The relationships between tropical Atlantic sea level variability and major climate indices

Relationships were examined between variability in tropical Atlantic sea level and major climate indices with the use of TOPEX/POSEIDON altimeter and island tide gauge data with the aim of learning more about the external influences on the variability of the tropical Atlantic ocean. Possible important connections were found between indices related to the El Niño–Southern Oscillation (ENSO) and the sea levels in all three tropical regions (north, equatorial, and south), although the existence of only one major ENSO event within the decade of available altimetry means that a more complete investigation of the ENSO-dependence of Atlantic sea level changes has to await for the compilation of longer data sets. An additional link was found with the Indian Ocean Dipole (IOD) in the equatorial region, this perhaps surprising observation is probably an artifact of the similarity between IOD and ENSO time series in the 1990s. No evidence was obtained for significant correlations between tropical Atlantic sea level and North Atlantic Oscillation or Antarctic Oscillation Index. The most intriguing relationship observed was between the Quasi-Biennial Oscillation and sea level in a band centered approximately on 10°S. A plausible explanation for the relationship is lacking, but possibilities for further research are suggested.     

Proximity to ice fields and lake depth as modulators of paleoclimate records: a regional study from southwest Yukon,Canada

Pronounced climate warming during the past century has been well documented in high-latitude regions. Nonetheless, considerable heterogeneity exists in northern climate trends. We examined the roles of cryospheric landscape and lake depth in modulating the rate and magnitude of local climate responses through a paleolimnological study of lakes from southwest Yukon, Canada. By sampling lakes at varying distances from the Wrangell-St. Elias ice fields, we hypothesized that, for lakes of similar maximum depth, sites closest to the ice fields would be relatively complacent in terms of their chironomid and diatom assemblage changes over the past ~200 years. This hypothesis is based on the moderating effect of the glaciers on local climate, which would be most pronounced in the lakes nearest to the ice fields. However, given the known ecological differences between deep and shallow lakes, we further predicted that, for a given distance from the ice fields, a sediment record from a shallower lake would show the greatest change in stratigraphic subfossil assemblages. Because of the complicated shape of the ice fields, we applied the longitude for each site (which decreases from west to east) to approximate the proximity of our study lakes to the ice fields. Consistent with our predictions, we observed a space-transgressive pattern in the chironomid assemblage turnover that was associated with their proximity to the ice fields (r = ?0.75, P = 0.034, n = 8) across lakes of similar depth (mean maximum depth ± 1, SE = 18.1 ± 2.6 m). Considering a broader network of lakes that represented a greater range in maximum depth (4.9–29 m), we found that differences in subfossil chironomid assemblages between the modern and ca. AD 1800 sediment layers were strongly related to lake depth (r = ?0.77, P < 0.001, n = 15), but failed to detect a significant relationship with latitude or longitude (i.e. our proxy for proximity to the ice fields). Similarly, our comparative high-resolution analyses of two lakes with distinct lake morphometries, but similar proximities to the ice fields, demonstrated the predicted contrasting pattern: we observed pronounced post-1880 changes in the biotic assemblages in the shallow lake and a muted and delayed response (i.e. ~1970s) in the deeper lake. Our findings confirm that cryospheric landscape features can strongly modulate regional climate. Furthermore, our work shows that investigators need to be conscious of how climate change affects the structure and functioning of lakes of different typologies, which influences the way in which paleoclimate signals are recorded and interpreted.     

