Tidal Patterns Research Articles

Correlation between ionospheric longitudinal harmonic components and upper atmospheric tides

There is strong correlation among the ionospheric longitudinal structures of wavenumber-3 (WN3), wavenumber-4 (WN4), and eastward-propagating diurnal tides with zonal wave numbers s = 2 and 3 (DE2 and DE3) in the upper atmosphere. The total electron content derived from the Global Ionospheric Maps of the Jet Propulsion Laboratory is used to deduce the latitudinally total electron content (ITEC) in the low-latitude ionosphere, and TIDE/TIMED observations are employed to obtain zonal and meridian winds of the mesopause and lower thermosphere. Through Fourier transformation, various ionospheric longitudinal harmonic components and tidal patterns are derived from the ionospheric and upper-atmospheric observations, and we compare the annual/inter-annual variations in ionospheric harmonic components WN3 and WN4 with those in atmospheric tides (DE2 and DE3). It is found that the annual and inter-annual variations in WN3 and WN4 are consistent with those in DE2 and DE3 zonal wind components respectively, while they are inconsistent with those in the meridian components. We then decompose the harmonic components into “tidal patterns”, finding that the “DE2” and “DE3” patterns are the main parts of WN3 and WN4 respectively. Their annual and inter-annual variations are similar to those of atmospheric tidal patterns (DE2 and DE3). Complex correlation results show that correlation between the ionospheric “DE2” in WN3 and the atmospheric tidal DE2 zonal wind component is quite strong in the Northern Hemisphere, while that between the ionospheric “DE3” in WN4 and the atmospheric tidal DE3 zonal wind component is much stronger at low latitudes. At the same time, the contribution of the meridian wind component is very weak. Above all, the atmospheric tidal DE2 and DE3 patterns are important factors of the ionospheric WN3 and WN4 structures.

Short-term and seasonal dynamics of bacterial biomass production and amino acid turnover in the water column of an intertidal ecosystem, the Wadden Sea

Intertidal flat systems exhibit systematic temporal patterns of suspended particulate matter (SPM) and associated properties (particulate organic carbon, chlorophyll) with enhanced con- centrations towards the current velocity maximum (CVM) and reduced concentrations towards slack water. It is unclear how these tidal patterns are reflected in organic matter processing by particle- associated (PA) and free-living (FL) heterotrophic bacteria. Therefore, we studied the abundance of PA and FL bacteria, bacterial biomass production (BP) and turnover of dissolved free amino acids (DFAA) during tidal cycles in a 13 to 16 m deep back-barrier intertidal flat system of the East Frisian Wadden Sea, Germany, in January, April, July and November 2005. Pronounced tidal patterns of microbial parameters were found with distinct differences around the CVM and at slack water. Tidal patterns varied seasonally with higher BP rates and bacterial generation times of 1 to 2 d in April and July. There was a trend of enhanced rates of BP from surface to bottom in April and July with an increasing significance of PA bacteria towards the bottom. Very high depth-integrated daily rates of BP and oxygen undersaturation suggest that this system is net-heterotrophic. A normalization proce- dure revealed systematic tidal patterns of most parameters irrespective of the seasonal situation. Our findings thus demonstrate the presence of tidal patterns of parameters reflecting microbial processes and thus complement previous findings of tidal patterns of SPM-associated properties. The tidally varying microbial activities indicate that the rhythmic tidal currents promote organic matter decom- position by heterotrophic bacteria in intertidal flat systems.

Vertical cell movement is a primary response of intertidal benthic biofilms to increasing light dose

