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Smith, RC, Baker KS, Vernet M.  1998.  Seasonal and interannual variability of phytoplankton biomass west of the Antarctic Peninsula. Journal of Marine Systems. 17:229-243.   10.1016/s0924-7963(98)00040-2   AbstractWebsite

The spatial and temporal variability of phytoplankton biomass, estimated as chlorophyll-a (chl-a) concentration, is examined in the continental shelf-slope region west of the Antarctic Peninsula. Relationships between temporal observations in the nearshore Palmer Station grid (64 degrees 46.77'S, 64 degrees 04.36'W) and spatial observations in a larger regional grid 200 km on/off-shore and 900 km alongshore are presented. Average chi-a concentrations in the upper layers of the water column in the immediate vicinity of Palmer Station show strong seasonal and interannual variability. Biomass accumulation typically starts during mid-November, while strong blooms develop from December through January. The 1991/1992 and 1994/1995 seasons developed higher overall chi-a concentrations (average maximum water column values reaching 8 and 16 mg chi-a m(-3), respectively) than the 1992/1993 and 1993/1994 seasons (average maximum water column values of less than 3 mg chi-a m(-3)). The 1994/1995 season of extremely high chi-a concentrations also showed a prolonged bloom period into February, while the 1991/1992 season did not. Similar interannual variability was observed in the regional grid. Average chi-a concentration in the top 30 m was 0.91, 1.24 and 1.66 mg chi-a m(-3) for January of 1993, 1994 and 1995, respectively. The regional grid contains an on/off-shore gradient in bottom topography, measured physical and optical characteristics, as well as chi-a concentrations. Regional inshore grid stations in January had, on average, almost four times more chi-a biomass than off-shore stations (2.18 vs. 0.59 mg chi-a m(-3), respectively). There is evidence that this on/off-shore gradient is modulated alongshore by latitudinal variability which follows the annual advance and retreat of sea ice.

Randelhoff, A, Reigstad M, Chierici M, Sundfjord A, Ivanov V, Cape M, Vernet M, Tremblay JE, Bratbak G, Kristiansen S.  2018.  Seasonality of the physical and biogeochemical hydrography in the inflow to the Arctic Ocean through Fram Strait. Frontiers in Marine Science. 5   10.3389/fmars.2018.00224   AbstractWebsite

Eastern Fram Strait and the shelf slope region north of Svalbard is dominated by the advection of warm, salty and nutrient-rich Atlantic Water (AW). This oceanic heat contributes to keeping the area relatively free of ice. The last years have seen a dramatic decrease in regional sea ice extent, which is expected to drive large increases in pelagic primary production and thereby changes in marine ecology and nutrient cycling. In a concerted effort, we conducted five cruises to the area in winter, spring, summer and fall of 2014, in order to understand the physical and biogeochemical controls of carbon cycling, for the first time from a year-round point of view. We document (1) the offshore location of the wintertime front between salty AW and fresher Surface Water in the ocean surface, (2) thermal convection of Atlantic Water over the shelf slope, likely enhancing vertical nutrient fluxes, and (3) the importance of ice melt derived upper ocean stratification for the spring bloom timing. Our findings strongly confirm the hypothesis that this "Atlantification," as it has been called, of the shelf slope area north of Svalbard resulting from the advection of AW alleviates both nutrient and light limitations at the same time, leading to increased pelagic primary productivity in this region.

Lowe, AT, Ross RM, Quetin LB, Vernet M, Fritsen CH.  2012.  Simulating larval Antarctic krill growth and condition factor during fall and winter in response to environmental variability. Marine Ecology-Progress Series. 452:27-43.   10.3354/meps09409   AbstractWebsite

