Seasonal and inter-annual temperature variability in the bottom waters over the western Black Sea shelf

Long-term changes in the state of the Bottom Shelf Water (BSW) on the Western shelf of the Black Sea are assessed using analysis of intra-seasonal and inter-annual temperature variations. For the purpose of this study the BSW is defined as such shelf water mass between the seabed and the upper mixed layer (bounded by the σθ = 14.2 isopycnal) which has limited ability to mix vertically with oxygen-rich surface waters during the warm season due to formation of a seasonal pycnocline. A long-term time series of temperature anomalies in the BSW is constructed from in-situ observations taken over the 2nd half of the 20th century. The BSW is shown to occupy nearly half of the shelf area during the summer stratification period (May–November).The results reveal a warm phase in the 1960s/70s, followed by a cold phase between 1985 and 1995 and a further warming after 1995. The transition between the warm and cold periods coincides with a regime shift in the Black Sea ecosystem. While it was confirmed that the memory of winter convection is well preserved over the following months in the deep sea, the signal of winter cooling in the BSW significantly reduces during the warm season. The potential of the BSW to ventilate horizontally during the warm season with the deep-sea waters is assessed using isopycnic analysis of temperature variations. It is shown that temperature in the BSW is stronger correlated with the temperature of Cold Intermediate Waters (CIW) in the deep sea than with the severity of the previous winters, thus indicating that the isopycnal exchanges with the deep sea are more important for inter-annual/inter-decadal variability of the BSW on the western Black Sea shelf than effects of winter convection on the shelf itself

A young lens of Red Sea water in the Arabian Sea

CTD data collected in March-April 1980 in the Arabian Sea during the 22nd cruise of R.V. Akademik Vernadsky were used to investigate the structure and dynamics of a young lens of Red Sea Water (Reddy) in the initial stage of its formation. The core of the young lens with maximum temperature of 11.07°C and maximum salinity of 35.56 was located at depths of 640-830 m, and had temperature and salinity anomalies of 0.75°C and 0 22 with respect to the background water. The lens core, of thickness of 190 m, was connected to the main Red Sea Water tongue by a thin layer with vertical extent of about 20 m. In contrast to Meddles frequently observed in the North Atlantic, the density anomaly of the Reddy did not exceed 0.04 kg m-3. A trajectory of the lens movement was reconstructed. The dynamic impact of a deep-reaching cyclonic meander on the large-scale tongue of Red Sea Water resulted in the Reddy formation near 16°N, 61°E and its subsequent movement to the south over a distance of about 370 km

The uplift principle for ordered trees

AbstractIn this paper, we describe the uplift principle for ordered trees which lets us solve a variety of combinatorial problems in two simple steps. The first step is to find the appropriate generating function at the root of the tree, the second is to lift the result to an arbitrary vertex by multiplying by the leaf generating function. This paper, though self contained, is a companion piece to Cheon and Shapiro (2008) [2] though with many more possible applications. It also may be viewed as an invitation, via the symbolic method, to the authoritative 800 page book of Flajolet and Sedgewick (2009) [8]. Our examples, with one exception, are different from those in this excellent reference

Protected points in ordered trees

AbstractIn this note we start by computing the average number of protected points in all ordered trees with n edges. This can serve as a guide in various organizational schemes where it may be desirable to have a large or small number of protected points. We will also look a few subclasses with a view to increasing or decreasing the proportion of protected points

Non-linearities, regime shifts and recovery: The recent influence of climate on Black Sea chlorophyll

