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Ferrario, ME, Sar EA, Vernet M.  1998.  Chaetoceros resting spores in the Gerlache Strait, Antarctic Peninsula. Polar Biology. 19:286-288.   10.1007/s003000050247   AbstractWebsite

The formation of resting spores in diatoms is a common phenomenon in neritic environments, Here we report on resting spores of the genus Chaetoceros associated with a layer of increased chlorophyll fluorescence, at a depth of more than 200 m, north of Brabant Island and in Wilhelmina Bay, southeast coast of the Gerlache Strait (64 degrees 41.0'S, 62 degrees 0.5'W). Six species of Chaetoceros were identified by the morphology and size of the resting spores. Given that Chaetoceros spp., both in vegetative cells and as resting sports, are commonly found in Antarctic coastal surface waters, their location at depth could represent the pelagic "waiting" or "seeding" populations mentioned for other environments.

Ferrario, ME, Almandoz GO, Cefarelli AO, Fabro E, Vernet M.  2013.  Stephanopyxis species (Bacillariophyceae) from shelf and slope waters of the Argentinean Sea: Ultrastructure and distribution. Nova Hedwigia. 96:249-263.   10.1127/0029-5035/2012/0077   AbstractWebsite

Stephanopyxis is a cosmopolitan planktonic marine diatom genus. It comprises a large number of fossil species but only four living species: S. nipponica, S. orbicularis, S. palmeriana and S. turns. In this study, the morphology and occurrence of Stephanopyxis species were studied by means of light and scanning electron microscopy from the inner shelf to slope waters of the Argentinean Sea. Two species, S. nipponica and S. turns, were found. In both species the ultrastructure of the valve showed two different morphological forms. One form had true poroid aereolae, with an external foramen and an internal cribral velum while the second one had a network of hexagonal compartments with an external opening but lacking an internal cribral velum. The structure of the linking rimoportulae and the presence of acceptant process in the vegetative cells of S. nipponica distinguished this species from the other living Stephanopyxis species. We consider that the orientation of the rimoportulae located on the mantle margin as well as the presence of scattered rimoportulae on the valve surface in the resting spores are not useful taxonomic characters to differentiate between the vegetative and resistance cells of S. nipponica. Stephanopyxis turns' main morphometric and ultrastructural features coincided with the diagnosis of this species. However, some lightly silicified specimens presented a different type of areolae in the valvar mantle, not previously described. We give also new information on cingulum structure for S. turns, which is high with a narrow valvocopula and numerous segmented girdle bands, similar to other species of the genus. Finally, we provide data on the S. nipponica and S. turris occurrence, cell abundance and environmental data in the Argentinean Sea, including remarks on their distribution in southern South America.

Ferrario, ME, Cefarelli AO, Robison B, Vernet M.  2012.  Thalassioneis signyensis (Bacillariophyceae) from northwest Weddell Sea icebergs, an emendation of the generic description. Journal of Phycology. 48:222-230.   10.1111/j.1529-8817.2011.01097.x   AbstractWebsite

We offer an emended description of the genus Thalassioneis based on new observations of the type species, T. signyensis Round, from material sampled in the northwest Weddell Sea. Specimens from algal communities attached to submerged flanks of several icebergs were collected with a remote-operated vehicle (ROV-Phantom DS 2). The analyses were carried out by LM and SEM. Fresh material and frustules without organic matter allowed us to observe details not included in the original description such as type and structure of colonies and chloroplasts. The frustule shows an asymmetry with respect to the location of the apical pore fields, one of them situated on the valvar face and the other one displaced toward the mantle; the former is involved in joining contiguous cells to form long chains. Furthermore, we present details on the ultrastructure of the cingulum that consists of three to four open copulae with one or more rows of poroids. A brief discussion on the habit and ecology of this taxon, which may be endemic to the northwest Weddell Sea, is also presented. A comparison with similar genera, such as Brandinia, Creania, Fossula, Fragilaria, Rimoneis, Synedropsis, and Ulnaria, is included with an evaluation of morphological characteristics useful to differentiate them.

