Permafrost at the Ice Base of Recent Pleistocene Glaciations–Inferences from Borehole Temperature Profiles

Paleo-temperature reconstruction from precise depth (>2.0 km) well temperature logs can offer information on whether the bed of an ice sheet was frozen. Inversion or upward extrapolation of the >2-km-deep geothermal profile is the only method by which temperature evolution at the base of long-disappeared ice sheets such as the Laurentide and Fennoscandian in the northern part of the Northern Hemisphere in North America and Europe can be inferred. It is obvious from the results from well temperature profiles that there were spatial variations in temperature at the base of the ice sheets during glaciations. This comes as no surprise, since modern-day measurements of temperature profiles through the ice of existing glaciers show a similarly large variability. Present bedrock temperatures measured beneath the central part of the Yukon Rusty glacier are near 0°C to -2°C while Greenland ice sheet base temperatures are -8 and -13°C. In case of very low paleo-temperatures derived from the interpretation of temperature profiles in the areas presently outside the current extent of glacial ice it can be shown that low temperature conditions under glacial ice could facilitate the existence of moderate (some 100-200 m) to thick (0.5 km-1 km) permafrost conditions. It is speculated here that, in many cases, paleo-glacial cold base ice could have existed right on top of paleo-permafrost in sediments just below. Such ice-bonded permafrost may have been frozen to glacial ice above, forming pillars which fixed glacial ice to permafrost below, thus limiting ice movement in such places and resulting in the -extended persistence of permafrost

Shallow geothermal heat in Western Canada: climatic warming impact changes with time– depth

Gain of heat and temperature in the shallow subsurface over the last decades/century has been impacted by the industrial period climatic surface air temperature (SAT) increase. Detailed study of the available temperature-depth data based on 43 wells with single and repeated temperature logs done by the first author has been combined with data base information (Jessop et al 2005) to create temperature maps at depth. Based on these 43 logs it is shown that the heat flux increases with depth in most cases for the available depth data range from surface to some 200m. Model of heat flow versus depth based on the surface air temperature changes through the industrial epoque climatic warming explains the data. Spatial and depth distribution of available temperature and heat gain through the provinces of the Western Canadian Sedimentary Basin WCSB shows that drilling closer to surface is more economic than deeper to 50-100m

Paleoclimatic reconstructions in western Canada from boreholetemperature logs: surface air temperature forcing and groundwater flow

International audienceModelling of surface temperature change effect on temperature vs.~depth and temperature-depth logs in Western Canada Sedimentary Basin show that SAT (surface air temperature) forcing is the main driving factor for the underground temperature changes diffusing with depth. It supports the validity of the basic hypothesis of borehole temperature paleoclimatology, namely that the ground surface temperature is systematically coupled with the air temperature in the longer term (decades, centuries). While the highest groundwater recharge rate used in the modelling suggests that for this extreme case some of the observed curvature in the profile, could be due to groundwater flow, it is more likely that the low recharge rates in this semi-arid region would have minimal impact. We conclude that surface temperature forcing is responsible for most of the observed anomalous temperature profile

Differences between repeated borehole temperature logs in the southern Canadian Prairies-validating borehole climatology

International audienceTemperature-depth (T-z) profiles from twenty-four shallow boreholes of less than 250 m in depth located in flat, semi-arid areas of the southern Canadian Prairie Provinces initially measured in the late 1980's and early 1990's and repeated between 2004 and 2006 show strong ground surface temperature (GST) warming signatures. GST changes of 0.1?0.2°C, and 0.4°C, are observed between the measurements for the shorter (decade) and longer (two decades) time spans, respectively. Borehole sites with repeated temperature logs are selected to demonstrate that multiple T-z profiles provide general agreement between GST warming and observed surface air temperature (SAT) warming measured at nearby historical climate stations. A comparison of measured changes from repeated temperature logs with those simulated from SAT forcing demonstrates the influence of SAT on the observed deviation of temperature with depth despite variations in snow cover. Repeated borehole measurements from the northern Great Plains of the USA also identify a similar positive temperature change but of lower magnitude. Temperature changes since 1900 in the southern Canadian Prairies and the adjoining northern Great Plains of the USA, as derived from the functional state inversion (FSI) of deeper borehole logs, average 2.5°C but show a strong latitudinal gradient

Paleoclimatic reconstructions in Western Canada from subsurface temperatures: consideration of groundwater flow

International audienceThe surface temperature forcing is responsible for the majority of the observed deviation of temperature with depth. In some cases, differences higher than the error of measurements are observed between the model and measurements. These can be an indication that other factors than surface temperature change influence subsurface temperature. Groundwater flow is one of the possible candidates

The last millennium climate change in Northern Poland derived from well temperature profiles, tree-rings and instrumental data

In order to reconstruct the air temperature variations in Northern Poland for the last millennium observational and proxy (tree-ring widths) data were used. For the first time the ground surface temperature (GST) for Northern Poland was reconstructed based on geothermal data (well temperature profiles). A general warming trend is observed for both the GSTH (GST Histories) derived from geothermal data and instrumental data, in particular, for the last 200 years

