Periglacial mass-wasting landforms on Mars suggestive of transient liquid water in the recent past: Insights from solifluction lobes on Svalbard     

A. Johnsson  D. Reiss  E. Hauber  M. Zanetti  H. Hiesinger  L. Johansson  M. Olvmo 《Icarus》2012,218(1):489-505

On Earth, periglacial solifluction is a slow mass-wasting process related to freeze–thaw activity. We compare the morphology of small-scale lobate features on Mars to solifluction lobes in Svalbard to constrain their processes of formation. The analysis is based on high-resolution satellite imagery of Mars (HiRISE, ～25 cm/pxl), aerial images of Svalbard with a similar spatial resolution (HRSC–AX, ～20 cm/pxl) acquired through an air campaign in summer 2008, and ground truth obtained during two summer expeditions in 2009 and 2011 on Svalbard. We present a detailed study of two crater environments on Mars displaying two types of lobate forms, characterized as sorted (clast-banked) and non-sorted lobes. On both Svalbard and Mars such lobes typically occur as clusters of overlapping risers (lobe fronts), pointing to differential velocities in the soil. The martian small-scale lobes have well-defined arcuate risers and lobe treads (surface). Lobe widths range between 14 and 127 m and tread lengths between 13 and 105 m. Riser height is estimated to be approximately 1–5 m. The lobes on Mars share the plan view morphology of solifluction lobes on Svalbard and their morphometry is within the range of values of terrestrial solifluction lobes. The lobes are distinct from permafrost-creep landforms such as rock glaciers. We show the results of a survey of 53 HiRISE images covering latitudes between 59°N and 81°N. Similar to Svalbard, the studied lobate features on Mars occur in close spatial proximity to gullies and thermal contraction polygons. The widespread distribution of the lobate forms in the northern hemisphere and their close association to ground-ice and gullies are best explained by mass-wasting processes related to frost creep, gelifluction and/or plug-like flow. This suggests a protracted process (thousand to several thousands of years) of freeze–thaw activity at the northern high latitudes on Mars. Age constraints on lobe deposits and superposition relationships with gullies and polygons imply a process involving liquid water within the last few million years.  相似文献   

Increased photosynthesis compensates for shorter growing season in subarctic tundra—8 years of snow accumulation manipulations     

Julia Bosiö  Christian Stiegler  Margareta Johansson  Herbert N. Mbufong  Torben R. Christensen 《Climatic change》2014,127(2):321-334

This study was initiated to analyze the effect of increased snow cover on plant photosynthesis in subarctic mires underlain by permafrost. Snow fences were used to increase the accumulation of snow on a subarctic permafrost mire in northern Sweden. By measuring reflected photosynthetic active radiation (PAR) the effect of snow thickness and associated delay of the start of the growing season was assessed in terms of absorbed PAR and estimated gross primary production (GPP). Six plots experienced increased snow accumulation and six plots were untreated. Incoming and reflected PAR was logged hourly from August 2010 to October 2013. In 2010 PAR measurements were coupled with flux chamber measurements to assess GPP and light use efficiency of the plots. The increased snow thickness prolonged the duration of the snow cover in spring. The delay of the growing season start in the treated plots was 18 days in 2011, 3 days in 2012 and 22 days in 2013. Results show higher PAR absorption, together with almost 35 % higher light use efficiency, in treated plots compared to untreated plots. Estimations of GPP suggest that the loss in early season photosynthesis, due to the shortening of the growing season in the treatment plots, is well compensated for by the increased absorption of PAR and higher light use efficiency throughout the whole growing seasons. This compensation is likely to be explained by increased soil moisture and nutrients together with a shift in vegetation composition associated with the accelerated permafrost thaw in the treatment plots.  相似文献   

Mechanism on how the spring Arctic sea ice impacts the East Asian summer monsoon   总被引：2，自引：0，他引：2  

Dong Guo  Yongqi Gao  Ingo Bethke  Daoyi Gong  Ola M. Johannessen  Huijun Wang 《Theoretical and Applied Climatology》2014,115(1-2):107-119

