scholarly journals Circumpolar Mapping of Antarctic Coastal Polynyas and Landfast Sea Ice: Relationship and Variability

2015 ◽  
Vol 28 (9) ◽  
pp. 3650-3670 ◽  
Author(s):  
Sohey Nihashi ◽  
Kay I. Ohshima
Keyword(s):  
Climate Change ◽  
Sea Ice ◽  
Climate Projections ◽  
Coastal Current ◽  
Validation Data ◽  
Key Factor ◽  
Primary Determinant ◽  
Fast Ice ◽  
Landfast Sea Ice ◽  
Ice Production

Abstract Sinking of dense water from Antarctic coastal polynyas produces Antarctic Bottom Water (AABW), which is the densest water in the global overturning circulation and is a key player in climate change as a significant sink for heat and carbon dioxide. Very recent studies have suggested that landfast sea ice (fast ice) plays an important role in the formation and variability of the polynyas and possibly AABW. However, they have been limited to regional and case investigations only. This study provides the first coincident circumpolar mapping of Antarctic coastal polynyas and fast ice. The map reveals that most of the polynyas are formed on the western side of fast ice, indicating an important role of fast ice in the polynya formation. Winds diverging from a boundary comprising both coastline and fast ice are the primary determinant of polynya formation. The blocking effect of fast ice on westward sea ice advection by the coastal current would be another key factor. These effects on the variability in sea ice production for 13 major polynyas are evaluated quantitatively. Furthermore, it is demonstrated that a drastic change in fast ice extent, which is particularly vulnerable to climate change, causes dramatic changes in the polynyas and possibly AABW formation that can potentially contribute to further climate change. These results suggest that fast ice and precise polynya processes should be addressed by next-generation models to produce more accurate climate projections. This study provides the boundary and validation data of fast ice and sea ice production for such models.

scholarly journals Estimation of Thin Ice Thickness and Detection of Fast Ice from SSM/I Data in the Antarctic Ocean

2007 ◽  
Vol 24 (10) ◽  
pp. 1757-1772 ◽  
Author(s):  
Takeshi Tamura ◽  
Kay I. Ohshima ◽  
Thorsten Markus ◽  
Donald J. Cavalieri ◽  
Sohey Nihashi ◽  
...  
Keyword(s):  
Sea Ice ◽  
Ross Sea ◽  
Weddell Sea ◽  
Ice Thickness ◽  
Coastal Current ◽  
Antarctic Ocean ◽  
Coastal Polynya ◽  
Fast Ice ◽  
Ice Production ◽  
The Antarctic

Abstract Antarctic coastal polynyas are important areas of high sea ice production and dense water formation, and thus their detection including an estimate of thin ice thickness is essential. In this paper, the authors propose an algorithm that estimates thin ice thickness and detects fast ice using Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave Imager (SSM/I) data in the Antarctic Ocean. Detection and estimation of sea ice thicknesses of <0.2 m are based on the SSM/I 85- and 37-GHz polarization ratios (PR85 and PR37) through a comparison with sea ice thicknesses estimated from the Advanced Very High Resolution Radiometer (AVHRR) data. The exclusion of data affected by atmospheric water vapor is discussed. Because thin ice and fast ice (specifically ice shelves, glacier tongues, icebergs, and landfast ice) have similar PR signatures, a scheme was developed to separate these two surface types before the application of the thin ice algorithm to coastal polynyas. The probability that the algorithm correctly distinguishes thin ice from thick ice and from fast ice is ∼95%, relative to the ice thicknesses estimated from AVHRR. Although the standard deviation of the difference between the thin ice thicknesses estimated from the SSM/I algorithm and AVHRR is ∼0.05 m and thus not small, the estimated ice thicknesses from the microwave algorithm appear to have small biases and the accuracies are independent of region and season. A distribution map of thin ice occurrences derived from the SSM/I algorithm represents the Ross Sea coastal polynya being by far the largest among the Antarctic coastal polynyas; the Weddell Sea coastal polynyas are much smaller. Along the coast of East Antarctica, coastal polynyas frequently form on the western side of peninsulas and glacier tongues, downstream of the Antarctic Coastal Current.

