Spatiotemporal variability of dissolved inorganic macronutrients along the northern Antarctic Peninsula (1996–2019)

The northern Antarctic Peninsula is a key region of the Southern Ocean due to its complex ocean dynamics, distinct water mass sources, and the climate-driven changes taking place in the region. Despite the importance of macronutrients in supporting strong biological carbon uptake and storage, little is known about their spatiotemporal variability along the northern Antarctic Peninsula. Hence, we explored for the first time a 24-year time series (1996–2019) in this region to understand the processes involved in the spatial and interannual variability of macronutrients. We found high macronutrient concentrations, even in surface waters and during strong phytoplankton blooms. Minimum concentrations of dissolved inorganic nitrogen (DIN; 16 μmol kg−1), phosphate (0.7 μmol kg−1), and silicic acid (40 μmol kg−1) in surface waters are higher than those recorded in surrounding regions. The main source of macronutrients is the intrusions of Circumpolar Deep Water and its modified variety, while local sources (organic matter remineralization, water mass mixing, and mesoscale structures) can enhance their spatiotemporal variability. However, we identified a depletion in silicic acid due to the influence of Dense Shelf Water from the Weddell Sea. Macronutrient concentrations show substantial interannual variability driven by the balance between the intrusions of modified Circumpolar Deep Water and advection of Dense Shelf Water, which is largely modulated by the Southern Annular Mode (SAM) and to some extent by El Niño-Southern Oscillation (ENSO). These findings are critical to improving our understanding of the natural variability of this Southern Ocean ecosystem and how it is responding to climate changes

Impact of sea ice on the structure of phytoplankton communities in the northern Antarctic Peninsula

The seasonal advance and retreat of sea ice around the northern Antarctic Peninsula can have a significant impact on phytoplankton, mainly due to alterations in the availability of ice-free areas, micronutrient inputs by meltwater and variations in water column structure. The aim of this work was to evaluate the effect of sea ice conditions on phytoplankton biomass and community composition in an area off the northern Antarctic Peninsula, a region undergoing important warming processes. In two consecutive summer cruises (2013 and 2014), seawater samples were analysed for nutrients and phytoplankton (through HPLC-CHEMTAX approach), and measurements were made for water column physical structure evaluation. Two contrasting conditions were studied: a strong environmental gradient around the sea ice edge, with a marked meltwater signal (summer 2013) and the same area with little indication of meltwater and no detectable sea ice conditions (summer 2014). In the first year, the phytoplankton communities were massively dominated by nanoflagellates such as cryptophytes, small dinoflagellates and Phaeocystis antarctica, but with differences between stations with less influence of meltwater (dominance of dinoflagellates type B, mainly Gymnodinium spp., mean chlorophyll a = 1.37 mg m−3) and stations closer to the sea ice edge (dominance of cryptophytes, mean chlorophyll a = 0.98 mg m−3). In the second year, cryptophytes were apparently replaced by diatoms type B (mainly Pseudonitzschia spp., 24% contribution, mean chlorophyll a = 0.93 mg m−3), although dinoflagellates were also important. Therefore, there was a clear distinction between the phytoplankton communities under sea ice influence, where mainly cryptophytes were associated with shallow mixed layers and high water column stability in 2013 and an important presence of diatoms in 2014, associated with deeper mixed layers, lower silicic acid concentrations and higher magnitudes of both salinity and temperature, under very little sea ice influence. Gymnodinioid dinoflagellates were an important component in both years, apparently occupying sites/conditions less favourable to cryptophytes. These results support previous suggestions that climate factors leading to shortening of the sea ice season in the region do have an important impact particularly in shaping the dominance of the main phytoplankton functional groups in the region

Large diatom bloom off the Antarctic Peninsula during cool conditions associated with the 2015/2016 El Niño

