Dust deposition during the EarlyHolocene on the loess plateaus of the Vojvodina region in Northern Serbia
Slobodan Markovic (1), Alida Timar-Gabor (2), Thomas Stevens (3), Zhengtang Guo (4), Qingzhen Hao (4), Yang Song (4), Ulrich Hambach (5), Frank Lehmkuhl (6), Zoran Peric (1), Igor Obreht (6), Christian Zeeden (6), Daniel Veres (7,2), and Milivoj Gavrilov (1)
Abstract. Partly coeval flowstones formed in fractured gneiss and schist were studied to test the palaeoclimate significance of this new type of speleothem archive on a decadal-to-millennial timescale. The samples encompass a few hundred to a few thousand years of the Late Glacial and the earlyHolocene. The speleothem fabric is primar- ily comprised of columnar fascicular optic calcite and aci- cular aragonite, both indicative of elevated Mg / Ca ratios in the groundwater. Stable isotopes suggest that aragonite is more prone to disequilibrium isotope fractionation driven by evaporation and prior calcite/aragonite precipitation than calcite. Changes in mineralogy are therefore attributed to these two internal fracture processes rather than to palaeo- climate. Flowstones formed in the same fracture show sim- ilar δ 18 O changes on centennial scales, which broadly cor- respond to regional lacustrine δ 18 O records, suggesting that such speleothems may provide an opportunity to investigate past climate conditions in non-karstic areas. The shortness of overlapping periods in flowstone growth and the complexity of in-aquifer processes, however, render the establishment of a robust stacked δ 18 O record challenging.
The warming of the Holocene again allowed the expansion of forests in the study area. Paper IV first uses high resolution pollen (accumulation rate) data to study the successive forest formation, including the immigration of hazel. The results show that (thermophilous) tree taxa expanded step wise, possibly reflecting the stepwise character of the warming. Pine and tree birch started to expand during an initial warming period (between ~11,600 and 11,500). Temporarily, also first stands of hazel may have established. A second warmer period at 11,200 cal. BP, following the cold Preboreal oscillation, enabled the permanent establishment of hazel, yet it widely spread only after 11,000 cal. BP. Further thermophilous taxa only expanded in possibly again warmer conditions after 10,000 cal. BP. Paper IV then explores vegetation patterns and composition during these suc- cessive stages using the extended Downscaling Approach. This version of the Downscaling Approach again uses pollen percentage data. It addresses the problems related to differential pollen production, dispersal and the use of percentage data by applying a simulation approach. Based on a pre-defined pattern of site types, the approach searches for that vegetation composition, which in simulations produces pollen deposition most similar to empiric pollen deposition from sediment cores. The approach reveals that initially pine and birch es- tablished, as during the Allerød period, in largely separate stands with pine dominating on sandy soils and birch dominating on fine grained soils. Also open vegetation persisted, possibly due to seasonal drought, mainly on fine grained soils. Hazel later mainly spread on sites that received additional wetness from ground or surface water; it did not enter pine dominated forests on well drained sandy soils. Overall, the early Holo- cene vegetation of the study area was sharply differentiated by soil humidity and fertility.
The flood loam was deposited by the Chaco rivers (Ríos Pilcomayo, Bermejo, Salado and other small rivers) originat- ing in the Andes mountains. These rivers transported fine grained material and remobilized aeolian sediments from the upper courses. These processes are still going on. After excessive rainfall events in the 1980’s, rivers in the Chaco in- undated wide areas from the lower to the middle parts of the fans and flood loam was deposited. This material is unsorted due to short distance transport by water and re-deposition processes (flooding) in the flat area. The fine grained sedi- ments sometimes block and displace the river courses. The Río Paraguay-Paraná base level system caused widely ex- tended inundations due to backwater during periods with heavy rainfall as observed during the 1990s. Its tributar- ies retained more than 200 km upstream in the Chaco and formed temporary lakes and ponds. OSL ages of the corre- sponding sediments (Table 2) cluster around the humid Late Glacial-earlyHolocene period coinciding with the humid Tauca Phase in the High Andes.
