Extent Of Ice Cover Research Articles

Effects on zooplankton of a warmer ocean: Recent evidence from the Northeast Pacific

The consequences for pelagic communities of warming trends in mid and high latitude ocean regions could be substantial, but their magnitude and trajectory are not yet known. Environmental changes predicted by climate models (and beginning to be confirmed by observations) include warming and freshening of the upper ocean and reduction in the extent and duration of ice cover. One way to evaluate response scenarios is by comparing how “similar” zooplankton communities have differed among years and/or locations with differing temperature. The subarctic Pacific is a strong candidate for such comparisons, because the same mix of zooplankton species dominates over a wide range of temperature climatologies, and observations have spanned substantial temperature variability at interannual-to-decadal time scales. In this paper, we review and extend copepod abundance and phenology time series from net tow and Continuous Plankton Recorder surveys in the subarctic Northeast Pacific. The two strongest responses we have observed are latitudinal shifts in centers of abundance of many species (poleward under warm conditions), and changes in the life cycle timing of Neocalanus plumchrus in both oceanic and coastal regions (earlier by several weeks in warm years and at warmer locations). These zooplankton data, plus indices of higher trophic level responses such as reproduction, growth and survival of pelagic fish and seabirds, are all moderately-to-strongly intercorrelated (∣ r∣ = 0.25–0.8) with indices of local and basin-scale temperature anomalies. A principal components analysis of the normalized anomaly time series from 1979 to 2004 shows that a single “warm-and-low-productivity” vs. “cool-and-high-productivity” component axis accounts for over half of the variance/covariance. Prior to 1990, the scores for this component were negative (“cool” and “productive”) or near zero except positive in the El Niño years 1983 and 1987. The scores were strongly and increasingly positive (“warm” and “low productivity”) from 1992 to 1998; negative from 1999 to 2002; and again increasingly positive from 2003-present. We suggest that, in strongly seasonal environments, anomalously high temperature may provide misleading environmental cues that contribute to timing mismatch between life history events and the more-nearly-fixed seasonality of insolation, stratification, and food supply.

Coevolution of continental ice cover and permafrost extent over the last glacial‐interglacial cycle in North America

The bed thermal characteristics of a glacial systems model that has been calibrated against a large set of relative sea level, geodetic, and strandline observations are examined for the previously glaciated sector of the North American continent. The model compares favorably against the present‐day extent of permafrost and against the observed temperature profiles from three deep boreholes when appropriate bed thermal conductivities are employed. Estimates for the present‐day depth field of the lower permafrost boundary are presented. We find a significant disequilibrium in the lower permafrost boundary for most of the Arctic region, with present‐day depth as much as 250 m shallower than the equilibrium value for present‐day climate forcing. This is largely due to the ongoing response to the loss of ice cover from the glacial period. The time evolution of the subglacial warm‐based area fraction is also presented together with calibration‐derived confidence intervals. A peak warm‐based fraction of 50% ± 6% is obtained at Last Glacial Maximum. The timing of the three largest ice volume maxima that were produced in response to the obliquity component of orbital forcing during the last glacial cycle matches that of the maxima for the warm‐based area fraction with no significant phase delay. Warm‐based conditions are required to enable ice streaming (fast flow) in the model. It is therefore hypothesized that the expansion of the area covered by warm‐based ice played a critical role in producing a highly dynamic ice sheet during both the most intense growth and recession phases.

Factors affecting seasonality of lithogenic and biogenic particle flux in a large estuarine ecosystem

Seasonal patterns of vertical flux over two years (2001–2003) at two stations in the Bras d'Or Lakes, a large estuary in Cape Breton Island, Nova Scotia, were determined using aluminum and organic carbon in settled particles collected in moored traps to calculate lithogenic (terrigenous) and marine biogenic fractions. On an annual basis, lithogenic material comprised 53% and 81% of dry weight and 48% and 66% of organic carbon in settled particles at the deep- (128 m) and shallow-water (41 m) locations, respectively. Peaks in runoff, inferred from rain and snowfall precipitation, ice cover and possible horizontal transport of resuspended sediment coincided with maximum sedimentation rates of lithogenic material during unstratified periods between October and March. Biological factors correlated with phytoplankton and ice algal primary production and seasonal changes in zooplankton grazing inferred from phaeopigments controlled biogenic particle fluxes under stratified conditions between June and September and during winter. Year-to-year variations in deposition of lithogenic and marine biogenic material depended on seasonal differences in stratification, precipitation, freeze/melt conditions and the extent of ice cover.

