Variability of the Arctic front during the last climatic cycle: application of a novel molecular proxy

In the Nordic Seas, the Arctic front (AF) marks the boundary between the waters of the North Atlantic Drift/Norwegian Current and those of the Arctic domain. Long- or short-term shifts in the position of the AF may affect climate conditions in the northern hemisphere. Arctic water masses are also the loci of modern open ocean convection; hence, defining these areas in the past is important for reconstructing and modelling ocean circulation and its variability. C₃₇ alkenones are biomarkers for some algae of the Class Prymnesiophyceae (e.g. coccolitho-phorids such as Emiliania huxleyi). These alga occur in most parts of the oceans, in ice-free conditions, and are found nowadays throughout the Nordic Seas. We have related the sedimentary abundance of the tetraunsaturated C₃₇ alkenone (C_37:4) to two types of water masses in the Nordic seas. In locations affected by Atlantic water masses percentages of C_37:4 are less than 5%, whereas in Arctic type water masses these increase to more than 5%. We propose that this observation can be used as a modern analogue to reconstruct the position of the AF in North Atlantic Quaternary sediments. Using this novel molecular proxy we can infer that the southward migration of the AF in the NE Atlantic reached ≈ 50 °N during the last glacial maximum (LGM), but perhaps only 60 °N during the Younger Dryas, and that ocean conditions free of sea ice prevailed throughout the Northern North Atlantic in summer.     

海洋的生产率

冰期海洋生产率的增高可能为降低冰期大气CO2分压起了很大的作用。主要有三个因素促进了海洋生产率的提高:（1）强的风力作用使赤道洋流和沿岸上升流加强;（2）上升水体营养成分的增加,反过来,这又要受全球营养物质重新分配的机制控制;（3）来源于陆地的、携带营养物质的河水和（或）粉尘的增加。海洋高生产率对降低大气CO2浓度     

Sedimentologische Merkmale für die Untergrenze der Wellenwirkung im Persischen Golf

Zusammenfassung In den rezenten Kalksedimenten der Flache und Inselbereiche des Persischen Golfs gibt die Korngrößenverteilung einen deutlichen Hinweis auf die Basis der Wellentransportkraft in 40 m (vor Inseln) bis gegen 70 m (über den Flanken der Flache) (Abb. 6).In den feinkörnigen Mergelsedimenten vor der iranischen Küste hängt jedoch die Korngrößenverteilung allein von der Verfügbarkeit ab und erlaubt somit keinerlei Schluß auf den Tiefgang der Wellentätigkeit (Abb. 3 und 4).In diesen Mergeln findet sida eine eng begrenzte, bandartige Zone mit maximaler Produktion und Sedimentation von Echinodermen-Hartteilen (Echiniden und Ophiuren) (Abb. 5). Die wechselnde Tiefenlage dieser Zone (12–14 m im Schutze hinter einer Insel, sonst 20–30 m, je nach Exposition der Probenlokalität zum freien Seegang) läßt sich mit der Untergrenze der Wellenwirkung in Beziehung setzen. Dafür sprechen unter anderem hydrographische Messungen und zahlreiche Beobachtungen von Biologen.Faßt man alle diese Wassertiefenangaben über die Untergrenze der Wellenwirkung in einem schematischen Querprofil des Persischen Golfs zusammen, so ergeben sie einen schüsselförmigen Querschnitt (Abb. 7), dessen tiefste Punkte (50–70 m) entsprechen ungefähr den theoretisch berechenbaren Maximalwerten der Wellentiefenwirkung.

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The grain size distribution in recent carbonate sediments of the shoals and island areas of the Persian Gulf yields clear evidence of an effective wave base in depths ranging from 40 m (near islands) to about 70 m (on the flanks of shallows) (Fig. 6).In contrast, the grain size distribution of the fine grained marl sediments off the Iranian coast is controlled solely by sediment availability and cannot be used as evidence for water movement and wave action (Fig. 3 and 4).A widespread, vertically restricted zone exists within these marly sediments which shows maximum production and sedimentation of echinoderm hard parts (Echinids and Ophiurans) (Fig. 5). The various depths in which this zone is found (12–14 m on the lee side of islands, otherwise 20–30 m depending upon the sample location in relation to fetch) can be easily correlated with the maximum depth of wave activity. This relationship is supported by biologic and other observations.A projection of all of these wave base depths into a composite cross-section of the Persian Gulf results in a bowl-shaped profile whose deepest points (50–70 m) correspond well with the theoretically calculated maximum wave base (Fig. 7).

