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

2015 ◽  
Vol 12 (6) ◽  
pp. 1925-1940 ◽  
Author(s):  
L. Farías ◽  
L. Florez-Leiva ◽  
V. Besoain ◽  
G. Sarthou ◽  
C. Fernández
Keyword(s):  
Nitrous Oxide ◽  
Southern Ocean ◽  
Greenhouse Gases ◽  
Phytoplankton Bloom ◽  
Polar Front ◽  
Austral Spring ◽  
Kerguelen Islands ◽  
The North ◽  
Ch4 Production ◽  
Natural Iron

Abstract. The concentrations of greenhouse gases (GHGs), such as nitrous oxide (N2O) and methane (CH4), were measured in the Kerguelen Plateau region (KPR). The KPR is affected by an annual microalgal bloom caused by natural iron fertilization, and this may stimulate the microbes involved in GHG cycling. This study was carried out during the KEOPS 2 cruise during the austral spring of 2011. Oceanographic variables, including N2O and CH4, were sampled (from the surface to 500 m depth) in two transects along and across the KRP, the north–south (TNS) transect (46°–51° S, ~ 72° E) and the east–west (TEW) transect (66°–75° E, ~ 48.3° S), both associated with the presence of a plateau, polar front (PF) and other mesoscale features. The TEW presented N2O levels ranging from equilibrium (105%) to slightly supersaturated (120%) with respect to the atmosphere, whereas CH4 levels fluctuated dramatically, being highly supersaturated (120–970%) in areas close to the coastal waters of the Kerguelen Islands and in the PF. The TNS showed a more homogenous distribution for both gases, with N2O and CH4 levels ranging from 88 to 171% and 45 to 666% saturation, respectively. Surface CH4 peaked at southeastern stations of the KPR (A3 stations), where a phytoplankton bloom was observed. Both gases responded significantly, but in contrasting ways (CH4 accumulation and N2O depletion), to the patchy distribution of chlorophyll a. This seems to be associated to the supply of iron from various sources. Air–sea fluxes for N2O (from −10.5 to 8.65, mean 1.25 ± 4.04 μmol m−2 d−1) and for CH4 (from 0.32 to 38.1, mean 10.01 ± 9.97 μmol−2 d−1) indicated that the KPR is both a sink and a source for N2O, as well as a considerable and variable source of CH4. This appears to be associated with biological factors, as well as the transport of water masses enriched with Fe and CH4 from the coastal area of the Kerguelen Islands. These previously unreported results for the Southern Ocean suggest an intense microbial CH4 production in the study area.

scholarly journals Chemometric perspectives on plankton community responses to natural iron fertilization over and downstream of the Kerguelen Plateau in the Southern Ocean

2014 ◽  
Vol 11 (9) ◽  
pp. 13841-13903 ◽  
Author(s):  
T. W. Trull ◽  
D. M. Davies ◽  
F. Dehairs ◽  
A.-J. Cavagna ◽  
M. Lasbleiz ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Growth Rates ◽  
High Growth ◽  
Large Cell ◽  
Polar Front ◽  
Community Responses ◽  
Kerguelen Plateau ◽  
Austral Spring ◽  
Particulate Nitrogen ◽  
Natural Iron

Abstract. We examined phytoplankton community responses to natural iron fertilisation at 32 sites over and downstream from the Kerguelen Plateau in the Southern Ocean during the austral spring bloom in October–November 2011. Community structure was estimated from chemical and isotopic measurements (particulate organic carbon POC, 13C-POC, particulate nitrogen PN, 15N-PN, and biogenic silica BSi) on size-fractionated samples from surface waters (300, 210, 50, 20, 5, and 1 μm fractions). Higher values of 13C-POC (vs. co-located 13C-DIC source values) were taken as indicative of faster growth rates, and higher values of 15N-PN (vs. co-located 15N-NO3 source values) as indicative of greater nitrate use. Community responses varied in relation to both regional circulation and the advance of the bloom. Iron fertilised waters over the plateau developed dominance by very large diatoms (50–210 μm) with high BSi / POC ratios, high growth rates, and significant ammonium recycling as biomass built up. In contrast, downstream Polar Frontal waters with similar or higher iron supply were dominated by smaller diatoms (20–50 μm) and exhibited greater ammonium recycling. Stations in a deep water bathymetrically trapped recirculation south of the Polar Front with lower iron levels showed the large cell dominance observed on the plateau, but much less biomass. Comparison of these communities to surface water nitrate (and silicate) depletions as a proxy for export shows that the low biomass recirculation feature exported similar amounts of nitrogen to the high biomass blooms over the plateau and north of the Polar Front. This suggests that trophodynamic and export responses differed between regions with persistent low levels vs. punctual high levels of iron fertilisation.

