Oxygen export to the deep ocean following Labrador Sea Water formation

The Labrador Sea in the North Atlantic Ocean is one of the few regions globally where oxygen from the atmosphere can reach the deep ocean directly. This is the result of wintertime convection, which homogenizes the water column to a depth of up to 2000 m, and brings deep water undersaturated in oxygen into contact with the atmosphere. In this study, we analyze how the intense oxygen uptake during Labrador Sea Water (LSW) formation affects the properties of the outflowing deep western boundary current, which ultimately feeds the upper part of the North Atlantic Deep Water layer in much of the Atlantic Ocean. Seasonal cycles of oxygen concentration, temperature, and salinity from a two-year time series collected by sensors moored at 600 m nominal depth in the outflowing boundary current at 53° N show that LSW is primarily exported in the months following the onset of convection, from March to August. During the rest of the year, properties of the outflow resemble those of Irminger Water, which enters the basin with the boundary current from the Irminger Sea. The input of newly ventilated LSW increases the oxygen concentration from 298 μmol L−1 in January to a maximum of 306 μmol L−1 in April. As a result of this LSW input, 1.57 × 1012 mol year−1 of oxygen are added to the outflowing boundary current, mostly during summer, equivalent to 49 % of the wintertime uptake from the atmosphere in the interior of the basin. The export of oxygen from the subpolar gyre associated with this direct southward pathway of LSW is estimated to supply about 71 % of the oxygen consumed annually in the upper North Atlantic Deep Water layer in the Atlantic Ocean between the equator and 50° N. Our results show that the formation of LSW is important for replenishing oxygen to the deep oceans, meaning that possible changes in its formation rate and ventilation due to climate change could have wide-reaching impacts on marine life.

Retreat of Pine Island Glacier: The impact of El Nino Southern Oscillation events

<p>The Amundsen Sea sector in West Antarctica is undergoing dramatic changes, with thinning ice shelves and accelerating, retreating glaciers. One of the largest and fastest flowing ice streams in the region is Pine Island Glacier (PIG). In recent decades it has retreated over 30 km, experienced a 75% increase in velocity and thinned by more than 100m. However, these changes have not been constant, there have been alternating periods of acceleration and stabilisation since the start of the observational era in the 1970s. This has been attributed to variable ocean conditions, where interannual and decadal changes in the Circumpolar Deep Water layer have been linked to large-scale climate variability. The initial ungrounding and subsequent retreat of PIG from a submarine ridge is believed to have been caused by extreme changes in ocean conditions linked to El Niño Southern Oscillation (ENSO) events during the 1940s and 1970s. However, the exact role that these events have played over the last century is not fully understood.</p><p>In this study the ice flow model Úa is used to assess how the retreat of PIG has been impacted by ENSO events. During these events, variations in thermocline depth affect the amount of heat available for basal melting beneath the ice shelf. To represent these changing ocean conditions a melt rate parameterisation based on a 1D plume model is used, which depends on ice shelf geometry, grounding line depth and ambient ocean properties. Results will show if a gradually warming ocean is enough to initiate grounding line retreat or if brief, large changes in temperature are required. Further investigations will determine whether cooler years contributed to a slow down of the ice stream. This work will help us understand and model the response of other glaciers to extreme changes in ocean conditions caused by ENSO events in a warming future.</p>

Dynamics of Deep Recirculation Cells Offshore of the Deep Western Boundary Current in the Subtropical North Atlantic (15°–30°N)

The dynamics of the deep recirculation offshore of the deep western boundary current (DWBC) between 15° and 30°N within the upper North Atlantic Deep Water layer (1000 ≤ z ≤ 3000 m) is investigated with two different eddy-resolving numerical simulations. Despite some differences in the recirculation cells, our assessment of the modeled deep isopycnal circulation patterns (36.77 ≤ σ2 ≤ 37.06 kg m−3) shows that both simulations predict the DWBC flowing southward along the continental slope, while the so-called Abaco Gyre and two additional cyclonic cells recirculate waters northward in the interior. These cells are a few degrees wide, located along the DWBC path, and characterized by potential vorticity (PV) changes occurring along their mean streamlines. The analysis of the mean PV budget reveals that these changes result from the action of eddy forcing that tends to erode the PV horizontal gradients. The lack of a major upper-ocean boundary current within the study region, and the fact that the strongest eddy forcing is constrained within a few hundreds of kilometers of the western boundary, suggest that the DWBC is the primary source of eddy forcing. Finally, the eddies responsible for forcing the recirculation have dominant time scales between 100 and 300 days, which correspond to the primary observed variability scales of the DWBC transport at 26.5°N.

Preconditioning and Formation of Maud Rise Polynyas in a High-Resolution Earth System Model

Open-ocean polynyas (OOPs) in the Southern Ocean are ice-free areas within the winter ice pack that are associated with deep convection, potentially contributing to the formation of Antarctic Bottom Water. To enhance the credibility of Earth system models (ESMs), their ability to simulate OOPs realistically is thus crucial. Here we investigate OOPs that emerge intermittently in a high-resolution (HR) preindustrial simulation with the Energy Exascale Earth System Model, version 0.1 (E3SMv0), an offspring of the Community Earth System Model (CESM). While low-resolution (LR) simulations with E3SMv0 show no signs of OOP formation, the preindustrial E3SMv0-HR simulation produces both large Weddell Sea polynyas (WSPs) as well as small Maud Rise polynyas (MRPs). The latter are associated with a prominent seamount in the eastern Weddell Sea, and their preconditioning and formation is the focus of this study. The steep flanks of the rugged topography in this region are in E3SMv0-HR sufficiently well resolved for the impinging flow to produce pronounced Taylor caps that precondition the region for convection. Aided by an accumulation of heat in the Weddell Deep Water layer, the ultimate trigger of convection that leads to MRPs is the advection of anomalously high upper-ocean-layer salinity. The crucial difference to WSP-producing LR ESM simulations is that in E3SMv0-HR, WSPs are realistically preceded by MRPs, which in turn are a result of the flow around bathymetry being represented with unprecedented detail.

