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

2013 ◽  
Vol 10 (7) ◽  
pp. 10811-10858
Author(s):  
I. Borrione ◽  
O. Aumont ◽  
M. C. Nielsdóttir ◽  
R. Schlitzer
Keyword(s):  
Southern Ocean ◽  
Phytoplankton Bloom ◽  
Biogeochemical Model ◽  
Minor Role ◽  
Dust Deposition ◽  
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, most likely due to an enhanced supply of the limiting micronutrient iron. Shallow sediments and atmospheric dust deposition are believed to be the main iron sources. However, their relative importance is still unclear and in the South Georgia region have yet not been ascertained because iron measurements are very few. In this study, we use austral summer dissolved iron (dFe) data around South Georgia (January and February 2008) with a coupled regional hydrodynamic and biogeochemical model to investigate natural iron fertilization 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 the very shallow shelf-sediments (depths < 20 m) while dust deposition plays a minor role, with almost no effects on surface chlorophyll a concentrations. Iron sources such as run-off not represented explicitly in the model, but that likely contribute to the iron plumes observed around South Georgia, are also discussed together with the potential effects their temporal variability may have on the system.

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

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.

Dust and pyrogenic iron boost phytoplankton blooms in sub-Antarctic waters of the Tasman Sea

2020 ◽  
Author(s):  
Joan Llort ◽  
Richard J. Matear ◽  
Pete G. Strutton ◽  
Andrew R. Bowie ◽  
Zanna Chase
Keyword(s):  
Atmospheric Deposition ◽  
Atmospheric Aerosols ◽  
Phytoplankton Bloom ◽  
Early Summer ◽  
Biogeochemical Model ◽  
Dust Deposition ◽  
Bloom Period ◽  
Tasman Sea ◽  
Dust Events ◽  
Upper Mixed Layer

&lt;p&gt;Although it is commonly accepted that atmospheric deposition of Fe particles can fertilise phytoplankton, there is yet no clear evidence on how such a fertilisation effect takes place. Several studies have attempted to link individual dust events with surface chlorophyll responses but generally, they do not find a clear correspondence between dust deposition and its impact on chlorophyll. In this work, we use a biogeochemical model to show that the atmospheric deposition of Fe in high-latitude seas, rather than creating instantaneous phytoplankton responses, replenish the upper mixed layer of the ocean during the pre-bloom period, from winter to early summer. The Fe accumulated at the surface boosts the phytoplankton bloom of the following summer, resulting in surface chlorophyll accumulations of up to 3 times larger than the years without atmospheric deposition. We used this mechanism to explain the strong inter-annual variability of the phytoplankton bloom in sub-Antarctic iron-limited waters east of Australia. Putting together more than a 15-years-long record of ocean colour observations and atmospheric aerosols reanalysis we uncovered a strong correlation (r&lt;sup&gt;2&lt;/sup&gt;&gt;0.6) between the dust that crossed the region during the pre-bloom period and the magnitude of the surface chlorophyll bloom. Interestingly, the correlation increased when taking into account pyrogenic aerosols in addition to dust. Our study presents the first observational link between Climate Change-enhanced droughts and wildfires, atmospheric aerosols and primary production of iron-limited waters.&lt;/p&gt;

scholarly journals Labile Fe(II) concentrations in the Atlantic sector of the Southern Ocean along a transect from the subtropical domain to the Weddell Sea Gyre

2011 ◽  
Vol 8 (9) ◽  
pp. 2461-2479 ◽  
Author(s):  
G. Sarthou ◽  
E. Bucciarelli ◽  
F. Chever ◽  
S. P. Hansard ◽  
M. González-Dávila ◽  
...  
Keyword(s):  
Detection Limit ◽  
Southern Ocean ◽  
Weddell Sea ◽  
Surface Mixed Layer ◽  
Data Set ◽  
Atlantic Sector ◽  
Local Maxima ◽  
Oxidation Rates ◽  
The North ◽  
Deep Waters

Abstract. Labile Fe(II) distributions were investigated in the Sub-Tropical South Atlantic and the Southern Ocean during the BONUS-GoodHope cruise from 34 to 57° S (February–March 2008). Concentrations ranged from below the detection limit (0.009 nM) to values as high as 0.125 nM. In the surface mixed layer, labile Fe(II) concentrations were always higher than the detection limit, with values higher than 0.060 nM south of 47° S, representing between 39 % and 63 % of dissolved Fe (DFe). Apparent biological production of Fe(II) was evidenced. At intermediate depth, local maxima were observed, with the highest values in the Sub-Tropical domain at around 200 m, and represented more than 70 % of DFe. Remineralization processes were likely responsible for those sub-surface maxima. Below 1500 m, concentrations were close to or below the detection limit, except at two stations (at the vicinity of the Agulhas ridge and in the north of the Weddell Sea Gyre) where values remained as high as ~0.030–0.050 nM. Hydrothermal or sediment inputs may provide Fe(II) to these deep waters. Fe(II) half life times (t1/2) at 4°C were measured in the upper and deep waters and ranged from 2.9 to 11.3 min, and from 10.0 to 72.3 min, respectively. Measured values compared quite well in the upper waters with theoretical values from two published models, but not in the deep waters. This may be due to the lack of knowledge for some parameters in the models and/or to organic complexation of Fe(II) that impact its oxidation rates. This study helped to considerably increase the Fe(II) data set in the Ocean and to better understand the Fe redox cycle.

