Description: The eastern tropical South Pacific (ETSP) hosts the Peruvian upwelling system, which represents one of the most productive areas in the world ocean. High primary production followed by rapid heterotrophic utilization of organic matter supports the formation of one of the most intense oxygen minimum zones (OMZs) in the world ocean, where dissolved oxygen (O2) concentrations reach less than 1 µmol kg−1. The high productivity leads to an accumulation of dissolved organic matter (DOM) in the surface layers that may serve as a substrate for heterotrophic respiration. However, the importance of DOM utilization for O2 respiration in the Peruvian upwelling system in general and for shaping the upper oxycline in particular remains unclear so far. This study reports the first estimates of diapycnal fluxes and supply of O2, dissolved organic carbon (DOC), dissolved organic nitrogen, dissolved hydrolysable amino acids (DHAA) and dissolved combined carbohydrates (DCCHO) for the ETSP off Peru. Diapycnal flux and supply estimates were obtained by combining measured vertical diffusivities and solute concentration gradients. They were analysed together with the molecular composition of DCCHO and DHAA to infer the transport of labile DOM into the upper OMZ and the potential role of DOM utilization for the attenuation of the diapycnal O2 flux that ventilates the OMZ. The observed diapycnal O2 flux (50 mmol O2 m−2 d−1 at maximum) was limited to the upper 80 m of the water column; the O2 supply of ∼1 µmol kg−1 d−1 was comparable to previously published O2 consumption rates for the North and South Pacific OMZs. The diapycnal DOM flux (31 mmol C m−2 d−1 at maximum) was limited to ∼30 m water depth, suggesting that the labile DOM is extensively consumed within the upper part of the shallow oxycline off Peru. The analyses of DCCHO and DHAA composition support this finding, suggesting that DOM undergoes comprehensive remineralization within the upper part of the oxycline, as the DOM within the core of the OMZ was found to be largely altered. Estimated by a simple equation for carbon combustion, aerobic respiration of DCCHO and DHAA, supplied by diapycnal mixing (0.46 µmol kg−1 d−1 at maximum), could account for up to 38 % of the diapycnal O2 supply in the upper oxycline, which suggests that DOM utilization plays a significant role for shaping the upper oxycline in the ETSP.

Description: The availability of the micronutrient iron (Fe) in surface waters determines primary production, N2 fixation, and microbial community structure in large parts of the world's ocean, and thus it plays an important role in ocean carbon and nitrogen cycles. Eastern boundary upwelling systems and the connected oxygen minimum zones (OMZs) are typically associated with elevated concentrations of redox-sensitive trace metals (e.g., Fe, manganese (Mn), and cobalt (Co)), with shelf sediments typically forming a key source. Over the last 5 decades, an expansion and intensification of OMZs has been observed and this trend is likely to proceed. However, it is unclear how trace-metal (TM) distributions and transport are influenced by decreasing oxygen (O2) concentrations. Here we present dissolved (d; 〈0.2 µm) and leachable particulate (Lp; 〉0.2 µm) TM data collected at seven stations along a 50 km transect in the Mauritanian shelf region. We observed enhanced concentrations of Fe, Co, and Mn corresponding with low O2 concentrations (〈50 µmol kg−1), which were decoupled from major nutrients and nutrient-like and scavenged TMs (cadmium (Cd), lead (Pb), nickel (Ni), and copper (Cu)). Additionally, data from repeated station occupations indicated a direct link between dissolved and leachable particulate Fe, Co, Mn, and O2. An observed dFe (dissolved iron) decrease from 10 to 5 nmol L−1 coincided with an O2 increase from 30 to 50 µmol kg−1 and with a concomitant decrease in turbidity. The changes in Fe (Co and Mn) were likely driven by variations in their release from sediment pore water, facilitated by lower O2 concentrations and longer residence time of the water mass on the shelf. Variations in organic matter remineralization and lithogenic inputs (atmospheric deposition or sediment resuspension; assessed using Al as indicator for lithogenic inputs) only played a minor role in redox-sensitive TM variability. Vertical dFe fluxes from O2-depleted subsurface-to-surface waters (0.08–13.5 µmol m−2 d−1) driven by turbulent mixing and vertical advection were an order of magnitude larger than atmospheric deposition fluxes (0.63–1.43 µmol m−2 d−1; estimated using dAl inventories in the surface mixed layer) in the continental slope and shelf region. Benthic fluxes are therefore the dominant dFe supply to surface waters on the continental margins of the Mauritanian upwelling region. Overall, our results indicated that the projected future decrease in O2 concentrations in OMZs may result in increases in Fe, Mn, and Co concentrations.