Intertidal soft sediment microphytobenthic biofilms are often dominated by diatoms, which are able to regulate their photosynthesis by physiological processes (e.g. down-regulation through the xanthophyll cycle, referred to as non-photochemical quenching, NPQ) and behavioural processes (e.g. vertical cell movement in the sediment–biofilm matrix). This study investigated these 2 processes over a 6 h emersion period using chemical inhibitors under 2 light treatments (ambient and constant light at 300 µmol m–2 s–1). Latrunculin A (Lat A) was used to inhibit cell movement and dithiothreitol (DTT) to inhibit NPQ. HPLC analysis for chlorophyll a and spectral analysis (Normalised Difference Vegetation Index) indicated that Lat A significantly inhibited cell movement. Photosynthetic activity was measured using variable chlorophyll fluorescence and radiolabelled carbon uptake and showed that the non-migratory, Lat A-treated biofilms were severely inhibited as a result of the high accumulated light dose (significantly reduced maximum relative electron transport rate, rETRmax, and light utilisation coefficient, α, compared to the migratory DTT and control-treated biofilms). No significant patterns were observed for 14C data, although a decrease in uptake rate was observed over the measurement period. NPQ was investigated using HPLC analysis of xanthophyll pigments (diatoxanthin and the percentage de-epoxidation of diadinoxanthin), chlorophyll fluorescence (change in maximum fluorescence yield) and the 2nd order spectral derivative index (diatoxanthin index). Patterns between methods varied, but overall data indicated greater NPQ induction in the non-migratory Lat A treatment and little or no NPQ induction in the DTT and control treatments. Overall, the data resulted in 2 main conclusions: (1) the primary response to accumulated light dose was vertical movement, which when inhibited resulted in severe down-regulation/photoinhibition; (2) diatoms down-regulated their photosynthetic activity in response to accumulated light dose (e.g. over an emersion period) using a combination of vertical migration and physiological mechanisms that may contribute to diel and/or tidal patterns in productivity.

Tidal changes in estuarine systems induced by local geomorphologic modifications

Although rising global sea levels will affect the estuarine flooded areas over the coming decades, the local and regional-scale processes will also induce important changes in these coastal systems. The main aim of this work is to investigate possible tidal changes in estuarine systems induced by local geomorphologic modifications, analysing the particular case of Ria de Aveiro which is in risk of inundation. Located in the Portuguese west coast, this tidally driven lagoon has a large area of mostly abandoned salt pans, which are in progressive degradation caused by the lack of maintenance and by the strong currents which erode their protective walls. To explore possible tidal changes the hydrodynamic model ELCIRC was applied to Ria de Aveiro to simulate and analyse the impact in the lagoon hydrodynamics of this degradation which results in the enlargement of the lagoon flooded area. A high-resolution grid (grid spacing of the order of 1 m) was developed in order to represent the narrow channels adjacent to the salt pans. The hydrodynamic model was then successfully calibrated and assessed for skill for the Aveiro lagoon through comparison between measurements and model results and quantification of the numerical accuracy. The model was subsequently used to investigate the effect of the flooded lagoon area enlargement on tidal propagation in Ria de Aveiro. Simulations were performed for three geomorphologic configurations, representing the reference or present situation and two flooded scenarios. Results were compared through the analysis of tidal currents, tidal asymmetry and tidal prism. The increase of the lagoon flooded area results in an intensification of the tidal currents, tidal prism and tidal asymmetry. Results also indicate that the tidal prism further increases when the flooding depth increases. Otherwise, changes in tidal currents and in tidal asymmetry pattern are negligible with the increase of the flooded area depth. These results indicate that modifications of the flooded area of estuarine systems will result in tidal changes, with an intensification of the actual tidal patterns induced by the enlargement of inundation areas.

Fluvial modulation of hydrodynamics and salt transport in a highly stratified estuary

An oceanographic campaign was conducted in the Araranguá river estuary during the period from May 11th to 13th of 2006 in order to produce a first hydrographic characterization of this system. The campaign was carried out during the spring tide period, and coincidentally after an intense rain event in the region which produced a peak in river discharge. Water level, currents and salinity time series were recorded hourly during a 50-hour period, at a site nearly 7 km upstream from the estuarine mouth. Two longitudinal distributions of salinity along the estuary were also recorded. The hydrographic data time-series were used to compute the advective salt flux in order to investigate the changes in the transport terms as a function of the change in discharge. The results showed that the estuarine structure was strongly modulated by the river discharge. The drop in water level of about 0.5 m during the first 24 hours was directly related to the ebb phase of the river flood. The water column was highly stratified throughout the period, therefore the stratification increased during the last 24 hours. The currents were stronger, ebbing and uni-directional at the beginning and became weaker and bidirectional as the water level went down, assuming a tidal pattern. The total salt transport in the first 25 hours was of -13.6 kg.m-1.s-1 (seawards), decreasing to 3 Kg.m-1.s-1 during the last 25 hours (landwards). It was also noticeable that the pH in the estuary, recorded together with the salinity, was around 5, showing that the water quality in the estuary is affected by the coal mining activity in the hydrographic basin.

