Volatile C1C8 organic compounds in sediments from the Peru upwelling region

Volatile C₁C₈ organic compounds were analyzed in seven cores recovered from a transect across the Peru Shelf Upwelling Region. Compounds detected in ng/g dry weight quantities included methane, ethane, propane and other C₄C₇ alkanes as well as functionalized compounds including alkenes, furans and aldehydes. Strong correlations were observed between some groups of compounds with similar structures. Maxima in two groups of compounds were observed: (1) C₁, C₂, C₃, furans, and butanals (plus sporadic alkanes) as nitrate levels decreased below about 2–4 μM in the subsurface, and (2) C₄C₆ alkenes together with predominantly branched and cycloalkanes at the sediment-water interface in cores recovered from oxygenated bottom waters. The levels of C₁C₇ alkanes in these sediments are comparable to levels found in DSDP cores buried to depths of less than 600 m (or not exposed to geothermal temperatures exceeding about 30°C).     

Influences of the Gulf of Maine intrusion on the Massachusetts Bay spring bloom: A comparison between 1998 and 2000

The Boston Harbor, Massachusetts Bay and Cape Cod Bay system (MBS) is a semi-enclosed coastal embayment located in the western Gulf of Maine (GOM). The strength of the spring bloom in the MBS varies dramatically and the underlying mechanisms are not well understood. It has been hypothesized that the weak (or missing) 1998 spring bloom was due to increased zooplankton grazing pressure after a relatively warmer winter that led to earlier development of zooplankton populations. However, chlorophyll concentrations were low in the entire GOM region during the spring bloom period of 1998. These low chlorophyll waters would enter the MBS by persistent intrusion from the GOM and affect the MBS spring bloom by reducing the accumulation of phytoplankton biomass, suggesting an alternative explanation for the missing bloom. In this study, the influences of the intruding GOM waters on the MBS spring bloom are examined using numerical simulations and observations to compare two contrasting spring blooms (a weak bloom in 1998 versus a strong bloom in 2000). The results indicate that intruding waters from the GOM significantly reduced the strength of spring bloom in 1998, but enhanced the spring bloom in 2000. A theoretical analysis suggests that the influence of the intrusion on the MBS spring bloom is mostly limited to the northern portion of the MBS, and the impact area is determined by local net growth, velocity of intruding flow and horizontal mixing. The intrusion of GOM waters carries the signal of long-term variability in the GOM region and thus may be an important oceanic pathway for climate changes to impact the MBS ecosystem.     

Pre-seismic electromagnetic phenomena in the framework of percolation and fractal theories

Understanding the electromagnetic response to geodynamic processes occurring in the earth's upper crust, in particular pre-seismic and seismic processes, is a challenging task in modern geophysics. There is increasing evidence that seismo-electromagnetic (SEM) phenomena are difficult to describe quantitatively by “linear” models using “averaged” parameters of the medium, such as electrical and hydraulic conductivities. Because the upper crust is highly inhomogeneous (at all scales), porous, and can be fully or partially water-saturated, the most natural way to describe its parameters is via fractal-theoretic and percolation-theoretic models.Recent studies indicate that the electrokinetic effect is the most likely driving mechanism for the various types of SEM signals. Here we considered the hydraulic, electric, and electrokinetic conductances of a porous water-saturated medium as a function of porosity () and moisture content (θ), utilizing a percolation/fractal approach. We show that the electric conductivity and electrokinetic current in such a medium are both proportional to (–_c)² and (θ–θ_c)², where _c and θ_c are the critical values of porosity and moisture content, respectively. This behavior admits the possibility of a relatively large change in the respective electric and electrokinetic parameters due to a small change in the mechanical strain field. This is significant because it may account for the appearance of some types of SEM signals at large distances from the earthquake origin, which is the main deficiency of most models. Indeed, the anticipated strain changes related to pre-earthquake processes is usually very small except near the focal area. The expected ‘averaged’ electromagnetic response also would be very small, unless a local underground water system exists, not necessarily near the focal area, but which is close to critical point(s).We discuss the conditions under which electrotelluric and geomagnetic variations can accompany mechanical disturbances in the earth's crust.     

Self-Similar Fold Evolution Under Prescribed End-Shortening

The evolution of single-layer folds under prescribed end-shortening conditions displays folds of varying wavelength. We investigate a simple model of this kind and characterize the long-term behaviour of fold profiles. In particular we determine the evolution of the axial load and the variation of the wavelength, and we show that fold profiles are highly self-similar.     

