Estimation of the variability of production by simulating annual cycles of phytoplankton in the central North Sea

A physical and a biological one-dimensional upper layer model for the stimualtion of the annual cycles of both the physical and the phytoplankton dynamics, are used to estimate the annual primary production in the central North Sea. The simulations are driven with actual 3-hourly meteorological standard observations and estimated radiation data for the 25 years 1962 to 1986. The high variability of the forcing generates a considerable variability in the physical and biological oceanic mixed layer dynamics.As an example, the model results from two years with contrasting meteorological conditions, 1963 and 1967, are discussed in detail. The mixing regimes generated are very different which result in different annual phytoplankton cycles. During 1963 when conditions were warm and windless, the early establishment of a calm upper layer water mass enabled a strong spring plankton bloom; whereas in 1967, which was stormy and cold, convective overturning continued until April, suppressing an early spring bloom and prolonging the blooming into summer.For the meteorological conditions observed in 1962 to 1986, the simulations yield an integrated annual water column gross production of 83.5–99.0 gC m⁻²a⁻¹ and an integrated annual water column net production ranging between 43.0 and 64.2 gC m⁻²a⁻¹ for the central North Sea. Grazing by the prescribed copepod population ranges from 24.5 to 40.0 gC m⁻²a⁻¹. The production events are described irregularly over the different years, total gross production varies only about 17%, and total net production by about 21%. The nutrient taken up by the algae is 2.6 to 3.2 times the winter concentration of that layer which in summer is situated above the seasonal thermocline. The additional nutrient is provided by local regeneration and by turbulent entrainment from below the thermocline. Local regeneration in the upper layer provides about 2.4 and 0.3 times the entrained amount of phosphate during spring and summer, respectively. In the 25 years 16 late summer or early fall storm events entrained more than 1.2mmol P m⁻²d⁻¹ into the depleted upper layer, potentially initiating new production events.The simulated annual cycles can be validated with the available data only in the sense that the variability, but not single events, can be compared to measurements. Such comparisons between simulated and field data show that the simulation reproduces the general features of annual phytoplankton cycles. This establishes confidence in those calculated estimates, for which field data are not directly comparable. It is concluded that weather-induced variability can explain most of the observed variability in phytoplankton in annual cycles.A typical annual cycle of phytoplankton biomass dynamics is presented. Ratios of daily process contributions show that the balances between the different processes change during the annual cycle. Diagrams of the mean and seasonal phosphorus flow are derived from the simulations. Two thirds of the primary production are channelled through the copepods, and one third is lost by other processes. Organic matter corresponding to more than the initial amount of nutrients in the mixed layer is sedimenting out of the upper layer, and about the same amount is regenerated at the bottom and mixed into the water column at the end of the year.The critical points in the model: grazing, recycling of nutrients and mixing in the bottom boundary layer, are discussed. The model still needs to be refined with respect to these processes in order to achieve the delicate balances required to generate fall blooms. A series problem is the appropriateness of primary production measurements for a comparison with simulated quantities. Attempts should be made to establish a one-to-one correspondence between model-derived production quantities and measurements.Single events are important, so both sampling strategies and the estimation of fluxes from data should take account of the possible occurrence of such events, which may have been missed in the observations, by presenting ranges covering the realistic variance rather than mean values.     

Analysis and mapping of present and future drought conditions over Greek areas with different climate conditions

Estimation of drought in a certain temporal and spatial scale is crucial in climate change studies. The current study targets on three agricultural areas widespread in Greece, Ardas River Basin in Northeastern Greece, Sperchios River Basin in Central Greece, and Geropotamos River Basin in Crete Island in South Greece that are characterized by diverse climates as they are located in various regions. The objective is to assess the spatiotemporal variation of drought conditions prevailing in these areas. The Standardized Precipitation Index (SPI) was used to identify and assess the present and future drought conditions. Future simulated data were derived from a number of Regional Climatic Models (RCMs) from the ENSEMBLES European Project. The analysis was performed for the future periods of 2021–2050 and 2071–2100, implementing A1B and B1 scenarios. The spatial analysis of the drought conditions was performed using a combined downscaling technique and the Ordinary Kriging. The Mann-Kendall test was implemented for trend investigation. During both periods and scenarios, drought conditions will tend to be more severe in the upcoming years. The decrease of the SPI values in the Sperchios River Basin is expected to be the strongest, as it is the only study area that will show a negative balance (in SPI values), regarding the drought conditions. For the Ardas and the Geropotamos River Basins, a great increase of the drought conditions will occur during the 2021–2050 period, while for 2071–2100 period, the decrease will continue but it will be tempered. Nevertheless, the situation in all study areas according to the SPI classification is characterized as “Near-normal”, in terms of drought conditions.     