Dynamics of the semi-diurnal and quarter-diurnal internal tides in the Bay of Biscay. Part 2: Baroclinic tides

A regional baroclinic model forced with several tidal constituents at different frequencies is used to investigate the internal tide of the Bay of Biscay. The regional ocean model is free surface, sigma-coordinate and it is implemented in order to accurately take into account the barotropic forcing, the strong bathymetry gradients and the temperature and salinity stratifications. In a previous paper, the barotropic component of the tides was studied in details and the boundary conditions of the three-dimensional model were extracted from the atlases. In the present paper, we focus on the baroclinic component of the tides and the simulations are validated against observations from the MINT94 experiment. The observed currents and stratification are accurately reproduced by the model. The internal tide pattern is consistent with the descriptions found in the literature. Combining wavelet and principal component analysis we extract the patterns of generation and propagation of the internal tide at the semi-diurnal and quarter-diurnal frequencies. Secondary internal wave generation areas are identified over the plain. The vertical displacements of isopycnal surfaces for the M4 internal tide are found to be locally half those induced by the semi-diurnal internal tide. A sensitivity study shows the impact of using a three-dimensional initial stratification over the direction of propagation and wavelengths of the internal tides.

Westward rotation of the atmospheric angular momentum vector of Titan by thermal tides

The orientation of the atmospheric angular momentum vector of Titan and its temporal variation predicted by a general circulation model are analysed and interpreted. The atmospheric angular momentum vector is tilted by a few degrees from the polar axis and the vector rotates (precesses) westward with a constant period of 1 Titan day. The fast westward rotation is likely to be caused by migrating diurnal thermal tides. The tilt is almost cancelled out in the troposphere by the wavenumber 2 pattern of Saturn's gravitational tide, but is more pronounced in the stratosphere, where thermal tides are significant. The predicted tilt angle and the equatorial angular momentum vary with season and maximize when the hemispheric asymmetry of the axial angular momentum or superrotation attains its peak.

Storms and surges in Irish coastal waters

Abstract Mechanisms of storm surge formation and severity on the north European continental shelf and, in particular, in the Irish coastal waters are examined in this paper. A numerical surge model was developed and used in combination with meteorological forcing and hydrographic records to analysis aspects of surge mechanics. An attempt is made to estimate sea level response to meteorology and to quantify pressure and wind contributions as a driving force. Results show that the inverted barometer term contributes to more than 80% of surge residual in the Celtic Sea and to approximately 55% along the British coast in the Irish Sea. Local winds on the Irish Sea have less of an impact on storm surge heights than previously reported; the Irish Sea surges are predominantly caused by the propagation of external surges into the basin from the north and south channels. An analysis of sea level variability due to wind or pressure was undertaken to select regions of positive and negative interactions. Negative correlation between wind and pressure-driven surges found in the Celtic Sea explains generally low magnitudes of surges in this region, while medium level correlation coefficients could be responsible for generally high surges in the eastern Irish Sea and coast of Scotland. Following a regression analysis, it was determined that in these regions a drop of atmospheric pressure by 1 mbar implies a rise of sea level by 1.2 cm. Non-linear tide–surge interactions are also investigated. Relationships between surge and tidal phase are determined at numerous locations in the Irish coastal waters. Analysis shows that interaction characteristics vary from site to site due to shallow water dynamics and variations in topography. The regional pattern of tide–surge interactions is quite remarkable. Finally, a characterisation of the statistical properties of extreme surges is given. An efficient approach is adopted considering statistics of extremes. A hybrid GEV-EV1 statistical solution was used to estimate the 10, 50 and 200-years extreme surge in the Irish coastal waters.