Ecosystem responses to recent oceanographic variability in high-latitude Northern Hemisphere ecosystems

As part of the international MENU collaboration, we compared and contrasted ecosystem responses to climate-forced oceanographic variability across several high latitude regions of the North Pacific (Eastern Bering Sea (EBS) and Gulf of Alaska (GOA)) and North Atlantic Oceans (Gulf of Maine/Georges Bank (GOM/GB) and the Norwegian/Barents Seas (NOR/BAR)). Differences in the nitrate content of deep source waters and incoming solar radiation largely explain differences in average primary productivity among these ecosystems. We compared trends in productivity and abundance at various trophic levels and their relationships with sea-surface temperature. Annual net primary production generally increases with annual mean sea-surface temperature between systems and within the EBS, BAR, and GOM/GB. Zooplankton biomass appears to be controlled by both top-down (predation by fish) and bottom-up forcing (advection, SST) in the BAR and NOR regions. In contrast, zooplankton in the GOM/GB region showed no evidence of top-down forcing but appeared to control production of major fish populations through bottom-up processes that are independent of temperature variability. Recruitment of several fish stocks is significantly and positively correlated with temperature in the EBS and BAR, but cod and pollock recruitment in the EBS has been negatively correlated with temperature since the 1977 shift to generally warmer conditions. In each of the ecosystems, fish species showed a general poleward movement in response to warming. In addition, the distribution of groundfish in the EBS has shown a more complex, non-linear response to warming resulting from internal community dynamics. Responses to recent warming differ across systems and appear to be more direct and more pronounced in the higher latitude systems where food webs and trophic interactions are simpler and where both zooplankton and fish species are often limited by cold temperatures.     

Invasive species and climate change: an agronomic perspective

In the current review we wish to draw attention to an additional aspect of invasive species and climate change, that of agricultural productivity and food security. We recognize that at present, such a review remains, in part, speculative, and more illustrative than definitive. However, recent events on the global stage, particularly in regard to the number of food riots that occurred during 2008, even at a time of record harvests, have prompted additional interest in those factors, including invasive species, which could, through climatic uncertainty, alter food production. To that end, as agricultural scientists, we wish to begin an initial evaluation of key questions related to food production and climate change including: how vulnerable is agriculture to invasive species?; are current pest management strategies sufficient to control invasive outbreaks in the future?; what are the knowledge gaps?; can we provide initial recommendations for scientists, land managers and policy makers in regard to available resources? Our overall goals are to begin a synthesis of potential impacts on productivity, to identify seminal research areas that can be addressed in future research, and to provide the scientific basis to allow agronomists and land managers to formulate mitigation and adaptation options regarding invasive species and climate change as a means to maintain food security.     

The source and distribution of polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofurans in sediments of Port Jackson, Australia

Concentrations of polychlorinated dibenzo-p-dioxins (dioxins)(PCDDs) and polychlorinated dibenzofurans (PCDFs)(furans) in sediments from Port Jackson ranged from 32 to 4352 pg WHO-TEQ DF g(-1)dw with a mean of 712 pg g(-1)dw. Maximum total dioxins plus furans concentrations in this sediment was 6,290,000 pg g(-1)dw, which is the highest recorded in Australia and among the highest reported for sediment globally. Permanent bans were placed on fin fishing and prawn trawling in February, 2006 for the whole estuary, based on dioxin tissue burdens. A distinct congener profile corresponded to chemicals known to have been produced by industry on the shores of Homebush Bay in the upper estuary. These chemicals are being dispersed extensively and exceed pre-anthropogenic concentrations in even distant, less developed parts of the harbour. Remediation of sediments is currently being undertaken, with the intention of containing dispersion of dioxins and reducing body burdens in fin fish and prawn populations.     

Constraints on large-scale inhomogeneities from WMAP5 and SDSS: confrontation with recent observations

Measurements of the Type Ia supernovae Hubble diagram which suggest that the Universe is accelerating due to the effect of dark energy may be biased because we are located in a 200–300 Mpc underdense 'void' which is expanding 20–30 per cent faster than the average rate. With the smaller global Hubble parameter, the Wilkinson Microwave Anisotropy Probe 5 data on cosmic microwave background (CMB) anisotropies can be fitted without requiring dark energy if there is some excess power in the spectrum of primordial perturbations on 100 Mpc scales. The Sloan Digital Sky Survey (SDSS) data on galaxy clustering can also be fitted if there is a small component of hot dark matter in the form of 0.5 eV mass neutrinos. We show however that if the primordial fluctuations are Gaussian, the expected variance of the Hubble parameter and the matter density are far too small to allow such a large local void. Nevertheless, many such large voids have been identified in the SDSS Luminous Red Galaxy survey in a search for the late integrated Sachs–Wolfe effect due to dark energy. The observed CMB temperature decrements imply that they are nearly empty, thus these real voids too are in gross conflict with the concordance Λ cold dark matter model. The recently observed high peculiar velocity flow presents another challenge for the model. Therefore, whether a large local void actually exists must be tested through observations and cannot be dismissed a priori.