New estimates of Arctic and Antarctic sea ice extent during September 1964 from recovered Nimbus I satellite imagery

Abstract. Satellite imagery from the 1964 Nimbus I satellite has been recovered, digitized, and processed to estimate Arctic and Antarctic sea ice extent for September 1964. September is the month when the Arctic reaches its minimum annual extent and the Antarctic reaches its maximum. Images were manually analyzed over a three-week period to estimate the location of the ice edge and then composited to obtain a hemispheric average. Uncertainties were based on limitations in the image analysis and the variation of the ice cover over the three week period. The 1964 Antarctic extent is higher than estimates from the 1979–present passive microwave record, but is in accord with previous indications of higher extents during the 1960s. The Arctic 1964 extent was near the 1979–2000 average from the passive microwave record, suggesting relatively stable summer extents until the recent large decrease. This early satellite record puts the recently observed into a longer-term context.

Download Full-text

New estimates of Arctic and Antarctic sea ice extent during September 1964 from recovered Nimbus I satellite imagery

The Cryosphere ◽

10.5194/tc-7-699-2013 ◽

2013 ◽

Vol 7 (2) ◽

pp. 699-705 ◽

Cited By ~ 38

Author(s):

W. N. Meier ◽

D. Gallaher ◽

G. G. Campbell

Keyword(s):

Sea Ice ◽

Satellite Imagery ◽

Arctic Sea Ice ◽

Passive Microwave ◽

The Arctic ◽

Sea Ice Extent ◽

Antarctic Sea Ice ◽

1960S And 1970S ◽

The 1960S ◽

The Antarctic

Abstract. Visible satellite imagery from the 1964 Nimbus I satellite has been recovered, digitized, and processed to estimate Arctic and Antarctic sea ice extent for September 1964. September is the month when the Arctic sea ice reaches its minimum annual extent and the Antarctic sea ice reaches its maximum. Images from a three-week period were manually analyzed to estimate the location of the ice edge and then composited to obtain a hemispheric estimate. Uncertainties were based on limitations in the image analysis and the variation of the ice cover over the three-week period. The 1964 Antarctic extent is higher than estimates from the 1979–present passive microwave record, but is in accord with previous indications of higher extents during the 1960s. The Arctic 1964 extent is near the 1979–2000 average from the passive microwave record, suggesting relatively stable summer extents during the 1960s and 1970s preceding the downward trend since 1979 and particularly the large decrease in the last decade. These early satellite data put the recently observed record into a longer-term context.

Download Full-text

Antarctic summer sea ice concentration and extent: comparison of ODEN 2006 ship observations, satellite passive microwave and NIC sea ice charts

The Cryosphere Discussions ◽

10.5194/tcd-2-623-2008 ◽

2008 ◽

Vol 2 (4) ◽

pp. 623-647 ◽

Cited By ~ 3

Author(s):

B. Ozsoy-Cicek ◽

H. Xie ◽

S. F. Ackley ◽

K. Ye

Keyword(s):