Tide-related periodicity of manta rays and sharks to cleaning stations on a coral reef

Although the movements of fishes on coral reefs have been well studied, there are few data on the movement of elasmobranchs on and around cleaning stations. The visitation to cleaning stations by elasmobranchs was documented by direct observation and remote video capture at an oceanic reef in the Coral Sea and the outer Great Barrier Reef at time scales of hours to weeks. Cleaning was only observed at Osprey Reef and duration of occupancy was recorded for all elasmobranch clients. Strong tidal patterns were detected, with 49% of sharks and 59% of mantas engaging in cleaning interactions on ebb tides. Forty-four per cent of non-cleaned sharks were also observed on ebb tides. Some manta rays (n = 19) were individually identified through ventral skin pigmentation to determine site fidelity; three were seen more than once with repeat observations occurring within days. This was consistent among weeks and days within weeks, regardless of time of day. Hypotheses for tidal behaviour are discussed and we argue that these observations are critical in elucidating previously unknown behaviours in elasmobranch ecology. Our study indicates that observations of large elasmobranchs at cleaning stations are another tool to elucidate elasmobranch ecology.

Highly Skewed Tidal Circulation Pattern and Water Quality in Puerto Galera Bay, Mindoro Island, Philippines

Coastal waters in and around Puerto Galera Bay, Mindoro, Philippines, is drastically contaminated generally due to poorly constructed sanitation and household facilities and runoff from the hillsides associated with the tourism development. In this study, a field survey on tidal currents and water quality in and around Puerto Galera Bay was conducted with hydrodynamic numerical simulations of tidal currents, in which a nesting technique was employed for properly incorporating the effects of complicated tidal fluctuation outside the bay. The results reveal the existence of a highly asymmetrical pattern of tidal flow fluctuation having strong tidal residual flow and the vulnerability of the flow field to water quality deterioration within the semi-enclosed innermost bay area. The highly asymmetrical tidal flow fluctuation is attributed to the asymmetrical generation of detached eddying motion around Puerto Galera as a highly nonlinear phenomenon producing strong tidal residual currents. These results are useful in understanding the physical conditions of the bay, which are needed for consideration in the local government's coastal management plan.

Large-scale variation in seasonal swimming patterns of plaice in the North Sea

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 392:167-178 (2009) - DOI: https://doi.org/10.3354/meps08213 Large-scale variation in seasonal swimming patterns of plaice in the North Sea E. Hunter1,*, R. J. Cotton2, J. D. Metcalfe1, J. D. Reynolds3 1Centre for Environment, Fisheries and Aquaculture Science, Lowestoft Laboratory, Pakefield Road, Lowestoft, Suffolk NR33 0HT, UK 2Mathematical Sciences Unit, Health & Safety Laboratory, Harpur Hill, Buxton, Derbyshire SK17 9JN, UK 3Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada *Email: ewan.hunter@cefas.co.uk ABSTRACT: We examined the mid-water swimming activity of 139 mature female plaice Pleuronectes platessa L. These were tagged with electronic data storage tags (DST1s and DST3s) to test whether swimming at different times of the year differed among areas of the North Sea with average tidal current velocities ranging from fast (West), to intermediate (East), to slow (North). Longer swimming duration and more tidal activity were predicted for the western group, where fast-flowing tidal currents allow efficient selective tidal stream transport. Individual depth data were converted into binary records representing either swimming or resting; repeated patterns of swimming were analysed according to cycle-length frequencies. Most swimming occurred during expected times of migration and spawning (October to March). Plaice infrequently spent >5 h in mid-water, and rarely left the sea-bed during summer. DST1 tagged plaice (West only) spent the longest times swimming (p > 0.001), but there was no significant effect of Area for DST3s (all areas), suggesting that swimming plays an important behavioural role in migration in addition to transport between feeding and spawning areas. Tidal patterns of activity occurred in all 3 sub-stocks, predominantly during the migratory period (albeit at a significantly lower frequency in the North). These data provide one of few examples where the annual behaviour patterns of a fish stock have been recorded across a large part of its geographical range. The results have important implications for understanding the energetics of fish migration and the availability of demersal stocks to capture by commercial and survey vessels. KEY WORDS: Plaice · Migration · Data storage tags · Swimming · Behaviour · Fisheries Full text in pdf format PreviousNextCite this article as: Hunter E, Cotton RJ, Metcalfe JD, Reynolds JD (2009) Large-scale variation in seasonal swimming patterns of plaice in the North Sea. Mar Ecol Prog Ser 392:167-178. https://doi.org/10.3354/meps08213 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 392. Online publication date: October 19, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

