Mountain David G.
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ArticleRemote climate forcing of decadal-scale regime shifts in Northwest Atlantic shelf ecosystems(Association for the Sciences of Limnology and Oceanography, 2013-05) Greene, Charles H. ; Meyer-Gutbrod, Erin ; Monger, Bruce C. ; McGarry, Louise P. ; Pershing, Andrew J. ; Belkin, Igor M. ; Fratantoni, Paula S. ; Mountain, David G. ; Pickart, Robert S. ; Proshutinsky, Andrey ; Ji, Rubao ; Bisagni, James J. ; Hakkinen, Sirpa M. A. ; Haidvogel, Dale B. ; Wang, Jia ; Head, Erica ; Smith, Peter ; Reid, Philip C. ; Conversi, AlessandraDecadal-scale regime shifts in Northwest Atlantic shelf ecosystems can be remotely forced by climate-associated atmosphere–ocean interactions in the North Atlantic and Arctic Ocean Basins. This remote climate forcing is mediated primarily by basin- and hemispheric-scale changes in ocean circulation. We review and synthesize results from process-oriented field studies and retrospective analyses of time-series data to document the linkages between climate, ocean circulation, and ecosystem dynamics. Bottom-up forcing associated with climate plays a prominent role in the dynamics of these ecosystems, comparable in importance to that of top-down forcing associated with commercial fishing. A broad perspective, one encompassing the effects of basin- and hemispheric-scale climate processes on marine ecosystems, will be critical to the sustainable management of marine living resources in the Northwest Atlantic.
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.
ArticleSuppression of the 2010 Alexandrium fundyense bloom by changes in physical, biological, and chemical properties of the Gulf of Maine(Association for the Sciences of Limnology and Oceanography, 2011-11) McGillicuddy, Dennis J. ; Townsend, David W. ; He, Ruoying ; Keafer, Bruce A. ; Kleindinst, Judith L. ; Li, Y. ; Manning, James P. ; Mountain, David G. ; Thomas, Maura A. ; Anderson, Donald M.For the period 2005–2009, the abundance of resting cysts in bottom sediments from the preceding autumn was a first-order predictor of the overall severity of spring–summer blooms of Alexandrium fundyense in the western Gulf of Maine and southern New England. Cyst abundance off mid-coast Maine was significantly higher in autumn 2009 than it was preceding a major regional bloom in 2005. A seasonal ensemble forecast was computed using a range of forcing conditions for the period 2004–2009, suggesting that a large bloom was likely in the western Gulf of Maine in 2010. This did not materialize, perhaps because environmental conditions in spring–summer 2010 were not favorable for growth of A. fundyense. Water mass anomalies indicate a regional-scale change in circulation with direct influence on A. fundyense's niche. Specifically, near-surface waters were warmer, fresher, more stratified, and had lower nutrients than during the period of observations used to construct the ensemble forecast. Moreover, a weaker-than-normal coastal current lessened A. fundyense transport into the western Gulf of Maine and Massachusetts Bay. Satellite ocean color observations indicate the 2010 spring phytoplankton bloom was more intense than usual. Early season nutrient depletion may have caused a temporal mismatch with A. fundyense's endogenous clock that regulates the timing of cyst germination. These findings highlight the difficulties of ecological forecasting in a changing oceanographic environment, and underscore the need for a sustained observational network to drive such forecasts.
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.