Revista Chilena de Historia Natural 83 (3): 409-420, 2010
RESEARCH ARTICLE
Spatial and temporal variability of water masses, nutrients and sedimentation of organic and
inorganic matter, in Mejillones del sur bay (23º S), Chile
This study addresses the spatial and temporal variability of physical-chemical properties
and sedimentation rates of particulate matter of the water column at a fixed station set within Bahía de Mejillones del Sur, during the
austral summer of 2003-2004. The water column was generally characterized by warmer oxygen-rich surface waters, marked
stratification gradients between about 10 to 20 m depths and by colder, denser and sub-oxic upwelling waters from 30 m depths to the
bottom throughout studied period. The bay was governed by three different water masses: the Surface Sub-Tropical Waters (SSTW),
Sub-Antarctic Waters (SAAW) and the Equatorial Sub-Surface Waters (ESSW). The surface waters exhibited a clear alternation
between weak and short (three to eight days) upwelling events and longer (29 days) periods of stratification. During the weak upwelling
events and at the onset of the stratification periods, sub-oxic to micro-oxic conditions prevailed with elevated nutrient concentrations at
the 10 to 15 m depth layer. The variability of oxygen saturation levels and of the dissolved inorganic nutrients nitrogen (N), phosphorus
(P) and silicic acid (Si), as well as the behavior of the N:P and Si:NID ratios, indicated the important combined effects of internal
recycling of the organic matter in the surface water column and of the contribution of allochthonous nutrients from upwelled bottom
waters. The fortnightly variability of the total flux of particulate material collected in sediment traps in the bay suggest that material
deposition from the water column is governed by the alternation of upwelling and stratification events. In addition, the sediment traps
registered nitrogen impoverishment with increasing depths, suggesting that remineralisation processes affected the settling of particles
and the denitrification of the oxydo-reducting deeper waters of the bay.
Key words:
Chile, Mejillones bay,
nutrients, particle sedimentation, upwelling.
