scholarly journals Supercooled Southern Ocean Waters

2021 ◽  
Author(s):  
F. Alexander Haumann ◽  
Ruth Moorman ◽  
Stephen C. Riser ◽  
Lars H. Smedsrud ◽  
Ted Maksym ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Freezing Point ◽  
Polar Regions ◽  
Tracer Transport ◽  
Ice Shelves ◽  
Polar Ocean ◽  
Winter Time ◽  
Surface Freezing

<p>In cold polar waters, temperatures sometimes drop below the freezing point, a process referred to as supercooling. However, observational challenges in polar regions limit our understanding of the spatial and temporal extent of this phenomenon. We here provide observational evidence that supercooled waters are much more widespread in the seasonally ice-covered Southern Ocean than previously reported. In 5.8% of all analyzed hydrographic profiles south of 55° S, we find temperatures below the surface freezing point (‘potential’ supercooling), and half of these have temperatures below the local freezing point (‘in-situ’ supercooling). Their occurrence doubles when neglecting measurement uncertainties. We attribute deep coastal-ocean supercooling to melting of Antarctic ice shelves, and surface-induced supercooling in the seasonal sea-ice region to winter-time sea-ice formation. The latter supercooling type can extend down to the permanent pycnocline due to convective sinking plumes—an important mechanism for vertical tracer transport and water-mass structure in the polar ocean.</p>

Causes and consequences of Southern Ocean change: the IPCC SROCC assessment

2020 ◽  
Author(s):  
Michael Meredith ◽  
Martin Sommerkorn ◽  
Sandra Cassotta ◽  
Chris Derksen ◽  
Alexey Ekaykin ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Sea Level ◽  
Ocean Circulation ◽  
Global Climate ◽  
Ice Sheets ◽  
The Arctic ◽  
Polar Regions ◽  
Ice Shelves

<p>Climate change in the polar regions exerts a profound influence both locally and over all of our planet.  Physical and ecosystem changes influence societies and economies, via factors that include food provision, transport and access to non-renewable resources.  Sea level, global climate and potentially mid-latitude weather are influenced by the changing polar regions, through coupled feedback processes, sea ice changes and the melting of snow and land-based ice sheets and glaciers.</p><p>Reflecting this importance, the IPCC Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) features a chapter highlighting past, ongoing and future change in the polar regions, the impacts of these changes, and the possible options for response.  The role of the polar oceans, both in determining the changes and impacts in the polar regions and in structuring the global influence, is an important component of this chapter.</p><p>With emphasis on the Southern Ocean and through comparison with the Arctic, this talk will outline key findings from the polar regions chapter of SROCC. It will synthesise the latest information on the rates, patterns and causes of changes in sea ice, ocean circulation and properties. It will assess cryospheric driving of ocean change from ice sheets, ice shelves and glaciers, and the role of the oceans in determining the past and future evolutions of polar land-based ice. The implications of these changes for climate, ecosystems, sea level and the global system will be outlined.</p>

scholarly journals Thermohaline structure and circulation beneath the Langhovde Glacier ice shelf in East Antarctica

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Masahiro Minowa ◽  
Shin Sugiyama ◽  
Masato Ito ◽  
Shiori Yamane ◽  
Shigeru Aoki
Keyword(s):  
Freezing Point ◽  
East Antarctica ◽  
Ice Shelf ◽  
Rate Estimate ◽  
Ice Shelves ◽  
Plume Water ◽  
Warm Deep Water ◽  
Glacier Ice ◽  
Basal Melting

AbstractBasal melting of ice shelves is considered to be the principal driver of recent ice mass loss in Antarctica. Nevertheless, in-situ oceanic data covering the extensive areas of a subshelf cavity are sparse. Here we show comprehensive structures of temperature, salinity and current measured in January 2018 through four boreholes drilled at a ~3-km-long ice shelf of Langhovde Glacier in East Antarctica. The measurements were performed in 302–12 m-thick ocean cavity beneath 234–412 m-thick ice shelf. The data indicate that Modified Warm Deep Water is transported into the grounding zone beneath a stratified buoyant plume. Water at the ice-ocean interface was warmer than the in-situ freezing point by 0.65–0.95°C, leading to a mean basal melt rate estimate of 1.42 m a−1. Our measurements indicate the existence of a density-driven water circulation in the cavity beneath the ice shelf of Langhovde Glacier, similar to that proposed for warm-ocean cavities of larger Antarctic ice shelves.

scholarly journals Formation of sea ice ponds from ice-shelf runoff, adjacent to the McMurdo Ice Shelf, Antarctica