scholarly journals Chemometric perspectives on plankton community responses to natural iron fertilisation over and downstream of the Kerguelen Plateau in the Southern Ocean

2015 ◽  
Vol 12 (4) ◽  
pp. 1029-1056 ◽  
Author(s):  
T. W. Trull ◽  
D. M. Davies ◽  
F. Dehairs ◽  
A.-J. Cavagna ◽  
M. Lasbleiz ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Growth Rates ◽  
Dissolved Inorganic Carbon ◽  
High Growth ◽  
Polar Front ◽  
Community Responses ◽  
Kerguelen Plateau ◽  
Austral Spring ◽  
Particulate Nitrogen ◽  
Natural Iron

Abstract. We examined phytoplankton community responses to natural iron fertilisation at 32 sites over and downstream from the Kerguelen Plateau in the Southern Ocean during the austral spring bloom in October–November 2011. The community structure was estimated from chemical and isotopic measurements (particulate organic carbon – POC; 13C-POC; particulate nitrogen – PN; 15N-PN; and biogenic silica – BSi) on size-fractionated samples from surface waters (300, 210, 50, 20, 5, and 1 μm fractions). Higher values of 13C-POC (vs. co-located 13C values for dissolved inorganic carbon – DIC) were taken as indicative of faster growth rates and higher values of 15N-PN (vs. co-located 15N-NO3 source values) as indicative of greater nitrate use (rather than ammonium use, i.e. higher f ratios). Community responses varied in relation to both regional circulation and the advance of the bloom. Iron-fertilised waters over the plateau developed dominance by very large diatoms (50–210 μm) with high BSi / POC ratios, high growth rates, and significant ammonium recycling (lower f ratios) as biomass built up. In contrast, downstream polar frontal waters with a similar or higher iron supply were dominated by smaller diatoms (20–50 μm) and exhibited greater ammonium recycling. Stations in a deep-water bathymetrically trapped recirculation south of the polar front with lower iron levels showed the large-cell dominance observed on the plateau but much less biomass. Comparison of these communities to surface water nitrate (and silicate) depletions as a proxy for export shows that the low-biomass recirculation feature had exported similar amounts of nitrogen to the high-biomass blooms over the plateau and north of the polar front. This suggests that early spring trophodynamic and export responses differed between regions with persistent low levels vs. intermittent high levels of iron fertilisation.

Spatial and temporal variability of the phytoplankton community structure in the North Water Polynya, investigated using pigment biomarkers

2004 ◽  
Vol 61 (11) ◽  
pp. 2038-2052 ◽  
Author(s):  
Francesca Vidussi ◽  
Suzanne Roy ◽  
Connie Lovejoy ◽  
Marie Gammelgaard ◽  
Helge Abildhauge Thomsen ◽  
...  
Keyword(s):  
Community Structure ◽  
Phytoplankton Community ◽  
Phytoplankton Bloom ◽  
Circulation Pattern ◽  
Spatial And Temporal Variability ◽  
Phytoplankton Community Structure ◽  
Southeastern Part ◽  
Chl A ◽  
The North ◽  
North Water

