Failure to bloom: Intense upwelling results in negligible phytoplankton response and prolonged CO₂ outgassing over the Oregon shelf

Abstract

During summer, upwelled water with elevated CO 2 partial pressure (pCO 2 ) and nutrients outcrops over the Oregon (OR) inner shelf. As this water transits across the shelf, high rates of primary production fueled by the upwelled nutrients results in net atmospheric CO 2 drawdown. Upwelled source-waters typically have pCO 2 approaching 1000 matm that is then reduced to 200 matm. For almost the entire month of July 2008, strong and persistent upwelling brought cold (8 C), saline (33.5), high-pCO 2 (>600 matm) water to our midshelf buoy site, and high-pCO 2 water was broadly distributed over the shelf. Chlorophyll levels, as a proxy for phytoplankton biomass, were low (< 2 mg m 23 ) on the shelf during the period of most intense upwelling, and satellite data showed no evidence of a downstream phytoplankton bloom. A small chlorophyll increase to 4 mg m 23 was observed at our buoy site following a decrease in the strength of southward wind stress 10 days after upwelling initiated. Chlorophyll levels further increased to 10 mg m 23 only after a cease in upwelling. These higher levels were coincident with the appearance of water masses having temperature and salinity properties distinct from recently upwelled water. We suggest that rapid offshore transport and subsequent subduction before phytoplankton populations could respond is the most likely explanation for the persistent low chlorophyll and elevated surface-water pCO 2 throughout the July upwelling event. This mechanism likely dominates under conditions of strong and persistent upwelling-favorable winds that coincide with close proximity of low-density offshore waters, which may have implications for the biogeochemical functioning of this system under future climate scenarios.

Acidification mediated by a river plume and coastal upwelling on a fringing reef at the east coast of Hainan Island, Northern South China Sea

“…On the contrary, organic production turned to degradation (CO 2 releasing) which intensified the acidification during July 2015 cruise (Figure ). Short residence time of upwelled water which subducts by rapid offshore transport before response of phytoplankton population [ Evans et al ., ] is not an explanation for this shift due to DIC removal had been observed in the source upwelling water. Besides, observed relatively lower sea surface Chl a over reefs during July 2015 cruise (Table ) demonstrated that consumption of excessive production of algae induced by high load of nutrients in subsurface water [ Cai et al ., ] also cannot explain the inverse contribution of organic carbon metabolism between cruises.…”

The Influence of a Submarine Canyon on the Circulation and Cross-Shore Exchanges around an Upwelling Front

“…3), which may have a significant impact on the productivity and the budget of tracers in the upper layer of the continental shelf. Upwelling waters are also characterized by low pH and elevated CO 2 partial pressure (e.g., Torres et al 2011;Evans et al 2015). Thus, under enhanced upwelling conditions (i.e., as result of the combined effect of frontal instabilities over a canyon) increased CO 2 outgassing occurs in regions characterized by reduced biological efficiency (uptake of CO 2 is low compared to the content being upwelled) such as in the central California and the southern Canary current systems (Lachkar and Gruber 2013).…”

Vertical segregation among pathways mediating nitrogen loss (N&lt;sub&gt;2&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O production) across the oxygen gradient in a coastal upwelling ecosystem

“…The coupling between primary production at the surface and anaerobic N-based metabolisms in the subsurface seems to depend on alternations between upwellingfavourable wind pulses and relaxed or inverted wind events, which allows for phytoplankton blooms (Daneri et al, 2012;Evans et al, 2015), and in turn, the concomitant settling of these organic particles to the sediment. An optimal window (e.g.…”