Winter Ice Extent Research Articles

Nutrient and environmental factors regulating western Lake Erie cyanobacterial blooms

Abstract Over the past two decades, western Lake Erie has experienced recurring summer cyanobacterial blooms that pose severe negative impacts on human, animal, and ecological health. Previous research has identified a strong correlation between annual cyanobacterial bloom intensity and preceding spring (March-July) phosphorus loading from the Maumee river, the largest tributary to western Lake Erie, which is used to predict upcoming summer bloom severity. Maumee river spring phosphorus load, however, does not explain all the variation of bloom severity between years. Considering additional environmental parameters may help to better capture the physical and biogeochemical processes that regulate bloom severity, eventually leading to improved cyanobacterial forecasts which serve as an early warning for Lake Erie stakeholders. We aggregated various environmental parameters that may influence western Lake Erie cyanobacterial blooms to examine these factors as potential predictors for annual bloom severity. These included nitrogen and phosphorus loading from the Maumee river, freshwater discharge from the primary rivers and tributaries (Detroit, Huron, Raisin, Maumee, and Portage rivers), seasonal lake surface water temperature (mean winter, spring, and summer temperature), and Lake Erie winter ice extent and duration from 2002-2022. Empirical model results show that spring phosphorus loading, as total bioavailable phosphorus, from the Maumee river remains the dominant environmental factor controlling cyanobacterial blooms. However, additional environmental factors, such as Maumee river winter phosphorus loads and Lake Erie winter ice extent and timing, are likely important in modulating bloom severity, particularly in years with moderate phosphorus loads. Finally, we suggest incorporating mechanistic or rule-based models, in addition to empirical models, to better understand and predict annual cyanobacterial bloom severity. The updated models not only improve seasonal forecast accuracy which provides advanced warning of bloom severity to Lake Erie stakeholders, but also helps identify which factors we can better manage to reduce the frequency of severe blooms.

Modulation of the seasonal cycle of the Antarctic sea ice extent by sea ice processes and feedbacks with the ocean and the atmosphere

Abstract. The seasonal cycle of the Antarctic sea ice extent is strongly asymmetric, with a relatively slow increase after the summer minimum followed by a more rapid decrease after the winter maximum. This cycle is intimately linked to the seasonal cycle of the insolation received at the top of the atmosphere, but sea ice processes as well as the exchanges with the atmosphere and ocean may also play a role. To quantify these contributions, a series of idealized sensitivity experiments have been performed with an eddy-permitting (1/4∘) NEMO-LIM3 (Nucleus for European Modelling of the Ocean–Louvain-la-Neuve sea ice model version 3) Southern Ocean configuration, including a representation of ice shelf cavities, in which the model was either driven by an atmospheric reanalysis or coupled to the COSMO-CLM2 regional atmospheric model. In those experiments, sea ice thermodynamics and dynamics as well as the exchanges with the ocean and atmosphere are strongly perturbed. This perturbation is achieved by modifying snow and ice thermal conductivities, the vertical mixing in the ocean top layers, the effect of freshwater uptake and release upon sea ice growth and melt, ice dynamics, and surface albedo. We find that the evolution of sea ice extent during the ice advance season is largely independent of the direct effect of the perturbation and appears thus mainly controlled by initial state in summer and subsequent insolation changes. In contrast, the melting rate varies strongly between the experiments during the retreat, in particular if the surface albedo or sea ice transport are modified, demonstrating a strong contribution of those elements to the evolution of ice coverage through spring and summer. As with the advance phase, the retreat is also influenced by conditions at the beginning of the melt season in September. Atmospheric feedbacks enhance the model winter ice extent response to any of the perturbed processes, and the enhancement is strongest when the albedo is modified. The response of sea ice volume and extent to changes in entrainment of subsurface warm waters to the ocean surface is also greatly amplified by the coupling with the atmosphere.

