On the influence of ram-pressure stripping on interacting galaxies in clusters

We investigate the influence of ram pressure on the star-formation rate and the distribution of gas and stellar matter in interacting model galaxies in clusters. To simulate the baryonic and non-baryonic components of interacting disc galaxies moving through a hot, thin medium we use a combined N-body/hydrodynamic code GADGET2 with a description for star formation based on density thresholds. Two identical model spiral galaxies on a collision trajectory with three different configurations were investigated in detail. In the first configuration the galaxies collide without the presence of an ambient medium, in the second configurations the ram pressure acts face on on the interacting galaxies and in the third configuration the ram pressure acts edge on. The ambient medium is thin ($10^{-28}$ g/cm$^3$), hot (3 keV $\approx 3.6\times10^7$K) and has a relative velocity of 1000 km/s, to mimic an average low ram pressure in the outskirts of galaxy clusters. The interaction velocities are comparable to galaxy interactions in groups, falling along filaments into galaxy clusters. The global star formation rate of the interacting system is enhanced in the presence of ram pressure by a factor of three in comparison to the same interaction without the presence of an ambient medium. The tidal tails and the gaseous bridge of the interacting system are almost completely destroyed by the ram pressure. The amount of gas in the wake of the interacting system is $\sim50$% of the total gas of the colliding galaxies after 500 Myr the galaxies start to feel the ram pressure. Nearly $\sim10-15$ in mass of all newly formed stars are formed in the wake of the interacting system at distances larger than 20 kpc behind the stellar discs. (abrigded)Comment: 11 pages, 12 figures, accepted for publication in MNRA

Observing biogeochemical cycles at global scales with profiling floats and gliders: prospects for a global array

Chemical and biological sensor technologies have advanced rapidly in the past five years. Sensors that require low power and operate for multiple years are now available for oxygen, nitrate, and a variety of bio-optical properties that serve as proxies for important components of the carbon cycle (e.g., particulate organic carbon). These sensors have all been deployed successfully for long periods, in some cases more than three years, on platforms such as profiling floats or gliders. Technologies for pH, pCO2, and particulate inorganic carbon are maturing rapidly as well. These sensors could serve as the enabling technology for a global biogeochemical observing system that might operate on a scale comparable to the current Argo array. Here, we review the scientific motivation and the prospects for a global observing system for ocean biogeochemistry

The Argo Program : present and future

Author Posting. © The Oceanography Society, 2017. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 30, no. 2 (2017): 18–28, doi:10.5670/oceanog.2017.213.The Argo Program has revolutionized large-scale physical oceanography through its contributions to basic research, national and international climate assessment, education, and ocean state estimation and forecasting. This article discusses the present status of Argo and enhancements that are underway. Extensions of the array into seasonally ice-covered regions and marginal seas as well as increased numbers of floats along the equator and around western boundary current extensions have been proposed. In addition, conventional Argo floats, with their 2,000 m sampling limit, currently observe only the upper half of the open ocean volume. Recent advances in profiling float technology and in the accuracy and stability of float-mounted conductivity-temperature-depth sensors make it practical to obtain measurements to 6,000 m. The Deep Argo array will help observe and constrain the global budgets of heat content, freshwater, and steric sea level, as well as the full-depth ocean circulation. Finally, another extension to the Argo Program is the addition of a diverse set of chemical sensors to profiling floats in order to build a Biogeochemical-Argo array to understand the carbon cycle, the biological pump, and ocean acidification.S.R.J. was supported by US Argo Program through NOAA Grant NA14OAR4320158 (CINAR). D.R. and N.Z. were supported by the US Argo Program through NOAA Grant NA10OAR4310139 (CIMEC). S.C.R. was supported by the US Argo Program through NOAA Grants NAOAR4320063 and NA16OAR4310161 (JISAO). K.S.J. was supported by the David and Lucile Packard Foundation and by the Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) Project funded by National Science Foundation, Division of Polar Programs (NSF PLR-1425989). G.C.J. is supported by the Ocean Observations and Monitoring Division, Climate Program Office, National Oceanic and Atmospheric Administration (NOAA), US Department of Commerce and NOAA Research

Links between topography, wind, deflation, lakes and dust: The case of the Bodélé Depression, Chad

