Karl Stattegger

Spectrum: spectral analysis of unevenly spaced paleoclimatic time series

Abstract A menu-driven PC program (SPECTRUM) is presented that allows the analysis of unevenly spaced time series in the frequency domain. Hence, paleoclimatic data sets, which are usually irregularly spaced in time, can be processed directly. The program is based on the Lomb–Scargle Fourier transform for unevenly spaced data in combination with the Welch-Overlapped-Segment-Averaging procedure. SPECTRUM can perform: (1) harmonic analysis (detection of periodic signal components), (2) spectral analysis of single time series, and (3) cross-spectral analysis (cross-amplitude-, coherency-, and phase-spectrum). Cross-spectral analysis does not require a common time axis of the two processed time series. (4) Analytical results are supplemented by statistical parameters that allow the evaluation of the results. During the analysis, the user is guided by a variety of messages. (5) Results are displayed graphically and can be saved as plain ASCII files. (6) Additional tools for visualizing time series data and sampling intervals, integrating spectra and measuring phase angles facilitate the analysis. Compared to the widely used Blackman–Tukey approach for spectral analysis of paleoclimatic data, the advantage of SPECTRUM is the avoidance of any interpolation of the time series. Generated time series are used to demonstrate that interpolation leads to an underestimation of high-frequency components, independent of the interpolation technique.

Fundamental Modes and Abrupt Changes in North Atlantic Circulation and Climate over the last 60 ky — Concepts, Reconstruction and Numerical Modeling

Centennial- to millennial-scale changes in global climate over the last 60 ky were first documented in ice cores from Greenland, with ice sheets around the North Atlantic and its thermohaline circulation (THC) as prime candidates for a potential trigger mechanism. To reach a new quality in understanding the origin and causal links behind these changes, two strategies were intimately tied together in this synthesis, high-resolution 3-D ocean modeling and paleoceanographic reconstructions. Here, five time series with a time resolution of several decades and various time slices of surface and deep-water paleoceanography were established from hundreds of deep-sea cores for the purpose of monitoring rapid changes across the North Atlantic and testing or initiating model results. Three fundamental modes were found to operate Atlantic THC. Today, mode I shows intensive formation of North Atlantic Deep Water (NADW) and strong heat and moisture fluxes to the continents adjacent to the North Atlantic. Peak glacial mode II leads to a reduction in NADW formation by 30-50%, in line with a clear drop in heat flux to Europe. The glacial Nordic Seas, however, remain ice-free during summer and little influenced by meltwater, in contrast to the sea west ofIreland, where iceberg meltwater blocks an eastbound flow into the Norwegian Sea and induces a cold longshore current from Faeroe to the Pyrenees. The subsequent Heinrich 1 (HI) meltwater mode III leads to an entire stop in NADW and intermediate-water production as well as a reversed pattern of THC, stopping any heat advection from the central and South Atlantic to the north. In contrast to earlier views, the Younger Dryas, possibly induced by Siberian meltwater, began with mode I and ended with mode III, continuing into the Preboreal. Modeling the impact of modes I to III on the global carbon budget, we find that the atmosphere has lost 34-54 ppmv CO2 from interglacial to glacial times, but has gained 23-62 ppmv CO2 at the end of HI within a few decades, equivalent to 33-90% of modem, man-made CO2 release. The robust 1500-y Dansgaard- Oeschger (D-O) cycles and their multiples of as much as 7200 years, the Heinrich event cycles, are tied to periodical changes between THC modes I/II and II/III. In the Irminger Sea rapid D-O coolings are in phase with initial meltwater injections from glaciers on East Greenland, here suggesting an internal trigger process in accordance with binge-purge models. Ice rafting from East Greenland and Iceland occurs only 240-280 y later, probably inducing a slight sea-level rise and, in tum, Heinrich ice rafting from the Laurentian ice sheet during H1, H2, H4, H5. At H1 a major surge from the Barents shelf has lagged initial cooling by 1500 y and entails the most prominent and extended reversal in Atlantic THC over the last 60 ky (probably also at the end of glacial stage 4, at H6). Meltwater stratification in the Inninger Sea reaches its maximum only 640 y after initial meltwater injection and induces, via seasonal sea-ice formation, brine-water injections down to 4 km water depth, signals leading the classic D-O jump to maximum warmth by only 125 y. It may be inferred from this short-phase lag that brine water-controlled deep-water formation probably entrains warm water from further south, thereby forming the key trigger mechanism for the final tum-on of the Atlantic THC mode II roughly within a decade (or mode I, in case of favorable Milankovitch forcing).