Nearshore bathymetric changes along the Alaska Beaufort Sea coast and possible physical drivers

Erosion rates along Alaska's Beaufort Sea coast, among the highest in the world, are negatively impacting communities, industrial and military infrastructure, and wildlife habitat. Decreasing maximal winter ice extent and increasing summer open water duration and extent in the Beaufort Sea may be making the coast more vulnerable to destructive storm waves than during recent, colder, icier decades. Previous studies of Beaufort Sea coastal change have been limited to subaerial analyses of the shoreline. Here we describe nearshore seafloor change by comparing post-World War II (WWII) (1945-53) bathymetry data to recently acquired (1985–2018) bathymetry data and relate the observed seafloor change to adjacent shoreline change near Utqiagvik, within Stefansson Sound, and immediately west of Barter Island and Kaktovik. Within the Utqiagvik region, seabed erosion was generally highest (>1.0 m of loss) offshore of Point Barrow and along the eastern end of the Tapkaluk Islands, while there were lesser amounts of deposition (<0.5 m of gain) within the protected waters of Elson Lagoon. Sedimentation was generally highest offshore of Point Barrow, in a region of converging currents, and on the landward side of the barrier islands and spits fronting Elson Lagoon, which is likely related to a regional trend of westerly sediment transport and landward migration of the barrier islands. Within Stefansson Sound, perhaps the most notable changes from post-WWII bathymetry data compared to recent data are a switch from mixed, low erosion and deposition in 1997 to low deposition (<0.5 m) in 2018 east of the Boulder Patch, a switch from low erosion in 1997 to neutral depth change in 2018 in the channel between the north and south Boulder Patch areas, and higher deposition from 1997 to 2018 landward of the rapidly retreating barrier islands along the Sound's northern border. At Barter Island, high erosion near north-facing shorelines and high deposition near west-facing shorelines generally matched shoreline changes. One of our goals is to identify possible processes responsible for the depth changes we quantified. Using simple metrics that relate sediment characteristics with modeled waves and non-wave induced currents, we show that sediment resuspension and transport by both wave and non-wave driven currents likely contribute to the overall patterns of change within the ∼13 m isobath along the open coast, and that the influence of wave action affecting sediment transport is expanding seaward.

Satellite‐observed drop of Arctic sea ice growth in winter 2015–2016

AbstractAn anomalous warm winter 2015–2016 lead to the lowest winter ice extent and highlights the sensitivity of the Arctic sea ice. Here we use the 6 year record of an improved sea ice thickness product retrieved from data fusion of CryoSat‐2 radar altimetry and Soil Moisture and Ocean Salinity radiometry measurements to examine the impact of recent temperature trend on the Arctic ice mass balance. Between November 2015 and March 2016, we find a consistent drop of cumulative freezing degree days across the Arctic, with a negative peak anomaly of about 1000 degree days in the Barents Sea, coinciding with an Arctic‐wide average thinning of 10 cm in March with respect to the 6 year average. In particular, the loss of ice volume is associated with a significant decline of March first‐year ice volume by 13%. This reveals that due to the loss of multiyear ice during previous years, the Arctic ice cover becomes more sensitive to climate anomalies.

Winter and spring controls on the summer food web of the coastal West Antarctic Peninsula.

Understanding the mechanisms by which climate variability affects multiple trophic levels in food webs is essential for determining ecosystem responses to climate change. Here we use over two decades of data collected by the Palmer Long Term Ecological Research program (PAL-LTER) to determine how large-scale climate and local physical forcing affect phytoplankton, zooplankton and an apex predator along the West Antarctic Peninsula (WAP). We show that positive anomalies in chlorophyll-a (chl-a) at Palmer Station, occurring every 4-6 years, are constrained by physical processes in the preceding winter/spring and a negative phase of the Southern Annular Mode (SAM). Favorable conditions for phytoplankton included increased winter ice extent and duration, reduced spring/summer winds, and increased water column stability via enhanced salinity-driven density gradients. Years of positive chl-a anomalies are associated with the initiation of a robust krill cohort the following summer, which is evident in Adélie penguin diets, thus demonstrating tight trophic coupling. Projected climate change in this region may have a significant, negative impact on phytoplankton biomass, krill recruitment and upper trophic level predators in this coastal Antarctic ecosystem.

