The effect of Congo River freshwater discharge on Eastern Equatorial Atlantic climate variability

The surface ocean explains a considerable part of the inter-annual Tropical Atlantic variability. The present work makes use of observational datasets to investigate the effect of freshwater flow on sea surface salinity (SSS) and temperature (SST) in the Gulf of Guinea. In particular, the Congo River discharges a huge amount of freshwater into the ocean, affecting SSS in the Eastern Equatorial Atlantic (EEA) and stratifying the surface layers. The hypothesis is that an excess of river runoff emphasize stratification, influencing the ocean temperature. In fact, our findings show that SSTs in the Gulf of Guinea are warmer in summers following an anomalously high Congo spring discharge. Vice versa, when the river discharges low freshwater, a cold anomaly appears in the Gulf. The response of SST is not linear: temperature anomalies are considerable and long-lasting in the event of large freshwater flow, while in dry years they are less remarkable, although still significant. An excess of freshwater seems able to form a barrier layer, which inhibits vertical mixing and the entrainment of the cold thermocline water into the surface. Other processes may contribute to SST variability, among which the net input of atmospheric freshwater falling over EEA. Likewise the case of continental runoff from Congo River, warm anomalies occur after anomalously rainy seasons and low temperatures follow dry seasons, confirming the effect of freshwater on SST. However, the two sources of freshwater anomaly are not in phase, so that it is possible to split between atypical SST following continental freshwater anomalies and rainfall anomalies. Also, variations in air-sea fluxes can produce heating and cooling of the Gulf of Guinea. Nevertheless, atypical SSTs cannot be ascribed to fluxes, since the temperature variation induced by them is not sufficient to explain the SST anomalies appearing in the Gulf after anomalous peak discharges. The interaction processes between river runoff, sea surface salinity and temperature play an effective role in the interannual variability in the EEA region. Our results add a new source of variability in the area, which was often neglected by previous studies.     

The Jiddat al Harasis 073 strewn field,Sultanate of Oman

Abstract— The recently discovered Jiddat al Harasis (JaH) 073 strewn field is the largest found so far in the Sultanate of Oman, covering an area of 19 × 6 km. The 3463 single stones collected range in weight from 52.2 kg down to <1 g (total weight 600.8 kg) and show a pronounced mass sorting. The strewn field shape can be approximated by a NW‐SE‐oriented ellipsoid, indicating an atmospheric entry from SE at a low angle relative to the surface. The meteorite belongs to the L6 ordinary chondrite group and shows S4 average shock grade. Smaller stones generally show a higher weathering grade resulting in a spread from W2 and W4. Enhanced weathering of the stones causing fragmentation after the fall is observed in sandy depressions. Five ¹⁴C measurements on stones of variable size and weathering grade yielded ¹⁴C from 3.8 to 49.9 dpm/kg. Three samples give a ¹⁴C/ ¹⁰Be age consistent with about 14.4 ka. For two samples the cosmogenic, trapped, and radiogenic noble gases were measured. The ratio of the ⁴He and ⁴⁰Ar gas retention ages of 0.29 ± 0.10 and that of the ³He and ²¹Ne cosmic ray exposure ages of 0.36 ± 0.08 Ma indicate that JaH 073 experienced a complex exposure history and lost ⁴He and ⁴⁰Ar due to a major collision. Fragmentation statistics indicate a single major atmospheric disruption and an originally relatively spherical shape of the object. Assuming the material collected represents the majority of fallen mass, and 90–99% of the original weight was lost by ablation, the pre‐atmospheric minimum radius of the meteoroid with density 3.4 g cm^?3would have been at least 75 cm.     

Considerazioni intorno ad alcuni metodi per il calcolo delle riduzioni topografiche nei rilievi eötvössiani

Riassunto L'Autore in questa Nota confronta un procedimento grafico, proposto ed illustrato in precedenti ricerche, con le formole delloSchweydar che sono senza dubbio le più adoperate attualmente nella valutazione delle correzioni topografiche da apportare agli elementi rilevati con la bilancia di torsione, e richiama, fra l'altro, l'attenzione sulle condizioni di applicabilità degli sviluppi e sull'espressione generale dei coefficienti che entrano nella formazione di questi. Completano il lavoro alcune relazioni per il controllo del calcolo dei coefficienti.