During the late Holocene, more frequent and/or intensified El Niño conditions might be responsible for drier conditions over northern Borneo (Partin et al., 2007). Decreased pre- monsoonal rainfall observed in northern Australia around ~2 ka point to intensified El Niño (Denniston et al., 2013). In contrast, Dubois et al. (2014) suggest that prolonged dry periods in response to enhance rainfall seasonality and a weaker AISM resulted in drier conditions around 2 ka (Dubois et al., 2014). On the other hand, speleothem stable oxygen isotope records from Flores indicate a Holocene maximum in rainfall between 3 and 2 ka and a slight decrease in rainfall thereafter (Griffiths et al., 2009; 2010). Overall, monsoonal rainfall reconstructions reveal a strengthening of the AISM over southern Indonesia during the late Holocene either related to shifts in the ITCZ (Tierney et al., 2010; Mohtadi et al., 2011; Russell et al., 2014; Kuhnt et al., 2015) or solar activity (Steinke et al., 2014). In contrast to an intensified AISM, upwelling off Java and thus AIWM winds were weaker during the late Holocene compared to the earlyHolocene, which is most likely associated with a weaker northern Hemisphere summer insolation during the late Holocene (Mohtadi et al., 2011). In line with slightly positive SST anomalies as deduced from corals of the eastern Indian Ocean (Abram et al., 2009), increased rainfall between 2 ka and 1 ka in Sumatra suggests a more negative IOD-like mean state of the Indian Ocean (Niedermeyer et al., 2014).
The results from the NW Black Sea cores show that the Black Sea underwent significant hydrological changes during its lake stage. While the Last Glacial Maximum was characterised by a stable hydrologic budget, late glacial meltwater pulses derived from the Scandinavian Ice Sheet caused the deposition of characteristic reddish-brown clay layers. The strongly depleted isotopic signature of the meltwater led to a temporary drop in the δ 18 O values of the Black Sea. A sudden shift in the hydrochemical properties of the Black Sea is marking the transition from the cold Oldest Dryas to the warm Bølling-Allerød period. The favourable conditions during this period initiated the precipitation of authigenic calcite through enhanced phytoplankton activity that increased the Sr and Mg concentration in the water column as reflected in an abrupt rise of the Mg/Ca and Sr/Ca ratios. The Mg/Ca record shows, that a 1-2°C cooling of the Black Sea deep waters took place during the Younger Dryas, which was also manifested by an interruption of the authigenic calcite precipitation, that resumed later during the earlyHolocene. δ 18 O values became heavier since 15 kyr calBP but this increase occurred in a more gradual manner than in the trace element record and largely reflects the influence of enriched δ 18 O of meteoric precipitation.
export of fresher and cooler subpolar waters to the SPMW formation region in the eastern SPG. Assuming this link can be applied to longer timescales, a stronger polar vortex would also have led to an intensification of the Trade Winds. This is in line with enhanced local upwelling off Northwest Africa during the earlyHolocene (deMenocal, 2000) . Accordingly, we propose that an increase in upwelling and thus higher local primary productivity between 9.0 and 8.0 ka resulted in higher carbon rain rates over the core site. The decomposition of organic matter causes steeper δ 13 C dissolved inorganic carbon gradients in surface sediments, and thus lighter δ 13 C values (Schmiedl et al., 2004) are recorded by infaunal benthic foraminifera communities. The significant co-variation between the three intermediate water proxy records demonstrates that lighter δ 13 C values correlate with the formation of colder (r = 0.35, p < 0.01, n = 53) and fresher (r = 0.57, p < 0.0001, n = 52) ENACW and thus as discussed above, with a reduced upper AMOC limb.
Clay mineral investigations were carried out to study sediments in general and delta in particular. The variation of the clay mineral distribution in Yangtze delta plain in different Holocene stages is determined by several major physical factors, i.e. sea level fluctuation, climate change, and sediment sources (WANG Z. et al. 2005). Smectite distribution of earlyHolocene was linked to the rapid sea-level rise, which induced land inundation. As verified by pollen assemblages, high amount of chlorite in earlyHolocene can be correlated to colder temperature and high amount of kaolinite in mid-Holocene were possibly associated with a warm climate. The terrigenous sediment sources of late Pleistocene and earlyHolocene were primarily derived from the provincial highlands and the sediments of late Holocene were proved from the Yangtze basin. Moreover, after MOON (2000), the abundance of chlorite is inversely related to that of smectite. The kaolinite content is constant, and so it is clear that chlorite originating from the Han River was transformed to smectite by pedogenesis during regression periods. Therefore, the relative contents of clay minerals from the unconsolidated materials in the tidal flat of Youngjong Island can be used as indicators of transgression and regression in accordance with the sea-level fluctuation.
