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Hidrobiológica

versão impressa ISSN 0188-8897

Resumo

URCADIZ-CAZARES, Francisco J.; CRUZ-ESCALONA, Víctor H.; NAVA-SANCHEZ, Enrique H.  e  ORTEGA-RUBIO, Alfredo. Classification of seafloor units based on the spatial distribution of superficial sediments in La Paz Bay, Gulf of California. Hidrobiológica [online]. 2017, vol.27, n.3, pp.399-409. ISSN 0188-8897.

Background:

Seafloor mapping provides valuable information for ecological studies and conservation of marine areas; however, the methods used to delimit seafloor units in areas dominated by unconsolidated sediments are scarce.

Goals:

To classify and characterize seafloor units based on the spatial distribution of four variables: calcium carbonate content, mean grain size, sorting, and the depth in La Paz Bay (LPB).

Methods:

The spatial distribution of the four variables men tioned above was obtained from interpolation models. The models were created with the data of 85 samples of superficial sediment and by using a geographic information system. The classification of units was determined by grouping polygons that were constructed based on models and by implementing a hierarchical cluster analysis. Characterization was obtai ned from values predicted by the models.

Results:

The models produced values between 2.7 to 95% of CaCO3, -0.9 to 7.8 Φ (mean grain size), 0.1 to 4 Φ (sorting), and depth values ranging from 0 to 680 m. The hierarchical cluster analysis found14 units on the seafloor. Four units comprise 91% of the study area. Unit 4a stands out for its high content of CaCO3 (72±20%). Unit 3a shows poor sorting (2.2±0.7 Φ), whereas unit 2a had moderate sorting (1.1±0.3 Φ). Finally, unit 1a includes fine sediments (4.5±0.6 Φ).

Conclusions:

This study is one of the first seafloor-unit-classification proposals of unconsolidated sediments in LPB. The methodology allowed us to separate four main units reflecting environmental conditions with intrinsic properties. In addition, it establishes the first distribution models by calculating the mean error and the root mean square error contrasting a set of independent observations versus the modelling values of the variables mentioned previously. This proposal can be used as a baseline for studies of coastal areas and continental shelves in the Gulf of California and other sea areas, if such distribution is not affected by extreme hydro-meteorological events, in which case a similar study would be required.

Palavras-chave : Calcium carbonate; grain size; interpolation models; marine sediments; seafloor mapping; sorting.

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