Vernet, M, Hunter JR, Vetter RD.  1988.  Accumulation of age pigments (lipofuscin) in 2 cold-water fishes. Fishery Bulletin. 86:401-407. AbstractWebsite
Vernet, M, Mitchell BG, Holmhansen O.  1990.  Adaptation of Synechococcus in situ determined by variability in intracellular phycoerythrin-543 at a coastal station off the Southern California coast, USA. Marine Ecology-Progress Series. 63:9-16.   10.3354/meps063009   AbstractWebsite

Concentrations of extracted phycobiliproteins were measured at a station off the Southern California coast, USA, from November 1985 to March 1986. The main pigment found was phycoerythrin-543 (PE) from Synechococcus spp. as described by Alberte et al. (1984). Concentrations of PE in water column, between 3 and 40 m, varied between 0.01 and 1.60 microg/l. Maximum values were found between 3 and 22 m. In situ concentrations of PE were positively correlated with cell numbers of Synechococcus spp., which ranged from 1.4 to 116 X 10^6cells/l, and showed maximal values between 3 and 13 m. Because no other types of PE were detected, all PE measured was considered to come from Synechococcus-type cells. Cellular concentrations of PE varied between 2.1 and 40.3 X 10^-9 microg PE/cell, with an average value of 10 5±4.1 X 10^-9 microg PE/cell above the 1 % isolume for PAR (Photosynthetically Available Radiation). Pigment per cell increased consistently with depth dunng autumn and spring and had low and relatively constant values in the winter. High PE:cell (>20 X 10^-9 microg PE/cell) was observed only below the 1 % isolume for PAR. For all samples, cellular concentration of PE was inversely correlated with incident PAR and was positively correlated to dissolved inorganic nitrogen (nitrate) concentration. Cyanobactena were not a dominant component of phytoplankton standing stock during this study, contributing an estimated 4 to 15 % of total chlorophyll in the water column, but had high specific growth rates, with maximal values of >0.75 d^-1 close to the surface. Absorption of light at 540 nm, as measured by in vivo absorption spectra of phytoplankton, was not correlated with PE concentration in the water column.

Robison, BH, Vernet M, Smith KL.  2011.  Algal communities attached to free-drifting, Antarctic icebergs. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 58:1451-1456.   10.1016/j.dsr2.2010.11.024   AbstractWebsite

Disintegration of the Antarctic Peninsula's eastern ice shelves has increased the population of icebergs traversing the Weddell Sea, but until recently little was known about their ecological impact on the pelagic environment. Here we describe a class of algal communities that occur on the submerged flanks of large, free-drifting, glacially-derived tabular icebergs. We used remotely operated vehicles to examine these icebergs directly for the first time, to survey the algal communities and collect material for shipboard laboratory studies. The communities, principally diatoms, were associated with a characteristic cupped configuration of the ice surface, and they served as feeding sites for aggregations of Antarctic krill. Production rate measurements indicate that these communities are providing a substantial contribution to regional primary production in summer. As the number of icebergs grows, the number of algae communities may also be increasing, along with their cumulative contribution to organic carbon flux. (C) 2010 Elsevier Ltd. All rights reserved.

Moline, MA, Claustre H, Frazer TK, Schofield O, Vernet M.  2004.  Alteration of the food web along the Antarctic Peninsula in response to a regional warming trend. Global Change Biology. 10:1973-1980.   10.1111/j.1365-2486.2004.00825.x   AbstractWebsite

In the nearshore coastal waters along the Antarctic Peninsula, a recurrent shift in phytoplankton community structure, from diatoms to cryptophytes, has been documented. The shift was observed in consecutive years (1991-1996) during the austral summer and was correlated in time and space with glacial melt-water runoff and reduced surface water salinities. Elevated temperatures along the Peninsula will increase the extent of coastal melt-water zones and the seasonal prevalence of cryptophytes. This is significant because a change from diatoms to cryptophytes represents a marked shift in the size distribution of the phytoplankton community, which will, in turn, impact the zooplankton assemblage. Cryptophytes, because of their small size, are not grazed efficiently by Antarctic krill, a keystone species in the food web. An increase in the abundance and relative proportion of cryptophytes in coastal waters along the Peninsula will likely cause a shift in the spatial distribution of krill and may allow also for the rapid asexual proliferation of carbon poor gelatinous zooplankton, salps in particular. This scenario may account for the reported increase in the frequency of occurrence and abundance of large swarms of salps within the region. Salps are not a preferred food source for organisms that occupy higher trophic levels in the food web, specifically penguins and seals, and thus negative feedbacks to the ecology of these consumers can be anticipated as a consequence of shifts in phytoplankton community composition.

