Ice Breakup Research Articles

Nearshore ice complex breakup is controlled by a balance between thermal and mechanical processes

AbstractShore ice is an important facet of cold‐climate coastal geomorphology yet is generally understudied in comparison to other aspects such as nearshore hydrodynamics. Climate change is resulting in more dynamic shore ice regimes (i.e., shortened ice season and multiple freeze–thaw cycles); thus, a clear understanding of the role of shore ice in coastal geomorphic evolution is needed. The presence of shore ice is generally thought to provide the coast a protective buffer from storm waves though some studies have indicated enhanced nearshore erosion and sediment transport associated with ice development. This is particularly apparent during the breakup phase of shore ice as sediment can be scoured from the bed, deposited in place, or transported offshore. Given this, understanding the mechanics of shore ice breakup is critical. This study documents the first combined field and laboratory evaluation of the physical conditions leading to shore ice breakup, detailing the complex interplay between thermal and mechanical processes in ice deterioration. Through a wave tank experiment as well as field observations, wave impacts alone are shown to be unlikely to cause breakup of shore ice and thermal weakening is required. This has important implications both for predicting when ice will break up as well as for identifying potential nearshore sediment transport pathways. If ice breaks up entirely from thermal degradation, then sediment is likely to be deposited in place, whereas if ice breaks up from a combination of thermal degradation and wave impact, then sediment can be redistributed across the shoreface. Monitoring of meteorological conditions during ice breakup can likely be used as a first‐order predictor of geomorphic changes resulting from shore ice deterioration.

Record low 2022 Antarctic sea ice led to catastrophic breeding failure of emperor penguins

The spring season of 2022 saw record low sea ice extent in Antarctica that persisted throughout the year. At the beginning of December, the Antarctic sea ice extent was tracking with the all-time low set in 2021. The greatest regional negative anomaly of this low extent was in the central and eastern Bellingshausen Sea region, west of the Antarctic Peninsula where, during November, some regions experienced a 100% loss in sea ice concentration. We provide evidence of a regional breeding failure of emperor penguin colonies due to sea ice loss using Sentinel2 satellite imagery. Of the five breeding sites in the region all but one experienced total breeding failure after sea ice break-up before the start of the fledging period of the 2022 breeding season. This is the first recorded incident of a widespread breeding failure of emperor penguins that is clearly linked with large-scale contractions in sea ice extent.

Calving, ice flow, and thickness of outlet glaciers controlled by land-fast sea ice in Lützow-Holm Bay, East Antarctica

Abstract To investigate the mechanisms driving recent changes in outlet glaciers in Antarctica, we measured the glacier front position, flow velocity and surface elevation of five outlet glaciers flowing into Lützow-Holm Bay in East Antarctica. After a steady advance from 2008 to 2015, all the glaciers synchronously retreated by 0.4–6.0 km between 2016 and 2018. The initiation of the retreat coincided with the breakup of land-fast sea ice in Lützow-Holm Bay in 2016, which resulted in the largest sea-ice loss in the region since 1998. Similar flow variations and surface elevation changes were observed near the grounding line of Shirase, Skallen and Telen glaciers. The slowdown in 2011–15 (by 13%) and the speedup in 2016–18 (by 7%) coincided with the respective increase and decrease in surface elevation. Simultaneous retreat and acceleration after the land-fast sea-ice breakup implies that sea ice has a significant influence on glacier dynamics. Thickening/thinning observed near the grounding line was attributed to a reduced/enhanced stretching flow regime during the deceleration/acceleration period. Our results demonstrate that land-fast sea ice affects not only terminus positions, but also the flow speed and ice thickness of the Antarctic glaciers.

