwischen ~31.5 bis ~18 ka cal BP nur wenig produktiv und nur wenig Karbonate sind in den Sedimenten erhalten. Entsprechend war die Sedimentation zu dieser Zeit durch terrestrischen Eintrag stark geprägt. Während des letzten Glazials (~26 bis ~18 ka cal BP) traten verschiedene Phasen auf, in denen die Wassersäule nur unvollständig durchmischte. Während dieser Zeitspanne variierte die Seetiefe kaum und Karbonate sind geochemisch nur wenig stabil. Somit fehlen Karbonate während des letzten glazialen Maximums (LGM) beinahe vollständig. Mit Beginn des finalen Rückzugs der Vereisung (~18 ka cal BP) zeigt der Iznik See ausgeprägte Seespiegelschwankungen. Tiefstände finden sich bei ~16.5 ka cal BP und zwischen ~14 und ~9 ka cal BP. Das marine Isotopenstadium 1 (MIS 1) ist im Allgemeinen durch erhöhte Aragoniterhaltung und eine höhere chemische Verwitterung charakterisiert. Der terrestrisch-organische Eintrag erhöht sich graduell und entsprechend nimmt die Trophie des Sees zu. Die Klima-Eventstratigraphie der Sedimente des Iznik Sees lässt sich gut und eindeutig in den Kontext der regionalen Klimaentwicklung der Marmara Region integrieren. So scheint die endogene Karbonatakkumulation in Phase mit der Klimavariabilität der Nordhemisphäre zu sein. Zudem lassen sich beispielsweise anhand der Karbonatphasen die warmen Interstadiale deutlich von den kälteren Stadialen unterscheiden. Dansgaard-Oeschger-Interstadiale sind in den Iznik Sedimenten durch Aragoniterhaltung gekennzeichnet. Während der Heinrich- Stadiale wird in den Sedimenten für kurze Phasen hoch Mg-Kalzit erhalten. Außerdem, sind im Allgemeinen die kälteren Phasen mit höherem Eintrag von terrestrischem Kalzit verknüpft, so auch während der Jüngeren Dryas (~12 ka cal BP). Zu Beginn des Holozäns zeigt die Sedimentgeochemie ein gutes Mischverhältnis des Sees an, was mit einer niedrigen Wassersäule einhergeht. Das mittlere Holozän ist generell feuchter, was anhand einer höheren chemischen Verwitterung und zwei ausgeprägten Seespiegelanstiegen zu erkennen ist. Der Erste dieser Anstiege ist zeitgleich mit der ‚Wieder' -Verbindung der Wasserstraße zwischen dem Schwarzen Meer und dem Mittelmeer, um ~9 ka cal BP. Im Anschluss an dieses geologische Ereignis folgte im Einzugsgebiet des Iznik Sees die menschliche Erstbesiedlung die durch Ackerbau gekennzeichnet ist. Ein zweiter ausgeprägte Seespiegelanstieg im Holozän ist bei ~6.5 ka cal BP dokumentiert. Um ~5 ka cal BP ist eine Veränderung der Verhältnisse der Korngrößen zu beobachten die auf anthropogenen Einfluss im Einzugsgebiet in Folge höherer Erosion durch Bodennutzung hindeutet.O lago Iznik, localizado na região de Marmara (NE, Turquia), possui águas alcalinas, área superficial de cerca 300 km2, e está inserido em uma área de clima tipicamente Mediterrâneo. Durante o verão, carbonatos são precipitados na coluna d'água. Espera-se que a acumulação de carbonatos endógenos, e.g. aragonita, retenha informações sobre o clima do passado. A fim de diferenciar entre sinais específicos do lago e respostas à forçantes climáticas, é necessário um entendimento em detalhe sobre o sistema limnológico. Registros geoquímicos e mineralógicos foram documentados para um perfil contínuo e composto em escala de tempo decadal a secular. Um novo modelo de idades mostra que o perfil sedimentar alcança até ~31.5 ka cal BP. O uso da análise de dados composicionais (Compositional Data – CoDa) permitiu a identificação de três grupos de elementos que reagem de maneira similar às condições hidrogeoquímcias. O uso da análise CoDa também permitiu a caracterização geoquímica das unidades lito-estratigráficas. Análises granulométricas foram realizadas a fim de determinar o nível de energia do ambiente físico deposicional. O detalhamento das análises de granulometria permitiu estimar um parâmetro que mede variações relativas da concentração de sílica amorfa. A partir da análise granulométrica siliciclástica, a razão silte coarso/argila foi identificada como indicator sensível para inferir mudanças na profundidade da coluna d'água. Esta razão foi calibrada para o regime deposicional moderno. A produção de carbonatos endógenos se mostrou um indicator sensível para variações climáticas. Mudanças