The first winter in the life cycle of Antarctic krill Euphausia superba is a critical period in which larval survival and recruitment to the adult population are highly sensitive to environmental conditions, yet little is known about larval physiological dynamics during this period. An individual-based model was developed to investigate patterns of larval krill growth and condition factor in response to environmental variability during fall and winter, west of the Antarctic Peninsula. Field and experimental observations from Southern Ocean Global Ocean Ecosystems Dynamics cruises in 2001 and 2002 and the Palmer Long-Term Ecological Research program were used to parameterize the model. Growth was modeled by partitioning total body carbon between length and condition factor. Total body carbon was simulated with empirical temperature-dependent rates of ingestion of phytoplankton and respiration, and ingestion of algae grown on a surface to simulate sea ice algae. Light-driven diel vertical migration modulated ingestion of phytoplankton and sea ice algae as a function of latitude, season and sea ice cover. Simulations highlighted 3 environmental processes that controlled food availability, and consequently, physiological condition of krill: the fall phytoplankton decline, sea ice advance and development of sea ice microbial communities, and the late winter increase in sea ice microbial community biomass. Fall phytoplankton dynamics were identified as a major driver of the physiological condition of larval krill throughout this critical period. The model presents a mechanism that links larval krill survival and recruitment to fall and winter variability in phytoplankton and sea ice dynamics along the western Antarctic Peninsula.

Diaz, S, Camilion C, Escobar J, Deferrari G, Roy S, Lacoste K, Demers S, Belzile C, Ferreyra G, Gianesella S, Gosselin M, Nozais C, Pelletier E, Schloss I, Vernet M.  2006.  Simulation of ozone depletion using ambient irradiance supplemented with UV lamps. Photochemistry and Photobiology. 82:857-864.   10.1562/2005-09-28-ra-700   AbstractWebsite

In studies of the biological effects of UV radiation, ozone depletion can be mimicked by performing the study under ambient conditions and adding radiation with UV-B lamps. We evaluated this methodology at three different locations along a latitudinal gradient: Rimouski (Canada), Ubatuba (Brazil) and Ushuaia (Argentina). Experiments of the effect of potential ozone depletion on marine ecosystems were carried out in large outdoor enclosures (mesocosms). In all locations we simulated irradiances corresponding to 60% ozone depletion, which may produce a 130-1900% increase in 305 nm irradiance at noon, depending on site and season. Supplementation with a fixed percentage of ambient irradiance provides a better simulation of irradiance increase due to ozone depletion than supplementation with a fixed irradiance value, particularly near sunrise and sunset or under cloudy skies. Calculations performed for Ushuaia showed that, on very cloudy days, supplementation by the square-wave method may produce unrealistic irradiances. Differences between the spectra of the calculated supplementing irradiance and the lamp for a given site and date will be a function of the time of day and may become more or less pronounced according to the biological weighting function of the effect under study.

Sastre, MP, Vernet M, Steinert S.  2001.  Single-cell gel/comet assay applied to the analysis of UV radiation-induced DNA damage in Rhodomonas sp. (Cryptophyta). Photochemistry and Photobiology. 74:55-60.   10.1562/0031-8655(2001)074<0055:scgcaa>;2   AbstractWebsite

The single-cell gel/comet assay is an electrophoretic technique used to detect single-strand breaks in DNA, Damage is assessed examining individual cells under an epifluorescent microscope. UV-induced DNA damage consists mostly of the formation of pyrimidine dimers; therefore, most of the damage cannot be detected using a standard comet assay. The enzyme T4 endonuclease V breaks DNA strands at sites of pyrimidine dimers, The main objective of this work is to evaluate the comet assay to detect UV-induced damage in DNA after an initial treatment of cells with T4 endonuclease V, This work was conducted on Rhodomonas sp, (Cryptophyta), a marine unicellular flagellate, Cells of Rhodomonas sp, were exposed to 12 h visible + ultraviolet-A + ultraviolet-B (VIS + UVA + UVB) and VIS (control), with and without T4 endonuclease V. Cells exposed to VIS + UVA + UVB showed approximately 200% more damage than control if these were treated with T4 endonuclease V, Rhodomonas sp, were exposed to 3, 6, 9 and 12 h of VIS, VIS + UVA and VIS + UVA + UVB, Damage induced by VIS + UVA + UVB as detected by the comet assay increased along with exposure time. However, damage caused by VIS and VIS + UVA remained relatively constant at all times. Results of this study indicate that the comet assay is more sensitive to UV radiation damage when used in conjunction with T4 endonuclease V. This modification of the comet assay can be used as an alternative technique to detect DNA damage in single cells caused by UV radiation.