A hybrid ontology‐based semantic and machine learning model for the prediction of spring breakup

AbstractRiver ice breakups carry the potential for high flows and flooding and are of great interest to accurately predict. A challenge in forecasting these events is the management of the massive amounts of data associated with an ice season. This study couples ontological and machine learning models in a new hybrid modeling framework to predict spring breakup on a national scale. The Ice Season Ontology sorts the data and allows for a user‐friendly means of analyzing any ice season, providing insight on which variables are most and least central. With this, a refined variable selection is able to be made for machine learning models. The most successful developed model, a random forest, produced highly accurate forecasts when applied to a national scale case study, with a mean absolute error of 10.85 days and an R2 of .884. This new modeling framework provides a means for decision‐making support for river bound communities and a new methodology for modeling applications in other fields.

Terrestrial Snowmelt as a Precursor to Landfast Sea Ice Break-up in Hudson Bay and James Bay

Numerous studies have been conducted to enhance our understanding of how climate change impacts landfast ice and its break-up in spring or summer. Yet, predictions of break-up timing have proven elusive illusive, and dependent on multiple environmental drivers. In this study, we investigate whether/to what extent snow melt on land adjacent to the coast can serve as a precursor to landfast ice break-up. For the study, we used MODIS snowmelt timing products to explore the pattern of snowmelt across the study area. This was compared against landfast ice break-up dates generated mainly from CIS ice-chart, across the Hudson Bay and James Bay coast. Snowmelt timings recorded across the study area followed the same latitudinal gradient as the landfast ice break-up dates, with almost a 50-day difference between the south and the north snowmelt and ice break-up timings. The data shows that the timing of landfast ice break-up across the Hudson Bay and James Bay region showed significantly stronger correlations with the timing of terrestrial snowmelt, as compared to air temperature thresholds, with an average 17-day gap observed between snowmelt to landfast ice break-up. Based on the observations, we believe snowmelt can be a reliable precursor to landfast ice break-up.

Spatial and temporal harvest risk to polar bears in the Canadian Beaufort Sea

Subsistence harvest in Arctic marine ecosystems is influenced by sea ice conditions affecting species distributions, abundance, and accessibility. We tracked 78 polar bears ( Ursus maritimus Phipps, 1774) of different age, sex, and reproductive classes via satellite telemetry in the Canadian Beaufort Sea (2007–2014, n = 71 258). We assessed vulnerability to harvest (no/low/medium/high) based on telemetry data overlap with density of historical harvest locations (1985–1987, n = 121). All classes of polar bears were detected in historical harvest areas of low to high risk in greater proportion than expected from available area during the harvest period (January to ice breakup), and all but solitary adult females had >50% of locations in the risk areas. Subadult males were proportionally more often inside risk areas yet were not observed in the high-risk areas. Other classes were observed <1% of the time in high-risk areas yet still proportionally greater than expected from available area. Landfast ice has declined in the pre-melt (January–March) and end-of-harvest (June–July) seasons (1980–2021), with the rate of decline being greater in lower-risk areas ( p ≤ 0.05). With sea ice predicted to decline in the future, we suggest that polar bears in the Beaufort Sea may become more concentrated into areas of higher harvest risk.

Seasonality of zooplankton communities in the Hudson Bay system

The strong seasonality of sub-Arctic seas needs to be considered to understand their ecosystems. The Hudson Bay system undergoes strong seasonal changes in 1) sea ice conditions, alternating between complete ice cover in winter and open water in summer; 2) river discharge, which peaks in the spring and influences the stratification of the bay; and 3) surface circulation that consists of a weak double gyre system in spring and summer and a cyclonic system in the autumn. Recent studies that included data collected during spring have shown that the annual primary productivity in the Hudson Bay system is higher than previously reported. Similarly, the regional zooplankton assemblages have been studied mostly in late summer, possibly leading to an underestimation of the annual secondary production. Here, we use data collected during five one to six week-long expeditions of the CCGS Amundsen in the Hudson Bay system between 2005 and 2018 to describe the seasonality in mesozooplankton assemblages and investigate how it depends on environmental variables. In general, small pan-Arctic and boreal copepods such as Microcalanus spp., Oithona similis and Pseudocalanus spp. dominated the assemblages. From spring to summer, the relative abundance of the Arctic-adapted Calanus hyperboreus and Calanus glacialis decreased, while the proportion of the boreal Pseudocalanus spp. and Acartia spp. increased. The day of the year and the ice break-up date explained most of the variation in mesozooplankton assemblages. Physical processes explained most of the species distribution in spring, while the lack of lipid-rich zooplankton species in late summer and autumn, especially in coastal regions, suggests some top-down control. This lack of lipid-rich zooplankton late in the season contrasts with other seasonally ice-covered seas. More data are needed to fully understand the implications of these dynamics under climate change, but this study establishes a baseline against which future changes can be compared.