Chronology of the Pueblo Viejo epithermal gold–silver deposit,Dominican Republic: formation in an Early Cretaceous intra-oceanic island arc and burial under ophiolite

The Pueblo Viejo deposit (production to 1996: 166 t Au, 760 t Ag) is located in the Dominican Republic on the Caribbean island of Hispaniola and ranks as one of the largest high-sulfidation/acid-sulfate epithermal deposits (reserves in 2007: 635 t Au, 3,648 t Ag). One of the advanced argillic ore bodies is cut by an inter-mineral andesite porphyry dike, which is altered to a retrograde chlorite–illite assemblage but overprinted by late-stage quartz–pyrite–sphalerite veins and associated low-grade Au, Ag, Zn, Cd, Hg, In, As, Se, and Te mineralization. The precise TIMS U–Pb age (109.6 ± 0.6 Ma) of the youngest zircon population in this dike confirms that the deposit is part of the Early Cretaceous Los Ranchos intra-oceanic island arc. Intrusion-related gold–sulfide mineralization took place during late andesite–dacite volcanism within a thick pile (>200 m) of carbonaceous sand- and siltstones deposited in a restricted marine basin. The high-level deposit was shielded from erosion after burial under a late Albian (109–100 Ma) ophiolite complex (8 km thick), which was in turn covered by the volcano-sedimentary successions (>4 km) of a Late Cretaceous–Early Tertiary calc-akaline magmatic arc. Estimates of stratigraphic thickness and published alunite, illite, and feldspar K-Ar ages and closure temperatures (alunite 270 ± 20°C, illite 260 ± 30°C, K-feldspar 150°C) indicate a burial depth of about 12 km at 80 Ma. During peak burial metamorphism (300°C and 300 MPa), the alteration assemblage kaolinite + quartz in the deposit dehydrated to pyrophyllite. Temperature–time relations imply that the Los Ranchos terrane then cooled at a rate of 3–4°C/Ma during slow uplift and erosion.     

On weighted total least-squares adjustment for linear regression

The weighted total least-squares solution (WTLSS) is presented for an errors-in-variables model with fairly general variance–covariance matrices. In particular, the observations can be heteroscedastic and correlated, but the variance–covariance matrix of the dependent variables needs to have a certain block structure. An algorithm for the computation of the WTLSS is presented and applied to a straight-line fit problem where the data have been observed with different precision, and to a multiple regression problem from recently published climate change research.     

Solifluction rates and environmental controls at local and regional scales in central Austria

Solifluction is a widespread periglacial phenomenon. Little is known about present solifluction rates in Austria. The author monitored five solifluction lobes during a four-year period. Annual rates of surface velocity, vertical velocity profiles, depths of movement, and volumetric velocities were quantified using near-surface markers and painted lines. Environmental conditions were assessed using air temperature, soil texture, and ground temperature-derived parameters. The latter were used to estimate the relevance of needle-ice creep, diurnal frost creep, annual frost creep, and gelifluction. The mean surface velocity rates were 3.5–6.1 cm yr^?1 (near-surface markers) and 6.2–8.9 cm yr^?1 (painted lines), respectively, indicating a high relevance of needle-ice creep. The mean depth of movement was 32.5–40 cm. The mean volumetric velocities were 71–102 cm³ cm^?1 yr^?1. Solifluction rates at the five sites did not correlate with each other due to site-specific controls. No statistically significant correlations were quantified between solifluction rates and different environmental parameters due to data gaps and short time series, thus highlighting the importance of long-term monitoring. Nevertheless, the results suggest that longer zero curtain periods, longer seasonal ground thawing periods, later start of the seasonal snow cover, more freeze-thaw cycles, and cooler early summer temperatures promote solifluction.     

Identification of bicyclic terpenoid hydrocarbons in the saturate fraction of Athabasca oil sand bitumen

The bicyclic terpanes reported to be present in numerous petroleums have been detected in the saturate fraction of the Athabasca oil sand bitumen. This series of compounds has been found to extend from C₁₅ to at least C₂₄ and their structures have been established by means of comparisons with synthetic C₁₈ and C₂₀ samples of known stereochemistry.