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Smith, KL, Sherman AD, Shaw TJ, Murray AE, Vernet M, Cefarelli AO.  2011.  Carbon export associated with free-drifting icebergs in the Southern Ocean. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 58:1485-1496.   10.1016/j.dsr2.2010.11.027   AbstractWebsite

Enrichment of the pelagic ecosystem associated with the proliferation of free-drifting icebergs prompts questions about increased productivity and the export flux of organic carbon to the deep ocean with continued climate warming. Lagrangian Sediment Traps (LST) were deployed autonomously beneath a large tabular, free-drifting iceberg (C-18a) in the NW Weddell Sea during March and April 2009 to collect sinking particles at a depth of 600 m. Three LST deployments associated with C-18a, within a 30-km radius, collected sinking diatom frustules, dominated by Corethron pennatum and Fragilariopsis nana, euphausiid fragments, crustacean and fish fecal material, detrital aggregates and mineral grains. One LST deployment at a "control" site 74 km away in open water devoid of icebergs collected diatom frustules, euphausiid molts, crustacean fecal material and detrital aggregates. Phytoplankton abundance, microbial abundance and biomass were significantly higher in the LST samples than in open-water collections at 500 m depth. The mean mass flux and organic carbon flux associated with iceberg C-18a were twice as high, 124 mg m(-2) d(-1) and 5.6 mg C(org) m(2) d(-1), respectively, than at the control site. A similar trend was observed in C(org)/(234)Th activity, being highest near C-18a and lowest at the control site. Extrapolation of the area of enrichment to 30 km radius around C-18a, 2826 km(2), produces an estimated mass flux of 350 tons d(-1) and carbon flux of 15.8 tons C(org) d(-1). Five similar sized icebergs to C-18a were identified in satellite images in a surrounding 47,636 km(2) area at the same time of sampling. Assuming a 30-km radius as the area of influence around each of these five icebergs, 46% of the total area would be enhanced with an export flux at 600 m of 122.4 tons C(org) d(-1). The large numbers of smaller icebergs identified visually in this area would only increase this area of influence. Icebergs serve as areas of local enrichment and with increased proliferation, must be considered in the cycling of carbon in the Southern Ocean. (C) 2010 Elsevier Ltd. All rights reserved.

Bjerkeng, B, Vernet M, Nielsen MV, Liaaenjensen S.  1990.  Carotenoids of Chrysochromulina polylepis (Prymnesiophyceae). Biochemical Systematics and Ecology. 18:303-306.   10.1016/0305-1978(90)90001-v   AbstractWebsite

The carotenoid composition is reported of the ichthyotoxic phytoplankton Chrysochromulina polylepis (Prymnesiophyceae), grown in pure cultures. Carotenoid yields correspond to ca 1 mg/20 I culture. The carotenoid composition consisted of (3S, 5R,6S,3′S,5′R,6′S)-19′-hexanoyloxyfucoxanthin (81% of total carotenoid), fucoxanthin (10%), diadinoxanthin (9%), 19 hexanoyloxyparacentrone 3-acetate (1%), tentatively diatoxanthin (trace) and β,β-carotene (trace). The identifications included 500 MHz 1H NMR and mass spectral evidence. The high proportion of 19′-hexanoyloxyfucoxanthin, readily detected by HPLC, serves to characterize this microalga.

Helly, JJ, Vernet M, Murray AE, Stephenson GR.  2015.  Characteristics of the meltwater field from a large Antarctic iceberg using delta O-18. Journal of Geophysical Research-Oceans. 120:2259-2269.   10.1002/2015jc010772   AbstractWebsite

