Isoprenoid and branched GDGT-based proxies for surface sediments from marine, fjord and lake environments in Chile

Proxies based on glycerol dialkyl glycerol tetraether (GDGT) lipids from archaea [isoprenoid GDGTs] and bacteria [branched (br) GDGTs] in 33 surface sediments from marine, fjord and lake systems between 25°S and 50°S in Chile were analyzed. The regional TEXH86 calibration obtained from the marine and fjord sediments and mean annual surface temperature (T = 59.6 × TEXH86 + 33.0; r2 0.9; n = 23) is statistically identical to the global ocean calibration based on suspended particulate material in terms of slope, but not in terms of intercept. The regional surface and subsurface TEXH86 calibrations were statistically different from the existing global ocean core top calibrations. The TEX86 calibration model based on most of the relatively large lakes studied here (T = 50.7 × TEX86 - 11.8; r2 0.9; n = 5) is statistically identical to the global lake calibration. The relatively high TEX86 values from smaller lakes suggested an additional source for isoprenoid GDGTs, likely terrestrial or aquatic methanogenic archaea. Application of the soil-calibrated MBT'/CBT (methylation and cyclization of br GDGTs, respectively) temperature proxy to the marine and fjord sediments resulted in an overestimation of continental mean annual air temperature (MAAT), suggesting in situ production of certain br GDGTs in the water column or surface sediment. For the lakes, MBT'/CBT-based surface air temperature estimates were 3–6 °C below MAAT. However, temperature estimates from the lake-specific MBT/CBT global calibration were in good agreement with mean annual surface temperature for all the lakes. The results highlight the need for testing local vs. global calibrations of GDGT-based proxies before their application for palaeoenvironmental reconstruction

Dokumentation von kurzfristigen Klimaschwankungen des Spaetquartaers in Sedimenten des westlichen aequatorialen Atlantiks

SIGLEAvailable from TIB Hannover: RO 7630(124) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Holocene salinity changes in the southwestern Black Sea: a reconstruction based on dinoflagellate cysts

Dinoflagellate cysts were used as a proxy for reconstructing the salinity variations during the Holocene in the southwestern Black Sea. The aim of this study was to determine the timing of the reconnection between the Black and Marmara seas. Core GeoB 7625-2, located 50 km northeast of the mouth of the Sakarya River, was sampled with a 200-year resolution between 7.42 and 0.52 ka BP. The lower part of the core was sampled with varying resolution. A distinct change in the dinoflagellate cyst assemblages from freshwater/brackish water to saltwater was observed between ~ 8.25 and ~ 7.97 ka BP, which is ~ 0.6 ka earlier than observed in other dinoflagellate cyst studies. This discrepancy may indicate the diachronous salinification of the Black Sea. The freshwater to brackish water assemblage is dominated by Pyxidinopsis psilata and Spiniferites cruciformis, while the most important euryhaline species are Lingulodinium machaerophorum and cysts of Pentapharsodinium dalei. The average process length of Lingulodinium machaerophorum was used as a salinity proxy. Both proxies suggest a gradual reconnection between the Black and Marmara seas, and these findings confirm earlier studies. Peridinium ponticum is restricted to the Black Sea; abundance fluctuations of this species were controlled by salinity variations and changes in nutrient concentrations. Earlier studies have demonstrated that the 800 to 500 year cycles observed in the sedimentary record are related to the intensity of the discharge of the Sakarya River, and linked to the North Atlantic Oscillations. Cysts of Pentapharsodinium dalei and Spiniferites spp. fluctuated synchronously with the clay layer frequency. The poor preservation of these forms may indicate shelfal transport during periods of intense river discharge. The variation in relative abundance of heterotrophic species does not correlate with the clay layer frequency, since upwelling and nutrient supply also influenced their abundances. Lingulodinium machaerophorum shows the highest relative abundances during periods with reduced river input