A numerical model study on Grasse River ice-control structures

Ice jams in the Grasse River have caused the erosion of capping material designed to prevent the resurfacing of the bed sediment in the polychlorinated biphenyl (PCB)-contaminated area. Two in-stream ice-control structures are proposed to avoid the jam-induced erosion of the capping material. These two ice-control options are a pier-type ice-control structure and a reconstruction of a small hydropower dam upstream of the capping site. A numerical model study using the DynaRICE model is conducted to evaluate the effectiveness of the proposed design. Flow and ice conditions corresponding to the 100-year return period of ice jam events obtained from analyzing historical breakup ice jam data are used in the evaluation. The results showed that these ice-control structures could reduce the ice discharge downstream and the size of the ice jam at the capping site to prevent the erosion and scour of the PCB-contaminated bed.

High interannual surface pCO2 variability in the southern Canadian Arctic Archipelago's Kitikmeot Sea

Abstract. Warming of the Arctic due to climate change means the Arctic Ocean is now free from ice for longer, as sea ice melts earlier and refreezes later. Yet, it remains unclear how this extended ice-free period will impact carbon dioxide (CO2) fluxes due to scarcity of surface ocean CO2 measurements. Baseline measurements are urgently needed to understand spatial and temporal air–sea CO2 flux variability in the changing Arctic Ocean. There is also uncertainty as to whether the previous basin-wide surveys are representative of the many smaller bays and inlets that make up the Canadian Arctic Archipelago (CAA). By using a research vessel that is based in the remote Inuit community of Ikaluqtuutiak (Cambridge Bay, Nunavut), we have been able to reliably survey pCO2 shortly after ice melt and access previously unsampled bays and inlets in the nearby region. Here we present 4 years of consecutive summertime pCO2 measurements collected in the Kitikmeot Sea in the southern CAA. Overall, we found that this region is a sink for atmospheric CO2 in August (average of all calculated fluxes over the four cruises was −4.64 mmol m−2 d−1), but the magnitude of this sink varies substantially between years and locations (average calculated fluxes of +3.58, −2.96, −16.79 and −0.57 mmol m−2 d−1 during the 2016, 2017, 2018 and 2019 cruises, respectively). Surface ocean pCO2 varied by up to 156 µatm between years, highlighting the importance of repeat observations in this region, as this high interannual variability would not have been captured by sparse and infrequent measurements. We find that the surface ocean pCO2 value at the time of ice melt is extremely important in constraining the magnitude of the air–sea CO2 flux throughout the ice-free season. However, further constraining the air–sea CO2 flux in the Kitikmeot Sea will require a better understanding of how pCO2 changes outside of the summer season. Surface ocean pCO2 measurements made in small bays and inlets of the Kitikmeot Sea were ∼ 20–40 µatm lower than in the main channels. Surface ocean pCO2 measurements made close in time to ice breakup (i.e. within 2 weeks) were ∼ 50 µatm lower than measurements made > 4 weeks after breakup. As previous basin-wide surveys of the CAA have focused on the deep shipping channels and rarely measure close to the ice breakup date, we hypothesize that there may be an observational bias in previous studies, leading to an underestimate of the CO2 sink in the CAA. These high-resolution measurements constitute an important new baseline for gaining a better understanding of the role this region plays in the uptake of atmospheric CO2.