Large tabular icebergs represent a disruptive influence on a stable water column when drifting in the open ocean. This is a study of one iceberg, C18A, encountered in the Powell Basin in the Weddell Sea in March 2009, formed from iceberg C18 ( 76x7km) originating from the Ross Ice Shelf in May 2002. C18A was lunate in shape with longest dimensions of 31kmx7kmx184m. The meltwater field from C18A was characterized using 18O from water samples collected near C18A (Near-field, 0.4-2 km) and contrasted with a Far-field comprised of samples from an Away site (19 km from C18A), a Control site (70 km away), and a region populated with small icebergs (Iceberg Alley, 175 km away). The in-sample fractions of meteoric water were calculated relative 18O in iceberg ice and Weddell Deep Water and converted to meteoric water height (m) and a percentage within 100 m depth bins. The Near-field and Far-field difference from surface to 200 m was 0.510.28%. The concentration of meteoric water dropped to approximately half that value below 200 m, approximate keel depth of the iceberg, although detectable to 600 m. From surface to 600 m, the overall difference was statistically significant ( P<0.0001). From this, we estimate the Near-field volume astern of the iceberg ( 0.16km3d-1) as a continuous source of meteoric water.

Cape, MR, Vernet M, Pettit EC, Wellner J, Truffer M, Akie G, Domack E, Leventer A, Smith CR, Huber BA.  2019.  Circumpolar deep water impacts glacial meltwater export and coastal biogeochemical cycling along the West Antarctic Peninsula. Frontiers in Marine Science. 6   10.3389/fmars.2019.00144   AbstractWebsite

Warming along the Antarctic Peninsula has led to an increase in the export of glacial meltwater to the coastal ocean. While observations to date suggest that this freshwater export acts as an important forcing on the marine ecosystem, the processes linking ice-ocean interactions to lower trophic-level growth, particularly in coastal bays and fjords, are poorly understood. Here, we identify salient hydrographic features in Barilari Bay, a west Antarctic Peninsula fjord influenced by warm modified Upper Circumpolar Deep Water. In this fjord, interactions between the glaciers and ocean act as a control on coastal circulation, contributing to the redistribution of water masses in an upwelling plume and a vertical flux of nutrients toward the euphotic zone. This nutrient-rich plume, containing glacial meltwater but primarily composed of ambient ocean waters including modified Upper Circumpolar Deep Water, spreads through the fjord as a 150-m thick layer in the upper water column. The combination of meltwater-driven stratification, long residence time of the surface plume owing to weak circulation, and nutrient enrichment promotes phytoplankton growth within the fjord, as evidenced by shallow phytoplankton blooms and concomitant nutrient drawdown at the fjord mouth in late February. Gradients in meltwater distributions are further paralleled by gradients in phytoplankton and benthic community composition. While glacial meltwater export and upwelling of ambient waters in this way contribute to elevated primary and secondary productivity, subsurface nutrient enhancement of glacially modified ocean waters suggests that a portion of these macronutrients, as well any iron upwelled or input in meltwater, are exported to the continental shelf. Sustained atmospheric warming in the coming decades, contributing to greater runoff, would invigorate the marine circulation with consequences for glacier dynamics and biogeochemical cycling within the fjord. We conclude that ice-ocean interactions along the Antarctic Peninsula margins act as an important control on coastal marine ecosystems, with repercussions for carbon cycling along the west Antarctic Peninsula shelf as a whole.

Neori, A, Vernet M, Holmhansen O, Haxo FT.  1988.  Comparison of chlorophyll far-red and red fluorescence excitation spectra with photosynthetic oxygen action spectra for photosystem II in algae. Marine Ecology-Progress Series. 44:297-302.   10.3354/meps044297   AbstractWebsite

The shapes of excitation spectra for chlorophyll a fluorescence in the far-red (730 nm) were compared under physiological conditions to those for chlorophyll a fluorescence in the red (685 nm) and to action spectra for photosynthetic oxygen production in deversely pigmented algae. Species examed as representatives of the prominent oceanic light harvesting systems were Chaeotoceros gracilis, Glenodinium sp., Ulva sp., Porphyridium cruentum and Chroomonas sp. Qualitatively, for any one alga, all 3 action spectra exhibited broadly similar spectral features, suggesting initial light harvesting for photosynthesis by the same major pigments, i.e. those commonly assoicated with photosystem II. As such, measurement of F730 fluorescence (in preference to F685) may provide a useful and facile alternative to oxygen action spectra in assessing the full phoosynthetic spectral performance (320 to 700 nm) of individual phytoplankton species or assemblages.