Submarine Ground Water Discharge Driven by Tidal Pumping in a Heterogeneous Aquifer

Submarine ground water discharge (SGD) is now recognized as an important water pathway between land and sea. It is difficult to quantitatively predict SGD owing to its significant spatial and temporal variability. This study focuses on quantitative estimation of SGD caused by tidally induced sea water recirculation and a terrestrial hydraulic gradient. A two-dimensional hydrogeological model was developed to simulate SGD from a coastal unconfined aquifer in the northeastern Gulf of Mexico, where previous SGD studies were performed. A density-variable numerical code, SEAWAT2000, was applied to simulate SGD. To accurately predict discharge, various influencing factors such as heterogeneity in conductivity, uncertain boundary conditions, and tidal pumping were systematically assessed. The tidally influenced sea water recirculation zone and the fresh water-salt water mixing zone under various tidal patterns, tidal ranges, and water table heights were also investigated. The model was calibrated and validated from long-term, intensive measurements at the study site. The percentage of fresh SGD relative to total SGD ranged from 4% to 50% under normal conditions. Based on simulations of two field measurements in summer and spring, respectively, the fresh water ratios were 9% and 15%, respectively. These results support the hypothesis that the SGD induced by tidally driven sea water recirculation is much larger than terrestrial fresh ground water discharge at this site. The estimates of total and fresh SGD are at the low and high ends, respectively, of the estimation ranges obtained from geochemical tracers (e.g., (222)Rn).

Diurnal and tidal pattern influencing the behaviour of Sotalia guianensis on the north-eastern coast of Brazil

The present study demonstrates the influence of the time of the day and tide on the frequency of individuals and on the social and foraging behaviour of an equatorial population of Sotalia guianensis. A population of S. guianensis from enseada do Curral (6°13′00″S 35°3′36″W), north-eastern Brazil, was investigated from October 1999 to September 2003. Social and foraging activities oscillated significantly, being less intense at high tide in comparison to other analysed tides. Socialization was more intense between 1000 and 1300 hours and foraging was more intense in between tides, than at high tide. No diurnal or tidal fluctuation was found on the frequency of individuals, which remained constant throughout the day. These results demonstrate the influence of circadian factors on an equatorial population which is highly impacted by human activities and highlights a need for protective measures.

Effects of Tidal and Diel Cycles on Dugong Habitat Use

ABSTRACT Quantifying the factors influencing behaviors of aquatic mammalian grazers may enhance the generic understanding of grazer ecology. We investigated diel and tidal patterns in movements of the dugong (Dugong dugon) by Global Positioning System—tracking 12 animals in 5 inshore—intertidal and 3 offshore—subtidal habitats along the coast of Queensland, Australia. We examined effects of tide height and time of day on the dugong's distance from 1) the nearest coast, 2) water >3 m deep, 3) actual water depth (bathymetry + tide ht) experienced, and 4) distribution of the directions of movements. Both tidal and diel cycles influenced dugong movement. Tracked dugongs tended to be closer to shore at high tide than at low tide and closer to shore at night than during the day. Onshore movement was more prevalent on incoming tides and in the afternoon and evening. Offshore movement was more prevalent on outgoing tides and from midnight through the morning until midday. Tidal and diel variation in water depths used by the inshore—intertidal dugongs was small, but probably underestimated, hidden by a sampling bias in the telemetry equipment. Onshore movement at high tide allowed dugongs to exploit intertidal seagrass beds. Dugongs are closer to shore in afternoons and evenings than in mornings. This behavior may be related to the avoidance of predators or watercraft. Our findings can be used to predict spatial patterns of dugongs within areas of conservation management significance and to assess, avoid, and mitigate adverse effects of anthropogenic disturbance.