The Bodélé Depression, Chad is the planet's largest single source of dust. Deflation from the Bodélé could be seen as a simple coincidence of two key prerequisites: strong surface winds and a large source of suitable sediment. But here we hypothesise that long term links between topography, winds, deflation and dust ensure the maintenance of the dust source such that these two apparently coincidental key ingredients are connected by land-atmosphere processes with topography acting as the overall controlling agent. We use a variety of observational and numerical techniques, including a regional climate model, to show that: 1) contemporary deflation from the Bodélé is delineated by topography and a surface wind stress maximum; 2) the Tibesti and Ennedi mountains play a key role in the generation of the erosive winds in the form of the Bodélé Low Level Jet (LLJ); 3) enhanced deflation from a stronger Bodélé LLJ during drier phases, for example, the Last Glacial Maximum, was probably sufficient to create the shallow lake in which diatoms lived during wetter phases, such as the Holocene pluvial. Winds may therefore have helped to create the depression in which erodible diatom material accumulated. Instead of a simple coincidence of nature, dust from the world's largest source may result from the operation of long term processes on paleo timescales which have led to ideal conditions for dust generation in the world's largest dust source. Similar processes plausibly operate in other dust hotspots in topographic depressions

The Global Ocean Biogeochemistry (GO-BGC) array of profiling floats to observe changing ocean chemistry and biology

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Matsumoto, G., Johnson, K., Riser, S., Talley, L., Wijffels, S., & Hotinski, R. The Global Ocean Biogeochemistry (GO-BGC) array of profiling floats to observe changing ocean chemistry and biology. Marine Technology Society Journal, 56(3), (2022): 122–123, https://doi.org/10.4031/mtsj.56.3.25.The Global Ocean Biogeochemistry (GO-BGC) Array is a project funded by the US National Science Foundation to build a global network of chemical and biological sensors on Argo profiling floats. The network will monitor biogeochemical cycles and ocean health. The floats will collect from a depth of 2,000 meters to the surface, augmenting the existing Argo array that monitors ocean temperature and salinity. Data will be made freely available within a day of being collected via the Argo data system. These data will allow scientists to pursue fundamental questions concerning ocean ecosystems, monitor ocean health and productivity, and observe the elemental cycles of carbon, oxygen, and nitrogen through all seasons of the year. Such essential data are needed to improve computer models of ocean fisheries and climate, to monitor and forecast the effects of ocean warming and ocean acidification on sea life, and to address key questions identified in “Sea Change: 2015–2025 Decadal Survey of Ocean Sciences” such as: What is the ocean’s role in regulating the carbon cycle? What are the natural and anthropogenic drivers of open ocean deoxygenation? What are the consequences of ocean acidification? How do physical changes in mixing and circulation affect nutrient availability and ocean productivity?Funding for the GO-BGC Array is provided through the NSF’s Mid-Scale Research Infrastructure-2 Program (MSRI-2; NSF Award 1946578)

Salinity and temperature balances at the SPURS central mooring during fall and winter

Author Posting. © The Oceanography Society, 2015. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 28, no. 1 (2015): 56-65, doi:10.5670/oceanog.2015.06.One part of the Salinity Processes in the Upper-ocean Regional Study (SPURS) field campaign focused on understanding the physical processes affecting the evolution of upper-ocean salinity in the region of climatological maximum sea surface salinity in the subtropical North Atlantic (SPURS-1). An upper-ocean salinity budget provides a useful framework for increasing this understanding. The SPURS-1 program included a central heavily instrumented mooring for making accurate measurements of air-sea surface fluxes, as well as other moorings, Argo floats, and gliders that together formed a dense observational array. Data from this array are used to estimate terms in the upper-ocean salinity and heat budgets during the SPURS-1 campaign, with a focus on the first several months (October 2012 to February 2013) when the surface mixed layer was becoming deeper, fresher, and cooler. Specifically, we examine the salinity and temperature balances for an upper-ocean mixed layer, defined as the layer where the density is within 0.4 kg m–3 of its surface value. The gross features of the evolution of upper-ocean salinity and temperature during this fall/winter season are explained by a combination of evaporation and precipitation at the sea surface, horizontal transport of heat and salt by mixed-layer currents, and vertical entrainment of fresher, cooler fluid into the layer as it deepened. While all of these processes were important in the observed seasonal (fall) freshening at this location in the salinity-maximum region, the variability of salinity on monthly-to-intraseasonal time scales resulted primarily from horizontal advection.J.T. Farrar, A.J. Plueddemann, J.B. Edson, and the deployment of the central mooring were supported by NASA grant NNX11AE84G. L. Rainville, C. Lee, C. Eriksen, and the Seaglider program were supported by NASA grant NNX11AE78G. R. Schmitt was supported by NSF grant OCE-1129646. B. Hodges and D. Fratantoni were supported by NASA grant NNX11AE82G. The Prawler moorings were funded by PMEL. The data analysis was also supported by NASA grant NNX14AH38G

