scholarly journals Coccolithophore populations and their contribution to carbonate export during an annual cycle in the Australian sector of the Antarctic Zone

2017 ◽  
Author(s):  
Andrés S. Rigual Hernández ◽  
José A. Flores ◽  
Francisco J. Sierro ◽  
Miguel A. Fuertes ◽  
Lluïsa Cros ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Ocean Acidification ◽  
Deep Ocean ◽  
Sediment Traps ◽  
Emiliania Huxleyi ◽  
Global Ocean ◽  
Field Observations ◽  
Allochthonous Species ◽  
Circumpolar Current ◽  
The Antarctic

Abstract. The Southern Ocean is experiencing rapid and relentless change in its physical and biogeochemical properties. The rate of warming of the Antarctic Circumpolar Current exceeds that of the global ocean, and the enhanced uptake of carbon dioxide is causing basin-wide ocean acidification. Observational data suggest that these changes are influencing the distribution and composition of pelagic plankton communities. Long-term and annual field observations on key environmental variables and organisms are a critical basis for predicting changes in Southern Ocean ecosystems. These observations are particularly needed, since high-latitude systems have been projected to experience the most severe impacts of ocean acidification and invasions of allochthonous species. Coccolithophores are the most prolific calcium carbonate producing phytoplankton group, playing an important role in Southern Ocean biogeochemical cycles. Satellite imagery has revealed elevated particulate inorganic carbon concentrations near the major circumpolar fronts of the Southern Ocean, that can be attributed to the coccolithophore Emiliania huxleyi. Recent studies have suggested changes during the last decades in the distribution and abundance of Southern Ocean coccolithophores. However, due to limited field observations, the distribution, diversity and state of coccolithophore populations in the Southern Ocean remain poorly characterized. We report here on seasonal variations in the abundance and composition of coccolithophore assemblages collected by two moored sediment traps deployed in the deep ocean (~ 2000 and 3700 m) in the Australian sector of the Antarctic Zone for one year in 2001–02. Additionally, seasonal changes in coccolith weights of E. huxleyi populations were estimated using circularly polarized micrographs analysed with C-Calcita software. Our findings indicate that (1) coccolithophore sinking assemblages were nearly monospecific for Emiliania huxleyi morphotype B/C in the Antarctic Zone waters in 2001–2002; (2) coccolith assemblages experienced weight and length reduction during the summer months; (3) the estimated annual coccolith weight of E. huxleyi at both sediment trap depths (2.11 ± 0.96 and 2.13 ± 0.90 pg at 2000 m and 3700 m) was consistent with previous studies for morphotype B/C in other Southern Ocean settings; (4) coccolithophores accounted for approximately 2–5 % of the annual, deep-ocean CaCO3 flux. Our results are the first annual record of coccolithophore abundance, composition and degree of calcification in the Antarctic Zone. They provide a baseline against which to monitor coccolithophorid responses to changes in environmental conditions expected for this region in coming decades.

scholarly journals Coccolithophore populations and their contribution to carbonate export during an annual cycle in the Australian sector of the Antarctic zone

2018 ◽  
Vol 15 (6) ◽  
pp. 1843-1862 ◽  
Author(s):  
Andrés S. Rigual Hernández ◽  
José A. Flores ◽  
Francisco J. Sierro ◽  
Miguel A. Fuertes ◽  
Lluïsa Cros ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Ocean Acidification ◽  
Deep Ocean ◽  
Sediment Traps ◽  
Global Ocean ◽  
Field Observations ◽  
Scotia Sea ◽  
Allochthonous Species ◽  
Circumpolar Current ◽  
The Antarctic

