Bert Rein

El Niño variability off Peru during the last 20,000 years

Here we present a high-resolution marine sediment record from the El Nino region off the coast of Peru spanning the last 20,000 years. Sea surface temperature, photosynthetic pigments, and a lithic proxy for El Nino flood events on the continent are used as paleo–El Nino–Southern Oscillation proxy data. The onset of stronger El Nino activity in Peru started around 17,000 calibrated years before the present, which is later than modeling experiments show but contemporaneous with the Heinrich event 1. Maximum El Nino activity occurred during the early and late Holocene, especially during the second and third millennium B.P. The recurrence period of very strong El Nino events is 60–80 years. El Nino events were weak before and during the beginning of the Younger Dryas, during the middle of the Holocene, and during medieval times. The strength of El Nino flood events during the last millennium has positive and negative relationships to global and Northern Hemisphere temperature reconstructions.

A late Eemian aridity pulse in central Europe during the last glacial inception.

Investigating the processes that led to the end of the last interglacial period is relevant for understanding how our ongoing interglacial will end, which has been a matter of much debate (see, for example, refs 1, 2). A recent ice core from Greenland demonstrates climate cooling from 122,000 years ago driven by orbitally controlled insolation, with glacial inception at 118,000 years ago. Here we present an annually resolved, layer-counted record of varve thickness, quartz grain size and pollen assemblages from a maar lake in the Eifel (Germany), which documents a late Eemian aridity pulse lasting 468 years with dust storms, aridity, bushfire and a decline of thermophilous trees at the time of glacial inception. We interpret the decrease in both precipitation and temperature as an indication of a close link of this extreme climate event to a sudden southward shift of the position of the North Atlantic drift, the ocean current that brings warm surface waters to the northern European region. The late Eemian aridity pulse occurred at a 65° N July insolation of 416 W m-2, close to todays value of 428 W m-2 (ref. 9), and may therefore be relevant for the interpretation of present-day climate variability.

A quantitative high-resolution summer temperature reconstruction based on sedimentary pigments from Laguna Aculeo, central Chile, back to AD 850

We present a pigment-based quantitative high-resolution (five years) austral summer DJF (December to February) temperature reconstruction for Central Chile back to AD 850. We used non-destructive in situ multichannel reflection spectrometry data from a short sediment core of Laguna Aculeo (33°50′S/70°54′W, 355 m a.s.l., central Chile). Calibration-in-time (period AD 1901—2000, cross-validated with split periods) revealed robust correlations between local DJF temperatures and total sedimentary chlorin (relative absorption band depth (RABD) centred in 660—670 nm RABD660;670: r=0.79, P<0.01; five-years triangular filtered) and the degree of pigment diagenesis (R 660nm/670 nm: r=0.82, P<0.01; five-years triangular filter). Root Mean Squared Error values are small (between 0.24 and 0.34°C) suggesting that most of the reconstructed decadal-scale climate variability is significant. Our data provide quantitative evidence for the presence of a Medieval Climate Anomaly (in this case, warm summers between AD 1150 and 1350; ΔT = +0.27 to +0.37°C with respect to (wrt) twentieth century) and a very cool period synchronous to the ‘Little Ice Age’ starting with a sharp drop between AD 1350 and AD 1400 (−0.3°C/10 yr, decadal trend) followed by constantly cool (ΔT = −0.70 to −0.90°C wrt twentieth century) summers until AD 1750. The structure of variability is consistent in great detail with annually resolved tree-ring based warm-season temperature and river discharge reconstructions from northern Patagonia (42°S) for the past 400 years, with qualitative climate reconstructions from Andean glacier fluctuations, and with hydrological changes in Patagonian lake sediment records.