Film spreading from a miscible drop on a deep liquid layer

We study the spreading of a film from ethanol–water droplets of radii $0.9~\text{mm}<r_{d}<1.1~\text{mm}$ on the surface of a deep water layer for various concentrations of ethanol in the drop. Since the drop is lighter ($\unicode[STIX]{x1D709}=\unicode[STIX]{x1D70C}_{l}/\unicode[STIX]{x1D70C}_{d}>1.03$), it stays at the surface of the water layer during the spreading of the film from the drop; the film is more viscous than the underlying water layer since $\unicode[STIX]{x1D712}=\unicode[STIX]{x1D707}_{l}/\unicode[STIX]{x1D707}_{d}>0.38$. Inertial forces are not dominant in the spreading since the Reynolds numbers based on the film thickness $h_{f}$ are in the range $0.02<Re_{f}<1.4$. The spreading is surface-tension-driven since the film capillary numbers are in the range $0.0005<Ca_{f}<0.0069$ and the drop Bond numbers are in the range $0.19<Bo_{d}<0.56$. We observe that, when the drop is brought in contact with the water surface, capillary waves propagate from the point of contact, followed by a radially expanding, thin circular film of ethanol–water mixture. The film develops instabilities at some radius to form outward-moving fingers at its periphery while it is still expanding, till the expansion stops at a larger radius. The film then retracts, during which time the remaining major part of the drop, which stays at the centre of the expanding film, thins and develops holes and eventually mixes completely with water. The radius of the expanding front of the film scales as $r_{f}\sim t^{1/4}$ and shows a dependence on the concentration of ethanol in the drop as well as on $r_{d}$, and is independent of the layer height $h_{l}$. Using a balance of surface tension and viscous forces within the film, along with a model for the fraction of the drop that forms the thin film, we obtain an expression for the dimensionless film radius $r_{f}^{\ast }=r_{f}/r_{d}$, in the form $fr_{f}^{\ast }={t_{\unicode[STIX]{x1D707}d}^{\ast }}^{1/4}$, where $t_{\unicode[STIX]{x1D707}d}^{\ast }=t/t_{\unicode[STIX]{x1D707}d}$, with the time scale $t_{\unicode[STIX]{x1D707}d}=\unicode[STIX]{x1D707}_{d}r_{d}/\unicode[STIX]{x0394}\unicode[STIX]{x1D70E}$ and $f$ is a function of $Bo_{d}$. Similarly, we show that the dimensionless velocity of film spreading, $Ca_{d}=u_{f}\unicode[STIX]{x1D707}_{d}/\unicode[STIX]{x0394}\unicode[STIX]{x1D70E}$, scales as $4f^{4}Ca_{d}={r_{f}^{\ast }}^{-3}$.

THE ELECTROCOAGULATION/ADVANCED OXIDATION TREATMENT OF THE WELL WATER FROM ŽUPANJA

The work was development and application of the purification system suitable for the treatment of groundwater used for human consumption as well as watering of the plants in the system for the hydroponic cultivation of tomatoes. For that purpose the well water from the 60 m deep water layer situated near the city of Županja (Eastern Croatia) was processed. Most of the measured parameters exceeded upper permissible limit (UPL) for drinking water. The concentrations of the parameters color, turbidity, iron, manganese, arsenic, phosphates, chemical oxygen demand and ammonia were as follows 292±20 mg/PtCo, 21±5 NTU, 1.72±0.34 mg/L, 0.075±0.014 mg/L, 0.074±0.011 mg/L, 10.4±1.7 mg/L, 37±1 mg/L and 1.2±0.1 mg/L, respectively. Due to the complex composition of the treated water, the purification system required the combination of electrochemical treatment, using iron and aluminum electrode plates with simultaneous ozonation followed by post treatment with hydrogen peroxide and ozone. The electrocoagulation/ozonation approach was used for the removal of heavy metals, color, turbidity, phosphates and partially organic matter while the rest of the organic contaminants and ammonia were removed by the treatment with hydrogen peroxide and ozone. Following the combined electrochemical treatment and post treatment with hydrogen peroxide and ozone all measured parameters in the treated water were in agreement with regulated values. The combined treatment resulted in total removal of arsenic, color, turbidity, ammonia and organic contaminants while the removal of other parameters of interest was up to 97.98%.

Oceanic hypervelocity impact events: a viable mechanism for successful panspermia?

The idea that life migrates naturally between planetary bodies has grown in strength in recent years. This idea (panspermia) is believed to be possible via the mechanism of impact events. Previous research on this topic has concentrated on small meteoroids (micrometres to centimetres in diameter), with giant objects (metres to kilometres in diameter) being relatively ignored. This is due to the common belief that the larger objects vaporize on impact with the Earth's surface, which in most studies is taken as rock. Here we examine experimentally whether hypervelocity impacts into water result in significant survival of the impactors. For this study the University of Kent's two-stage light gas gun was used to accelerate millimetre-sized shale projectiles obliquely into a relatively deep water layer, at approximately 5 km s−1. Two shots have been made with surviving fragments being recovered from each. The surviving fragments appear highly shocked and display clear signs of cracking. The fragments that have been isolated contribute to a significant percentage (~10%) of the original unfired projectile mass and are as large as ~20% of the original projectile diameter. This indicates that oceanic hypervelocity impact events of large asteroids may deliver significant volumes of solid material to the Earth and thus provide a possible mechanism for successful panspermia.