Major and trace elements of stream sediments from the lowermost Amazon River

Geochemical results from river-bottom sediments taken from the lowermost Amazon River are presented. Bedload sediments were analyzed for 10 major and 38 minor elements. Mud bulk sediments exhibit a tendency to a slight enrichment in Cr, Mn, Rb, Sr, Zr, Cs, Ba and Hf, pointing to the importance of these elements in the silt fraction. Generally, Cu, Zn, Rb, Cs, Ba and Sn are clearly associated with clay minerals, while Y, Zr, Hf, Th and U are associated with heavy minerals. The location of this area in an intensive chemical weathering environment results in the strong modification of sediment composition. Chemical weathering processes strongly modify original sediment composition and can be recognized apart from provenance processes on the basis of their geochemical signature. Discriminant analysis makes the detection of less marked differences in sediment characteristics possible, thus, improving the accuracy of distinctions between groups. The Amazon Mouth and Xingu Mouth (XM) are discriminated principally by the textural maturity of their sediments. The Jari Mouth (JM) shows highest Co and Fe2O3 contents. Despite similarities between the Amazon North Branch (ANB) and Amazon South Branch (ASB), the ANB can be differentiated on the basis of its higher Sr, P2O5, and Na2O contents, the ASB on the basis of its higher Zn, MnO, and CaO contents, and the Estreitos de Breves (EST) based on its higher abundance of Ni and Cu. Higher contents in P2O5, Fe, and Mn are related to laterite covers.

North Atlantic ocean circulation during the last glacial maximum and subsequent meltwater event: A numerical model

A numerical model that was forced with reconstructed sea surface temperature and sea surface salinity values of the North Atlantic was used to investigate three major states of the North Atlantic ocean circulation since the last glaciation: the modern state, the last glacial maximum (LGM), and an important meltwater event (MWE) near 14,200 - 13,200 C-14 yr B.P. Preliminary results of numerical experiments show significant differences of the three outlined modes in the northern North Atlantic and especially in the Norwegian Greenland Seas (NGS). The overturning strength of the North Atlantic salinity conveyor belt and northward heat transport decreased somewhat in the LGM and drastically in the MWE case. Accordingly, the North Atlantic Deep Water production decreased by 30% during the LGM and almost ceased at the MWE. The climatologically most important changes occurred during the MWE and are characterized by a reversal in the circulation of the surface water in the northeastern part of the NGS, Implying that the North Atlantic Current did not reach the Norwegian Sea anymore.

Depositional sequences on a late Pleistocene–Holocene tropical siliciclastic shelf (Sunda Shelf, southeast Asia)

This study describes, and reviews, the stratigraphic architecture of the worlds largest but least known tropical siliciclastic shelf using the sequence-stratigraphic concept. The Sunda Shelf provides conditions particularly suited for reconstructing its depositional history due to a low gradient and extreme width, the presence of huge paleo-valley systems and abundant filled channels, tectonic stability during the Quaternary, and high sediment input due to a large catchment area. We investigated the subsurface along the most prominent paleo-valley by shallow-seismic surveying and 36 gravity cores controlled by 80 radiocarbon dates. The deposits during sea-level fall prior to the last glacial maximum lowstand and the subsequent deglacial rise correspond to four systems tracts: (a) wide, partly detached prograding deltaic clinoforms indicate forced regression related to a regressive systems tract; (b) sparse shoreline deposits and widespread soil formation refer to a lowstand systems tract; (c) rapidly backstepping coastline-related deposits form a confined transgressive systems tract without stacking patterns and are mainly restricted to the paleo-valley system; (d) a thin marine mud cover extends as a condensed section over the whole shelf area (the base of a highstand systems tract). The stratigraphic architecture on the central Sunda Shelf strata over the past 50,000 years is the result of the interplay of three major factors: (1) rapid sea-level changes, (2) locally pronounced physiography and (3) changes in sediment supply that determined the distribution and accumulation pattern