Rapid climate change during the early Holocene in western Europe and Greenland

Based on microfacies analyses of seasonally laminated varved sediments from lake Holzmaar, Germany, we report evidence of decadal-to century-scale climate variability during the early Holocene. The shifts in climate are documented in the thickness variations and changes in the composition of the varves in response to subtle shifts in limnological conditions. The close similarity between the Holzmaar varve record and the GRIP oxygen isotope record during 7.4-9.0 calendar (cal.) ka suggests that the high frequency climatic variations in both regions were controlled by the same mechanism. Our more detailed studies covering the central 409-yr period (∼7.846-8.255 cal. ka, encompassing the 8.2 ka event) document for the first time, on a seasonal scale, the changing precipitation regimes in western Europe during these climate shifts. We show (i) that winters were drier and summers shorter and cooler in western Europe during colder periods in Greenland, (ii) in contrast to the present-day climate in the Holzmaar region, summer rains were clearly reduced during the early Holocene, and (iii) the climate not only changed rapidly (< 5 years) but recurring drier events were common during the studied period. In the Holzmaar record, the 8.2 ka event is the most prominent and longest of a series of short-term clirnatic oscillations.

Geochemical evidence for Holocene palaeodischarge variations in lacustrine records from the Westeifel Volcanic Field, Germany : Schalkenmehrener Maar and Meerfelder Maar

Various chemical elements (Fe, Mn, U, Mo) can be transported in both dissolved and solid form and then deposited into lakes. Geochemical profiles of these elements in lacustrine records are therefore potential palaeoclimatic proxies since there should be a positive correlation between discharge from the catchment and dissolved element input. Flux rates for the dissolved input of uranium Ul(t) and the total allochthonous minerog enic deposit were calculated for an annually laminated sediment record from the Lake Schalkenmehrener Maar (SMM). Calculated Ul(t) values were critically examined with the help of monitoring data (hydrochemistry, soil chemistry) from the modern Meerfelder Maar (MFM) catchment. The calculated Ul(t)-profile and the variation of varve thickness show a corresponding pattern. The palaeoproductivity of Lake SMM with respect to diatomaceous matter was clearly controlled by the discharge from the catchment. The deposition rate of allochthonous minerogenic matter, which received significant aeolian contributions from a remote source during the early Holocene, has been found to correlate with the Ul(t) values. The deposit of dust on the lake surface is undoubtedly influenced by rainfall events during which fine particles are washed out from the atmosphere. A higher discharge of groundwater from the lakes catchment is indicated at around 10 200 (D1), 8500 (D2), 7150 (D3), 6000 (D4) and between about 4050 and 3300 varve years BP (D5), Significantly lower discharge was obtained for periods around 11 000, 9500, 5000 and after about 3050 varve years BP. There are several indications of a lowering of the SMM lake level between 8100 and 7300 varve years BP. A drier climate can, therefore, be suggested as likely for this period. In addition to three early Holocene periods, which display an increase in element input into Lake MFM (thus supporting the positive discharge indications D1, D2, D3 from the SMM sediment profile), a general increase of discharge since the Neolithic period due to anthropogenic forest clearance can be inferred from the MFM sediment record.

Young tectonic and halokinetic movements in the North-German-Basin: its effect on formation of modern rivers and surface morphology

Field mapping of fluvial terraces, aerial photographs, ground penetrating radar and seismic data from gas and oil exploration were used at four different locations to detect young tectonic and halokinetic movements in the North-German-Basin. i) The course of the Rivers Weser and Aller follow precisely a shallow Tertiary graben on the northwestern flank of the Verden salt diapir. Recent local depressions and vegetation anomalies on the alluvial plain have the same orientation as the strike direction of the faults at subsurface depth. Apparently, the river follows tectonic lines, and thus the river sediments can be used for the interpretation of recent crustal movements. ii) The Wedehof diapir, in contrast, is topped by a local topographic high which follows exactly the shape of the underlying salt. Either the diapir formed an obstacle for the advance of the continental glaciers or one has to assume halokinetic uplift of more than 50 m during the post-Saalian Pleistocene. Either way, the Wedehof diapir shows control of the modern surface morphology by halokinesis. iii) The course of the river Hunte, in contrast, outside the area of salt diapirism, shows anomalies of incision and terrace width over a local updoming caused by tectonic inversion of distinct blocks in the basin. The confluence of several tributaries of the Hunte lies exactly over the updoming of Barnstorf. Thus, the rivers do not avoid the local high, but focus in this area, which is characterised by a graben on top of the domestructure, as visible in seismic profiles. Again, tectonism controls river development. iv) The last case study is from Lake Plon, where seismic profiles reveal that linear shorelines of the lake parallel the flanks of two local graben structures of Tertiary age. It is apparent that the Weichselian glaciers that formed the lake and the surrounding moraines interacted with the existing grabens. The Tertiary morphology in the North German basin was apparently draped by Quaternary glacial deposits, but rivers and lakes that dominate the topography of the modern landscape still reflect the geodynamic centers of Tertiary tectonism and halokinesis. Faults from the depth of the Tertiary penetrate the Quaternary strata and allow upward fluid migration, which becomes visible on aerial photographs as linear vegetation anomalies.