Modellrechnungen zu winderzeugten Bewegungen in einem Meer mit Sprungschicht

Zusammenfassung Nach Erörterung der benutzten vertikal integrierten Bewegungsgleichungen für ein Meer mit Sprungschicht sowie der Ansätze für Schubspannung und Reibung werden die Beziehungen zwischen Spiegel- und Sprungflächenlage und die Wirkung des Windschubs auf einen geschichteten Kanal diskutiert. Es folgt die Beschreibung der Windschubwirkung auf tropische Modellmeere mit Sprungschicht. Insbesondere wird das Ergebnis einer den Verhältnissen im Arabischen Meer bei beginnendem Sommermonsun nahekommenden Modellrechnung beschrieben, in der sich die Sprungschicht vor der afrikanisch-arabischen Küste um mehrere Dekameter hebt (upwelling), vor der indischen Küste ebenso stark absenkt. Parallel diesen Küsten treten zwischen dem 8. und 16. Tag Wellenkämme und-täler in der Sprungschicht und in der Oberfläche in genau gleicher Art auf, wie sie A. Defant [1950/1951] aus Beobachtungen vor der kalifornischen Küste im Zusammenhang mit auf- und ablandigem Windschub abgeleitet hat. Wir zeigen noch, daß diese Wellen nichts mit fortschreitenden zu tun haben können und leiten die dafür gebräuchliche Formel für die Fortpflanzungsgeschwindigkeit aus den vertikal integrierten Bewegungsgleichungen ab.Abschließend wird das Modell einer idealisierten Nordsee mit sommerlicher Sprungschicht beschrieben, in dem das Massen- und Geschwindigkeitsfeld durch ein vorüberziehendes Tiefdruckgebiet Änderungen erfährt. Dem Luftdruckminimum folgt eine Mulde mit zyklonaler Wasserzirkulation in der Oberschicht nach, welche noch geraume Zeit nach Abzug des Tiefs anhält. Die Sprungschicht hebt sich südlich der Bahn des Tiefs um einige Meter und entfaltet eine kräftige, südwärts fortschreitende Wellenbewegung an der östlichen Begrenzung. Auch in der Unterschicht herrscht eine zyklonale Wasserzirkulation vor; das untere Wirbelzentrum bleibt aber hinter dem der Oberschicht zurück und holt es erst nach Abzug der Zyklone ein. Beide Wirbelzentren liegen dann unter einer sich abschwächenden Mulde in der Wasseroberfläche.Unsere Modelle zeigen, daß es mit den heutigen Hilfsmitteln im Prinzip möglich ist, nicht nur die Einflüsse aktueller meteorologischer Faktoren auf die Wasseroberfläche, sondern auch ihre Wirkung auf die Massenverteilung innerhalb des Meeres zu ermitteln. Zur modellmäßigen Darstellung der allgemeinen Zirkulation des Meeres sind allerdings die hier nicht berücksichtigten Vermischungsvorgänge in Rechnung zu stellen.

---

Numerical models on wind produced motions in a sea with a pycnocline

Summary After a treatment of the system of vertically integrated equations of motion concerning a sea with a pycnocline we discuss the stress and friction terms used here and the general relations connecting the variation of the surface with that of the pycnocline as well as the effect of wind stress in a double-layered canal. After that we regard the effects of wind stress and pressure of air on tropical model oceans with a pycnocline. Especially the result of a numerical computation of the behaviour of an idealized Arabian Sea in the beginning of the summer monsoon is described: The pycnocline is lifting by several decameters in front of the African and Arabian shores (upwelling) and is descending by the same number of decameters in front of the Indian coast. Between the eighth and sixteenth day there are contrary wave crests and troughs in the surface and in the pycnocline parallel to the African and Indian shores of exactly the same kind as those already derived from observations in front of the Californian coast by A. Defant [1950/1951] in connection with on-shore an off-shore winds.Concluding, we describe the model of an idealized North Sea with a summer thermocline where the fields of mass and velocity are affected by a passing low. Its centre is followed by a trough in the surface and a cyclonic circulation in the upper layer continuing even a long time after the low had passed. In the south of its path the thermocline ascents some meters and at the eastern shore it develops a vigorous wave motion propagating southward. A cyclonic circulation prevails also in the layer beneath the thermocline; its centre lags behind the curl centre of the upper layer but at last joins it after the low left the model sea. Both curl centres then come to lie underneath the gradually diminishing trough in the sea surface.As shown by our models, the modern aids make it possible, not only to compute the effects of the actual meteorological events on the sea surface but also their effects on the mass distribution within the sea. If, however, a model of the general circulation in the oceans is to be given, there should, at any rate, be taken into account the mixing processes of water masses neglected here.

---

Modèles numériques pour le calcul des mouvements dûs au vent dans une mer ayant une couche de densité à discontinuité

