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Lange, CB, Reid FMH, Vernet M.  1994.  Temporal distribution of the potentially toxic diatom Pseudonitzschia australis at a coastal site in southern Califormia. Marine Ecology-Progress Series. 104:309-312.   10.3354/meps104309   AbstractWebsite

Species of the genus Pseudonitzschia have been implicated in outbreaks of domoic acid (DA) toxicity off the coasts of North America, This led us to look at the historical (1930-1939, 1967, 1983, 1991-1993) occurrence and abundance of these species off the Scripps Institution of Oceanography pier, Southern California, USA, with special emphasis on P. australis Frenguelli for which we have the most complete data. The organism occurs sporadically in high numbers (10(4) to 10(6) cells l(-1)) between February and August but no major toxic episodes have been reported. The periods of high abundance were associated with intrusion of cool, high-nutrient waters probably related to upwelling events. To date, there have been no major DA outbreaks in the Southern California Bight.

Shaw, TJ, Smith KL, Hexel CR, Dudgeon R, Sherman AD, Vernet M, Kaufmann RS.  2011.  Th-234-Based Carbon Export around Free-Drifting Icebergs in the Southern Ocean. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 58:1384-1391.   10.1016/j.dsr2.2010.11.019   AbstractWebsite

The impact of free-drifting icebergs on the efficiency of carbon export from the upper water column was measured using the disequilibrium of Th-234 and its parent U-238. The study addressed the null hypothesis that free-drifting icebergs do not alter Th-234 deficiency and carbon export compared to surrounding waters. Upper-water-column inventories of Th-234 were measured at six stations in the Weddell Sea concurrently with four deployments of Lagrangian Sediment Traps (LSTs) during a cruise in March/April 2009. Four stations were sampled ranging from 0.3 km to <20 km of the edge of a large free-drifting iceberg (C-18a) and two were sampled at distances > 60 km from C-18a. Temperature and salinity anomalies indicated enhanced upwelling and turbulent mixing extending downstream of the iceberg to a minimum of similar to 20 km from the iceberg edge. Separate studies of the impact of C-18a on water column physical properties were used to define the extent of the iceberg's influence on surrounding waters. The largest upper-water-column deficiencies in the inventories of Th-234 were measured in close proximity and downstream of the iceberg and extending to below 100 m depth. A steady-state model was used to estimate the export of Th-234 from the upper water column. Organic carbon export was calculated using C/Th from the concurrent LST collections. Comparison of stations within the iceberg's influence (close proximity and downstream to within 20 km of the iceberg) and far-field (greater than 60 km) measurements showed a factor of 3 increase in organic carbon export near the iceberg. The factor correlated well with the results from the near- and far-field LST measurements. Differences in the magnitude of carbon export at 100 and 600 m indicate that similar to 90 percent of the exported material is regenerated by 600 m depth. This study confirms that the increased abundance of large free-drifting icebergs in the Southern Ocean can contribute to the drawdown of atmospheric CO2 through increased organic carbon export. (C) 2011 Elsevier Ltd. All rights reserved.

Fritsen, CH, Memmott JC, Ross RM, Quetin LB, Vernet M, Wirthlin ED.  2011.  The timing of sea ice formation and exposure to photosynthetically active radiation along the Western Antarctic Peninsula. Polar Biology. 34:683-692.   10.1007/s00300-010-0924-7   AbstractWebsite

Understanding the flow of solar energy into ecosystems is fundamental to understanding ecosystem productivity and dynamics. To gain a better understanding of this fundamental process in the Antarctic winter sea ice, we produced a model that estimates the time-integrated exposure of seasonal Antarctic sea ice to PAR through the use of remotely sensed sea ice concentrations, sea ice movement and spatially distributed PAR calculations that account for cloud cover and have applied this model over the past three decades. The resulting spatially distributed estimates of sea ice exposure to PAR by mid-winter are evaluated in context of changes in the timing of sea ice formation that have been documented along the Western Antarctic Peninsula (WAP) region and its potential effects on the variation (seasonal and inter-annual) in the accumulation of sea ice algae in this region. The analysis shows the ice pack is likely to have large inter-annual variations (10-100 fold) in productivity throughout the autumn to winter transition in the sea ice along the WAP. Moreover, the pack ice is likely to have spatial structure in regards to biological processes that cannot be determined from analysis of sea ice concentration information alone. The resulting inter-annual variations in winter processes are likely to affect the dynamics of Antarctic krill (Euphausia superba).

Smith, SR, Gl√© C, Abbriano RM, Traller JC, Davis A, Trentacoste E, Vernet M, Allen AE, Hildebrand M.  2016.  Transcript level coordination of carbon pathways during silicon starvation-induced lipid accumulation in the diatom Thalassiosira pseudonana. New Phytologist.   10.1111/nph.13843   Abstract

* Diatoms are one of the most productive and successful photosynthetic taxa on Earth and possess attributes such as rapid growth rates and production of lipids, making them candidate sources of renewable fuels. Despite their significance, few details of the mechanisms used to regulate growth and carbon metabolism are currently known, hindering metabolic engineering approaches to enhance productivity. * To characterize the transcript level component of metabolic regulation, genome-wide changes in transcript abundance were documented in the model diatom Thalassiosira pseudonana on a time-course of silicon starvation. Growth, cell cycle progression, chloroplast replication, fatty acid composition, pigmentation, and photosynthetic parameters were characterized alongside lipid accumulation. * Extensive coordination of large suites of genes was observed, highlighting the existence of clusters of coregulated genes as a key feature of global gene regulation in T. pseudonana. The identity of key enzymes for carbon metabolic pathway inputs (photosynthesis) and outputs (growth and storage) reveals these clusters are organized to synchronize these processes. * Coordinated transcript level responses to silicon starvation are probably driven by signals linked to cell cycle progression and shifts in photophysiology. A mechanistic understanding of how this is accomplished will aid efforts to engineer metabolism for development of algal-derived biofuels.