Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
11024880 | Progress in Oceanography | 2018 | 60 Pages |
Abstract
Ongoing global warming caused by climate change has been suggested to produce an intensification of upwelling-favorable winds along the coast of south-central Chile due to a poleward displacement of the South Pacific Anticyclone (SPA). Here we explore the extent to which these changes have influenced water column properties, inorganic nutrients, primary production, diatom abundances and net community metabolism (GPP/CR) in these shelf waters. Our analysis is based on a monthly time series (2003-2013) of in situ oceanographic and biological observations and experiments to assess gross primary production (GPP) and community respiration (CR) at a shelf station in central Chile (â¼36.5°S), along with ancillary data on alongshore wind variability, river outflow and MODIS-derived surface fluorescence (nFLH). A reduction in river outflow from 2007 onwards, forced remotely by the poleward displacement of the SPA, resulted in a cooler and saltier water column, with lower dissolved Si:N ratios (Si(OH)4: NO3â) and net community metabolism shifting from high net autotrophy (mean GPP/CRâ¯=â¯10.9â¯Â±â¯14) to a balance between production and respiration (GPP/CRâ¯=â¯1.17â¯Â±â¯0.6). A key finding was that most of the observed inter-annual variability in diatom abundance and primary production rates from 2003 to 2013 could be explained by two opposite trends: a significant intensification of upwelling-favorable winds during early spring (October-November) post-2009, and a sustained drop in freshwater discharged by the main local river during the same period. A combination of more intense equatorward winds and weaker stratification of the water column may have driven mixing and turbulence beyond the levels that are suitable for diatom growth when the upwelling period began (October-November), and subsequently may have enhanced the offshore transport of nutrients and productivity during late summer months (February-March). Patterns revealed by the analysis of monthly composites of normalized surface fluorescence (nFLH) are consistent with this interpretation. Further intensification of upwelling-favorable winds, combined with changes in the pattern of precipitation and river discharges, may have negative effects on the composition, productivity, and carbon export in shelf waters of this and other coastal upwelling ecosystems.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Geology
Authors
Bárbara G. Jacob, Fabián J. Tapia, Renato A. Quiñones, Rodrigo Montes, Marcus Sobarzo, Wolfgang Schneider, Giovanni Daneri, Carmen E. Morales, Paulina Montero, Humberto E. González,