Effects of Epiphyte Load on Optical Properties and Photosynthetic Potential of the Seagrasses Thalassia Testudinum Banks ex König and Zostera Marina L

The biomass and optical properties of seagrass leaf epiphytes were measured to evaluate their potential impact on the photosynthetic performance of the seagrasses Thalassia testudinum Banks ex König (turtlegrass) and Zostera marina L. (eelgrass). Turtlegrass was obtained from oligotrophic waters near Lee Stocking Island, Bahamas; eelgrass was collected from a eutrophic environment in Monterey Bay, California. Leaf–epiphyte loads were characterized visually and quantified using measurements of their phospholipid biomass. Light absorption and reflectance of the intact epiphyte layer were determined spectrophotometrically. Turtlegrass epiphytes from the oligotrophic site absorbed a maximum of 36% of incident light in peak chlorophyll absorption bands, whereas higher epiphyte loads on eelgrass from the more eutrophic Monterey Bay absorbed 60% of incident light in peak chlorophyll absorption bands. The combination of intact epiphyte–leaf complexes and spectral measurements enabled us to construct a quantitative relationship between epiphyte biomass and light attenuation, and, by extension, between epiphyte bio- mass and seagrass photosynthesis. The model yielded a robust, positive relationship between epiphyte biomass and the absorption of photons in photosynthetically important wavelengths, and it generated a strong negative relationship between epiphyte biomass and spectral photosynthesis of their seagrass hosts. Furthermore, the calculations of photosynthesis highlighted the significant differences between PAR and spectral models of photosynthesis, illustrating that the spectral quality of the incident flux must be considered when evaluating the effects of epiphyte load on seagrass leaf photosynthesis. Verification of the model—using direct measurements of photosynthesis and a variety of epiphyte and macrophyte combinations from different locations--is warranted

Potential Export of Unattached Benthic Macroalgae to the Deep Sea Through Wind Driven Langmuir Circulation

Carbon export to the deep sea is conventionally attributed to the sinking of open ocean phytoplankton. Here, we report a Langmuir supercell event driven by high winds across the shallow Great Bahama Bank that organized benthic non-attached macroalgae, Colpomenia sp., into visible windrows on the seafloor. Ocean color satellite imagery obtained before and after the windrows revealed a 588 km2 patch that rapidly shifted from highly productive macroalgae to bare sand. We assess a number of possible fates for this macroalgae and contend that this event potentially transported negatively buoyant macroalgae to the deep Tongue of the Ocean in a pulsed export of \u3e 7 x 1010 g of carbon. This is equivalent to the daily carbon flux of phytoplankton biomass in the pelagic tropical North Atlantic and 0.2-0.8% of daily carbon flux from the global ocean. Coastal banks and bays are highly productive ecosystems that may contribute substantially to carbon export to the deep sea. Citation: Dierssen, H. M., R. C. Zimmerman, L. A. Drake, and D. J. Burdige (2009), Potential export of unattached benthic macroalgae to the deep sea through wind-driven Langmuir circulation, Geophys. Res. Lett., 36, L04602, doi: 10.1029/2008GL036188

Benthic Ecology From Space: Optics and Net Primary Production in Seagrass and Benthic Algae Across the Great Bahama Bank

Development of repeatable and quantitative tools are necessary for determining the abundance and distribution of different types of benthic habitats, detecting changes to these ecosystems, and determining their role in the global carbon cycle. Here we used ocean color remote sensing techniques to map different major groups of primary producers and estimate net primary productivity (NPP) across Great Bahama Bank (GBB). Field investigations on the northern portion of the GBB in 2004 revealed 3 dominant types of benthic primary producers: seagrass, benthic macroalgae, and microalgae attached to sediment. Laboratory measurements of NPP ranged from barely net autotrophic for grapestone sediment with thin microalgal biofilm to highly productive for dense accumulations of brown macroalgae. A logarithmic relationship between NPP and green seafloor reflectance described the general trend in NPP across various benthic constituents. Using a radiative transfer-based approach, satellite-derived estimates of NPP for the region totaled similar to ~2 x 1013 gC yrˉ¹ across the GBB. The prevailing benthic habitat was mapped as sediment with little to no microalgal biofilm. Moderate to dense seagrass meadows of Thalassia testudinumwere the dominant primary producers and contributed over 80% of NPP in the region. If the vast majority of seagrass leaves decompose in the primarily carbonate sediments, carbonate dissolution processes associated with this decomposition may result in sequestration of seagrass above- and below-ground carbon into the bicarbonate pool (2.4 x 1013 gC yrˉ¹), where it has a residence time on the order of tens of thousands of years

