Representing Grounding Line Dynamics in Numerical Ice Sheet Models: Recent Advances and Outlook

Recent satellite observations of the Antarctic and Greenland ice sheets show accelerated ice flow and associated ice sheet thinning along coastal outlet glaciers in contact with the ocean. Both processes are the result of grounding line retreat due to melting at the grounding line (the grounding line is the contact of the ice sheet with the ocean, where it starts to float and forms an ice shelf or ice tongue). Such rapid ice loss is not yet included in large-scale ice sheet models used for IPCC projections, as most of the complex processes are poorly understood. Here we report on the state-of-the art of grounding line migration in marine ice sheets and address different ways in which grounding line migration can be attributed and represented in ice sheet models. Using one-dimensional ice flow models of the ice sheet/ice shelf system we carried out a number of sensitivity experiments with different spatial resolutions and stress approximations. These are verified with semi-analytical steady state solutions. Results show that, in large-scale finite-difference models, grounding line migration is dependent on the numerical treatment (e.g. staggered/non-staggered grid) and the level of physics involved (e.g. shallow-ice/shallow-shelf approximation).     

Greenland and Antarctica Ice Sheet Mass Changes and Effects on Global Sea Level

Thirteen years of GRACE data provide an excellent picture of the current mass changes of Greenland and Antarctica, with mass loss in the GRACE period 2002–2015 amounting to 265 ± 25 GT/year for Greenland (including peripheral ice caps), and 95 ± 50 GT/year for Antarctica, corresponding to 0.72 and 0.26 mm/year average global sea level change. A significant acceleration in mass loss rate is found, especially for Antarctica, while Greenland mass loss, after a corresponding acceleration period, and a record mass loss in the summer of 2012, has seen a slight decrease in short-term mass loss trend. The yearly mass balance estimates, based on point mass inversion methods, have relatively large errors, both due to uncertainties in the glacial isostatic adjustment processes, especially for Antarctica, leakage from unmodelled ocean mass changes, and (for Greenland) difficulties in separating mass signals from the Greenland ice sheet and the adjacent Canadian ice caps. The limited resolution of GRACE affects the uncertainty of total mass loss to a smaller degree; we illustrate the “real” sources of mass changes by including satellite altimetry elevation change results in a joint inversion with GRACE, showing that mass change occurs primarily associated with major outlet glaciers, as well as a narrow coastal band. For Antarctica, the primary changes are associated with the major outlet glaciers in West Antarctica (Pine Island and Thwaites Glacier systems), as well as on the Antarctic Peninsula, where major glacier accelerations have been observed after the 2002 collapse of the Larsen B Ice Shelf.     

Evidence for glaciation in the Northern Hemisphere back to 44 Ma from ice-rafted debris in the Greenland Sea

The widely accepted age estimate for the onset of glaciation in the Northern Hemisphere ranges between 2 and 15 million years ago (Ma). However, recent studies indicate the date for glacial onset may be significantly older. We report the presence of ice-rafted debris (IRD) in ～ 44 to 30 Ma sediments from the Greenland Sea, evidence for glaciation in the North Atlantic during the Middle Eocene to Early Oligocene. Detailed sedimentological evidence indicates that glaciers extended to sea level in the region, allowing icebergs to be produced. IRD may have been sourced from tidewater glaciers, small ice caps, and/or a continental ice sheet.     

Ice Sheets and Sea Level: Thinking Outside the Box

Until quite recently, the mass balance (MB) of the great ice sheets of Greenland and Antarctica was poorly known and often treated as a residual in the budget of oceanic mass and sea level change. Recent developments in regional climate modelling and remote sensing, especially altimetry, gravimetry and InSAR feature tracking, have enabled us to specifically resolve the ice sheet mass balance components at a near-annual timescale. The results reveal significant mass losses for both ice sheets, caused by the acceleration of marine-terminating glaciers in southeast, west and northwest Greenland and coastal West Antarctica, and increased run-off in Greenland. At the same time, the data show that interannual variability is very significant, masking the underlying trends.     

