scholarly journals In situ measurement of the biogeochemical properties of Southern Ocean mesoscale eddies in the Southwest Indian Ocean, April 2014

2015 ◽  
Vol 8 (2) ◽  
pp. 809-825
Author(s):  
S. de Villiers ◽  
K. Siswana ◽  
K. Vena
Keyword(s):  
Southern Ocean ◽  
Polar Front ◽  
Open Ocean ◽  
Southwest Indian Ridge ◽  
Cyclonic Eddy ◽  
Southwest Indian Ocean ◽  
Data Archiving ◽  
Chl A ◽  
Ocean Eddies ◽  
Warm Core

Abstract. Several open-ocean mesoscale features, a "young" warm-core (anti-cyclonic) eddy at 52° S, an "older" warm-core eddy at 57.5° S, as well as an adjacent cold-core (cyclonic) eddy at 56° S, were surveyed during a M/V S.A. Agulhas II cruise in April 2014. The main aim of the survey was to obtain hydrographical and biogeochemical profile data for contrasting open-ocean eddies in the Southern Ocean, that will be suitable for comparison and modelling of their heat, salt and nutrient characteristics, and the changes that occur in these properties as warm-core eddies migrate from the polar front southwards into the Southern Ocean. Results show that the older warm-core eddy at 57.5° S is, at its core, 2.7 °C colder than a younger eddy at 52° S, while its dissolved silicate levels are almost 500 % higher and accompanied by chl a levels that are more than 200 % higher than that in the younger eddy. A total of 18 CTD stations were occupied in a sector south of the Southwest Indian Ridge, along three transects crossing several mesoscale features identified from satellite altimetry data prior to the cruise. The CTD data, as well as chl a and dissolved nutrient data (for NO3−, NO2−, PO43− and SiO2) have been processed, quality-controlled and made available via the PANGAEA Data Archiving and Publication database at doi:10.1594/PANGAEA.848875.

scholarly journals In situ measurement of the biogeochemical properties of Southern Ocean mesoscale eddies in the Southwest Indian Ocean, April 2014

2015 ◽  
Vol 7 (2) ◽  
pp. 415-422
Author(s):  
S. de Villiers ◽  
K. Siswana ◽  
K. Vena
Keyword(s):  
Southern Ocean ◽  
Chlorophyll A ◽  
Polar Front ◽  
Open Ocean ◽  
Southwest Indian Ridge ◽  
Cyclonic Eddy ◽  
Southwest Indian Ocean ◽  
Data Archiving ◽  
Ocean Eddies ◽  
Warm Core

Abstract. Several open-ocean mesoscale features – a "young" warm-core (anti-cyclonic) eddy at 52° S, an "older" warm-core eddy at 57.5° S and an adjacent cold-core (cyclonic) eddy at 56° S – were surveyed during a R/V S.A. Agulhas II cruise in April 2014. The main aim of the survey was to obtain hydrographical and biogeochemical profile data for contrasting open-ocean eddies in the Southern Ocean, which will be suitable for comparative study and modelling of their heat, salt and nutrient characteristics, and the changes that occur in these properties as warm-core eddies migrate from the polar front southwards. The major result is that the older warm-core eddy at 57.5° S is, at its core, 2.7 °C colder than a younger eddy at 52° S, while its dissolved silicate levels are almost 500 % higher and accompanied by chlorophyll a levels that are more than 200 % higher than that in the younger eddy. A total of 18 CTD stations were occupied in a sector south of the Southwest Indian Ridge, along three transects crossing several mesoscale features identified from satellite altimetry data prior to the cruise. The CTD data, as well as chlorophyll a and dissolved nutrient data (for NO3−, NO2−, PO43− and SiO2), have been processed, quality controlled and made available via the PANGAEA Data Archiving and Publication database at doi:10.1594/PANGAEA.848875.