Rapid Quantification of Biofouling With an Inexpensive, Underwater Camera and Image Analysis

To reduce the transport of potentially invasive species on ships\u27 submerged surfaces, rapid-and accurate-estimates of biofouling are needed so shipowners and regulators can effectively assess and manage biofouling. This pilot study developed a model approach for that task. First, photographic images were collected in situ with a submersible, inexpensive pocket camera. These images were used to develop image processing algorithms and train machine learning models to classify images containing natural assemblages of fouling organisms. All of the algorithms and models were implemented in a widely available software package (MATLAB©). Initially, an unsupervised clustering model was used, and three types of fouling were delineated. Using a supervised classification approach, however, seven types of fouling could be identified. In this manner, fouling was successfully quantified over time on experimental panels immersed in seawater. This work provides a model for the easy, quick, and cost-effective classification of biofouling

X-ray emission from radiative shocks in Type II supernovae

The X-ray emission from the circumstellar interaction in Type II supernovae with a dense circumstellar medium is calculated. In Type IIL and Type IIn supernovae mass loss rates are generally high enough for the region behind the reverse shock to be radiative, producing strong radiation, particularly in X-rays. We present a model for the emission from the cooling region in the case of a radiative reverse shock. Under the assumption of a stationary flow, a hydrodynamic model is combined with time dependent ionization balance and multilevel calculations. The applicability of the steady state approximation is discussed for various values of the ejecta density gradient and different sets of chemical composition. We show how the emerging spectrum depends strongly on the reverse shock velocity and the composition of the shocked gas. We discuss differences between a spectrum produced by this model and a single-temperature spectrum. Large differences for especially the line emission are found, which seriously can affect abundance estimates. We also illustrate the effects of absorption in the cool shocked ejecta. The applicability of our model for various types of supernovae is discussed.Comment: 25 pages, 15 figures, 4 tables. Accepted for publication in A&

Dust Devil Tracks

Dust devils that leave dark- or light-toned tracks are common on Mars and they can also be found on the Earth’s surface. Dust devil tracks (hereinafter DDTs) are ephemeral surface features with mostly sub-annual lifetimes. Regarding their size, DDT widths can range between ∼1 m and ∼1 km, depending on the diameter of dust devil that created the track, and DDT lengths range from a few tens of meters to several kilometers, limited by the duration and horizontal ground speed of dust devils. DDTs can be classified into three main types based on their morphology and albedo in contrast to their surroundings; all are found on both planets: (a) dark continuous DDTs, (b) dark cycloidal DDTs, and (c) bright DDTs. Dark continuous DDTs are the most common type on Mars. They are characterized by their relatively homogenous and continuous low albedo surface tracks. Based on terrestrial and martian in situ studies, these DDTs most likely form when surficial dust layers are removed to expose larger-grained substrate material (coarse sands of ≥500 μm in diameter). The exposure of larger-grained materials changes the photometric properties of the surface; hence leading to lower albedo tracks because grain size is photometrically inversely proportional to the surface reflectance. However, although not observed so far, compositional differences (i.e., color differences) might also lead to albedo contrasts when dust is removed to expose substrate materials with mineralogical differences. For dark continuous DDTs, albedo drop measurements are around 2.5 % in the wavelength range of 550–850 nm on Mars and around 0.5 % in the wavelength range from 300–1100 nm on Earth. The removal of an equivalent layer thickness around 1 μm is sufficient for the formation of visible dark continuous DDTs on Mars and Earth. The next type of DDTs, dark cycloidal DDTs, are characterized by their low albedo pattern of overlapping scallops. Terrestrial in situ studies imply that they are formed when sand-sized material that is eroded from the outer vortex area of a dust devil is redeposited in annular patterns in the central vortex region. This type of DDT can also be found in on Mars in orbital image data, and although in situ studies are lacking, terrestrial analog studies, laboratory work, and numerical modeling suggest they have the same formation mechanism as those on Earth. Finally, bright DDTs are characterized by their continuous track pattern and high albedo compared to their undisturbed surroundings. They are found on both planets, but to date they have only been analyzed in situ on Earth. Here, the destruction of aggregates of dust, silt and sand by dust devils leads to smooth surfaces in contrast to the undisturbed rough surfaces surrounding the track. The resulting change in photometric properties occurs because the smoother surfaces have a higher reflectance compared to the surrounding rough surface, leading to bright DDTs. On Mars, the destruction of surficial dust-aggregates may also lead to bright DDTs. However, higher reflective surfaces may be produced by other formation mechanisms, such as dust compaction by passing dust devils, as this may also cause changes in photometric properties. On Mars, DDTs in general are found at all elevations and on a global scale, except on the permanent polar caps. DDT maximum areal densities occur during spring and summer in both hemispheres produced by an increase in dust devil activity caused by maximum insolation. Regionally, dust devil densities vary spatially likely controlled by changes in dust cover thicknesses and substrate materials. This variability makes it difficult to infer dust devil activity from DDT frequencies. Furthermore, only a fraction of dust devils leave tracks. However, DDTs can be used as proxies for dust devil lifetimes and wind directions and speeds, and they can also be used to predict lander or rover solar panel clearing events. Overall, the high DDT frequency in many areas on Mars leads to drastic albedo changes that affect large-scale weather patterns