Inferred gas hydrate and permafrost stability history models linked to climate change in the Beaufort-Mackenzie Basin, Arctic Canada

Atmospheric methane from episodic gas hydrate (GH) destabilization, the "clathrate gun" hypothesis, is proposed to affect past climates, possibly since the Phanerozoic began or earlier. In the terrestrial Beaufort-Mackenzie Basin (BMB), GHs occur commonly below thick ice-bearing permafrost (IBP), but they are rare within it. Two end-member GH models, where gas is either trapped conventionally (Case 1) or where it is trapped dynamically by GH formation (Case 2), were simulated using profile (1-D) models and a 14 Myr ground surface temperature (GST) history based on marine isotopic data, adjusted to the study setting, constrained by deep heat flow, sedimentary succession conductivity, and observed IBP and Type I GH contacts in Mallik wells. Models consider latent heat effects throughout the IBP and GH intervals. Case 1 GHs formed at ~0.9 km depth only ~1 Myr ago by in situ transformation of conventionally trapped natural gas. Case 2 GHs begin to form at ~290–300 m ~6 Myr ago in the absence of lithological migration barriers. During glacial intervals Case 2 GH layers expand both downward and upward as the permafrost grows downward through and intercalated with GHs. The distinctive model results suggest that most BMB GHs resemble Case 1 models, based on the observed distinct and separate occurrences of GHs and IBP and the lack of observed GH intercalations in IBP. Case 2 GHs formed >255 m, below a persistent ice-filled permafrost layer that is as effective a seal to upward methane migration as are Case 1 lithological seals. All models respond to GST variations, but in a delayed and muted manner such that GH layers continue to grow even as the GST begins to increase. The models show that the GH stability zone history is buffered strongly by IBP during the interglacials. Thick IBP and GHs could have persisted since ~1.0 Myr ago and ~4.0 Myr ago for Cases 1 and 2, respectively. Offshore BMB IBP and GHs formed terrestrially during Pleistocene sea level low stands. Where IBP is sufficiently thick, both IBP and GHs persist even where inundated by a Holocene sea level rise and both are also expected to persist into the next glacial even if atmospheric CO<sub>2</sub> doubles. We do not address the "clathrate gun" hypothesis directly, but our models show that sub-IBP GHs respond to, rather than cause GST changes, due to both how GST changes propagates with depth and latent heat effects. Models show that many thick GH accumulations are prevented from contributing methane to the atmosphere, because they are almost certainly trapped below either ice-filled IBP or lithological barriers. Where permafrost is sufficiently thick, combinations of geological structure, thermal processes and material properties make sub-IBP GHs unlikely sources for significant atmospheric methane fluxes. Our sub-IBP GH model histories suggest that similar models applied to other GH settings could improve the understanding of GHs and their potential to affect climate

Temperature changes in Poland from the 16th to the 20th centuries

A standardized tree-ring width chronology of the Scots pine (Pinus sylvestris L.) along with different types of documentary evidence (e.g. annals, chronicles, diaries, private correspondence, records of public administration, early newspapers) have been used to reconstruct air temperature in Poland. The ground surface temperature (GST) history has been reconstructed based on the continuous temperature logs from 13 wells, using a new method developed recently by Harris and Chapman (1998; Journal of Geophysical Research 103: 7371–7383) which is compared with the functional space inversion (FSI) method applied to all available Polish temperature–depth profiles analysed before. Response function calculations conducted for trees growing in Poland (except in mountainous regions) reveal a statistically significant correlation between the annual ring widths of the Scots pine and the monthly mean air temperatures, particularly from February and March, but also from January and April. Therefore, it was only possible to reconstruct the mean January–April air temperature. The following periods featured a warm late winter/early spring: 1530–90, 1656–70 (the warmest period), 1820–50, 1910–40, and after 1985. On the other hand, a cold January–April occurred in the following periods: 1600–50, 1760–75, 1800–15, 1880–1900, and 1950–80. Reconstructions of thermal conditions using documentary evidence were carried out for winter (December–February) and summer (June–August) from 1501 to 1840 and, therefore, their results cannot be directly compared with reconstructions based on tree-ring widths. Winter temperatures in this period were colder than air temperature in the 20th century. On the other hand, ‘historical’ summers were generally warmer than those occurring in the 20th century. Such situations dominated in the 16th and 17th centuries, as well as at the turn of the 18th and 19th centuries. Throughout almost the entire period from 1501 to 1840, the thermal continentality of the climate in Poland was greater than in the 20th century. GST reconstructions show that its average pre-instrumental level (1500–1778) is about 0.9–1.5 °C lower than the mean air temperature for the period 1951–81. Lower amplitude of GST warming (0.9 ± 0.1 °C) results from the individual and simultaneous inversions of well temperature data using the FSI method. A very good correspondence of the results has been found between series of annual mean GSTs from the FSI method and mean seasonal air temperatures reconstructed using documentary evidence

Daily, seasonal, and annual relationships between air and subsurface temperatures

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95285/1/jgrd11942.pd