The distribution and abundance of viruses in the Southern Ocean during spring

2000 ◽  
Vol 12 (4) ◽  
pp. 414-417 ◽  
Author(s):  
Harvey Marchant ◽  
Andrew Davidson ◽  
Simon Wright ◽  
John Glazebrook
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Surface Waters ◽  
Significant Relationship ◽  
Polar Front ◽  
Open Ocean ◽  
Bacterial Concentration ◽  
Viral Abundance ◽  
Chroococcoid Cyanobacteria ◽  
Bacterial Concentrations

The concentrations of viruses, bacteria, chroococcoid cyanobacteria and chlorophyll a were determined in surface waters of the Southern Ocean during spring. Viral concentrations declined southward from around 4 × 106 ml−1 near Tasmania to a minimum of around 1 × 106 ml−1 at the Polar Front. South of the Front, virus concentrations increased again, reaching around 4 × 106 ml−1 in the sea-ice zone south of 60°S. Bacterial concentration decreased southwards across the Southern Ocean from around 6.5 × 105 ml−1 near Tasmania to < 1.0 × 105 ml−1 in the sea-ice zone. Cyanobacteria accounted for < 8% of the prokaryotes. There was no significant relationship between viral abundance and eithercyanobacterial or chl a concentration. Viral and bacterial concentrations were not significantly correlated north (P {0.10 < r < 0.20}) or south (P {0.20 < r < 0.5}) of the Polar Front. The virus to bacteria ratio (VBR) was between 3 and 15 in the open ocean but varied between 15 and 40 in the sea-ice region. These virus concentrations and VBRs indicate that viruses are no less important in Southern Ocean ecosystems than elsewhere in the world's oceans.

scholarly journals Dissolved greenhouse gases (nitrous oxide and methane) associated with the natural iron-fertilized Kerguelen region (KEOPS 2 cruise) in the Southern Ocean

2014 ◽  
Vol 11 (8) ◽  
pp. 12531-12569 ◽  
Author(s):  
L. Farías ◽  
L. Florez-Leiva ◽  
V. Besoain ◽  
C. Fernández
Keyword(s):  
Nitrous Oxide ◽  
Southern Ocean ◽  
Greenhouse Gases ◽  
Phytoplankton Bloom ◽  
Polar Front ◽  
Austral Spring ◽  
Chl A ◽  
The North ◽  
Natural Iron ◽  
Nutrient Fertilization

Abstract. The concentrations of greenhouse gases (GHGs) like nitrous oxide (N2O) and methane (CH4) were measured in the Kerguelen Plateau Region (KPR), an area with annual microalgal bloom caused by natural Fe fertilization, which may stimulate microbes involved in GHG cycling. This study was carried out during the KEOPS 2 cruise during the austral spring of 2011. Two transects were sampled along and across the KRP, the north–south (N–S) transect (46–51° S, 72° E meridian) and the west–east (W–E) transect (66–75° E, 48.3° S latitude), both associated with the presence of a plateau, polar fronts and other mesoscale features. The W–E transect had N2O levels ranging from equilibrium (105%) to light supersaturation (120%) with respect to the atmosphere. CH4 levels fluctuated dramatically, with intense supersaturations (120–970%) in areas close to the coastal waters of Kerguelen Island and in the polar front (PF). There, Fe and nutrient fertilization seem to promote high total chlorophyll a (TChl a) levels. The distribution of both gases was more homogenous in the N–S transect, but CH4 peaked at southeastern stations of the KPR (A3 stations), where phytoplankton bloom was observed. Both gases responded significantly to the patchy distribution of particulate matter as Chl a, stimulated by Fe supply by complex mesoscale circulation. While CH4 appears to be produced mainly at the pycnoclines, N2O seems to be consumed superficially. Air–sea fluxes for N2O (from −10.5 to 8.65, mean 1.71 μmol m−2d−1), and for CH4 (from 0.32 to 38.1, mean 10.07 μmol m−2d−1) reflected sink and source behavior for N2O and source behavior for CH4, with considerable variability associated with a highly fluctuating wind regime and, in the case of CH4, due to its high superficial levels that had not been reported before in the Southern Ocean and may be caused by an intense microbial CH4 cycling.

scholarly journals Nitrogen fixation in the Southern Ocean: a case of study of the Fe-fertilized Kerguelen region (KEOPS II cruise)

2014 ◽  
Vol 11 (12) ◽  
pp. 17151-17185 ◽  
Author(s):  
M. L. González ◽  
V. Molina ◽  
L. Florez-Leiva ◽  
L. Oriol ◽  
A. J. Cavagna ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Molecular Analysis ◽  
N2 Fixation ◽  
Chlorophyll Concentration ◽  
Polar Front ◽  
Chl A ◽  
Heterotrophic Bacterioplankton ◽  
High Chlorophyll Concentration ◽  
Composition Structure ◽  
Diazotrophic Community

