Wind forcing and short-term variability of phytoplankton and heterotrophic bacterioplankton in the coastal zone of the Concepciَn upwelling system (Central Chile)

Along South-Central Chile, upwelling-favorable winds do not blow steadily equatorward, and may remain calm or even reverse for periods of 2–8 days shifting the balance between water column stability and replenishment of inorganic nutrients to the photic zone. In this study, we focus on the short-term variability of phytoplankton and heterotrophic bacterioplankton associated with the temporal variability in upwelling at a single nearshore station at the entrance of Coliumo Bay, Central Chile. In situ sampling took place every other day between 24 January and 14 February 2007. Observed variability of wind, sea surface temperature, and surface chlorophyll concentrations during the preceding weeks and throughout our experiments indicated that nearshore productivity was tightly coupled to local upwelling conditions. Gross primary production remained relatively low (22.5 ± 6.1 μg C L−1 h−1) during the first 8 days (24 January–1 February), and increased six fold (142.4 ± 67.1 μg C L−1 h−1) during the second period (3–14 February). Average in situ chlorophyll concentrations increased from 2.0 ± 0.6 mg m−3 to 6.3 ± 3.8 mg m−3 over the same period. ial Carbon Demand presented higher values (5–29.2 μg C L−1 h−1) during the first 6 days of sampling and lower values (<0.1 μg C L−1 h−1) for the rest of study period. Our results show that both biological productivity and the structure of the planktonic community can vary considerably due to short-term changes in wind conditions. Hence, previous productivity estimates for the Concepción upwelling ecosystem – based on observations gathered at lower frequencies – may not truly reflect its productivity potential.