scholarly journals Potential effects of climate change on inundation patterns in the Amazon Basin

2013 ◽  
Vol 17 (6) ◽  
pp. 2247-2262 ◽  
Author(s):  
F. Langerwisch ◽  
S. Rost ◽  
D. Gerten ◽  
B. Poulter ◽  
A. Rammig ◽  
...  
Keyword(s):  
Climate Change ◽  
Amazon Basin ◽  
Climate Models ◽  
Climate Projections ◽  
Flooding Regime ◽  
Key Factor ◽  
Inundation Duration ◽  
Flooded Area ◽  
Global Vegetation ◽  
Ipcc Ar4

Abstract. Floodplain forests, namely the Várzea and Igapó, cover an area of more than 97 000 km2. A key factor for their function and diversity is annual flooding. Increasing air temperature and higher precipitation variability caused by climate change are expected to shift the flooding regime during this century, and thereby impact floodplain ecosystems, their biodiversity and riverine ecosystem services. To assess the effects of climate change on the flooding regime, we use the Dynamic Global Vegetation and Hydrology Model LPJmL, enhanced by a scheme that realistically simulates monthly flooded area. Simulation results of discharge and inundation under contemporary conditions compare well against site-level measurements and observations. The changes of calculated inundation duration and area under climate change projections from 24 IPCC AR4 climate models differ regionally towards the end of the 21st century. In all, 70% of the 24 climate projections agree on an increase of flooded area in about one third of the basin. Inundation duration increases dramatically by on average three months in western and around one month in eastern Amazonia. The time of high- and low-water peak shifts by up to three months. Additionally, we find a decrease in the number of extremely dry years and in the probability of the occurrence of three consecutive extremely dry years. The total number of extremely wet years does not change drastically but the probability of three consecutive extremely wet years decreases by up to 30% in the east and increases by up to 25% in the west. These changes implicate significant shifts in regional vegetation and climate, and will dramatically alter carbon and water cycles.

scholarly journals Ice platelets below Weddell Sea landfast sea ice

2015 ◽  
Vol 56 (69) ◽  
pp. 175-190 ◽  
Author(s):  
Mario Hoppmann ◽  
Marcel Nicolaus ◽  
Stephan Paul ◽  
Priska A. Hunkeler ◽  
Günther Heinemann ◽  
...  
Keyword(s):  
Sea Ice ◽  
Volume Fraction ◽  
Weddell Sea ◽  
Ice Shelf ◽  
Platelet Volume ◽  
Local Maxima ◽  
Model Studies ◽  
Warm Surface Water ◽  
Fast Ice ◽  
Landfast Sea Ice

AbstractBasal melt of ice shelves may lead to an accumulation of disc-shaped ice platelets underneath nearby sea ice, to form a sub-ice platelet layer. Here we present the seasonal cycle of sea ice attached to the Ekström Ice Shelf, Antarctica, and the underlying platelet layer in 2012. Ice platelets emerged from the cavity and interacted with the fast-ice cover of Atka Bay as early as June. Episodic accumulations throughout winter and spring led to an average platelet-layer thickness of 4 m by December 2012, with local maxima of up to 10 m. The additional buoyancy partly prevented surface flooding and snow-ice formation, despite a thick snow cover. Subsequent thinning of the platelet layer from December onwards was associated with an inflow of warm surface water. The combination of model studies with observed fast-ice thickness revealed an average ice-volume fraction in the platelet layer of 0.25 ± 0.1. We found that nearly half of the combined solid sea-ice and ice-platelet volume in this area is generated by heat transfer to the ocean rather than to the atmosphere. The total ice-platelet volume underlying Atka Bay fast ice was equivalent to more than one-fifth of the annual basal melt volume under the Ekström Ice Shelf.

scholarly journals Antarctic Bacteria, Sea Ice Ecosystem Dynamics, and Global Climate Change