Diatoms play crucial functions in trophic structure and biogeochemical cycles. Due to poleward warming, there has been a substantial decrease in diatom biomass, especially in Antarctic regions that experience strong physical changes. Here we analyze the phytoplankton contents of water samples collected in the spring/summer of 2015/2016 off the North Antarctic Peninsula during the extreme El Niño event and compare them with corresponding satellite chlorophyll-a data. The results suggest a close link between large diatom blooms, upper ocean physical structures and sea ice cover, as a consequence of the El Niño effects. We observed massive concentrations (up to 40 mg m–3 of in situ chlorophyll-a) of diatoms coupled with substantially colder atmospheric and oceanic temperatures and high mean salinity values associated with a lower input of meltwater. We hypothesize that increased meltwater concentration due to continued atmospheric and oceanic warming trends will lead to diatom blooms becoming more episodic and spatially/temporally restricted

The effect of irradiance on production and growth of the marine bloom-forming dinoflagellate Gyrodinium aureolum

The morphological and physiological responses of cultured cells of the marine dinoflagellate Gyrodinium aureolum grown at various irradiance levels has been investigated. Production rates were determined at a range of light intensities in cultures acclimated to various irradiances using two techniques: the oxygen light and dark bottle method and the 14C-CO2 radiotracer technique. Growth rates of G. aureolum have also been measured in cultures grown at various light levels. Gyrodinium aureolum cells showed adaptation to low irradiances by increasing cellular levels of chlorophyll a and reducing cell volume and carbon content. The enhanced pigmentation of low light adapted cells resulted in improvement of both light saturated and light limited rates of photosynthesis in relation to cells grown at higher irradiances. Production rates normalized per chlorophyll a were similar for low and high light adapted G. aureolum cultures. These photosynthetic responses have been identified as an indication of increases in the number of photosynthetic units (PSU's) within the cell, under low light adaptation. A similar set of experiments have been conducted with the marine Chlorophyte Brachiomonas sp. This organism also displayed a number of photoadaptation responses on growth at low light levels and these have been compared with results obtained with Gyrodinium aureolum. Production rates have been measured in natural bloom populations of Gyrodinium aureolum, during a cruise to the Western approaches of the English Channel in July 1987 and an estimation of water column production in the bloom waters attempted. Physiological data obtained with the field populations of G. aureolum are compared with results from culture studies. Finally, a comparison of production measurements obtained with the oxygen flux and the 14C methods has been made and possible factors influencing the photosynthetic quotient discussed. (DX89575)</p

Relação entre a densidade de cistos de dinoflagelados e o tipo de sedimento na Baía de Sepetiba, Rio de Janeiro, Brasil

Submitted by Camila Schuck ([email protected]) on 2012-04-20T20:31:00Z No. of bitstreams: 1 11_RELACAO_ENTRE_A_DESINDADE.pdf: 262335 bytes, checksum: 098001c04b541e1d8384f475a58494e8 (MD5)Rejected by Sabrina Andrade([email protected]), reason: on 2012-07-06T18:56:10Z (GMT)Submitted by Camila Schuck ([email protected]) on 2012-07-10T02:37:16Z No. of bitstreams: 1 11_RELACAO_ENTRE_A_DESINDADE.pdf: 262335 bytes, checksum: 098001c04b541e1d8384f475a58494e8 (MD5)Approved for entry into archive by Sabrina Andrade([email protected]) on 2013-06-05T18:47:28Z (GMT) No. of bitstreams: 1 11_RELACAO_ENTRE_A_DESINDADE.pdf: 262335 bytes, checksum: 098001c04b541e1d8384f475a58494e8 (MD5)Made available in DSpace on 2013-06-05T18:47:28Z (GMT). No. of bitstreams: 1 11_RELACAO_ENTRE_A_DESINDADE.pdf: 262335 bytes, checksum: 098001c04b541e1d8384f475a58494e8 (MD5) Previous issue date: 200

Accumulations of the surf diatom Asterionellopsis glacialis in Cassino beach, southern Brazil, and its relationship with environmental factors

