Analysing the tidal state of a pre-plate tectonic Earth during the Archean Eon (3.9 Ga)

<p>Deep time investigations of the Earth have revealed a relationship between plate tectonic motion and the intensity of the tide. Tidal energetics change as continental plates disperse and aggregate in the supercontinent cycle, altering ocean basins around them. The question is, could enhanced tides occur on Earth before plate tectonics started e.g., during the Archean?  </p><p>Here we have coupled an established tidal model with an ensemble of potential topographies of the Archean Earth to establish a statistically significant approximation of Archean tidal energetics. Land area is restricted to 5 – 15% with the rest representing primordial ocean – containing no major plate tectonic features i.e., trenches and ridges. Ocean volume is preserved at close to present-day which means oceans are on average 1 km shallower than present-day oceans. Archean day length is set at 13.1 hours with the semi-diurnal tide occurring every 6.8 hours. Equilibrium tide is around 3.4x the present-day value due to the proximity of the Moon.</p><p>The aim of this study is to assess the relationship of the Earth Moon system during this primordial stage to better understand the potential role tides had in the origin of life, and to quantify the tidal state of a primordial rocky planet with a young, nearby moon. Understanding the tidal state of Earth at this early time is important for exoplanetary studies as it broadens our scope of planets which may be hospitable to life.</p><p>We found coastal and open ocean resonance in many of the ensemble topographies. Total global dissipation in the ensembles varies from 75 – 150% of present-day dissipation rates due to elevated equilibrium tide and greater area where the tide can dissipate. When regional and open ocean resonance does occur, it can raise total global dissipation to >150% of present-day values and can cause regional macrotidal amplitudes (>2m).</p>

Variation in environmental characteristics of waters among Amazon coast oyster culture units

ABSTRACT Oyster culture has benefited traditional coastal communities along the Amazon macrotidal mangrove coast of Pará state in Brazil since 2006. Currently, seven oyster culture units in five municipalities are expanding production, but with no environmental monitoring, which is important for the control of the impacts of oyster culture on waters as well as for oyster management and conservation. Seasonal variation in environmental characteristics of the water was evaluated at all oyster culture units in Pará, from September to November 2013 (dry season) and February to April 2014 (wet season), to generate baseline data to evaluate future impacts and aid strategic planning, such as diversifying seed production. Salinity, dissolved oxygen, pH, oxidation-reduction potential, depth, temperature, and chlorophyll-a concentration were measured during flooding and ebbing tides, and compared between seasons and among culture units using uni- and multivariate statistics. All variables were significantly higher in the dry season, except depth, which was significantly greater in the wet season. Mean salinity, which varied from 2.4 to 46, explained most of the variation among culture units in relation to season, sampling date within each season and tidal state. However, dissolved oxygen, pH and depth were also important. Oyster culture units in Pará may be suitable for sustainable harvesting of seed/spat from the wild (lower salinity and pH), or for on-growing (higher salinity, higher pH, and greater depth). Seasonal variation is sufficient to allow both activities at most units at appropriate times of the year, which would help increase oyster production in Pará.

The role of wind-forcing in the distribution of larval fish in Galway Bay, Ireland

The ichthyoplankton of Galway Bay was sampled over the spring and summer of 2007 and 2008 to determine what environmental factors influenced the distribution of larval and early juvenile fish. A total of 549 fish representing 27 taxa were caught. Catches decreased throughout each sampling season, and were generally poor in 2007. Catches were numerically dominated by sprat (Sprattus sprattus), dab (Limanda limanda), sand eel (Hyperoplus immaculatus) and whiting (Merlangius merlangus). Environmental factors driving distribution of fish were modelled using a binomial generalized linear model. The strength and direction of wind in the five days preceding sampling was the only significant environmental factor. Sustained onshore winds increased the probability of encountering larval fish in the areas sampled. The rainfall, tidal state, tow depth and wind conditions during sampling were not significant. Among the parameters measured it appears that onshore winds sufficiently strong to overcome the residual circulation are the main physical driver for the distribution of larval fish in Galway Bay.

Effect of Tide on Sewage Disposal by Bio-Film Process Dosing with Enzyme

The paper studied the effect of tide on the removal rate of COD, NH3-N and TP in the dosing pool in order to provide data to simulate disorderly discharged sewage in tidal rivers. Due to the dilute effect of rivers, the removal rate of COD, NH3-N and TP at the tidal state was higher than that at no tidal state. At the tidal state, the average removal rate of COD, NH3-N and TP was 60.8%, 55.7%, 55.6%. At no tidal state, the average removal rate of COD, NH3-N and TP was 57.5%, 47.5%, 8.6%. At the tidal state, the upper bio-film was exposed to air and the activity of microorganism decreased, and the activity of microorganism was high at middle-level bio-film. Therefore, the utilization of bio-film at the tidal state was lower than that at no tidal state. However, due to the tidal action, rivers entered into the dosing pool and the dilute effect of rivers on the pollutants was obvious.