Garibotti, IA, Vernet M, Ferrario ME.  2005.  Annually recurrent phytoplanktonic assemblages during summer in the seasonal ice zone west of the Antarctic Peninsula (Southern Ocean). Deep-Sea Research Part I-Oceanographic Research Papers. 52:1823-1841.   10.1016/j.dsr.2005.05.003   AbstractWebsite

The distribution of phytoplankton composition, cell abundance and biomass from an area along the Western Antarctic Peninsula was studied during three summers, with the aim of understanding its dynamics over spatial and interannual scales. The studied area is characterized by seasonal sea-ice retreat and advance. Algae composition and concentration were found to be highly variable through the area as well as from year to year. Small unidentified phytoflagellates, diatoms and cryptophytes were the main phytoplankton groups, contributing the major proportion of total phytoplankton cell abundance and biomass concentration. Three annually recurrent phytoplankton assemblages were recognized in the area according to the algae composition and abundance: a diatom bloom associated with the seaice edge, an assemblage dominated by small unidentified phytoflagellates and cryptophytes, and a diatom-enriched assemblage in open waters. The distribution of these assemblages varied from year-to-year. During the summers preceded by early sea-ice retreat, the diatom bloom was spatially restricted and the other two assemblages occupied extended regions, whereas during the late sea-ice retreat year, the diatom bloom extended over a larger region and the other assemblages occupied smaller regions or were just absent. It was detected that these assemblages resemble different stages of the phytoplankton seasonal cycle, and that their distribution through the area can be related to a latitudinal and longitudinal gradient in the phytoplankton growth onset timing, associated with the progressive sea-ice retreat during spring. The local environmental conditions associated with each assemblage were also analyzed, but further study is needed for understanding the causes of the replacement of one assemblage by another through the area. On the other hand, the interannual variability in the distribution of the assemblages can be related to year-to-year differences in the timing of phytoplankton growth onset, associated with variations in the timing of the sea-ice retreat. (c) 2005 Elsevier Ltd. All rights reserved.

Paulsen, ML, Seuthe L, Reigstad M, Larsen A, Cape MR, Vernet M.  2018.  Asynchronous accumulation of organic carbon and nitrogen in the Atlantic gateway to the Arctic Ocean. Frontiers in Marine Science. 5   10.3389/fmars.2018.00416   AbstractWebsite

Nitrogen (N) is the main limiting nutrient for biological production in the Arctic Ocean. While dissolved inorganic N (DIN) is well studied, the substantial pool of N bound in organic matter (OM) and its bioavailability in the system is rarely considered. Covering a full annual cycle, we here follow N and carbon (C) content in particulate (P) and dissolved (D) OM within the Atlantic water inflow to the Arctic Ocean. While particulate organic carbon (POC), particulate organic nitrogen (PON), and dissolved organic carbon (DOC) accumulated in the surface waters from January to May, the dissolved organic nitrogen (DON)-pool decreased substantially (Delta - 50 mu g N L-1). The DON reduction was greater than the simultaneous reduction in DIN (Delta - 30 mu g N L-1), demonstrating that DON is a valuable N-source supporting the growing biomass. While the accumulating POM had a C/N ratio close to Redfield, the asynchronous accumulation of C and N in the dissolved pool resulted in a drastic increase in the C/N ratio of dissolved organic molecules (DOM) during the spring bloom. This is likely due to a combination of the reduction in DON, and a high release of carbon-rich sugars from phytoplankton, as 32% of the spring primary production (PP) was dissolved. Our findings thus caution calculations of particulate PP from DIN drawdown. During post-bloom the DON pool increased threefold due to an enhanced microbial processing of OM and reduced phytoplankton production. The light absorption spectra of DOM revealed high absorption within the UV range during spring bloom indicating DOM with low molecular weight in this period. The absorption of DOM was generally lower in the winter months than in spring and summer. Our results demonstrate that the change in ecosystem function (i.e., phytoplankton species and activity, bacterial activity and grazing) in different seasons is associated with strong changes in the C/N ratios and optical character of DOM and underpin the essential role of DON for the production cycle in the Arctic.