Garibotti, IA, Vernet M, Kozlowski WA, Ferrario ME.  2003.  Composition and biomass of phytoplankton assemblages in coastal Antarctic waters: a comparison of chemotaxonomic and microscopic analyses. Marine Ecology-Progress Series. 247:27-42.   10.3354/meps247027   AbstractWebsite

We describe the distribution of phytoplanktonic community composition and biomass from the Western Antarctic Peninsula coast (between 64degrees and 68degrees S) using 2 analytical techniques: microscopy and HPLC of photosynthetic pigments. Phytoplankton biomass was estimated as chlorophyll a (chl a) by HPLC and chemotaxonomic quantification of microalgae biomass was performed by multiple regression analysis of pigment concentrations. For the estimation of chl a: diagnostic pigment ratios, it was found of primary importance to differentiate between phytoplankton assemblages within the study area. Three assemblages were differentiated according to their total standing stock and analyzed independently. Phytoplankton biomass was also estimated as carbon (C) concentration by microscopic analysis of cell abundance and biovolumes. Microscopy and chemotaxonomy give a high level of agreement for phytoplankton characterization, showing an on/offshore gradient, with high diatom and cryptophyte biomass in coastal waters, and a mixed assemblage with low biomass in open waters. This gradient was not observed in total cell abundance, indicating that the biomass gradient is controlled by cell size. Microscopy also showed shifts in diatom species throughout the area, C and chl a biomass estimates for the individual microalgae groups were strongly correlated for cryptophytes, chlorophytes and most diatoms, but did poorly for dinoflagellates, prymnesiophytes and chrysophytes. From this study, we conclude that both microscopy and chemotaxonomy can be used to accurately characterize phytoplankton assemblages, but some limitations are present in both techniques. Based on phytoplankton C concentrations, we estimated an average in situ growth rate of 0.28 d(-1). In situ cell C:chl a ratios had high variability (from 40 to 220) and were non-linearly related to sample growth rates. Significant differences were found among average C:chl a ratios of low (<1 mug chl a l(-1)) and high biomass communities (>1 mug chl a l(-1)), with values of 112 and 74 mug C mug(-1) chl a, respectively. In addition, our results support the hypothesis that C quotas of diatoms and other microalgae do not differ greatly from each other, as previously believed.

Helly, JJ, Kaufmann RS, Stephenson GR, Vernet M.  2011.  Cooling, dilution and mixing of ocean water by free-drifting icebergs in the Weddell Sea. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 58:1346-1363.   10.1016/j.dsr2.2010.11.010   AbstractWebsite

Iceberg C-18a (35 x 7 x 0.184 km) was studied repeatedly by five circumnavigational surveys in March-April 2009. During the period of the surveys, C-18a travelled 109 nautical miles in 23 days covering an area of 8.1 x 10(3) km(2). This iceberg was formed from iceberg C-18 (76 x 7 km) that originated from the Ross Ice Shelf in May, 2002. Ship-based measurements show that this iceberg produced fresh meltwater above the seasonal pycnocline that diluted and chilled the water it passed through from the surface to a depth of approximately 50 m (summer mixed layer). The surface meltwater effects were detectable as far away as 19 km and persisted for at least 10 days. We also found evidence that this iceberg was disrupting the Weddell Deep Water to depths up to 1500 m. If we include these deep effects through the water column, the estimate of ocean water altered by this single iceberg reaches 3 x 10(12) m(3) over 23 days. Chemical and biological effects were detected at the same space and time scales as the physical properties, with decreasing partial pressure of carbon dioxide (pCO(2)) close to the iceberg and lower particle and chlorophyll concentration. Ten days after the passage of C-18a, chlorophyll-a had increased by 15%. These results are consistent with alternative hypotheses regarding the role of icebergs as mediators of a localized geophysical disturbance (H(1)) as well as promoters of chlorophyll-a production (H(2)). (C) 2010 Elsevier Ltd. All rights reserved.