Tidal and sub-tidal sea level variability at the northern shelf of the Brazilian Northeast Region

Abstract

A characterization of the sea level variability at tidal and sub-tidal frequencies at the northern shore of the Brazilian Northeast shelf for the period 2009-2011 is presented. The sea level data used was obtained from the Permanent Geodetic Tide Network from the Brazilian Institute of Geography and Statistics for the Fortaleza gauge station. Local wind data was also used to assess its effects on the low-frequency sea level variability. The variability of the sea level was investigated by classical harmonic analysis and by morphology assessment over the tidal signal. The low frequencies were obtained by low-pass filtering. The tidal range oscillated with the highest value of 3.3 m during the equinox and the lowest value of 0.7 m during the solstice. Differences between the spring and neap tides were as high as 1 m. A total of 59 tidal constituents were obtained from harmonic analysis, and the regional tide was classified as semi-diurnal pure with a form number of 0.11. An assessment of the monthly variability of the main tidal constituents (M 2 , S 2 , N 2 , O 1 , and K 1 ) indicated that the main semi-diurnal solar S 2 presented the highest variability, ranging from 0.21 to 0.41 m; it was the main element altering the form number through the years. The low frequency sea-level variability is negligible, although there is a persistent signal with an energy peak in the 10-15 day period, and it cannot be explained by the effects of local winds.

Tidal flood area mapping fronts the climate change scenarios: case study in a tropical estuary of Brazilian semiarid

“…When applying the Mann-Kendall test, no statistically significant trend (Tau = -0.123; p= 0.16147) was observed in the dataset.The astronomical tide is the result of the interaction of the gravitational forces of Earth, Moon and the Sun, being completely predictable. With the DHN data set provided by the Brazilian Navy, it was observed that the maximum annual astronomical tide quota presented an average of 2.80 m and a 13 cm amplitude, with a maximum of 2.84 m and a minimum of 2.71 m. In the same study, when the Mann-Kendall test was applied, no statistically significant trend was observed (Tau = 0; p= 1),showing a steady pattern.The descriptive values on the tides presented to corroborate the values found in the literature Frota et al (2016),. studying the tidal behavior in the Brazilian Northeast during the period from 2009 to 2011 in buoys about 200 km from the Piranhas-Açú estuary, found that the average maximum tide height was 2.79 m, ranging from 2.23 at 3.34 m. In the same study, Frota et al(2016) found that the sea level variability in the sub-FT (The non-astronomical sea level signal) represents low oscillation, with a maximum of 0.12 m. Mattos et al (2019), conducted a campaign from December 2010 to February 2011 to study significant wave heights, found that the tide table of Guamaré-RN (approximately 40km East of the table of Macau-RN) had averages of 2.34 m (in syzygy tides) and 2.21 m (in quadrature tides), both above the reduction level.…”

Comparing the effect of larval dispersal strategies on morphological versus genetic differentiation in two neotropical fiddler crabs

“…Also, the populations of L. leptodactyla could be clustered in three groups, corresponding to significant differences in carapace shape along a macrogeographic scale. Brazilian estuarine systems have a high variability of abiotic conditions (e.g., salinity, temperature, tidal regimes), with higher tidal regimes and mean temperatures in the north and northeast coast, that may account for the local morphological divergence and phenotypic plasticity (Frota et al., 2016). Nevertheless, an overlap of morphotypes with no clear pattern could still be observed (Figure 7).…”

Tidal flood area mapping in the face of climate change scenarios: case study in a tropical estuary in the Brazilian semi-arid region

“…The descriptive values of the tides are presented to corroborate the values found in the literature. Frota et al (2016), studying the tidal behaviour in the Brazilian northeast during the period from 2009 to 2011 with buoys about 200 km from the Piranhas-Açu estuary, found that the average maximum tide height was 2.79 m, ranging from 2.23 to 3.34 m. In the same study, Frota et al (2016) found that the sea level variability in the sub-FT (the non-astronomical sea level signal) represents low oscillation, with a maximum of 0.12 m. Matos et al (2019) made a scientific expedition from December 2010 to February 2011 to study significant wave heights and found that the tide table of Guamaré (approximately 40 km east of the table of Macau) had averages of 2.34 m (in syzygy tides) and 2.21 m (in quadrature tides), both above the reduction level.…”