Mean Annual Isotherm Research Articles

A centennial record of fluvial organic matter input from the discontinuous permafrost catchment of Lake Torneträsk

High‐latitude regions are underlain by the most organic carbon (OC)‐rich soils on earth and currently subject to intense climate warming, potentially increasing remobilization and mineralization of soil OC. Sub‐Arctic Scandinavia is located on the 0°C mean annual isotherm and is therefore particularly vulnerable to climate change. This study aimed to establish a baseline for soil OC release over the past century into Lake Torneträsk, the largest lake in sub‐Arctic Scandinavia, through bulk geochemical and molecular radiocarbon analyses in chronologically constrained sediment cores. Our results suggest a dominance of peat‐derived terrestrial OC inflow. We show that the annual terrestrial OC inflow to the lake is ∼12 times higher than the in‐lake produced particulate OC, and consists for a large part (ca. 60%) of old OC from deep reservoirs in the catchment. The sedimentary record shows signs of increasing inflow of more degraded terrestrial matter since ∼1975, as indicated by increasing %TOC concentrations, a lowerδ13C value and lower TOC:TN ratios. Based on simultaneous changes in local climate and reported signs of permafrost degradation (e.g., active layer deepening, mire/peat erosion), the observed changes in the sedimentary record of Scandinavia's largest mountain lake likely reflect a climate warming‐induced change in terrestrial OC inflow.

Examining Holocene stability of Antarctic Peninsula ice shelves

Temperatures on the Antarctic Peninsula are increasing at a rate of 3.4°C per century, more than five times the global mean. At the same time, the region's ice shelves have retreated and collapsed, with an area of more than 14,000 square kilometers disappearing within the past two decades. Ice shelf retreat has followed the southward migration of the −9°C mean annual isotherm, referred to as the ‘climatic limit of ice shelf stability’ (Figure 1).Thus, present‐day ice shelf retreats on the Antarctic Peninsula have been linked to increased atmospheric temperature [Vaughan et al., 2003].

Land Cover Change and Its Impacts on Soil C and N in Two Watersheds in the Center of the Qinghai-Tibetan Plateau

The responses of the ecosystems along the 0°C mean annual isotherm to global climate change are intense and involve significant changes in land cover at the watershed scale. This paper evaluates changes in land cover in the center of Qinghai-Tibet, the headwater region of the Yangtze and Yellow Rivers, on the basis of two sets of remote sensing data (1986 and 2000) and field investigations. Over a period of 15 years, 23% and 34% of alpine cold swamp were recently turned into alpine cold meadow or alpine cold steppe, and decreased in area by 25.9% and 42.7% in the headwater areas of the Yellow and Yangtze Rivers, respectively. Moreover, more than 20% of high-coverage alpine cold meadow and alpine cold steppe were converted to lower-coverage alpine cold meadow (vegetation coverage > 80%) and alpine cold steppe (vegetation coverage > 50%). Desertified land increased by 18.4% (bare rocks and sparse land) and 31.1% (sandy land) in the headwater area of the Yellow River and by 17.8%–18.5% in the headwater area of the Yangtze River. Land cover change in this region involves a complex transition between land cover types, which have a great influence on soil nutrients and the soil organic carbon (SOC) pool. Land cover changes in the study area over the 15-year study period led to the loss of 336.6 Gg of SOC, of which 61.6% were lost by alpine cold swamp transformation, and a total nitrogen (N) loss of 26.9 Gg, of which 81.9% occurred in the headwater area of the Yangtze River. The changes in the carbon and nitrogen cycles have serious implications for greenhouse gas emissions due to land cover change caused by climate warming in the Qinghai-Tibetan Plateau.

Thawing sub‐arctic permafrost: Effects on vegetation and methane emissions

Ecosystems along the 0°C mean annual isotherm are arguably among the most sensitive to changing climate and mires in these regions emit significant amounts of the important greenhouse gas methane (CH4) to the atmosphere. These CH4 emissions are intimately related to temperature and hydrology, and alterations in permafrost coverage, which affect both of those, could have dramatic impacts on the emissions. Using a variety of data and information sources from the same region in subarctic Sweden we show that mire ecosystems are subject to dramatic recent changes in the distribution of permafrost and vegetation. These changes are most likely caused by a warming, which has been observed during recent decades. A detailed study of one mire show that the permafrost and vegetation changes have been associated with increases in landscape scale CH4 emissions in the range of 22–66% over the period 1970 to 2000.

