SDSS galaxy clustering: luminosity and colour dependence and stochasticity

Differences in clustering properties between galaxy subpopulations complicate the cosmological interpretation of the galaxy power spectrum, but can also provide insights about the physics underlying galaxy formation. To study the nature of this relative clustering, we perform a counts-in-cells analysis of galaxies in the Sloan Digital Sky Survey in which we measure the relative bias between pairs of galaxy subsamples of different luminosities and colours. We use a generalized  χ²  test to determine if the relative bias between each pair of subsamples is consistent with the simplest deterministic linear bias model, and we also use a maximum likelihood technique to further understand the nature of the relative bias between each pair. We find that the simple, deterministic model is a good fit for the luminosity-dependent bias on scales above  ∼2  h ⁻¹ Mpc  , which is good news for using magnitude-limited surveys for cosmology. However, the colour-dependent bias shows evidence for stochasticity and/or non-linearity which increases in strength towards smaller scales, in agreement with previous studies of stochastic bias. Also, confirming hints seen in earlier work, the luminosity-dependent bias for red galaxies is significantly different from that of blue galaxies: both luminous and dim red galaxies have higher bias than moderately bright red galaxies, whereas the biasing of blue galaxies is not strongly luminosity dependent. These results can be used to constrain galaxy formation models and also to quantify how the colour and luminosity selection of a galaxy survey can impact measurements of the cosmological matter power spectrum.     

Florida Current transport variability: An analysis of annual and longer-period signals

More than forty years of Florida Current transport estimates are combined to study annual and longer-term variability in this important component of the MOC and subtropical gyre. A detailed analysis with error estimates illustrates the difficulties in extracting annual and longer time scale variability given the strong higher frequency energy present. The annual cycle represents less than 10% of the total Florida Current transport variance in a 16 yr segment of the record, while interannual (13–42 month) variability represents only 13% of the total and periods longer than 42 months represents less than 10% of the total. Given the observed high frequency variability of the Florida Current, in order to get a monthly mean that is accurate to within 0.5 Sv (one standard error level) more than 20 daily observations are needed. To obtain an estimate of the annual climatology that is “accurate” to within 20% of its own standard deviation, at least 24 yr of data is needed. More than 40 observations spread throughout a year are required to obtain an annual mean that is accurate to within 0.5 Sv. Despite these daunting data requirements, there is sufficient data now to evaluate both the annual cycle of the Florida Current transport with a high degree of accuracy and to begin to determine the longer period transport variability. Comparison of the Florida Current, NAO and wind stress curl records shows that a recently described Sverdrup-based mechanism explains a significant fraction of the long-period variability primarily during the 1986–1998 time window, with other mechanisms clearly dominating before and after.     

A 1998–1992 comparison of inorganic carbon and its transport across 24.5°N in the Atlantic

In January and February 1998, when an unprecedented fourth repetition of the zonal hydrographic transect at 24.5°N in the Atlantic was undertaken, carbon measurements were obtained for the second time in less than a decade. The field of total carbon along this section is compared to that provided by 1992 cruise which followed a similar path (albeit in a different season). Consistent with the increase in atmospheric carbon levels, an increase in anthropogenic carbon concentrations of 8±3 μmolkg⁻¹ was found in the surface layers. Using an inverse analysis to determine estimates of absolute velocity, the flux of inorganic carbon across 24.5° is estimated to be −0.74±0.91 and −1.31±0.99 PgCyr⁻¹ southward in 1998 and 1992, respectively. Estimates of total inorganic carbon flux depend strongly upon the estimated mass transport, particularly of the Deep Western Boundary Current. The 1998 estimate reduces the large regional divergence in the meridional carbon transport suggested by previous studies and brings into question the idea that the tropical Atlantic constantly outgasses carbon, while the subpolar Atlantic sequesters it. Uncertainty in the carbon transports themselves, dominated by the uncertainty in the total mass transport estimates, are a hindrance to determining the “true” picture.The flux of anthropogenic carbon (C_ANTH) across the two transects is estimated as northward at 0.20±0.08 and 0.17±0.06 PgCyr⁻¹ for the 1998 and 1992 sections, respectively. The net transport of C_ANTH across 24.5°N is strongly affected by the difference in concentrations between the northward flowing shallow Florida Current and the mass balancing, interior return flow. The net northward transport of C_ANTH is opposite the net flow of total carbon and suggests, as has been found by others, that the pre-industrial southward transport of carbon within the Atlantic was stronger than it is today. Combining these flux results with estimates of atmospheric and riverine inorganic carbon input, it is determined that today's oceanic carbon system differs from the pre-industrial system in that today there is an uptake of anthropogenic carbon to the south that is advected northward and stored within the North Atlantic basin.     

