Size Of Ice Caps Research Articles

Simple Climate Models to Illustrate How Bifurcations Can Alter Equilibria and Stability

AbstractClimate change is, by its nature, a truly interdisciplinary topic. While college level science classes now frequently include exposure to climate change issues, not all science majors, math majors and future math K‐12 teachers are likely to see climate issues in the course of their studies. Here we present one self‐contained topic that can be presented to those students without requiring too much additional explanation about climate change issues. This case study also can serve to illustrate the rather sophisticated concept of a “tipping point” to a diverse science audience without advanced training in dynamical systems. We consider the effect of solar radiation on the size of ice caps, and show that small changes in solar radiation can cause major irreversible changes in the size of ice caps. We present two sets of exercises that students can be asked to work on their own, after the overall conceptual model has been presented during the class. This material was inspired by the experience gained by one of the authors in teaching Interdisciplinary Modeling: Water‐Related Issues and Climate Change course in summer 2012. It was used by the authors in a Math 420/620 Mathematical Modeling class at the University of Nevada, Reno in Fall 2012.

Non-linear Holocene climate evolution in the North Atlantic: a high-resolution, multi-proxy record of glacier activity and environmental change from Hvítárvatn, central Iceland

Iceland is well situated to monitor North Atlantic Holocene climate variability. Terrestrial sites there offer the potential for well-dated, high-resolution, continuous records of environmental change and/or glacier activity. Laminated sediments from the proglacial lake Hvítárvatn provide a continuous record of environmental change and the development of the adjacent Langjökull ice cap for the past 10.2 ka. Replicate lake sediment cores, collected from multiple locations in the basin, are placed in a secure geochronology by splicing a varve chronology for the past 3 ka with a tephra-constrained, paleomagnetic secular variation derived chronology for older sediments. Multiple proxies, including sedimentation rate, bulk density, ice-rafted debris, sediment organic matter, biogenic silica, and diatom abundance, allow annual to multi-decadal resolution and reveal a dynamic Holocene terrestrial climate. Following regional deglaciation of the main Iceland Ice Sheet, summer temperatures were high enough that mountain ice caps had already melted, or were contributing insignificant sediment to the lake. Pronounced increases in sedimentation rate, sediment density, and the influx of terrestrial organic matter, between 8.7 and 7.9 ka suggest early Holocene warmth was interrupted by two distinct pulses of cold summers leading to widespread landscape destabilization and possibly glacier growth. The Holocene thermal maximum (HTM; 7.9 to 5.5 ka) was characterized by high within-lake productivity and ice-free conditions in the watershed. Neoglaciation is recorded as a non-linear transition toward cooler summers, landscape destabilization, and the inception and expansion of Langjökull beginning ca 5.5 ka, with notable increases in ice cap size and landscape instability at 4.2 and 3.0 ka. The past two millennia are characterized by the abrupt onset of sustained cold periods at ca 550 and 1250 AD, separated by an interval of relative warmth from ca 950 to 1150 AD. The greatest Holocene extent of Langjökull occurred in the nineteenth century and is coincident with peak landscape instability, followed by ice recession throughout the twentieth century.

A 3000-year varved record of glacier activity and climate change from the proglacial lake Hvítárvatn, Iceland

A suite of environmental proxies in annually laminated sediments from Hvítárvatn, a proglacial lake in the central highlands of Iceland, are used to reconstruct regional climate variability and glacial activity for the past 3000 years. Sedimentological analysis is supported by tephrostratigraphy to confirm the continuous, annual nature of the laminae, and a master varve chronology places proxies from multiple lake cores in a secure geochronology. Varve thickness is controlled by the rate of glacial erosion and efficiency of subglacial discharge from the adjacent Langjökull ice cap. The continuous presence of glacially derived clastic varves in the sediment fill confirms that the ice cap has occupied the lake catchment for the duration of the record. Varve thickness, varve thickness variance, ice-rafted debris, total organic carbon (mass flux and bulk concentration), and C:N of sedimentary organic matter, reveal a dynamic late Holocene climate with abrupt and large-scale changes in ice-cap size and landscape stability. A first-order trend toward cooler summers and ice-cap expansion is punctuated by notable periods of rapid ice cap growth and/or landscape instability at ca 1000 BC, 600 BC, 550 AD and 1250 AD. The largest perturbation began ca 1250 AD, signaling the onset of the Little Ice Age and the termination of three centuries of relative warmth during Medieval times. Consistent deposition of ice-rafted debris in Hvítárvatn is restricted to the last 250 years, demonstrating that Langjökull only advanced into Hvítárvatn during the coldest centuries of the Little Ice Age, beginning in the mid eighteenth century. This advance represents the glacial maximum for at least the last 3 ka, and likely since regional deglaciation 10 ka. The multi-centennial response of biological proxies to the Hekla 3 tephra deposition illustrates the significant impact of large explosive eruptions on local environments, and catchment sensitivity to perturbations.

