Sea Swell Research Articles

Infertility, embryonic mortality and nest-site selection in leatherback and green sea turtles in Suriname

Nest-site selection and causes of non-viability in eggs of leatherbacks Dermochelys coriacea and green turtles Chelonia mydas were investigated for two consecutive seasons on a beach used for nesting by both species in Suriname. Examination of nests and artificially incubated clutches after hatching showed that the main cause of an interspecies difference in hatching success was higher embryonic mortality in leatherbacks. Rupturing of eggs, used as an index of predation, was also greater in leatherback nests. Although infertility was slightly higher in leatherbacks, it was relatively low in both species. An interspecies difference in nest-site selection was found, with leatherbacks laying predominantly in open sand and green turtles in vegetated areas. Hatching success in the different areas was similar for green turtles, but only 12% of green turtle nests were occasionally washed over by sea swell compared to 40% of leatherback nests. Washover caused embryonic mortality in both species and is one of the causes of the increased embryonic mortality in leatherbacks. However, embryonic mortality was also higher in leatherback than in green turtle nests that were not washed over. Approximately half of the embryonic mortality occurred before days 22–24 of incubation in both species. Artificial incubation produced hatching successes similar to those in nests laid above spring high tide level. Predation was eliminated in styrofoam boxes and reduced in reburied clutches. Increased embryonic mortality during late development was found in the boxes. The implications for conservation of sea turtles are discussed.

Measurement of the acoustic Lloyd Mirror interference pattern at the midfrequency

Calibrated measurements of the Lloyd Mirror interference pattern were performed with two arrays at midfrequencies; one in the Western Gulf of Mexico during the Spring of 1979 and the other in the Northwest Atlantic during the Spring of 1980. These tests used a Webb organ‐pipe sound source driven at 175 Hz (170 dB re 1 μPa at 1 m) and 175 Hz (169 dB re 1 μPa at 1 m). These tests were designed to measure the sum of the surface reflected and direct sound path arrivals, which results in the reinforcements and cancellations of the sound field along a towed path. These tests performed with hydrophones of sensitivity −186 dB re IV/μPa showed a distinct interference pattern which previously had been clearly demonstrated only at the higher frequencies. Experimental results agreed extremely well with theoretical calculations and, assuming a reflection coefficient of (μ = 1), showed a mean difference of less than 0.9 dB at a sea state of 2. Theoretical results indicated that the Lloyd Mirror pattern becomes less distinct with increasing sea roughness (μ < 1) and increasing sea swell (μ = 1). Discrepancies on the order of ±3 dB were shown to be a result of a drift in position of the source relative to its anchor.

A spar buoy design for oceanographic data telemetry

Abstract The design of a spar buoy, employed as one component of a current monitoring system deployed during 1980 in Davis Strait, and some of its response characteristics to ocean waves are presented. The buoy was 36.5 ft (11.13 m) in length with upper and lower masts 0.5ft (15.2 cm) in diameter and buoyancy hulls, centrally located, 2 ft (61.0 cm) in diameter. Power for the system was supplied from lead‐acid batteries in a ballast tank on the lower end. Telemetry electronics were located in a 1‐ft (30.5‐cm) diameter case on the upper end, below the antenna. The buoy weighed about 1,635 lb (746kg) and could be man‐handled at sea with relatively light lifting equipment. It had a damped period of 16s and a significant heave response of about 62% of the significant wave height of the forcing spectrum. Scale model tests indicated that the buoy would be operational in heavy sea swell up to about 20ft in height with pitching angles of less than 10° off vertical. Observations at sea have shown that the buoy fol...

Wave setup of harbor water levels

Radiation stress by incoming sea surface waves or swell can raise the mean level of water in a harbor by an amount independent of the size of the harbor. This setup can be a significant confounding factor in determining sea level changes, if the sea level gauge is inside a harbor with a moderately shallow entrance. The mechanism is independent of ‘inverse barometer’ or wind setup effects, though it is likely to enhance them.

The Efficacy of Weather Routing in Reducing Damage

M.V. Geestport of the Geestline left the island of Dominica on 1 February 1970. She arrived at Barry on 10 February 1970. Between these dates the ship underwent a considerable ordeal, seldom experiencing a wind-force less than 7, while all the time she was pitching heavily, thereby shipping great amounts of water owing to the heavy swell and rough seas. From the 2 February the barometer pressure dropped about 1 millibar per hour and then, from 04.00 G.M.T. on the 3rd until 12.00 G.M.T. on 5 February, a slow rise was observed, finally steadying at 1034.6 mb. From the latter date the pressure began to fall at a slow rate and on arrival at Barry the barometer reading was 1002.8 mb. During these ten difficult days the speed of the vessel was varied continuously between 120 r.p.m. (about 20 knots) and 50 r.p.m. depending on the circumstances.

Measurement of Time-Varying Spectra of Surface Reverberation

Observations of the CW acoustic propagation between a fixed source and receiver in the Florida Straits have revealed fluctuations in both phase and amplitude with frequencies corresponding to surface waves. Comparison of the spectra of acoustic phase and amplitude to the spectra of surface wave height show proportionally more energy in the acoustic signal in the frequency range of sea swell than in the frequency range of wind-driven waves. To investigate the effects of sound-speed structure and wind speed and direction upon the surface modulation, online digital processing has been employed. Phase coherent demodulation and filtering followed by fast Fourier transform provide nearly continuous spectra of the acoustic signal. A spectrum is obtained every 3 min with a frequency resolution of 0.005 Hz from ±0.5 Hz about the 420-Hz carrier. Three dimensional displays of frequency, intensity, and time are presented for several 2-h samples on selected days having varying conditions of wind speed and direction. The presented data are discussed in light of single reflection experiments (Roderick) and known seasonal characteristics of acoustic propagation in the Florida Straits.

Ocean swell measurements from satellitephotographs

Fourier optical analyzer techniques have been used to measure sea swell wavelength and propagation direction from Apollo 7 space photography. Ocean swell wavelengths of 366 m (1200 ft) (originating from Typhoon Gloria, located at 23°N, 132°E) were measured in the region of Biak Island (0°30′S, 136°00′E) near New Guinea.

Photogrammetric measurement of the sea swell

Photogrammetric measurement of the sea swell

Photogrammetric measurement of the sea swell

Photogrammetric measurement of the sea swell