2021 ◽  
Author(s):  
◽  
Andrew Robert Martin
Keyword(s):  
Climate Change ◽  
Organic Matter ◽  
Microbial Community ◽  
Dissolved Organic Matter ◽  
Southern Ocean ◽  
Sea Ice ◽  
Metabolic Activity ◽  
Bacterial Response ◽  
Pack Ice ◽  
Fast Ice

<p>Productivity in the Southern Ocean reflects both the spatial and temporal dynamics of the sea ice ecosystem, as well as the complex cycling of energy through the microbial community. Marine bacteria are thought to be integral to trophodynamics and the functioning of a microbial loop within the ice matrix, but there is no clear understanding of the distribution and diversity of bacteria or the importance of bacterial production. Understanding the bacterial response to environmental change in the sea ice ecosystem may provide an insight into the potential changes to the physical oceanography and ecology of the Southern Ocean. In this study, a multivariate statistical approach was used to compare the distribution and abundance of bacteria occurring in pack ice at the tongue of the Mertz Glacier (George V Coast, Antarctica) with bacteria from fast ice at Cape Hallett (Victoria Land coastline, Antarctica). Estimates of bacterial abundance were derived using both epifluorescence microscopy and flow cytometry and correlated with algal and chlorophyll a data. Significant differences in the vertical distribution of cells within the ice were observed between the Mertz Glacier and Cape Hallett, but no overall difference in cell abundance was found between the two locations with 7.6 ± 1.2 x 109 cells per m2 and 8.7 ± 1.6 x 109 cells per m2 respectively. Bacteria and algae were positively correlated in pack ice of the Mertz Glacier indicating a functional microbial loop, but no discernable relationship was exhibited in multiyear ice at Cape Hallett. These findings support the general consensus that the generation of bacterial biomass from algal-derived dissolved organic matter is highly variable across seasons and habitats. The tetrazolium salt 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) was used to investigate the bacterial response to experimentally induced changes in light and salinity in fast ice at Cape Hallett. Two distinct assemblages were examined; the brine channel assemblage near the surface of the ice and the interstitial or bottom assemblage. This study presents preliminary evidence that the metabolic activity of brine bacteria is influenced by light stimulus, most likely as a response to increased levels of algal-derived dissolved organic matter. No cells were deemed to be metabolically active when incubated in the dark, while on average thirty-eight percent of the cells incubated at 150 =mol photons m-2 s-1 were metabolically active. Additional results indicate that salt concentration is more significant than light irradiance in influencing the metabolic response of cells present in the interstitial region of the sea ice profile. When acclimated over a period of eight hours, cells exhibited a tolerance to changing saline concentrations, but after a further eight hours there is some evidence to suggest activity is reduced at either end of the saline regime. Bacterial metabolic activity in each assemblage is thus thought to reflect the fundamentally different light and saline environments within the sea ice. Metabolic probes such as CTC will prove useful in providing a mechanistic understanding of productivity and trophodynamics in the Antarctic coastal ecosystem, and may contribute to prognostic models for qualifying the resilience of the microbial community to climate change.</p>

scholarly journals Insignificant effect of climate change on winter haze pollution in Beijing

2018 ◽  
Vol 18 (23) ◽  
pp. 17489-17496 ◽  
Author(s):  
Lu Shen ◽  
Daniel J. Jacob ◽  
Loretta J. Mickley ◽  
Yuxuan Wang ◽  
Qiang Zhang
Keyword(s):  
Climate Change ◽  
Sea Ice ◽  
21St Century ◽  
Climate Models ◽  
Eastern China ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Climate Projections ◽  
Haze Pollution ◽  
Arctic Sea