Long-chain alkenones in Baltic Sea surface sediments: New insights

C37 alkenones produced by certain haptophytes of the Isochrysidales are valuable sedimentary biomarkers used to estimate sea surface temperature (SST) in the open ocean. However, in coastal seas the role of salinity gradients on alkenone producing species and SST estimates is poorly known. Alkenones were analyzed in surface sediments from the marine Skagerrak region and the entire brackish Baltic Sea. Three types of alkenone distribution patterns were identified: type A distribution, which resembles the distribution in Emiliania huxleyi, type B distribution, which is similar to Ruttnera lamellosa, Isochrysis galbana and Pseudoisochrysis paradoxa distributions, although these haptophytes are absent from the Baltic Sea, and type C distribution, which is also found in worldwide lake sediments. These types of distribution are apparent in the percentage of C37:4 alkenone (%C37:4), which is significantly negatively correlated to sea surface salinity (SSS). The distribution of alkenones very likely results from distinct alkenone-producing haptophytes, whose spatial distribution is ultimately related to SSS, as supported by the hydrogen isotope fractionation (α) between alkenones and water. and correlate more significantly than with both SST and SSS, probably due to the superimposed effect of changing alkenone-producing species. The application of and as SST proxies results in unrealistic Holocene temperature records for the southern Baltic Sea, but %C37:4 as a SSS proxy reveals reasonable salinity changes. Interestingly, a C32 hopanoic acid was found abundantly as the methyl ester in the ketone fractions and may represent a marker for (cyano)bacterial biomass in the Baltic Sea

Long-chain alkenones in Baltic Sea surface sediments: New insights

C37 alkenones produced by certain haptophytes of the Isochrysidales are valuable sedimentary biomarkers used to estimate sea surface temperature (SST) in the open ocean. However, in coastal seas the role of salinity gradients on alkenone producing species and SST estimates is poorly known. Alkenones were analyzed in surface sediments from the marine Skagerrak region and the entire brackish Baltic Sea. Three types of alkenone distribution patterns were identified: type A distribution, which resembles the distribution in Emiliania huxleyi, type B distribution, which is similar to Ruttnera lamellosa, Isochrysis galbana and Pseudoisochrysis paradoxa distributions, although these haptophytes are absent from the Baltic Sea, and type C distribution, which is also found in worldwide lake sediments. These types of distribution are apparent in the percentage of C37:4 alkenone (%C37:4), which is significantly negatively correlated to sea surface salinity (SSS). The distribution of alkenones very likely results from distinct alkenone-producing haptophytes, whose spatial distribution is ultimately related to SSS, as supported by the hydrogen isotope fractionation (α) between alkenones and water. and correlate more significantly than with both SST and SSS, probably due to the superimposed effect of changing alkenone-producing species. The application of and as SST proxies results in unrealistic Holocene temperature records for the southern Baltic Sea, but %C37:4 as a SSS proxy reveals reasonable salinity changes. Interestingly, a C32 hopanoic acid was found abundantly as the methyl ester in the ketone fractions and may represent a marker for (cyano)bacterial biomass in the Baltic Sea

WESTROP: Wechselwirkung zwischen Land und Meer sowie ihre Bedeutung fuer die Stoffkreislaeufe und Stromsysteme im westlichen tropischen Atlantik: Palaeozeanographie, Sedimentologie und Biogeochemie. Teilprojekt C: Palaeozeanographische Rekonstruktion des Brasil und Nord Brasil Stromes im Spaetquartaer Abschlussbericht

Paleoceanographic studies on sediment cores from the upper continental slope of NE-Brazil, retrieved during R/V Victor Hensen cruise JOPS-II in spring '95, revealed high resolution climatic records of the last 85,000 years. Due to the influence from both continental processes and regional oceanography, these sediment records also present a good archive for the reconstruction of the history of land-ocean interactions. Using in total 35 AMS "1"4C ages and stable isotope records a detailed stratigraphical control was obtained. To reconstruct past oceanographic conditions we used X-ray fluorescence measurements, carbonate and organic carbon determinations of the bulk sediment and oxygen and carbon isotope measurements on the test of the planktonic foraminifera species Globigerinoides ruber (pink) and Globigerinoides sacculifer. Due to high sedimentation rates of the investigated cores and 2.5 to 5 cm sampling interval, the time resolution is about 100-500 years. We suggest that short termed climatic oscillations as described from Greenland and Antarctic ice core records and North Atlantic sediment cores are also documented in the marine records of low latitudes. A comparison of our sediment records with the GISP2 ice core signals reveals strong similarities. We assume that short termed variations in the atmospheric circulation, surface ocean currents, and sea level fluctuations during the isotope stages 2 to 4 are responsible for the modulation of the records. (orig.)Available from TIB Hannover: F98B222 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