Abrupt climate change revisited

Taken together, evidence from east Greenland's mountain moraines and results from atmospheric models appear to provide the answer to a question which has long dogged abrupt climate change research: namely, how were impacts of the Younger Dryas (YD), Dansgaard–Oeschger (D–O) and Heinrich (H) events transmitted so quickly and efficiently throughout the northern hemisphere and tropics? The answer appears to lie in extensive winter sea ice formation which created Siberian-like conditions in the regions surrounding the northern Atlantic. Not only would this account for the ultra cold conditions in the north, but, as suggested by models, it would have pushed the tropical rain belt southward and weakened the monsoons. The requisite abrupt changes in the extent of sea ice cover are of course best explained by the turning on and turning off of the Atlantic's conveyor circulation.

Sediment Geochemistry In The Canadian Arctic

Given the current threat of fast-paced global change, it has become urgent to understand the biogeochemical response of the Arctic environment to external forcing. The Canadian Arctic Shelf Exchange Study (CASES) is an interdisciplinary project put together by scientists from across Canada whose primary goal is to gain a better understanding of the Canadian Arctic environment. Objectives include evaluating issues such as the impact of climate change – extent of sea ice cover - on biological productivity and the carbon cycle. In order to predict the potential evolution of the complex Canadian Arctic system, the intricacies of its current dynamics must first be understood.

Autonomous detection of cryospheric change with hyperion on-board Earth Observing-1

On-board detection of cryospheric change in sea ice, lake ice, and snow cover is being conducted as part of the Autonomous Sciencecraft Experiment (ASE), using classifiers developed for the Hyperion hyper-spectral visible/infrared spectrometer on-board the Earth Observing-1 (EO-1) spacecraft. This classifier development was done with consideration for the novel limitations of on-board processing, data calibration, spacecraft targeting error and the spectral range of the instrument. During on-board tests, these algorithms were used to measure the extent of cloud, snow, and ice cover at a global suite of targets. Coupled with baseline imaging, uploaded thresholds were used to detect cryospheric changes such as the freeze and thaw of lake ice and the formation and break-up of sea ice. These thresholds were used to autonomously trigger follow-up observations, demonstrating the capability of the technique for future planetary missions where downlink is a constrained resource and there is high interest in data covering dynamic events, including cryospheric change. Before upload classifier performance was assessed with an overall accuracy of 83.3% as measured against manual labeling of 134 scenes. Performance was further assessed against field mapping conducted at Lake Mendota, Wisconsin as well as with labeling of scenes that were classified during on-board tests.

28th DeBeers Alex. Du Toit Memorial Lecture, 2004. On Cryogenian (Neoproterozoic) ice-sheet dynamics and the limitations of the glacial sedimentary record

28th DeBeers Alex. Du Toit Memorial Lecture, 2004. On Cryogenian (Neoproterozoic) ice-sheet dynamics and the limitations of the glacial sedimentary record

CLIMATE CHANGE AND RINGED SEAL (PHOCA HISPIDA) RECRUITMENT IN WESTERN HUDSON BAY

Climate warming is predicted to reduce the extent of ice cover in the Arctic and, within the Hudson Bay region, the annual ice may be significantly decreased or entirely lost in the foreseeable future. The ringed seal (Phoca hispida), a key species that depends on sea ice, will likely be among the first marine mammals to show the negative effects of climatic warming. We used 639 ringed seals killed by Inuit hunters from western Hudson Bay (1991–1992, 1999–2001) to assess trends in recruitment relative to snow depth, snowfall, rainfall, temperature in April and May, North Atlantic Oscillation (NAO) from the previous winter, and timing of spring break-up. Snowfall and ringed seal recruitment varied from lower than average in the 1970s, to higher in 1980s and lower in 1990s. Prior to 1990, seal recruitment appeared to be related to timing of spring ice break-up which was correlated with the NAO. However, recent 1990–2001 environmental data indicate less snowfall, lower snow depth, and warmer temperatures in April and May when pups are born and nursed. Decreased snow depth, particularly below 32 cm, corresponded with a significant decrease in ringed seal recruitment as indicated by pups born and surviving to adults that were later harvested. Earlier spring break-up of sea ice together with snow trends suggest continued low pup survival in western Hudson Bay.