2020 ◽  
Vol 61 (82) ◽  
pp. 73-77 ◽  
Author(s):  
Grant J. Macdonald ◽  
Predrag Popović ◽  
David P. Mayer
Keyword(s):  
Sea Ice ◽  
Added Mass ◽  
Surface Melting ◽  
Landsat 8 ◽  
Ice Shelf ◽  
Surface Hydrology ◽  
Ice Shelves ◽  
Arctic Ponds ◽  
Sentinel 2

AbstractPonds that form on sea ice can cause it to thin or break-up, which can promote calving from an adjacent ice shelf. Studies of sea ice ponds have predominantly focused on Arctic ponds formed by in situ melting/ponding. Our study documents another mechanism for the formation of sea ice ponds. Using Landsat 8 and Sentinel-2 images from the 2015–16 to 2018–19 austral summers, we analyze the evolution of sea ice ponds that form adjacent to the McMurdo Ice Shelf, Antarctica. We find that each summer, meltwater flows from the ice shelf onto the sea ice and forms large (up to 9 km2) ponds. These ponds decrease the sea ice's albedo, thinning it. We suggest the added mass of runoff causes the ice to flex, potentially promoting sea-ice instability by the ice-shelf front. As surface melting on ice shelves increases, we suggest that ice-shelf surface hydrology will have a greater effect on sea-ice stability.

Regional Classes of Sea Ice Cover in the East Antarctic Pack Observed from Satellite and In Situ Data during a Winter Time Period

1999 ◽  
Vol 68 (1) ◽  
pp. 61-76 ◽  
Author(s):  
R.A. Massom ◽  
J.C. Comiso ◽  
A.P. Worby ◽  
V.I. Lytle ◽  
L. Stock
Keyword(s):  
Sea Ice ◽  
Ice Cover ◽  
In Situ Data ◽  
Time Period ◽  
Winter Time

Evolution of supercooling under coastal Antarctic sea ice during winter

2011 ◽  
Vol 23 (4) ◽  
pp. 399-409 ◽  
Author(s):  
Gregory H. Leonard ◽  
Patricia J. Langhorne ◽  
Michael J.M. Williams ◽  
Ross Vennell ◽  
Craig R. Purdie ◽  
...  
Keyword(s):  
Sea Ice ◽  
Freezing Point ◽  
Circulation Pattern ◽  
Late Winter ◽  
Ice Shelf ◽  
Mcmurdo Sound ◽  
The North ◽  
Antarctic Sea Ice ◽  
Ice Production

AbstractHere we describe the evolution through winter of a layer of in situ supercooled water beneath the sea ice at a site close to the McMurdo Ice Shelf. From early winter (May), the temperature of the upper water column was below its surface freezing point, implying contact with an ice shelf at depth. By late winter the supercooled layer was c. 40 m deep with a maximum supercooling of c. 25 mK located 1–2 m below the sea ice-water interface. Transitory in situ supercooling events were also observed, one lasting c. 17 hours and reaching a depth of 70 m. In spite of these very low temperatures the isotopic composition of the water was relatively heavy, suggesting little glacial melt. Further, the water's temperature-salinity signature indicates contributions to water mass properties from High Salinity Shelf Water produced in areas of high sea ice production to the north of McMurdo Sound. Our measurements imply the existence of a heat sink beneath the supercooled layer that extracts heat from the ocean to thicken and cool this layer and contributes to the thickness of the sea ice cover. This sink is linked to the circulation pattern of the McMurdo Sound.

New insights into the ice-covered Southern Ocean circulation from multi-altimeter combination.

2021 ◽  
Author(s):  
Matthis Auger ◽  
Jean-Baptiste Sallée ◽  
Pierre Prandi
Keyword(s):  
Southern Ocean ◽  
Sea Level ◽  
Ocean Circulation ◽  
Sea Level Anomaly ◽  
Ice Shelves ◽  
Modes Of Variability ◽  
The Past ◽  
Circulation Patterns ◽  
Polar Ocean ◽  
Global Sea Level

<p>Subtle changes in the Southern Ocean subpolar ocean circulation patterns can lead to major changes in the global overturning circulation, as well as for floating ice-shelves with critical implications for global sea-level. It is therefore crucial to carefully understand Antarctic polar ocean circulation, but the lack of ocean observation has considerably blocked our advance in this field in the past.</p><p>In this study we benefit from a new high-resolution Sea Level Anomaly (SLA) product that has been specifically constructed to document sea-level in the ice-covered Southern Ocean. This product combines up to 3 satellite altimetry missions to map SLA data daily on an equal-area grid, including the ice-covered areas of the ocean from 2013 to 2019.</p><p>Results suggest that we can map ocean features with unprecedented resolution for the region. We characterize the main features of the subpolar Southern Ocean SLA and circulation seasonal cycle, being composed of three main modes of variability, significantly impacting the dynamics of the region. We explore how they are linked with atmospheric and sea-ice forcings. Dynamics at smaller scales are investigated, by identifying the properties of mesoscale variability where possible.</p>