The relationship between climate and rock glacier distribution in the ben ohau range, new zealand

Landforms of ice and debris transport marginal to the glacierized zone of the Southern Alps, New Zealand, have been classified into debris‐covered glaciers, cirque floor lobes, and talus‐derived rock glaciers. Mapping of fossil and active landforms reveals a zonation within the Ben Ohau Range in terms of both landform type and activity status. The dominant distinction of active forms is between relatively ice‐rich forms (glacial origins) in the humid north and relatively debris‐rich forms (periglacial origins) in the more arid south. A secondary altitudinal zonation distinguishes currently or recently active forms at high elevations from fossil forms at lower elevations. Estimates of mean annual precipitation and of the altitude of the –2°C mean annual isotherm indicate that glaciers and active talus rock glaciers are located within the climatic boundaries identified for the European Alps. However, many fossil forms also occur within these boundaries where cirques are broader and shallower. These findings confirm earlier suggestions that permafrost occurs in the Southern Alps, but is restricted to a narrow zone above 2000 m. The study demonstrates the importance of relative ice‐to‐debris fluxes in determining the developmental pathways of landform genesis over both space and time.

Jungle Stories: North American Representations of Tropical Panama

'Tis a land that still with potent charm And wondrous, lasting spell With mighty thrall enchaineth all Who long within it dwell 'Tis a land where the Pale Destroyer waits And watches eagerly; 'Tis, in truth, but a breath from life to death, In the Land of the Cocoanut Tree. - James Stanley Gilbert, Panama Patchwork, 1908 During the late nineteenth and early twentieth centuries, as tropical Central America came under increasing U.S. influence, U.S. policymakers, businesspeople, missionaries, and bureaucrats began to transform the region to meet their needs.(1) They built railways, led military invasions, established banana and coffee plantations, and eventually dug a canal across Panama. Their published accounts and artistic renderings of Central America drew on more generalized, archetypal ideas in the art, history, literature, and photographs of tropics around the world to form a specific discourse about the Central American tropics.(2) Two opposing narratives constituted this discourse: positive ones about Edenic paradises, fertile soil, and exotic beauty; and negative ones about moral laxity, dangerous landscapes, disease, and the threatening abundance of the jungle. These varied ways of seeing Central America revealed themselves in more than just semantic representations; they influenced U.S. actions and policies in the tropics. These contradictory narratives were used to legitimate imperialist intervention and actions in the Panama Canal Zone in the early twentieth century. THE DISCOURSE OF THE TROPICS Lines of latitude have long been used to demarcate tropical regions. Aristotle, for example, separated the world horizontally into frigid, temperate, and torrid (tropical) zones. Today the tropics are depicted as the region that lies between 23 [degrees] 30 [minutes] north latitude and 23 [degrees] 30 [minutes] south latitude - the Tropics of Cancer and Capricorn. Alternatively, the tropics have been defined using temperature and precipitation isolines. These have varied somewhat, from Ellen Churchill Semple's (1911) inclusion of areas within the 20 [degrees] mean annual isotherm to Isaiah Bowman's (1937, 381) use of the 25 [degrees] mean annual isotherm. A physical geography textbook today designates them as lands within the 18 [degrees] mean annual isotherm (Strahler and Strahler 1996, 165). Agreement on the climatic character of the region - the heat and humidity associated with the tropical lowlands - is more general. In fact, highland areas such as the Meseta Central of Costa Rica were excluded from the tropical discourse because, as one traveler stated, they are as cool and healthful as the coastal plains are torrid and fever-infested (Putnam 1913, 10). The interpretation of tropical heat and humidity has shifted over the past two centuries, however. At various times North Americans have imagined the Central American lowland tropics as distant paradises or fever coasts (in the nineteenth century), as banana republics (in the early to mid-twentieth century), as places for revolution (in the 1970s and 1980s), and as sites for romantic ecotravels (in the 1990s). In this article I use the word tropics to refer to the lowland tropics, and I deal exclusively with the late nineteenth and early twentieth centuries. In this geographical and historical context, the character of tropical climates was frequently expressed in subjective terms, even when placed within a so-called scientific framework. Turn-of-the-century U.S. natural science textbooks typically included a classification of the tropical flora, fauna, temperatures, and diseases in Central America. Such descriptions, however, were frequently intertwined with an author's opinions concerning heat, disease, dark-skinned peoples, hot or spicy foods, exotic fruit, fecund vegetation, and economic underdevelopment. For example, in his 1918 Handbook of Commercial Geography, Geo. G. Chisholm describes the specific rainfall amounts, humidity, and temperature that are characteristic of the tropics while noting the excessive heat and irksome humidity (p. …