Assessing trend and variation of Arctic sea-ice extent during 1979–2012 from a latitude perspective of ice edge

Arctic sea-ice extent (in summer) has been shrinking since the 1970s. However, we have little knowledge of the detailed spatial variability of this shrinking. In this study, we examine the (latitudinal) ice extent along each degree of longitude, using the monthly Arctic ice index data sets (1979–2012) from the National Snow and Ice Data Center. Statistical analysis suggests that: (1) for summer months (July–October), there was a 34-year declining trend in sea-ice extent at most regions, except for the Canadian Arctic Archipelago, Greenland and Svalbard, with retreat rates of 0.0562–0.0898 latitude degree/year (or 6.26–10.00 km/year, at a significance level of 0.05); (2) for sea ice not geographically muted by the continental coastline in winter months (January–April), there was a declining trend of 0.0216–0.0559 latitude degree/year (2.40–6.22 km/year, at a significance level of 0.05). Regionally, the most evident sea-ice decline occurred in the Chukchi Sea from August to October, Baffin Bay and Greenland Sea from January to May, Barents Sea in most months, Kara Sea from July to August and Laptev Sea and eastern Siberian Sea in August and September. Trend analysis also indicates that: (1) the decline in summer ice extent became significant (at a 0.05 significance level) since 1999 and (2) winter ice extent showed a clear changing point (decline) around 2000, becoming statistically significant around 2005. The Pacific–Siberian sector of the Arctic accounted for most of the summer sea-ice decline, while the winter recovery of sea ice in the Atlantic sector tended to decrease. Keywords: NSIDC ice index; Arctic; sea-ice extent; ice-edge latitude. (Published: 11 September 2014) Citation: Polar Research 2014, 33 , 21249, http://dx.doi.org/10.3402/polar.v33.21249

Arctic sea ice response to atmospheric forcings with varying levels of anthropogenic warming and climate variability

Numerical experiments are conducted to project arctic sea ice responses to varying levels of future anthropogenic warming and climate variability over 2010–2050. A summer ice‐free Arctic Ocean is likely by the mid‐2040s if arctic surface air temperature (SAT) increases 4°C by 2050 and climate variability is similar to the past relatively warm two decades. If such a SAT increase is reduced by one‐half or if a future Arctic experiences a range of SAT fluctuation similar to the past five decades, a summer ice‐free Arctic Ocean would be unlikely before 2050. If SAT increases 4°C by 2050, summer ice volume decreases to very low levels (10–37% of the 1978–2009 summer mean) as early as 2025 and remains low in the following years, while summer ice extent continues to fluctuate annually. Summer ice volume may be more sensitive to warming while summer ice extent more sensitive to climate variability. The rate of annual mean ice volume decrease relaxes approaching 2050. This is because, while increasing SAT increases summer ice melt, a thinner ice cover increases winter ice growth. A thinner ice cover also results in a reduced ice export, which helps to further slow ice volume loss. Because of enhanced winter ice growth, arctic winter ice extent remains nearly stable and therefore appears to be a less sensitive climate indicator.

Drivers of declining sea ice in the Arctic winter: A tale of two seas

While the summer perennial Arctic sea ice has declined markedly in recent decades, the maximum extent of the winter ice cover had decreased only slightly, until the past few years when it also receded dramatically. This investigation reveals that the timing of maximum extent varies greatly, and the drivers of ice‐edge location differ strikingly between two of the areas where it varies most: the Bering and Barents Seas. Between 1979 and 2005 in the Bering Sea, the ice edge is influenced mainly by anomalies in easterly winds associated with the Aleutian Low, which was particularly strong during the 1980s. The Barents Sea ice edge, in contrast, is driven primarily by two factors: anomalies in sea‐surface temperature, particularly close in time to the maximum extent, and by southerly wind (from the south) anomalies integrated back to mid‐ and early winter. The hemispheric‐mean decline in winter ice extent is due in large part to increasing sea‐surface temperatures in the Barents Sea and adjoining waters, which are consistent with increased concentrations of greenhouse gases.