E) Organisations Nationales

Abstract

Sudden rapid advances or surges of glaciers and sections of smail ice caps are well known. After remaining dormant or in retreat over long periods of time these ice masses suddenly move forward rapidly with speeds about 2 orders of magnitude greater than usual. If such surges were to occur in large sections of the Antarctic ice sheet serious consequences could result. These include a significant rise of sea level, a substantial increase in the high-albedo ice cover around the continent especially in summer, and a cooling of the Antarctic ocean by the additional ice melting.

A numerical model has now been developed which simulates surging in certain glaciers and ice sheets in an apparently realistic manner. This model has been found to give close representations to a number of existing real surging temperate ice masses from small mountain glaciers to large sectors of ice caps. The model reproduces realistically many features of these ice masses such as the period of the surge, the duration, the velocity of advance, the magnitude of the advance, and the changes in ice thickness.

The application of the model to the Antarctic ice sheet is made more difficult by the problem caused by the temperature dependence of the flow properties of ice. This means that for a complete study the interaction with the environment needs to be considered. However, at this stage preliminary calculations indicate a number of features that are relevant to the effect of Antarctic ice surges on the global climate. These include the period between surges, the duration of the surge, the amount of ice advanced and the changes in thickness of the ice sheet.     

A last glacial ice sheet on the Pacific Russian coast and catastrophic change arising from coupled ice–volcanic interaction

Controversy exists over the extent of glaciation in Eastern Asia at the Last Glacial Maximum: complete ice sheet cover vs. restricted mountain icefields (an area discrepancy equivalent to 3.7 Greenland Ice Sheets). Current arguments favour the latter. However, significant last glacial ice-rafted debris (IRD) exists in NW Pacific ocean cores, which must have been sourced from a major ice sheet somewhere bordering the North Pacific. The origin of this IRD is addressed through a combination of marine core analysis, iceberg trajectory modelling and remote sensing of glacial geomorphology. We find compelling evidence for two stages of glaciation centred on the Kamchatka area of maritime southeast Russia during the last glacial, with ice extent intermediate in size between previous maximum and minimum reconstructions. Furthermore, a significant increase in iceberg flux precedes, and accompanies, a substantial marine core ash deposit at around 40 ka BP. We speculate that rapid decay of the first stage of the ice sheet may have triggered substantial volcanic activity.     

Long-term impact of the proglacial lake Jökulsárlón on the flow velocity and stability of Breiðamerkurjökull glacier,Iceland

Proglacial lakes are becoming ubiquitous at the termini of many glaciers worldwide due to continued climate warming and glacier retreat, and such lakes have important consequences for the dynamics and future stability of these glaciers. In light of this, we quantified decadal changes in glacier velocity since 1991 using satellite remote sensing for Breiðamerkurjökull, a large lake-terminating glacier in Iceland. We investigated its frontal retreat, lake area change and ice surface elevation change, combined with bed topography data, to understand its recent rapid retreat and future stability. We observed highly spatially variable velocity change from 1991 to 2015, with a substantial increase in peak velocity observed at the terminus of the lake-terminating eastern arm from ~1.00 ± 0.36 m day⁻¹ in 1991 to 3.50 ± 0.25 m day⁻¹ in 2015, with mean velocities remaining elevated from 2008 onwards. This is in stark comparison to the predominately land-terminating arms, which saw no discernible change in their velocity over the same period. We also observed a substantial increase in the area of the main proglacial lake (Jökulsárlón) since 1982 of ~20 km², equating to an annual growth rate of 0.55 km² year⁻¹. Over the same period, the eastern arm retreated by ~3.50 km, which is significantly greater than the other arms. Such discrepancies between the different arms are due to the growth and, importantly, depth increase of Jökulsárlón, as the eastern arm has retreated into its ~300 m-deep reverse-sloping subglacial trough. We suggest that this growth in lake area, forced initially by rising air temperatures, combined with the increase in lake depth, triggered an increase in flow acceleration, leading to further rapid retreat and the initiation of a positive feedback mechanism. These findings may have important implications for how increased melt and calving forced by climate change will affect the future stability of large soft-bedded, reverse-sloped, subaqueous-terminating glaciers elsewhere. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd     

‘Detachment’ of icefield outlet glaciers: catastrophic thinning and retreat of the Columbia Glacier (Canada)

