Morphometry of Cyphocharax gouldingi in the Praquiquara river watershed, Apeu east, Eastern Amazon

Curimatídeos do gênero Cyphocharax Fowler, 1906 distribuem-se amplamente nas bacias hidrográficas da América do Sul, contudo essa ampla distribuição inequivale a quantidade de trabalhos relacionados ao gênero. Visto isso, objetivou-se contribuir ao conhecimento de Cyphocarax gouldingi (Vari, 1992) através da caracterização morfométrica de indivíduos coletados na microbacia do rio Praquiquara, localizado no médio Apeú, Amazônia Oriental. Para a determinação morfométrica da espécie, utilizou-se o software Adobe Photoshop CS6 Extended, mensurando os respectivos caracteres merísticos: comprimentos total, padrão, zoológico, cabeça e focinho, a medida da altura e o diâmetro do olho de 178 exemplares capturados entre os meses setembro (2014) e maio (2015). Verificou-se uma correlação forte positiva e alometria negativa, entre o comprimento total e as demais medidas externas, e observou a importância do rio Praquiquara durante o ciclo de vida da espécie. Conclui-se que as medidas morfométricas de C. gouldingi (1) satisfazem a estimação de comprimento total e (2) possibilitam o estudo sobre a dinâmica de crescimento da espécie estudada.

Carbon geochemistry of sediments from the Amazon deep sea fan

Sediment cores from the Amazon deep sea fan recovered during R/V Meteor cruise 16-2 show in detail the modern areal distribution of sedimentary organic carbon, stable organic carbon isotopes of the organic matter (OM), as well as variations in the depositional processes. In addition, we studied up to 300 m long drilled sediment records recovered during ODP Leg 155 which allow evaluation of temporal variations on the Amazon fan. Our results reveal new evidence for a very rapid change of fan depositional processes and organic carbon source at times of sea-level change over the middle and lower Amazon fan. To estimate the amount of terrestrial organic carbon stored in sediments from the last glacial in the Amazon fan we used stable organic carbon isotopes of the OM (delta13Corg), organic carbon content (Corg), and age models based on oxygen isotopes, faunal data, and magnetic excursions. Following our results, the organic carbon accumulation on the Amazon deep sea fan is controlled by glacio-eustatic sea-level oscillations. Interglacial sea-level high stand sediments are dominated by marine OM whereas during glacial sea-level low stands terrestrial organic carbon is transported beyond the continental shelf through the Amazon canyon and deposited directly onto the Amazon deep sea fan. Glacial sediments of the Amazon fan stored approximately 73*10**15 g terrestrial Corg in 20,000 years or 3.7*10**12 g terrestrial Corg/yr (equivalent to 7-12% of the riverine organic carbon discharge; assuming constant paleo discharge), which is about the same amount of terrestrial organic carbon as deposited on the Amazon shelf today (3.1*10**12 g terrestrial Corg/yr or 6-10% of the modern riverine organic carbon discharge).

Organic carbon and carbohydrates in waters of the Amazon River, Atlantic Ocean, and Tropical Indian Ocean

A method is presented to study carbohydrate composition of marine objects involved into sedimento- and diagenesis (plankton, particulate matter, benthos, and bottom sediments). Analysis of the carbohydrates is based on consecutive separation of their fractions with different solvents (water, alkali, and acid). Ratios of carbohydrate fractions allows to evaluate lability of carbohydrate complexes. They are also usable as an indicators of biogeochemical processes in the ocean, as well of genesis and degree of transformation of organic matter in bottom sediments and nodules. Similarity in monosaccharide composition is shown for dissolved organic matter and aqueous and alkaline fractions of seston and particulate matter.

Macrozoobenthos abundance on a tropical oyster culture in an Amazon estuary, Para state, northern Brazil

The present study describes the biofouling composition of the surface of the mangrove oyster Crassostrea rhizophorae (Guilding, 1828), cultivated in an Amazon estuary, located in the state of Pará, northern Brazil. In total, 6.124 macroinvertebrates were sampled in the months of July, August, October and December 2013. Collected epifauna was presented by five taxa (Bivalvia, Gastropoda, Polychaeta, Crustacea and Anthozoa), 20 families and 37 species. Bivalvia was the most abundant class, presenting 5.183 mussels Mytella charruana (d'Orbigny, 1842). Knowledge of biofouling composition associated to the surface cultured bivalves enables the implementation of mitigation measures to the impacts caused by this association.