Geolocation of North Sea cod (Gadus morhua) using hidden Markov models and behavioural switching

When geolocating fish based on archival tag data, a realistic assessment of uncertainty is essential. Here, we describe an application of a novel Fokker–Planck-based method to geolocate Atlantic cod ( Gadus morhua ) in the North Sea area. In this study, the geolocation relies mainly on matching tidal patterns in depth measurements when a fish spends a prolonged period of time at the seabed with a tidal database. Each day, the method provides a nonparametric probability distribution of the position of a tagged fish and therefore avoids enforcing a particular distribution, such as a Gaussian distribution. In addition to the tidal component of the geolocation, the model incoporates two behavioural states, either high or low activity, estimated directly from the depth data, that affect the diffusivity parameter of the model and improves the precision and realism of the geolocation significantly. The new method provides access to the probability distribution of the position of the fish that in turn provides a range of useful descriptive statistics, such as the path of the most probable movement. We compare the method with existing alternatives and discuss its potential in making population inference from archival tag data.

Value and applicability of tidal breathing pattern analysis and chest CT in assessment of pulmonary function in children with congenital heart disease

Objective To evaluate the value and applicality of tidal breathing pattern analysis and chest CT in assessing pulmonary function in children with congenital heart disease. Methods We measured tidal breathing pattern in 44 children with congenital heart disease and conducted three-dimensional spiral CT imaging of tracheobronchography among 28 children. As a contrast, we also measured tidal breathing pattern in 64 children with common pneumonia and conducted threa-dimensional spiral CT imaging of tracheobronehography among 49 children. Results Patients with congenital heart disease showed the increased respiratory rate and decreased inspiratory time. Tidal breathing analysis parameters (TPTEF/TE, VPTEF and VPEF/VE) decreased obviously, but PTEF and TEF 75 increased in 44 children with congenital heart disease. Chest CT confirmed pulmonary infection, airway stenosis, emphysema and atelectasis in patients with congenital heart disease. The incidence rate of pulmonary dysfunction in patients with congenital heart disease was higher than that of control group. Conclusion Tidal breathing analysis parameters (TPTEF/TE,VPTEF and VPTEF/VE) could reflect obstructive ventilation function disorder in children with congenital heart disease. Chest CT could further uncover the etiology of ventilation function disorder. The combination of theses two noninvasive techniques facilitate clinicians to have a better picture of pulmonary function status in children with congenital heart disease. Key words: Tidal breathing pattern; Chest CT; Congenital heart disease; Pulmonary function

Tidal settlement of the intertidal barnacles Chthamalus spp. in SW Portugal: interaction between diel and semi-lunar cycles

Patterns and processes of tidal settlement (within 1 tidal cycle) of Chthamalus spp. in SW Portugal were investigated during the summer of 2003. Settlement patterns in relation to differ- ent periods of the day (night and day) and semi-lunar tidal cycles (spring and neap tides) were assessed using artificial plates deployed in intertidal habitats dominated by C. montagui. Settlement of Chthamalus spp. varied at all temporal and spatial scales considered in this study. A strong inter- action between diel and semi-lunar tidal cycles was detected. Settlement was higher during diurnal spring tides (afternoon) than during diurnal and nocturnal neap tides (morning and early night) and was lowest during nocturnal spring tides (late night). In order to investigate putative physical mech- anisms of shoreward transport to explain our observations, the tidal variability of several physical variables (wind stress, seawater temperature and temperature stratification) was individually inves- tigated and correlated with settlement. Onshore wind stress was positively correlated with settle- ment, and exhibited the same night/day and tidal pattern. Onshore wind forcing could be acting as a mechanism promoting intensive larval delivery to the shore in the afternoon (sea breeze) and off- shore retention late at night, leading to the high frequency variability patterns observed in barnacle settlement.