na concentração de carbonatos estão associadas temporalmente com as mudanças inferidas para a profundidade da coluna d'água. As concentrações de aragonita estão associadas à temperatura regional, hidrologia da bacia e à dinâmica de mistura do lago. A dinâmica dos processos físicos de mistura lacustre se reflete (a) no comportamento de elementos móveis em diferentes condições de oxidação/anoxia, e (b) padrões geoquímicos para elementos ligados à carbonatos em lagos alcalinos, e (c) estabilidade de diversos minerais. Este estudo estabelece o conhecimento atual sobre a evolução geoquímica do lago Iznik. Além disso, este trabalho é uma contribuição para o entendimento da evolução paleoclimática na região de Marmara em escala temporal milenar. A partir de ~31 ka cal BP, até a deglaciação em ~18 ka cal BP, o lago Iznik é caracterizado por baixa produtividade e grande aporte terrígeno, em associação com baixa acumulação de carbonatos. Maior profundidade de epilímnio e menores estados de supersaturação podem ser inferidos em conjunto com uma maior profundidade geral da coluna d'água do lago. Durante o último glacial, i.e. de ~26 ka cal BP até ~18 ka cal BP, o lago Iznik passa por prolongados estágios de mistura incompleta da coluna d'água, sendo que o nível do lago provavelmente é mantido durante este período. Em adição, a estrutura cristalina dos carbonatos reflete instabilidade mineral. Durante o último máximo glacial (~22 ka cal BP) a acumulação de carbonatos no lago é praticamente ausente. Durante a deglaciação, começando em ~18 ka calBP, se inferem variações dinâmicas e pronunciadas do nível do lago. Uma queda do nível de água é inferida em ~ 16.5 ka cal BP, e uma coluna d'água rasa é identificada para o período entre ~14 e ~9 ka cal BP. Em geral, o Estágio isotópico marinho 1 (MIS 1) é marcado por um aumento nas concentrações de aragonita, e intemperismo químico elevado. O aporte orgânico terrígeno aumenta gradualmente, e é acompanhado pelas condições tróficas do lago. A estratigrafia de eventos climáticos do lago Iznik pode ser claramente correlacionada com o registro geológico regional. A acumulação de carbonatos endógenos ocorre em fase com a variabilidade climática do Hemisfério Norte, por exemplo é possivel diferenciar entre os interstadials quentes e os stadials frios. Em sincronia com os interstadials Dansgaard-Oeshger, os sedimentos do lago Iznik apontam para uma coluna d'água profunda, que descresce com o tempo. Após um curto intervalo de tempo, a geoquímica reage com aumento das concentrações de aragonita. Em sincronia com os stadials Heinrich, os sedimentos do lago Iznik passam por uma curta fase de preservação de calcita magnesiana, após a qual em geral teores mais elevados de calcita prevalecem. Em geral as fases frias estão associadas à maior aporte de calcita detrítica, da mesma maneira durante o evento Younger Dryas (~12 ka cal BP). O início do Holoceno (de ~12 até ~9 ka cal BP) é caracterizado por pronunciada estratificação da coluna d'água durante o verão e elevada supersaturação do epilímnio. Estágios recorrentes de boas condições de mistura do lago são acompanhados por uma coluna d'água rasa. O Holoceno médio é geralmente mais úmido, como indicado por um aumento do intemperismo químico e por dois aumentos marcantes do nível do lago. O primeiro destes aumentos ocorreu em ~9.3 ka cal BP, e está relacionado à reconexão da via aquática entre os mares Negro e Mediterrâneo. Este evento geológico foi seguido pelo estabelecimento das primeiras comunidades na bacia do lago Iznik. Além disso, em ~5 ka cal BP nas proporções granulométricas do aporte sedimentar se deve ao uso antrópico do solo na bacia.İznik Gölü Marmara Bölgesinde (KB Türkiye) konumlanmış, tipik olarak Akdeniz iklim kuşagi içerisinde yer alan, 300 km2'lik yüzey alanına sahip bir alkali göldür. Kuru yaz sezonu süresince su kolununda karbonat çökelmektedir. Endojenik karbonat çökelimi (örneğin, aragonit oluşumu), eski iklim hakkında bilgiler barındırır. Limnolojik sistemin iyi bir şekilde anlaşılması için, yöresel, kendine özgü sinyaller ve iklimsel etkiye olan tepkinin ayırt edilmesi gereklidir. Sürekli, birleşik bir çökel profili boyunca bin yıllık ve yüzyıllık zaman ölçeğinde jeokimyasal ve mineralojik bulgular belgelenmiştir. Yeni geliştirilmiş yaş modeli, sediment kaydının G.