Diaz, S, Vernet M, Paladini A, Fuenzalida H, Deferrari G, Booth CR, Cabrera S, Casiccia C, Dieguez M, Lovengreen C, Pedroni J, Rosales A, Vrsalovic J.  2011.  Availability of vitamin D photoconversion weighted UV radiation in southern South America. Photochemical & Photobiological Sciences. 10:1854-1867.   10.1039/c1pp05162h   AbstractWebsite

Ultraviolet radiation (UVR) plays a key role in several biological functions, including human health. Skin exposure to UVR is the main factor in vitamin D photoconversion. There is also evidence relating low levels of vitamin D with certain internal cancers, mainly colon, breast and prostate, as well as other diseases. Several epidemiological studies have shown an inverse relationship between the above-mentioned diseases and latitude, in accordance with the ultraviolet radiation latitudinal gradient. The aim of this study is to determine whether UV irradiance levels in the southern South America are sufficient to produce suitable levels of vitamin D year around. For this purpose, vitamin D photoconversion weighted-irradiance was analyzed between S.S. de Jujuy (24.17 degrees S, 65.02 degrees W) and Ushuaia (54 degrees 50'S, 68 degrees 18'W). In addition to irradiance, skin type and area of body exposed to sunlight are critical factors in vitamin D epidemiology. Due to a broad ethnic variability, it was assumed that the skin type in this region varies between II and V (from the most to the less sensitive). All sites except South Patagonia indicate that skin II under any condition of body area exposure and skin V when exposing head, hands, arms and legs, would produce suitable levels of vitamin D year round (except for some days in winter at North Patagonian sites). At South Patagonian sites, minimum healthy levels of vitamin D year round can be reached only by the more sensitive skin II type, if exposing head, hands, arms and legs, which is not a realistic scenario during winter. At these southern latitudes, healthy vitamin D levels would not be obtained between mid May and beginning of August if exposing only the head. Skin V with head exposure is the most critical situation; with the exception of the tropics, sun exposure would not produce suitable levels of vitamin D around winter, during a time period that varies with latitude. Analyzing the best exposure time during the day in order to obtain a suitable level of vitamin D without risk of sunburn, it was concluded that noon is best during winter, as determined previously. For skin type II when exposing head, exposure period in winter varies between 30 and 130 min, according to latitude, except for South Patagonian sites. During summer, noon seems to be a good time of day for short periods of exposure, while during leisure times, longer periods of exposure without risk of sunburn are possible at mid-morning and mid-afternoon. At 3 h from noon, solar zenith angles are almost the same for sites between the tropics and North Patagonia, and at 4 h from noon, for all sites. Then, in these cases, the necessary exposure periods varied slightly between sites, only due to meteorological differences.

Cardenas, P, Lange CB, Vernet M, Esper O, Srain B, Vorrath ME, Ehrhardt S, Muller J, Kuhn G, Arz HW, Lembke-Jene L, Lamy F.  2019.  Biogeochemical proxies and diatoms in surface sediments across the Drake Passage reflect oceanic domains and frontal systems in the region. Progress in Oceanography. 174:72-88.   10.1016/j.pocean.2018.10.004   AbstractWebsite