Hyperspectral imaging spectroscopy: a promising method for the biogeochemical analysis of lake sediments

Abstract. We investigate the potential of hyperspectral imaging spectrometry for the analysis of fresh sediment cores. A sediment-core-scanning system equipped with a camera working in the visual to near-infrared range (400 to 1000 nm) is described and a general methodology for processing and calibrating spectral data from sediments is proposed. We present an application from organic sediments of Lake Jaczno, a freshwater lake with biochemical varves in northern Poland. The sedimentary pigment bacteriopheophytin a (BPhe a) is diagnostic for anoxia in lakes and, therefore, an important ecological indicator. Calibration of the spectral data (BPhe a absorption ∼800 to 900 nm) to absolute BPhe a concentrations, as measured by high-performance-liquid-chromatography, reveals that sedimentary BPhe a concentrations can be estimated from spectral data with a model uncertainty of ∼10%. Based on this calibration model, we use the hyperspectral data from the sediment core to produce high-resolution intensity maps and time series of relative BPhe a concentrations (∼10 to 20 data points per year, pixel resolution 70×70  μm2). We conclude that hyperspectral imaging is a very cost- and time-efficient method for the analysis of lake sediments and provides insight into the spatiotemporal structures of biogeochemical species at a degree of detail that is not possible with wet chemical analyses.

10. Holocene and Eemian varve types of Eifel maar lake sediments

Abstract Varves of the Holocene and of the last interglacial were investigated in two sediment sequences from Eifel maar lakes. The modern maar with Schalkenmehrener Maar Lake and the dry maar lake West Hoher List have the same size, are two kilometres apart at the same altitude, but the Eemian lake was much deeper. The sediments of both lakes are dominated by autochthonous sediments, mainly from diatom-dominated algae. Differences in the palaeoproductivity and in calcite precipitation are probably not climatically controlled but due to lake basin morphometry and the carbonate reservoir in the catchment areas. The occurrence of dry periods with aeolian dust deposition during the last interglacial is the major difference of the last interglacial to the Holocene sedimentation. The discrimination of natural sedimentation processes versus human-controlled clastic input during the last 3000 years is however poorly understood and complicates the interpretation of the clastic sediments during the time of the Little Ice Age and their comparison with the sedimentation during the Late Eemian Aridity Pulse (LEAP).

Evidence for the Climate During the Late Maunder Minimum from Proxy Data and Model Simulations Available Within KIHZ

The knowledge constructed within the project “Klima in historischen Zeiten” (KIHZ) about the Late Maunder Minimum (LMM), based upon corals, lake and marine sediment records, ice cores and speleothems, is reviewed. The data are compared to a simulation with the climate model ECHO-G. It is found that the LMM was an event of global scale, with a cooling on the entire Northern hemisphere and in the tropics, while a weaker warming may have taken place on the Southern Hemisphere. The model results are mostly consistent with the empirical evidence. However, the empirical data are not very conclusive so that any claims that the dynamics behind the simulated LMM would equal the dynamics of the real event should be considered with care.