Sea Ice ◽

Linear Trend ◽

Passive Microwave ◽

The Arctic ◽

Poor Correlation ◽

Sea Ice Concentration ◽

Sea Ice Extent ◽

Antarctic Sea Ice ◽

Ice Concentration ◽

Ice Edge

Abstract. Antarctic sea ice cover has shown a slight increase in overall observed ice extent as derived from satellite mapping from 1979 to 2008, contrary to the decline observed in the Arctic regions. Spatial and temporal variations of the Antarctic sea ice however remain a significant problem to monitor and understand, primarily due to the vastness and remoteness of the region. While satellite remote sensing has provided and has great future potential to monitor the variations and changes of sea ice, uncertainties remain unresolved. In this study, the National Ice Center (NIC) ice edge and the AMSR-E (Advanced Microwave Scanning Radiometer – Earth Observing System) ice extent are examined, while the ASPeCt (Antarctic Sea Ice Process and Climate) ship observations from the Oden expedition in December 2006 are used as ground truth to verify the two products during Antarctic summer. While there is a general linear trend between ASPeCt and AMSR-E ice concentration estimates, there is poor correlation (R2=0.41) and AMSR-E tends to underestimate the low ice concentrations. We also found that the NIC sea ice edge agrees well with ship observations, while the AMSR-E shows the ice edge further south, consistent with its poorer detection of low ice concentrations. The northward extent of the ice edge at the time of observation (NIC) had mean values varying from 38 km to 102 km greater on different days for the area as compared with the AMSR-E sea ice extent. For the circumpolar area as a whole in the December period examined, AMSR-E therefore underestimates the area inside the ice edge at this time by up to 14% or, 1.5 million km2 less area, compared to the NIC ice charts. These differences alone can account for more than half of the purported sea ice loss between the pre 1960s and the satellite era suggested earlier from comparative analysis of whale catch data with satellite derived data. Preliminary comparison of satellite scatterometer data suggests better resolution of low concentrations than passive microwave, and therefore better fidelity with ship observations and NIC charts of the area inside the ice edge during Antarctic summer.

Download Full-text

Antarctic summer sea ice concentration and extent: comparison of ODEN 2006 ship observations, satellite passive microwave and NIC sea ice charts

The Cryosphere ◽

10.5194/tc-3-1-2009 ◽

2009 ◽

Vol 3 (1) ◽

pp. 1-9 ◽

Cited By ~ 12

Author(s):

B. Ozsoy-Cicek ◽

H. Xie ◽

S. F. Ackley ◽

K. Ye

Keyword(s):

Sea Ice ◽

Linear Trend ◽

Passive Microwave ◽

The Arctic ◽

Poor Correlation ◽

Sea Ice Extent ◽

Data Set ◽

Antarctic Sea Ice ◽

Ice Concentration ◽

Ice Edge

Abstract. Antarctic sea ice cover has shown a slight increase (<1%/decade) in overall observed ice extent as derived from satellite mapping from 1979 to 2008, contrary to the decline observed in the Arctic regions. Spatial and temporal variations of the Antarctic sea ice however remain a significant problem to monitor and understand, primarily due to the vastness and remoteness of the region. While satellite remote sensing has provided and has great future potential to monitor the variations and changes of sea ice, uncertainties remain unresolved. In this study, the National Ice Center (NIC) ice edge and the AMSR-E (Advanced Microwave Scanning Radiometer-Earth Observing System) ice extent are examined, while the ASPeCt (Antarctic Sea Ice Process and Climate) ship observations from the Oden expedition in December 2006 are used as ground truth to verify the two products during Antarctic summer. While there is a general linear trend between ASPeCt and AMSR-E ice concentration estimates, there is poor correlation (R2=0.41) and AMSR-E tends to underestimate the low ice concentrations. We also found that the NIC sea ice edge agrees well with ship observations, while the AMSR-E shows the ice edge further south, consistent with its poorer detection of low ice concentrations. The northward extent of the ice edge at the time of observation (NIC) had mean values varying from 38 km to 102 km greater on different days for the area as compared with the AMSR-E sea ice extent. For the circumpolar area as a whole in the December period examined, AMSR-E therefore may underestimate the area inside the ice edge at this time by up to 14% or, 1.5 million km2 less area, compared to the NIC ice charts. Preliminary comparison of satellite scatterometer data however, suggests better resolution of low concentrations than passive microwave, and therefore better agreement with ship observations and NIC charts of the area inside the ice edge during Antarctic summer. A reanalysis data set for Antarctic sea ice extent that relies on the decade long scatterometer and high resolution satellite data set, instead of passive microwave, may therefore give better fidelity for the recent sea ice climatology.

Download Full-text

A Regime Shift in Seasonal Total Antarctic Sea Ice Extent in the 20th Century

10.21203/rs.3.rs-828060/v1 ◽

2021 ◽

Author(s):

Ryan Fogt ◽

Amanda Sleinkofer ◽

Marilyn Raphael ◽

Mark Handcock

Keyword(s):