The Antarctic Circumpolar Current is the world's largest current system connecting all major ocean basins of the global ocean. Its flow, driven by strong westerly winds, is constricted to its narrowest extent in the Drake Passage, located between South America and the Antarctic Peninsula. Due to the remoteness of the area, harsh weather conditions and strong bottom currents, sediment recovery is difficult and data coverage is still inadequate. Here, we report on the composition of 51 surface sediments collected during the R/V Polarstern PS97 expedition (February-April 2016) across the western and central Drake Passage, from the Chilean/Argentinian continental margin to the South Shetland Islands and the Bransfield Strait (water depth: similar to 100-4000 m). We studied microfossils (diatoms), bulk sediment composition and geochemical proxies (biogenic opal, organic carbon, calcium carbonate, carbon and nitrogen stable isotopes, sterols and photosynthetic pigments), and evaluated how they respond to, and reflect oceanic domains and polar to subpolar frontal systems in this region. Our multi-proxy approach shows a strong relationship between the composition of surface sediments and ocean productivity, terrigenous input, intensity of ocean currents, and ice proximity, clearly differentiating among 4 biogeographical zones. The Subantarctic Zone was characterized by wanner-water diatoms, high carbonate ( > 45%) and low organic carbon contents (avg. 0.26%), as well as low concentrations of pigments (avg. 1.75 mu g/g) and sterols (avg. 0.90 mu g/g). A general N-S transition from carbonate-rich to opal-rich sediment was observed at Drake Passage sites of the Polar Front and Permanently Open Ocean Zone. These sites were characterized by low organic carbon content (0.22%), high relative abundances of heavily silicified diatoms (>= 60% Fragilariopsis kergueiensis), and abundant foraminifera at shallower stations. Approaching the Antarctic Peninsula in the Transitional Zone, an increase in the concentrations of pigments and sterols (avg. 2.57 mu g/g and 1.44 mu g/g, respectively) and a strong decrease in carbonate content was observed. The seasonal Sea-Ice Zone in the southern section of the study area, had the highest contents of biogenic opal (avg. 14.6%) and organic carbon (avg. 0.7%), low carbonate contents (avg. 2.4%), with the occurrence of sea-ice-related diatoms and sterols. In all zones, terrigenous input was detected, although carbon/nitrogen ratios and delta C-13(org) suggest a predominance of marinederived organic matter; lower values of delta C-13(org) occurred south of the Polar Front. The new results presented here constitute a highly valuable reference dataset for the calibration of microfossil and geochemical proxies against observational data and provide a useful regional baseline for future paleo-research.

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.

Herrmann, M, Najjar RG, Neeley AR, Vila-Costa M, Dacey JWH, DiTullio GR, Kieber DJ, Kiene RP, Matrai PA, Simo R, Vernet M.  2012.  Diagnostic modeling of dimethylsulfide production in coastal water west of the Antarctic Peninsula. Continental Shelf Research. 32:96-109.   10.1016/j.csr.2011.10.017   AbstractWebsite

The rate of gross biological dimethylsulfide (DMS) production at two coastal sites west of the Antarctic Peninsula, off Anvers Island, near Palmer Station, was estimated using a diagnostic approach that combined field measurements from 1 January 2006 through 1 March 2006 and a one-dimensional physical model of ocean mixing. The average DMS production rate in the upper water column (0-60 m) was estimated to be 3.1 +/- 0.6 nM d(-1) at station B (closer to shore) and 2.7 +/- 0.6 nM d(-1) at station E (further from shore). The estimated DMS replacement time was on the order of 1 d at both stations. DMS production was greater in the mixed layer than it was below the mixed layer. The average DMS production normalized to chlorophyll was 0.5 +/- 0.1 (nM d(-1))/(mg m(-3)) at station B and 0.7 +/- 0.2 (nM d(-1))/(mg m(-3)) at station E. When the diagnosed production rates were normalized to the observed concentrations of total dimethylsulfoniopropionate (DMSPt, the biogenic precursor of DMS), we found a remarkable similarity between our estimates at stations B and E (0.06 +/- 0.02 and 0.04 +/- 0.01 (nM DMS d(-1))/(nM DMSP), respectively) and the results obtained in a previous study from a contrasting biogeochemical environment in the North Atlantic subtropical gyre (0.047 +/- 0.006 and 0.087 +/- 0.014 (nM DMS d(-1))/(nM DMSP) in a cyclonic and anticyclonic eddy, respectively). We propose that gross biological DMS production normalized to DMSPt might be relatively independent of the biogeochemical environment, and place our average estimate at 0.06 +/- 0.01 (nM DMS d(-1))/(nM DMSPt). The significance of this finding is that it can provide a means to use DMSPt measurements to extrapolate gross biological DMS production, which is extremely difficult to measure experimentally under realistic in situ conditions. (C) 2011 Elsevier Ltd. All rights reserved.