Abstract. The Southern Ocean is experiencing rapid and relentless change in its physical and biogeochemical properties. The rate of warming of the Antarctic Circumpolar Current exceeds that of the global ocean, and the enhanced uptake of carbon dioxide is causing basin-wide ocean acidification. Observational data suggest that these changes are influencing the distribution and composition of pelagic plankton communities. Long-term and annual field observations on key environmental variables and organisms are a critical basis for predicting changes in Southern Ocean ecosystems. These observations are particularly needed, since high-latitude systems have been projected to experience the most severe impacts of ocean acidification and invasions of allochthonous species. Coccolithophores are the most prolific calcium-carbonate-producing phytoplankton group playing an important role in Southern Ocean biogeochemical cycles. Satellite imagery has revealed elevated particulate inorganic carbon concentrations near the major circumpolar fronts of the Southern Ocean that can be attributed to the coccolithophore Emiliania huxleyi. Recent studies have suggested changes during the last decades in the distribution and abundance of Southern Ocean coccolithophores. However, due to limited field observations, the distribution, diversity and state of coccolithophore populations in the Southern Ocean remain poorly characterised. We report here on seasonal variations in the abundance and composition of coccolithophore assemblages collected by two moored sediment traps deployed at the Antarctic zone south of Australia (2000 and 3700 m of depth) for 1 year in 2001–2002. Additionally, seasonal changes in coccolith weights of E. huxleyi populations were estimated using circularly polarised micrographs analysed with C-Calcita software. Our findings indicate that (1) coccolithophore sinking assemblages were nearly monospecific for E. huxleyi morphotype B/C in the Antarctic zone waters in 2001–2002; (2) coccoliths captured by the traps experienced weight and length reduction during summer (December–February); (3) the estimated annual coccolith weight of E. huxleyi at both sediment traps (2.11 ± 0.96 and 2.13 ± 0.91 pg at 2000 and 3700 m) was consistent with previous studies for morphotype B/C in other Southern Ocean settings (Scotia Sea and Patagonian shelf); and (4) coccolithophores accounted for approximately 2–5 % of the annual deep-ocean CaCO3 flux. Our results are the first annual record of coccolithophore abundance, composition and degree of calcification in the Antarctic zone. They provide a baseline against which to monitor coccolithophore responses to changes in the environmental conditions expected for this region in coming decades.

Has (anthropogenic) climate change driven subantarctic Emiliania huxleyi populations beyond their natural state?

2021 ◽  
Author(s):  
Andres S. Rigual-Hernandez ◽  
Francisco J. Sierro ◽  
José A. Flores ◽  
José M. Sánchez-Santos ◽  
Ruth S. Eriksen ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Environmental Change ◽  
Ocean Acidification ◽  
Emiliania Huxleyi ◽  
Global Ocean ◽  
Natural State ◽  
Sedimentary Record ◽  
Subtle Change ◽  
Assemblage Composition ◽  
Biogeographical Distribution

<p>The global ocean acts as a climate regulator through the uptake of Earth’s excess heat and the absorption of about 30% of anthropogenic CO<sub>2</sub> emissions since 1750.  Southern Ocean waters are warming faster than the global ocean average and their low temperatures and moderate alkalinity make this region especially vulnerable to ocean acidification. Coccolithophores are a major group of calcifying phytoplankton and an important component of the Southern Ocean carbon cycle. Controlled laboratory experiments on <em>Emiliania huxleyi </em>(the most abundant coccolithophore) over a broad range of carbonate chemistry scenarios suggest that this taxon may be susceptible to ongoing environmental change. However, it remains uncertain whether Southern Ocean coccolithophore populations have been modified by environmental change during the industrial era. The main reason for this knowledge gap is the lack of observational data since the onset of the Industrial Revolution. In particular, continuous monitoring of key Southern Ocean ecosystems only started a few decades ago, a period insufficiently long to permit assessments of whether anthropogenic impacts on the environment have affected coccolithophore populations beyond their natural state. In order to overcome this limitation, here we take advantage of the preservation capacity of coccolithophores in the sedimentary record to provide a benchmark of their pre-industrial state. We compare the morphotype assemblage composition and morphometric parameters in coccoliths of <em>E. huxleyi </em>from a suite of Holocene-aged sediments south of Tasmania with annual sediment trap records retrieved at the Southern Ocean Time Series observatory in the Australian sector of the Subantarctic Zone. Our results suggest that carbonate dissolution in the sediments reduced the coccolith mass and length of the coccoliths but, coccolith thickness appeared to be decoupled from dissolution. The biogeographical distribution of coccolith thickness in subtropical and subantarctic sediments mirrored the distribution of E. huxleyi morphotypes, highlighting the important role of <em>E. huxleyi </em>assemblage composition on the control of coccolith morphometrics. Moreover, comparison of coccolith assemblages from the sedimentary record with those collected from subantarctic sediment traps indicates that modern E. huxleyi coccoliths are about 2% thinner than those from the pre-industrial Holocene. The subtle change in coccolith thickness is in stark contrast with previous work that documented a dramatic reduction in shell calcification in the planktonic foraminifera <em>Globigerina bulloides </em>that resulted in a shell-weight decrease of 30-35%, most likely induced by ocean acidification. Overall, our results underscore the variable sensitivity of different marine calcifying plankton groups to ongoing environmental change in the Southern Ocean.</p>

