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 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 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.

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.

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.

A SEDIMENTARY RECORD OF ENVIRONMENTAL CHANGE SINCE 1720 FROM LAKE MATOAKA, WILLIAMSBURG, VIRGINIA

2017 ◽  
Author(s):  
M.G. Meyer ◽  
◽  
K.L. Smith ◽  
N.L. Balascio ◽  
J.M. Kaste
Keyword(s):  
Environmental Change ◽  
Sedimentary Record

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 Using Eulerian and Lagrangian Approaches to Investigate Wind-Driven Changes in the Southern Ocean Abyssal Circulation

2013 ◽  
Vol 44 (2) ◽  
pp. 662-675 ◽  
Author(s):  
Paul Spence ◽  
Erik van Sebille ◽  
Oleg A. Saenko ◽  
Matthew H. England
Keyword(s):  
Southern Ocean ◽  
Wind Stress ◽  
Climate Model ◽  
Meridional Overturning Circulation ◽  
Global Ocean ◽  
Lagrangian Particle ◽  
Stress Changes ◽  
Abyssal Circulation ◽  
Flow Pathways ◽  
Ocean Wind

Abstract This study uses a global ocean eddy-permitting climate model to explore the export of abyssal water from the Southern Ocean and its sensitivity to projected twenty-first-century poleward-intensifying Southern Ocean wind stress. The abyssal flow pathways and transport are investigated using a combination of Lagrangian and Eulerian techniques. In an Eulerian format, the equator- and poleward flows within similar abyssal density classes are increased by the wind stress changes, making it difficult to explicitly diagnose changes in the abyssal export in a meridional overturning circulation framework. Lagrangian particle analyses are used to identify the major export pathways of Southern Ocean abyssal waters and reveal an increase in the number of particles exported to the subtropics from source regions around Antarctica in response to the wind forcing. Both the Lagrangian particle and Eulerian analyses identify transients as playing a key role in the abyssal export of water from the Southern Ocean. Wind-driven modifications to the potential energy component of the vorticity balance in the abyss are also found to impact the Southern Ocean barotropic circulation.

The Southern Ocean benthic fauna and climate change: a historical perspective

1992 ◽  
Vol 338 (1285) ◽  
pp. 299-309 ◽  
Keyword(s):  
Global Warming ◽  
Southern Ocean ◽  
Environmental Change ◽  
Benthic Communities ◽  
Benthic Fauna ◽  
Marine Fauna ◽  
Short Term Change ◽  
Term Change ◽  
Continental Ice Sheets

Environmental change is the norm and it is likely that, particularly on the geological timescale, the temperature regime experienced by marine organisms has never been stable. These temperature changes vary in timescale from daily, through seasonal variations, to long-term environmental change over tens of millions of years. Whereas physiological work can give information on how individual organisms may react phenotypically to short-term change, the way benthic communities react to long-term change can only be studied from the fossil record. The present benthic marine fauna of the Southern Ocean is rich and diverse, consisting of a mixture of taxa with differing evolutionary histories and biogeographical affinities, suggesting that at no time in the Cenozoic did continental ice sheets extend sufficiently to eradicate all shallow-water faunas around Antarctica at the same time. Nevertheless, certain features do suggest the operation of vicariant processes, and climatic cycles affecting distributional ranges and ice-sheet extension may both have enhanced speciation processes. The overall cooling of southern high-latitude seas since the mid-Eocene has been neither smooth nor steady. Intermittent periods of global warming and the influence of Milankovitch cyclicity is likely to have led to regular pulses of migration in and out of Antarctica. The resultant diversity pump may explain in part the high species richness of some marine taxa in the Southern Ocean. It is difficult to suggest how the existing fauna will react to present global warming. Although it is certain the fauna will change, as all faunas have done throughout evolutionary time, we cannot predict with confidence how it will do so.

Detecting Climate Fingerprints in Southern Ocean Carbon using a Biogeochemical Ocean Model

2021 ◽  
Author(s):  
Rebecca Wright ◽  
Corinne Le Quéré ◽  
Erik Buitenhuis ◽  
Dorothee Bakker
Keyword(s):  
Climate Change ◽  
Climate Variability ◽  
Southern Ocean ◽  
Observational Data ◽  
Ecosystem Dynamics ◽  
Global Ocean ◽  
Subsurface Waters ◽  
Climatic Drivers ◽  
Ocean Carbon ◽  
And Storage

<p>The Southern Ocean plays an important role in the uptake, transport and storage of carbon by the global oceans. These properties are dominated by the response to the rise in anthropogenic CO<sub>2</sub> in the atmosphere, but they are modulated by climate variability and climate change. Here we explore the effect of climate variability and climate change on ocean carbon uptake and storage in the Southern Ocean. We assess the extent to which climate change may be distinguishable from the anthropogenic CO<sub>2</sub> signal and from the natural background variability. We use a combination of biogeochemical ocean modelling and observations from the GLODAPv2020 database to detect climate fingerprints in dissolved inorganic carbon (DIC).</p><p>We conduct an ensemble of hindcast model simulations of the period 1920-2019, using a global ocean biogeochemical model which incorporates plankton ecosystem dynamics based on twelve plankton functional types. We use the model ensemble to isolate the changes in DIC due to rising anthropogenic CO<sub>2</sub> alone and the changes due to climatic drivers (both climate variability and climate change), to determine their relative roles in the emerging total DIC trends and patterns. We analyse these DIC trends for a climate fingerprint over the past four decades, across spatial scales from the Southern Ocean, to basin level and down to regional ship transects. Highly sampled ship transects were extracted from GLODAPv2020 to obtain locations with the maximum spatiotemporal coverage, to reduce the inherent biases in patchy observational data. Model results were sampled to the ship transects to compare the climate fingerprints directly to the observational data.</p><p>Model results show a substantial change in DIC over a 35-year period, with a range of more than +/- 30 µmol/L. In the surface ocean, both anthropogenic CO<sub>2</sub> and climatic drivers act to increase DIC concentration, with the influence of anthropogenic CO<sub>2</sub> dominating at lower latitudes and the influence of climatic drivers dominating at higher latitudes. In the deep ocean, the anthropogenic CO<sub>2</sub> generally acts to increase DIC except in the subsurface waters at lower latitudes, while climatic drivers act to decrease DIC concentration. The combined fingerprint of anthropogenic CO<sub>2</sub> and climatic drivers on DIC concentration is for an increasing trend at the surface and decreasing trends in low latitude subsurface waters. Preliminary comparison of the model fingerprints to observational ship transects will also be presented.</p>

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