Résumé Pour une mer ayant une couche de densité à discontinuité on discute le système des équations de mouvements, intégrées verticalement et on expose les termes du frottement tangentiel dû au vent et ceux de la friction interne employés dans ce travail. Puis on traite les relations générales qui existent entre les variations de la surface et celles de la couche de discontinuité et on décrit les effets du frottement tangentiel dû au vent dans un canal à deux couches. Aprés cela on étudie l'effet du frottement tangentiel dû au vent et la pression atmosphérique exercée sur des modèles de mers tropiques ayant des couches de discontinuité. On décrit surtout le résultat du calcul numérique du comportement d'une mer idéalisée arabique au commencement de la mousson estivale. Suivant ce calcul, la couche de discontinuité s'élève par plusieurs décamètres (upwelling) devant la côte afro-arabique et elle s'abaisse en même degré devant la côte indienne. Entre le 8^ième et le 16^ième jour il se présente, parallèlement à ces côtes, des crêtes et des creux de vagues opposées dans la couche de discontinuité et dans celle de la surface. Ces vagues sont de la même espèce que celles que A. Defant [1950/1951] a déjà dérivées des observations faites devant la côte de la Californie en présence du frottement tangentiel dû aux vents de terre et de mer. On montrera que ces vagues ne peuvent avoir aucun rapport aux vagues progressives et nous dérivons des équations verticalement intégrées de mouvement la formule en usage pour la vitesse de propagation.Ênfin, on décrit le modèle de la mer idéalisée du Nord, dans laquelle on suppose une couche estivale de discontinuité. Dans ce modèle le champ de masse et le champ de vitesse subissent de changements par le passage d'une aire de basse pression, dont le minimum atmosphérique est suivi d'une dépression qui de sa part, dans la couche supérieure de l'eau, est accompagnée d'une circulation cyclonique, qui se maintient même quelque temps après le passage de l'aire de basse pression. Au sud de sa trajectoire la couche de discontinuité s'élève par plusieurs mètres; à sa limite orientale elle développe de fortes vagues qui se propagagent vers le sud. Dans la couche qui se trouve au-dessous de la couche de discontinuité, une circulation cyclonique est également prédominante; son centre est en retard sur celui de la couche supérieure qu'il ne rattrapera qu'après le passage du cyclone. Les deux centres cycloniques se trouvent alors au-dessous de la dépression en voie de s'exténuer à la surface de l'eau.Les modèles montrent que les ressources modernes permettent, en principe, de calculer non seulement les effets des facteurs météorologiques actuels à la surface de l'eau, mais aussi leurs effets sur la distribution des masses dans l'océan. Si l'on veut, cependant, représenter la circulation générale en mer au moyen d'un modèle, il est nécessaire de tenir compte des processus de mélange non considérés dans cette étude.

---

---

Hierzu Tafel 7 mit Abb. 7a-e, Tafel 8 mit Abb. 11a-d, Tafel 9 mit Abb. 12a-e

---

Herrn Professor A. Defant zum 81. Geburtstag gewidmet.     

Reconstructing recent sedimentation in two urbanised coastal lagoons (NSW,Australia) using radioisotopes and geochemistry

In this study, we combined grain size and geochemical analyses with radioisotope analysis of lead-210 (²¹⁰Pb), caesium-137 (¹³⁷Cs) and radiocarbon (¹⁴C) ages to reconstruct the sedimentation history of two urbanised coastal lagoons in south-east Australia. Towradgi and Fairy Lagoons were both found to exhibit slow initial sedimentation of less than 1 mm year⁻¹ prior to anthropogenic influences. Land clearing in the catchments increased runoff and erosion in the creeks feeding into the estuaries, and has resulted in progradation of fluvial material into the estuarine systems with a marked increase in sedimentation to between 2 and 7 mm year⁻¹. The upper 20–50 cm of the sediment column in both lagoons contained elevated concentrations of heavy metals such as Pb, Cu, Ni and Zn. This pollution trend was found to be consistent with the history of industrialisation and urbanisation in the region, which expanded rapidly post World War 2. The total metal concentrations were consistent with other urbanised/industrialised estuaries around the world. Despite the fairly disturbed nature of these coastal lagoons, the use of ²¹⁰Pb, ¹³⁷Cs and ¹⁴C dating in combination with bulk geochemical analyses allowed detailed reconstruction of sedimentation history.     