Synergy of active and passive satellite microwave data for the study of first-year sea ice in the Caspian and Aral seas

The paper discusses application of active and passive microwave data for assessment of time and space variations of first-year ice cover. The Caspian and Aral seas are chosen as main study areas. The Caspian Sea evolution is primarily climate driven, while for the Aral Sea there is a mix of anthropic and climate factors. We analyze ice cover conditions using a novel method that combines active and passive satellite measurements for ice discrimination. This method uses the synergy of simultaneous data from active (radar altimeter) and passive (radiometer) microwave instruments onboard the TOPEX/Poseidon (T/P) satellite, launched in 1992. The benefits, drawbacks, and potential of ice cover studies using the proposed method are discussed. We analyze in detail how this method is influenced by the difference in footprints of the T/P sensors and by the radiometric properties of ice and snow at different stages of ice cover evolution. In order to link the T/P-derived results to historical observations that end in the mid-1980s, long time series of passive microwave data from SMMR and SSM/I sensors have also been analyzed. Satellite time series of ice cover extent and duration of ice period have been obtained for the Caspian and Aral seas since 1978. A good agreement is obtained between historical and satellite data, with significant spatial and temporal variability of ice conditions. There is a marked decrease of both duration of ice season and ice extent during the winters 1998/1999-2001/2002. These satellite-derived time series of sea ice parameters are very valuable in view of the heterogeneous and mostly unpublished data on ice conditions over the Caspian and Aral seas since the mid-1980s.

Studies of the Antarctic sea ice edge and ice extent from satellite and ship observations

Passive microwave-derived ice edge locations in the Antarctic are assessed against in situ observations from ships between 1989 and 2000. During the growth season (March–October), the ship data agrees with satellite data very well, with r 2 values of 0.99 and 0.97 for the Bootstrap and Team algorithms, respectively. During the melt season (November–February), the agreement is not so good with the passive microwave ice edge typically 1–2° of latitude south of the observations. This is due to the low concentration and saturated nature of the ice, and the r 2 values for this period are 0.92 and 0.80 for the Bootstrap and Team algorithms, respectively. Sensitivity studies show that such an offset in the summer ice edge location can cause significant errors in trend studies of the extent of sea ice cover in the Southern Ocean. The passive microwave ice concentration at the ice edge observed by ship varies greatly, averaging 14% for the Team algorithm and 19% for the Bootstrap. Comparisons between passive microwave data and SAR, Landsat and OLS data during the ice growth season show that while small-scale details in ice edge location are lost, the passive microwave data generally provide good and consistent representation of the higher resolution imagery.

Modelling Pliocene warmth: contribution of atmosphere, oceans and cryosphere

The relative role of the atmosphere, oceans and cryosphere in contributing towards middle Pliocene warmth (ca 3 Ma BP) is investigated using the HadCM3 coupled ocean–atmosphere general circulation model. The model was initialised with boundary conditions from the USGS PRISM2 data set and a Pliocene atmospheric CO 2 level of 400 ppmv and run for 300 simulated years. The simulation resulted in a global surface temperature warming of 3°C compared to present-day. In contrast to earlier modelling experiments for the Pliocene, surface temperatures warmed in most areas including the tropics (1–5°C). Compared with present-day, the model predicts a general pattern of ocean warming (1–5°C) in both hemispheres to a depth of 2000 m, below which no significant differences are noted. Sea ice coverage is massively reduced (up to 90%). The flow of the Gulf Stream/North Atlantic Drift is up to 100 mm s −1 greater in the Pliocene case. Analysis of the model-predicted meridional streamfunction suggests a global pattern of reduced outflow of Antarctic bottom water (AABW; up to 5 Sv), a shallower depth for North Atlantic deep water formation and weaker thermohaline circulation (3 Sv). The decrease in AABW occurs mainly in the Pacific rather than Atlantic Ocean. Model diagnostics for heat transports indicate that neither the oceans nor the atmosphere are transporting significantly more heat in the Pliocene scenario. Rather, these results indicate that the major contributing mechanism to global Pliocene warmth was the reduced extent of high-latitude terrestrial ice sheets (50% reduction on Greenland, 33% reduction on Antarctica) and sea ice cover resulting in a strong ice-albedo feedback. These results highlight the need for further studies designed to improve our knowledge regarding Pliocene terrestrial ice configurations.

