Ítem


Compositional data analysis (CoDA) as a tool to study the (paleo)ecology of coccolithophores from coastal-neritic settings off central Portugal

Whereas using the species percentages is the standard analytical procedure used to infer species ecological preferences, independently of taphonomical effects, the closure problem associated with closed number systems and subsequent inconsistency of determining percentages may lead to spurious correlations, biased statistical analysis and misleading interpretations. To avoid these problems, we applied Compositional Data Analysis (CoDA) to investigate the (paleo)ecological preferences and spatial distribution of coccolith assemblages preserved in seafloor sediments, using as a case-study the central Portuguese submarine canyons and adjacent shelf-slope areas. Results from using the isometric log-ratio (ilr) approach from CoDA are compared with results from using classical analytical methods, and further discussed. While providing scale invariance and subcompositional coherence, CoDA is revealed to be a consistent statistical tool to infer the (paleo)ecological preferences of coccolithophores, corroborating earlier work based on from percentage determinations. Results of this study clearly confirmed the coastal-neritic distribution of coccoliths from Gephyrocapsa oceanica, Helicosphaera carteri and Coronosphaera mediterranea, whereas coccoliths from Calcidiscus leptoporus, Umbilicosphaera sibogae, Umbellosphaera irregularis and Rhabdosphaera spp. more typically occur offshore. Differences between canyons and adjacent shelf and slope areas were also confirmed, namely the (a) greater importance of the coastal-neritic assemblage possibly resulting from local and persistent nutrient pumping in these areas, and (b) stronger mixing of coccoliths from coastal and oceanic species in upper canyon reaches, resulting from the focused coastward advection of more oceanic water masses along their axes. Unlike the results from both ilr-coordinates and the percentage approaches, both coccolith concentrations and fluxes showed that spatial trends in which the species ecological inter-relationships appear to be masked by taphonomical phenomena, especially towards the coast and in the canyons, suggesting the two latter approaches are not suitable to perform (paleo)ecological inferences in more dynamic coastal-neritic settings. Our study suggests that the (paleo)ecological signal preserved in the studied sediment samples is persistent enough to be revealed by both CoDA and percentages. Yet, given that CoDA provides the only statistical solution to coherently draw (paleo)ecological interpretations from compositional data, our recommendation is that CoDA should always be used to test and validate any ecological signals obtained from percentage distributions

Data for this study were collected in the framework of the EU-funded EUROSTRATAFORM (contract EVK3-CT-2002-00079) and HERMES EU-funded projects (contract GOCE-CT-2005-511234), "Lead in Canyons" and "Pacemaker" projects funded by the Netherlands Organization for Scientific Research, and by the Portuguese project Cd Tox-CoN (FCTPTDC/MAR/102800/2008). Multicores were collected during RV Pelagia cruises which were funded by the Netherlands Organisation for Scientific Research. Samples were prepared and analysed at NANOLAB, CEGUL. A special thanks to Henko De Stigter for supplying sample material and for textual improvements and to Marc Comas for his help with CODAPACK. The first author benefited from a PhD grant (FCT-SFRH/BD/41330/2007), a post-doctoral fellowship from the University of Lisbon in the context of "Programa Estrategico do Instituto Dom Luiz" (PEST-OE/CTE/LA0019/2013-2014), funded by national funds of FCT/MEC (PIDDAC), and currently benefits from a Marie Curie post-doctoral fellowship attributed by the BREMEN-TRAC COFUND program, in the context of the 7th Framework Programme of the European Commission. V. Pawlowsky-Glahn is supported by the Spanish Ministry of Economy and Competitiveness through the project METRICS Ref. MTM2012-33236. The manuscript benefited from a detailed and helpful revision from Dr. Jasper Knight and two anonymous reviewers, for which the authors are most grateful