Terrigenous biomarker proxies analysed in the Amazon River system

Paleoenvironmental studies based on terrigenous biomarker proxies from sediment cores collected close to the mouth of large river systems rely on a proper understanding of the processes controlling origin, transport and deposition of biomarkers. Here, we contribute to the understanding of these processes by analyzing long-chain n-alkanes from the Amazon River system. We use the dD composition of long-chain n-alkanes from river bed sediments from the Amazon River and its major tributaries, as well as marine core-top samples collected off northeastern South America as tracers for different source areas. The d13C composition of the same compounds is used to differentiate between long-chain n-alkanes from modern forest vegetation and petrogenic organic matter. Our d13C results show depleted d13C values (-33 to -36 per mil) in most samples, indicating a modern forest source for most of the samples. Enriched values (-31 to -33 per mil) are only found in a few samples poor in organic carbon indicating minor contributions from a fossil petrogenic source. Long-chain n-alkane dD analyses show more depleted values for the western tributaries, the Madeira and Solimões Rivers (-152 to -168 per mil), while n-alkanes from the lowland tributaries, the Negro, Xingu and Tocantins Rivers (-142 to -154 per mil), yield more enriched values. The n-alkane dD values thus reflect the mean annual isotopic composition of precipitation, which is most deuterium-depleted in the western Amazon Basin and more enriched in the eastern sector of the basin. Samples from the Amazon estuary show a mixed long-chain n-alkane dD signal from both eastern lowland and western tributaries. Marine core-top samples underlying the Amazon freshwater plume yield dD values similar to those from the Amazon estuary, while core-top samples from outside the plume showed more enriched values. Although the variability in the river bed data precludes quantitative assessment of relative contributions, our results indicate that long-chain n-alkanes from the Amazon estuary and plume represent an integrated signal of different regions of the onshore basin. Our results also imply that n-alkanes are not extensively remineralized during transport and that the signal at the Amazon estuary and plume includes refractory compounds derived from the western sector of the Basin. These findings will aid in the interpretation of plant wax-based records of marine sediment cores collected from the adjacent ocean.

(Table 1) Average sea surface temperature, average sea surface salinity, C37 concentration, palmitic acid concentration, Uk'37, C37/C38 ratio, dD of water, dD of C37 and dD of palmitic acid of water samples from a transect across the Amazon Plume

The stable hydrogen isotope composition of lipid biomarkers, such as alkenones, is a promising new tool for the improvement of palaeosalinity reconstructions. Laboratory studies confirmed the correlation between lipid biomarker dD composition (dDLipid), water dD composition (dDH2O) and salinity; yet there is limited insight into the applicability of this proxy in oceanic environments. To fill this gap, we test the use of the dD composition of alkenones (dDC37) and palmitic acid (dDPA) as salinity proxies using samples of surface suspended material along the distinct salinity gradient induced by the Amazon Plume. Our results indicate a positive correlation between salinity and dDH2O, while the relationship between dDH2O and dDLipid is more complex: dDPAM correlates strongly with dDH2O (r2 = 0.81) and shows a salinity-dependent isotopic fractionation factor. dDC37 only correlates with dDH2O in a small number (n = 8) of samples with alkenone concentrations > 10 ng L**-1, while there is no correlation if all samples are taken into account. These findings are mirrored by alkenone-based temperature reconstructions, which are inaccurate for samples with low alkenone concentrations. Deviations in dDC37 and temperature are likely to be caused by limited haptophyte algae growth due to low salinity and light limitation imposed by the Amazon Plume. Our study confirms the applicability of dDLipid as a salinity proxy in oceanic environments. But it raises a note of caution concerning regions where low alkenone production can be expected due to low salinity and light limitation, for instance, under strong riverine discharge.