Adding sea ice effects to a global operational model (NEMO v3.6) for forecasting total water level: approach and impact

Abstract. In operational flood forecast systems, the effect of sea ice is typically neglected or parameterized solely in terms of ice concentration. In this study, an efficient way of adding ice effects to the global total water level prediction systems, via the ice–ocean stress, is described and evaluated. The approach features a novel, consistent representation of the tidal relative ice–ocean velocities, based on a transfer function derived from ice and ocean tidal ellipses given by an external ice–ocean model. The approach and its impact are demonstrated over four ice seasons in the Northern Hemisphere, using in situ observations and model predictions. We show that adding ice effects helps the model reproduce most of the observed seasonal modulations in tides (up to 40 % in amplitude and 50∘ in phase for M2) in the Arctic and Hudson Bay. The dominant driving mechanism for the seasonal modulations is shown to be the under-ice friction, acting in areas of shallow water (less than 100 m) and its accompanied large shifts in the amphidromes (up to 125 km). Important contributions from baroclinicity and tide–surge interaction due to ice–ocean stress are also found in the Arctic. Both mechanisms generally reinforce the seasonal modulations induced by the under-ice friction. In forecast systems that neglect or rely on simple ice concentration parameterizations, storm surges tend to be overestimated. With the inclusion of ice–ocean stress, surfaces stresses are significantly reduced (up to 100 % in landfast ice areas). Over the four ice seasons covered by this study, corrections up to 1.0 m to the overestimation of surges are achieved. Remaining limitations regarding the overestimated amphidrome shifts and insufficient ice break-up during large storms are discussed. Finally, the anticipated trend of increasing risk of coastal flooding in the Arctic, associated with decreasing ice and its profound impact on tides and storm surges, is briefly discussed.

Nunataryuk field campaigns: understanding the origin and fate of terrestrial organic matter in the coastal waters of the Mackenzie Delta region

Abstract. Climate warming and related drivers of soil thermal change in the Arctic are expected to modify the distribution and dynamics of carbon contained in perennially frozen grounds. Thawing of permafrost in the Mackenzie River watershed of northwestern Canada, coupled with increases in river discharge and coastal erosion, triggers the release of terrestrial organic matter (OMt) from the largest Arctic drainage basin in North America into the Arctic Ocean. While this process is ongoing and its rate is accelerating, the fate of the newly mobilized organic matter as it transits from the watershed through the delta and into the marine system remains poorly understood. In the framework of the European Horizon 2020 Nunataryuk programme, and as part of the Work Package 4 (WP4) Coastal Waters theme, four field expeditions were conducted in the Mackenzie Delta region and southern Beaufort Sea from April to September 2019. The temporal sampling design allowed the survey of ambient conditions in the coastal waters under full ice cover prior to the spring freshet, during ice breakup in summer, and anterior to the freeze-up period in fall. To capture the fluvial–marine transition zone, and with distinct challenges related to shallow waters and changing seasonal and meteorological conditions, the field sampling was conducted in close partnership with members of the communities of Aklavik, Inuvik and Tuktoyaktuk, using several platforms, namely helicopters, snowmobiles, and small boats. Water column profiles of physical and optical variables were measured in situ, while surface water, groundwater, and sediment samples were collected and preserved for the determination of the composition and sources of OMt, including particulate and dissolved organic carbon (POC and DOC), and colored dissolved organic matter (CDOM), as well as a suite of physical, chemical, and biological variables. Here we present an overview of the standardized datasets, including hydrographic profiles, remote sensing reflectance, temperature and salinity, particle absorption, nutrients, dissolved organic carbon, particulate organic carbon, particulate organic nitrogen, CDOM absorption, fluorescent dissolved organic matter intensity, suspended particulate matter, total particulate carbon, total particulate nitrogen, stable water isotopes, radon in water, bacterial abundance, and a string of phytoplankton pigments including total chlorophyll. Datasets and related metadata can be found in Juhls et al. (2021) (https://doi.org/10.1594/PANGAEA.937587).