scholarly journals Southern Ocean circulation

2005 ◽  
Vol 32 (2) ◽  
pp. 265-280 ◽  
Author(s):  
Stuart A. Cunningham
Keyword(s):  
Southern Ocean ◽  
Ocean Circulation ◽  
Antarctic Circumpolar Current ◽  
Three Dimensional ◽  
Deep Ocean ◽  
Ocean Basin ◽  
Ocean Dynamics ◽  
Circumpolar Current ◽  
Earth’S Climate ◽  
The Antarctic

The Discovery Investigations of the 1930s provided a compelling description of the main elements of the Southern Ocean circulation. Over the intervening years, this has been extended to include ideas on ocean dynamics based on physical principles. In the modern description, the Southern Ocean has two main circulations that are intimately linked: a zonal (west-east) circumpolar circulation and a meridional (north-south) overturning circulation. The Antarctic Circumpolar Current transports around 140 million cubic metres per second west to east around Antarctica. This zonal circulation connects the Atlantic, Indian and Pacific Oceans, transferring and blending water masses and properties from one ocean basin to another. For the meridional circulation, a key feature is the ascent of waters from depths of around 2,000 metres north of the Antarctic Circumpolar Current to the surface south of the Current. In so doing, this circulation connects deep ocean layers directly to the atmosphere. The circumpolar zonal currents are not stable: meanders grow and separate, creating eddies and these eddies are critical to the dynamics of the Southern Ocean, linking the zonal circumpolar and meridional circulations. As a result of this connection, a global three-dimensional ocean circulation exists in which the Southern Ocean plays a central role in regulating the Earth's climate.

scholarly journals Role of Residual Overturning for the Sensitivity of Southern Ocean Isopycnal Slopes to Changes in Wind Forcing

2019 ◽  
Vol 49 (11) ◽  
pp. 2867-2881
Author(s):  
Madeleine K. Youngs ◽  
Glenn R. Flierl ◽  
Raffaele Ferrari
Keyword(s):  
Southern Ocean ◽  
Wind Stress ◽  
Antarctic Circumpolar Current ◽  
Channel Model ◽  
Critical Level ◽  
Wind Forcing ◽  
Global Ocean ◽  
Circumpolar Current ◽  
The Antarctic

AbstractThe Antarctic Circumpolar Current plays a central role in the ventilation of heat and carbon in the global ocean. In particular, the isopycnal slopes determine where each water mass outcrops and thus how the ocean interacts with the atmosphere. The region-integrated isopycnal slopes have been suggested to be eddy saturated, that is, stay relatively constant as the wind forcing changes, but whether or not the flow is saturated in realistic present day and future parameter regimes is unknown. This study analyzes an idealized two-layer quasigeostrophic channel model forced by a wind stress and a residual overturning generated by a mass flux across the interface between the two layers, with and without a blocking ridge. The sign and strength of the residual overturning set which way the isopycnal slopes change with the wind forcing, leading to an increase in slope with an increase in wind forcing for a positive overturning and a decrease in slope for a negative overturning, following the usual conventions; this behavior is caused by the dominant standing meander weakening as the wind stress weakens causing the isopycnal slopes to become more sensitive to changes in the wind stress and converge with the slopes of a flat-bottomed simulation. Eddy saturation only appears once the wind forcing passes a critical level. These results show that theories for saturation must have both topography and residual overturning in order to be complete and provide a framework for understanding how the isopycnal slopes in the Southern Ocean may change in response to future changes in wind forcing.

scholarly journals The Effect of the Kerguelen Plateau on the Ocean Circulation

2016 ◽  
Vol 46 (11) ◽  
pp. 3385-3396 ◽  
Author(s):  
Jinbo Wang ◽  
Matthew R. Mazloff ◽  
Sarah T. Gille
Keyword(s):  
Southern Ocean ◽  
Ocean Circulation ◽  
Antarctic Circumpolar Current ◽  
Large Scale ◽  
Pressure Field ◽  
Global Ocean ◽  
Kerguelen Plateau ◽  
Local Pressure ◽  
Circumpolar Current ◽  
The Antarctic