An 8-year cycle in krill biomass density inferred from acoustic surveys conducted in the vicinity of the South Shetland Islands during the austral summers of 1991–1992 through 2001–2002

Data from single and multi-frequency active acoustic surveys conducted annually in the vicinity of the South Shetland Islands, Antarctica were re-analyzed using updated procedures for delineating volume backscattering due to Antarctic krill, adjusting for signal contamination due to noise, and compensating for diel vertical migration of krill outside of the acoustic observation window. Intra-and inter-seasonal variations in krill biomass density and dispersion were derived from the re-processed data set for surveys conducted in the austral summers of 1991/1992 through 2001/2002. Estimated biomass density ranged from 1 to 60 g m –2, decreasing from mid-range levels in 1991/1992 to a minimum in 1992/1993–1993/1994, increasing to a peak in 1996/1997–1997/1998, and decreasing again through 2000/2001–2001/2002. Although this variability may be attributed to changes in the spatial distribution of krill relative to the survey area, comparisons with the proportion of juvenile krill in simultaneous net samples suggest that the changes in biomass density are consistent with apparent changes in reproductive success. A truncated Fourier series fit to the biomass density time series is dominated by an 8-year cycle and predicts an increase in krill biomass density in 2002/2003 and 2003/2004. This prediction is supported by an apparent association between cycles in the extent of sea ice cover and per-capita krill recruitment over the last 23 years and indications that ice cover in the winter of 2002 is seasonally early and extensive.

Wind‐driven shelf/basin exchange on an Arctic shelf: The joint roles of ice cover extent and shelf‐break bathymetry

The efficiency of shelf/basin exchange (SBE) in polar regions during summer is strongly moderated by the location of the ice edge relative to underlying topography. Numerical model calculations suggest that upwelling‐favorable winds generate very little SBE so long as the ice edge remains shoreward of the shelf break, but an abrupt onset of shelf‐break upwelling takes place when the ice edge retreats beyond the shelf break. A climatology (1968–2000) of ice conditions from the Canadian Shelf of the Beaufort Sea shows large interannual variability in ice edge extent and duration of ice‐free conditions in summer. Similarly, available hydrographic data reflect a corresponding variability in water mass properties. Under scenarios of climate warming associated with greenhouse gas build‐up, both the extent and duration of summer melt‐back are predicted to increase, and this may have dramatic impacts on SBE and biological productivity.

Extent of partial ice cover due to carbon cycle feedback in a zonal energy balance model

Abstract. A global carbon cycle is introduced into a zonally averaged energy balance climate model. The physical model components are similar to those of Budyko (1969) and Sellers (1969). The new carbon components account for atmospheric carbon dioxide concentrations and the terrestrial and oceanic storage of carbon. Prescribing values for the sum of these carbon components, it is found that inclusion of a closed carbon cycle reduces the range of insolation over which stable partial ice cover solutions may occur. This highly simplified climate model also predicts that the estimated release of carbon from fossil fuel burning over the next hundred years could result in the eventual melting of the ice sheets. Keywords: climate, carbon cycle,zonal model, earth system modelling

Numerical reconstructions of LGM climate across the Eurasian Arctic

Although limits of the Eurasian Ice Sheet at the Last Glacial Maximum (LGM) are known relatively well from geological evidence, the palaeoclimate coexistent with this ice sheet has yet to be identified confidently. A simple ice-sheet model has been used to determine LGM climate conditions by finding the ice-sheet mass-balance configuration that permits model results to match with geological data relating to the extent of LGM ice cover. These conditions are compared with Atmospheric General Circulation Model (AGCM) calculations of the climate at the LGM, which reveal the meteorological conditions associated with the ice-sheet mass-balance. The western margin of Scandinavia is characterised by a maritime climate, influenced by the nearby warm, seasonally sea-ice free, ocean conditions. However, further east, the warming effect of the North Atlantic diminishes and an extreme polar desert climate dominates across the Kara Sea similar to East Antarctica today. The LGM climate that we establish is in contrast to many previous reconstructions involving snow-laden warm westerly winds originating from the North Atlantic affecting the entire Eurasian Arctic. Severely cold conditions across the Eurasian Arctic are compatible with a stable circulation cell over the Kara Sea that isolates the region climatically, and/or cold dry westerly winds from the Fennoscandian Ice Sheet that flow across the rest of the Eurasian Arctic.

Visualizing Laurentian Great Lakes ice cycles

In 1994, under the auspices of the National Oceanic and Atmospheric Administration's (NOAA) Earth System and Data Information Management (ESDIM) Program, a project was initiated to update a 20‐winter digital ice concentration database and ice concentration climatology (see Internet at http://www.glerl.noaa.gov/res/Task_rpts/ccassell l‐2.html). The data reduction phase of that project is now complete. The National Ice Center (NIC) and the Canadian Ice Service (CIS) contributed the historic ice charts used in this project. The first analysis product from the updated database is a set of computer animations of the seasonal progression of ice cover extent and concentration for 23 individual winter seasons.

