Glacial melt disturbance shifts community metabolism of an Antarctic seafloor ecosystem from net autotrophy to heterotrophy

AbstractClimate change-induced glacial melt affects benthic ecosystems along the West Antarctic Peninsula, but current understanding of the effects on benthic primary production and respiration is limited. Here we demonstrate with a series of in situ community metabolism measurements that climate-related glacial melt disturbance shifts benthic communities from net autotrophy to heterotrophy. With little glacial melt disturbance (during cold El Niño spring 2015), clear waters enabled high benthic microalgal production, resulting in net autotrophic benthic communities. In contrast, water column turbidity caused by increased glacial melt run-off (summer 2015 and warm La Niña spring 2016) limited benthic microalgal production and turned the benthic communities net heterotrophic. Ongoing accelerations in glacial melt and run-off may steer shallow Antarctic seafloor ecosystems towards net heterotrophy, altering the metabolic balance of benthic communities and potentially impacting the carbon balance and food webs at the Antarctic seafloor.

Download Full-text

Antarctic Peninsula warming triggers enhanced basal melt rates throughout West Antarctica

10.5194/egusphere-egu21-10418 ◽

2021 ◽

Author(s):

Andrew Thompson ◽

Mar Flexas ◽

Michael Schodlok ◽

Kevin Speer

Keyword(s):

Antarctic Peninsula ◽

Ocean Circulation ◽

Heat Fluxes ◽

Coastal Current ◽

West Antarctica ◽

Ice Shelf ◽

West Antarctic ◽

Freshwater Forcing ◽

Run Off ◽

The Antarctic

The acceleration of ice-shelf basal melt rates throughout West Antarctica, as well as their potential to destabilize the ice sheets they buttress, is well documented. &#160;Yet, the mechanisms that determine both trends and variability of these melt rates remain uncertain. &#160;Explanations for the intensification of melting have largely focused on local processes in seas surrounding the ice shelves, including variations in wind stress over the continental slope and shelf. &#160;Here, we show that non-local freshwater forcing, propagated between shelf seas by the Antarctic Coastal Current (AACC), can have a significant impact on ice-shelf melt rates. &#160;We present results from a suite of high-resolution (~3-km) numerical simulations of the ocean circulation in West Antarctica that includes a dynamic sea-ice field, ice-shelf cavities and forcing from ice shelf-ocean interactions. &#160;Motivated by persistent warming at the northern Antarctic Peninsula since the 1950&#8217;s, freshwater perturbations are applied to the West Antarctic Peninsula. &#160;This leads to a strengthening of the AACC and a westward propagation of the freshwater signal. &#160;Critically, basal melt rates increase throughout the WAP, Bellingshausen and Amundsen Seas in response to this perturbation. &#160;The freshwater anomalies stratify the ocean surface near the coast, enhancing lateral heat fluxes that lead to greater ice-shelf melt rates. &#160;A suite of sensitivity studies show that changes in meltrates are linearly proportional to the magnitude of the freshwater anomaly, changing by as much as 30% for realistic perturbations, but are relatively insensitive to the distribution of the perturbation across the WAP shelf. &#160;These results indicate that glacial run-off on the Antarctic Peninsula, one of the first signatures of a warming climate in Antarctica, could be a key trigger for increased melt rates in the Amundsen and Bellingshausen Seas.

Download Full-text

Temperate rainforests near the South Pole during peak Cretaceous warmth

10.5194/egusphere-egu2020-242 ◽

2020 ◽

Author(s):

Johann Philipp Klages ◽

Salzmann Ulrich ◽

Bickert Torsten ◽

Hillenbrand Claus-Dieter ◽

Gohl Karsten ◽

...