Autonomous multi-platform observations during the Salinity Processes in the Upper-ocean Regional Study

Author Posting. © The Oceanography Society, 2017. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 30, no. 2 (2017): 38–48, doi:10.5670/oceanog.2017.218.The Salinity Processes in the Upper-ocean Regional Study (SPURS) aims to understand the patterns and variability of sea surface salinity. In order to capture the wide range of spatial and temporal scales associated with processes controlling salinity in the upper ocean, research vessels delivered autonomous instruments to remote sites, one in the North Atlantic and one in the Eastern Pacific. Instruments sampled for one complete annual cycle at each of these two sites, which are subject to contrasting atmospheric forcing. The SPURS field programs coordinated sampling from many different platforms, using a mix of Lagrangian and Eulerian approaches. This article discusses the motivations, implementation, and first results of the SPURS-1 and SPURS-2 programs.SPURS is supported by multiple NASA grants, with important additional contributions from the US National Science Foundation, NOAA, and the Office of Naval Research, as well as international agencies. SVP drifters are deployed with support from NASA and the NOAA funded Global Drifter Program at the Lagrangian Drifter Laboratory of the Scripps Institution of Oceanography. SVP-S2 drifters are provided by NOAA-AOML and NASA. PRAWLER mooring development is supported by NOAA’s Office of Oceanic and Atmospheric Research, Ocean Observing and Monitoring Division, and by NOAA/PMEL

Bottom mixed layer oxygen dynamics in the Celtic Sea

The seasonally stratified continental shelf seas are highly productive, economically important environments which are under considerable pressure from human activity. Global dissolved oxygen concentrations have shown rapid reductions in response to anthropogenic forcing since at least the middle of the twentieth century. Oxygen consumption is at the same time linked to the cycling of atmospheric carbon, with oxygen being a proxy for carbon remineralisation and the release of CO2. In the seasonally stratified seas the bottom mixed layer (BML) is partially isolated from the atmosphere and is thus controlled by interplay between oxygen consumption processes, vertical and horizontal advection. Oxygen consumption rates can be both spatially and temporally dynamic, but these dynamics are often missed with incubation based techniques. Here we adopt a Bayesian approach to determining total BML oxygen consumption rates from a high resolution oxygen time-series. This incorporates both our knowledge and our uncertainty of the various processes which control the oxygen inventory. Total BML rates integrate both processes in the water column and at the sediment interface. These observations span the stratified period of the Celtic Sea and across both sandy and muddy sediment types. We show how horizontal advection, tidal forcing and vertical mixing together control the bottom mixed layer oxygen concentrations at various times over the stratified period. Our muddy-sand site shows cyclic spring-neap mediated changes in oxygen consumption driven by the frequent resuspension or ventilation of the seabed. We see evidence for prolonged periods of increased vertical mixing which provide the ventilation necessary to support the high rates of consumption observed

Beam-target helicity asymmetry for γ→n→→π−p in the N*resonance region

We report the first beam-target double-polarization asymmetries in the γ þ nðpÞ → π− þ pðpÞ reaction spanning the nucleon resonance region from invariant mass W ¼ 1500 to 2300 MeV. Circularly polarized photons and longitudinally polarized deuterons in solid hydrogen deuteride (HD) have been used with the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. The exclusive final state has been extracted using three very different analyses that show excellent agreement, and these have been used to deduce the E polarization observable for an effective neutron target. These results have been incorporated into new partial wave analyses and have led to significant revisions for several γnN* resonance photocouplings