We present an investigation of changes taking place on the Columbia Glacier, a lake-terminating outlet of the Columbia Icefield in the Canadian Rockies. The Columbia Icefield is the largest, and one of the most important, ice bodies in the Canadian Rockies. Like other ice masses, it stores water as snow and ice during the winter and releases it during warmer summer months, sustaining river flows and the ecosystems that rely on them. However, the Columbia Glacier and Icefield is shrinking. We use Landsat and Sentinel-2 imagery to show that the Columbia Glacier has retreated increasingly rapidly in recent years, and suggest that this looks set to continue. Importantly, we identify a previously undocumented process that appears to be playing an important role in the retreat of this glacier. This process involves the ‘detachment’ of the glacier tongue from its accumulation area in the Columbia Icefield. This process is important because the tongue is cut off from the accumulation area and there is no replenishment of ice that melts in the glacier's ablation area by flow from upglacier. As a consequence, for a given rate of ablation, the ice in the tongue will disappear much faster than it would if the local mass loss by melting/calving was partly offset by mass input by glacier flow. Such a change would alter the relationship between rates of surface melting and rates of glacier frontal retreat. We provide evidence that detachment has already occurred elsewhere on the Columbia Icefield and that it is likely to affect other outlet glaciers in the future. Modelling studies forecast this detachment activity, which ultimately results in a smaller ‘perched’ icefield without active outlets. © 2019 John Wiley & Sons, Ltd.     

New fjords,new coasts,new landscapes: The geomorphology of paraglacial coasts formed after recent glacier retreat in Brepollen (Hornsund,southern Svalbard)

Changes in the properties and dynamics of tidewater glacier systems are key indicators of the state of Arctic climate and environment. Calving of tidewater glacier fronts is currently the dominant form of ice mass loss and a major contributor to global sea-level rise. An important yet under-studied aspect of this process is transformation of Arctic landscapes, where new lands and coastal systems are revealed due to the recession of marine-terminating ice masses. The evolution of those freshly exposed paraglacial coastal environments is controlled by nearshore marine, coastal and terrestrial geomorphic processes, which rework glacial-derived sediments to create new coastal paraglacial landforms and landscapes. Here, we present the first study of the paraglacial coasts of Brepollen, one of the youngest bays of Svalbard revealed by ice retreat. We describe and classify coastal systems and the variety of landforms (deltas, cliffs, tidal flats, beaches) developed along the shores of Brepollen during the last 100 years. We further discuss the main modes of sediment supply to the coast in different parts of the new bay, highlighting the fast rate of coastal transformation as a paraglacial response to rapid deglaciation in the Arctic. This study provides an exemplar of likely coastal responses to be anticipated in similar tidewater settings under future climate change. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd     

Late Weichselian relative sea-level changes and ice sheet history in southeast Greenland

Relative sea-level (RSL) observations from the margins of the Greenland Ice Sheet (GIS) provide information regarding the timing and rate of deglaciation and constraints on geophysical models of ice sheet evolution. In this paper we present the first RSL record for the southeast sector of the GIS based on field observations completed close to Ammassalik. The local marine limit is c. 69 m above sea-level (asl) and is dated to c. 11 k cal. yrs BP (thousand calibrated years before present) and is a minimum date for ice free conditions at the study site. RSL fell to c. 24 m asl by 9.5 k cal. yrs BP and continued to fall at a decreasing rate to reach close to present by 6.5 k cal. yrs BP. Our chronology agrees with radiocarbon dates from offshore cores that indicate ice free conditions on the adjacent mid-shelf by 15 k cal. yrs BP. We compare the new RSL data with predictions generated using two recently published glaciological models of the GIS that differ in the amount and timing of ice loading and unloading over our study area. These two GIS models are coupled to the same Earth viscosity model and background (global) ice model to aid in the data-model comparison. Neither model provides a close fit to the RSL observations. Based on a preliminary sensitivity study using a suite of Earth viscosity models, we conclude that the poor data-model fit is most likely due to an underestimate of the local ice unloading. An improved fit could be achieved by delaying the retreat of a thicker ice sheet across the continental shelf. A thick ice sheet extending well onto the continental shelf is in agreement with other recent observations elsewhere in east and south Greenland.     