In contrast to the lakes in NW India that dried out or became seasonal after 4 cal ka (Prasad and Enzel, 2006), the Lonar Lake has retained water level until today and provides the best preserved, high resolution record of Holocene climate variability from the core monsoon region. The driest period (>11.4 cal ka) (Fig. 5.2a), was marked by soil developing on the dry lake bed and followed by a short period (~300 years) of intensive erosion, fluctuating salinity as indicated by the presence of evaporative gaylussite, and high aquatic productivity (low Corg/N, high δ 13 Corg and δ 15 N) that resulted from a sudden increase in precipitation (Fig. 5.3). During ~11–6.2 cal ka, wet conditions are indicated by the lowest δ 13 Corg values (indicating C3 plants) and low clastic influx. We infer stratified, deep- water conditions between 11–9 cal ka when seasonally laminated (varved) sediments were deposited. Counterintuitively, the earlyHolocene evaporative carbonates show less negative δ 18 O values that could be related to reduce dilution by the isotopically depleted stream inflow during periods of higher lake levels. However, the amplitude of spatial isotopic variability (8.5‰ for δ 13 C and 4‰ for δ 18 O) in surface bulk carbonates (Anoop et al., 2013b) cannot alone explain the range of variability seen in the core bulk carbonate isotopic composition. We exclude any contribution from the winter westerlies as this region was under the influence of the ISM during the Holocene (Prasad and Negendank, 2004) – the only possible explanation for the apparently reverse trend in carbonate isotope values is a change in source water composition or paths of precipitation tracks related to shifts in the mean position of the ITCZ (Haug et al., 2001).
Around ca. 10.000 BP a distinct change in sedimentology and pollen stratigraphy indicates an abrupt climatic change towards more humid condi- tions. The formation of black organic lake muds demonstrates the presence of permanent lakes at all four sites during the early and mid Holocene. The return of wetter conditions resulted in a rapid northward spread of southern tree taxa from the Sudanian and Guinean zone into the Manga Grasslands (e.g. Alchornea, Syzygium, Uapaca). However, most of these taxa were confined to extrazonal swamp forests, which became established within the interdune depressions. In terms of physiognomy, the vegetational change on the surrounding dune fields was only minor. The savanna remained substantially open although a gradual floristic change towards a Sahelo-Sudanian savanna is indicated by the occurrence of the Sudanian trees Butyrospermum and Bombax.
Our experiments reveal how temperature gradients, the most simple out-of-equilibrium setting, can give rise to local environments that stabilize molecular replication against the entropic tendencies of dilution, degradation and negative length selection. A thermal gra- dient drives replication of oligonucleotides with an inherent direc- tional selection of long over short sequence lengths. Interestingly, when replication and trapping inside the pore reach their steady state, the newly replicated molecules leave the trap with the feeding ﬂow. This ensures an efﬁcient transfer of the genetic poly- mers to neighbouring pore systems. Heat dissipation across porous rock was probably in close proximity to other non-equili- brium settings of pH, ultraviolet radiation and electrical potential gradients, all of which are able to drive upstream synthesis reactions that produce molecular building blocks. An exciting prospect of the presented experiments is the possible addition of mutation pro- cesses to achieve a sustained Darwinian evolution of the molecular population inside the thermal gradients of the early Earth. Accordingly, the onset of molecular evolution could have been facilitated by the natural thermal selection of rare, long nucleic acids in this geologically ubiquitous non-equilibrium environment.
84 S. Lorenz et al.: Late Glacial to Holocene dunes and palaeosols at Krakower See
Figure 1. Simplified map of Quaternary sediments and landforms in central Mecklenburg after ZGI (1968a) and ZGI (1968b). Important lakes are numbered: 1 Woseriner See, 2 Langsee, 3 Dobbertiner See, 4 Goldberger See, 5 Damerower See, 6 Krakower See, 7 Plauer See, 8 Drewitzer See, 9 Fleesensee, 10 Tiefer See (Klocksiner Seenkette). Krakow am See (A) and Goldberg (B) are small towns in the mapped area.