Permanent fast flow versus cyclic surge behaviour: numerical simulations of the Austfonna ice cap, Svalbard

AbstractA large part of the ice flux within ice caps occurs through spatially limited fast-flowing units. Some of them permanently maintain fast flow, whereas others operate in an oscillatory mode, characterized by short-lived active phases followed by long quiescent phases. This surge-type behaviour results from intrinsic rather than external factors, thus complicating estimates of glacier response to climate change. Here we present numerical model results from Austfonna, an ice cap on Svalbard that comprises several surge-type basins. Previous studies have suggested a thermally controlled soft-bed surge mechanism for Svalbard. We systematically change the parameters that govern the nature of basal motion and thereby control the transition between permanent and oscillatory fast flow. Surge-type behaviour is realized by a relatively abrupt onset of basal sliding when basal temperatures approach the pressure-melting point and enhanced sliding of marine grounded ice. Irrespective of the dynamic regime, the absence of considerable volumes of temperate ice, both in the observed and simulated ice cap, indicates that fast flow is accomplished by basal motion over a temperate bed. Given an idealized present-day climate, the equilibrium ice-cap size varies significantly, depending on the chosen parameters.

Interglacial theme and variations: 500 k.y. of orbital forcing and associated responses from the terrestrial and marine biosphere, U.S. Pacific Northwest

Sediments collected off northern California by Ocean Drilling Program Leg 167 contain time series that show strong, orbitally driven insolation forcing of surface oceanographic conditions. Orbital forcing caused a strong response in the distribution of major terrestrial vegetation but a less predictable response for primary productivity offshore. Terrestrial vegetation responded primarily to regional sea surface temperature (SST). Coastal ocean productivity appears highest when SST is moderately high, not during peak interglacial conditions nor during insolation maxima. When individual interglacial intervals are examined closely, each has a different signature. Two of six interglacials (MIS [marine isotope stage] 5 and MIS 11) have higher SST than modern conditions, but each elicits a different response from the terrestrial and marine communities. The type of vegetation and the strength of upwelling vary between interglacials, depending on the relative strength of factors that drive the warming, including insolation, ice-cap size, and level of greenhouse gases.

Landscapes of cold-centred Late Wisconsinan ice caps, Arctic Canada

Uplands of the Canadian Arctic Islands supported Late Wisconsinan ice caps that developed two landscape zones reflecting basal thermal conditions regulated by long-sustained ice flow patterns. Central cold-based zones protected older glacial and preglacial landscapes while peripheral warm-based zones scoured and otherwise altered their beds. Some geomorphic effects are independent of ice cap scale, others vary with scale. For ice caps of 30 km radius or more, scour-zone width remains proportionally constant to flowline length under similar flow conditions. But intensity of scouring, ice moulding of drift and rock eminences, size and abundance of subglacial meltwater features, and development of end moraines increase with ice cap size. Ice caps became entirely cold based early in retreat as the boundary between warm and cold ice shifted outward, probably because ice thinned and flow slackened. The frozen margins deflected meltwater, thus maximizing formation of lateral meltwater channels throughout retreat. The landform record of cold-based glaciers in this region is easily interpreted. Hence, regional ice sheet models invoking or based on the premise that cold-based ice leaves no geomorphic record seem untenable.

Palaeoclimatic interpretation of stable isotope ratios in molluscan fossils from Middle Pleistocene marine strata, Wanganui, New Zealand

Fossils molluscan shells from the Okehu and Kai-iwi Groups and Recent molluscan shells from New Zealand coastal waters exhibit considerable intraspecific variation in isotopic composition which is probably related to different (infaunal and epifaunal) modes of life. The epifaunal species Chlamys gemmulata proved the most reliable for providing information on changes in temperature or isotopic composition of ocean water during Okehuan time. Analyses of C. gemmulata shells indicate a substantial decrease in temperature or increase in size of ice-caps at about 0.75 Ma, probably in the latter part of the Günz Glaciation, and thereafter minor oscillations with a slight trend towards warming or decreasing ice until about 0.5 Ma (that is, during the Cromer Interglacial).