Keyword(s):

Land Surface ◽

Climate Model ◽

Model Simulation ◽

Temperate Climate ◽

West Antarctic ◽

Pollen And Spores ◽

Lowland Rainforest ◽

Temperate Rainforests ◽

The Antarctic

The mid-Cretaceous was one of the warmest intervals of the past 140 million years (Myr) driven by atmospheric CO2&#160;levels around 1000 ppmv. In the near absence of proximal geological records from south of the Antarctic Circle, it remains disputed whether polar ice could exist under such environmental conditions. Here we present results from a unique sedimentary sequence recovered from the West Antarctic shelf. This by far southernmost Cretaceous record contains an intact ~3 m-long network of in-situ fossil roots. The roots are embedded in a mudstone matrix bearing diverse pollen and spores, indicative of a temperate lowland rainforest environment at a palaeolatitude of ~82&#176;S during the Turonian&#8211;Santonian (93&#8211;83 Myr). A climate model simulation shows that the reconstructed temperate climate at this high latitude requires a combination of both atmospheric CO2&#160;contents of 1120&#8211;1680 ppmv and a vegetated land surface without major Antarctic glaciation, highlighting the important cooling effect exerted by ice albedo in high-CO2&#160;climate worlds.

Download Full-text

The Antarctic Coastal Current in the Bellingshausen Sea

10.5194/tc-2021-43 ◽

2021 ◽

Author(s):

Ryan Schubert ◽

Andrew F. Thompson ◽

Kevin Speer ◽

Lena Schulze Chretien ◽

Yana Bebieva

Keyword(s):

Coastal Current ◽

Boundary Current ◽

The West ◽

Amundsen Sea ◽

Ice Shelves ◽

West Antarctic ◽

Run Off ◽

Bellingshausen Sea ◽

Basal Melting ◽

The Antarctic

Abstract. The ice shelves of the West Antarctic Ice Sheet experience basal melting induced by underlying warm, salty Circumpolar Deep Water. Basal meltwater, along with run-off from ice sheets, supplies fresh buoyant water to a circulation feature near the coast, the Antarctic Coastal Current (AACC). The formation, structure and coherence of the AACC has been well documented along the West Antarctic Peninsula (WAP). Observations from instrumented seals collected in the Bellingshausen Sea offer extensive hydrographic coverage throughout the year, providing evidence of the continuation of the westward flowing AACC from the WAP towards the Amundsen Sea. The observations reported here demonstrate that the coastal boundary current enters the eastern Bellingshausen Sea from the WAP, flows westward along the face of multiple ice shelves, including the westernmost Abbot Ice Shelf. The presence of the AACC in the western Bellingshausen has implications for the export of water properties into the eastern Amundsen Sea, which we suggest may occur through multiple pathways either along the coast or along the continental shelf break. The temperature, salinity and density structure of the current indicates an increase in baroclinic transport as the AACC flows from the east to the west and as it entrains meltwater from the ice shelves in the Bellingshausen Sea. The AACC acts as a mechanism to transport meltwater out of the Bellingshausen Sea and into the Amundsen and Ross Seas, with the potential to impact basal melt rates and bottom water formation.

Download Full-text

Catchment to sea connection: Impacts of terrestrial run-off on benthic ecosystems in American Samoa

Marine Pollution Bulletin ◽

10.1016/j.marpolbul.2021.112530 ◽

2021 ◽

Vol 169 ◽

pp. 112530

Author(s):

Mia T. Comeros-Raynal ◽

Jon Brodie ◽

Zoe Bainbridge ◽

John Howard Choat ◽

Meagan Curtis ◽

...

Keyword(s):

American Samoa ◽

Run Off ◽

Benthic Ecosystems

Download Full-text

Rhodoliths in Brazil: Current knowledge and potential impacts of climate change

Brazilian Journal of Oceanography ◽

10.1590/s1679-875920160870064sp2 ◽

2016 ◽

Vol 64 (spe2) ◽

pp. 117-136 ◽

Cited By ~ 26

Author(s):

Paulo Antunes Horta ◽

Pablo Riul ◽

Gilberto M. Amado Filho ◽

Carlos Frederico D. Gurgel ◽

Flávio Berchez ◽

...