Atmospheric circulation impacts on winter maximum sea ice extent in the west Antarctic Peninsula region (1979–2001)

Increasing evidence exists that the strong warming of the West Antarctic Peninsula (WAP) region since the 1950s is related to reduced sea ice that is likely to be due to changes in the atmospheric circulation. Over twenty years of sea ice extent, ice motion and reanalysed near‐surface wind data are used to establish that winter ice extent in the West Antarctic Peninsula (WAP) region is largely determined by the meridional (north‐south) atmospheric circulation. A remarkably strong ice extent‐wind relationship is found in the WAP. No other Antarctic or comparable sub‐Arctic sea ice region shows this. Ice motion data confirm wind‐induced drift is crucial for extensive winter ice to occur. Reasons for winter ice extent and winds being more strongly correlated in the WAP than in other parts of the Antarctic are discussed along with implications for understanding the observed warming.

Twentieth century simulation of the southern hemisphere climate in coupled models. Part II: sea ice conditions and variability

We examine the representation of the mean state and interannual variability of Antarctic sea ice in six simulations of the twentieth century from coupled models participating in the Intergovernmental Panel on Climate Change fourth assessment report. The simulations exhibit a largely seasonal southern hemisphere ice cover, as observed. There is a considerable scatter in the monthly simulated climatological ice extent among different models, but no consistent bias when compared to observations. The scatter in maximum winter ice extent among different models is correlated to the strength of the climatological zonal winds suggesting that wind forced ice transport is responsible for much of this scatter. Observations show that the leading mode of southern hemisphere ice variability exhibits a dipole structure with anomalies of one sign in the Atlantic sector associated with anomalies of the opposite sign in the Pacific sector. The observed ice anomalies also exhibit eastward propagation with the Antarctic circumpolar current, as part of the documented Antarctic circumpolar wave phenomenon. Many of the models do simulate dipole-like behavior in sea ice anomalies as the leading mode of ice variability, but there is a large discrepancy in the eastward propagation of these anomalies among the different models. Consistent with observations, the simulated Antarctic dipole-like variations in the ice cover are led by sea-level pressure anomalies in the Amundsen/ Bellingshausen Sea. These are associated, to different degrees in different models, with both the southern annular mode and the El Nino-Southern Oscillation (ENSO). There are indications that the magnitude of the influence of ENSO on the southern hemisphere ice cover is related to the strength of ENSO events simulated by the different models.

The impact of winter ice retreat on Antarctic winter sea‐ice extent and links to the atmospheric meridional circulation

Abstract15 years of weekly Antarctic ice extent and 10 m winds from numerical meteorological reanalyses have been used to test the hypothesis that the Antarctic final winter ice extent (FWE) is brought about by ice retreats as much as by advances, and that both are strongly affected by the meridional (north–south) component of the atmospheric circulation. This hypothesis is found to be correct and it is shown that extensive FWE fails to occur when total winter retreat is anomalously large. This is the case even in the coldest Antarctic regions. Retreats reduce the time available for advance, notably when they are substantial, with the ice cover taking up to several weeks to recover. Systematic changes in the meridional winds between retreats and advance are also detected in all regions; retreats are consistently associated with northerly winds supporting ice compaction and ice drift. The results agree with Antarctic case studies.Close similarities are found between several Antarctic and sub‐Arctic regions in terms of the prevalence of retreat in some winters, its impact on the FWE and its relationship to the meridional atmospheric circulation. The study also reveals a more complex picture of the atmospheric circulation during sub‐monthly ice retreats and advances. In particular, retreats in some Pacific regions are, on average, associated with anomalous anticyclonic circulations. This helps to explain why evidence of strong cyclone–ice extent relationships has not been found previously. A meteorological explanation is also sought for total retreat in winter being small in a winter of limited ice extent in the Bellingshausen Sea despite this being the mildest Antarctic region. In such cases, limited winter ice extent is attended by reduced advance caused by ice compaction due to northerly winds and waves and also anomalously high air temperatures. Reduced advance then limits opportunities for retreat to take place compared with winters with more advance and sea ice reaching lower latitudes. Overall, the results point to sub‐monthly ice–atmospheric circulation interactions largely determining the winter ice extent throughout much of the Antarctic. Copyright © 2004 Royal Meteorological Society