MARBLE TOMBSTONE WEATHERING RATES: A TRANSECT OF THE UNITED STATES

Mean weathering rates measured on marble tombstones appear to vary linearly with mean annual rainfall at locations along the 10°C mean annual isotherm in the United States. Chemically-induced granular weathering is the dominant mechanism. Weathering is most rapid on upper portions of stone faces, which recede at about 1 mm/1,000 yrs where mean annual rainfall is 200 mm/yr, and 16 mm/1,000 yrs when rainfall is 1,000 mm/yr. These rates are about 50% greater than on central inscribed portions of vertical faces and on upward-facing horizontal slabs. Weathering rates of marble tombstones are perhaps one-quarter of those reported for limestone denudation in locations with similar climates and about one-half of the rates on marble tombstones in heavily polluted environments. Preliminary work in a high mountain environment with a mean annual temperature of 2°C indicates that marble weathering rates are an order of magnitude greater than at 10°C, possibly because of frost weathering. Where sprinkler irrigation is ...

The former southern distribution of New World manatees (Trichechus spp.)

Records of New World manatees in 16th and 17th century literature extend the former distribution of Trichechus manatus to about 20° S. Early 19th century records confirm this range, but the species has since been exterminated from these southerly localities and is now rarely found to the south of Cayenne (French Guiana). Manatees probably did not occur at Rio de Janeiro or Santos, the Sao Vicente “monster” most likely being a pinnepede. The former distribution of T. manatus seems to have been bounded by the 24° C mean annual isotherm.

Paleoclimatic Significance of Fossil Periglacial Phenomena in Hokkaidô, Northern Japan

In present paper some fossil forms of frozen ground phenomena such as earth hummocks (Fig. 1), sorted patterned grounds (Figs. 3 & 4), festoon: vertical stones (Figs. 4 & 5), involutions (Figs. 7 & 8), and ice-wedge casts (Fig. 6) are described.The zonal distribution of active frozen ground phenomena and related environments are tabulated from some literatures as well as the results of our own survey on them in Japan (Table 1). Paleoclimate of the last glacial period in the esatern part of Hokkaido is considered after distribution of fossil frozen ground phenomena comparing with distribution of active ones. Volcanic ash layers and river terraces are surveyed to determine tephorochronologically the age of phenomena.The main results are as follows. All kinds of frozen ground phenomena, even earth hummocks, carry involution structures in cross section (Fig. 2). Stratified sediments such as volcanic ash layers clarify involution structures. In Japan, the southern limit of active earth hummocks coincedes approximately with +6°C mean annual isotherm. Therefore, buried earth hummocks and small-scale involutions do not indicate ancient cold climate in eastern Hokkaido where present mean annual temerature is nearly+6°C.Festoon, a kind of involution, can easily be found in fine sediments overlying river terrace gravels. Because of prevention of dense vegetation cover gravels do not reach the ground surface to form sorted patterned ground in most cases although some fossil sorted patterned grounds are found. Vegetation profited by warmth in summer sets the limit of sorted patterned grounds on nearly 0°C mean annual isotherm in central Japan and on a isotherm of somewhat lower than 0°C in Hokkaido.Some large-scale involutions (Fig. 8) may be cross sectios of palsas. Ice-wedge casts, indicators of ancient permafrost, are also found in the lowlands of eastern Hokkaido. Based on Pewe's observation decreasing of temperature at the time should be estimated as 12°-14°C.In this region ice-wedge casts indicating the maximum coldness are buried by a markable layer (Erimo Volcanic Sand: Spfa; 32, 200 14C yr.B.P.). It is, therefore, concluded from chronological studies of river terraces and volcanic ash layers that in this region the maximum decreasing of temperature precedes the maximum lowering of sea level observed all over the world in 18, 000-20, 000yr.B.P.

Large Scale Patterned Ground in the Valley of the Worcestershire Avon

AbstractCrop markings reveal a polygonal network resembling that of “patterned ground” in arctic Alaska. From this the former presence of perennially frozen ground is inferred, with the implication that the mean annual isotherm of this part of Worcestershire was at least 13½° C. lower than it is at present. It is argued that this condition obtained at the period of the Irish Sea Glaciation maximum.