AbstractThe Kerguelen Plateau is a major topographic feature in the Southern Ocean. Located in the Indian sector and spanning nearly 2000 km in the meridional direction from the polar to the subantarctic region, it deflects the eastward-flowing Antarctic Circumpolar Current and influences the physical circulation and biogeochemistry of the Southern Ocean. The Kerguelen Plateau is known to govern the local dynamics, but its impact on the large-scale ocean circulation has not been explored. By comparing global ocean numerical simulations with and without the Kerguelen Plateau, this study identifies two major Kerguelen Plateau effects: 1) The plateau supports a local pressure field that pushes the Antarctic Circumpolar Current northward. This process reduces the warm-water transport from the Indian to the Atlantic Ocean. 2) The plateau-generated pressure field shields the Weddell Gyre from the influence of the warmer subantarctic and subtropical waters. The first effect influences the strength of the Antarctic Circumpolar Current and the Agulhas leakage, both of which are important elements in the global thermohaline circulation. The second effect results in a zonally asymmetric response of the subpolar gyres to Southern Hemisphere wind forcing.

On the impact of sea ice in a global ocean circulation model

1997 ◽  
Vol 25 ◽  
pp. 111-115 ◽  
Author(s):  
Achim Stössel
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Ocean Circulation ◽  
General Circulation ◽  
Thermohaline Circulation ◽  
Circulation Model ◽  
Deep Ocean ◽  
Global Ocean ◽  
Convective Activity ◽  
The Impact

This paper investigates the long-term impact of sea ice on global climate using a global sea-ice–ocean general circulation model (OGCM). The sea-ice component involves state-of-the-art dynamics; the ocean component consists of a 3.5° × 3.5° × 11 layer primitive-equation model. Depending on the physical description of sea ice, significant changes are detected in the convective activity, in the hydrographic properties and in the thermohaline circulation of the ocean model. Most of these changes originate in the Southern Ocean, emphasizing the crucial role of sea ice in this marginally stably stratified region of the world's oceans. Specifically, if the effect of brine release is neglected, the deep layers of the Southern Ocean warm up considerably; this is associated with a weakening of the Southern Hemisphere overturning cell. The removal of the commonly used “salinity enhancement” leads to a similar effect. The deep-ocean salinity is almost unaffected in both experiments. Introducing explicit new-ice thickness growth in partially ice-covered gridcells leads to a substantial increase in convective activity, especially in the Southern Ocean, with a concomitant significant cooling and salinification of the deep ocean. Possible mechanisms for the resulting interactions between sea-ice processes and deep-ocean characteristics are suggested.

scholarly journals Ventilation of the abyss in the Atlantic sector of the Southern Ocean

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Camille Hayatte Akhoudas ◽  
Jean-Baptiste Sallée ◽  
F. Alexander Haumann ◽  
Michael P. Meredith ◽  
Alberto Naveira Garabato ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Bottom Water ◽  
Climate Models ◽  
Deep Ocean ◽  
Analytical Framework ◽  
Weddell Sea ◽  
Global Ocean ◽  
Shelf Water ◽  
Antarctic Bottom Water ◽  
Atlantic Sector

AbstractThe Atlantic sector of the Southern Ocean is the world’s main production site of Antarctic Bottom Water, a water-mass that is ventilated at the ocean surface before sinking and entraining older water-masses—ultimately replenishing the abyssal global ocean. In recent decades, numerous attempts at estimating the rates of ventilation and overturning of Antarctic Bottom Water in this region have led to a strikingly broad range of results, with water transport-based calculations (8.4–9.7 Sv) yielding larger rates than tracer-based estimates (3.7–4.9 Sv). Here, we reconcile these conflicting views by integrating transport- and tracer-based estimates within a common analytical framework, in which bottom water formation processes are explicitly quantified. We show that the layer of Antarctic Bottom Water denser than 28.36 kg m$$^{-3}$$ - 3 $$\gamma _{n}$$ γ n is exported northward at a rate of 8.4 ± 0.7 Sv, composed of 4.5 ± 0.3 Sv of well-ventilated Dense Shelf Water, and 3.9 ± 0.5 Sv of old Circumpolar Deep Water entrained into cascading plumes. The majority, but not all, of the Dense Shelf Water (3.4 ± 0.6 Sv) is generated on the continental shelves of the Weddell Sea. Only 55% of AABW exported from the region is well ventilated and thus draws down heat and carbon into the deep ocean. Our findings unify traditionally contrasting views of Antarctic Bottom Water production in the Atlantic sector, and define a baseline, process-discerning target for its realistic representation in climate models.