Simulations of ice‐ocean dynamics in the Weddell Sea 1. Model configuration and validation

In the framework of the Bremerhaven Regional Ice Ocean Simulations a coupled sea ice‐ocean model, based on a dynamic‐thermodynamic sea ice model and the S‐coordinate Primitive Equation Model, has been developed. The model is run on a circumpolar grid that is focused on the Weddell Sea. It includes the major Antarctic ice shelves; ice shelf‐ocean interaction is described by the sea ice model's thermodynamic component. Numerical simulations are forced with 6 hourly data of the European Centre for Medium‐Range Weather Forecasts reanalysis of the period 1985–1993 and validated against observations of hydrography as well as sea ice extent, thickness, and drift. Qualitatively and quantitatively, a good agreement with observations is achieved. The basin‐wide circulation features a double‐cell structure of the Weddell Gyre with maximum transports close to recent observations. Summer sea ice coverage is underestimated, but winter ice extent, as well as sea ice thickness and drift, is well reproduced.

Atmospheric meridional circulation impacts on contrasting winter sea ice extent in two years in the Pacific sector of the Southern Ocean

An explanation is sought for the marked variation in maximum sea ice extent observed between 2 years in the 2 areas of greatest interannual variability in winter ice extent in the South Pacific sector of the Southern Ocean. The rôle of ice recession in controlling ice extent is highlighted, and the adjustments in the near-surface atmospheric meridional circulation and air temperature that attend winter periods of ice retreat and advance are noted. Distinct meridional flow and air temperature adjustments attend periods of sea ice retreat that limit ice to higher than normal latitudes as well as ice advance to lower than normal latitudes. Ice advance leading to above-normal ice extent, for instance, takes place only when a lowering of air temperatures is accompanied by equatorward flow. A lack of warm air advection is, however, needed to adequately account for the development and maintenance of above-normal ice extent. Systematic meridional circulation changes also take place during the development and over the duration of ice extent anomalies. These are shown to emanate from adjustments of the semi-annual cycle in the extra-tropical South Pacific atmospheric circulation.

Eucampia Index as an indicator of the Late Pleistocene oscillations of the winter sea-ice extent at the ODP Leg 119 Site 745B at the Kerguelen Plateau

A new paleoenvironmental proxy, Eucampia Index, was used to trace the Late Pleistocene oscillations of winter ice extent at ODP Leg 119, Site 745B (59° 35.71′ S and 85° 51.60′ E) on the Kerguelen Plateau. The index is calculated as the ratio of winter terminal to intercalary valves of the diatom Eucampia antarctica sensu lato. During the early Brunhes the winter sea-ice edge was positioned south from Site 745. It started expanding northward, closer to the site location soon after 0.4 Ma and progressed in a manner of a several wide oscillations. For approximately the last 0.1 Ma the winter sea-ice edge oscillated less and retained similar range of oscillations. The ice edge oscillated in periods which correspond closely to that of Milankovitch oscillations of Earth obliquity, although the significance of individual periods appears to vary in time.

Testing alternative parameterizations of lateral melting and upward basal heat flux in a thermodynamic sea ice model

A zonally averaged, physically based sea ice model is coupled to an energy balance climate model with prescribed observed atmospheric temperatures and used to investigate the sea ice model sensitivity to alternative parameterizations of (1) the upward heat flux Fb to the ice base, and (2) lateral melting of ice from open water. The parameterizations tested here are taken from the climate and sea ice modeling literature. The different parameterizations for each of these processes can lead to dramatically different results in simulated sea ice area, sea ice thickness, or both. Parameterizing Fb by prescribing (or computing) an upward heat flux at the mixed layer base and either constraining the subice mixed layer temperature to equal the freezing point of seawater or parameterizing Fb as a function of subice mixed layer temperature has the advantage of incorporating the effects on heat fluxes to the ice base of both convective overturning and meridional oceanic heat flux convergence. Parameterizing lateral melting as a function of lead temperature Tlead, rather than making it depend on ∂Tlead/∂t, has relatively little impact on simulated winter ice extent, and no impact on summer ice extent.