How the Hydrometeorological Parameters of the Curonian Lagoon Changed during Two Periods of Standard Climate Normal (1961–1990 and 1991–2020)

Coastal lagoons are recognized as specific and complex water bodies vulnerable to climate change. The focus of this study was the Curonian Lagoon, the largest freshwater lagoon in the Baltic Sea and the whole of Europe. The changes in the hydrometeorological parameters of the lagoon over six decades were evaluated using two periods of climatological standard normal: the most recent 30-year period, i.e., 1991–2020, and the period of 1961–1990. Before statistical analysis, data were checked for homogeneity, and breakpoints were determined by Pettitt and Buishand tests. The Mann–Kendall test was used to determine trends in the data series. The analysis revealed substantial changes in the hydrometeorological parameters of the lagoon during two climate normal periods. An exceptionally high rise in air temperature was detected. A considerable increase was identified in the lagoon water temperature and water level data series. The duration of permanent ice cover on the lagoon declined, as did the ice thickness, whereas the ice breakup advanced. A downward trend in wind speed data was detected, while the change in precipitation had a positive direction. Air and water temperatures were highly correlated with the Arctic Oscillation (AO) index and the water level with the Scandinavia pattern (SCAND).

Resistance of river ice covers to mobilization and implications for breakup progression in Peace River, Canada

AbstractPrediction and modelling of ice breakup initiation and progress over extended river reaches is largely unattainable at present, despite the ecological and socio‐economic significance of the breakup event and associated ice jams that form in many rivers of Asia, Europe and North America. A key question is how to quantify the driving and resisting forces that are applied on the winter ice cover, which control the timing of its dislodgment, mobilization and subsequent jamming locations. Using a physics‐based onset criterion, explicit expressions for these forces are formulated. The more complex of the two is the resistance, which comprises components related to ice strength and thickness, channel curvature, thermal degradation of the ice cover during the pre‐breakup period, and freezeup level (defined as peak 7‐day running average water level during late fall and early winter). This insight is then used in a case study of recent dynamic breakups in a major Canadian river, explaining apparently random differences in the rate of advance of the breakup front among three different years. It is shown further that contradictory results are obtained when the effect of the freezeup level is ignored.

Aerial observations of sea ice breakup by ship waves

Abstract. We provide high-resolution in situ observations of wave-induced sea ice breakup in the natural environment. In order to obtain such data, a drone was deployed from the Canadian Coast Guard ship Amundsen as it sailed in the vicinity of large ice floes in Baffin Bay and in the St. Lawrence Estuary, Canada. The footage recorded during these experiments was used to obtain the floe size distribution (FSD) and the temporal evolution of the breakup. Floe-area-weighted FSDs exhibit a modal shape, indicating that a preferential size is generated by wave-induced breakup. Furthermore, the increase of the mode of the distribution with greater thickness indicates that ice thickness plays a defined role in determining the preferential size. Comparison with relevant theory suggests that the maximum floe size is dictated not only by the ice rigidity but also by the incident wavelength. It was also observed that the in-ice wavelength is smaller than the estimated incident wavelength, suggesting that waves responsible for the breakup obey mass loading dispersion. The fact that the breakup advances almost as fast as the wave energy suggests that fatigue might not have been an important physical component during the experiments. Moreover, the observed breakup extents show that thicker ice can attenuate waves less than thinner ice. Overall, this dataset provides key information on wave-induced sea ice breakup and highlights the potential for better understanding the physics of natural sea ice in response to waves.

Changes in Sea Surface Temperature and Sea Ice Concentration in the Arctic Ocean over the Past Two Decades