Abstract. Several recent studies have suggested that 21st century climate change will significantly worsen the meteorological conditions, leading to very high concentrations of fine particulate matter (PM2.5) in Beijing in winter (Beijing haze). We find that 81 % of the variance in observed monthly PM2.5 during 2010–2017 winters can be explained by a single meteorological mode, the first principal component (PC1) of the 850 hPa meridional wind velocity (V850) and relative humidity (RH). V850 and RH drive stagnation and chemical production of PM2.5, respectively, and thus have a clear causal link to Beijing haze. PC1 explains more of the variance in PM2.5 than either V850 or RH alone. Using additional meteorological variables does not explain more of the variance in PM2.5. Therefore PC1 can serve as a proxy for Beijing haze in the interpretation of long-term climate records and in future climate projections. Previous studies suggested that shrinking Arctic sea ice would worsen winter haze conditions in eastern China, but we show with the PC1 proxy that Beijing haze is correlated with a dipole structure in the Arctic sea ice rather than with the total amount of sea ice. Beijing haze is also correlated with dipole patterns in Pacific sea surface temperatures (SSTs). We find that these dipole patterns of Arctic sea ice and Pacific SSTs shift and change sign on interdecadal scales, so that they cannot be used reliably as future predictors for the haze. Future 21st century trends of the PC1 haze proxy computed from the CMIP5 ensemble of climate models are statistically insignificant. We conclude that climate change is unlikely to significantly offset current efforts to decrease Beijing haze through emission controls.

scholarly journals Physical and Structural Characteristics of Antarctic Sea Ice

1982 ◽  
Vol 3 ◽  
pp. 113-117 ◽  
Author(s):  
A.J. Gow ◽  
S.F. Ackley ◽  
W.F. Weeks ◽  
J.W. Govoni
Keyword(s):  
Sea Ice ◽  
Structural Characteristics ◽  
Weddell Sea ◽  
The Arctic ◽  
Mcmurdo Sound ◽  
Frazil Ice ◽  
Antarctic Sea Ice ◽  
Pack Ice ◽  
Fast Ice ◽  
Ice Production

Observations during February and March 1980 of structures in 66 separate floes in Weddell Sea pack ice show widespread occurrence of frazil ice in amounts not previously reported in sea ice of comparable age and thickness in the Arctic. It is estimated that as much as 50% of the total ice production in the Weddell Sea is generated as frazil. Average floe salinities also appear higher than those of their Arctic counterparts. Comparative studies of fast ice at 28 locations in McMurdo Sound show this ice to be composed almost entirely of congelation ice that exhibits crystalline textures and orientations that are similar to those observed in Arctic fast ice. However, average fast-ice salinities in McMurdo Sound are higher than those reported for Arctic fast ice of comparable age and thickness.

scholarly journals East Antarctic Landfast Sea Ice Distribution and Variability, 2000–08

2012 ◽  
Vol 25 (4) ◽  
pp. 1137-1156 ◽  
Author(s):  
Alexander D. Fraser ◽  
Robert A. Massom ◽  
Kelvin J. Michael ◽  
Benjamin K. Galton-Fenzi ◽  
Jan L. Lieser
Keyword(s):  
Time Series ◽  
Indian Ocean ◽  
Sea Ice ◽  
Western Pacific Ocean ◽  
Indian Ocean Sector ◽  
Fast Ice ◽  
The Indian Ocean ◽  
Landfast Sea Ice ◽  
Ocean Sector ◽  
The Western Pacific

Abstract This study presents the first continuous, high spatiotemporal resolution time series of landfast sea ice extent along the East Antarctic coast for the period March 2000–December 2008. The time series was derived from consecutive 20-day cloud-free Moderate Resolution Imaging Spectroradiometer (MODIS) composite images. Fast ice extent across the East Antarctic coast shows a statistically significant (1.43% ±0.30% yr−1) increase. Regionally, there is a strong increase in the Indian Ocean sector (20°–90°E, 4.07% ±0.42% yr−1), and a nonsignificant decrease in the western Pacific Ocean sector (90°–160°E, −0.40% ±0.37% yr−1). An apparent shift from a negative to a positive extent trend is observed in the Indian Ocean sector from 2004. This shift also coincides with a greater amount of interannual variability. No such shift in apparent trend is observed in the western Pacific Ocean sector, where fast ice extent is typically higher and variability lower than the Indian Ocean sector. The limit to the maximum fast ice areal extent imposed by the location of grounded icebergs modulates the shape of the mean annual fast ice extent cycle to give a broad maximum and an abrupt, relatively transient minimum. Ten distinct fast ice regimes are identified, related to variations in bathymetry and coastal configuration. Fast ice is observed to form in bays, on the windward side of large grounded icebergs, between groups of smaller grounded icebergs, between promontories, and upwind of coastal features (e.g., glacier tongues). Analysis of the timing of fast ice maxima and minima is also presented and compared with overall sea ice maxima/minima timing.