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Résumé Dans le Golfe Persique la répartition granulométrique des sédiments calcaires récents, recueillis au niveau des «hauts-fonds» et devant les îles, indique de façon très nette la base du volume d'eau agitée par les vagues: elle varie de 40 m (autours des îles) à environ 70 m (sur les flancs des «hauts fonds») (fig. 6).Devant la côte Iranienne, par contre, la répartition granulométrique ne dépend, presque uniquement, que de la grande disponibilité de matériel fin à cet endroit; il n'est pas possible d'en déduire la limite de l'agitation de la mer par les vagues (fig. 3 et 4).Dans ces marnes se trouve une zone, longue et étroite, caractérisée par une production et une sédimentation maximale de pièces squelettiques d'échinodermes (Echinides-Ophiures) (fig. 5). Il est facile de mettre en relation cette zone (de 12 à 14 m à l'abri des îles, jusqu'à 20 et 30 m là où les vagues se propagent librement) et la limite inférieure, localement changeante, de l'effet des vagues; de nombreuses observations, de biologistes entre autres, abondent dans ce sens.Si l'on regroupe tous les résultats obtenus sur un profil transversal du Golfe Persique, ce profil est en forme de cuvette et les points les plus profonds (50–70 m) se situent à peu près à la profondeur déduite d'un calcul théorique (fig. 7).

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, 40 , — 70 . - . , . . . , , 50 70 .

     

Stratigraphic gaps at northern South China Sea margin reflect changes in Pacific deepwater inflow at glacial Termination Ⅱ

To constrain short-term changes of climate and oceanography in the northern South China Sea(SCS)over interglacial marine isotope stage(MIS)5.5,we studied planktic and benthic 18O records of seven marine sediment cores with a time resolution of70–700 yr.Using 6–8 tie points the planktic records were tuned to the U/Th chronology of speleothem 18O records in China and Europe.The last occurrence of pink Globigerinoides ruber marks the top of Heinrich stadial 11(HS-11)near 128.4 ka.HS-11 matches a 2300-yr long positive 18O excursion by 1.5/0.8‰both in planktic and benthic 18O records.Hence half of the planktic 18O signal was linked to increased upwelling of18O-and12C-enriched deep waters in the southwestern SCS.The increase was possibly linked to a strengthened inflow of Pacific deep waters through the Bashi Strait,that form a boundary current along the northern slope of the SCS,building a major sediment drift.At its lower margin near 2300–2400 m water depth(w.d.)Parasound records reveal a belt of modern erosion.At the end of glacial termination 2,stratigraphic gaps deleted HS-11 in core MD05-2904 and subsequent peak MIS 5.5 at ODP Site 1144.Likewise hiatuses probably earmarked all preceding glacial terminations at Site 1144 back to 650 ka.Accordingly,boundary current erosion then shifted~300 m upslope to~2040–2060 m w.d.These vertical shifts imply a rise in boundary current buoyancy,that in turn may be linked to transient events of North Pacific deepwater formation similar to that traced in SCS and North Pacific paleoceanographic records over glacial termination 1.     

Der äolische Sandstrom aus der W-Sahara zur Atlantikküste

Fairly constant winds from N to NNE (Fig. 2) prevail at present at the Western Sahara coast. Accordingly, a relatively narrow field of barchan dunes of only 80 km width reaches the coast SE of Cape Blanc (Fig. 1). Very uniform pebble plains form their ground of advance in the study area 60 km wide and 18 km long. Height H, volume V, and distance D from the southern border of the study area were determined for 963 dunes from aerial photographs (Figs. 5 and 6). Data on the dune advance rate were estimated for the particular region byCoursin (1964). Consequently it was possible to calculate a dune sand discharge amounting to 93 000 m³/yr/80 km crossing the southern border of the study area at the time the aerial photographs were taken. Based on the areal distribution pattern of the dunes this sand flow probably might increase threefold within the next 800 years (Fig. 7). Corresponding to the dune sand-discharge Q_T a saltation sand-discharge (Q and q), 50–100 times larger, of 5,0 and 7–13 Mio m³/yr/80 km, respectively, reaches the Atlantic from the Sahara. The estimates were derived from two independant calculations: the dune advance rate and the wind data. If one compares the wind transported load from the Sahara with that of the mouths of large rivers (e. g. Niger River: 40 Mio. m³/yr) it seems only of minor importance. Because of the relatively coarse grain sizes (Md≈220μm) the wind sand supply is deposited mainly along the strand line. Consequently, remarkably wide sebkha plains are built forward and the shelf becomes unusually narrow. Several independent criteria (e. g. Fig. 7) suggest a fairly young age, close to 500 years of the recent barchan field. A different wind direction, from the NE, and a lowered sea-level might have resulted during the ice-ages in as much as 5 times larger wind load (? 25 Mio m³/yr) arriving at the shelf edge and from there flowing down to the deep sea as turbidity currents. The present wind load has a content of iron oxides of roughly 1.2 per thousand. This value increased to 3.2 per thousand in Pleistocene dune sands.     

