Gláucia Bueno Benedetti Berbel

Mid-Pleistocene climate transition drives net mass loss from rapidly uplifting St. Elias Mountains, Alaska.

Significance In coastal Alaska and the St. Elias orogen, over the past 1.2 million years, mass flux leaving the mountains due to glacial erosion exceeds the plate tectonic input. This finding underscores the power of climate in driving erosion rates, potential feedback mechanisms linking climate, erosion, and tectonics, and the complex nature of climate−tectonic coupling in transient responses toward longer-term dynamic equilibration of landscapes with ever-changing environments. Erosion, sediment production, and routing on a tectonically active continental margin reflect both tectonic and climatic processes; partitioning the relative importance of these processes remains controversial. Gulf of Alaska contains a preserved sedimentary record of the Yakutat Terrane collision with North America. Because tectonic convergence in the coastal St. Elias orogen has been roughly constant for 6 My, variations in its eroded sediments preserved in the offshore Surveyor Fan constrain a budget of tectonic material influx, erosion, and sediment output. Seismically imaged sediment volumes calibrated with chronologies derived from Integrated Ocean Drilling Program boreholes show that erosion accelerated in response to Northern Hemisphere glacial intensification (∼2.7 Ma) and that the 900-km-long Surveyor Channel inception appears to correlate with this event. However, tectonic influx exceeded integrated sediment efflux over the interval 2.8–1.2 Ma. Volumetric erosion accelerated following the onset of quasi-periodic (∼100-ky) glacial cycles in the mid-Pleistocene climate transition (1.2–0.7 Ma). Since then, erosion and transport of material out of the orogen has outpaced tectonic influx by 50–80%. Such a rapid net mass loss explains apparent increases in exhumation rates inferred onshore from exposure dates and mapped out-of-sequence fault patterns. The 1.2-My mass budget imbalance must relax back toward equilibrium in balance with tectonic influx over the timescale of orogenic wedge response (millions of years). The St. Elias Range provides a key example of how active orogenic systems respond to transient mass fluxes, and of the possible influence of climate-driven erosive processes that diverge from equilibrium on the million-year scale.

Impact of harbour, industry and sewage on the phosphorus geochemistry of a subtropical estuary in Brazil

The distribution of different forms of phosphorus in surface sediment from 17 sites were investigated by SEDEX method. The sites were divided into three sectors: Santos Channel (SC - influenced by harbour, fertilizers plants and phosphogypsum mountains), São Vicente Channel (SVC- domestic waste) and Santos Bay (SB - sewage outfall). The average percentage of each P fraction of the surface sediments in this region followed the sequence P-Fe (38%)>P org (27%)>P exch (13%)>Detrital - P (12%)>Auth - P (10%). P total varied from 3.57 to 74.11 μmol g(-)(1) in both seasons. In SVC, P exch ranged from 13% to 27% and P org varied from 12% to 56%. These high percentages of P exch/P total (greater than 20%) may be related to low oxygen resulting from oxygen consumed by intensive organic matter decomposition as well as the salty water that leads to cation and anion flocculation. Also, the possibility of an influence related to the industrial source of P exch is not ruled out. No significant seasonal differences were found among sites, except for sewage outfall, with changing in the grain size and hence, the P geochemistry. During the summer in the sewage outfall station, Porg represented 37% of P total, which decreased to 13% in the winter. These results suggest that high percentages of organic phosphorus cannot be attributed only to autochthonous and allochthonous organic matter, but also to detergents and/or domestic waste. In contrast, spatial differences among sectors were observed, with the highest values of each fraction associated with sites near industrial and domestic waste activities.

Phosphorus in Antarctic surface marine sediments - chemical speciation in Admiralty Bay

Abstract This study describes the relation of the phosphorus chemical speciation in surface sediments with input processes in Admiralty Bay, King George Island, Antarctica. The sediments were analysed with a sequential extraction for phosphorus fractionation to measure: exchangeable P (Pexch), iron oxyhydroxide bound P (P-Fe), authigenic P (Auth-P), detrital P (Detrital-P) and organic P (Porg). The study revealed that Detrital-P (39–70%) was the main sedimentary phosphorus forms and Auth-P (40–54%) was the second largest pool. The average percentage of each fraction of P followed the sequence: Detrital-P (41%) > Auth-P (37%) > P-Fe (12%) > Porg = Pexch (5%). Spatial differences in grain size distribution were found. Silt and clay factions were predominant in the inlets, whereas sand and gravel were the main components in Central bay (unofficial name). Values were extremely low for organic carbon (< 0.30%) and total nitrogen (< 0.17%). Total sulfur was lower than 0.15%, except for Mackellar Inlet where values were 1%. The dominance of detrital apatite in the total sedimentary phosphorus demonstrates the importance of terrestrial inputs from ice melting in governing the abundance and speciation of sedimentary phosphorus in the Admiralty Bay sediments.

Diversions of the Ribeira River Flow and Their Influence on Sediment Supply in the Cananeia-Iguape Estuarine-Lagoonal System (SE Brazil)

The Cananeia-Iguape system is a combined estuarine-lagoonal sedimentary system, located along the SE coast of Brazil. It consists of a network of channels and islands oriented mainly parallel to the coast. About 165 years ago, an artificial channel, the Valo Grande, was opened in the northern part of this system to connect a major river of the region, the Ribeira River, to the estuarine-lagoon complex. The Valo Grande was closed with a dam and re-opened twice between 1978 and 1995, when it was finally left open. These openings and closures of the Valo Grande had a significant influence on the Cananeia-Iguape system. In this study we present mineralogical, chemical, palaeomagnetic, and geochronological data from a sediment core collected at the southern end of the 50-km long lagoonal system showing how the phases of the opening and closure of the channel through time are expressed in the sedimentary record. Despite the homogeneity of the grain size and magnetic properties throughout the core, significant variations in the mineralogical composition showed the influence of the opening of the channel on the sediment supply. Less mature sediment, with lower quartz and halite and higher kaolinite, brucite, and franklinite, corresponded to periods when the Valo Grande was open. On the other hand, higher abundance of quartz and halite, as well as the disappearance of other detrital minerals, corresponded with periods of absence or closure of the channel, indicating a more sea-influenced depositional setting. This work represented an example of anthropogenic influence in a lagoonal-estuarine sedimentary system, which is a common context along the coast of Brazil.