Ö. 31.5 bin kalibre edilmiş yıla kadar ulaştığını göstermektedir. Çökel bileşimi (CoDa) analizleri belirgin jeokimyasal süreçleri gösteren farklı jeokimyasal davranıştaki üç element gurubu ve özel elementlerin tanımlanmasını sağlamıştır. Ayrıca, CoDa analizleri litostratigrafik birimlerin anlaşılır jeokimyasal tanımlamasını sağlamıştır. Tane boyu analizleri çökelme ortamının fiziksel enerji düzeyinin saptanması için yürütülmüştür. Detaylı tane boyu analizleri amorf silika miktarının belirlenmesini sağlamıştır. Silisiklastik tane boyu analizlerinden elde edilen iri silt/kil oranınin su sütunu derinliğindeki değişimlerin anlaşılması için hassas bir gösterge oldugu saptanmistir. Bu oran güncel çökelme ortamlarına göre kalibre edilmiştir. Endojen karbonat üretiminin hassas iklim göstergesi olduğu kanıtlanmıştır. Karbonat bileşimindeki değişimler, su sütunu derinliğindeki salınımların zamana bağlı değişimleri ile ilişkilidir. Aragonit konsantrasyonu büyük olasılıkla yersel sıcaklık, havza hidrolojisi ve gölün karışım dinamiği ile ilgilidir. Gölün fiziksel karışım dinamiği; (a) oksik/anoksik şartlar altında hareketli elementlerin davranışını, ve (b) sert sulu göllerde karbonat oluşturan elementlerin jeokimyasal motiflerini, ve (c) çeşitli minerallerin duraylılığını yansıtmaktadır. Bu çalışma İznik Gölü'nün jeokimyasal evrimi ile ilgili güncel bilgilere ulaşmamızı ve ayrıca, Marmara bölgesinin bin yıl zaman ölçeğindeki eski iklimsel evriminin anlaşılmasını sağlamıştır. G.Ö. ~31 – ~18 bin yıllari arasinda, İznik Gölü düşük karbonat birikimi ile ilişkili olarak düşük üretkenlik ve yüksek detritik girdi ile karakterize edilir. Kalın epilimnion ve daha düşük doygunluk hali daha derin su kolonu ile ilişkilidir. Son buzul döneminde, örneğin G.Ö. ~26 – ~18 bin yıl, İznik Gölü uzunyarı-karışım dönemleri geçirirken, göl seviyesi muhtemelen buzul döneminin büyük bir kısmında değişmeden kalmıştır. Buna ilaveten, karbonatların kristal yapıları mineral duraysızlığını göstermektedir. Son Maksimum Buzul döneminde (G.Ö. ~22 bin yil) gölde karbonat birikimi neredeyse yoktur. G.Ö. ~18 bin yılında başlayan buzul erime döneminde, dinamik ve belirgin göl seviyesi değişimi yaşanır. Sığ su derinliği, G.Ö. ~16.5 bin yılında ortaya çıkar. G.Ö. ~14 – ~9 bin yılları arasındaki dönemde, düşük su seviyesi tespit edilmiştir. Genel olarak 1. Denizel İzotop Dönemi (MIS) hızlanan kimyasal ayrışma ve aragonit konsantrasyonu ile belirgindir. Gölün trofik şartlarına uyumlu olarak karasal organik girdi kademeli olarak artar. İznik Gölü'nün iklimsel olaylara bağlı stratigrafisi bölgesel jeoloji kayıtları ile büyük bir oranda örtüşmektedir. Endojen karbonat birikiminin Kuzey Yarım Küre iklim değişimi ile uyumlu olarak gerçekleştiği gözlenmekte, örneğin sıcak buzullararası ve soğuk buzullaşmalar tanımlanmaktadır. Dansgaard-Oeschger ısınmaları ile uyumlu olarak İznik çökelleri zaman içinde azalan derin su kolonuna işaret eder. Kısa bir zamansal gecikmeden sonra artan aragonit konsantrasyonu ile jeokimyasal tepkiyi gösterir. Heinrich soğumaları ile uyumlu olarak, İznik çökelleri kısa bir mağnezyum kalsit korunmasına maruz kalır, daha sonra genellikle daha yüksek konsantrasyonda kalsit yaygınlaşır. Genç Dryas soğuk olayında (G.Ö. ~12 bin yıl) olduğu gibi genel olarak soğuk evreler daha yüksek detritik kalsit girdisi ile bağdaştırılırlar. Erken Holosen (G.Ö. ~12 – ~9 bin yil) bariz yaz tabakalanması ve daha yüksek epilimnion karbonat doygunluğu ile temsil edilir. Tekrarlayan iyi göl karışımı evreleri sığ su kolonu ile birlikte gelişir. Orta Holosen artan kimyasal ayrışma ve iki ayrı göl seviyesi yükselimi ile belirtildiği gibi genellikle daha fazla nemlidir. Bunun gibi ilk evre yaklaşık G.Ö. ~9.3 bin yılında meydana gelir ve bu Karadeniz'in Akdeniz ile su geçişinin sağlanması ile ilgilidir. Bu jeolojik olayı, İznik havzasında ilk tarım topluluğunun yerleşmesi takip eder. Bunun dışında yaklaşık G.Ö. ~5 bin yılında, su kolonu derinliğine bağlı tane boyu oranlarında beklenen bir değişim meydana gelir. Bu değişim büyük olasılıkla havza içinde antropojenik arazi kullanımından kaynaklanmıştır

