Temporal variation of seston biomarkers within the Humboldt Current System off northern Chile (21°S): first simultaneous records on fatty acids, n-alkanes and glycerol-dialkyl-glycerol-tetraethers (GDGT)

Abstract

Proportions and concentrations of seston fatty acids, n-alkanes and glycerol dialkyl glycerol tetraethers (GDGTs) were used to assess potential differences in the phytoplankton composition and food quality in the Humboldt Current System (winter 2006, summer 2007 and winter 2007) in surface, oxycline, intermediate and bottom water layers. The zone below the intermediate depth was poorer in fatty acids (minimum 15 – maximum 117 µg fatty acids L⁻¹) than the upper water layers (minimum 36 – maximum 210 µg fatty acids L⁻¹), which were richer in saturated fatty acids (SAFA, up to 80%), but had a similar proportion of bacterial markers (13:0.15 iso/anteiso, 15:0, and 17:0 sum up to 67%). Isoprenoid GDGTs showed the presence of archaea in the different water layers. All the water layers also showed long chained fatty acids (22:0, 24:1 and 26:0), which can be considered to be of terrestrial origin. The n-alkanes were used to confirm this potential terrestrial origin through the Carbon Preference Index (CPI), which was always above the 4.3 due to the significant presence of c25, c27, and c31. Both lipid markers were positively related (R ²= 0.64, p < 0.05). In winter 2007, no clear phytoplankton dominance was detected through lipid markers, and there was a clear dominance of poor quality material along the water column coinciding with the development of La Niña 2007.

Keywords:

• upwelling
• Humboldt Current System
• oxycline
• fatty acids
• n-alkanes
• glycerol dialkyl glycerol tetraethers
• Carbon Preference Index
• bacterial biomarkers
• La Niña

Acknowledgements

We are grateful to Patricia Homs, Gabriel Claramunt and Ruben Escribano and their respective teams for field support in Chipana. We also thank the people of Chipana for their kind hospitality and efficient help. We also want to thank Antoni Rosell-Melé and Josep-María Gili for valuable suggestions and discussions in the first versions of the manuscript. Nuria Moraleda helped with the first set up of the fatty acid methodology. This study was funded by EU Project CENSOR (Climate Variability and El Niño Southern Oscillation: Implications for natural resources and Management, contract 511071). SR was co-financed by a Beatriu de Pinós Contract (2006 BP-B1 00069) and a Ramón y Cajal Contract (RyC-2007-01327). S.F. acknowledges the Juan de la Cierva fellowship at the Spanish Ministry of Education and Science (MICINN).