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Zusammenfassung Der Verf. vergleicht ein graphisches Verfahren, welches von ihm in früheren Untersuchungen angegeben und erläutert worden ist, mit den Formeln vonSchweydar, welche zweifellos in der Berechnung der topographischen Korrektionen der Grössen die mit der Drehwaage gemessen werden die mehr gebrauchten sind. Ausserdem, gibt er die Anwendungsbedingungen für die Entwicklungen und über den allgemeinen Ausdruck der Koeffizienten welche in der Bildung jener Entwicklungen auftreten. Zuletzt, ist die Arbeit mit einigen Verbindungen zur Kontrolle der Berechnung der Koeffizienten ergänzt.

     

Moto ondoso e vento nel Golfo di Trieste

Riassunto Dalle osservazioni dello stato del mare, eseguite a Trieste alle ore 8, 14 e 19, nel ventennio 1931–1950, si deducono le medie mensili, stagionali ed annue. Il moto ondoso risulta massimo alle ore 14 dei mesi estivi, minimo alle ore 8 degli stessi mesi. Il valore medio annuo è 1.7, lo stato medio del mare risulta poco meno che leggermente mosso. Nel ventennio l'andamento medio annuo non è nè crescente nè decrescente, presenta una concavità negli anni centrali. Tra la velocità del vento e lo stato ondoso sono stati determinati coefficienti di correlazione che variano, secondo i casi, da 0.49 a 0.94.

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Summary From the observations of the seawave-motion effectuated in Trieste at 8^h, 14^h and 19^h, during the years 1931–1950, the monthly and annual mean values are calculated. The maximum wave-motion results at 14^h of the summer months, the minimum one at 8^h of the same months. The mean annual value is 1.7, that is: a little inferior than «lightly moved». Between the wind-velocity and the wave-motion have been determined correlation-coefficients varying from 0.49 to 0.94.

     

Peptide decomposition by extracellular hydrolysis in coastal seawater and salt marsh sediment

Extracellular peptide hydrolysis rates were measured in seawater and sediment from Flax Pond salt marsh using peptide analogs (LYA-peptides) as substrates. This technique allows the direct measurement of specific hydrolysis products and thus provides insights into enzymatic hydrolysis pathways. In sediments, hydrolysis rate constants of LYA-peptides varied seasonally and with depth. Highest activity was found in spring and summer, and most cores exhibited a subsurface maximum. Calculations using the concentrations of chemically-measured peptides suggested that extracellular hydrolysis of peptides is faster than the rate of free amino acids uptake. However, not all peptides may be available for enzymatic hydrolysis. In both seawater and sediment, extracellular hydrolysis of peptides of up to 8 amino acids yielded smaller peptides and free amino acids. Hydrolysis rates depended on size of the peptide substrate, although a clear relationship with number of amino acid constituents was not evident. Peptides containing >2 amino acids were hydrolyzed 10–400 times faster than dipeptides or the fluorogenic substrate Leucine-MCA. Thus, dipeptidases are either uncommon in nature, or hydrolysis is carried out by nonspecific hydrolases that with a low affinity for dipeptides. This is also suggested by the presence of a lag time before dipeptide hydrolysis begins, and the absence of dipeptide hydrolysis in 0.2-μm-filtered. One implication of this finding is that measurements of hydrolysis rates using substrates like Leu-MCA may not accurately predict the magnitude of hydrolysis rates of macromolecules in the marine environment. Even though dipeptide hydrolysis is slow compared to that of larger peptides, LYA-dipeptides are preferentially produced from the hydrolysis of larger substrates. LYA-dipeptides do not penetrate cell membranes of microorganisms because of their size, but natural dipeptides are smaller and can be transported across the cell membrane. Since dipeptides do not appear to accumulate in natural waters, they must be rapidly removed by microorganisms.     