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The southern Levant is a Mediterranean climate zone of complex variability in which uncertainty remains in regional palaeoclimate reconstruction. In spite of the proven value of diatoms in circum-Mediterranean palaeoenvironmental research, their potential remains largely unexplored in the southern Levant region. In this study, we generate a new, high-resolution multi-proxy record for the last ca. 9000 cal. yr BP, supported by diatom data and key biological, mineralogical and geochemical indicators preserved in a 17.8-m-long sediment sequence recovered from Lake Kinneret (the Sea of Galilee), Israel. During the Holocene, well-correlated shifts in the diatom, minero-geochemical and palynological data indicate marked lake-level variation over time as well as changes in the trophic state of Lake Kinneret. Our results are particularly important in improving the reconstruction of Holocene lake-level variation, and thus past moisture availability. Diatom-inferred lake-level oscillations correlate well with the output from climatic models from the Levantine region and clarify previous uncertainty concerning regional variation in moisture availability. The Early Holocene (from ca. 9000 to 7400 cal. yr BP) was characterized by lake-level shifts due to fluctuating dry-wet climate conditions. During the mid-Holocene (from 7400 to 2200 cal. yr BP), a stable, deep lake-level phase persisted due to high humidity. The lake level of modern Lake Kinneret not only fluctuates seasonally with available moisture, but has also been influenced for ca. 2000 years by the impacts of water abstraction for human consumption and agriculture. Over the last 9000 cal. yr BP, the trophic state of Lake Kinneret has changed from an oligotrophic to a meso- to eutrophic environment, mainly triggered by increased human impact from around 2200 cal. yr BP onwards. The lake’s ecosystem status was not strongly affected by the documented major changes in human occupation patterns during the mid-Holocene, when a relatively stable environment persisted

