ON SEA LEVEL ALONG THE BRAZILIAN COAST

Abstract

ABSTRACT . This is Part II of a contribution on Brazilian sea levels – Part I dealt with the seasonal variability. It examines the sea level changes along the Brazilian coast from series with less than 40 years of measurement, against the background of changes in series of all continents and islands around the world, considering data distributed by the Permanent Service for Mean Sea Level (PSMSL). The method of analysis follows the display of the data in a: 1) first plot of relative sea level trends (C), against the length of the series (L) expressed in years and a: 2) second plot showing the relative sea level regression coefficients (C), versus the corresponding correlation values (m). The first plot of all PSMSL data exhibited a cusped like shape of the distribution of (C), having maxima values about 10-20 cm/cty for the longest series (120-137 years), indicating the overall positive value of the global relative sea level trend. Similar first plot, a regional plot of African and South American data adjusted to the same global relative mean level, showed that the Brazilian trends (C), are mostly concentrated in the positive side of the cusped: (ports of Bel´em, Fortaleza. Recife, Canavieiras, Salvador, Ilha Fiscal, Rio de Janeiro, Ubatuba, Cananeia, and Imbituba) which have a mean value within 30 to 40 cm/cty. The second plot, with all set of PSMSL data, was necessary in order to display trend values of non simultaneous series of different continental borders and lengths in the same bin. The plot gave two different linear inclinations for trend values within ± 0.3 cm/y, in the positive and negative sides of the figure. The global ratio obtained for the trends was R = − 1.2, suggesting also, from the linearity of the plot, that the trends and correlation values are statistically dependent variables. The graph produced a different value for global balance of the value C obtained in the first plot. Similar regional second plot of the African Atlantic and South American borders, which include the Brazilian data, also gave rise to two new regression lines with trend C*1 0, with a ratio R = − 2.2, involving bins of m and C values that are also null in the vicinity of zero. This regionally plot confirmed the result of the second plot with PSMSL series that they (C and m), globally, should be dependent statistical variables. These findings, however, do not change the fact that the regional series with trends 0.2 cm/year have correlation values m 0 construidas a partir dos valores das tendencias C das series PSMSL, com inclinacoes dentro da faixa de 0,2 cm/ano na parte positiva e negativa da figura, sugerindo uma nao equivalencia entre essas inclinacoes, em favor de valor global negativo de C* para o Nivel Relativo do Mar. Figura semelhante produzida com as s´eries Africanas e Sul Americanas, que incluiram as series brasileiras, mostrou caracteristica similar, alem de indicar que series com tendencias ± 0,2 cm/ano tem valores de correlacao m < 0,3 qualquer que seja o comprimento da serie. Os resultados interessantes, mas contraditorios, que incluem a dependencia linear global entre correlacao e tendencias das series fornecidas pelo PSMSL, devem ser analisados em continuacao aos presentes estudos, que indicam que o nivel relativo do mar na costa brasileira esta aumentando a razao de 30 a 40 cm/seculo. Palavras-chave: nivel do mar, costa brasileira, series do PSMSL, nivel relativo do mar global, balanco do nivel relativo do mar.