Spatial pattern of localized disturbance along a Southeastern salt marsh tidal creek

Geomorphology may be an important predictor of vegetation pattern in systems where suceptibility to disturbance is unevenly distributed across the landscape. Salt marsh communities exhibit spatial pattern in vegetation at a variety of spatial scales. In coastal Georgia, the low marsh is a virtual monoculture ofSpartina alterniflora interspersed with patches of species that are more typical of the high marsh. These localized disturbances are most likely created by wrack mats, mats of dead vegetation which can compact and smother underlying vegetation creating bare patches for colonization by high marsh species. We investigated the spatial pattern of disturbed patches along a 2 km section of Dean Creek, a tidal creek at the southwestern end of Sapelo Island, Georgia, U.S. We used a discriminant model to explore the relationship between tidal creek morphology (e.g., the presence of drainage channels and creek bends) and the spatial distribution of disturbed patches. The model predicted vegetation pattern along the creek with relatively high accuracy (>70%). Areas where water movement is slowed or multidirectional (e.g., along creek bends and near drainage channels) were most susceptible to disturbance. Our findings suggest an important functional linkage between geomorphology and vegetation pattern in salt marsh communities.     

Mutual validation of GNSS height measurements and high-precision geometric-astronomical leveling

The method of geometric-astronomical leveling is presented as a suited technique for the validation of GNSS (Global Navigation Satellite System) heights. In geometric-astronomical leveling, the ellipsoidal height differences are obtained by combining conventional spirit leveling and astronomical leveling. Astronomical leveling with recently developed digital zenith camera systems is capable of providing the geometry of equipotential surfaces of the gravity field accurate to a few 0.1 mm per km. This is comparable to the accuracy of spirit leveling. Consequently, geometric-astronomical leveling yields accurate ellipsoidal height differences that may serve as an independent check on GNSS height measurements at local scales. A test was performed in a local geodetic network near Hanover. GPS observations were simultaneously carried out at five stations over a time span of 48 h and processed considering state-of-the-art techniques and sophisticated new approaches to reduce station-dependent errors. The comparison of GPS height differences with those from geometric-astronomical leveling shows a promising agreement of some millimeters. The experiment indicates the currently achievable accuracy level of GPS height measurements and demonstrates the practical applicability of the proposed approach for the validation of GNSS height measurements as well as the evaluation of GNSS height processing strategies.     

Mesozoic thermal evolution of the southern African mantle lithosphere

The thermal structure of Archean and Proterozoic lithospheric terranes in southern Africa during the Mesozoic was evaluated by thermobarometry of mantle peridotite xenoliths erupted in alkaline magmas between 180 and 60 Ma. For cratonic xenoliths, the presence of a 150–200 °C isobaric temperature range at 5–6 GPa confirms original interpretations of a conductive geotherm, which is perturbed at depth, and therefore does not record steady state lithospheric mantle structure.

Xenoliths from both Archean and Proterozoic terranes record conductive limb temperatures characteristic of a “cratonic” geotherm (40 mW m⁻²), indicating cooling of Proterozoic mantle following the last major tectonothermal event in the region at 1 Ga and the probability of thick off-craton lithosphere capable of hosting diamond. This inference is supported by U–Pb thermochronology of lower crustal xenoliths [Schmitz and Bowring, 2003. Contrib. Mineral. Petrol. 144, 592–618].

The entire region then suffered a protracted regional heating event in the Mesozoic, affecting both mantle and lower crust. In the mantle, the event is recorded at 150 Ma to the southeast of the craton, propagating to the west by 108–74 Ma, the craton interior by 85–90 Ma and the far southwest and northwest by 65–70 Ma. The heating penetrated to shallower levels in the off-craton areas than on the craton, and is more apparent on the southern margin of the craton than in its western interior. The focus and spatial progression mimic inferred patterns of plume activity and supercontinent breakup 30–100 Ma earlier and are probably connected.

Contrasting thermal profiles from Archean and Proterozoic mantle result from penetration to shallower levels of the Proterozoic lithosphere by heat transporting magmas. Extent of penetration is related not to original lithospheric thickness, but to its more fertile character and the presence of structurally weak zones of old tectonism. The present day distribution of surface heat flow in southern Africa is related to this dynamic event and is not a direct reflection of the pre-existing lithospheric architecture.     