Contemplative Practices and Mental Training: Prospects for American Education

This article draws on research in neuroscience, cognitive science, developmental psychology, and education, as well as scholarship from contemplative traditions concerning the cultivation of positive development, to highlight a set of mental skills and socioemotional dispositions that are central to the aims of education in the 21st century. These include self‐regulatory skills associated with emotion and attention, self‐representations, and prosocial dispositions such as empathy and compassion. It should be possible to strengthen these positive qualities and dispositions through systematic contemplative practices, which induce plastic changes in brain function and structure, supporting prosocial behavior and academic success in young people. These putative beneficial consequences call for focused programmatic research to better characterize which forms and frequencies of practice are most effective for which types of children and adolescents. Results from such research may help refine training programs to maximize their effectiveness at different ages and to document the changes in neural function and structure that might be induced.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/92125/1/cdep240.pd

O Quadril?tero Ferr?fero - MG, Brasil : aspectos sobre sua hist?ria, seus recursos minerais e problemas ambientais relacionados.

O fundador da Escola de Minas de Ouro Preto, o mineralogista Franc?s Claude Henrique Gorceix, definiu certa vez o estado de Minas Gerais como aquele com o peito de a?o e o cora??o de ouro. Essa compara??o vale em especial para o Quadril?tero Ferr?fero (QF), uma regi?o cl?ssica da geologia e da minera??o brasileira, que se estende entre as cidades de Belo Horizonte (NW), Itabira (NE), Ouro Preto (SE) e Congonhas (SW). Ocorrem aqui jazidas de ferro (Fe), mangan?s (Mn), ouro (Au), bauxita e pedras preciosas, como top?zio e esmeralda. A ?rea foi descoberta pelos bandeirantes no final do s?culo XVII quando buscavam pela esmeralda, raridade sobre a qual circulavam na ?poca colonial os boatos mais insanos. Entretanto, eles encontraram o ouro, e este era preto, motivo pelo qual a localidade do descobrimento passou a ser chamada de Ouro Preto. Os primeiros achados do metal nobre em torno de 1693 levaram a uma verdadeira febre aur?fera. Houve naquele tempo uma migra??o enorme em dire??o ?s montanhas ao redor desse lugar, denominado inicialmente Villa Rica. E essa migra??o trouxe todos os seus aspectos positivos e negativos. Assim, antigas cr?nicas mencionam que no norte do pa?s monast?rios inteiros eram despovoados, porque tamb?m os monges foram atra?dos pelo novo Eldorado. A procura dos aventureiros pelo metal nobre foi t?o grande que a superpopula??o da ?rea causou em 1701 uma enorme emerg?ncia de fome, que suprimiu grande parte da popula??o. Muitos morreram com os bolsos cheios de ouro, mas n?o havia nada comest?vel que pudesse ser adquiridos com seus tesouros. Uma vez que as ocorr?ncias mais produtivas nos aluvi?es e sedimentos do rio do Carmo foram exploradas rapidamente, a febre aur?fera chegou a um fim j? ap?s aproximadamente quarenta anos. Somente muito mais tarde surgiu na regi?o a explora??o subterr?nea organizada do ouro. Como conseq??ncia a regi?o em torno de Ouro Preto perdeu muito de sua import?ncia econ?mica, ainda assim a cidade permaneceu por muito tempo o centro administrativo de Minas e posteriormente foi promovida ? capital do Estado. Com o reconhecimento geol?gico e a explora??o das enormes ocorr?ncias do min?rio de ferro na ?rea do QF ap?s a segunda guerra mundial, Minas Gerais viveu um renascimento econ?mico e transformou-se num dos estados mais ricos do Brasil. Ouro Preto com seu centro hist?rico bem conservado, suas igrejas barrocas ricas em ouro e obras de arte, seus museus, entre eles o bem conhecido museu mineral?gico da Escola de Minas, e outros monumentos e aspectos interessantes se transformou em uma j?ia tur?stica nacional

