Resolving sea ice dynamics in the north-western Ross Sea during the last 2.6 ka: From seasonal to millennial timescales

Sea ice cover is arguably the longest and best observed climate variable from space, with over four decades of highly reliable daily records of extent in both hemispheres. In Antarctica, a slight positive decadal trend in sea ice cover is driven by changes in the western Ross Sea, where a variation in weather patterns over the wider region forced a change in meridional winds. The distinguishing wind driven sea ice process in the western Ross Sea is the regular occurrence of the Ross Sea, McMurdo Sound, and Terra Nova Bay polynyas. Trends in sea ice volume and mass in this area unknown, because ice thickness and dynamics are particularly hard to measure.Here we present the first comprehensive and direct assessment of large-scale sea-ice thickness distribution in the western Ross Sea. Using an airborne electromagnetic induction (AEM) ice thickness sensor towed by a fixed wing aircraft (Basler BT-67), we observed in November 2017 over a distance of 800 km significantly thicker ice than expected from thermodynamic growth alone. By means of time series of satellite images and wind data we relate the observed thickness distribution to satellite derived ice dynamics and wind data. Strong southerly winds with speeds of up to 25 ms-1 in early October deformed the pack ice, which was surveyed more than a month later.We found strongly deformed ice with a mean and maximum thickness of 2.0 and 15.6 m, respectively. Sea-ice thickness gradients are highest within 100-200 km of polynyas, where the mean thickness of the thickest 10% of ice is 7.6 m. From comparison with aerial photographs and satellite images we conclude that ice preferentially grows in deformational ridges; about 43% of the sea ice volume in the area between McMurdo Sound and Terra Nova Bay is concentrated in more than 3 m thick ridges which cover about 15% of the surveyed area. Overall, 80% of the ice was found to be heavily deformed and concentrated in ridges up to 11.8 m thick.Our observations hold a link between wind driven ice dynamics and the ice mass exported from the western Ross Sea. The sea ice statistics highlighted in this contribution forms a basis for improved satellite derived mass balance assessments and the evaluation of sea ice simulations.

Download Full-text

Seasonal Food Web Dynamics in the Antarctic Benthos of Tethys Bay (Ross Sea): Implications for Biodiversity Persistence Under Different Seasonal Sea-Ice Coverage

Frontiers in Marine Science ◽

10.3389/fmars.2020.594454 ◽

2020 ◽

Vol 7 ◽

Author(s):

Simona Sporta Caputi ◽

Giulio Careddu ◽

Edoardo Calizza ◽

Federico Fiorentino ◽

Deborah Maccapan ◽

...

Keyword(s):

Sea Ice ◽

Food Web ◽

Ross Sea ◽

Food Web Structure ◽

Ice Dynamics ◽

Web Architecture ◽

Sea Ice Dynamics ◽

Before And After ◽

Basal Resources ◽

Break Up

Determining food web architecture and its seasonal cycles is a precondition for making predictions about Antarctic marine biodiversity under varying climate change scenarios. However, few scientific data concerning Antarctic food web structure, the species playing key roles in web stability and the community responses to changes in sea-ice dynamics are available. Based on C and N stable isotope analysis, we describe Antarctic benthic food webs and the diet of species occurring in shallow waters (Tethys Bay, Ross Sea) before and after seasonal sea-ice break-up. We hypothesized that the increased availability of primary producers (sympagic algae) following sea-ice break-up affects the diet of species and thus food web architecture. Basal resources had distinct isotopic signatures that did not change after sea-ice break-up, enabling a robust description of consumer diets based on Bayesian mixing models. Sympagic algae had the highest δ13C (∼−14‰) and red macroalgae the lowest (∼−37‰). Consumer isotopic niches and signatures changed after sea-ice break-up, reflecting the values of sympagic algae. Differences in food web topology were also observed. The number of taxa and the number of links per taxon were higher before the thaw than after it. After sea-ice break-up, sympagic inputs allowed consumers to specialize on abundant resources at lower trophic levels. Foraging optimization by consumers led to a simpler food web, with lower potential competition and shorter food chains. However, basal resources and Antarctic species such as the bivalve Adamussium colbecki and the sea-urchin Sterechinus neumayeri were central and highly connected both before and after the sea-ice break-up, thus playing key roles in interconnecting species and compartments in the web. Any disturbance affecting these species is expected to have cascading effects on the entire food web. The seasonal break-up of sea ice in Antarctica ensures the availability of resources that are limiting for coastal communities for the rest of the year. Identification of species playing a key role in regulating food web structure in relation to seasonal sea-ice dynamics, which are expected to change with global warming, is central to understanding how these communities will respond to climate change.