With global warming, the decrease in sea ice creates favorable conditions for Arctic activities. Sea surface temperature (SST) is not only an important driven factor of sea ice concentration (SIC) changes but also an important medium of the ocean–atmosphere interaction. However, the response of sea surface temperature to Arctic sea ice varies in different sea areas. Using the optimal interpolated SST data from the National Centers for Environmental Information (NCEI) and SIC data from the University of Bremen, the temporal and spatial characteristics of SST and SIC in the Arctic above 60°N and their relationship are studied, and the melting and freezing time of sea ice are calculated, which is particularly important for the prediction of Arctic shipping and sea ice. The results show that (1) the highest and lowest monthly mean Arctic SST occur in August and March, respectively, while those of SIC are in March and September. The maximum trends of SST and SIC changes are in autumn, which are +0.01 °C/year and −0.45%/year, respectively. (2) There is a significant negative correlation between the Arctic SST and SIC with a correlation coefficient of −0.82. (3) The sea ice break-up occurs on Day of the Year (DoY) 143 and freeze-up occurs on DoY 296 in the Arctic. The melting and freezing processes lasted for 27 days and 14 days, respectively. (4) The Kara Sea showed the strongest trend of sea ice melting at −1.22 d/year, followed by the Laptev Sea at −1.17 d/year. The delay trend of sea ice freezing was the most significant in the Kara Sea +1.75 d/year, followed by the Laptev Sea +1.70 d/year. In the Arctic, the trend toward earlier melting of sea ice is smaller than the trend toward later freezing.

Understanding two key processes associated with alpine lake ice phenology using a coupled atmosphere-lake model

Study regionLake Nam-Co, a typical deep alpine lake in the central of Tibetan Plateau. Study focusThis study investigates the role of surface turbulent fluxes in simulating lake freeze-up and the role of solar radiation transfer (when lake ice exists) in simulating the lake ice break-up. New hydrological insightsIn the coupled model, the realistic representation of surface turbulent heat fluxes is crucial to simulate the lake freeze-up. This is because turbulent heat fluxes, especially the latent heat, directly controlling the lake water temperature through energy exchange between water and atmosphere. Additionally, the partitioning of solar radiation transfers when lake ice exist is crucial in simulating lake ice break-up. The proportion absorbed by the ice surface will be released associated with upward longwave radiation and turbulent heat fluxes, and only a fraction is used for surface ice-water phase change. The proportion absorbed by the subsurface layer ice is directly used for ice-water phase changes. The proportion absorbed by the water, through ice penetration, is temporarily stored and used for ice melting through heat exchange between the ice and water. The offline FLake model is much less sensitive to the above two processes, implying the importance and necessity in improving the model physics in coupled model.

Increasing Alaskan river discharge during the cold season is driven by recent warming

Arctic hydrology is experiencing rapid changes including earlier snow melt, permafrost degradation, increasing active layer depth, and reduced river ice, all of which are expected to lead to changes in stream flow regimes. Recently, long-term (>60 years) climate reanalysis and river discharge observation data have become available. We utilized these data to assess long-term changes in discharge and their hydroclimatic drivers. River discharge during the cold season (October–April) increased by 10% per decade. The most widespread discharge increase occurred in April (15% per decade), the month of ice break-up for the majority of basins. In October, when river ice formation generally begins, average monthly discharge increased by 7% per decade. Long-term air temperature increases in October and April increased the number of days above freezing (+1.1 d per decade) resulting in increased snow ablation (20% per decade) and decreased snow water equivalent (−12% per decade). Compared to the historical period (1960–1989), mean April and October air temperature in the recent period (1990–2019) have greater correlation with monthly discharge from 0.33 to 0.68 and 0.0–0.48, respectively. This indicates that the recent increases in air temperature are directly related to these discharge changes. Ubiquitous increases in cold and shoulder-season discharge demonstrate the scale at which hydrologic and biogeochemical fluxes are being altered in the Arctic.

The role of sea ice in the distribution, habitat use, and phenology of eastern North Pacific gray whales

A strong negative relationship has been observed between calf production of eastern North Pacific gray whales Eschrichtius robustus and Pacific Arctic sea ice area with the exception of 2 potentially anomalous periods: 2013-2014 and 2017-2019. Sea ice may play a role in reproductive variability by blocking gray whale access to foraging hotspot habitats. We tested this ‘sea ice exclusion’ hypothesis using complementary aerial survey and moored hydrophone data sets that together provide broad spatial and temporal coverage. A negative relationship (generalized additive model, p < 0.001) was found between gray whale aerial counts and ice concentration in the northeast Chukchi Sea (2008-2019), with a nonlinear increase in negative slope above 45-55% concentration. A comparison of distribution patterns between years further indicated the absence of sightings within northern Bering and northeastern Chukchi foraging hotspots during years with delayed ice break-up versus years with an early-to-average ice retreat. Passive acoustic recordings likewise showed the near-absence of detections during periods of dense ice cover and indicated a strongly positive relationship between ice break-up dates and the timing of acoustic detection onset. Together, these analyses point to the important role of sea ice in gray whale distribution, habitat use, and phenology. However, a relatively consistent 10-15 d lag observed between ice break-up and acoustic onset dates suggested that the mechanism(s) underpinning gray whale interactions with sea ice may be more complex than simply ‘sea ice exclusion.’ Here, we propose ‘prey quality timing’ as a potential alternative hypothesis that warrants further investigation.

