the humboldt current system of northern and central chile - figema

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MARTIN THIEL ET AL.degradation rates of dissolved organic carbon in Concepción Bay (1–21 µM h −1 ; G. Daneri unpublisheddata) and the high BSP rates (range of 1100–2300 mg C m −2 d −1 or 19–50% of PP). Microbialcommunity respiration rates (Eissler & Quiñones 1999) are also very high along the HCS, reachingaverage values of 1450 mg C m −2 d −1 (~28% of PP). Finally, both zooplankton grazing and exportproduction (González et al. 2000b, Grünewald et al. 2002) gave values between 100 and 500 mgC m −2 d −1 (or mean values between 2% and 10% of PP). These carbon flows are more representativeof the coastal upwelling systems of Antofagasta and Concepción because they are the most studiedareas (from an oceanographic point of view) along the Chilean coast. Estimations of PP for theHCS along the Chilean coast are similar to those of the Peru (4000 mg C m −2 d −1 ; Walsh 1981)and about 2-fold higher than those of the California (1000–2500 mg C m −2 d −1 ; Olivieri & Chavez2000) upwelling systems. In addition, typical upwelling values for the flow of OM through bacteriain the HCS (19–50% of PP) are well within the range (3–55% of PP) of those described for otherupwelling systems in the world oceans (Ducklow 2000).Processes affecting primary production and export processesIn coastal areas of central and southern Chile there is a distinctive seasonal pattern involving thedevelopment of maxima (spring) and minima (winter) in phytoplankton biomass and PP during anannual cycle (Ahumada 1989, González et al. 1989). In contrast, high and more constant phytoplanktonicbiomass and PP has been observed during an annual cycle along the northern coast offChile (Marín et al. 1993, Rodríguez et al. 1996, Marín & Olivares 1999). Among the factors thatmight control the PP, light limitation (P. Montero & G. Daneri unpublished data) and Fe availability(Hutchins et al. 2002, R. Torres unpublished data) have been suggested for the Concepción andCoquimbo upwelling systems, respectively. In addition, high microzooplankton grazing mightcontrol the PP during non-upwelling conditions (i.e., winter) in Concepción Bay upwelling (Böttjer& Morales 2005).The understanding of the factors that regulate the magnitude and the variability of phytoplanktonPP is quite complex in the HCS due to the geographically distinctive upwelling areas (wind stress,topography), seasonal changes (winter vs. spring) and coastal–oceanic gradients. Integrated valuesin Table 1 indicate that the variation in chlorophyll concentration is coherent with changes in PP;that is, estimates are lowest in the Coquimbo upwelling system and highest in Antofagasta andConcepción coastal upwelling areas. Higher chlorophyll-specific productivity at Coquimbo andAntofagasta during EN 1997–1998 (2.5–2.8 vs. 1.0–2.0) indicates that the increase in specificproductivity did not result solely from a biomass decrease, but from a change in the phytoplanktonsize distribution (therefore in species composition), from the larger size class (microphytoplankton)to smaller size classes (pico- and nanoplankton). The intrusion of oligotrophic oceanic waters intothe coastal area off Coquimbo (Shaffer et al. 1995) and Antofagasta (Iriarte & González 2004)during an EN could be a possible explanation for the low productivity and the dominance of smallerphytoplankton size fractions and their large contribution to total PP. This feature suggests thatbiological and physiological shifts occur at the phytoplankton species level in order to counteractthe change in prevailing physical and chemical conditions in those areas (Montecino & Quiroz2000, Pizarro et al. 2002). On the other hand, in the permanent/seasonal coastal upwelling of coldnutrient-rich waters in enclosed areas like Concepción Bay and Mejillones Bay, PP estimatesincrease up to 12 g C m −2 d −1 . In the above-mentioned areas, the microphytoplankton fractionaccounted for >50% for the total autotrophic biomass and PP. In general, the range of specific rateof productivity in the three upwelling areas could indicate that physiological factors such as nutrientsupply and/or light availability may regulate the seasonal signal of productivity in those areas,whereas top-down processes such as grazing and production export might be important in removinga fraction of the generated photosynthetic carbon (Figure 4, Table 1). Furthermore, high biological212
THE HUMBOLDT CURRENT SYSTEM OF NORTHERN AND CENTRAL CHILETable 1 Range of primary productivity, chlorophyll, chlorophyll specific primary productivity rate and main phytoplankton taxa between the22° to 37°S Humboldt Current System. Primary productivity and chlorophyll estimates are integrated to the 1% light penetration depthStudy areaPP(mg C m –2 d –1 )Chl. a(mg m –2 )P B(mmol C mgChl. a –1 d –1 )Dominant sizeclass (as % ofthe total Chl. a) Main phytoplankton taxa ReferenceAntofagasta(22–2°S)El Niño 1997-1998Antofagasta(22–23°S)Non El Niño2000–2002Coquimbo-Valparaíso(30-33°S)1992–1994, 1995Humboldt CurrentSystem(19–22°S)Las Cruces (33°S)1999–2000Concepción Bay andGulf of Arauco(36–37°S)338–6063 11.7–175.4 2.8 48–68%nanoplankton1100–8100 47–695 1.0 60–86% microphytoplanktonTotal: 140–2955Summer: 605–2224Winter: 602–1012Total: 200–21,000Winter: 481–1600Spring:1770–16,6708.0–92.5 2.5 Winter: 59%nanoplankton53–141 Winter: >50%1–13.5(mg m –3 )Spring:208–544Spring: 2.0Spring: 65%microphytoplanktonWinter: 48%nanoplanktonSpring: 84%microphytoplanktonGymnodinium sp., Pseudo-nitzschia cf. delicatissimaAutotrophic flagellatesChaetoceros spp., Thalassiosira spp., Rhisozoleniaspp., Detonula pumila, Guinardia delicatula,Eucampia cornutaDetonula pumila, Leptocylindrus danicus,Pseudo-nitzschia pseudoseriata,Prorocentrum micansCoast: Pseudo-nitzschia pseudoseriata, Chaetoceroscompressus, Leptocylindrus danicus, Rhizosoleniaimbricata, Ceratium tripos, Diplopsalis lenticulaOceanic: Chaetoceros coarctatus, Ch. dadayi,Ceratium contortum, C. gibberum, C. macroceros,Dinophysis rapa, Ornithocercus magnificusThalassiosira spp., Detonula pumila,Chaetoceros socialis, Chaetoceros curvisetus,Skeletonema costatum, Leptocylindrus danicus,Guinardia delicatulaPizarro et al. 2002Iriarte et al. 2000Ulloa et al. 2001Troncoso et al. 2003Iriarte & González 2004Montecino et al. 1996Montecino & Pizarro 1995Avaria & Muñoz 1982Montecino & Quiroz 2000Troncoso et al. 2003Morales et al. 1996Avaria et al. 1982Narvaez et al. 2004González et al. 1989Iriarte & Bernal 1990Ahumada 1989Daneri et al. 2000Troncoso et al. 2003Montecino et al. 2004Cuevas et al. 2004213
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