Sea Ice ◽

20Th Century ◽

Climate Models ◽

Historical Context ◽

The Arctic ◽

Sea Ice Extent ◽

Antarctic Sea Ice ◽

Coupled Climate Models ◽

High Degree ◽

The Antarctic

Abstract In stark contrast to the Arctic, there have been statistically significant positive trends in total Antarctic sea ice extent since 1979, despite a sudden decline in sea ice in 2016(1–5) and increasing greenhouse gas concentrations. Attributing Antarctic sea ice trends is complicated by the fact that most coupled climate models show negative trends in sea ice extent since 1979, opposite of that observed(6–8). Additionally, the short record of sea ice extent (beginning in 1979), coupled with the high degree of interannual variability, make the record too short to fully understand the historical context of these recent changes(9). Here we show, using new robust observation-based reconstructions, that 1) these observed recent increases in Antarctic sea ice extent are unique in the context of the 20th century and 2) the observed trends are juxtaposed against statistically significant decreases in sea ice extent throughout much of the early and middle 20th century. These reconstructions are the first to provide reliable estimates of total sea ice extent surrounding the continent; previous proxy-based reconstructions are limited(10). Importantly, the reconstructions continue to show the high degree of interannual Antarctic sea ice extent variability that is marked with frequent sudden changes, such as observed in 2016, which stress the importance of a longer historical context when assessing and attributing observed trends in Antarctic climate(9). Our reconstructions are skillful enough to be used in climate models to allow better understanding of the interconnected nature of the Antarctic climate system and to improve predictions of the future state of Antarctic climate.

Download Full-text

A spurious jump in the satellite record: has Antarctic sea ice expansion been overestimated?

The Cryosphere ◽

10.5194/tc-8-1289-2014 ◽

2014 ◽

Vol 8 (4) ◽

pp. 1289-1296 ◽

Cited By ~ 43

Author(s):

I. Eisenman ◽

W. N. Meier ◽

J. R. Norris

Keyword(s):

Sea Ice ◽

Ice Cover ◽

Current Data ◽

The Arctic ◽

Sea Ice Extent ◽

Data Set ◽

Antarctic Sea Ice ◽

Ice Retreat ◽

Bootstrap Algorithm ◽

The Antarctic

Abstract. Recent estimates indicate that the Antarctic sea ice cover is expanding at a statistically significant rate with a magnitude one-third as large as the rapid rate of sea ice retreat in the Arctic. However, during the mid-2000s, with several fewer years in the observational record, the trend in Antarctic sea ice extent was reported to be considerably smaller and statistically indistinguishable from zero. Here, we show that much of the increase in the reported trend occurred due to the previously undocumented effect of a change in the way the satellite sea ice observations are processed for the widely used Bootstrap algorithm data set, rather than a physical increase in the rate of ice advance. Specifically, we find that a change in the intercalibration across a 1991 sensor transition when the data set was reprocessed in 2007 caused a substantial change in the long-term trend. Although our analysis does not definitively identify whether this change introduced an error or removed one, the resulting difference in the trends suggests that a substantial error exists in either the current data set or the version that was used prior to the mid-2000s, and numerous studies that have relied on these observations should be reexamined to determine the sensitivity of their results to this change in the data set. Furthermore, a number of recent studies have investigated physical mechanisms for the observed expansion of the Antarctic sea ice cover. The results of this analysis raise the possibility that much of this expansion may be a spurious artifact of an error in the processing of the satellite observations.

Download Full-text

Spatio-temporal variability and decadal trends of snowmelt processes on Antarctic sea ice observed by satellite scatterometers

10.5194/tc-2019-27 ◽

2019 ◽

Author(s):

Stefanie Arndt ◽

Christian Haas

Keyword(s):