Keyword(s):

Climate Change ◽

Global Change ◽

Ocean Acidification ◽

Heat Waves ◽

Current Knowledge ◽

Coastal Pollution ◽

Brazil Current ◽

Run Off ◽

Benthic Ecosystems ◽

Impacts Of Climate Change

Abstract Rhodolith beds are important marine benthic ecosystems, representing oases of high biodiversity among sedimentary seabed environments. They are found frequently and abundantly, acting as major carbonate 'factories' and playing a key role in the biogeochemical cycling of carbonates in the South Atlantic. Rhodoliths are under threat due to global change (mainly related to ocean acidification and global warming) and local stressors, such as fishing and coastal run-off. Here, we review different aspects of the biology of these organisms, highlighting the predicted effects of global change, considering the additional impact of local stressors. Ocean acidification (OA) represents a particular threat that can reduce calcification or even promote the decalcification of these bioengineers, thus increasing the eco-physiological imbalance between calcareous and fleshy algae. OA should be considered, but this together with extreme events such as heat waves and storms, as main stressors of these ecosystems at the present time, will worsen in the future, especially if possible interactions with local stressors like coastal pollution are taken into consideration. Thus, in Brazil there is a serious need for starting monitoring programs and promote innovative experimental infrastructure in order to improve our knowledge of these rich environments, optimize management efforts and enhance the needed conservation initiatives.

Download Full-text

In situ Enclosure Experiment Using a Benthic Chamber System to Assess the Effect of High Concentration of CO2 on Deep-Sea Benthic Communities

Journal of Oceanography ◽

10.1007/s10872-006-0003-4 ◽

2005 ◽

Vol 61 (5) ◽

pp. 835-843 ◽

Cited By ~ 27

Author(s):

Hiroshi Ishida ◽

Yuji Watanabe ◽

Tatsuo Fukuhara ◽

Sho Kaneko ◽

Kazushi Furusawa ◽

...

Keyword(s):

Deep Sea ◽

Benthic Communities ◽

Chamber System ◽

High Concentration ◽

Enclosure Experiment ◽

Benthic Chamber

Download Full-text

Antarctic Ice-Sheet Volume at 18000 Years B.P. and Holocene Sea-Level Changes at the West Antarctic Margin

Journal of Glaciology ◽

10.3189/s0022143000014751 ◽

1979 ◽

Vol 24 (90) ◽

pp. 213-230 ◽

Cited By ~ 1

Author(s):

Craig S. Lingle ◽

James A. Clark

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Ice Sheet ◽

Sea Level Changes ◽

Ice Shelf ◽

Relative Sea Level ◽

Antarctic Ice Sheet ◽

West Antarctic Ice Sheet ◽

West Antarctic ◽

The Antarctic

AbstractThe Antarctic ice sheet has been reconstructed at 18000 years b.p. by Hughes and others (in press) using an ice-flow model. The volume of the portion of this reconstruction which contributed to a rise of post-glacial eustatic sea-level has been calculated and found to be (9.8±1.5) × 106 km3. This volume is equivalent to 25±4 m of eustatic sea-level rise, defined as the volume of water added to the ocean divided by ocean area. The total volume of the reconstructed Antarctic ice sheet was found to be (37±6) × 106 km3. If the results of Hughes and others are correct, Antarctica was the second largest contributor to post-glacial eustatic sea-level rise after the Laurentide ice sheet. The Farrell and Clark (1976) model for computation of the relative sea-level changes caused by changes in ice and water loading on a visco-elastic Earth has been applied to the ice-sheet reconstruction, and the results have been combined with the changes in relative sea-level caused by Northern Hemisphere deglaciation as previously calculated by Clark and others (1978). Three families of curves have been compiled, showing calculated relative sea-level change at different times near the margin of the possibly unstable West Antarctic ice sheet in the Ross Sea, Pine Island Bay, and the Weddell Sea. The curves suggest that the West Antarctic ice sheet remained grounded to the edge of the continental shelf until c. 13000 years b.p., when the rate of sea-level rise due to northern ice disintegration became sufficient to dominate emergence near the margin predicted otherwise to have been caused by shrinkage of the Antarctic ice mass. In addition, the curves suggest that falling relative sea-levels played a significant role in slowing and, perhaps, reversing retreat when grounding lines approached their present positions in the Ross and Weddell Seas. A predicted fall of relative sea-level beneath the central Ross Ice Shelf of as much as 23 m during the past 2000 years is found to be compatible with recent field evidence that the ice shelf is thickening in the south-east quadrant.

