Nitrous oxide in the surface layer of the tropical North Atlantic Ocean along a west to east transect

Nitrous oxide (N2O) was measured during the first German SOLAS (Surface Ocean – Lower Atmosphere Study) cruise in the tropical North Atlantic Ocean on board R/V Meteor during October/November 2002. About 900 atmospheric and dissolved N2O measurements were performed with a semi-continuous GC-ECD system equipped with a seawater-gas equilibrator. Surface waters along the main transect at 10°N showed no distinct longitudinal gradient. Instead, N2O saturations were highly variable ranging from 97% to 118% (in the Guinea Dome Area, 11°N, 24°W). When approaching the continental shelf of West Africa, N2O surface saturations went up to 113%. N2O saturations in the region of the equatorial upwelling (at 0–1.5°N, 23.5–26°W) were correlated with decreasing sea surface temperatures and showed saturations up to 109%. The overall mean N2O saturation was 104 ± 4% indicating that the tropical North Atlantic Ocean is a net source of atmospheric N2O

Phonon anharmonicity and negative thermal expansion in SnSe

The anharmonic phonon properties of SnSe in the Pnma phase were investigated with a combination of experiments and first-principles simulations. Using inelastic neutron scattering (INS) and nuclear resonant inelastic X-ray scattering (NRIXS), we have measured the phonon dispersions and density of states (DOS) and their temperature dependence, which revealed a strong, inhomogeneous shift and broadening of the spectrum on warming. First-principles simulations were performed to rationalize these measurements, and to explain the previously reported anisotropic thermal expansion, in particular the negative thermal expansion within the Sn-Se bilayers. Including the anisotropic strain dependence of the phonon free energy, in addition to the electronic ground state energy, is essential to reproduce the negative thermal expansion. From the phonon DOS obtained with INS and additional calorimetry measurements, we quantify the harmonic, dilational, and anharmonic components of the phonon entropy, heat capacity, and free energy. The origin of the anharmonic phonon thermodynamics is linked to the electronic structure.Comment: 14 pages, 12 figure

North Atlantic production of nitrous oxide in the context of changing atmospheric levels

We use transit time distributions calculated from tracer data together with in situ measurements of N(2)O to estimate the concentration of biologically produced N(2)O ([N(2)O](xs)) and N(2)O production rates in the central North Atlantic Ocean. Our approach to estimation of N(2)O production rates integrates the effects of potentially varying production and decomposition mechanisms along the transport path of a water mass. We find that previously used approaches overestimate the oceanic equilibrium N(2)O concentrations by 8-13% and thus underestimate the strength of N(2)O sources in large parts of the water column. Thus the quantitative characteristics of the [N(2)O](xs)/AOU relationship used as an indicator of nitrification are distorted. We developed a new parameterization of N(2)O production during nitrification depending linearly on AOU and exponentially on temperature and depth, which can be applied to calculate N(2)O production due to nitrification in the entire ocean including oxygen minimum zones

Contrasting biogeochemistry of nitrogen in the Atlantic and Pacific oxygen minimum zones

We present new data for the stable isotope ratio ofinorganic nitrogen species from the contrasting oxygen minimum zones (OMZs) of the Eastern Tropical North Atlantic, south of Cape Verde, and the Eastern Tropical South Pacific off Peru. Differences in minimum oxygen concentration and corresponding N-cycle processes for the two OMZs are reflected in strongly contrasting δ15N distributions. Pacific surface waters are marked by strongly positive values for δ15N-NO−3) reflecting fractionation associated withsubsurface N loss and partial NO−3 utilization. This contrasts with negative values in NO−3 depleted surface waters of the Atlantic which are lower than can be explained by N supply via N2 fixation. We suggest the negative values reflect inputs of nitrate, possibly transient, associated withdeposition of Saharan dust. Strong signals of N-loss processes in the subsurfacePacific OMZ are evident in the isotope and N2O data, both ofwhich are compatible with a contribution of canonical denitrification to overall N-loss. However the apparent N isotope fractionation factor observed is relatively low (ɛd=11.4 ‰) suggesting an effect of influence from denitrification in sediments. Identical positive correlation of N2O vs. AOU for waters with oxygen concentrations ([O2]<5 μmol l−1) in both regions reflect a nitrification source. Sharp decrease in N2O concentrations is observed in the Pacific OMZ due to denitrification under oxygen concentrations O2 <5 μmol l−1