Time Series ◽

Sea Ice ◽

Weddell Sea ◽

Passive Microwave ◽

The Arctic ◽

Signal Frequency ◽

Onset Date ◽

Sea Ice Extent ◽

Antarctic Sea Ice ◽

Perennial Ice

Abstract. The timing and intensity of snowmelt processes on sea ice are key drivers determining the seasonal sea-ice energy and mass budgets. In the Arctic, satellite passive microwave and radar observations have revealed a trend towards an earlier snowmelt onset during the last decades, which is an important aspect of Arctic amplification and sea ice decline. Around Antarctica, snowmelt on perennial ice is weak and very different than in the Arctic, with most snow surviving the summer. Here we compile time series of snowmelt-onset dates on seasonal and perennial Antarctic sea ice from 1992 to 2014/15 using active microwave observations from European Remote Sensing Satellite (ERS-1/2), Quick Scatterometer (QSCAT) and Advanced Scatterometer (ASCAT) radar scatterometers. We define two snowmelt transition stages: A weak backscatter rise indicating the initial warming and metamorphism of the snowpack (pre-melt), followed by a rapid backscatter rise indicating the onset of thaw-freeze cycles (snowmelt). Results show large interannual variability with an average pre-melt onset date of 29 November and melt onset of 10 December, respectively, on perennial ice, without any significant trends over the study period, consistent with the small trends of Antarctic sea ice extent. There was a latitudinal gradient from early snowmelt onsets in mid-November in the northern Weddell Sea to late (end-December) or even absent snowmelt conditions in the southern Weddell Sea. We show that QSCAT Ku-band (13.4 GHz signal frequency) derived pre-melt and snowmelt onset dates are earlier by 25 and 11 days, respectively, than ERS and ASCAT C-band (5.6 GHz) derived dates. This offset has been considered when constructing the time series. Snowmelt onset dates from passive microwave observations (37 GHz) are later by 13 and 5 days than those from the scatterometers, respectively. Based on these characteristic differences between melt onset dates observed by different microwave wavelengths, we developed a conceptual model which illustrates how the evolution of seasonal snow temperature profiles affects different microwave bands with different penetration depths. These suggest that future multi-frequency active/passive microwave satellite missions could be used to resolve melt processes throughout the vertical snow column.

Download Full-text

Brief communication: Increasing shortwave absorption over the Arctic Ocean is not balanced by trends in the Antarctic

The Cryosphere ◽

10.5194/tc-11-2111-2017 ◽

2017 ◽

Vol 11 (5) ◽

pp. 2111-2116 ◽

Cited By ~ 3

Author(s):

Christian Katlein ◽

Stefan Hendricks ◽

Jeffrey Key

Keyword(s):

Sea Ice ◽

Cloud Cover ◽

Arctic Sea Ice ◽

Shortwave Radiation ◽

The Arctic ◽

Sea Ice Extent ◽

Antarctic Sea Ice ◽

Arctic Sea ◽

The Antarctic

Abstract. On the basis of a new, consistent, long-term observational satellite dataset we show that, despite the observed increase of sea ice extent in the Antarctic, absorption of solar shortwave radiation in the Southern Ocean poleward of 60° latitude is not decreasing. The observations hence show that the small increase in Antarctic sea ice extent does not compensate for the combined effect of retreating Arctic sea ice and changes in cloud cover, which both result in a total increase in solar shortwave energy deposited into the polar oceans.

Download Full-text

Impact of ice sheet – ocean interactions on the Southern Ocean using fully coupled models over a circumpolar domain

10.5194/egusphere-egu21-4325 ◽

2021 ◽

Author(s):

Charles Pelletier ◽

Lars Zipf ◽

Konstanze Haubner ◽

Deborah Verfaillie ◽

Hugues Goosse ◽

...

Keyword(s):

Southern Ocean ◽

Sea Ice ◽

Ice Sheet ◽

The Arctic ◽

Surface Cooling ◽

Coupled Models ◽

Sea Ice Extent ◽

Antarctic Ice Sheet ◽

Antarctic Sea Ice ◽

The Antarctic

<p>From at least 1979 up until 2016, the surface of the Southern Ocean cooled down, leading to a small Antarctic sea ice extent increase, which is in stark contrast with the Arctic Ocean. The attribution of the origin of these robust observations is still very uncertain. Among other phenomena, the direct, two-way interactions between the Southern Ocean and the Antarctic ice sheet, through basal melting of its numerous and large ice-shelf cavities, have been suggested as a potentially important contributor of this cooling. In order to address this question, we perform multidecadal coupled ice sheet &#8211; ocean numerical simulations relying on f.ETISh-v1.7 and NEMO3.6-LIM3 for simulating the Antarctic ice sheet and Southern Ocean (including sea ice), respectively. This presentation is twofold. First, we present the technical aspects of the coupling infrastructure (e.g. workflow and exchanged information in between models). Second, we investigate the ice sheet &#8211; ocean feedbacks on the Southern Ocean, their interactions, and the roles of the related physical mechanisms on the ocean surface cooling.</p>

Download Full-text

A spurious jump in the satellite record: is Antarctic sea ice really expanding?

