Depletion of oxygen, nitrate and nitrite in the Peruvian oxygen minimum zone cause an imbalance of benthic nitrogen fluxes

Highlights • Sulphidic event on the shelf resulted in a temporal imbalance of the benthic N cycle. • Bacterial NOx storage is a major source of oxidative power during euxinia. • Peruvian shelf and upper slope sediments are strong recycling sites of fixed N. Abstract Oxygen minimum zones (OMZ) are key regions for fixed nitrogen loss in both the sediments and the water column. During this study, the benthic contribution to N cycling was investigated at ten sites along a depth transect (74–989 m) across the Peruvian OMZ at 12 °S. O2 levels were below detection limit down to ~ 500 m. Benthic fluxes of N2, NO3–, NO2–, NH4+, H2S and O2 were measured using benthic landers. Flux measurements on the shelf were made under extreme geochemical conditions consisting of a lack of O2, NO3– and NO2– in the bottom water and elevated seafloor sulphide release. These particular conditions were associated with a large imbalance in the benthic nitrogen cycle. The sediments on the shelf were densely covered by filamentous sulphur bacteria Thioploca, and were identified as major recycling sites for DIN releasing high amounts of NH4+up to 21.2 mmol m−2 d−1 that were far in excess of NH4+release by ammonification. This difference was attributed to dissimilatory nitrate (or nitrite) reduction to ammonium (DNRA) that was partly being sustained by NO3– stored within the sulphur oxidizing bacteria. Sediments within the core of the OMZ (ca. 200 to 400 m) also displayed an excess flux of N of 3.5 mmol m−2 d−1 mainly as N2. Benthic nitrogen and sulphur cycling in the Peruvian OMZ appears to be particularly susceptible to bottom water fluctuations in O2, NO3−and NO2−, and may accelerate the onset of pelagic euxinia when NO3−and NO2−become depleted

Reconstructing the Deep Population History of Central and South America

We report genome-wide ancient DNA from 49 individuals forming four parallel time transects in Belize, Brazil, the Central Andes, and the Southern Cone, each dating to at least 9,000 years ago. The common ancestral population radiated rapidly from just one of the two early branches that contributed to Native Americans today. We document two previously unappreciated streams of gene flow between North and South America. One affected the Central Andes by 4,200 years ago, while the other explains an affinity between the oldest North American genome associated with the Clovis culture and the oldest Central and South Americans from Chile, Brazil, and Belize. However, this was not the primary source for later South Americans, as the other ancient individuals derive from lineages without specific affinity to the Clovis-associated genome, suggesting a population replacement that began at least 9,000 years ago and was followed by substantial population continuity in multiple regions

Linnéfest och doktorspromotion 23 och 26 maj 2007

Dust storms that develop along the Pisco-Ica desert in Southern Peru, locally known as "Paracas" winds have ecological, health and economic repercussions. Here we identify dust sources through MODIS (Moderate Resolution Imaging Spectroradiometer) imagery and analyze HYSPLIT (Hybrid Single Particles Lagrangian Integrated Trajectory) model trajectories and dispersion patterns, along with concomitant synoptic-scale meteorological conditions from National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis (NCEP/NCAR). Additionally, surface pressure data from the hourly METeorological Aerodrome Report (METAR) at Arica (18.5 degrees S, 70.3 degrees W) and Pisco (13.7 degrees S, 76.2 degrees W) were used to calculate Alongshore (sea-level) Pressure Gradient (APG) anomalies during Paracas dust storms, their duration and associated wind-speeds and wind directions. This study provides a review on the occurrence and strength of the Paracas dust storms as reported in the Pisco airfield for five-year period and their correspondence with MODIS true-color imagery in terms of dust-emission source areas. Our results show that most of the particle fluxes moving into the Ica-Pisco desert area during Paracas wind events originate over the coastal zone, where strong winds forced by steep APGs develop as the axis of a deep mid-troposphere trough sets in along north-central Chile. Direct relationships between Paracas wind intensity, number of active dust-emission sources and APGs are also documented, although the scarcity of simultaneous METAR/MODIS data for clearly observed MODIS dust plumes prevents any significant statistical inference. Synoptic-scale meteorological composites from NCEP/NCAR reanalysis data show that Paracas wind events (steep APGs) are mostly associated with the strengthening of anticyclonic conditions in northern Chile, that can be attributed to cold air advection associated with the incoming trough. Compared to the MODIS images, HYSPLIT outputs were able to spatially reproduce trajectories and dust dispersion plumes during the Paracas wind storms. HYSPLIT trajectories revealed that part of the wind-eroded lithological material can be transported downwind several kilometers along the Peruvian coast and also deposited over the nearby coastal ocean, giving support to the presence of an aeolian signal in continental shelf sediments, of great importance for paleoenvironmental studies

Surface wind strength and sea surface temperature connections along the south peruvian coast during the last 150 years

International audienc

Calcareous benthic foraminifera from the upper central Peruvian margin : control of the assemblage by pore water redox and sedimentary organic matter

We studied 'living' (stained) benthic foraminifera in the upper border of the Peruvian oxygen minimum zone (OMZ) to determine the relationship between species' distribution and pore water and sediment geochemistry under oxygen deficiency. Superficial sediments were sampled between 2009 and 2011 from 2 bathymetric transects off central Peru (45 to 300 m depth). The quantity (total organic carbon, total nitrogen and chloroplastic pigment equivalents [CPE]) and quality (chlorophyll a/phaeopigments ratio) of organic matter (OM) were evaluated. Benthic foraminifera were sampled in the top 5 cm of sediment. Commonly, the inner shelf sediments were sulfidic and labile OM-rich, whereas the outer shelf and upper slope sediments exhibited postoxic conditions (e.g. anoxic and non-sulfidic) with less labile OM, typical of OMZ core sediments. Mixed conditions were found in shelf sediment samples from April 2010, when the effects of El Nino 2009/2010 were withdrawing. Foraminiferal assemblages exhibited differences according to redox conditions and OM quality, and were concentrated in the topmost sediment. A canonical correspondence analysis and non-parametric correlations indicated that Bolivina costata, Nonionella auris and Virgulinella fragilis were characteristic of sulfidic/labile OM sediments, thriving slightly deeper in the sediment. In contrast, Bolivina pacifica headed the assemblage representative of postoxia/less labile OM. Bolivina seminuda and Buliminella tenuata (both dominant under postoxia) were not associated with any specific measured parameter, although were present in sulfidic sediments, suggesting other factors were involved in their distribution