Welschmeyer, NA, Copping AE, Vernet M, Lorenzen CJ.  1984.  Diel Fluctuation in Zooplankton Grazing Rate as Determined from the Downward Vertical Flux of Pheopigments. Marine Biology. 83:263-270.   10.1007/bf00397458   AbstractWebsite

The diel grazing activity of zooplankton was measured at a single study site in a temperate fjord, Dabob Bay, Washington, USA at several periods during spring, summer and fall of 1979–1981. Pheopigments were used as an indicator of herbivorous zooplankton activity. The downward vertical flux of pheopigment-containing fecal pellets was measured with sediment traps deployed over repetitive 4 h periods. Experiments were run for 24 to 36 h. A maximum in the flux of pheopigments was consistently noted within the euphotic zone during hours of darkness. Diel fluctuations in pheopigment flux showed amplitudes up to 29-fold. Nightly grazing activity accounted for 41 to 82% of the daily (24 h) grazing and was indirectly related to seasonal changes in daylength.

Cefarelli, AO, Ferrario ME, Almandoz GO, Atencio AG, Akselman R, Vernet M.  2010.  Diversity of the diatom genus Fragilariopsis in the Argentine Sea and Antarctic waters: morphology, distribution and abundance. Polar Biology. 33:1463-1484.   10.1007/s00300-010-0794-z   AbstractWebsite

Fragilariopsis species composition and abundance from the Argentine Sea and Antarctic waters were analyzed using light and electron microscopy. Twelve species (F. curta, F. cylindrus, F. kerguelensis, F. nana, F. obliquecostata, F. peragallii, F. pseudonana, F. rhombica, F. ritscheri, F. separanda, F. sublinearis and F. vanheurckii) are described and compared with samples from the Frenguelli Collection, Museo de La Plata, Argentina. F. peragallii was examined for the first time using electron microscopy, and F. pseudonana was recorded for the first time in Argentinean shelf waters. New information on the girdle view is included, except for the species F. curta, F. cylindrus and F. nana, for which information already existed. In the Argentine Sea, F. pseudonana was the most abundant Fragilariopsis species, and in Antarctic waters, F. curta was most abundant. Of the twelve species of Fragilariopsis documented, four occurred in the Argentine Sea, nine in the Drake Passage and twelve in the Weddell Sea. F. curta, F. kerguelensis, F. pseudonana and F. rhombica were present everywhere.

Matrai, PA, Vernet M.  1997.  Dynamics of the vernal bloom in the marginal ice zone of the Barents Sea: Dimethyl sulfide and dimethylsulfoniopropionate budgets. Journal of Geophysical Research-Oceans. 102:22965-22979.   10.1029/96jc03870   AbstractWebsite

Phytoplankton is known to be a I;ey element in the production and eventual oceanic efflux of dimethyl sulfide (DMS) to the atmosphere. We hypothesized that the alternation of Phaeocystis pouchetii and diatoms, the two major algal components of the spring bloom, would modulate the input of particulate organic sulfur (POS), dimethylsulfoniopropionate (DMSP), and DMS into the mixed layer of the marginal ice zone. A bloom of diatoms is expected to present similar pathways but to have very different rates of POS/DMSP/DMS production and POS/DMSP sinking and no or low DMS flux to the atmosphere as contrasted to the cycling occurring during the P. pouchetii phase of the bloom. Our initial hypothesis cannot be accepted based on our observations in the Barents Sea during the spring of 1993. The contribution of diatoms to the water column budgets of DMSP and DMS was significant and cannot be overlooked. We suggest that the physiological stage of the bloom is perhaps more important to biogeochemical cycling than its phytoplankton species composition in controlling DMSP and DMS fluxes in Arctic waters. Loss of particulate DMSP in the mixed layer was mainly by release into the dissolved pool and by sedimentation rather than by grazing, except in ice-free waters. Cycling of DMS in the mixed layer was predominantly biological in ice-free waters, while in Polar Front waters, ventilation was proportionally more important due to depressed microbiology.