Vegetation and environmental dynamics in the southern Black Sea region since 18 kyr BP derived from the marine core 22-GC3

Sediments from the Black Sea, a region historically dominated by forests and steppe landscapes, are a valuable source of detailed information on the changes in regional terrestrial and aquatic environments at decadal to millennial scales. Here we present multi-proxy environmental records (pollen, dinoflagellate cysts, Ca, Ti and oxygen isotope data) from the uppermost 305 cm of the core 22-GC3 (42°13.53′N, 36°29.55′E) collected from a water depth of 838 m in the southern part of the Black Sea in 2007. The records span the last ~ 18 kyr (all ages are given in cal kyr BP). The pollen data reveal the dominance of the Artemisia-steppe in the region, suggesting rather dry/cold environments ~ 18–14.5 kyr BP. Warming/humidity increase during melt-water pulses (~ 16.1–14.5 kyr BP), indicated by δ18O records from the 22-GC3 core sediment and from the Sofular Cave stalagmite, is expressed in more negative δ13C values from the Sofular Cave, usually interpreted as the spreading of C3 plants. The records representing the interstadial complex (~ 14.5–12.9 kyr BP) show an increase in temperature and moisture, indicated by forest development, increased primary productivity and reduced surface run-off, whereas the switch from primary terrigenous to primary authigenic Ca origin occurs ~ 500 yr later. The Younger Dryas cooling is clearly demonstrated by more negative δ13C values from the Sofular Cave and a reduction of pines. The early Holocene (11.7–8.5 kyr BP) interval reveals relatively dry conditions compared to the mostly moist and warm middle Holocene (8.5–5 kyr BP), which is characterized by the establishment of the species-rich warm mixed and temperate deciduous forests in the low elevation belt, temperate deciduous beech-hornbeam forests in the middle and cool conifer forest in upper mountain belt. The border between the early and middle Holocene in the vegetation records coincides with the opening of the Mediterranean corridor at ~ 8.3 kyr BP, as indicated by a marked change in the dinocyst assemblages and in the sediment lithology. Changes in the pollen assemblages indicate a reduction in forest cover after ~ 5 kyr BP, which was likely caused by increased anthropogenic pressure on the regional vegetation

Forearc uplift rates deduced from sediment cores of two coastal lakes in south-central Chile

The present paper introduces a newapproach for deriving information about local forearc tectonics and related uplift rates based on the study of lake sediments.We investigated two coastal lakes at the south-central Chile margin, lakes Lanalhue and Lleu Lleu, located south of the Arauco Peninsula (38°S). Both lakes developed within the valleys of ancient rivers that once drained to the Pacific Ocean, being subsequently dammed by rising sills in the late Pleistocene/early Holocene. Seismic profiling and sedimentological analyses of cores from both lakes revealed similar successions consisting of marine to brackish sediments covered by lacustrine deposits. Radiocarbon dating indicates that the marine–lacustrine transition occurred at 8 ka and 8.15 ka, respectively. The correlation of this transition with global sea-level curves allowed the calculation of local uplift rates for the Holocene.Uplift rates for the lake basins amount to 0.42±0.71 and 0.49±0.44 mm/a, respectively, which are consistent with rates determined from a late Pleistocene marine terrace in the area. However, conspicuously higher, though likely transient, vertical movements at 8.83±2.7 mm/a and 11.36±1.77 mm/a, respectively, were calculated for the sills that block both lakes nowadays. These barriers are interpreted to be the surface expression of a blind reverse fault associated to the Morguilla fault system, a seismically-active structure that controls uplift and folding along the adjacent Arauco Peninsula