Abundance, distribution and haul-out behaviour of grey seals (Halichoerus grypus) in Cornwall and the Isles of Scilly, UK

This study investigated the phenology, patterns of haul-out habitat use and distribution of the grey seal around Cornwall and the Isles of Scilly. A full census of the coast was carried out by boat over 4 days, in order to make a full count of seals hauled out and close to the coast, and to document all haul-out sites. Regular land-based surveys were made of three haul-out sites in Cornwall, to investigate the effects of spatial, temporal and environmental factors on seal haul-out behaviour. Data from 2004 to 2007 were analysed to describe long-term temporal variation in seal abundance at two haul-out sites. A total of 592 sightings were made along the coast of Cornwall and the Isles of Scilly over the four-day census period; 476 of these sightings (80.4%) were recorded at six main haul-out sites. The highest proportion of seals was observed at three haul-out areas on the Isles of Scilly. In Cornwall, seals were observed in higher numbers on the north coast, where the three largest mainland haul-out sites were documented, than on the south coast. At one key haul-out site in Cornwall, a distinct seasonal pattern was evident in data collected between 2004 and 2007, with higher numbers of seals present during the moulting and breeding seasons than over the summer months. There was considerable inter-annual variability in peak seal abundance, during the moulting season, at this site. There was no significant variation in haul-out behaviour with tidal state at this site, although haul-out counts were generally highest at mid-ebb tides. Data on seal abundance, distribution and haul-out behaviour may aid the designation of Special Areas of Conservation for the protection of grey seals in Cornwall and the Isles of Scilly.

Tidal fish connectivity of reef and sea grass habitats in the Indo-Pacific

The present study considered the influence of the tide on shallow water fish assemblages within the Wakatobi Marine National Park, Indonesia. Timed underwater visual observations were made across a gradient of intertidal to subtidal habitats from near-shore to reef crest at different tidal heights. Transient fish were found to dominate shallow water fish assemblages and the assemblage composition varied with tidal state. Fish assemblages were more diverse and abundant at higher tides in both coral and sea grass habitats, however, this was more pronounced within sea grass habitats. A tidal reduction from ≈2.0m to ≈0.8m (above chart datum) corresponded to a 30% reduction in fish abundance, while species richness also significantly decreased from 13.5 to 10.8 species per standardized timed observation. Fifty fish groups were reported from sea grass habitats with the most abundant being from the Engraulidae family and Lethrinus harak, which form important local subsistence fisheries. This research confirms the importance of tidal changes in structuring the fish fauna of Indonesian sea grass habitats and underlines the connectivity that exists between these habitats and nearby coral reefs.

Using T-PODs to investigate the echolocation of coastal bottlenose dolphins

We investigated the feasibility of using a T-POD, a passive acoustic dolphin detector system, to monitor bottlenose dolphins in the Shannon Estuary, Ireland, from 27 June to 18 August 2005. A v.3 T-POD, logging alternate minutes, was moored in view of an observation site. Land-based theodolite tracking was used to record the position of the closest animal, school size and activity of the closest dolphin school to the T-POD. All cetacean detections on the T-POD synchronous with shore watches in sea states ≤2 were analysed. A total of 94 schools were observed at distances up to 8000 m from the observer. Acoustic detections corresponded well with visual detections, with 82% of the dolphin schools observed within 500 m of the T-POD detected acoustically. The furthest distance dolphins were observed from the T-POD during periods of acoustic detection was 1246 m. Twelve acoustic encounters were logged without corresponding visual detections, four of which may represent false positives. School size did not affect the acoustic detectability of the dolphins, as there was no difference in the size of schools observed with or without corresponding acoustic detections (Kruskal–Wallis, P=0.64). Similarly no relationship was found between acoustic detections and school sizes at different distances to the T-POD (linear regression P=0.5, r2=0.01). Acoustic encounters did not vary in relation to diel patterns (Mann–Whitney, P=0.13) but were related to tidal state (χ2=40.2, P=0.00, df=11) with more encounters logged in the 4 h after high water, probably reflecting prey-related changes in habitat use. T-POD detections correlated well with visual observations and although detection is likely to vary according to T-POD specification, sensitivity and the conditions at the deployment site, the T-POD is a useful tool that has been shown to offer the possibility of continuous monitoring, something that is difficult to achieve with visual methods alone.

Foraging habitat selection by American and Magellanic oystercatchers (Haematopus palliatus and H. leucopodus) on Patagonian tidal flats

I examined the foraging behaviour of American and Magellanic oystercatchers on Patagonian tidal flats in the context of several abiotic and social factors. I analyzed the simultaneous effect of tidal state, wind speed, temperature, habitat preference, and species abundance of one species on the other by means of multiway contingency tables and loglinear models. Diets of both species were similar and reflected the natural abundances of prey items in the tidal flats. Both species were strongly influenced by tidal state when selecting foraging habitat, but other factors modified their preferences. I found that the foraging behavior of American Oystercatchers was determined solely by abiotic factors; i.e., tidal state, foraging period, and a higher order interaction effect between wind speed and tidal state. By contrast, no combination of abiotic factors was sufficient to explain the observed abundances of Magellanic Oystercatchers. Instead, their foraging behavior was facilitated by the presence of congeners in addition to abiotic factors.