scholarly journals 18 year record of circum-Antarctic landfast sea ice distribution allows detailed baseline characterisation, reveals trends and variability

2021 ◽  
Author(s):  
Alexander D. Fraser ◽  
Robert A. Massom ◽  
Mark S. Handcock ◽  
Phillip Reid ◽  
Kay I. Ohshima ◽  
...  
Keyword(s):  
Sea Ice ◽  
Ross Sea ◽  
Significant Advance ◽  
Positive Trend ◽  
Coastal System ◽  
Ice Coverage ◽  
Current State ◽  
Wide Range ◽  
Fast Ice ◽  
Landfast Sea Ice

Abstract. Landfast sea ice (fast ice) is an important though poorly-understood component of the cryosphere on the Antarctic continental shelf, where it plays a key role in atmosphere-ocean-ice sheet interaction and coupled ecological and biogeochemical processes. Here, we present a first in-depth baseline analysis of variability and change in circum-Antarctic fast-ice distribution (including its relationship to bathymetry), based on a new high-resolution satellite-derived time series for the period 2000 to 2018. This reveals a) an overall trend of −882 ± 824 km²/y (−0.19 ± 0.18 %/y); and b) eight distinct regions in terms of fast-ice coverage and modes of formation. Of these, four exhibit positive trends over the 18 y period and four negative. Positive trends are seen in East Antarctica and in the Bellingshausen sea, with this region claiming the largest positive trend of +1,198 ± 359 km²/y (+1.10 ± 0.35 %/y). The four negative trends predominantly occur in West Antarctica, with the largest negative trend of −1,206 ± 277 km²/y (−1.78 ± 0.41 %/y) occurring in the Victoria and Oates Lands region in the eastern Ross Sea. All trends are significant. This new baseline analysis represents a significant advance in our knowledge of the current state of both the global cryosphere and the complex Antarctic coastal system that is vulnerable to climate variability and change. It will also inform a wide range of other studies.

scholarly journals Antarctic Bacteria, Sea Ice Ecosystem Dynamics, and Global Climate Change

2021 ◽  
Author(s):  
◽  
Andrew Robert Martin
Keyword(s):  
Climate Change ◽  
Organic Matter ◽  
Microbial Community ◽  
Dissolved Organic Matter ◽  
Southern Ocean ◽  
Sea Ice ◽  
Metabolic Activity ◽  
Bacterial Response ◽  
Pack Ice ◽  
Fast Ice