Present State and Prospects of Ice Sheet and Glacier Modelling

Since the late 1970s, numerical modelling has become established as an important technique for the understanding of ice sheet and glacier dynamics, and several models have been developed over the years. Ice sheet models are particularly relevant for predicting the possible response of ice sheets to climate change. Recent observations suggest that ice dynamics could play a crucial role for the contribution of ice sheets to future sea level rise under global warming conditions, and the need for further research into the matter was explicitly stated in the Fourth Assessment Report (AR4) of the United Nations Intergovernmental Panel on Climate Change (IPCC). In this paper, we review the state of the art and current problems of ice sheet and glacier modelling. An outline of the underlying theory is given, and crucial processes (basal sliding, calving, interaction with the solid Earth) are discussed. We summarise recent progress in the development of ice sheet and glacier system models and their coupling to climate models, and point out directions for future work.     

A modified monthly degree‐day model for evaluating glacier runoff changes in China. Part I: model development

The retreat of mountain glaciers and ice caps has dominated the rise in global sea level and is likely to remain an import component of eustatic sea‐level rise in the 21st century. Mountain glaciers are critical in supplying freshwater to populations inhabiting the valleys downstream who heavily rely on glacier runoff, such as arid and semi‐arid regions of western China. Owing to recent climate warming and the consequent rapid retreat of many glaciers, it is essential to evaluate the long‐term change in glacier melt water production, especially when considering the glacier area change. This paper describes the structure, principles and parameters of a modified monthly degree‐day model considering glacier area variation. Water balances in different elevation bands are calculated with full consideration of the monthly precipitation gradient and air temperature lapse rate. The degree‐day factors for ice and snow are tuned by comparing simulated variables to observation data for the same period, such as mass balance, equilibrium line altitude and glacier runoff depth. The glacier area–volume scaling factor is calibrated with the observed glacier area change monitored by remote sensing data of seven sub‐basins of the Tarim interior basin. Based on meteorological data, the glacier area, mass balance and runoff are estimated. The model can be used to evaluate the long‐term changes of melt water in all glacierized basins of western China, especially for those with limited observation data. Copyright © 2011 John Wiley & Sons, Ltd.     

Recent advances in understanding ice sheet dynamics

Glaciers and ice sheets play a dynamic role in Earth's climate system, influencing regional- and global-scale climate and responding to climate change on time scales from years to millennia. They are also an integral part of Earth's landscape in alpine and polar regions, where they are an active agent in isostatic, tectonic, and Earth surface processes. This review paper summarizes recent progress in understanding and modelling ice sheet dynamics, from the microphysical processes of ice deformation in glaciers to continental-scale processes that influence ice dynamics. Based on recent insights and research directions, it can be expected that a new generation of ice sheet models will soon replace the current standard. Improvements that can be foreseen in the near future include: (i) the addition of internally-consistent evolutionary equations for ice crystal fabric (anisotropic flow laws), (ii) more generalized flow laws that include different deformation mechanisms under different stress regimes, (iii) explicit incorporation of the effects of chemical impurities and grain size (dynamic recrystallization) on ice deformation, (iv) higher-order stress solutions to the momentum balance (Stokes' equation) that governs ice sheet flow, and (v) the continued merger of ice sheet models with increasingly complex Earth systems models, which include fully-coupled subglacial hydrological and geological processes. Examples from the Greenland Ice Sheet and Vatnajökull Ice Cap, Iceland are used to illustrate several of these new directions and their importance to glacier dynamics.     

Observed Mass Balance of Mountain Glaciers and Greenland Ice Sheet in the 20th Century and the Present Trends