The Cryosphere Discussions ◽

10.5194/tcd-8-273-2014 ◽

2014 ◽

Vol 8 (1) ◽

pp. 273-288 ◽

Cited By ~ 4

Author(s):

I. Eisenman ◽

W. N. Meier ◽

J. R. Norris

Keyword(s):

Sea Ice ◽

Ice Cover ◽

The Arctic ◽

Sea Ice Extent ◽

Physical Mechanisms ◽

Antarctic Sea Ice ◽

Ice Retreat ◽

Bootstrap Algorithm ◽

Sea Ice Retreat ◽

The Antarctic

Abstract. Recent estimates indicate that the Antarctic sea ice cover is expanding at a statistically significant rate with a magnitude one third as large as the rapid rate of sea ice retreat in the Arctic. However, during the mid-2000s, with several fewer years in the observational record, the trend in Antarctic sea ice extent was reported to be considerably smaller and statistically indistinguishable from zero. Here, we show that the increase in the reported trend occurred primarily due to the effect of a previously undocumented change in the way the satellite sea ice observations are processed for the widely-used Bootstrap algorithm dataset, rather than a physical increase in the rate of ice advance. Although our analysis does not definitively identify whether this undocumented change introduced an error or removed one, the resulting difference in the trends suggests that a substantial error exists in either the current dataset or the version that was used prior to the mid-2000s, and numerous studies that have relied on these observations should be reexamined to determine the sensitivity of their results to this change in the dataset. Furthermore, a number of recent studies have investigated physical mechanisms for the observed expansion of the Antarctic sea ice cover. The results of this analysis raise the possibility that this expansion may be a spurious artifact of an error in the satellite observations, and that the actual Antarctic sea ice cover may not be expanding at all.

Download Full-text

Inter-annual variations observed in spring and summer Antarctic sea ice extent in recent decade

MAUSAM ◽

10.54302/mausam.v62i4.381 ◽

2021 ◽

Vol 62 (4) ◽

pp. 633-640

Author(s):

SANDIP R.OZA ◽

R.K.K. SINGH ◽

ABHINAV SRIVASTAVA ◽

MIHIR K.DASH ◽

I.M.L. DAS ◽

...

Keyword(s):

Southern Ocean ◽

Sea Ice ◽

Large Scale ◽

Ross Sea ◽

Ice Cover ◽

Weddell Sea ◽

The Arctic ◽

Sea Ice Extent ◽

Antarctic Sea Ice ◽

The Antarctic

The growth and decay of sea ice are complex processes and have important feedback onto the oceanic and atmospheric circulation. In the Antarctic, sea ice variability significantly affects the primary productivity in the Southern Ocean and thereby negatively influences the performance and survival of species in polar ecosystem. In present days, the awareness on the sea ice variability in the Antarctic is not as matured as it is for the Arctic region. The present paper focuses on the inter-annual trends (1999-2009) observed in the monthly fractional sea ice cover in the Antarctic at 1 × 1 degree level, for the November and February months, derived from QuikSCAT scatterometer data. OSCAT scatterometer data from India’s Oceansat-2 satellite were used to asses the sea ice extent (SIE) observed in the month of November 2009 and February 2010 and its deviation from climatic maximum (1979-2002) sea ice extent (CMSIE). Large differences were observed between SIE and CMSIE, however, trend results show that it is due to the high inter-annual variability in sea ice cover. Spatial distribution of trends show the existence of positive and negative trends in the parts of Western Pacific Ocean, Ross Sea, Amundsen and Bellingshausen Seas (ABS), Weddell Sea and Indian ocean sector of southern ocean. Sea ice trends are compared with long-term SST trends (1982-2009) observed in the austral summer month of February. Large-scale cooling trend observed around Ross Sea and warming trend in ABS sector are the distinct outcome of the study.

Download Full-text