Cassino Beach (lat. 32°13’S, long. 52°15’W, Southern Brazil) is an exposed, intermediate to dissipative sandy beach, where dense accumulations of the diatom Asterionellopsis glacialis occur in the surf zone. The frequency of these accumulations, their forcing factors and resulting biomass have been investigated along a weekly sampling program from June/1992 to August/1993 at a fixed station. Data on cell densities, chlorophyll a, physical-chemical variables of surf-zone water, beach morphodynamics features and local meteorological conditions were collected. In addition, nearshore sediment and water (just behind the surf-zone) were collected to determine the density of A. glacialis cells, along with some physical-chemical variables of sea water. Results have shown that cell stocks of A. glacialis are resuspended from the nearshore epibenthic habitat by breaking waves and accumulated at the inner surf zone by shoreward water motion. This physically controlled process result in large phytoplankton biomass concentration, which is available to the trophic chains of the beach and surf zone ecosystem.. Mean chlorophyll a concentration(50.2 μg.l-1) was greater than levels found in adjacent neritic and estuarine waters.Dissolved inorganic nutrients concentrations were relatively high during most of the study period (average values: NO3+NO2+NH4=3.41μM; PO4=1.10μM; SiO4=28.5μM). Although accumulations have been more frequent in winter months, the process could not be regarded as seasonal, since its forcing factors can be effective in any season. These diatom accumulations in Cassino Beach provide an important carbon source for the system, which tends to be self-sustained or even an exporter of organic matter

Occurrence of dinoflagellate cysts in the sediment close to the Patos Lagoon entrance (RS) with emphasis on potentially harmful species

Submitted by Camila Schuck ([email protected]) on 2012-06-26T21:51:36Z No. of bitstreams: 1 22_OCORRENCIA_DE_cistos.pdf: 216330 bytes, checksum: 5f4502333650f3453daddfa12552656e (MD5)Rejected by Sabrina Andrade([email protected]), reason: on 2012-07-06T19:00:07Z (GMT)Submitted by Camila Schuck ([email protected]) on 2012-07-10T03:06:17Z No. of bitstreams: 1 22_OCORRENCIA_DE_cistos.pdf: 216330 bytes, checksum: 5f4502333650f3453daddfa12552656e (MD5)Approved for entry into archive by Sabrina Andrade([email protected]) on 2013-06-03T19:04:36Z (GMT) No. of bitstreams: 1 22_OCORRENCIA_DE_cistos.pdf: 216330 bytes, checksum: 5f4502333650f3453daddfa12552656e (MD5)Made available in DSpace on 2013-06-03T19:04:36Z (GMT). No. of bitstreams: 1 22_OCORRENCIA_DE_cistos.pdf: 216330 bytes, checksum: 5f4502333650f3453daddfa12552656e (MD5) Previous issue date: 2003A formação de cistos de resistência em microalgas ocorre através da reprodução sexuada quando as condições ambientais encontram-se desfavoráveis para as células vegetativas. As principais funções dos cistos de resistência são permitir a sobrevivência, a dispersão e a recombinação genética dos organismos. Muitas espécies potencialmente nocivas de dinoflagelados produzem cistos durante o seu ciclo de vida, os quais podem afundar durante o t rmino de uma floração e ser acumulados no sedimento. Este trabalho teve por objetivo investigar a ocorrência de cistos de dinoflagelados em sedimento lamoso superficial, na área próxima à desembocadura da Laguna dos Patos, entre as latitudes 32°04' e 32°30' S e longitudes 52o10' e 51°49' W, no sul do Brasil (RS). Foram registrados cistos das espécies nocivas Alexandrium tamarense (até 180 cistos.cm-3), Scripsiella trochoidea (até 117 cistos.cm-3) e Gymnodinium cf. catenatum (máximo de 25 cistos.cm-3). Outros cistos de dinoflagelados freqüentemente observados em baixas concentrações foram Protoperidinium cf. compressum, Protoperidinium cf. oblongum, Protoperidinium cf. claudicans, Protoperidinium cf. pentagonum, Protoperidinium cf. minutum, Polykrikos cf. schwartzii e Gonyaulax verior. Apesar das concentrações relativamente baixas encontradas, sob condições ótimas para a germinação, crescimento e acúmulo de células, poderia ocorrer o início de florações a partir da germinação local dos cistos mais abundantes. Áreas profundas e lamosas, mais favoráveis ao acúmulo de cistos não foram amostradas neste estudo e deveriam ser incluídas em pesquisas futuras sobre cistos no sul do Brasil.Microalgae can form resting cysts under unfavorable environmental conditions for the vegetative cell, through sexual reproduction. The main functions of the cysts are the ability to survive under unfavorable conditions, allow the dispersion of the population to other areas and genetic recombination through sexual reproduction. Many harmful dinoflagellate species produce cysts during their life cycle, which sink to the bottom during the latest stages of a bloom. In order to detect dinoflagellate cysts, samplings were carried out in muddy sediment, close to the Patos Lagoon entrance, approximately from 32°04' to 32°30' S and 52o10' to 51°49' W, on the Southern Brazilian coast. Cysts of the potentially harmful dinoflagellates Alexandrium tamarense(up to 180 cysts.cm-3), Scripsiella trochoidea (up to 117 cysts.cm-3) and Gymnodinium cf. catenatum (up to 25 cysts.cm-3) were detected in the samples. Besides these species, other dinoflagellate cysts frequently detected in low concentrations were Protoperidinium cf. compressum, Protoperidinium cf. oblongum, Protoperidinium cf. claudicans, Protoperidinium cf. pentagonum, Protoperidinium cf. minutum, Polykrikos cf. schwartzii and Gonyaulax verior. Although relatively low cyst concentrations were found in the present work, under optimal growing conditions they could germinate and start microalgae blooms. However, deeper and muddy areas, more favorable to cyst settlement, were not sampled at this time and should be included in the next studies about these cysts in south Brazil