Transient pulsed radio emission from a magnetar

Anomalous X-ray pulsars (AXPs) are slowly rotating neutron stars with very bright and highly variable X-ray emission that are believed to be powered by ultra-strong magnetic fields of >1e14 G, according to the 'magnetar' model. The radio pulsations that have been observed from more than 1,700 neutron stars with weaker magnetic fields have never been detected from any of the dozen known magnetars. The X-ray pulsar XTE J1810-197 was revealed (in 2003) as the first AXP with transient emission when its luminosity increased 100-fold from the quiescent level; a coincident radio source of unknown origin was detected one year later. Here we show that XTE J1810-197 emits bright, narrow, highly linearly polarized radio pulses, observed at every rotation, thereby establishing that magnetars can be radio pulsars. There is no evidence of radio emission before the 2003 X-ray outburst (unlike ordinary pulsars, which emit radio pulses all the time), and the flux varies from day to day. The flux at all radio frequencies is approximately equal -- and at >20 GHz XTE J1810-197 is currently the brightest neutron star known. These observations link magnetars to ordinary radio pulsars, rule out alternative accretion models for AXPs, and provide a new window into the coronae of magnetars.Comment: accepted by Nature; some new data and significantly revised discussio

The Long-Baseline Neutrino Experiment: Exploring Fundamental Symmetries of the Universe

The preponderance of matter over antimatter in the early Universe, the dynamics of the supernova bursts that produced the heavy elements necessary for life and whether protons eventually decay --- these mysteries at the forefront of particle physics and astrophysics are key to understanding the early evolution of our Universe, its current state and its eventual fate. The Long-Baseline Neutrino Experiment (LBNE) represents an extensively developed plan for a world-class experiment dedicated to addressing these questions. LBNE is conceived around three central components: (1) a new, high-intensity neutrino source generated from a megawatt-class proton accelerator at Fermi National Accelerator Laboratory, (2) a near neutrino detector just downstream of the source, and (3) a massive liquid argon time-projection chamber deployed as a far detector deep underground at the Sanford Underground Research Facility. This facility, located at the site of the former Homestake Mine in Lead, South Dakota, is approximately 1,300 km from the neutrino source at Fermilab -- a distance (baseline) that delivers optimal sensitivity to neutrino charge-parity symmetry violation and mass ordering effects. This ambitious yet cost-effective design incorporates scalability and flexibility and can accommodate a variety of upgrades and contributions. With its exceptional combination of experimental configuration, technical capabilities, and potential for transformative discoveries, LBNE promises to be a vital facility for the field of particle physics worldwide, providing physicists from around the globe with opportunities to collaborate in a twenty to thirty year program of exciting science. In this document we provide a comprehensive overview of LBNE's scientific objectives, its place in the landscape of neutrino physics worldwide, the technologies it will incorporate and the capabilities it will possess.Comment: Major update of previous version. This is the reference document for LBNE science program and current status. Chapters 1, 3, and 9 provide a comprehensive overview of LBNE's scientific objectives, its place in the landscape of neutrino physics worldwide, the technologies it will incorporate and the capabilities it will possess. 288 pages, 116 figure

Long-Baseline Neutrino Facility (LBNF) and Deep Underground Neutrino Experiment (DUNE) Conceptual Design Report Volume 2: The Physics Program for DUNE at LBNF

The Physics Program for the Deep Underground Neutrino Experiment (DUNE) at the Fermilab Long-Baseline Neutrino Facility (LBNF) is described