Temporal dynamics of dissolved oxygen in a floating–leaved macrophyte bed

Summary1. Oxygen concentrations in shallow vegetated areas of aquatic systems can be extremely dynamic. In these waters, characterizing the average oxygen content or frequency of low oxygen events (hypoxia) may require high frequency measurements that span seasons and even years. In this study, moored sondes were used to collect 15‐min interval dissolved oxygen (DO) readings in an embayment of the tidal Hudson River with dense coverage by an invasive floating leaved plant (Trapa natans) and in adjacent open waters. Measurements were made from late spring to summer over a 2‐year period (2005, 2006).2. Oxygen concentrations were far more dynamic in the vegetated embayment than in the adjacent open waters and while hypoxic conditions never occurred in the open waters, they occurred frequently in the vegetated site. Overall the vegetated site was hypoxic (DO < 2.5 mg L−1) 30% of the time and had an average oxygen concentration of 5.1 mg L−1. Oxygen concentration was significantly (P < 0.0001, anova) related to season, year and tide. Low tide periods during summer of 2006 had the lowest average oxygen concentration and the highest frequency of hypoxia.3. The greater hypoxia in summer than spring is related to changes in plant morphology. In the spring and early summer when plants are submersed hypoxia occurs at lower frequency and duration than in the summer when dense floating vegetation covers the water. The tidal pattern in oxygen is related to hydrologic exchange with the non‐vegetated open waters. Year‐to‐year variation may be related to relatively small changes in plant biomass between years.4. Oxygen concentrations in aquatic systems can be critical to habitat quality and can have cascading impacts on redox sensitive nutrient and metal cycling. For some systems with dynamic oxygen patterns neither weekly spot sampling nor short‐duration, high‐frequency measurements may be sufficient to characterize oxygen conditions of the system.

Applications of network analysis for adaptive management of artificial drainage systems in landscapes vulnerable to sea level rise

The vulnerability of coastal landscapes to sea level rise is compounded by the existence of extensive artificial drainage networks initially built to lower water tables for agriculture, forestry, and human settlements. These drainage networks are found in landscapes with little topographic relief where channel flow is characterized by bi-directional movement across multiple time-scales and related to precipitation, wind, and tidal patterns. The current configuration of many artificial drainage networks exacerbates impacts associated with sea level rise such as salt-intrusion and increased flooding. This suggests that in the short-term, drainage networks might be managed to mitigate sea level rise related impacts. The challenge, however, is that hydrologic processes in regions where channel flow direction is weakly related to slope and topography require extensive parameterization for numerical models which is limited where network size is on the order of a hundred or more kilometers in total length. Here we present an application of graph theoretic algorithms to efficiently investigate network properties relevant to the management of a large artificial drainage system in coastal North Carolina, USA. We created a digital network model representing the observation network topology and four types of drainage features (canal, collector and field ditches, and streams). We applied betweenness-centrality concepts (using Dijkstra’s shortest path algorithm) to determine major hydrologic flowpaths based off of hydraulic resistance. Following this, we identified sub-networks that could be managed independently using a community structure and modularity approach. Lastly, a betweenness-centrality algorithm was applied to identify major shoreline entry points to the network that disproportionately control water movement in and out of the network. We demonstrate that graph theory can be applied to solving management and monitoring problems associated with sea level rise for poorly understood drainage networks in advance of numerical methods.

Megatides in the Arctic Ocean under glacial conditions

Over the history of the Earth, changes in ocean depth and coastal configuration have led to considerable variations in the pattern and amplitude of ocean tides. Here we perform global simulations of ocean tides for the Last Glacial Maximum, using new data sets for both ocean depth and density stratification. We show how the configuration of the Arctic Ocean, which was almost entirely enclosed by continents at that time, leads to the near‐resonant excitation of large semi‐diurnal tides. Under certain conditions, this previously unidentified Arctic tide is massively amplified in the Canadian Archipelago. Such tides may have played a role in destabilizing the coastal margins of North American ice sheets, with implications for rapid changes in the Earth's climate and ocean circulation.