Abstract. N2 fixation rates were measured during the KEOPS2 cruise in the HNLC area of Southern Ocean and in naturally iron-fertilized waters (Kerguelen Island 49.25° S, 69.58° E) using the 15N isotopic technique. We detected N2 fixation within the mixed layer at all stations, from the surface to 140 m depth. The data shows high variability with rates ranging between 0.42 and 20.11 nmol N L−1 d−1. The highest rates were concentrated in the euphotic layer and maximum values were obtained north of polar front (station F-L), which coincide with a positive N* ([NO3]–16[PO4]), high chlorophyll concentration and dissolved iron. N2 fixation rates were also obtained in stations with moderate (A3-2; E-4W) and also low (R-2) iron levels as well as Chl a, suggesting that beside the microbial biomass, its composition/structure is a driving factor controlling N2 fixation activities. Molecular analysis showed a diazotrophic community dominated by heterotrophic bacterioplankton. Size fractioned experiments indicated that most of N2 fixating activities came from <5 μm community and it was on line with molecular analysis revealing a low diversity diazotrophic community dominated by heterotrophic bacterioplankton. This study shows for first time N2 fixation is occurring in the Southern Ocean, at rates exceeding previous reports for high latitudes. Our findings suggest an indirect role of dFe in the regulation of N2 fixation through the enhancement of regenerated primary production and the availability of phytoplankton-derived dissolved organic matter, which in turn may stimulate heterotrophic bacterioplankton.

Collaborating robots sample the primary production in the ocean

2021 ◽  
Vol 6 (50) ◽  
pp. eabf4317
Author(s):  
Martin Ludvigsen
Keyword(s):  
Primary Production ◽  
Heterogeneous Network ◽  
Genetic Material ◽  
Open Ocean ◽  
Ocean Eddies

Sampling genetic material from phytoplankton in open ocean eddies becomes more precise and efficient using a heterogeneous network of autonomous marine robots.

scholarly journals Unveiling the Si cycle using isotopes in an iron-fertilized zone of the Southern Ocean: from mixed-layer supply to export

2016 ◽  
Vol 13 (21) ◽  
pp. 6049-6066 ◽  
Author(s):  
Ivia Closset ◽  
Damien Cardinal ◽  
Mathieu Rembauville ◽  
François Thil ◽  
Stéphane Blain
Keyword(s):  
Southern Ocean ◽  
Isotopic Composition ◽  
Mass Balance ◽  
Silicic Acid ◽  
Surface Waters ◽  
Polar Front ◽  
Biogeochemical Cycle ◽  
Reference Station ◽  
Kerguelen Plateau ◽  
Fractionation Factor

Abstract. A massive diatom bloom forms annually in the surface waters of the naturally iron-fertilized Kerguelen Plateau (Southern Ocean). In this study, silicon isotopic signatures (δ30Si) of silicic acid (DSi) and suspended biogenic silica (BSi) were investigated through the whole water column with unprecedented spatial resolution, during the KEOPS-2 experiment (spring 2011). We used δ30Si measurements to track the sources of silicon that fuelled the bloom, and investigated the seasonal evolution of the Si biogeochemical cycle in the iron-fertilized area. We compared the results from stations with various degrees of iron enrichment and bloom conditions to an HNLC reference station. Dissolved and particulate δ30Si signatures were highly variable in the upper 500 m, reflecting the effect of intense silicon utilization in spring, while they were quite homogeneous in deeper waters. The Si isotopic and mass balance identified a unique Winter Water (WW) Si source for the iron-fertilized area that originated from southeast of the Kerguelen Plateau and spread northward. When the WW reached a retroflection of the Polar Front (PF), the δ30Si composition of the silicic acid pool became progressively heavier. This would result from sequential diapycnal and isopycnal mixings between the initial WW and ML water masses, highlighting the strong circulation of surface waters that defined this zone. When comparing the results from the two KEOPS expeditions, the relationship between DSi depletion, BSi production, and their isotopic composition appears decoupled in the iron-fertilized area. This seasonal decoupling could help to explain the low apparent fractionation factor observed in the ML at the end of summer. Taking into account these considerations, we refined the seasonal net BSi production in the ML of the iron-fertilized area to 3.0 ± 0.3 mol Si m−2 yr−1, which was exclusively sustained by surface water phytoplankton populations. These insights confirm that the isotopic composition of dissolved and particulate silicon is a promising tool to improve our understanding of the Si biogeochemical cycle since the isotopic and mass balance allows resolution of processes in the Si cycle (i.e. uptake, dissolution, mixing).