scholarly journals Interannual response of global ocean hindcasts to a satellite-based correction of precipitation fluxes

2012 ◽  
Vol 9 (2) ◽  
pp. 611-648 ◽  
Author(s):  
A. Storto ◽  
I. Russo ◽  
S. Masina
Keyword(s):  
Ocean Circulation ◽  
Surface Current ◽  
Global Ocean ◽  
Surface Salinity ◽  
Near Surface ◽  
Convergence Zones ◽  
Circumpolar Current ◽  
The Tropics ◽  
Spatially Varying ◽  
The Antarctic

Abstract. We present a methodology to correct precipitation fluxes from the ECMWF atmospheric reanalysis (ERA-Interim) for oceanographic applications. The correction is performed by means of a spatially varying monthly climatological coefficient, computed within the period 1989–2008 by comparison between ERA-Interim and a satellite-based passive microwave precipitation product. ERA-Interim exhibits a systematic over-estimation of precipitation within the inter-tropical convergence zones (up to 3 mm d−1) and under-estimation at mid- and high- latitudes (up to −4 mm d−1). The correction has been validated within eddy-permitting resolution global ocean hindcasts (1989–2009), demonstrating the ability of our strategy in attenuating the 20-yr mean global EMP negative imbalance by 16%, reducing the near-surface salinity fresh bias in the Tropics up to 1 psu and improving the representation of the sea level interannual variability, with an SSH error decrease of 8%. The ocean circulation is also proved to benefit from the correction, especially in correspondence of the Antarctic Circumpolar Current, where the error in the near-surface current speed decreases by a 9%. Finally, we show that the correction leads to volume and freshwater transports that better agree with independent estimates.

scholarly journals The Effects of Combined Ocean Acidification and Nanoplastic Exposures on the Embryonic Development of Antarctic Krill

2021 ◽  
Vol 8 ◽  
Author(s):  
Emily Rowlands ◽  
Tamara Galloway ◽  
Matthew Cole ◽  
Ceri Lewis ◽  
Victoria Peck ◽  
...  
Keyword(s):  
Embryonic Development ◽  
Southern Ocean ◽  
Ocean Acidification ◽  
Antarctic Krill ◽  
Gravid Female ◽  
Limb Bud ◽  
Global Ocean ◽  
Plastic Pollution ◽  
Atlantic Sector ◽  
Scotia Sea

In aquatic environments, plastic pollution occurs concomitantly with anthropogenic climate stressors such as ocean acidification. Within the Southern Ocean, Antarctic krill (Euphausia Superba) support many marine predators and play a key role in the biogeochemical cycle. Ocean acidification and plastic pollution have been acknowledged to hinder Antarctic krill development and physiology in singularity, however potential multi-stressor effects of plastic particulates coupled with ocean acidification are unexplored. Furthermore, Antarctic krill may be especially vulnerable to plastic pollution due to their close association with sea-ice, a known plastic sink. Here, we investigate the behaviour of nanoplastic [spherical, aminated (NH2), and yellow-green fluorescent polystyrene nanoparticles] in Antarctic seawater and explore the single and combined effects of nanoplastic (160 nm radius, at a concentration of 2.5 μg ml–1) and ocean acidification (pCO2 ∼900, pHT 7.7) on the embryonic development of Antarctic krill. Gravid female krill were collected in the Atlantic sector of the Southern Ocean (North Scotia Sea). Produced eggs were incubated at 0.5 °C in four treatments (control, nanoplastic, ocean acidification and the multi-stressor scenario of nanoplastic presence, and ocean acidification) and their embryonic development after 6 days, at the incubation endpoint, was determined. We observed that negatively charged nanoplastic particles suspended in seawater from the Scotia Sea aggregated to sizes exceeding the nanoscale after 24 h (1054.13 ± 53.49 nm). Further, we found that the proportion of embryos developing through the early stages to reach at least the limb bud stage was highest in the control treatment (21.84%) and lowest in the multi-stressor treatment (13.17%). Since the biological thresholds to any stressors can be altered by the presence of additional stressors, we propose that future nanoplastic ecotoxicology studies should consider the changing global ocean under future climate scenarios for assessments of their impact and highlight that determining the behaviour of nanoplastic particles used in incubation studies is critical to determining their toxicity.

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