Download Full-text

Simultaneous solution for mass trends on the West Antarctic Ice Sheet

The Cryosphere Discussions ◽

10.5194/tcd-8-2995-2014 ◽

2014 ◽

Vol 8 (3) ◽

pp. 2995-3035 ◽

Cited By ~ 1

Author(s):

N. Schön ◽

A. Zammit-Mangion ◽

J. L. Bamber ◽

J. Rougier ◽

T. Flament ◽

...

Keyword(s):

Mass Loss ◽

Antarctic Peninsula ◽

Ice Sheet ◽

The West ◽

Spatial Error ◽

Antarctic Ice Sheet ◽

Forward Models ◽

West Antarctic Ice Sheet ◽

West Antarctic ◽

The Antarctic

Abstract. The Antarctic Ice Sheet is the largest potential source of future sea-level rise. Mass loss has been increasing over the last two decades in the West Antarctic Ice Sheet (WAIS), but with significant discrepancies between estimates, especially for the Antarctic Peninsula. Most of these estimates utilise geophysical models to explicitly correct the observations for (unobserved) processes. Systematic errors in these models introduce biases in the results which are difficult to quantify. In this study, we provide a statistically rigorous, error-bounded trend estimate of ice mass loss over the WAIS from 2003–2009 which is almost entirely data-driven. Using altimetry, gravimetry, and GPS data in a hierarchical Bayesian framework, we derive spatial fields for ice mass change, surface mass balance, and glacial isostatic adjustment (GIA) without relying explicitly on forward models. The approach we use separates mass and height change contributions from different processes, reproducing spatial features found in, for example, regional climate and GIA forward models, and provides an independent estimate, which can be used to validate and test the models. In addition, full spatial error estimates are derived for each field. The mass loss estimates we obtain are smaller than some recent results, with a time-averaged mean rate of −76 ± 15 GT yr−1 for the WAIS and Antarctic Peninsula (AP), including the major Antarctic Islands. The GIA estimate compares very well with results obtained from recent forward models (IJ05-R2) and inversion methods (AGE-1). Due to its computational efficiency, the method is sufficiently scalable to include the whole of Antarctica, can be adapted for other ice sheets and can easily be adapted to assimilate data from other sources such as ice cores, accumulation radar data and other measurements that contain information about any of the processes that are solved for.

Download Full-text

In Situ Estimation of Carbon Balance of In Vitro Sweetpotato and Tomato Plantlets Cultured with Varying Initial Sucrose Concentrations in the Medium

Journal of the American Society for Horticultural Science ◽

10.21273/jashs.127.6.963 ◽

2002 ◽

Vol 127 (6) ◽

pp. 963-970 ◽

Cited By ~ 3

Author(s):

Chieri Kubota ◽

Makiko Ezawa ◽

Toyoki Kozai ◽

Sandra B. Wilson

Keyword(s):