<p>Productivity in the Southern Ocean reflects both the spatial and temporal dynamics of the sea ice ecosystem, as well as the complex cycling of energy through the microbial community. Marine bacteria are thought to be integral to trophodynamics and the functioning of a microbial loop within the ice matrix, but there is no clear understanding of the distribution and diversity of bacteria or the importance of bacterial production. Understanding the bacterial response to environmental change in the sea ice ecosystem may provide an insight into the potential changes to the physical oceanography and ecology of the Southern Ocean. In this study, a multivariate statistical approach was used to compare the distribution and abundance of bacteria occurring in pack ice at the tongue of the Mertz Glacier (George V Coast, Antarctica) with bacteria from fast ice at Cape Hallett (Victoria Land coastline, Antarctica). Estimates of bacterial abundance were derived using both epifluorescence microscopy and flow cytometry and correlated with algal and chlorophyll a data. Significant differences in the vertical distribution of cells within the ice were observed between the Mertz Glacier and Cape Hallett, but no overall difference in cell abundance was found between the two locations with 7.6 ± 1.2 x 109 cells per m2 and 8.7 ± 1.6 x 109 cells per m2 respectively. Bacteria and algae were positively correlated in pack ice of the Mertz Glacier indicating a functional microbial loop, but no discernable relationship was exhibited in multiyear ice at Cape Hallett. These findings support the general consensus that the generation of bacterial biomass from algal-derived dissolved organic matter is highly variable across seasons and habitats. The tetrazolium salt 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) was used to investigate the bacterial response to experimentally induced changes in light and salinity in fast ice at Cape Hallett. Two distinct assemblages were examined; the brine channel assemblage near the surface of the ice and the interstitial or bottom assemblage. This study presents preliminary evidence that the metabolic activity of brine bacteria is influenced by light stimulus, most likely as a response to increased levels of algal-derived dissolved organic matter. No cells were deemed to be metabolically active when incubated in the dark, while on average thirty-eight percent of the cells incubated at 150 =mol photons m-2 s-1 were metabolically active. Additional results indicate that salt concentration is more significant than light irradiance in influencing the metabolic response of cells present in the interstitial region of the sea ice profile. When acclimated over a period of eight hours, cells exhibited a tolerance to changing saline concentrations, but after a further eight hours there is some evidence to suggest activity is reduced at either end of the saline regime. Bacterial metabolic activity in each assemblage is thus thought to reflect the fundamentally different light and saline environments within the sea ice. Metabolic probes such as CTC will prove useful in providing a mechanistic understanding of productivity and trophodynamics in the Antarctic coastal ecosystem, and may contribute to prognostic models for qualifying the resilience of the microbial community to climate change.</p>

scholarly journals Seasonal and interannual variability of landfast sea ice in Atka Bay, Weddell Sea, Antarctica

2020 ◽  
Author(s):  
Stefanie Arndt ◽  
Mario Hoppmann ◽  
Holger Schmithüsen ◽  
Alexander D. Fraser ◽  
Marcel Nicolaus
Keyword(s):  
Sea Ice ◽  
Interannual Variability ◽  
Snow Accumulation ◽  
Weddell Sea ◽  
Critical Element ◽  
Subsequent Formation ◽  
Seasonal And Interannual Variability ◽  
Meteorological Observatory ◽  
Fast Ice ◽  
Landfast Sea Ice

Abstract. Landfast sea ice (fast ice), attached to Antarctic coastal and near-coastal elements, is a critical element of the local physical and ecological systems. Through its direct coupling with the atmosphere and ocean, fast ice and its snow cover are also potential indicators of processes related to climate change. However, in-situ fast-ice observations in Antarctica are extremely sparse because of logistical challenges. Since 2010, a monitoring program, which is part of the Antarctic Fast Ice Network (AFIN), has been conducted on the seasonal evolution of fast ice of Atka Bay. The bay is located on the north-eastern edge of Ekström Ice Shelf in the eastern Weddell Sea, close to the German wintering station Neumayer Station III. A number of sampling sites have been regularly revisited between annual ice formation and breakup each year to obtain a continuous record of snow depth, freeboard, sea-ice- and sub-ice platelet layer thickness across the bay. Here, we present the time series of these measurements over the last nine years. Combining them with observations from the nearby meteorological observatory at Neumayer Station as well as satellite images allows to relate the seasonal and interannual fast-ice cycle to the factors that influence its evolution. On average, the annual consolidated fast-ice thickness at the end of the growth season is about two meters, with a loose platelet layer accumulation of four meters beneath and 0.70 meters snow on top. Results highlight the predominately seasonal character of the fast-ice regime in Atka Bay without a significant trend in any of the observed variables over the nine-year observation period. Also, no changes are evident when comparing with measurements in the 1980s. However, strong easterly winds in the area govern the year-round snow redistribution and also trigger the breakup event in the bay during summer months. Due to the substantial snow accumulation on the ice, a characteristic feature is frequent negative freeboard, associated flooding of the snow/ice interface and subsequent formation of snow ice. The buoyant platelet-ice layer beneath negates the snow weight to some extent, but snow thermodynamics is identified as the main driver of the energy and mass budgets for the fast-ice cover in Atka Bay. An enhanced knowledge on the seasonal and interannual variability of the fast-ice properties will improve our understanding of interactions between atmosphere, fast ice, ocean and ice shelves in one of the key regions of Antarctica.

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