Bio-Optical Models for Estimating Euphotic Zone Depth in the Western Atlantic Sector of the Southern Ocean in the Antarctic Summer

2021 ◽  
pp. 241-250
Author(s):  
Pavel A. Salyuk ◽  
Vladimir A. Artemiev ◽  
Dmitry I. Glukhovets ◽  
Alexander N. Khrapko ◽  
Anatoly V. Grigoriev ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Euphotic Zone ◽  
Western Atlantic ◽  
Atlantic Sector ◽  
Zone Depth ◽  
The Antarctic

Decadal Relationship between European Blocking and the North Atlantic Oscillation during 1978–2011. Part I: Atlantic Conditions

2015 ◽  
Vol 72 (3) ◽  
pp. 1152-1173 ◽  
Author(s):  
Dehai Luo ◽  
Yao Yao ◽  
Aiguo Dai
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Western Europe ◽  
Storm Track ◽  
Western Atlantic ◽  
Atlantic Sector ◽  
The North ◽  
Nao Index ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract Both the positive and negative phases of the North Atlantic Oscillation (NAO+ and NAO−, respectively) and atmospheric blocking in the Euro-Atlantic sector reflect synoptic variability over the region and thus are intrinsically linked. This study examines their relationship from a decadal change perspective. Since the winter-mean NAO index is defined as a time average of instantaneous NAO indices over the whole winter, it is unclear how the activity of European blocking (EB) events can be related to the variation of the positive mean NAO index. Here, this question is examined by dividing the winter period 1978–2011 into two decadal epochs: 1978–94 (P1) with an increasing and high NAO index and 1995–2011 (P2) with a decreasing and low NAO index. Using atmospheric reanalysis data, it is shown that there are more intense and persistent EB events in eastern Europe during P1 than during P2, while the opposite is true for western Europe. It is further shown that there are more NAO+ (NAO−) events during P1 (P2). The EB events associated with NAO+ events extend more eastward and are associated with stronger Atlantic mean zonal wind and weaker western Atlantic storm track during P1 than during P2, but EB events associated with NAO− events increase in western Europe under opposite Atlantic conditions during P2. Thus, the increase in the number of individual NAO+ (NAO−) events results in more EB events in eastern (western) Europe during P1 (P2). The EB change is also associated with the increased frequency of NAO− to NAO+ (NAO+ to NAO−) transition events.

Abrupt Cooling of Antarctic Surface Waters and Sea Ice Expansion in the South Atlantic Sector of the Southern Ocean at 5000 cal yr B.P.

2001 ◽  
Vol 56 (2) ◽  
pp. 191-198 ◽  
Author(s):  
David A. Hodell ◽  
Sharon L. Kanfoush ◽  
Aldo Shemesh ◽  
Xavier Crosta ◽  
Christopher D. Charles ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Surface Waters ◽  
Climate Changes ◽  
Ice Core ◽  
South Atlantic ◽  
The South ◽  
Atlantic Sector ◽  
Middle Holocene ◽  
The North

AbstractAntarctic surface waters were warm and ice free between 10,000 and 5000 cal yr B.P., as judged from ice-rafted debris and microfossils in a piston core at 53°S in the South Atlantic. This evidence shows that about 5000 cal yr B.P., sea surface temperatures cooled, sea ice advanced, and the delivery of ice-rafted detritus (IRD) to the subantarctic South Atlantic increased abruptly. These changes mark the end of the Hypsithermal and onset of Neoglacial conditions. They coincide with an early Neoglacial advance of mountain glaciers in South America and New Zealand between 5400 and 4900 cal yr B.P., rapid middle Holocene climate changes inferred from the Taylor Dome Ice Core (Antarctica), cooling and increased IRD in the North Atlantic, and the end of the African humid period. The near synchrony and abruptness of all these climate changes suggest links among the tropics and both poles that involved nonlinear response to gradual changes in Northern Hemisphere insolation. Sea ice expansion in the Southern Ocean may have provided positive feedback that hastened the end of the Hypsithermal and African humid periods in the middle Holocene.

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 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.

Was the onset of interhemispheric AMOC slightly prior to Antarctic glaciation at the Eocene-Oligocene transition?

2020 ◽  
Author(s):  
Meir Abelson ◽  
Jonathan Erez
Keyword(s):  
Southern Ocean ◽  
North Atlantic ◽  
Deep Ocean ◽  
Meridional Overturning Circulation ◽  
Atlantic Sector ◽  
The North ◽  
Global Cooling ◽  
Circulation Cell ◽  
Meridional Overturning ◽  
Circumpolar Current

&lt;p&gt;A compilation of benthic &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O from the whole Atlantic and the Southern Ocean (Atlantic sector), shows two major jumps in the interbasinal gradient of d&lt;sup&gt;18&lt;/sup&gt;O (&amp;#916;&amp;#948;&lt;sup&gt;18&lt;/sup&gt;O) during the Eocene and the Oligocene: One at ~40 Ma and the second concomitant with the isotopic event of the Eocene-Oligocene transition (EOT), ~33.7 Ma ago. From previously published circulation models, we show that the first &amp;#916;&amp;#948;&lt;sup&gt;18&lt;/sup&gt;O jump reflects the thermal isolation of Antarctica associated with the proto-Antarctic circumpolar current (ACC). The second marks the onset of interhemispheric northern-sourced circulation cell, similar to the modern Atlantic meridional overturning circulation (AMOC). The onset of AMOC-like circulation probably slightly preceded (100-300 ky) the EOT, as we show by the high resolution profiles of &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O and &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C previously published from DSDP/ODP sites in the Southern Ocean and South Atlantic. We suggest that while the shallow proto-ACC supplied the energy for deep ocean convection in the Southern Hemisphere, the onset of the interhemispheric northern circulation cell was due to the significant EOT intensification of deepwater formation in the North Atlantic driven by the Nordic anti-estuarine circulation. This onset of the interhemispheric northern-sourced circulation cell could have prompted the EOT global cooling.&lt;/p&gt;

Sign in / Sign up

Export Citation Format

Share Document