Computerized Modeling of Sedimentary Systems

Computerized modeling is a powerful tool to describe the complex interrelations between measured data and the dynamics of sedimentary systems. Complex interaction of environmental factors with natural variations and increasing anthropogenic intervention is reflected in the sedimentary record at varying scales. The understanding of these processes gives way to the reconstruction of the past and is a key to the prediction of future trends. Especially in cases where observations are limited and/or expensive, computer simulations may substitute for the lack of data. State-of-the-art research work requires a thorough knowledge of processes at the interfaces between atmosphere, hydrosphere, biosphere, and lithosphere, and is therefore an interdisciplinary approach.

Depositional style and subsidence history of the Turpan Basin (NW China)

The Turpan Basin has a complex polycyclic sedimentary and tectonic history from Late Permian to late Tertiary time. Main stratigraphic boundaries are unconformities that bound tectonically induced sedimentary cycles. The depositional style reflects a continental environment exhibiting changes from alluvial fan/fluvial to lacustrine conditions within each cycle. More than 7000 m of clastic sediments accumulated during the evolution of the basin. Paleocurrent analysis reveals a complex pattern of sediment dispersal pathways into the basin. On the southern margin of the basin, the transport direction is always directed from south to north indicating sediment sources in the Jueluotage Shan, while in the northern part the Late Jurassic uplift of the Bogda Shan provided an important source area from the Early Cretaceous onwards with transport directions from north to south. After basin formation during the Late Permian, the Turpan Basin underwent first thermal subsidence and then flexural subsidence. The thermal subsidence took place during the Late Permian and Early Triassic following the period of magmatic activities in this region. The flexural subsidence was throughout the Middle Triassic to early Tertiary induced by collisions and accretions onto the south Asian continental margin of the Qiangtang Block in the Late Triassic/Early Jurassic, the Gangdise Block in latest Jurassic/earliest Cretaceous, and the Indian Subcontinent in the latest Cretaceous/early Cenozoic.

THE FOUNDATION SEAMOUNT CHAIN : A FIRST SURVEY AND SAMPLING

The Foundation Seamounts form a 1400 km-long chain on the Pacific plate from 32 °S, 127 °W to the Pacific-Antarctic spreading axis at 38 °S, 111 °W. Previously only known from sparse single-beam echosoundings and satellite altimetry, we present here the first multibeam bathymetric survey and geological sampling results. We confirm that the submarine topography correlates with the altimetry, and that the chain is volcanic rather than tectonic or microcontinental in origin. The chain can be divided up morphologically and geochemically into three section: (1) west of 125 °W large flat-topped volcanoes composed of incompatible-element depleted lavas ( ≈ 1) of a near-ridge origin with little or no plume influence, (2) between 125 and 115 °W true intraplate volcanoes with incompatible element enrichment ( > 1.9) generated over the Foundation plume, (3) east of 115 °W E-W-trending volcanic ridges with compositions ( 2.0-0.3) suggestive of interaction between the plume and the Pacific-Antarctic spreading axis. On the spreading axis moderate incompatible element enrichments ( ≈0.8, cf. ≈ 0.3 outside the Foundation area) also suggest plume influence. It appears that the activity of the Foundation plume in the last few million years has (1) significantly waned and (2) become wholly channeled towards the spreading axis. The Foundation plume may be in the process of “dying”.

Mikrofazies, Fossilien und Herkunft der Kalk-Gerölle im Karbon-“Flysch” der Betischen Kordilleren, Spanien