Productivity and carbon export potential in the Weddell Sea, with a focus on the waters near Larsen C Ice Shelf

2020 ◽  
Author(s):  
Raquel Flynn ◽  
Jessica Burger ◽  
Shantelle Smith ◽  
Kurt Spence ◽  
Thomas Bornman ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Phytoplankton Community ◽  
Late Summer ◽  
Weddell Sea ◽  
Global Ocean ◽  
Ice Shelf ◽  
Carbon Export ◽  
Study Region ◽  
Ice Shelves

<p>Net primary production (NPP) is indicative of the energy available to an ecosystem, which is central to ecological functioning and biological carbon cycling. The Southern Ocean’s Weddell Sea (WS) represents a point of origin where water masses form and exchange with the atmosphere, thereby setting the physical and chemical conditions of much of the global ocean. The WS is particularly understudied near Larsen C Ice Shelf (LCIS) where harsh sea-ice conditions persist year-round. We measured size-fractionated rates of NPP, nitrogen (N; as nitrate, ammonium, and urea) uptake, and nitrification, and characterized the phytoplankton community at 19 stations in summer 2018/2019, mainly near LCIS, with a few stations in the open Weddell Gyre (WG) and at Fimbul Ice Shelf (FIS). Throughout the study region, NPP and N uptake were dominated by nanophytoplankton (3-20 μm), with microphytoplankton (>20 μm) becoming more abundant later in the season, particularly at FIS. Here, we observed high phytoplankton biomass and diversity, and the community was dominated by diatoms known to enhance carbon export (e.g., <em>Thalassiosira spp</em>.). At LCIS, by contrast, the community comprised mainly <em>Phaeocystis Antarctica</em>. In the open WG, a population of small and weakly-silicified diatoms of the genus <em>Corethron</em> dominated the phytoplankton community. Here, euphotic zone-integrated uptake rates were similar to those at LCIS even though the depth-specific rates were lower. Mixed-layer nitrification was below detection at all stations such that nitrate uptake can be used as a proxy for carbon export potential <em>sensu</em> the new production paradigm – this was highest near FIS in late summer. Our observations can be explained by melting sea ice near the ice shelves that supplies iron and enhances water column stratification, thus alleviating iron and/or light limitation of phytoplankton and allowing them to consume the abundant surface macronutrients. That the sea ice melted completely at FIS but not LCIS may explain why late-summer productivity and carbon export potential were highest near FIS, more than double the rates measured in early summer and near LCIS. The early-to-late summer progression near the ice shelves contrasts that of the open Southern Ocean where iron is depleted by late summer, driving a shift towards smaller phytoplankton that facilitate less carbon export.</p>

Extending the Ice Watch system as a citizen science project for the collection of In-Situ sea ice observations

2020 ◽  
Author(s):  
Ole Jakob Hegelund ◽  
Alistair Everett ◽  
Ted Cheeseman ◽  
Penelope Wagner ◽  
Nick Hughes ◽  
...  
Keyword(s):  
Sea Ice ◽  
Citizen Science ◽  
European Space Agency ◽  
Earth Observation ◽  
Machine Learning Algorithms ◽  
The Arctic ◽  
Polar Regions ◽  
User Engagement ◽  
The Antarctic

<p>The Ice Watch program coordinates routine visual observations of sea-ice including icebergs and meteorological parameters. The development and use of the Arctic Shipborne Sea Ice Standardization Tool (ASSIST) software has enabled the program to collect over 6 800 records from numerous ship voyages and it is complementary to the Antarctic Sea-ice Processes and Climate (ASPeCt) in the Antarctic. These observations will enhance validation and calibration of data from the Copernicus Sentinel satellites and other Earth Observation missions where the lack of routine spatially and temporally coincident data from the Polar Regions hinders the development of automatic classification products. A critical piece of information for operations and research, photographic records of observations, is often missing. As mobile phones are nearly ubiquitous and feature high-quality cameras, capable of recording accurate ancillary timing and positional information we are developing the IceWatchApp to aid users in supplementing observations with a photographic record.</p><p>The IceWatchApp has been funded by the Citizen Science Earth Observation Lab (CSEOL) programme of the European Space Agency and the Polar Citizen Science Collective, which has successfully implemented similar observation projects within atmospherics, biology and marine geosciences, is collaborating in its development. The image database will aid the training of machine learning algorithms for automatic sea ice type classification and provide a mechanism for crowd-sourcing identification through an “ask a scientist” feedback feature. The app will also have the capability to provide near real-time satellite and Copernicus services products back to the user, thereby educating them on Earth Observation, and giving them an improved understanding of the surrounding environment.</p><p> </p><p><strong>Keywords</strong>: Polar regions, Arctic, Antarctic, data collection, In-Situ measurements, remote sensing, Sea Ice, user engagement, citizen science, Earth Observation.<br><strong>Abstract</strong>: to session 35413</p><p> </p>

scholarly journals Mapping the in situ microspatial distribution of ice algal biomass through hyperspectral imaging of sea-ice cores