The progressive intensification of northern hemisphere glaciation as seen from the North Pacific

Ocean Drilling Project (ODP) site 882 (50°22′N, 167°36′E) provides the first high-resolution GRAPE density, magnetic susceptibility, carbonate, opal and foraminifera (planktonic and benthic) stable isotopes records between 3.2 and 2.4 Ma in the Northwest Pacific. We observed a dramatic increase in ice rafting debris at site 882 at 2.75 Ma, which is coeval with that found in the Norwegian Sea, suggesting that the Eurasian Arctic and Northeast Asia were significantly glaciated from 2.75 Ma onwards. Prior to 2.75 Ma planktonic foraminifera δ¹⁸O records indicate a warming or freshening trend of 4°C or 2‰ over 80 ka. If this is interpreted as a warm pre-glacial Pliocene North Pacific, it may have provided the additional moisture required to initially build up the northern hemisphere continental ice sheet. The dramatic drop in sea surface temperatures (SST>7.5°C) at 2.75 Ma ended this suggested period of enhanced SST and thus the proposed moisture pump. Moreover, at 2.79 and 2.73 Ma opal mass accumulation rates (MAR) decrease in two steps by five fold and is accompanied by a more gradual long-term decrease in CaCO₃ MARs. Evidence from the Southern Ocean (ODP site 704) indicates that just prior to 2.6 Ma there is a massive increase in opal MARs, the opposite to what is found in the North Pacific. This indicates that the intensification of northern hemisphere glaciation was accompanied by a major reorganisation of global oceanic chemical budget, possibly caused by changes in deep ocean circulation. The initiation of northern hemisphere glaciation occurred in the late Miocene with a significant build up of ice on southern Greenland. However, the progressive intensification did not occur until 3.5–3 Ma when the Greenland ice sheet expanded to include northern Greenland. Following this stage we suggest that the Eurasian Arctic and Northeast Asia glaciated at 2.75 Ma, approximately 100 ka before the glaciation of Alaska (2.65 Ma) and 200 ka before the glaciation of the North East American continent (2.54 Ma).     

Versuch einer Rekonstruktion der mitteltriadischen Paläogeographie um Innsbruck. Österreich

Zusammenfassung Zahlreiche detaillierte Profile wurden in der Serie des Alpinen Muschelkalks, in der Faziesgruppe des Wettersteinkalks und in den Partnach-Schichten aufgenommen. Die Analyse dieser Profile mit Hilfe karbonatsedimentologischer Methoden ermöglichte es, die mitteltriadischen Karbonatgesteine nach ihrer Fazies einer Reihe von verschiedenartigen Ablagerungsräumen vom Beckenbereich bis zu Riffplatten mit Inselbildungen zuzuordnen, einschließlich zahlreicher Faziesübergänge.Große Mächtigkeitsunterschiede (17,4) zeigen sich zwischen der Beckenfazies der Partnach-Schichten (234 m) und der Riffplattenfazies des Wetterstein-kalks (1730 m); weiters gibt es Gefüge- und komponentenmäßige Daten, die verläßlich für relativ flache Wassertiefen in beiden Bereichen sprechen. Beide Kriterien zusammengenommen, lassen in der Mitteltrias auf große synsedimentäre tektonische Bewegungen anläßlich Absenkungsdifferenzen von beinahe 1400 m schließen.Bei konkreter Umgrenzung der einzelnen Faziesräume im Bereich Karwendel —Inntal—Brennermesozoikum—Tamtaler Berge erweist es sich als heuristisch durchaus wertvoll, bestehende großtektonische Theorien vorerst einmal außer acht zu lassen, um zu einem einfachen, sedimentologisch zusammensetzbaren paläogeographischen Schema zu gelangen: ein küstenbeeinflußter Riffkomplex im S (Zentralalpen) und eine weitausgedehnte Riffplatte im Karwendel wachsen allmählich von N und S her in das zwischengelagerte breite Partnach-Becken (Inntal und südlich anschließendes Gebiet).