Satellite-observed variability and trend in sea-ice extent, surface temperature, albedo and clouds in the Arctic

AbstractRecent observations of a decreasing ice extent and a possible thinning of the ice cover in the Arctic make it imperative that detailed studies of the current Arctic environment are made, especially since the region is known to be highly sensitive to a potential change in climate. A continuous dataset of microwave, thermal infrared and visible satellite data has been analyzed for the first time to concurrently study in spatial detail the variability of the sea-ice cover, surface temperature, albedo and cloud statistics in the region from 1987 to 1998. Large warming anomalies during the last four years (i.e. 1995−98) are indeed apparent and spatially more extensive than previous years. The largest surface temperature anomaly occurred in 1998, but this was confined mainly to the western Arctic and the North American continent, while cooling occurred in other areas. The albedo anomalies show good coherence with the sea-ice concentration anomalies except in the central region, where periodic changes in albedo are observed, indicative of interannual changes in duration and areal extent of melt ponding and snow-free ice cover. The cloud-cover anomalies are more difficult to interpret, but are shown to be well correlated with the expected warming effects of clouds on the sea-ice surface. The results from trend analyses of the data are consistent with a general warming trend and an ice-cover retreat that appear to be even larger during the last dozen years than those previously reported.

The semi-annual oscillation and Antarctic climate. Part 4: a note on sea ice cover in the Amundsen and Bellingshausen Seas

The climate of Faraday, situated at the west coast of the Antarctic Peninsula (AP), is strongly influenced by the extent of sea ice cover in the Amundsen and Bellingshausen Seas (ABS). ABS sea ice cover is negatively correlated with Faraday annual mean temperature, wind speed and cloudiness, while a positive correlation was found with precipitation frequency. The amplitude of the semi-annual oscillation (SAO) and wintertime ABS sea ice extent are coupled as follows: in years with a poorly-developed SAO, the northwestward migration of the circumpolar pressure trough from April to July is suppressed, causing negative sea ice anomalies in the ABS that persist throughout the winter. The weakening of the SAO since the late 1970s has led to: an increase of annual mean wind speed and cloudiness in the region, one of the possible causes for the onset of the long-term ABS sea ice cover decrease; and changes in the annual cycles of wind speed and cloudiness such that sea ice growth in the period April-July has decreased, causing negative winter sea ice anomalies in the ABS and enhanced regional warming.

A 1.0 Myr Record of Glacial North Atlantic Intermediate Water Variability from ODP Site 982 in the Northeast Atlantic

Changes in the intermediate water structure of the North Atlantic were reconstructed using benthic foraminiferal δ13C at Ocean Drilling Program (ODP) site 982 for the past 1.0 Myr. During most terminations of the late Pleistocene, melting of icebergs and low‐salinity surface waters caused production of Glacial North Atlantic Intermediate Water to cease, resulting in decreased ventilation of the middepth North Atlantic. Poor ventilation of intermediate water masses lasted well into some interglacial stages until upper North Atlantic Deep Water (NADW) production resumed under full interglacial conditions. The magnitude of benthic δ13C minima and ice‐rafted debris maxima at terminations at site 982 generally match the degree of glacial suppression of NADW inferred from site 607. These processes may be related and controlled by the spatial and seasonal extent of sea ice cover during glaciations in the Nordic Seas.

Introduction To The Special Section On The Electromagnetic Properties Of Sea Ice

PPROXIMATELY 13% of the world’s oceans is covered by sea ice during some portion of the year. This volume of ice has significant effects on the world’s climate, ocean currents, and biological ecosystems. Furthermore, the extent of sea ice cover is used as an input parameter in many meteorological forecasting models. It is difficult to obtain ground-based measurements over large regions of the Arctic, where the distances are vast, the climate is hostile, and the operations are expensive. The material composition of sea ice varies with temperature and winds. Thus, remote sensing of sea ice may be the preferred method to obtain quantitative information about sea ice. This Special Section of the IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING presents results obtained by the Accelerated Research Initiative (ARI) on the Electromagnetic Properties of Sea Ice (EMPOSI) that was sponsored by the Office of Naval Research (ONR), Washington, DC. Briefly stated, the ARI had three broad objectives, as follows. To better understand the mechanisms and processes that link the morphological characteristics with its electromagnetic properties. To further develop and verify predictive models for the interactions of visible and microwave radiation with sea ice. To develop and verify the techniques in the mathematical theory of inverse scattering theory that are applicable