Late Cenozoic stable isotope stratigraphy and paleoceanography of DSDP sites from the east equatorial and central north Pacific Ocean

Stable isotopic analyses of Middle Miocene to Quaternary foraminiferal calcite from east equatorial and central north Pacific DSDP cores have provided much new information on the paleoceanography of the Pacific Neogene. The history of δ 18O change in planktonic foraminifera reflects the changing isotopic composition and temperature of seawater at the time of test formation. Changes in the isotopic composition of benthonic foraminifera largely reflect changes in the volume of continental ice. Isotopic data from these cores indicates the following sequence of events related to continental glaciation: (1) A permanent Antarctic ice sheet developed late in the Middle Miocene (about 13 to 11.5 m.y. ago). (2) The Late Miocene (about 11.5 to 5 m.y. ago) is marked by significant variation in δ 18O of about 0.5‰ throughout, indicating instability of Antarctic ice cap size or bottom-water temperatures. (3) The early Pliocene (5 to about 3 m.y. ago) was a time of relative stability in ice volume and bottom-water temperature. (4) Growth of permanent Northern Hemisphere ice sheets is inferred to have begun about 3 m.y. ago. (5) The late Pliocene (3 to about 1.8 m.y. ago) is marked by one major glaciation or bottom-water cooling dated between about 2.1 to 2.3 m.y. (6) There is some evidence that the frequency of glacial-interglacial cycles increased at about 0.9 m.y. There is significant variation in δ 13C at these sites but no geochemical interpretation is offered in this paper. The most outstanding feature of δ 13C results is a permanent shift of about −0.8‰ found at about 6.5 m.y. in east equatorial and central north Pacific benthonic foraminifera. This benthonic carbon shift may form a useful marker in deep-sea cores recovering Late Miocene carbonates.

Evolution of Martian polar landscapes: Interplay of long‐term variations in perennial ice cover and dust storm intensity

Recent Viking Orbiter observations of the Martian polar layered deposits, thought to be thick accumulations of dust, have provided new insights into the mechanisms of topographic evolution of these terrains. Here we report the discovery of wavelike topographic relief on north polar surfaces previously supposed to be flat plains. These undulations have wavelengths of a few kilometers and amplitudes of probably only a few tens of meters. The crests and troughs extend laterally up to hundreds of kilometers and have radii of curvature in plan of several hundred kilometers. Much steeper slopes, exhibiting fine terracing due to layering in the deposits, occur within troughs that separate areas of undulating plains and that parallel in strike the topographic grain of the undulations. In the model presented here, both the undulations on the plains surfaces and the layers that appear in cross section on steeper slopes are attributed to the same basic cause—periodic episodes of dust accumulation. These are probably associated with variations in global dust storm intensity and perennial polar ice cap size, brought about by periodic changes in the eccentricity of the Martian orbit and the orientation of its spin axis with respect to the ecliptic. In earlier work it has been proposed that each layer formed in a single cycle of deposition. Specifically, it was argued that dust from global dust storms is swept from the atmosphere by the accumulating annual ice and retained in the place of deposition by a matrix of perennial ice. Here we propose a mechanism for generating the undulating topography at the edge of the advancing or receding perennial ice cap in an environment of periodic deposition of dust. We have recognized several families of topographic undulations with markedly different orientations. In regions where two differently oriented sets of undulations overlap, the wave crests and troughs break up into mounds and shallow basins. We attribute this type of landscape to the occurrence of two passages of the perennial ice cap edge across the same area with the ice cap margin oriented differently on the two occasions. This implies past variations in both the size of the perennial polar cap and the location of its center if we assume that the shape of the perennial cap has not varied drastically from circular. Also reported here is evidence for a genetic relationship between undulating plains and the curvilinear defrosted bands which are the dominant physiographic features of the summer residual polar cap. We establish here that most of these curvilinear features are topographic troughs, and we propose that they are derived from a primary undulating landscape by an insolation‐controlled process. First, areas of steeper slopes within the undulating terrain lose their perennial ice cover because of a change in insolation conditions. Then, these slopes evolve into topographic troughs because in the absence of perennial ice cover they are unable to trap deposited dust. We attribute the planimetric complexity of the troughs—sharp changes in orientation, lateral offsets, and branching—to derivation from intersecting sets of primary topographic undulations with different orientations. In summary, undulating landscapes and trough complexes of the Martian polar layered deposits appear to record both lateral migration and expansion and contraction of perennial ice caps over geological history. Detailed mapping of the planimetric and stratigraphic relationships of the polar landscapes may ultimately provide the basis for a detailed model of landscape evolution and a historical record of variations on the size and location of the perennial ice cap.