Glacier mass balance and secular changes in mountain glaciers and ice caps are evaluated from the annual net balance of 137 glaciers from 17 glacierized regions of the world. Further, the winter and summer balances for 35 glaciers in 11 glacierized regions are analyzed. The global means are calculated by weighting glacier and regional surface areas. The area-weighted global mean net balance for the period 1960?C2000 is ?270 ± 34 mm a^?1 w.e. (water equivalent, in mm per year) or (?149 ± 19 km³ a^?1 w.e.), with a winter balance of 890 ± 24 mm a^?1 w.e. (490 ± 13 km³ a^?1 w.e.) and a summer balance of ?1,175 ± 24 mm a^?1 w.e. (?647 ± 13 km³ a^?1 w.e.). The linear-fitted global net balance is accelerating at a rate of ?9 ± 2.1 mm a^?2. The main driving force behind this change is the summer balance with an acceleration of ?10 ± 2.0 mm a^?2. The decadal balance, however, shows significant fluctuations: summer melt reached its peak around 1945, followed by a decrease. The negative trend in the annual net balance is interrupted by a period of stagnation from 1960s to 1980s. Some regions experienced a period of positive net balance during this time, for example, Europe. The balance has become strongly negative since the early 1990s. These decadal fluctuations correspond to periods of global dimming (for smaller melt) and global brightening (for larger melt). The total radiation at the surface changed as a result of an imbalance between steadily increasing greenhouse gases and fluctuating aerosol emissions. The mass balance of the Greenland ice sheet and the surrounding small glaciers, averaged for the period of 1950?C2000, is negative at ?74 ± 10 mm a^?1 w.e. (?128 ± 18 km³ a^?1 w.e.) with an accumulation of 297 ± 33 mm a^?1 w.e. (519 ± 58 km³ a^?1 w.e.), melt ablation ?169 ± 18 mm a^?1 w.e. (?296 ± 31 km³ a^?1 w.e.), calving ablation ?181 ± 19 mm a^?1 w.e. (?316 ± 33 km³ a^?1 w.e.) and the bottom melt-21 ± 2 mm a^?1 w.e. (?35 ± 4 km³ a^?1 w.e.). Almost half (?60 ± 3 km³ a^?1) of the net mass loss comes from mountain glaciers and ice caps around the ice sheet. At present, it is difficult to detect any statistically significant trends for these components. The total mass balance of the Antarctic ice sheet is considered to be too premature to evaluate. The estimated sea-level contributions in the twentieth Century are 5.7 ± 0.5 cm by mountain glaciers and ice caps outside Antarctica, 1.9 ± 0.5 cm by the Greenland ice sheet, and 2 cm by ocean thermal expansion. The difference of 7 cm between these components and the estimated value with tide-gage networks (17 cm) must result from other sources such as the mass balance of glaciers of Antarctica, especially small glaciers separated from the ice sheet.     

Grain size record of microparticles in the Muztagata ice core

Dust grain size is a proxy for wind strength that en-trains it. Mineral aerosol blown from arid continent to remote sites has a broad diameter range, from less than 0.5 μm to larger than 75 μm[1]. For a long time, geolo-gists reveal the transport and sediment characteristics using grain size and size distribution. In loess research, grain size is widely used as the proxy for winter mon-soon strength[2,3]. Fractions entrained by the westerlies and winter monsoon can be discerned by grain size…     

Response of the Greenland and Antarctic Ice Sheets to Multi-Millennial Greenhouse Warming in the Earth System Model of Intermediate Complexity LOVECLIM

Calculations were performed with the Earth system model of intermediate complexity LOVECLIM to study the response of the Greenland and Antarctic ice sheets to sustained multi-millennial greenhouse warming. Use was made of fully dynamic 3D thermomechanical ice-sheet models bidirectionally coupled to an atmosphere and an ocean model. Two 3,000-year experiments were evaluated following forcing scenarios with atmospheric CO₂ concentration increased to two and four times the pre-industrial value, and held constant thereafter. In the high concentration scenario the model shows a sustained mean annual warming of up to 10°C in both polar regions. This leads to an almost complete disintegration of the Greenland ice sheet after 3,000 years, almost entirely caused by increased surface melting. Significant volume loss of the Antarctic ice sheet takes many centuries to initiate due to the thermal inertia of the Southern Ocean but is equivalent to more than 4 m of global sea-level rise by the end of simulation period. By that time, surface conditions along the East Antarctic ice sheet margin take on characteristics of the present-day Greenland ice sheet. West Antarctic ice shelves have thinned considerably from subshelf melting and grounding lines have retreated over distances of several 100 km, especially for the Ross ice shelf. In the low concentration scenario, corresponding to a local warming of 3?C4°C, polar ice-sheet melting proceeds at a much lower rate. For the first 1,200 years, the Antarctic ice sheet is even slightly larger than today on account of increased accumulation rates but contributes positively to sea-level rise after that. The Greenland ice sheet loses mass at a rate equivalent to 35 cm of global sea level rise during the first 1,000 years increasing to 150 cm during the last 1,000 years. For both scenarios, ice loss from the Antarctic ice sheet is still accelerating after 3,000 years despite a constant greenhouse gas forcing after the first 70?C140 years of the simulation.     

