Time filter

Source Type

Guerreiro C.,University of Bremen | Guerreiro C.,University of Lisbon | Guerreiro C.,Portuguese Hydrographic Institute IH | Guerreiro C.,Netherlands Institute for Sea Research | And 4 more authors.
Sedimentary Geology

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. © 2015 Elsevier B.V. Source

Guerreiro C.,University of Lisbon | Guerreiro C.,Netherlands Institute for Sea Research | Guerreiro C.,Portuguese Hydrographic Institute IH | de Stigter H.,Netherlands Institute for Sea Research | And 3 more authors.
Marine Micropaleontology

In this study we describe recent coccolith assemblages from surface sediments of the central Portuguese continental margin. By investigating variation in coccolith concentrations and relative abundances along north-south and onshore-offshore gradients and between submarine canyons and open shelf and slope areas, and by correlation of coccolith distribution with sediment characteristics (sediment bulk composition and particle-size, Corg/Ntot and sediment accumulation rate), we assess to what extent (paleo)ecological information can be distinguished from taphonomical effects (dissolution and mechanical destruction, lateral transport and dilution with terrigenous material).The main finding of this study is that original distribution patterns reported for living coccolithophores from the Portuguese margin surface waters are reflected by patterns in relative abundances of coccoliths in the underlying sediment, despite the vigorous current dynamics and active sediment transport on the shelf and in the canyons. Like in the surface water assemblages, Gephyrocapsa oceanica, Coronosphaera mediterranea, Helicosphaera carteri and Coccolithus pelagicus are more prevalent in sediments of the continental shelf and upper canyon reaches, whereas Gephyrocapsa muellerae, Calcidiscus leptoporus and the group comprising Umbilicosphaera sibogae, Umbellosphaera irregularis and Rhabdosphaera spp. have higher relative abundances in sediments of the open slope. Greater abundance of the coastal assemblage in sediments of the upper Nazaré Canyon appears associated with persistent high productivity driven by amplification of coastal upwelling and internal tidal pumping in the canyon head and the shelf area south of it. Enrichment of oceanic species in the upper reaches of both the Nazaré and Lisbon-Setúbal Canyon, compared with adjacent shelf areas, suggests displacement of oceanic coccolithophores in oceanic surface water masses advected coastwards along the canyon axes.While coccolith relative abundances in the sediment thus seem to reflect original distribution patterns, precluding major post-mortem redistribution of coccoliths, we found a distinct inverse relationship between coccolith concentration and sediment particle size, suggesting that sedimentary processes control the accumulation of coccoliths in the sediment. We propose a taphonomy-driven scenario, in which coccolith preservation is favored by rapid incorporation in the sediment near their area of origin, while coccoliths reworked by currents and transported away from their area of origin are subject to non-selective destructive processes, including dissolution and mechanical abrasion. This scenario would explain the observed apparent paradox of the preservation of the primary ecological signal in an environment known for its dynamic sedimentary processes.This study provides important insights on the processes governing the preservation of the ecological signature in the sedimentary record and testifies on the enormous potential of coccoliths in paleoapplications. © 2014 Elsevier B.V. Source

Guerreiro C.,Portuguese Hydrographic Institute IH | Guerreiro C.,University of Lisbon | Guerreiro C.,Netherlands Institute for Sea Research | Oliveira A.,Portuguese Hydrographic Institute IH | And 8 more authors.
Continental Shelf Research

Coccolithophore communities collected during late winter (9-19 March of 2010) over the central Portuguese margin showed a major change in species abundance and composition within a few days' time, closely related to the highly transient meteorological and oceanographic conditions.Particularly favourable conditions for coccolithophore growth resulted from late winter continental runoff combined with northerly winds prevailing over the shelf, under clear sky conditions. A nutrient-rich Buoyant Plume (BP) resulting from intense river water runoff prior to and during the start of the cruise, was observed to spread out over the denser winter mixed layer water beneath, and extend equatorwards and offshore under influence of Ekman superficial dynamics. Stabilization of buoyancy, settling of suspended sediment from the BP and the prevailing clear sky conditions in the transition to the 2nd leg of the cruise resulted in optimum conditions for coccolithophores to develop, at the expense of nutrient availability in the superficial sunlit layer. Within a few days, coccolithophore cell densities and associated phytoplankton biomass more than tripled, reaching maximum values of 145,000. cells/l and ~13. μg/l Chl-a, respectively.Often considered as a uniform functional group of calcifying phytoplankton thriving in low-turbulence, low-nutrients and high-light environments, results presented in this study clearly show that coccolithophore life strategies are much more diverse than expected. The increase of cell densities was mainly due to the bloom of Emiliania huxleyi and Gephyrocapsa oceanica in the coastal region west off Cape Carvoeiro, together with other opportunistic phytoplankton genera (Chaetoceros s.l., Thalassiosira s.l and Skeletonema s.l.). This confirms their role as early succession r-selected taxa, capable of rapid growth within nutrient-rich environments. On the contrary, Syracosphaera spp. and Ophiaster spp. displayed the characteristics of K-selected species, being consistently more abundant in more oceanic and less eutrophic waters, away from the influence of the BP, during both low- and high-productive periods.A general description of coccolithophore communities as well as the environmental conditions during this period is presented in this study (i.e. hydrography and nutrient availability). Multivariate analysis was used to investigate the impact of short-term environmental changes on the productivity and ecology of this group. In view of the observed dominance of coccolithophores off Portugal during winter, this transitional period appears particularly favourable for coccolithophores to develop. The results highlight the importance of taking short-term hydrographic and meteorological variability into account when interpreting the ecological preferences of coccolithophores from coastal-neritic-oceanic transitional settings. © 2013 Elsevier Ltd. Source

Guerreiro C.,Portuguese Hydrographic Institute IH | Guerreiro C.,Netherlands Institute for Sea Research | Guerreiro C.,University of Lisbon | Sa C.,University of Lisbon | And 9 more authors.
Deep-Sea Research Part II: Topical Studies in Oceanography

This paper presents a first attempt to characterize coccolithophore assemblages occurring in the context of an active submarine canyon. Coccolithophores from the upper-middle sections of the Nazaré Canyon (central Portuguese margin) - one of the largest canyons of the European continental margin - were investigated during a late winter period (9-12 March 2010). Species distributions were analyzed in a multiparameter environmental context (temperature, salinity, turbidity, Chl-a and nutrient concentrations). Monthly averaged surface water Chl-a concentrations between 2006 and 2011 assessed from satellite data are also presented, as a framework for interpreting spatial and temporal distribution of phytoplankton in the Nazaré Canyon. The Nazaré Canyon was observed to act as a conduit for advection of relatively nutrient-poor oceanic waters of ENACWst origin into nearshore areas of the continental shelf (less than 10. km off the coast), whilst at the surface a nutrient-rich buoyant plume resulting from intensive coastal runoff prior and during the beginning of the cruise was spreading in oceanward direction. Two distinct coccolithophore assemblages appear representative for the coast to open-ocean gradient: (1) Emiliania huxleyi together with Gephyrocapsa ericsonii and Coronosphaera mediterranea dominated the more productive assemblage present within coastal-neritic surface waters; and (2) Syracosphaera spp. and Ophiaster spp. displayed a higher affinity with open-ocean conditions, and also generally a broader vertical distribution. Local "hotspots" of coccolithophore and phytoplankton biomass potentially associated with perturbations of surface water circulation by the canyon are discussed. © 2013 Elsevier Ltd. Source

Discover hidden collaborations