Carbon Balance ◽

Ipomoea Batatas ◽

Dry Weight ◽

Photon Flux ◽

Sugar Uptake ◽

Relative Contribution ◽

Carbon Balances ◽

Species Specific

The effects of initial sucrose (suc) concentrations in the medium (S0) on the carbon balance and growth of sweetpotato [Ipomoea batatas (L.) Lam. `Beniazuma'] and tomato (Lycopersicon esculentum Mill. `HanaQueen') plantlets were studied under controlled environmental conditions. Plantlets were cultured with 0, 7.5, 15, or 30 g·L-1 of S0 under high photosynthetic photon flux (160 to 200 μmol·m-2·s-1) and CO2 enriched (1400 to 2050 μmol·mol-1) conditions. Net photosynthetic rate per leaf area (Pl) decreased and dry weight per plantlet (Wd) increased with increasing S0, but did not differ significantly between S0 of 7.5 to 30 g·L-1 for sweetpotato or 15 to 30 g·L-1 for tomato. Carbon influxes and effluxes of the plantlets by metabolism of medium suc and/or photosynthesis, and respiration were estimated based on measurements of in situ and steady state CO2 exchange rates and sugar uptake during culture. At S0 from 7.5 to 30 g·L-1, photosynthesis was responsible for 82% to 92% and 60% to 67% of carbohydrate assimilation for sweetpotato and tomato, respectively. Estimated carbon balances of plantlets based on the estimated and actual increases of moles of carbon in plant tissue demonstrated that in situ estimation of carbon balance was reasonably accurate for sweetpotato at S0 of 0 to 15 g·L-1 and for tomato at S0 of 0 g·L-1 and that the actual contribution of photosynthesis for tomato at high S0 might be lower than the values estimated in the present experiment. Results showed that initial suc concentration affected the relative contribution of photosynthesis on their carbon balances and that the responses were species specific. The failure of validation at S0 in a range specific to each species suggested the need for further study on carbon metabolism of in vitro plantlets cultured with sugar in the medium.

Download Full-text

In situ filamentous communities from the Ediacaran (approx. 563 Ma) of Brazil

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2020.2618 ◽

2021 ◽

Vol 288 (1942) ◽

pp. 20202618

Author(s):

Bruno Becker-Kerber ◽

Gabriel Eduardo Baréa de Barros ◽

Paulo Sergio Gomes Paim ◽

Gustavo M. E. M. Prado ◽

Ana Lucia Zucatti da Rosa ◽

...

Keyword(s):

Oxygen Concentration ◽

Benthic Communities ◽

Preferred Orientation ◽

Redox Condition ◽

Taxonomic Assignment ◽

Diagnostic Features ◽

Ecological Dynamics ◽

Widespread Occurrence ◽

Biological Affinity

Precambrian filamentous microfossils are common and diverse. Nevertheless, their taxonomic assignment can be difficult owing to their overall simple shapes typically lacking in diagnostic features. Here, we report in situ communities of well-preserved, large filamentous impressions from the Ediacaran Itajaí Basin ( ca 563 Ma) of Brazil. The filaments are uniserial (unbranched) and can reach up to 200 µm in width and up to 44 mm in length. They occur as both densely packed or sparsely populated surfaces, and typically show a consistent orientation. Although simple in shape, their preferred orientation suggests they were tethered to the seafloor, and their overall flexibility (e.g. bent, folded and twisted) supports a biological (rather than sedimentary) affinity. Biometric comparisons with modern filamentous groups further support their biological affinity, suggesting links with either large sulfide-oxidizing bacteria (SOB) or eukaryotes. Other morphological and palaeoecological characteristics further corroborates their similarities with modern large filamentous SOB. Their widespread occurrence and association with complex Ediacaran macrobiota (e.g. frondose organisms, Palaeopascichnus ) suggest that they probably played an important role in the ecological dynamics of these early benthic communities by providing firm substrates for metazoans to inhabit. It is further hypothesized that the dynamic redox condition in the latest Ediacaran, with the non-continuous rise in oxygen concentration and periods of hypoxia, may have created ideal conditions for SOB to thrive.

Download Full-text