Download Full-text

Macrobenthic communities of the north-western Ross Sea shelf: links to depth, sediment characteristics and latitude

Antarctic Science ◽

10.1017/s0954102010000489 ◽

2010 ◽

Vol 22 (6) ◽

pp. 793-804 ◽

Cited By ~ 25

Author(s):

V.J. Cummings ◽

S.F. Thrush ◽

M. Chiantore ◽

J.E. Hewitt ◽

R. Cattaneo-Vietti

Keyword(s):

Ross Sea ◽

Fine Sand ◽

Sediment Characteristics ◽

Explanatory Variables ◽

The North ◽

Biogenic Habitat ◽

Community Variability ◽

North Western ◽

Western Ross Sea ◽

Ross Sea Shelf

AbstractIn early 2004 the Victoria Land Transect project sampled coastal north-western Ross Sea shelf benthos at Cape Adare, Cape Hallett, Cape Russell and Coulman Island from 100–500 m deep. We describe the benthic macrofaunal assemblages at these locations and, to assess the use of seafloor sediment characteristics and/or depth measures in bioregionalizations, determine the extent to which assemblage compositions are related to measured differences in these factors. Percentages of fine sand and silt, the ratio of sediment chlorophyllato phaeophytin, and depth were identified as important explanatory variables, but in combination they explained only 17.3% of between-location differences in assemblages. Consequently, these variables are clearly not strong determinants of macrofaunal assemblage structure. Latitudeper sewas not a useful measure of community variability and change. A significant correlation between both number of individuals and number of taxa and sediment phaeophytin concentration across locations suggests that the distribution of the benthos reflects their response to seafloor productivity. A number of factors not measured in this study have probably influenced the structure and function of assemblages and habitats. We discuss the implications of the results to marine classifications, and stress the need to incorporate biogenic habitat complexity into protection strategies.

Download Full-text

On the effect of sea-ice dynamics on oceanic thermohaline circulation

Annals of Glaciology ◽

10.3189/s0260305500016074 ◽

1995 ◽

Vol 21 ◽

pp. 361-368

Author(s):

W. D. Hibler ◽

Jinlun Zhang

Keyword(s):

Sea Ice ◽

Thermohaline Circulation ◽

Ocean Model ◽

Flat Bottom ◽

Ice Dynamics ◽

Surface Ocean ◽

The North ◽

Air Temperatures ◽

Sea Ice Dynamics ◽

Ocean Salinity

An idealized planetary flat-bottom geostrophic ice–ocean model is constructed with boundaries at latitudes 5° and 65° N and longitudes 50° W and 10° E in order to approximate the North Atlantic. The model is driven by fixed zonally averaged wind, surface air temperatures and surface ocean salinity. A dynamic thermodynamic sea-ice model is coupled to the ocean model. Only the thermodynamic insulating effects of the sea ice are considered, and no salt fluxes due to melting and freezing are included. Four equilibrium simulations of about 5000 years each are performed: two with interactive sea ice with and without ice dynamics, and two control simulations with either a fixed or no ice cover.In the two simulations including interactive sea ice, characteristic oscillations in the ice thickness and ocean temperature are found to occur. The oscillations are smaller when sea-ice dynamics are included. The dominant oscillation occurs at about a 5 year period, with the key feature being that the presence of sea ice tends to insulate the ocean and hence allows an oceanic warming. This warming in turn eventually causes a melt-back of the ice and a subsequent cool-down of the ocean. Oscillations at longer periods of about 20 years in the thermohaline circulation are also observed. These longer-period oscillations are particularly pronounced in the northward surface water transport.

Download Full-text

On the effect of sea-ice dynamics on oceanic thermohaline circulation

Annals of Glaciology ◽

10.1017/s0260305500016074 ◽

1995 ◽

Vol 21 ◽

pp. 361-368 ◽

Cited By ~ 5

Author(s):

W. D. Hibler ◽

Jinlun Zhang

Keyword(s):

Sea Ice ◽

Thermohaline Circulation ◽

Ocean Model ◽

Flat Bottom ◽

Ice Dynamics ◽

Surface Ocean ◽

The North ◽

Air Temperatures ◽

Sea Ice Dynamics ◽

Ocean Salinity

An idealized planetary flat-bottom geostrophic ice–ocean model is constructed with boundaries at latitudes 5° and 65° N and longitudes 50° W and 10° E in order to approximate the North Atlantic. The model is driven by fixed zonally averaged wind, surface air temperatures and surface ocean salinity. A dynamic thermodynamic sea-ice model is coupled to the ocean model. Only the thermodynamic insulating effects of the sea ice are considered, and no salt fluxes due to melting and freezing are included. Four equilibrium simulations of about 5000 years each are performed: two with interactive sea ice with and without ice dynamics, and two control simulations with either a fixed or no ice cover. In the two simulations including interactive sea ice, characteristic oscillations in the ice thickness and ocean temperature are found to occur. The oscillations are smaller when sea-ice dynamics are included. The dominant oscillation occurs at about a 5 year period, with the key feature being that the presence of sea ice tends to insulate the ocean and hence allows an oceanic warming. This warming in turn eventually causes a melt-back of the ice and a subsequent cool-down of the ocean. Oscillations at longer periods of about 20 years in the thermohaline circulation are also observed. These longer-period oscillations are particularly pronounced in the northward surface water transport.

Download Full-text