Biological productivity in the Mauritanian upwelling estimated with a triple gas approach

Due to their high biological productivity coastal upwelling regions are important for biogeochemical cycles in the ocean and for fisheries. Upwelled water is not only enriched in nutrients but also supersaturated with respect to atmospheric CO2 and N2O and undersaturated for O2. We present a novel approach to estimate carbon based net community production (NCP) using surface ocean data for CO2, O2 and N2O from three cruises to the Mauritanian upwelling region (Northwest Africa) that were conducted in different seasons. Through combination of the saturation patterns of CO2, O2 and N2O effects of air–sea gas exchange and NCP could be separated. NCP values ranges from 0.6 ± 0.1g C m−2 d−1 during times of weak upwelling to 1.6 ± 0.4 g C m−2 d−1 during strong upwelling. The estimated NCP values show a strong relationship with a wind derived upwelling index, which was used to estimate annual NCP

Introduction to special section: Results of the Meteor 55: Tropical SOLAS expedition

This special section presents results from an interdisciplinary research cruise to the northern tropical Atlantic Ocean, which took place in October–November 2002. The cruise was planned as a pilot study for the international Surface Ocean – Lower Atmosphere Study (SOLAS) project. This introduction summarizes the goals as well as the hydrographic and atmospheric setting of the expedition. We also present a brief review of the findings published in this section and elsewhere concerning controls on trace gas fluxes and the biogeochemical significance of dust composition and deposition

A 30 ‐Year Time Series of Transient Tracer‐Based Estimates of Anthropogenic Carbon in the Central Labrador Sea

We use a 30-year time series (1986–2016) of dichlorodifluoromethane (CFC-12) concentrations with a refined transit time distribution (TTD) method, to estimate the temporal variation of anthropogenic carbon (Cant) in the Central Labrador Sea. We determined that the saturation of CFC-12 and sulfur hexafluroide (SF6) in newly-formed Labrador Sea Water had departed significantly from 100% and varied systematically with time. Multiple linear regression of the time-varying saturation, with the tracer's atmospheric growth rate and the wintertime mixed layer depth as independent variables, allowed reconstruction of the saturation history of CFC-12 and SF6 in wintertime surface waters, which was implemented in the TTD method. Use of the time-varying saturation for CFC-12 gave Cant concentrations ∼7 μmol kg−1 larger than estimates obtained assuming a constant saturation of 100%. The resulting Cant column inventories were ∼20% larger and displayed lower interannual variability compared to conventional TTD-based estimates. The column inventory of Cant increased at an average rate of 1.8 mol m−2 y−1 over the 30-year period. However, the accumulation rate of Cant was higher than this average in the early 1990s and since 2013, whereas inventories remained almost unchanged between 2003 and 2012. The variation in the Cant accumulation rate is shown to be linked to temporal variability in the relative layer thickness of the annually ventilated Labrador Sea Water and the underlying Deep Intermediate Water. The non-steady Cant accumulation highlights the importance of sampling frequency, especially in regions of variable deep mixing and high carbon inventories, and potential misinterpretation of Cant dynamic

KYTC Maintenance Field Operations Guide Supplement

The Kentucky Transportation Cabinet (KYTC) is tasked with managing an asset portfolio that includes over 27,500 miles of roadway and 9,000 bridges. Keeping these assets in sound condition demands significant effort from KYTC’s Division of Maintenance, which includes activities ranging from mowing and litter pickup to cleaning out culverts and performing emergency roadway work. Despite the immense responsibilities shouldered by Maintenance personnel, until this project the Cabinet’s 12 districts lacked a systematic method for capturing and recording maintenance activities. Through a series of workshops held in each KYTC’s district with Section Engineer and Maintenance Supervisors, researchers at the Kentucky Transportation Center (KTC) facilitated efforts to inventory routine maintenance activities, document how frequently each activity is done, and capture the ways in which maintenance functions are adjusted in response to special projects (which generally receive priority over general maintenance functions). Key products of this research include a Statewide Maintenance Calendar, which defines — based on a combination of stakeholder feedback and statistical analysis — optimal time intervals for undertaking key maintenance activities, as well as district-specific maintenance calendars. Having recourse to these calendars will help district staff more efficiently plan, schedule, and coordinate maintenance functions