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North and South of Innsbruck, Austria the Alpine Middle Triassic is represented by three main lithologic units: the Alpine Muschelkalk Series, the Facies Complex of the Wettersteinkalk, and the Partnach-Schichten. Their sedimentology was examined with detailed measured sections. The mostly pure carbonate rocks show an enormous variety of facies ranging from basinal to reef complex.The 234 m thick Partnach-Schichten-basin-fazies and the 1730 m thick Wettersteinkalk-reef-complex represent, respectively, shallow basinal shelf deposition and the shallow water environment of a reef plate. This conclusion is supported by paleontologic, lithologic and structural evidence. These contrasting facts, great thickness differences and relatively similar water depths, are best explained by synsedimentary tectonic movements which took place in the Middle Triassic and are expressed by difference of subsidence amounting to about 1400 m. The Partnach-basin-facies is then the result of deposition on tectonic horst structures.Trying to define the exact regional distribution of the facies environments within the area Karwendel Mts.-Inn Valley-Brenner Mesozoika-Tarntaler Mts., heuristicaly it proves most advantageous first of all to disregard most of the existing great tectonic hypothesis. Only by sedimentologic means a simple paleogeographical pattern is developed: in the Central Alps a Southern, shore influenced reef-complex grew North into a wide, flat Partnach-basin which extended to the Inn Valley. Concurrently the large, E-W running, isolated reef plate of the Karwendel Mts. expanded on both sides into the bordering Part-nach-basins: the Inn Valley basin to the South and the Karwendel-Mulde basin to the North.

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Résumé Dans la série du Muschelkalk alpin et dans le faciès du Wettersteinkalk et dans les couches de Partnach de nombreuses coupes détaillées ont été prises. L'étude de ces profils, à l'aide de méthodes sédimentologiques concernant les roches carbonatées, a permis de coordonner, d'après leurs faciès, les sédiments carbonatés aux différents milieux de sédimentation représentés par toute une suite de différents faciès, allant du milieu des îles fossiles sur un platier récifal jusqu'au faciès d'un bassin.Les grandes différences d'épaisseur (1 7,4) que présentent les couches de Partnach (234 m) — faciès de bassin — et le Wettersteinkalk (1730 m) — faciès de récif -, de même la texture et les composants des roches, qui en outre indiquent la profondeur de l'eau, nous amènent à déduire des différences de niveau d'effondrement de 1400 m, conséquence des mouvements tectoniques synsédimentaires au Trias moyen. Par là on a également constaté que les couches de Partnach s'étaient déposées sur des horstes.La reconstruction des limites des différentes faciès des régions de Karwendel, de la vallée de l'Inn, du mésozoique du Brenner et des montagnes de Tarntal donne le schéma paléogéographique suivant, si on laisse de côté tout d'abord les théories de la tectonique alpine: Un complexe récifal literal au sud (mésozoique du Brenner et de Tarntal) et un vaste platier du récif au nord (Karwendel), qui impiètent de deux côtés sur le bassin de Partnach (la région méridionale de la vallée de l'Inn).

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( ). (Partnach — Muschelkalk — Wettersteinkalk), , . (234 ) (1730 ); . , , .

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Vortrag, gehalten auf der 56. Jahrestagung der Geolog. Vereinigung in Wien am 26. Februar 1966.     

Palaeoclimatic signals recognized by chemometric treatment of molecular stratigraphic data

The high-resolution stratigraphy of various marker compounds has been studied, using GC, HPLC and GC-MS, in a 13 m gravity core recovered from the Kane Gap region, eastern equatorial Atlantic, which provides a record of the glacial/interglacial episodes over the last million years. Downhole variations in many presumed source-specific components are observed (e.g. in n-alkanes from terrigenous land plants and dinosterol from dinoflagellates), which may be due to perturbations or cyclicities resulting from climatic change. Fluctuations in the unsaturation of alkenones attributable to variations in water temperatures show correlations with the glacial/interglacial cycles recorded in the δ¹⁸O values for planktonic foraminifera, thereby providing a potential organic geochemical measure of past climates. These molecular abundance data can be linked to the palaeotemperature record, following computer treatments using principal component and spectral analyses. Molecular stratigraphy shows promise as a new chemostratigraphical tool where other means of stratigraphy fail, for example, through calcium carbonate dissolution.