Impacts of climate and humans on the vegetation in northwestern Turkey: palynological insights from Lake Iznik since the Last Glacial

The Marmara region in northwestern Turkey provides a unique opportunity for studying the vegetation history in response to climate changes and anthropogenic impacts because of its location between different climate and vegetation zones and its long settlement history. Geochemical and mineralogical investigations of the largest lake in the region, Lake Iznik, already registered climate-related changes of the lake level and the lake mixing. However, a palynological investigation encompassing the Late Pleistocene to Middle Holocene was still missing. Here, we present the first pollen record of the last ca. 31 ka cal BP (calibrated kilo years before 1950) inferred from Lake Iznik sediments as an independent proxy for paleoecological reconstructions. Our study reveals that the vegetation in the Iznik area changed generally between (a) steppe during glacials and stadials indicating dry and cold climatic conditions, (b) forest-steppe during interstadials indicating milder and moister climatic conditions, and (c) oak-dominated mesic forest during interglacials indicating warm and moist climatic conditions. Moreover, a pronounced succession of pioneer trees, cold temperate, warm temperate, and Mediterranean trees appeared since the Lateglacial. Rapid climate changes, which are reflected by vegetation changes, can be correlated with Dansgaard-Oeschger (DO) events such as DO-4, DO-3, and DO-1, the Younger Dryas, and probably also the 8.2 event. Since the mid-Holocene, the vegetation was influenced by anthropogenic activities. During early settlement phases, the distinction between climate-induced and human-induced changes of the vegetation is challenging. Still, evidence for human activities consolidates since the Early Bronze Age (ca. 4.8 ka cal BP): cultivated trees, crops, and secondary human indicator taxa appeared, and forests were cleared. Subsequent fluctuations between extensive agricultural uses and regenerations of the natural vegetation become apparent

Carbonates and selected geochemistry composition for sediments from Lake Iznik for the past 31 ka cal BP

