Contrasting Sea-Ice Algae Blooms in a Changing Arctic Documented by Autonomous Drifting Buoys

Novel observations of the seasonal evolution of an ice algal bloom on the Chukchi shelf were collected by two autonomous buoys deployed 180 km apart in first-year drifting sea ice. High attenuation of blue light in the bottom of the ice indicated considerable accumulation of ice algae biomass with derived Chlorophyll-a concentrations (Chl a) up to 184 mg m−2. Differences in the magnitude and persistence of ice algae biomass under each buoy appear to have been driven by differences in snow thickness, as ice thickness was similar between the sites. Minimal snow cover (0.02 m) around one buoy was associated with algae growth beginning in mid-May and lasting 70 days. The second buoy had notably more snow (0.4 m), causing ice algae production to lag behind the first site by approximately 4 weeks. The delay in growth diminished the peak of ice algae Chl a and duration compared to the first site. Light attenuation through the ice was intense enough at both buoys to have a potentially inhibiting impact on water column phytoplankton Chl a. Modeling ice algae growth with observed light intensities determined that nutrients were the limiting resource at the low snow site. In contrast, the algae at the high snow site were light-limited and never nutrient-limited. These data point toward changes in ice algae phenology with an earlier and longer window for growth; and nutrients rather than light determining the longevity and magnitude of production

Traumatic ventricular septal defect in a 4-year-old boy after blunt chest injury

Traumatic ventricular septal defect (VSD) resulting from blunt chest injury is a very rare event. The mechanisms of traumatic VSD have been of little concern to dateuntil now, but two dominant theories have been described. In one, the rupture occurs due to acute compression of the heart; in the other, it is due to myocardial infarction of the septum. The clinical symptoms and timing of presentation are variable, so appropriate diagnosis can be difficult or delayed. Closure of traumatic VSD has been based on a combination of heart failure symptoms, hemodynamics, and defect size. Here, we present a case of a 4-year-old boy who presented with a traumatic VSD following a car accident. He showed normal cardiac structure at the time of injury, but after 8 days, his repeated echocardiography revealed a VSD. He was successfully treated by surgical closure of the VSD, and has been doing well up to the present. This report suggests that the clinician should pay great close attention to the patients injured by blunt chest trauma, keeping in mind the possibility of cardiac injury

Frontal circulation and submesoscale variability during the formation of a Southern Ocean mesoscale eddy

AbstractObservations made in the Scotia Sea during the May 2015 Surface Mixed Layer Evolution at Submesoscales (SMILES) research cruise captured submesoscale, O(1-10 km), variability along the periphery of a mesoscale O(10-100 km) meander precisely as it separated from the Antarctic Circumpolar Current (ACC) and formed a cyclonic eddy ~ 120 km in diameter. The meander developed in the Scotia Sea, an eddy-rich region east of the Drake Passage where the Subantarctic and Polar fronts converge and modifications of Subantarctic mode water (SAMW) occur. In situ measurements reveal a rich submesoscale structure of temperature and salinity and a loss of frontal integrity along the newly-formed southern sector of the eddy. A mathematical framework is developed to estimate vertical velocity from co-located drifter and horizontal water velocity time series, under certain simplifying assumptions appropriate for the current data set. Upwelling (downwelling) rates of O(100 m day-1) are found in the northern (southern) eddy sector. Favorable conditions for submesoscale instabilities are found in the mixed layer, particularly at the beginning of the survey in the vicinity of density fronts. Shallower mixed layer depths and increased stratification are observed later in the survey on the inner edge of the front. Evolution in T-S space indicates modification of water mass properties in the upper 200 m over 2 days. Modifications along �θ 27 - 27.2 kg m�3 have climate-related implications for mode and intermediate water transformation in the Scotia Sea on finer spatiotemporal scales than observed previously