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Emiliano Cimoli ◽  
Vanessa Lucieer ◽  
Klaus M. Meiners ◽  
Arjun Chennu ◽  
Katerina Castrisios ◽  
...  
Keyword(s):  
Sea Ice ◽  
Hyperspectral Imaging ◽  
Ice Cores ◽  
Horizontal Distribution ◽  
Ex Situ ◽  
Polar Regions ◽  
Vertical And Horizontal Distribution ◽  
Research Goal ◽  
Set Up

AbstractIce-associated microalgae make a significant seasonal contribution to primary production and biogeochemical cycling in polar regions. However, the distribution of algal cells is driven by strong physicochemical gradients which lead to a degree of microspatial variability in the microbial biomass that is significant, but difficult to quantify. We address this methodological gap by employing a field-deployable hyperspectral scanning and photogrammetric approach to study sea-ice cores. The optical set-up facilitated unsupervised mapping of the vertical and horizontal distribution of phototrophic biomass in sea-ice cores at mm-scale resolution (using chlorophyll a [Chl a] as proxy), and enabled the development of novel spectral indices to be tested against extracted Chl a (R2 ≤ 0.84). The modelled bio-optical relationships were applied to hyperspectral imagery captured both in situ (using an under-ice sliding platform) and ex situ (on the extracted cores) to quantitatively map Chl a in mg m−2 at high-resolution (≤ 2.4 mm). The optical quantification of Chl a on a per-pixel basis represents a step-change in characterising microspatial variation in the distribution of ice-associated algae. This study highlights the need to increase the resolution at which we monitor under-ice biophysical systems, and the emerging capability of hyperspectral imaging technologies to deliver on this research goal.

scholarly journals Intercomparison of Antarctic ice-shelf, ocean, and sea-ice interactions simulated by MetROMS-iceshelf and FESOM 1.4

2018 ◽  
Vol 11 (4) ◽  
pp. 1257-1292 ◽  
Author(s):  
Kaitlin A. Naughten ◽  
Katrin J. Meissner ◽  
Benjamin K. Galton-Fenzi ◽  
Matthew H. England ◽  
Ralph Timmermann ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Water Mass ◽  
Horizontal Resolution ◽  
Ocean Model ◽  
Small Scale ◽  
Ice Shelf ◽  
Vertical Coordinate ◽  
Ice Shelves ◽  
Basal Melting

Abstract. An increasing number of Southern Ocean models now include Antarctic ice-shelf cavities, and simulate thermodynamics at the ice-shelf/ocean interface. This adds another level of complexity to Southern Ocean simulations, as ice shelves interact directly with the ocean and indirectly with sea ice. Here, we present the first model intercomparison and evaluation of present-day ocean/sea-ice/ice-shelf interactions, as simulated by two models: a circumpolar Antarctic configuration of MetROMS (ROMS: Regional Ocean Modelling System coupled to CICE: Community Ice CodE) and the global model FESOM (Finite Element Sea-ice Ocean Model), where the latter is run at two different levels of horizontal resolution. From a circumpolar Antarctic perspective, we compare and evaluate simulated ice-shelf basal melting and sub-ice-shelf circulation, as well as sea-ice properties and Southern Ocean water mass characteristics as they influence the sub-ice-shelf processes. Despite their differing numerical methods, the two models produce broadly similar results and share similar biases in many cases. Both models reproduce many key features of observations but struggle to reproduce others, such as the high melt rates observed in the small warm-cavity ice shelves of the Amundsen and Bellingshausen seas. Several differences in model design show a particular influence on the simulations. For example, FESOM's greater topographic smoothing can alter the geometry of some ice-shelf cavities enough to affect their melt rates; this improves at higher resolution, since less smoothing is required. In the interior Southern Ocean, the vertical coordinate system affects the degree of water mass erosion due to spurious diapycnal mixing, with MetROMS' terrain-following coordinate leading to more erosion than FESOM's z coordinate. Finally, increased horizontal resolution in FESOM leads to higher basal melt rates for small ice shelves, through a combination of stronger circulation and small-scale intrusions of warm water from offshore.

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