The Northeast Water polynya as an atmospheric CO2 sink: a seasonal rectification hypothesis

During the multidisciplinary ‘NEW92’ cruise of the United States Coast Guard Cutter (USCGC) Polar Sea to the recurrent Northeast Water (NEW) Polynya (77–81°N, 6–17°W; July–August 1992), total dissolved inorganic carbon and total alkalinity in the water column were measured with high precision to determine the quantitative impact of biological processes on the regional air-sea flux of carbon. Biological processes depleted the total inorganic carbon of summer surface waters by up to 2 mol C m−2 or about 3%. On a regional basis this depletion correlated with depth-integrated values of chlorophyll a, particulate organic carbon, and the inorganic nitrogen deficit. Replacement of this carbon through exchange with the atmosphere was stalled owing to the low wind speeds during the month of the cruise, although model calculations indicate that the depletion could be replenished by a few weeks of strong winds before ice forms in the autumn. These measurements and observations allowed formulation of a new hypothesis whereby seasonally ice-covered regions like the NEW Polynya promote a unique biologically and physically mediated “rectification” of the typical (ice free, low latitude) seasonal cycle of air-sea CO2 flux. The resulting carbon sink is consistent with other productivity estimates and represents an export of biologically cycled carbon either to local sediments or offshore. If this scenario is representative of seasonally ice-covered Arctic shelves, then the rectification process could provide a small, negative feedback to excess atmospheric CO2

Kentucky Transportation Cabinet Right of Way Process Review (Phase I)

From the Executive Summary: The Kentucky Transportation Cabinet (KYTC) is responsible for planning, developing, constructing, and maintaining a prodigious inventory of roadway and bridge assets throughout the state. Project development is a complex process involving the coordination of numerous divisions and preconstruction disciplines across the Cabinet. On many projects, right-of-way (ROW) acquisition presents many challenges. Frequently, the ROW process is found on the critical path, meaning that it effectively governs a project’s overall duration. In some cases — especially on more complex projects — acquiring the ROW may take several years. Recognizing the need to shorten the duration and improve the efficiency of the ROW process, Cabinet leadership commissioned researchers at the Kentucky Transportation Center (KTC) to organize and facilitate the activities of a ROW Process Review Team. All members of the team were selected by KYTC leadership, and it consisted entirely of current and retired Cabinet personnel. Cabinet leadership envisioned a two-phase project. During Phase I (the subject of this report) the ROW Process Review Team mapped out the current ROW processand generated process improvement ideas. Phase II, if authorized, will focus on the implementation of selected process improvements. This report begins with a discussion of the methodological approach used for this project. At the project’s outset, ROW Process Review Team members documented KYTC’s current ROW process by estimating activity durations and preparing timelines for a concept project. Team members focused on the most critical, or limiting, activities, finding that tasks associated with Appraisals, Acquisitions, and Relocations have the longest durations. Seventeen Gantt charts mapping the ROW process were prepared; each chart delineates major tasks and their constitutive steps (Appendix C). Team members subsequently turned their attention to identifying measures that could shorten the process’s overall duration. Invited speakers from the Federal Highway Administration and Indiana Department of Transportation shared their experiences,thoughts on best practices,and strategies that had been used effectively at other state transportation agencies to expedite and streamline ROW acquisition. Using its review of the Cabinet’s current ROW process and information on other state policies and practices as a springboard, team members embarked on a series of intensive brainstorming sessions, eventually generating over 100 prospective ideas to bolster the efficiency of the ROW process. Concurrently, the research team administered surveys to and conducted interviews with consultants and KYTC district-level attorneys to solicit their ideas on amending the ROW process