Quetin, LB, Ross RM, Fritsen CH, Vernet M.  2007.  Ecological responses of Antarctic krill to environmental variability: can we predict the future? Antarctic Science. 19:253-266.   10.1017/s0954102007000363   AbstractWebsite

Antarctic krill are a key species in the Southern Ocean ecosystem, and their life cycle appears to be correlated with, and by implication dependent upon, seasonal sea ice dynamics. Moving from correlations with environmental parameters to an understanding of the mechanisms that lead to these correlations may allow predictions of the consequences of climate change on the distribution of favourable habitat for Antarctic krill. During winter cruises in 2001 and 2002 in the region west of the Antarctic Peninsula, one of the most rapidly warming regions on the planet, ice camps were established for periods of 3-9 days. Timing of sea ice advance, chlorophyll a concentrations in ice cores, and growth rates and pigment content of larval krill all differed significantly between winters. Growth rates and pigment content of larval krill from the same ice floe were correlated, suggesting that growth rates in winter are a function of the biomass of the sea ice microbial community. A possible mechanism underlying the correlation between recruitment success and timing of ice advance is proposed. In conjunction with other postulated habitat requirements, this proposed mechanism allows for speculation about future changes in the geographic location of favourable habitat for Antarctic krill.

Thomas, WH, Vernet M, Gibson CH.  1995.  Effects of small-scale turbulence on photosynthesis, pigmentation, cell division, and cell size in the marine dinoflagellate Gonyaulax polyedra (Dinophyceae). Journal of Phycology. 31:50-59.   10.1111/j.0022-3646.1995.00050.x   AbstractWebsite

Several experiments were conducted to understand better the physiological mechanisms underlying growth inhibition of the dinoflagellate Gonyaulax polyedra Stein due to small-scale turbulence shear. To measure photosynthetic C-14 uptake, a ''phytoplankton wheel'' device for rotating cultures in closed bottles was used. Turbulence was quantified biologically in the bottles by comparing growth inhibition with that in cultures with constant shear between a fixed cylinder and an outer concentric rotating cylinder (a stable Couette flow). At saturating irradiances, particulate photosynthesis (P-sat) or photosynthesis per unit chlorophyll (P-sat(B)) were not inhibited completely at the highest turbulence level (26.6 rad(.)s(-1)), and photosynthesis was less sensitive than growth. Photosynthesis per cell (P-sat(C)) was increased by turbulence. In three experiments on the effects of turbulence on photosynthesis versus irradiance curves, the slope of the curve, alpha, for particulate photosynthesis at limiting irradiances did not change. Photosynthesis per unit chlorophyll per unit irradiance (alpha(B)) decreased at high (but not intermediate) turbulence levels. Photosynthesis per cell per unit irradiance, alpha(C), increased with turbulence, suggesting an increase in photosynthetic efficiency in turbulent cultures. In two of the three experiments, respiration rates increased with turbulence, and in one experiment excretion of photosynthetically fixed C-14 was not affected by motion. Ratios of accessory pigments to chlorophyll alpha did not change with turbulence, but pigments per cell and per dry weight increased with turbulence These findings suggest little or no disruption of the photosynthetic apparatus. When turbulence was applied for 1 week, beta-carotene increased while peridinin and diadinoxanthin decreased, suggesting inhibition of synthesis of these latter pigments by prolonged turbulence. Since cell numbers did not increase or decreased during turbulent 72-h incubations, cell division was inhibited and also the cells were very much enlarged. Increases in alpha(C) per cell suggest that, in the sea, photosynthetic metabolism can persist efficiently without cell division during turbulent episodes. After turbulence ceases or reaches low levels again, cells can then divide and blooms may form. Thus, blooms can come or go fairly, rapidly in the ocean depending on the degree of wave- and wind-induced turbulence.