This study examines the forcing mechanisms driving long-term carbonate accumulation and preservation in lacustrine sediments in Lake Iznik (northwestern Turkey) since the last glacial. Currently, carbonates precipitate during summer from the alkaline water column, and the sediments preserve aragonite and calcite. Based on X-ray diffraction data, carbonate accumulation has changed significantly and striking reversals in the abundance of the two carbonate polymorphs have occurred on a decadal time scale, during the last 31 ka cal BP. Different lines of evidence, such as grain size, organic matter and redox sensitive elements, indicate that reversals in carbonate polymorph abundance arise due to physical changes in the lacustrine setting, for example, water column depth and lake mixing. The aragonite concentrations are remarkably sensitive to climate, and exhibit millennial-scale oscillations. Extending observations from modern lakes, the Iznik record shows that the aerobic decomposition of organic matter and sulphate reduction are also substantial factors in carbonate preservation over long time periods. Lower lake levels favour aragonite precipitation from supersaturated waters. Prolonged periods of stratification and consequently enhanced sulphate reduction favour aragonite preservation. In contrast, prolonged or repeated exposure of the sediment-water interface to oxygen results in in situ aerobic organic matter decomposition, eventually leading to carbonate dissolution. Notably, the Iznik sediment profile raises the hypothesis that different states of lacustrine mixing lead to selective preservation of different carbonate polymorphs. Thus, a change in the entire lake water chemistry is not strictly necessary to favour the preservation of one polymorph over another

Pollen and non-pollen palynomorph data from Lake Iznik, NW Turkey (last 31 ka cal BP)

The Marmara region in northwestern Turkey provides a unique opportunity for studying the vegetation history in response to climate changes and anthropogenic impacts because of its location between different climate and vegetation zones and its long settlement history. Geochemical and mineralogical investigations of the largest lake in the region, Lake Iznik, already registered climate-related changes of the lake level and the lake mixing. However, a palynological investigation encompassing the Late Pleistocene to Middle Holocene was still missing. Here, we present the first pollen record of the last ca. 31 ka cal BP (calibrated kilo years before 1950) inferred from Lake Iznik sediments as an independent proxy for paleoecological reconstructions. Our study reveals that the vegetation in the Iznik area changed generally between (a) steppe during glacials and stadials indicating dry and cold climatic conditions, (b) forest-steppe during interstadials indicating milder and moister climatic conditions, and (c) oak-dominated mesic forest during interglacials indicating warm and moist climatic conditions. Moreover, a pronounced succession of pioneer trees, cold temperate, warm temperate, and Mediterranean trees appeared since the Lateglacial. Rapid climate changes, which are reflected by vegetation changes, can be correlated with Dansgaard-Oeschger (DO) events such as DO-4, DO-3, and DO-1, the Younger Dryas, and probably also the 8.2 event. Since the mid-Holocene, the vegetation was influenced by anthropogenic activities. During early settlement phases, the distinction between climate-induced and human-induced changes of the vegetation is challenging. Still, evidence for human activities consolidates since the Early Bronze Age (ca. 4.8 ka cal BP): cultivated trees, crops, and secondary human indicator taxa appeared, and forests were cleared. Subsequent fluctuations between extensive agricultural uses and regenerations of the natural vegetation become apparent

Characterization of organic sedimentation in an Amazonian floodplain by lignin phenols, Lago Santa Ninha, PA, Brazil

International audienceFloodplains are areas of carbon production, storage and exportation. The Amazon River and its tributaries are accompanied in its low course by floodplains that cover an area of about 300,000-500,000 km2. There are many different vegetal communities in the floodplain and its drainage basin. Changes in the community structures have an influence in the quantities and kinds of organic matter deposited. The TA11 core was collected in the Santa Ninha Lake, 3.5 km from the channel that connects the floodplain to the Amazonas River. Samples have been collected from the following plants found in the region: Aquatic poaceae, Pistia stratiotes, Echinochloa polystachia, Echinochloa spectabilis, Eichornia azurea, Eichornia crassipes and Paspalum repens. Elementary analysis (C,N), isotopic analysis (C,N and moleculary analysis (lignin phenols) have been performed on these samples and on the sediment. Lignin is a biomarker found in the vasculary plants. It is divided in four different groups of phenols and the reasons between the groups reveal the contribution of the terrestrial vegetation to the whole organic matter and may be used to set apart different organic matter sources. Researches about the vegetal distribution and the focus of phenols that come from the lignin of lacustrine cores may reveal information about the taxonomic changes in the terrestrial paleovegetation and consequently about the paleoenvironments and paleohydrology of the floodplain. The aquatic poaceae, Echinochloa polystachia, Echinochloa spectabilis, and Paspalum repens present the highest values from 13C (-12.5; -12.7 and -13.1 respectively), typical of C4 plants and high values of lignin (5.97; 8.51 e 16.50 mg/100mg CO). Three different rates of sedimentation have been observed in the TA11 core: 0,42; 1,16 and 1,10 g m-2 yr-1 which allowed to estimate the core base age at about 110 years. The core average for lignin is 1.96mg/100mg CO. At the depths of 30.5; 30 e 110 cm, lignin values are 3.23; 3.86 and 2.95 mg/100mg CO respectively, some of the largest in the region. In all the sub-samples analyzed, the values of the Siringil group were larger than the values of the Vanilil group. These data indicate a high contribution of organic matter from woody origin in the floodplain sedimentation. Although phytoplankton production is high in these systems, this more labile matter is probably degraded in the water column during settling and resuspension phases