Lorenzen, CJ, Welschmeyer NA, Copping AE, Vernet M.  1983.  Sinking rates of organic particles. Limnology and Oceanography. 28:766-769.   10.4319/lo.1983.28.4.0766   AbstractWebsite

The flux of organic particles collected by sediment traps decreases in a nonlinear fashion with depth. This implies a loss of organic carbon with time as the particles sink. Samples of such particles held in the laboratory or left in situ do in fact decay, showing a significant loss of carbon.Particles were collected in the upper 1,000 m of the water column with sediment traps south of the Hawaiian Islands. Aliquots from the traps were placed in combusted glass bottles and returned to the depths from which they were collected. After 5 days the bottles were recovered and the carbon content determined. On the average, about 30% of the particulate carbon was lost during the experiment.With this knowledge of the decay rate, one can estimate the expected change in "apparent carbon flux" with time. This in combination with the measured vertical flux can by used to calculate the depth interval required for this change to occur. Average sinking rates of 92 m/d were thus estimated.

Helly, JJ, Kaufmann RS, Vernet M, Stephenson GR.  2011.  Spatial characterization of the meltwater field from icebergs in the Weddell Sea. Proceedings of the National Academy of Sciences of the United States of America. 108:5492-5497.   10.1073/pnas.0909306108   AbstractWebsite

We describe the results from a spatial cyberinfrastructure developed to characterize the meltwater field around individual icebergs and integrate the results with regional- and global-scale data. During the course of the cyberinfrastructure development, it became clear that we were also building an integrated sampling planning capability across multidisciplinary teams that provided greater agility in allocating expedition resources resulting in new scientific insights. The cyberinfrastructure-enabled method is a complement to the conventional methods of hydrographic sampling in which the ship provides a static platform on a station-by-station basis. We adapted a sea-floor mapping method to more rapidly characterize the sea surface geophysically and biologically. By jointly analyzing the multisource, continuously sampled biological, chemical, and physical parameters, using Global Positioning System time as the data fusion key, this surface-mapping method enables us to examine the relationship between the meltwater field of the iceberg to the larger-scale marine ecosystem of the Southern Ocean. Through geospatial data fusion, we are able to combine very fine-scale maps of dynamic processes with more synoptic but lower-resolution data from satellite systems. Our results illustrate the importance of spatial cyberinfrastructure in the overall scientific enterprise and identify key interfaces and sources of error that require improved controls for the development of future Earth observing systems as we move into an era of peta- and exascale, data-intensive computing.

Vernet, M, Neori A, Haxo FT.  1989.  Spectral properties and photosynthetic action in red-tide populations of Prorocentrum micans and Gonyaulax polyedra. Marine Biology. 103:365-371.   10.1007/bf00397271   AbstractWebsite

Spectral attenuance and photosynthetic performance over the range 300 to 700 nm were examined in red-tide populations of Prorocentrum micans and Gonyaulax polyedra collected off La Jolla, California, USA, in May 1969 and May–June 1985; and in spring 1969, November 1981 and April–May 1982, respectively. In the near ultraviolet (UV), high attenuance and diminished photosynthetic effectiveness were observed in both dinoflagellates. This decline in relative quantum yield is ascribed to masking absorption by unidentified and spectrally different UV-absorbing compounds which were soluble in methanol. In the visible region, photosynthetic action spectra displayed the characteristic shapes expected from efficient Photosystem II light harvesting by peridinin, chlorophylls a and c 2 , in conformity with previous studies on cultured dinoflagellates. In the case of P. micans, a high content of diadinoxanthin was found and the possible role of this yellow xanthophyll as a photoprotective pigment is discussed. However, photosynthetic enhancement spectra suggest that some portion of the diadinoxanthin pool functions as a Photosystem I antenna in this species. Our data on P. micans and G. polyedra support the hypothesis that UV-absorbing compounds and diadinoxanthin play protective roles in screening harmful radiation in red-tide dinoflagellates exposed to high-light conditions in nature.

Wassmann, P, Ratkova T, Andreassen I, Vernet M, Pedersen C, Rey F.  1999.  Spring bloom development in the marginal ice zone and the central Barents Sea. Marine Ecology-Pubblicazioni Della Stazione Zoologica Di Napoli I. 20:321-346.   10.1046/j.1439-0485.1999.2034081.x   AbstractWebsite