muchclosertootherrecordsfromthenorthernhemisphere than previousstudiessuggested:NeitherwerestrongneoglacialadvancesevidentnorwastheLIA maximum advancelimitedtothephaseafter1750CE.AconceptualglacierchronologyfortheeastͲ ern NyainqêntanglhaRangehasthusbeenachieved.ThisimpliescommonlargeͲscaleclimaticforcing for allglaciersintheregion.OurresultssuggestthattemperaturechangesarepredominantlyconͲ trolling theLIAglacierfluctuationsintheinvestigatedsettings.ProxydataindicatesmonsoonalpreͲ cipitation washighthroughouttheLIA,providingsufficientaccumulationmaterial.However,monͲ soonal precipitationandtemperaturesarecloselylinkedthroughcloudcoverinthestudyarea.FurͲ thermore, themorphologicaldetailsofthestudiedglaciersareheterogeneous,underliningthegreat influence oflocaltopoclimaticsettings.NumericaldatingofHolocenemorainesremainsagreatchalͲ lenge inthisremotearea,asdemonstratedforOSLand 14 C methods.Thus,furtherworkisneededto obtain betterdatingresults;besideminimumagesfromtreerings,highͲsensitivitycosmogenicnuͲ clide datingisapromisingapproachtoachieveabsoluteagesofLIAmorainedepositsinthefuture. Additionally, morepaleoclimatearchivesareneeded tofurther clarify theregional climateforcing mechanisms duringthelast1000years.WesuggestthatfuturestudiesonglacierchangeandpaleoͲ climate, at least in complex high mountain environments such as the eastern Nyainqêntanglha Range, should carefully consider whether and how the local geomorphological configuration may influence theinvestigatedarchives,owingtothegreatimpactthisfactormayhaveontheinterpretaͲ
much closer to other records from the northern hemisphere than previous studies suggested: Neither were strong neoglacial advances evident nor was the LIA maximum advance limited to the phase after 1750 CE. A conceptual glacier chronology for the east‐ ern Nyainqêntanglha Range has thus been achieved. This implies common large‐scale climatic forcing for all glaciers in the region. Our results suggest that temperature changes are predominantly con‐ trolling the LIA glacier fluctuations in the investigated settings. Proxy data indicates monsoonal pre‐ cipitation was high throughout the LIA, providing sufficient accumulation material. However, mon‐ soonal precipitation and temperatures are closely linked through cloud cover in the study area. Fur‐ thermore, the morphological details of the studied glaciers are heterogeneous, underlining the great influence of local topoclimatic settings. Numerical dating of Holocene moraines remains a great chal‐ lenge in this remote area, as demonstrated for OSL and 14 C methods. Thus, further work is needed to obtain better dating results; beside minimum ages from tree rings, high‐sensitivity cosmogenic nu‐ clide dating is a promising approach to achieve absolute ages of LIA moraine deposits in the future. Additionally, more paleoclimate archives are needed to further clarify the regional climate forcing mechanisms during the last 1000 years. We suggest that future studies on glacier change and paleo‐ climate, at least in complex high mountain environments such as the eastern Nyainqêntanglha Range, should carefully consider whether and how the local geomorphological configuration may influence the investigated archives, owing to the great impact this factor may have on the interpreta‐
The circumstances, formats, configurations of resources, and contexts that make these various temporal configurations possible are explored in the contributions to this special issue. They present empirical studies across a variety of settings, ranging from ordinary conversation (Pekarek Doehler; Vatanen et al.) to various types of institutional interactions (Deppermann & Schmidt; De Stefani; Heath & Luff; Mondada). They analyze verbal and embodied responses in terms of the grounds for their production, the sequential environments in which they occur, their orderly coordination with the action that prompts them, and their interactional import: What cues do participants orient to in order to be able to provide an adequate response before the responded-to action is completed? What do such early responsive actions tell us about the complex interplay of syntax, prosody, and bodily-visual conduct? And how do such on-line features interact with participants’ orientation to institutional expectancies, shared mutual knowledge and experience, or routine concatenation of actions known to members?
Mapping by Lehmkuhl (1998) in the Turgen-Kharkhiraa mountains (Fig. 1a, No. 4) found almost no moraines preserved between the above-described LIA limits and the late Pleistocene LLGM ice margin. Based on luminescence dating of aeolian cover beds overlying the local moraines, alluvial fans and lake terraces, Grunert and others (2000) suggested two major ice advances in the area and correlated them to expanded glaciation during MIS2 and 4. Pötsch and others (2015) presented new CRN dating results from the Kharkhiraa gol valley supporting this view. Their results indicate major ice advances during early MIS4 (74–71 ka) and MIS2 (25–20 and 18–17 ka). During the late Pleistocene,
Fig. 3: Comparison of weathering indices (Kronberg & Nesbitt 1981) from Bw horizons in NE Germany; (A) Late Glacial Bw horizon (“Finow soil”) from Blankenförde (Küster & Preusser 2009); (B) Late Glacial – Holocene Bw horizon from Blankenförde (Küster & Preusser 2009); (C) Late Glacial – Holocene Bw horizon from the Hirschfelder Heide (Bussemer 2005); (D) Late Glacial – Holocene Bw horizon from Prötzel (Bussemer 1999); (E) Holocene Bw Horizon (red) from Kratzeburg (this study). The theoretical weathering path according to Kronberg & Nesbitt (1981) is shown by the arrow.