Lagrangian drifter dispersion in the southwestern Atlantic Ocean

In the framework of Monitoring by Ocean Drifters (MONDO) Project, a set of Lagrangian drifters were released in proximity of the Brazil Current, the western branch of the Subtropical Gyre in the South Atlantic Ocean. The experimental strategy of deploying part of the buoys in clusters offers the opportunity to examine relative dispersion on a wide range of scales. Adopting a dynamical systems approach, we focus our attention on scale-dependent indicators, like the finite-scale Lyapunov exponent (FSLE) and the finite-scale (mean square) relative velocity (FSRV) between two drifters as function of their separation, and compare them with classic time-dependent statistical quantities like the mean square relative displacement between two drifters and the effective diffusivity as functions of the time lag from the release. We find that, dependently on the given observable, the quasigeostrophic turbulence scenario is overall compatible with our data analysis, with discrepancies from the expected behavior of 2D turbulent trajectories likely to be ascribed to the non stationary and non homogeneous characteristics of the flow, as well as to possible ageostrophic effects. Submesoscale features of O(1) km are considered to play a role, to some extent, in determining the properties of relative dispersion as well as the shape of the energy spectrum. We present, also, numerical simulations of an OGCM of the South Atlantic, and discuss the comparison between experimental and model data about mesoscale dispersion.Comment: 26 pages, 16 figure

From sea ice to seals: a moored marine ecosystem observatory in the Arctic

Although Arctic marine ecosystems are changing rapidly, year-round monitoring is currently very limited and presents multiple challenges unique to this region. The Chukchi Ecosystem Observatory (CEO) described here uses new sensor technologies to meet needs for continuous, high-resolution, and year-round observations across all levels of the ecosystem in the biologically productive and seasonally ice-covered Chukchi Sea off the northwest coast of Alaska. This mooring array records a broad suite of variables that facilitate observations, yielding better understanding of physical, chemical, and biological couplings, phenologies, and the overall state of this Arctic shelf marine ecosystem. While cold temperatures and 8 months of sea ice cover present challenging conditions for the operation of the CEO, this extreme environment also serves as a rigorous test bed for innovative ecosystem monitoring strategies. Here, we present data from the 2015–2016 CEO deployments that provide new perspectives on the seasonal evolution of sea ice, water column structure, and physical properties, annual cycles in nitrate, dissolved oxygen, phytoplankton blooms, and export, zooplankton abundance and vertical migration, the occurrence of Arctic cod, and vocalizations of marine mammals such as bearded seals. These integrated ecosystem observations are being combined with ship-based observations and modeling to produce a time series that documents biological community responses to changing seasonal sea ice and water temperatures while establishing a scientific basis for ecosystem management.</p

Mesoscale, cyclonic eddies as larval fish habitat along the southeast United States shelf: A Lagrangian description of the zooplankton community

The Charleston Gyre region is characterized by continuous series of cyclonic eddies that propagate northeastwards before decaying or coalescing with the Gulf Stream south of Cape Hatteras, NC, USA. Over 5 d, chlorophyll-a concentration, zooplankton displacement volume, and zooplankton composition and abundance changed as the eddy moved to the northeast. Surface chlorophyll-a concentration decreased, and zooplankton displacement remained unchanged as the eddy propagated. Zooplankton taxa known to be important dietary constituents of larval fish increased in concentration as the eddy propagated. The concurrent decrease in chlorophyll-a concentration and static zooplankton displacement volume can be explained by initial stimulation of chlorophyll-a concentration by upwelling and nutrient enrichment near the eddy core and to possible grazing as zooplankton with short generation times and large clutch sizes increased in concentration. The zooplankton community did not change significantly within the 5 d that the eddy was tracked, and there was no indication of succession. Mesoscale eddies of the region are dynamic habitats as eddies propagate northeastwards at varying speeds within monthly periods. The abundance of zooplankton important to the diets of larval fish indicates that the region can provide important pelagic nursery habitat for larval fish off the southeast coast of the United States. A month of feeding and growth is more than half the larval duration of most fish spawned over the continental shelf of the southeastern United States in winter