联合GRACE、Swarm、GRACE-FO卫星观测确定格陵兰岛冰盖质量时空变化特征

GRACE(Gravity Recovery and Climate Experiment)重力卫星任务的成功实施,极大推进了极地冰盖质量平衡、全球水循环和海水质量变化等领域的研究,其后续任务GRACE-FO(Gravity Recovery and Climate Experiment Follow-On)于2018...     

Using ground gravity to improve ice mass change estimation from GOCE gravity gradients in mid-west Greenland

Vertical gravity gradient anomalies from the Gravity and steady-state Ocean Circulation Explorer (GOCE) DIR-3 model have been used to determine gravity anomalies in mid-west Greenland by using Least-Squares Collocation (LSC) and the Reduced Point Mass (RPM) method. The two methods give nearly identical results. However, compared to LSC, the RPM method needs less computational time as the number of equations to be solved in LSC equals the number of observations. The advantage of the LSC, however, is the acquired error estimates. The observation periods are winter 2009 and summer 2012. In order to enhance the accuracy of the calculated gravity anomalies, ground gravity data from West Greenland is used over locations where the gravity change resulting from ice mass changes is negligible, i.e. over solid rock. In the period considered, the gravity anomaly change due to changes in ice mass varies from ?5 mGal to 4 mGal. It is negative over the outlet glacier Jacobshavn Isbræ, where the mass loss corresponds to a gravity change of approximately ?4 mGal. When using only GOCE vertical gravity gradients, the error estimates range from 5 mGal at the coast to 17 mGal over the ice sheet. Introducing the ground gravity data from West Greenland in the prediction reduces the errors to range from 2 to 10 mGal.     

A Review of Recent Updates of Sea-Level Projections at Global and Regional Scales

Sea-level change (SLC) is a much-studied topic in the area of climate research, integrating a range of climate science disciplines, and is expected to impact coastal communities around the world. As a result, this field is rapidly moving, and the knowledge and understanding of processes contributing to SLC is increasing. Here, we discuss noteworthy recent developments in the projection of SLC contributions and in the global mean and regional sea-level projections. For the Greenland Ice Sheet contribution to SLC, earlier estimates have been confirmed in recent research, but part of the source of this contribution has shifted from dynamics to surface melting. New insights into dynamic discharge processes and the onset of marine ice sheet instability increase the projected range for the Antarctic contribution by the end of the century. The contribution from both ice sheets is projected to increase further in the coming centuries to millennia. Recent updates of the global glacier outline database and new global glacier models have led to slightly lower projections for the glacier contribution to SLC (7–17 cm by 2100), but still project the glaciers to be an important contribution. For global mean sea-level projections, the focus has shifted to better estimating the uncertainty distributions of the projection time series, which may not necessarily follow a normal distribution. Instead, recent studies use skewed distributions with longer tails to higher uncertainties. Regional projections have been used to study regional uncertainty distributions, and regional projections are increasingly being applied to specific regions, countries, and coastal areas.     

Depth to Moho in Greenland: receiver-function analysis suggests two Proterozoic blocks in Greenland

The GLATIS project (Greenland Lithosphere Analysed Teleseismically on the Ice Sheet) with collaborators has operated a total of 16 temporary broadband seismographs for periods from 3 months to 2 years distributed over much of Greenland from late 1999 to the present. The very first results are presented in this paper, where receiver-function analysis has been used to map the depth to Moho in a large region where crustal thicknesses were previously completely unknown. The results suggest that the Proterozoic part of central Greenland consists of two distinct blocks with different depths to Moho. North of the Archean core in southern Greenland is a zone of very thick Proterozoic crust with an average depth to Moho close to 48 km. Further to the north the Proterozoic crust thins to 37–42 km. We suggest that the boundary between thick and thin crust forms the boundary between the geologically defined Nagssugtoqidian and Rinkian mobile belts, which thus can be viewed as two blocks, based on the large difference in depth to Moho (over 6 km). Depth to Moho on the Archean crust is around 40 km. Four of the stations are placed in the interior of Greenland on the ice sheet, where we find the data quality excellent, but receiver-function analyses are complicated by strong converted phases generated at the base of the ice sheet, which in some places is more than 3 km thick.