Mountain David G.
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ArticleInfluence of ocean freshening on shelf phytoplankton dynamics(American Geophysical Union, 2007-12-28) Ji, Rubao ; Davis, Cabell S. ; Chen, Changsheng ; Townsend, David W. ; Mountain, David G. ; Beardsley, Robert C.Climate change-induced freshening of the ocean can enhance vertical stratification and alter circulation patterns in ways that influence phytoplankton dynamics. We examined the timing of spring phytoplankton blooms and the magnitude of net primary productivity in the Nova Scotian Shelf (NSS) - Gulf of Maine (GoM) region with respect to seasonal and interannual changes in surface water freshening from 1998 to 2006. The general pattern of temporal westward progression of the phytoplankton bloom corresponds with the gradient of increasing sea surface salinity from the NSS in the east to the western GoM. Increased freshening enhances the spatial gradients in bloom timing by stimulating earlier blooms upstream (NSS), but it has less impact downstream (the western GoM). Strong spatial gradients (increasing westward) of mean chlorophyll concentration and net primary productivity during post-bloom months (May–June) indicate that lower sea surface salinity upstream can likely impede nutrient fluxes from deep water and therefore affect overall productivity.
ArticleRecent Arctic climate change and its remote forcing of Northwest Atlantic shelf ecosystems(The Oceanography Society, 2012-09) Greene, Charles H. ; Monger, Bruce C. ; McGarry, Louise P. ; Connelly, Matthew D. ; Schnepf, Neesha R. ; Pershing, Andrew J. ; Belkin, Igor M. ; Fratantoni, Paula S. ; Mountain, David G. ; Pickart, Robert S. ; Ji, Rubao ; Bisagni, James J. ; Chen, Changsheng ; Hakkinen, Sirpa M. A. ; Haidvogel, Dale B. ; Wang, Jia ; Head, Erica ; Smith, Peter ; Conversi, AlessandraDuring recent decades, historically unprecedented changes have been observed in the Arctic as climate warming has increased precipitation, river discharge, and glacial as well as sea-ice melting. Additionally, shifts in the Arctic's atmospheric pressure field have altered surface winds, ocean circulation, and freshwater storage in the Beaufort Gyre. These processes have resulted in variable patterns of freshwater export from the Arctic Ocean, including the emergence of great salinity anomalies propagating throughout the North Atlantic. Here, we link these variable patterns of freshwater export from the Arctic Ocean to the regime shifts observed in Northwest Atlantic shelf ecosystems. Specifically, we hypothesize that the corresponding salinity anomalies, both negative and positive, alter the timing and extent of water-column stratification, thereby impacting the production and seasonal cycles of phytoplankton, zooplankton, and higher-trophic-level consumers. Should this hypothesis hold up to critical evaluation, it has the potential to fundamentally alter our current understanding of the processes forcing the dynamics of Northwest Atlantic shelf ecosystems.