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Biogeochemistry in oligotrophic ocean gyres
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The biological boundary between phosphorus and iron limitation in an oligotrophic ocean (Invited)
Tuesday 8th @ 1330-1350, Multifunction Hall
Ricardo M Letelier* , College of Earth, Ocean, and Atmospheric Sciences
Oregon State University
Presenter Email: letelier@coas.oregonstate.edu |
| Nutrient supply into the well lite upper layers of the water column through mixing, diffusion, advection and dust deposition, regulates the productivity of subtropical oceanic oligotrophic regions. Changes in the relative strength of these distinct input mechanisms can cause shifts in the elemental ratio of the nutrient supply, leading to shifts in the proximate elemental control of the pelagic ecosystem productivity. Multi-decadal observations in the North Pacific Subtropical Gyre reveal that the pelagic microbial assemblage oscillates between phosphorus (P) sufficiency and limitation on sub-decadal time-scales, indicating shifts in the proximate elemental control of primary productivity and nitrogen fixation. These fluctuations display a significant correlation with the Pacific Decadal Oscillation (PDO) suggesting that a common atmospheric forcing modulates both the PDO and P-sufficiency. Using in situ observations and model simulations we explore how different mechanisms contributing to the input of nutrients in the NPSG respond to Climate forcing. Our results indicate that inter-annual oscillations in P availability in the Eastern North Pacific Subtropical Gyre are strongly correlated to shifts in the Sea Level Pressure in the western subarctic (r > 0.8). Furthermore, regional dust transport models suggest that climate-induced variations in Asian iron-rich dust transport and deposition across the North Pacific contribute significantly to the observed oscillation in P-limitation; while periods experiencing enhanced dust deposition, corresponding to positive PDO phases, are characterized by a microbial ecosystem capable of removing P as to become limiting (below 50 nM), periods with diminished dust deposition are characterized by a P-sufficient environment, suggesting that other nutrient - probably iron - becomes the proximal elemental control of microbial productivity during negative PDO phases. These results highlight the critical need to include both atmospheric and ocean circulation variability when modeling the evolution of open ocean pelagic ecosystems under different climate change scenarios. |
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