© Sedimentary Geology, 2015, vol. 319, p. 134-146

Elsevier

Autor: Guerreiro, Catarina
Cachão, Mário
Pawlowsky-Glahn, Vera
Oliveira, Anabela
Rodrigues, Aurora
Data: 15 abril 2015
Resum: Whereas using the species percentages is the standard analytical procedure used to infer species ecological preferences, independently of taphonomical effects, the closure problem associated with closed number systems and subsequent inconsistency of determining percentages may lead to spurious correlations, biased statistical analysis and misleading interpretations. To avoid these problems, we applied Compositional Data Analysis (CoDA) to investigate the (paleo)ecological preferences and spatial distribution of coccolith assemblages preserved in seafloor sediments, using as a case-study the central Portuguese submarine canyons and adjacent shelf-slope areas. Results from using the isometric log-ratio (ilr) approach from CoDA are compared with results from using classical analytical methods, and further discussed. While providing scale invariance and subcompositional coherence, CoDA is revealed to be a consistent statistical tool to infer the (paleo)ecological preferences of coccolithophores, corroborating earlier work based on from percentage determinations. Results of this study clearly confirmed the coastal-neritic distribution of coccoliths from Gephyrocapsa oceanica, Helicosphaera carteri and Coronosphaera mediterranea, whereas coccoliths from Calcidiscus leptoporus, Umbilicosphaera sibogae, Umbellosphaera irregularis and Rhabdosphaera spp. more typically occur offshore. Differences between canyons and adjacent shelf and slope areas were also confirmed, namely the (a) greater importance of the coastal-neritic assemblage possibly resulting from local and persistent nutrient pumping in these areas, and (b) stronger mixing of coccoliths from coastal and oceanic species in upper canyon reaches, resulting from the focused coastward advection of more oceanic water masses along their axes. Unlike the results from both ilr-coordinates and the percentage approaches, both coccolith concentrations and fluxes showed that spatial trends in which the species ecological inter-relationships appear to be masked by taphonomical phenomena, especially towards the coast and in the canyons, suggesting the two latter approaches are not suitable to perform (paleo)ecological inferences in more dynamic coastal-neritic settings. Our study suggests that the (paleo)ecological signal preserved in the studied sediment samples is persistent enough to be revealed by both CoDA and percentages. Yet, given that CoDA provides the only statistical solution to coherently draw (paleo)ecological interpretations from compositional data, our recommendation is that CoDA should always be used to test and validate any ecological signals obtained from percentage distributions
Data for this study were collected in the framework of the EU-funded EUROSTRATAFORM (contract EVK3-CT-2002-00079) and HERMES EU-funded projects (contract GOCE-CT-2005-511234), "Lead in Canyons" and "Pacemaker" projects funded by the Netherlands Organization for Scientific Research, and by the Portuguese project Cd Tox-CoN (FCTPTDC/MAR/102800/2008). Multicores were collected during RV Pelagia cruises which were funded by the Netherlands Organisation for Scientific Research. Samples were prepared and analysed at NANOLAB, CEGUL. A special thanks to Henko De Stigter for supplying sample material and for textual improvements and to Marc Comas for his help with CODAPACK. The first author benefited from a PhD grant (FCT-SFRH/BD/41330/2007), a post-doctoral fellowship from the University of Lisbon in the context of "Programa Estrategico do Instituto Dom Luiz" (PEST-OE/CTE/LA0019/2013-2014), funded by national funds of FCT/MEC (PIDDAC), and currently benefits from a Marie Curie post-doctoral fellowship attributed by the BREMEN-TRAC COFUND program, in the context of the 7th Framework Programme of the European Commission. V. Pawlowsky-Glahn is supported by the Spanish Ministry of Economy and Competitiveness through the project METRICS Ref. MTM2012-33236. The manuscript benefited from a detailed and helpful revision from Dr. Jasper Knight and two anonymous reviewers, for which the authors are most grateful
Format: application/pdf
ISSN: 0037-0738
Accés al document: http://hdl.handle.net/10256/10924
Llenguatge: eng
Editor: Elsevier
Col·lecció: MINECO/PN 2013-2015/MTM2012-33236
Reproducció digital del document publicat a: http://dx.doi.org/10.1016/j.sedgeo.2015.01.012
Articles publicats (D-IMA)
És part de: © Sedimentary Geology, 2015, vol. 319, p. 134-146
Drets: Tots els drets reservats
Matèria: Anàlisi multivariable
Multivariate analysis
Correlació (Estadística)
Correlation (Statistics)
Paleoecologia -- Mètodes estadístics
Paleoecology -- Statistical methods
Títol: Compositional data analysis (CoDA) as a tool to study the (paleo)ecology of coccolithophores from coastal-neritic settings off central Portugal
Tipus: info:eu-repo/semantics/article
Repositori: DUGiDocs

Matèries

Autors