The knowledge of the relative contribution of algal groups and the environmental factors that control their abundance in the marginal ice zone of the Parents Sea is rather limited. Therefore, a field investigation to study the hydrography and the phytoplankton composition of the marginal ice zone (M1Z) in the central Parents Sea was carried out along a south-north transect in May 1993. The weakly stratified Atlantic sector of the transect appeared to be in a prebloom state and had intermittent intrusions from the meandering Polar Front and the Norwegian Coastal Current, introducing water of a more advanced bloom state. Pico- and nanoplankton flagellates and monads dominated, with a few diatoms and Phaeocystis pouchetii colonies. The average new production rate of 26 g C.m(-2) as reflected by NO, depletion in the euphotic zone, however, indicated that the vernal bloom had been in progress for some time in the Atlantic sector without leaving specific signals in the suspended fraction. The ice-edge and Polar Front area was characterized by a dominance of centric colonial diatom genera Chaetoceros and Thalassiosira with some development of P. pouchetii. In the densely ice-covered and stratified Arctic zone the vernal bloom was at its maximum and dominated by the diatom genera Fragilariopsis and Chaetoceros. Diatoms were limited by silicate concentrations <2 mu M in 32% of all samples. New production, as revealed by the C equivalent of nitrate depletion in the upper layer, ranged between 12 g C m(-2) in the north to 45 g C.m(-2) in the meandering Polar Front, with an average of about 27 +/- 28% g C.m(-2). The time development of the vernal bloom in the marginal ice zone and the central Parents Sea in late May 1993, with its complicated zonal structure, was not from south to north, but intermittently from north to south. Later during the year the general development of the vernal bloom was, as expected, from south to north.

Stephenson, GR, Sprintall J, Gille ST, Vernet M, Helly JJ, Kaufmann RS.  2011.  Subsurface melting of a free-floating Antarctic iceberg. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 58:1336-1345.   10.1016/j.dsr2.2010.11.009   AbstractWebsite

Observations near a large tabular iceberg in the Weddell Sea in March and April 2009 show evidence that water from ice melting below the surface is dispersed in two distinct ways. Warm, salty anomalies in T-S diagrams suggest that water from the permanent thermocline is transported vertically as a result of turbulent entrainment of meltwater at the iceberg's base. Stepped profiles of temperature, salinity, and density in the seasonal thermocline are more characteristic of double-diffusive processes that transfer meltwater horizontally away from the vertical ice face. These processes contribute comparable amounts of meltwater-O(0.1 m(3)) to the upper 200 m of a 1 m(2) water column-but only basal melting results in significant upwelling of water from below the Winter Water layer into the seasonal thermocline, suggesting that these two processes may have different effects on vertical nutrient transport near an iceberg. (C) 2010 Elsevier Ltd. All rights reserved.

Vernet, M, Matrai PA, Andreassen I.  1998.  Synthesis of particulate and extracellular carbon by phytoplankton at the marginal ice zone in the Barents Sea. Journal of Geophysical Research-Oceans. 103:1023-1037.   10.1029/97jc02288   AbstractWebsite

Large phytoplankton biomass accumulates during ice-edge blooms in Arctic waters, where taxa such as diatoms or the prymnesiophyte Phaeocystis pouchetii usually dominate. Based on characteristics from temperate phytoplankton, we hypothesized that in Barents Sea waters, a larger fraction of primary production would be extracellular (for synthesis of colonial mucilage) during periods of dominance by P. pouchetii as opposed to periods when diatoms dominated. This alternation of P. pouchetii and diatoms would affect the relationship between the particulate and dissolved carbon pools in the upper water column of the marginal ice zone (MIZ). Results presented in this paper do not support this hypothesis. Although P. pouchetii contributed strongly to the extracellular carbon pool (mucilage and dissolved organic carbon, DOC) during an ice-edge bloom in May 1993, arctic diatoms contributed an equal amount of exuded carbon. Three process stations visited along a north-south transect in the MIZ in the Barents Sea, presented between 36% and 55% of the primary production as extracellular carbon, defined as labeled organic matter which passes through a Whatman GF/C filter. No difference in the carbon allocation between diatom-and P. pouchetii-rich phytoplankton was observed in these stations. In contrast, the station located ire ice-free waters had 18% of primary production in the extracellular fraction. These results (1) highlight similar carbon allocation for diatom-and P. pouchetii-dominated phytoplankton in surface waters of the Barents Sea during the spring and/or ice-edge bloom at the MIZ and (2) suggest that polar phytoplankton may be stronger producers of extracellular carbon, and possibly DOG, than previously thought.