Variability of chlorophyll-a from ocean color images in the La Plata continental shelf region

Satellite-derived chlorophyll-a fields have been used to investigate temporal and spatial variability of chlorophyll-a concentration over the continental shelf zone (25–401S and 60–451W) close to the La Plata River estuary. Ocean color data used in this study were obtained by the Sea-viewing Wide Field-of- view Sensor (SeaWiFS) and consisted of 368 weekly averaged Standard Mapped Images (SMI), from October 1997 to September 2005. Fourier harmonic and EOF analyses were used to study the variability of log-transformed chlorophyll-a concentration in the region. The harmonic analysis has shown that the annual cycle was the most dominant signal followed by the semi- and quadri-annual cycles, in certain areas. The strong annual cycle is mainly present in latitudes lower than 341S where relatively high amplitudes ($1.9 mg mÀ3) in pigment variation are seen over the southern Brazilian continental shelf. The semi-annual cycle is mainly associated with the Brazil–Malvinas frontal zone oscillation while the ̃ 4-year signal is related to positive La Plata discharge anomalies influenced by El Nino events. After removing the annual signal from the log-transformed chlorophyll anomalies, the EOF results showed that the first three modes captured 85.1% of the variability associated with the regional mean phytoplankton chlorophyll pattern in our smoothed data set. The first three modes explained, respectively, 63.4%, 14.1% and 7.6%. The EOF results showed that the long-term chlorophyll time/space patterns are associated with both La Plata discharge anomaly (mode 1) and alongshore wind stress (mode 2). A reconstruction of the chlorophyll anomaly fields has been made using the two leading EOF modes over two periods of high La Plata River discharge, during ENSO events. In the first event, the spatial patterns of high chlorophyll anomaly were confined to the southern portion of the region, associated with NE winds, which push the plume near the estuary mouth. The second period revealed an elongated tongue of positive chlorophyll anomalies over the Uruguayan and Brazilian middle continental shelves, associated with favorable SW winds. The analyses performed in this study allowed identification of the main modes of variability in SeaWiFS-derived chlorophyll in the region, which were consistent with modulations of important regional environmental forcing mechanisms