Description: In early 2017 sea surface temperatures in the far eastern tropical Pacific were anomalously high while central Pacific SST anomalies remained neutral or negative. Associated to this anomaly pattern were strong anomalous precipitation events in northern Peru causing severe flooding. During April and May 2017 the near-coastal temperature anomalies declined. In-situ observations from four consecutive research cruises and a glider survey collected between 12°S and 14°S off the coast of Peru are used to describe the eastern boundary circulation and hydrography during declining surface temperature anomalies. The observational data base consists of ship-board hydrography, oxygen and upper-ocean velocity observations, hydrography from glider surveys and velocity time series from mooring deployments. Hydrography at 12°S shows a pronounced warm anomaly near the surface and on the shelf where the full water column warmed by more than 2°C with respect to climatology. Further offshore, a weaker warming was observed below the surface layer as well. The oxycline was displaced downwards and well-oxygenated waters occupied the upper 50m of the water column. Poleward velocities of the Peru-Chile Undercurrent strongly intensified in late-April and May reaching velocities above 50 cm s-1. During this period, near-surface temperature anomalies decreased but subsurface temperatures on the shelf remained high. The forcing of the observed variability of the eastern boundary circulation and of the hydrography during the late phase of the “Coastal El Niño” event is investigated and related to local and remote processes.

Description: Dissolved oxygen (O2) and nutrient concentrations at the continental margin of the eastern tropical south Pacific (ETSP) exhibit elevated intra-seasonal, seasonal and inter-annual variability. Here, we discuss the impact of remotely forced and locally generated intra-seasonal variability of the eastern boundary circulation at 12°S. Data from a multi-cruise physical and biogeochemical measurement program conducted during the declining phase of the 2017 Coastal El Niño event between April and June (austral autumn) are used. Upper ocean temperatures were anomalously high and during the latter cruises the oxycline was displaced downward compared with previous observations in austral summer 2008/09 and 2012/13. We observed the offshore propagation of a freshly generated eddy and an associated phase of weak poleward flow. After the reestablishing of the poleward Peru-Chile Undercurrent (PCUC) the passage of a remotely-generated downwelling coastal trapped wave (CTW) causes an intensification of poleward velocities exceeding 50 cm s-1. Warm temperature anomalies persisted during the intensified PCUC while sea surface temperature anomalies declined after the peak of the Coastal El Niño event. During the period of PCUC acceleration, nitrate concentrations increased while the nitrogen deficit became reduced. This suggests the advection of water less affected by anoxic biogeochemistry whereas during the period of weak poleward flow the water was biogeochemically altered more. The upper boundary of anoxic water was displaced downward increasing the depth range where bottom waters were ventilated while nitrite was depleted concurrently. We will analyze the different response of temperature, nutrients, and O2 to the varying circulation and discuss the implications for the biogeochemical element cycling in the water column and the sediments.

Description: Developmental roadmap for antimicrobial susceptibility testing systems Developmental roadmap for antimicrobial susceptibility testing systems, Published online: 17 October 2018; doi:10.1038/s41579-018-0098-9 This Consensus Statement presents the barriers that currently prevent the timely development and implementation of novel and rapid antimicrobial susceptibility testing platforms, including the costs involved, uptake of new tools, legal and regulatory aspects, difficulties conducting clinical trials and quality control, and presents possible solutions.

Description: PREFCLIM is a mixed-layer climatology for the Eastern Tropical Atlantic. The climatology contains a high-resolution (0.25 degrees) monthly-mean mixed-layer hydrography (mixed-layer depth, temperature, salinity), and coarse-resolution (2.5 degrees) estimates of the mixed-layer heat and salt balance, as well as of near-surface velocities and of air-sea fluxes. All existing hydrographic products of the region were hampered by the sparse availability of near-shore data owned by the West-African coastal countries, which could, however, be included in the new climatology.