Geochemical focusing and sequestration of manganese during eutrophication of Lake Stechlin (NE Germany)

Significant sedimentation of manganese (Mn) in form of manganese oxides (MnOx) and the subsequent formation of authigenic calcium-rich rhodochrosite (Mn(Ca)CO3) were observed in the seasonally stratified hard water Lake Stechlin in north-eastern Germany. This manganese enrichment was assumed to be associated with recent eutrophication of the formerly oligotrophic lake. The mechanisms and processes involved were examined by analysing: (i) short sediment cores obtained from seven locations along a depth transect ranging from 69.5 m (the deepest point) to 38 m; (ii) sediment traps located at 20 m and 60 m water depths; (iii) water column profiles; and (iv) porewater profiles at 69.5 m and 58 m depths. Sedimentary Mn enrichment was observed at water depths below 56 m and increased to more than 25 wt% at the deepest site. Between 2010 and 2017, Mn accumulation at the deepest site was 815 g Mn m−2. Transfer of Mn from the shallower towards the deepest parts of the lake was initiated by reductive dissolution of MnOx and diffusion of dissolved Mn from the sediment to the overlying water column. Manganese was then dissipated via turbulent mixing and subsequently oxidised to MnOx before being transported towards the deepest zone. Transformation of the redeposited MnOx to Mn(Ca)CO3 favoured the final burial of Mn. We show that eutrophication and the areal spreading of anoxic conditions may intensify diagenetic processes and cause the spatial redistribution of Mn as well as its effective burial. Contrary to many previous findings, we show that increases of Mn and Mn/Fe can also be used as indicators for increasing anoxic conditions in previously oligotrophic lakes.Leibniz-Gemeinschaft http://dx.doi.org/10.13039/501100001664Leibniz-Institut für Gewässerökologie und Binnenfischerei (IGB) im Forschungsverbund Berlin e.V. (3473

Delayed Western Gotland Basin (Baltic Sea) ventilation in response to the onset of a Mid-Holocene climate oscillation

The marine-terrestrial Baltic ecosystem is sensitive to a range of environmental forcing and thresholds. Multi-archive investigations of its evolution require a precise synchronization of the considered archives. Here, we apply globally common cosmogenic radionuclide production rate variations to synchronize 10Be records from brackish Western Gotland Basin (Baltic Sea) and terrestrial lake Tiefer See (NE Germany) sediments to the atmospheric 14C time-scale and investigate phase-relationships in proxy responses in the southern Baltic realm associated with the onset of a centennial Mid-Holocene climate oscillation ∼5800 a BP. Based on paired molybdenum and titanium records, we identify a 98 ± 81-year delay in Western Gotland Basin ventilation, compared to the terrestrial response at the onset of the recorded Mid-Holocene climate oscillation. Most plausible mechanism for this delay is strengthened stratification in response to enhanced freshwater input during the first decades of the oscillation