Phytoplankton taxonomic pigments were measured by high-performance liquid chromatography (HPLC) during a 3-month survey (April–June 1998) in the North Water (NOW) Polynya (Canadian Arctic) to investigate changes in phytoplankton biomass and composition and the physical–chemical factors that influence these changes. A phytoplankton bloom with high chlorophyll a (Chl a) concentrations (up to 17.45 mg·m–3 at 15 m) occurred in mid-May along the Greenland coast in the southeastern part of the NOW Polynya. The initiation of the phytoplankton bloom was linked to shallow mixed-layer depths. The contribution of the different phytoplankton groups to Chl a inferred using a factorization program (CHEMTAX) indicated that the bloom was diatom-dominated (maximum 94% diatoms). The phytoplankton community structure was influenced by the water mass characteristics and the surface circulation pattern. Autotrophic flagellates dominated in April and May along the Canadian coast, where cold Arctic waters with relatively deep mixed layers were found. In contrast, diatoms dominated in May along the Greenland coast in warmer water masses of Atlantic origin and during June in the whole polynya, except in the southernmost part.

scholarly journals Distribution and recurrence of phytoplankton blooms around South Georgia, Southern Ocean

2013 ◽  
Vol 10 (1) ◽  
pp. 217-231 ◽  
Author(s):  
I. Borrione ◽  
R. Schlitzer
Keyword(s):  
Southern Ocean ◽  
Austral Summer ◽  
Wide Field ◽  
Phytoplankton Blooms ◽  
Chl A ◽  
South Georgia ◽  
The North ◽  
Wide Field Of View ◽  
Georgia Basin ◽  
Second Peak

Abstract. South Georgia phytoplankton blooms are amongst the largest of the Southern Ocean and are associated with a rich ecosystem and strong atmospheric carbon drawdown. Both aspects depend on the intensity of blooms, but also on their regularity. Here we use data from 12 yr of SeaWiFS (Sea-viewing Wide Field-of-view Sensor) ocean colour imagery and calculate the frequency of bloom occurrence (FBO) to re-examine spatial and temporal bloom distributions. We find that upstream of the island and outside the borders of the Georgia Basin, blooms occurred in less than 4 out of the 12 yr (FBO < 4). In contrast, FBO was mostly greater than 8 downstream of the island, i.e., to the north and northwest, and in places equal to 12, indicating that blooms occurred every year. The typical bloom area, defined as the region where blooms occurred in at least 8 out of the 12 yr, covers the entire Georgia Basin and the northern shelf of the island. The time series of surface chlorophyll a (Chl a) concentrations averaged over the typical bloom area shows that phytoplankton blooms occurred in every year between September 1997 and September 2010, and that Chl a values followed a clear seasonal cycle, with concentration peaks around December followed in many years by a second peak during late austral summer or early autumn, suggesting a bi-modal bloom pattern. The bloom regularity we describe here is in contrast with results of Park et al. (2010) who used a significantly different study area including regions that almost never exhibit bloom conditions.

scholarly journals Spatial hydrochemical structure in surface waters of the Southern ocean between Africa and Antarctica

2021 ◽  
Vol 67 (4) ◽  
pp. 328-347
Author(s):  
K. V. Artamonova ◽  
I. A. Gangnus ◽  
L. A. Dukhova ◽  
V. V. Maslennikov ◽  
N. A. Lavinen
Keyword(s):  
Surface Layer ◽  
Southern Ocean ◽  
Interannual Variability ◽  
High Latitude ◽  
Polar Front ◽  
Hydrochemical Characteristics ◽  
The South ◽  
The North ◽  
The Antarctic ◽  
Subantarctic Front

