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Ohman, MD, Barbeau K, Franks PJS, Goericke R, Landry MR, Miller AJ.  2013.  Ecological transitions in a coastal upwelling ecosystem. Oceanography. 26:210-219. AbstractWebsite

The southern California Current Ecosystem (CCE) is a dynamic eastern boundary current ecosystem that is forced by ocean-atmosphere variability on interannual, multidecadal, and long-term secular time scales. Recent evidence suggests that apparent abrupt transitions in ecosystem conditions reflect linear tracking of the physical environment rather than oscillations between alternative preferred states. A space-for-time exchange is one approach that permits use of natural spatial variability in the CCE to develop a mechanistic understanding needed to project future temporal changes. The role of (sub)mesoscale frontal systems in altering rates of nutrient transport, primary and secondary production, export fluxes, and the rates of encounters between predators and prey is an issue central to this pelagic ecosystem and its future trajectory because the occurrence of such frontal features is increasing.

Brzezinski, MA, Krause JW, Bundy RM, Barbeau KA, Franks P, Goericke R, Landry MR, Stukel MR.  2015.  Enhanced silica ballasting from iron stress sustains carbon export in a frontal zone within the California Current. Journal of Geophysical Research-Oceans. 120:4654-4669.   10.1002/2015jc010829   AbstractWebsite

Nutrient dynamics, phytoplankton rate processes, and export were examined in a frontal region between an anticyclone and a pair of cyclones 120 km off the coast in the southern California Current System (sCCS). Low silicic acid: nitrate ratios (Si:N) and high nitrate to iron ratios (N: Fe) characteristic of Fe-limiting conditions in the sCCS were associated with the northern cyclone and with the transition zone between the cyclones and the anticyclone. Phytoplankton growth in low-Si:N, high-N:Fe waters responded strongly to added Fe, confirming growth limitation by Fe of the diatom-dominated phytoplankton community. Low Si: N waters had low biogenic silica content, intermediate productivity, but high export compared to intermediate Si: N waters indicating increased export efficiency under Fe stress. Biogenic silica and particulate organic carbon (POC) export were both high beneath low Si: N waters with biogenic silica export being especially enhanced. This suggests that relatively high POC export from low Si: N waters was supported by silica ballasting from Fe-limited diatoms. Higher POC export efficiency in low Si: N waters may have been further enhanced by lower rates of organic carbon remineralization due to reduced grazing of more heavily armored diatoms growing under Fe stress. The results imply that Fe stress can enhance carbon export, despite lowering productivity, by driving higher export efficiency.

King, AL, Barbeau K.  2007.  Evidence for phytoplankton iron limitation in the southern California Current System. Marine Ecology-Progress Series. 342:91-103.   10.3354/meps342091   AbstractWebsite

Observations of phytoplankton iron limitation in the world's oceans have primarily been confined to high-nutrient, low-chlorophyll (HNLC) regimes, found in the western equatorial and subarctic Pacific, Southern Ocean, and coastal upwelling zones off California and Peru. We investigated the potential for phytoplankton iron limitation in coastal transition zones (50 to 200 km offshore) of the southern California Current System, a weak upwelling regime that is relatively low in nutrients (< 4 mu mol nitrate 1(-1)) and low in chlorophyll (< 1 mu g chl a 1(-1)). In grow-out incubation experiments conducted during summer, July 2003 and 2004, phytoplankton responded to nanomolar iron additions, despite the non-HNLC initial conditions, Observed changes in phytoplankton and nutrient parameters upon iron addition were significant, although markedly lower in amplitude relative to typical grow-out experiments in HNLC regimes. While we cannot disprove alternate explanations for the observed limitation of phytoplankton growth, such as a proximate grazing control, our results indicate that phytoplankton growth in the southern California Current System is, at times, limited by the supply of iron. Based on our findings and the results of previous studies in this region, we suggest that phytoplankton biomass is generally limited by the supply of nitrate, while iron, directly or indirectly, influences macronutrient utilization, community species composition, and phytoplankton spatial and temporal distribution.