The Black Sea ecosystem experienced severe eutrophication-related degradation during the 1970s and 1980s. However, in recent years the Black Sea has shown some signs of recovery which are often attributed to a reduction in nutrient loading. Here, SeaWiFS chlorophyll a (chl a), a proxy for phytoplankton biomass, is used to investigate spatio-temporal patterns in Black Sea phytoplankton dynamics and to explore the potential role of climate in the Black Sea's recovery. Maps of chl a anomalies, calculated relative to the 8 year mean, emphasize spatial and temporal variability of phytoplankton biomass in the Black Sea, particularly between the riverine-influenced Northwest Shelf and the open Black Sea. Evolution of phytoplankton biomass has shown significant spatial variability of persistence of optimal bloom conditions between three major regions of the Black Sea. With the exception of 2001, chl a has generally decreased during our 8 year time-series. However, the winter of 2000-2001 was anomalously warm with low wind stress, resulting in reduced vertical mixing of the water column and retention of nutrients in the photic zone. These conditions were associated with anomalously high levels of chl a throughout much of the open Black Sea during the following spring and summer. The unusual climatic conditions occurring in 2001 may have triggered a shift in the Black Sea's chl a regime. The long-term significance of this recent shift is still uncertain but illustrates a non-linear response to climate forcing that makes future ecosystem changes in the pelagic Black Sea ecosystem difficult to predict. © 2008 Elsevier B.V. All rights reserved

Self-similarity of the meddy family in the eastern North Atlantic

In this study we analyze two groups of Mediterranean salt lenses: "mid-life' lenses, typically 1-2 years old, observed in the Canary Basin, and younger Meddies from the Iberian Basin. Nonlinear transformation of variables is used to find a unique function describing vertical profiles at different locations inside the lens. When this function is found, its existence is considered as "self-similarity' of the lens structure. A common function was also found that describes each group of Meddy, Canary and Iberian, and a remarkable difference between the groups was noted. A possible reason for this result might lie in the difference in lens age. -from Author

Tidally induced lateral dispersion of the Storfjorden overflow plume

We investigate the flow of brine-enriched shelf water from Storfjorden (Svalbard) into Fram Strait and onto the western Svalbard Shelf using a regional set-up of NEMO-SHELF, a 3-D numerical ocean circulation model. The model is set up with realistic bathymetry, atmospheric forcing, open boundary conditions and tides. The model has 3 km horizontal resolution and 50 vertical levels in the sh-coordinate system which is specially designed to resolve bottom boundary layer processes. In a series of modelling experiments we focus on the influence of tides on the propagation of the dense water plume by comparing results from tidal and non-tidal model runs. Comparisons of non-tidal to tidal simulations reveal a hotspot of tidally induced horizontal diffusion leading to the lateral dispersion of the plume at the southernmost headland of Spitsbergen which is in close proximity to the plume path. As a result the lighter fractions in the diluted upper layer of the plume are drawn into the shallow coastal current that carries Storfjorden water onto the western Svalbard Shelf, while the dense bottom layer continues to sink down the slope. This bifurcation of the plume into a diluted shelf branch and a dense downslope branch is enhanced by tidally induced shear dispersion at the headland. Tidal effects at the headland are shown to cause a net reduction in the downslope flux of Storfjorden water into the deep Fram Strait. This finding contrasts previous results from observations of a dense plume on a different shelf without abrupt topography

Seasonal variability of eddy kinetic energy in the central indian ocean: Polygon-67 revised

Purpose. The main goal of this study is to analyse the seasonal variability of meso-scale eddy activity in the north tropical Indian Ocean. The selected area coincides with the location of POLYGON-67 experiment where the mesoscale eddies of the open ocean were first discovered. Methods and results. The variability of mesoscale eddy kinetic energy in surface ocean layer, enstrophy of larger scale circulation, spatial and temporal patterns of surface currents and surface winds are jointly analysed using a 20-year long daily time series of eddy-resolving ocean reanalysis data obtained from EU Copernicus Marine Environment Monitoring Service and climatic wind data from US National Oceanographic and Atmospheric Administration. The fast mesoscale and slow large-scale processes are separated using a Savitsky – Golay filter with the cut-off time of 103 days which corresponds to a local minimum in the full kinetic energy power spectrum. In contrast to other parts of the tropical ocean, the seasonal variability of EKE exhibits 2 maxima – the largest being in April, and the secondary being in October which are related to the maxima in enstrophy of larger scale currents. Conclusions. The double peak variability in EKE corresponds to the seasonal variability of large scale enstrophy and monsoon wind circulation and supports a hypothesis that the main mechanism of EKE generation is barotropic instability of larger scale currents. The EKE variability within P67 is mostly controlled by advection of energy from neighbouring areas, and to a lesser extent by local generation