scholarly journals Recent trends in SST, Chl‐ a , productivity and wind stress in upwelling and open ocean areas in the upper Eastern North Atlantic subtropical gyre

2021 ◽  
Author(s):  
J. P. Siemer ◽  
F. Machín ◽  
A. González‐Vega ◽  
J. M. Arrieta ◽  
M. A. Gutiérrez‐Guerra ◽  
...  
Keyword(s):  
Wind Stress ◽  
North Atlantic ◽  
Open Ocean ◽  
Subtropical Gyre ◽  
Chl A ◽  
Recent Trends ◽  
Eastern North Atlantic

scholarly journals Carbonate saturation state of surface waters in the Ross Sea and Southern Ocean: controls and implications for the onset of aragonite undersaturation

2015 ◽  
Vol 12 (11) ◽  
pp. 8429-8465 ◽  
Author(s):  
H. B. DeJong ◽  
R. B. Dunbar ◽  
D. A. Mucciarone ◽  
D. A. Koweek
Keyword(s):  
Southern Ocean ◽  
Surface Waters ◽  
Ross Sea ◽  
Polar Front ◽  
Early Spring ◽  
Total Alkalinity ◽  
Saturation State ◽  
System Data ◽  
Algal Photosynthesis ◽  
Carbon System

Abstract. Predicting when surface waters of the Ross Sea and Southern Ocean will become undersaturated with respect to biogenic carbonate minerals is challenging in part due to the lack of baseline high resolution carbon system data. Here we present ~ 1700 surface total alkalinity measurements from the Ross Sea and along a transect between the Ross Sea and southern Chile from the austral autumn (February–March 2013). We calculate the saturation state of aragonite (ΩAr) and calcite (ΩCa) using measured total alkalinity and pCO2. In the Ross Sea and south of the Polar Front, variability in carbonate saturation state (Ω) is mainly driven by algal photosynthesis. Freshwater dilution and calcification have minimal influence on Ω variability. We estimate an early spring surface water ΩAr value of ~ 1.2 for the Ross Sea using a total alkalinity–salinity relationship and historical pCO2 measurements. Our results suggest that the Ross Sea is not likely to become undersaturated with respect to aragonite until the year 2070.

scholarly journals Watermasses as a unifying framework for understanding the Southern Ocean carbon cycle

2010 ◽  
Vol 7 (3) ◽  
pp. 3393-3451 ◽  
Author(s):  
D. Iudicone ◽  
I. Stendardo ◽  
O. Aumont ◽  
K. B. Rodgers ◽  
G. Madec ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Large Scale ◽  
Thermohaline Circulation ◽  
Model Simulation ◽  
Polar Front ◽  
Global Ocean ◽  
Inversion Method ◽  
Co2 Fluxes ◽  
Meridional Transport ◽  
Regional Patterns

Abstract. A watermass-based framework is presented for a quantitative understanding of the processes controlling the cycling of carbon in the Southern Ocean. The approach is developed using a model simulation of the global carbon transports within the ocean and with the atmosphere. It is shown how the watermass framework sheds light on the interplay between biology, air-sea gas exchange, and internal ocean transport including diapycnal processes, and the way in which this interplay controls the large-scale ocean-atmosphere carbon exchange. The simulated pre-industrial regional patterns of DIC distribution and the global distribution of the pre-industrial air-sea CO2 fluxes compare well with other model results and with results from an ocean inversion method. The main differences are found in the Southern Ocean where the model presents a stronger CO2 outgassing south of the polar front, a result of the upwelling of DIC-rich deep waters into the surface layer. North of the subantarctic front the typical temperature-driven solubility effect produces a net ingassing of CO2. The biological controls on surface CO2 fluxes through primary production is generally smaller than the temperature effect on solubility. Novel to this study is also a Lagrangian trajectory analysis of the meridional transport of DIC. The analysis allows to evaluate the contribution of separate branches of the global thermohaline circulation (identified by watermasses) to the vertical distribution of DIC throughout the Southern Ocean and towards the global ocean. The most important new result is that the overturning associated with Subantarctic Mode Waters sustains a northward net transport of DIC (15.7×107 mol/s across 30° S). This new finding, which has also relevant implications on the prediction of anthropogenic carbon redistribution, results from the specific mechanism of SAMW formation and its source waters whose consequences on tracer transports are analyzed for the first time in this study.

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