Some hydrochemical characteristics and, first of all, the main nutrients (phosphorus, nitrogen, silicon) can be used as markers for distinguishing different types of water masses and positions of the main fronts of the Southern Ocean. The seasonal and interannual variability of these characteristics also reflects the character of biological processes in the surface layer of the ocean, which is important for assessing biological productivity. The aim of this study was to analyze the main features of the spatial distribution of hydrochemical characteristics in the surface layer in the Atlantic and Indian Ocean sectors of the Southern Ocean between the Subantarctic Front and the shores of Antarctica and assess their seasonal (spring–autumn) and interannual variability for the observation period from 2008 to 2020. We describe the surface nutrient concentrations between Africa and Antarctica along the transects that cross the Subantarctic Front (SAF) in the north, the Polar Frontal Zone (PFS), Polar Front (PF) and Antarctic Zone water in the south. The findings revealed an increase in dissolved oxygen and nutrients towards the south. Nitrates changed values within the SAF from 15 μM to 24 μM, whereas values from 1.2 μM to 1.7 μM were observed for phosphates. Silicate increased considerably within the Polar Front, from 6.6 μM to 20.8 μM. An analysis was carried out of the seasonal and interannual variability of the hydrochemical conditions in the surface layer of the Southern Ocean. The interannual variability of the nutrients was determined by the spatial variability of the main fronts of the Antarctic Circumpolar Current (ACC) and the intensity of the largescale Weddell Gyre (WG). Since 2017, there has been an increase in the meridional transfer of waters: in the Antarctic Summer 2017–2018, there was a spreading of high-nutrient WG waters toward the north, and in the Summer 2019–2020, the low-nutrient waters anomaly was transferred far to the south (up to 60°S).According to the data obtained, the seasonal dynamics of the nutrients in the surface layer of the Southern Ocean was rather weakly expressed. An exception is the high-latitude waters of the Cooperation and Davis Seas, where maximum seasonal variability of the hydrochemical characteristics was observed. The highest rate of nutrient consumption was observed in the coastal area of the Cooperation Sea near the fast ice edge from mid–December to early January and reached 3.2 μM per day for silicate, 1.8 μM per day for nitrates, and 0.12 μM per day for mineral phosphorus. The results of the long-term monitoring of the hydrochemical conditions in the Cooperation Sea made it possible to distinguish conditionally “warm” years with early vegetation (at the end of December) and intensive consumption of nutrients by phytoplankton, and “cold” years, when the formation of high-latitude “oases” in December–January was not observed.

scholarly journals A Benchmark for Trace Greenhouse Gases in the Arctic Ocean

Eos ◽  
2017 ◽  
Author(s):  
Terri Cook
Keyword(s):  
Nitrous Oxide ◽  
Greenhouse Gases ◽  
Arctic Ocean ◽  
North American ◽  
The Arctic ◽  
The North ◽  
The Arctic Ocean ◽  
North American Arctic

Samples of seawater from the North American Arctic show that the region is neither a major source nor sink of methane and nitrous oxide to the overlying atmosphere.

scholarly journals Sedimentary and atmospheric sources of iron around South Georgia, Southern Ocean: a modelling perspective

2014 ◽  
Vol 11 (7) ◽  
pp. 1981-2001 ◽  
Author(s):  
I. Borrione ◽  
O. Aumont ◽  
M. C. Nielsdóttir ◽  
R. Schlitzer
Keyword(s):  
Southern Ocean ◽  
Phytoplankton Bloom ◽  
Biogeochemical Model ◽  
Dust Deposition ◽  
Data Set ◽  
Western Atlantic ◽  
Atlantic Sector ◽  
South Georgia ◽  
The North ◽  
Mean Square Errors

Abstract. In high-nutrient low-chlorophyll waters of the western Atlantic sector of the Southern Ocean, an intense phytoplankton bloom is observed annually north of South Georgia. Multiple sources, including shallow sediments and atmospheric dust deposition, are thought to introduce iron to the region. However, the relative importance of each source is still unclear, owing in part to the scarcity of dissolved iron (dFe) measurements in the South Georgia region. In this study, we combine results from a recently published dFe data set around South Georgia with a coupled regional hydrodynamic and biogeochemical model to further investigate iron supply around the island. The biogeochemical component of the model includes an iron cycle, where sediments and dust deposition are the sources of iron to the ocean. The model captures the characteristic flow patterns around South Georgia, hence simulating a large phytoplankton bloom to the north (i.e. downstream) of the island. Modelled dFe concentrations agree well with observations (mean difference and root mean square errors of ~0.02 nM and ~0.81 nM) and form a large plume to the north of the island that extends eastwards for more than 800 km. In agreement with observations, highest dFe concentrations are located along the coast and decrease with distance from the island. Sensitivity tests indicate that most of the iron measured in the main bloom area originates from the coast and very shallow shelf-sediments (depths < 20 m). Dust deposition exerts almost no effect on surface chlorophyll a concentrations. Other sources of iron such as run-off and glacial melt are not represented explicitly in the model, however we discuss their role in the local iron budget.