Space weathering of small Koronis family members

The space weathering process and its implications for the relationships between S- and Q-type asteroids and ordinary chondrite meteorites is an often debated topic in asteroid science. Q-type asteroids have been shown to display the best spectral match to ordinary chondrites (McFadden, L.A., Gaffey, M.J., McCord, T.B. [1985]. Science 229, 160–163). While the Q-types and ordinary chondrites share some spectral features with S-type asteroids, the S-types have significantly redder spectral slopes than the Q-types in visible and near-infrared wavelengths. This reddening of spectral slope is attributed to the effects of space weathering on the observed surface composition. The analysis by Binzel et al. (Binzel, R.P., Rivkin, A.S., Stuart, J.S., Harris, A.W., Bus, S.J., Burbine, T.H. [2004]. Icarus 170, 259–294) provided a missing link between the Q- and S-type bodies in near-Earth space by showing a reddening of spectral slope in objects from 0.1 to 5 km that corresponded to a transition from Q-type to S-type asteroid spectra, implying that size, and therefore surface age, is related to the relationship between S- and Q-types. The existence of Q-type asteroids in the main-belt was not confirmed until Mothé-Diniz and Nesvorny (Mothé-Diniz, T., Nesvorny, D. [2008]. Astron. Astrophys. 486, L9–L12) found them in young S-type clusters. The young age of these families suggest that the unweathered surface could date to the formation of the family. This leads to the question of whether older S-type main-belt families can contain Q-type objects and display evidence of a transition from Q- to S-type. To answer this question we have carried out a photometric survey of the Koronis family using the Kitt Peak 2.1 m telescope. This provides a unique opportunity to compare the effects of the space weathering process on potentially ordinary chondrite-like bodies within a population of identical initial conditions. We find a trend in spectral slope for objects 1–5 km that shows the transition from Q- to S-type in the main-belt. This data set will prove crucial to our understanding of the space weathering process and its relevant timescales.     

Conventional Oil—The Forgotten Part of the Water-Energy Nexus

The impacts of unconventional oil and gas production via high-volume hydraulic fracturing (HVHF) on water resources, such as water use, groundwater and surface water contamination, and disposal of produced waters, have received a great deal of attention over the past decade. Conventional oil and gas production (e.g., enhanced oil recovery [EOR]), which has been occurring for more than a century in some areas of North America, shares the same environmental concerns, but has received comparatively little attention. Here, we compare the amount of produced water versus saltwater disposal (SWD) and injection for EOR in several prolific hydrocarbon producing regions in the United States and Canada. The total volume of saline and fresh to brackish water injected into depleted oil fields and nonproductive formations is greater than the total volume of produced waters in most regions. The addition of fresh to brackish “makeup” water for EOR may account for the net gain of subsurface water. The total amount of water injected and produced for conventional oil and gas production is greater than that associated with HVHF and unconventional oil and gas production by well over a factor of 10. Reservoir pressure increases from EOR and SWD wells are low compared to injection of fluids for HVHF, however, the longer duration of injections could allow for greater solute transport distances and potential for contamination. Attention should be refocused from the subsurface environmental impacts of HVHF to the oil and gas industry as a whole.     

Inter-annual variability in larval supply to populations of three invertebrate taxa in the northern California Current

We investigated sources of inter-annual variability in larval supply to crab and sea urchin populations at Bodega Head and Point Reyes in northern California. During the spring and summer upwelling seasons of the years 1992 through 1997 we monitored the weekly settlement rates of nine species of crabs and two species of sea urchins. As observed in previous studies, daily values of alongshore windstress, temperature and salinity provided evidence for the poleward flow of relatively warm, low salinity water from south of Point Reyes, an apparent retention zone, during upwelling relaxation events. In years dominated by these events (1992, 1993, 1995 and 1996) we observed that alongshore windstress, temperature and salinity were coherent and temperature was significantly correlated with cancrid crab settlement. During these years the magnitude of cancrid crab settlement and the fraction of cancrid crabs relative to other crab species settling were high. Over four years of concurrent sampling there was consistently greater cancrid crab settlement at the Point Reyes site, within the retention zone, than at Bodega Head. Settlement of non-cancrid crabs (porcellanids, grapsids, pagurids and majids) was not as closely linked to intra-annual patterns of upwelling and relaxation, possibly due to the shorter seasonal availability of larvae allowing for the influence of fewer relaxation events. Settlement of this group among years was positively correlated with environmental indicators of strong seasonal upwelling; high salinity, Bakun upwelling index and low temperature. Sea urchin settlement events were observed in June and July of 1992, 1994 and 1997 during warming periods when salinity and temperature were increasing and alongshore windstress was low. Across the six years of the study, we found that cancrid crab larvae had a more even seasonal availability than larvae of non-cancrid species, which settled in greatest numbers during the early portion of the upwelling season. Sea urchins settled in greatest numbers during the later part of the upwelling season. Together these patterns demonstrate the taxon-specific way that inter-annual variability in larval supply is forced by the coincidence of larval availability with favorable physical transport mechanisms.