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Sensitivity of marine ecosystems to climate change: Insights from the novel appearance of inner-shelf hypoxia in the California Current System.
Chan, Francis*,1, 2, Grantham, Brian1, 2, Nielsen, Karina2, Menge, Bruce1, 2, Lubchenco, Jane1, 2, 1 Oregon State University, Corvallis, OR, USA2 PISCO, Partnership for Interdisciplinary Studies of Coastal Oceans, Corvallis, OR, USA
ABSTRACT- Detecting the imprint of climatic change on ecosystems and causally linking observed ecological shifts to climatic changes are two fundamental challenges in ecological research. In marine systems, our emerging understanding of the impacts of climate change have drawn most directly from studies on temperature-mediated shifts in species abundance and range distributions and alterations of species interactions in benthic communities. In comparisons, our understanding of the sensitivity and responses of coastal marine ecosystems to climate-mediated perturbations in oceanic circulation and biogeochemical cycles remains poorly developed. Here, we report the novel appearance of an hypoxic (oxygen-depleted) zone in the inner-shelf off Oregon′s Central Coast in the summer of 2002 and its apparent coupling to discontinuous shifts in regional oceanographic conditions. The bottom water hypoxic zone was extensive (covering ca. 650 km2) and persistent (lasting ca. 2 months), -resulting in widespread die-off and habitat displacement of marine invertebrates and fishes. The oceanography of the Oregon shelf is dominated by seasonal wind-driven upwelling of nutrient-rich and oxygen-poor water from depth. Upwelled nutrients further fuel intensive primary production in surface waters that are exported to and respired at depth. Our results from cross-shelf biogeochemical and physical transect cruises identify accelerated fluxes of nutrient-rich and oxygen poor water as the proximate causes of hypoxia development. Analyses of near- and long-term records of oceanographic conditions at the regional and basin (northeast Pacific Ocean) scales point to the propagation of large-scale circulation anomalies to local but dramatic physical and biogeochemical changes in the Central Oregon Coast in 2002. Changes in ocean conditions may thus be a strong and surprisingly dynamic pathway by which climatic change can impact coastal marine ecosystems. Our emerging understanding of the coupling between oceanographic processes and local-scale ecological dynamics further highlights the sensitivity, and potential non-linear responses of coastal marine ecosystems to climatic perturbations.
Key words: climate, upwelling, pisco, hypoxia