Long-term model of planimetric and bathymetric evolution of a tidal lagoon

This model is based on the concept of transport concentration, defined as the time-averaged concentration in a given location of a lagoon, which determines the long-term net transport of sediments as the sum of a dispersive and an advective flux. Dispersive net flux of sediments is due to the alternate components of the tidal flow, while the advective net flux of sediments is due to the residual (Eulerian) component of the tidal, fluvial and littoral flow and possibly to the asymmetry between flow and ebb tide.     

Seasonality in the relationship between El Nino and Indian Ocean dipole

The seasonal change in the relationship between El Nino and Indian Ocean dipole (IOD) is examined using the European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40), and the twentieth century simulations (20c3m) from the Geophysical Fluid Dynamics Laboratory Coupled Model, version 2.1. It is found that, both in ERA-40 and the model simulations, the correlation between El Nino (Nino3 index) and the eastern part of the IOD (90?C110°E; 10°S-equator) is predominantly positive from January to June, and then changes to negative from July to December. Correlation maps of atmospheric and oceanic variables with respect to the Nino3 index are constructed for each season in order to examine the spatial structure of their seasonal response to El Nino. The occurrence of El Nino conditions during January to March induces low-level anti-cyclonic circulation anomalies over the southeastern Indian Ocean, which counteracts the climatological cyclonic circulation in that region. As a result, evaporation decreases and the southeastern Indian Ocean warms up as the El Nino proceeds, and weaken the development of a positive phase of an IOD. This warming of the southeastern Indian Ocean associated with the El Nino does not exist past June because the climatological winds there develop into the monsoon-type flow, enhancing the anomalous circulation over the region. Furthermore, the development of El Nino from July to September induces upwelling in the southeastern Indian Ocean, thereby contributing to further cooling of the region during the summer season. This results in the enhancement of a positive phase of an IOD. Once the climatological circulation shifts from the boreal summer to winter mode, the negative correlation between El Nino and SST of the southeastern Indian Ocean changes back to a positive one.     

Preliminary Interlaboratory Trial for ISO/DIS 12010: Determination of Short Chain Polychlorinated Alkanes (SCCP) in Water

A first preliminary interlaboratory trial was planned to prepare ISO/DIS 12010: Water quality – determination of short chain polychlorinated alkanes (SCCP) in water – method using GC/MS and electron capture negative ionisation (ECNI). The task was to determine the sum of short chain polychlorinated n‐alkanes with carbon chain lengths of C₁₀–C₁₃ and a chlorine content between 49 and 67% in water by GC‐ECNI‐MS and quantification by multiple linear regression described in ISO/DIS 12010 as the compulsory method. Distributed samples were obtained from a real water extract spiked with a target concentration of 0.4 µg/mL sum of SCCP, i.e. the environmental quality target level according to the Water Framework Directive. The interlaboratory trial included the calibration, a column chromatographic clean up, a concentration step and an integration of chromatographic unresolved humps as well as the quantification with multiple linear regression. Reproducibility standard deviations between 21.5 and 22.9% were achieved by 17 participating laboratories from four countries. The method outlined no significant difference of the results between the standard solution and a real water matrix extract. On the basis of this succeeded preliminary interlaboratory trial the final interlaboratory trial for validation of ISO 12010 was prepared in autumn 2010.     

Chemosynthetic trophic support for the benthic community at an intertidal cold seep site at Mocha Island off central Chile

We analyzed C and N stable isotope ratios of benthic fauna and their potential food sources at an intertidal methane seep site and a control site without emanation at Mocha Island (central Chile). The objective was to trace the origin of the main food sources used by the local heterotrophic fauna, based on the hypothesis that chemosynthetic production could be partially fueling the local food web at the seep site. Food sources sampled at both sites included macroalgae, particulate organic matter and bacteria-like filaments found growing over the red algae Gelidium lingulatum within the areas of active methane release.