scholarly journals Distribution and recurrence of phytoplankton blooms around South Georgia, Southern Ocean

2012 ◽  
Vol 9 (8) ◽  
pp. 10087-10120 ◽  
Author(s):  
I. Borrione ◽  
R. Schlitzer
Keyword(s):  
Southern Ocean ◽  
Seasonal Cycle ◽  
Austral Summer ◽  
Ocean Colour ◽  
Phytoplankton Blooms ◽  
Chl A ◽  
South Georgia ◽  
The North ◽  
Georgia Basin ◽  
Second Peak

Abstract. South Georgia phytoplankton blooms are amongst the largest of the Southern Ocean and are associated with a rich ecosystem and strong atmospheric carbon drawdown. Both aspects depend on the intensity of blooms, but also on their regularity. Here we use data from 12 yr of SeaWiFS ocean colour imagery and calculate the frequency of bloom occurrence (FBO) to re-examine spatial and temporal bloom distributions. We find that upstream of the island and outside the borders of the Georgia Basin, blooms occurred in less than 4 out of the 12 yr (FBO < 4). In contrast, FBO was mostly greater than 8 downstream of the island, i.e. to the north and northwest, and in places equal to 12, indicating that blooms occurred every year. The typical bloom area, defined as the region where blooms occurred in at least 8 out of the 12 yr, covers the entire Georgia Basin and the northern shelf of the island. The time series of surface chlorophyll-a (chl-a) concentrations averaged over the typical bloom area shows that phytoplankton blooms occurred in every year between September 1997 and September 2010, and that chl-a values followed a clear seasonal cycle, with concentration peaks around December followed in many years by a second peak during late austral summer or early autumn, suggesting a bi-modal bloom pattern. The bloom regularity we describe here is in contrast with results of Park et al. (2010) who used a significantly different study area including regions that almost never exhibit bloom conditions.

scholarly journals High variability of dissolved iron concentrations in the vicinity of Kerguelen Island (Southern Ocean)

2015 ◽  
Vol 12 (1) ◽  
pp. 231-270 ◽  
Author(s):  
F. Quéroué ◽  
G. Sarthou ◽  
H. F. Planquette ◽  
E. Bucciarelli ◽  
F. Chever ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Sediment Resuspension ◽  
Polar Front ◽  
High Variability ◽  
Eastern Coast ◽  
Water Release ◽  
Kerguelen Island ◽  
The North ◽  
Atmospheric Inputs ◽  
Lateral Advection

Abstract. Dissolved Fe (dFe) concentrations were measured in the upper 1300 m of the water column in the vicinity of Kerguelen Island as part of the second Kerguelen Ocean Plateau compared Study (KEOPS2). Concentrations ranged from 0.06 nmol L−1 in offshore, Southern Ocean waters, to 3.82 nmol L−1 within Hillsborough Bay, on the north-eastern coast of Kerguelen Island. Direct island runoff, glacial melting and resuspended sediments were identified as important inputs of dFe that could potentially fertilize the northern part of the plateau. A significant deep dFe enrichment was observed over the plateau with dFe concentrations increasing up to 1.30 nmol L−1 close to the seafloor, probably due to sediment resuspension and pore water release. Biological uptake was identified as a likely explanation for the decrease in dFe concentrations between two visits (28 days apart) at a station above the plateau. Our results allowed studying other processes and sources, such as atmospheric inputs, lateral advection of enriched seawater, remineralization processes and the influence of the Polar Front (PF) as a vector for Fe transport. Overall, heterogeneous sources of Fe over and off the Kerguelen Plateau, in addition to strong variability in Fe supply by vertical or horizontal transport, may explain the high variability in dFe concentrations observed during this study.

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