Evaluating Common Characteristics of Antarctic Tropopause Polar Vortices

Abstract Tropopause polar vortices (TPVs) are coherent circulations that occur over polar regions and can be identified by a local minimum in potential temperature and local maximum in potential vorticity. Numerous studies have focused on TPVs in the Arctic region; however, no previous studies have focused on the Antarctic. Given the role of TPVs in the Northern Hemisphere with surface cyclones and other extreme weather, and the role that surface cyclones can play on moisture transport and sea ice breakup, it is important to understand whether similar associations exist in the Southern Hemisphere. Here, characteristics of TPVs in the Antarctic are evaluated for the first time under the hypothesis that their characteristics do not significantly differ from those of the Northern Hemisphere. To improve understanding of Antarctic TPV characteristics, this study examines TPVs of the Southern Hemisphere and compares them to their Northern Hemisphere counterparts from 1979 to 2018 using ERA-Interim data. Common characteristics of TPVs including frequency, locations, lifetimes, strength, and seasonality are evaluated. Results indicate that topography correlates to the geographic distribution of TPVs and the locations of local maxima TPV occurrence, as observed in the Northern Hemisphere. Additionally, TPVs in the Southern Hemisphere exhibit seasonal variations for amplitude, lifetime, and minimum potential temperature. Southern Hemisphere TPVs share many similar characteristics to those observed in the Northern Hemisphere, including longer summer lifetimes. The association of Southern Hemisphere TPVs and surface cyclone frequency is explored, and it appears that TPVs have a precursory role to surface cyclones, as seen in the Northern Hemisphere.

Effects of sea ice retreat and ocean warming on the Laptev Sea continental slope ecosystem (1993 vs 2012)

The central Arctic Ocean is rapidly changing due to amplified warming and sea ice retreat. Nonetheless, it remains challenging to document and decipher impacts on key ecosystem processes such as primary production and pelagic-benthic coupling, due to limited observations in this remote area. Here we investigated environmental changes at the Laptev Sea continental slope (60-3400 m water depth) from the surface to the seafloor, by replicating sample transects two decades apart. Mean break-up of sea ice occurred earlier and mean freeze-up occurred later in 2012 compared to 1993, extending the ice-free period by more than 30 days. On average, observations and model results showed an annual increase in primary production of 30% and more in the study area in 2012. In contrast, calculated and modelled fluxes of particulate organic carbon (POC) to the seafloor were only slightly higher in 2012 and did not extend as far into the deep Laptev Sea as the increase in primary production, possibly due to a more developed retention system. Nevertheless, benthic surveys revealed a substantial increase in phytodetritus availability at the seafloor along the entire transect from the shelf edge to the deep sea. This calls for carbon input by lateral advection from the shelves, additional input from sea ice, and/or a late summer bloom. We also investigated the composition and activity of bacterial communities at the seafloor and potential linkages to the observed environmental changes. While bacterial abundance, biomass and overall community structure showed no systematic differences between the two contrasting years at all depths, extracellular enzymatic activities had increased as a result of higher food availability. This was partly reflected in higher benthic oxygen uptake, indicating a moderate impact on benthic remineralization rates at the time of sampling. Our results show considerable effects of ocean warming and sea ice loss on the ecosystem from the surface ocean to the seafloor in the Laptev Sea, which are likely to continue in the coming decades.