Oil spill in Hong Kong

Fish farming was seriously but only temporarily affected by a large spill of a very toxic product oil at Hong Kong. Field experiments were set up to follow tainting and depuration. Studies were made of hydrography, water quality, oil in sands, macro- and meio-fauna of shores, and some observations made of possible effects on plankton and open-water fisheries.     

Soil moisture response to white ash mortality following emerald ash borer invasion

Emerald ash borer (EAB) (Agrilus planipennis Fairmaire), an invasive forest insect first identified in southeastern Michigan in 2002, is established in at least 32 US states and three Canadian provinces. Ash (Fraxinus spp.) mortality rates in some forested areas exceed 90%, but to date, little is known about the potential effects of EAB-caused ash mortality on hydrological processes. More broadly, there is a need for information on the timing and magnitude of soil moisture response to species-specific mortality of overstory vegetation in deciduous forest systems. Soil moisture was examined in 28 forested sites where 0–100% of the white ash basal area (Fraxinus americana L.) was killed by EAB. Synoptic measurements of near-surface (0–6 cm depth) soil moisture were collected from 112 plots (18 m radius) within the sites. Three plots were also instrumented with soil moisture sensors at 10 and 25 cm depth to log hourly measurements from May to October. Synoptic data showing white ash mortality and soil moisture were positively correlated in the 34 plots with ≥?5% mortality (by total basal area). In the intensively monitored plots, volumetric soil moisture declined from 37 to 16% between July and September where white ash mortality was low (0.6% of basal area killed), but remained near field capacity (~?30%) throughout the monitoring period in the high mortality plot (8.6% of basal area killed), meriting further investigation to assess effects of white ash mortality on evapotranspiration and soil moisture dynamics in heterogeneous upland forests. Altered soil moisture may have implications for regrowth dynamics, infiltration/runoff partitioning, and nutrient cycling, but additional study to quantify the extent and duration of EAB-related ash mortality on hydrology at the plot and watershed scale is necessary.     

A climate trend analysis of Ethiopia: examining subseasonal climate impacts on crops and pasture conditions

Ethiopia experiences significant climate-induced drought and stress on crop and livestock productivity, contributing to widespread food insecurity. Here, we present subseasonal crop water stress analyses that indicate degrading, growing conditions along Ethiopia’s eastern highlands, including productive and populated highland regions. These seasonally shifting areas of increasing water stress stretch from the north to south across eastern Ethiopia, intersecting regions of acute food insecurity and/or high population. Crop model simulations indicate that between 1982 and 2014, parts of eastern Amhara and eastern Oromia experienced increasing water deficits during the critical sowing, flowering, and ripening periods of crop growth. These trends occurred while population in these regions increased by 143% between 2000 and 2015. These areas of enhanced crop water stress in south-central Ethiopia coincide with regions of high population growth and ongoing crop extensification. Conversely, large regions of relatively unpopulated western Ethiopia are becoming wetter. These areas may therefore be good targets for agricultural development.     

Effects of Environmental Variation and Non-point Source (NPS) Nutrient Pollution on Aquatic Plant Communities in Weeks Bay National Estuarine Research Reserve (WBNERR), AL

This study was designed to investigate non-point source nutrient pollution and its influences on submerged aquatic plant community structure and biological invasion in the Weeks Bay National Estuarine Research Reserve (WBNERR). A monthly vegetation survey was conducted to document plant abundance and changes in community structure; physicochemical data and water samples were collected on a bi-monthly basis to monitor environmental conditions (i.e., pH, salinity, dissolved oxygen, light intensity, and attenuation) and water column nutrient (NO₂⁻/NO₃⁻ and NH₄⁺) and chlorophyll a concentrations. A total of seven submerged aquatic species were identified at the WBNERR with the occurrence of only one non-native species (Hydrilla verticillata). Statistical analyses suggest that water column nitrogen concentrations along with variations in dissolved oxygen (0.6–11.5 mg L⁻¹), light attenuation, pH (5.6–8.6), and temperature (11–33°C) play key roles in determining the aquatic plant abundance and distribution in the WBNERR.