ZusammenfassungDie im Karbon-“Flysch” von Ardales, La Peluca und Velez Rubio in den Betischen Kordilleren in Konglomerathorizonten auftretenden Kalk-Gerölle werden hinsichtlich ihrer Mikrofazies typisiert und durch Conodonten, Foraminiferen, Korallen und Kalkalgen zeitlich eingestuft. Die Gerölle haben Givet- bis Oberdevon- sowie Unterkarbon-bis Bashkirium-Alter. Nach Fazies und Fossilführung der Gerölle sind zwei Konglomerathorizonte zu unterscheiden (Polymiktes Konglomerat und Marbella-Konglomerat). Die mikrofazielle Analyse der Gerölle aus dem höheren Visé bis Bashkirium legt eine Ableitung aus einer differenzierten, wahrscheinlich im nordafrikanischen Raum beheimateten Flachwasser-Plattform nahe. Schwermineralanalysen der paläozoischen granatführenden Sandsteine innerhalb der flyschoiden Serien ergeben keine eindeutige Antwort auf die Frage nach dem metamorphen Liefergebiet dieser Sedimente. Bei einem Vergleich der untersuchten Konglomerate mit den Karbon-Konglomeraten von Menorca (siehe M. BUCHROITHNER et al. 1980) zeigen sich trotz fazieller Ähnlichkeiten Unterschiede im Alter und in der Mikrofazies eines Teiles der Kalk-Gerölle.SummaryLimestone pebbles within several conglomerates of Carboniferous “flysch” sediments near Ardales, La Peluca and Velez Rubio (Betic Cordillera) were studied with regard to the microfacies types and to the age which can be determined according to conodonts, foraminifera, corals and calcareous algae. The pebbles are Givetian to Upper Devonian and Lower Carboniferous to Bashkirian in age. Two conglomerate horizons (Polymict Conglomerate and Marbella Conglomerate) can be differentiated according to facies and fossils. Microfacies analysis of Late Viséan to Bashkirian limestone pebbles indicates a source area within a facially differentiated shallow-water platform which may have been located originally in North Africa. Heavy mineral analysis of the garnet bearing sandstones within the flyschoid series give no distinct indication of the metamorphic source area of these sediments. When conglomerates of the Betic Cordillera are compared with those of the Carboniferous of Menorca (see M. BUCHROITHNER et al., 1980) similarities in facies as well as dissmilarities with respect to the age and the microfacies of some limestone pebbles can be seen.RésuméLe microfaciès et la faune des cailloux calcaires des gisements conglomératiques du “flysch” Carbonifère près d’Ardales, de La Peluca et de Velez Rubio (Cordillères Bétiques) sont examinés. Les cailloux sont d’un âge Givétien à Dévonien supérieur et Carbonifère inférieur à Bashkirien. On peut distinguer deux niveaux (Conglomérat Polymict, Conglomérat de Marbella) à cause du faciès et de la faune des cailloux. Des analyses microfacièlles des cailloux Viséens supérieurs à Bashkiriens démonstrent la démonstrant d’une plateforme marine peu profonde et bien differenciée. Cela indique que leur origine se trouve en Afrique du Nord. La question de la région d’erosion métamorphe de grenateux sédiments clastiques et Paléozoiques est encore plus difficile. En dépit des ressemblances une concordance complète avec les conglomérats Carbonifères des Minorque ne peut pas être constatée.

Modeling sediment drifts: A coupled oceanic circulation‐sedimentation model of the northern North Atlantic

Modeling of sediment drifts in the northern North Atlantic is achieved by coupling the ocean general circulation model sensitivity and circulation in the northern North Atlantic (SCINNA) to the sedimentation models sedimentation in the northern North Atlantic (SENNA) and particle tracing in the northern North Atlantic (PATRINNA). SCINNA is based on the primitive equations with conservation of mass, momentum, heat, and salt. SENNA and PATRINNA are driven by temperature, salinity, and velocity fields derived from SCINNA. Sediments are supplied from the surface and from the continental margins. The modeling includes three-dimensional sediment transport in the water column and two-dimensional processes in a thin bottom layer. Sediments are allowed to resuspend repeatedly, thus offering the possibility of stepwise transport. SENNA calculates erosion, transport, and deposition of sediments, resulting in sedimentation patterns for specific time intervals. PATRINNA models the transport paths of single sediment grains corresponding to the ocean circulation. Sensitivity experiments for the modern state and for the last glacial maximum show differences in the large sediment; drifts between the Charlie Gibbs Fracture Zone and the Greenland-Scotland Ridge for these two time slices. The sediment supply changes with the differing circulation modes and is strongly constrained by topography.