Observational analysis and purposely designed coupled atmosphere–ocean (AOGCM) and atmosphere-only (AGCM) model simulations are used together to investigate a new mechanism describing how spring Arctic sea ice impacts the East Asian summer monsoon (EASM). Consistent with previous studies, analysis of observational data from 1979 to 2009 show that spring Arctic sea ice is significantly linked to the EASM on inter-annual timescales. Results of a multivariate Empirical Orthogonal Function analysis reveal that sea surface temperature (SST) changes in the North Pacific play a mediating role for the inter-seasonal connection between spring Arctic sea ice and the EASM. Large-scale atmospheric circulation and precipitation changes are consistent with the SST changes. The mechanism found in the observational data is confirmed by the numerical experiments and can be described as follows: spring Arctic sea ice anomalies cause atmospheric circulation anomalies, which, in turn, cause SST anomalies in the North Pacific. The SST anomalies can persist into summer and then impact the summer monsoon circulation and precipitation over East Asia. The mediating role of SST changes is highlighted by the result that only the AOGCM, but not the AGCM, reproduces the observed sea ice-EASM linkage.  相似文献   

Greenland Ice Sheet Contribution to Future Global Sea Level Rise based on CMIP5 Models简     

YAN Qing  WANG Huijun  Ola M.JOHANNESSEN  ZHANG Zhongshi 《大气科学进展》2014,31(1):8-16

Sea level rise （SLR） is one of the major socioeconomic risks associated with global warming. Mass losses from the Greenland ice sheet （GrIS） will be partially responsible for future SLR, although there are large uncertainties in modeled climate and ice sheet behavior. We used the ice sheet model SICOPOLIS （Simulation COde for POLythermal Ice Sheets） driven by climate projections from 20 models in the fifth phase of the Coupled Model Intercomparison Project （CMIP5） to estimate the GrlS contribution to global SLR. Based on the outputs of the 20 models, it is estimated that the GrIS will contribute 0-16 （0-27） cm to global SLR by 2100 under the Representative Concentration Pathways （RCP） 4.5 （RCP 8.5） scenarios. The projected SLR increases further to 7-22 （7-33） cm with 2~basal sliding included. In response to the results of the multimodel ensemble mean, the ice sheet model projects a global SLR of 3 cm and 7 cm （10 cm and 13 cm with 2~basal sliding） under the RCP 4.5 and RCP 8.5 scenarios, respectively. In addition, our results suggest that the uncertainty in future sea level projection caused by the large spread in climate projections could be reduced with model-evaluation and the selective use of model outputs.  相似文献   

Obituary          下载免费PDF全文

WANG Hui-Jun  Ola M. JOHANNESSEN 《大气和海洋科学快报》2014,(4)

正In Memory of Dr.Peter James LAMB(21 June 1947-28 May 2014)Dr.Peter James LAMB,Editor of Atmospheric and Oceanic Science Letters(AOSL);George Lynn Cross Research Professor of Meteorology at the University of Oklahoma;Director,NOAA Cooperative Institute of Mesoscale Meteorological Studies,passed away in his home in Norman,Oklahoma on 28 May 2014.He was born on 21 June 1947  相似文献   

Sedimentary evolution and environmental history of Lake Van (Turkey) over the past 600 000 years   总被引：1，自引：0，他引：1  

Mona Stockhecke  Michael Sturm  Irene Brunner  Hans‐Ulrich Schmincke  Mari Sumita  Rolf Kipfer  Deniz Cukur  Ola Kwiecien  Flavio S. Anselmetti 《Sedimentology》2014,61(6):1830-1861

The lithostratigraphic framework of Lake Van, eastern Turkey, has been systematically analysed to document the sedimentary evolution and the environmental history of the lake during the past ca 600 000 years. The lithostratigraphy and chemostratigraphy of a 219 m long drill core from Lake Van serve to separate global climate oscillations from local factors caused by tectonic and volcanic activity. An age model was established based on the climatostratigraphic alignment of chemical and lithological signatures, validated by ⁴⁰Ar/³⁹Ar ages. The drilled sequence consists of ca 76% lacustrine carbonaceous clayey silt, ca 2% fluvial deposits, ca 17% volcaniclastic deposits and 5% gaps. Six lacustrine lithotypes were separated from the fluvial and event deposits, such as volcaniclastics (ca 300 layers) and graded beds (ca 375 layers), and their depositional environments are documented. These lithotypes are: (i) graded beds frequently intercalated with varved clayey silts reflecting rising lake levels during the terminations; (ii) varved clayey silts reflecting strong seasonality and an intralake oxic–anoxic boundary, for example, lake‐level highstands during interglacials/interstadials; (iii) CaCO₃‐rich banded sediments which are representative of a lowering of the oxic–anoxic boundary, for example, lake level decreases during glacial inceptions; (iv) CaCO₃‐poor banded and mottled clayey silts reflecting an oxic–anoxic boundary close to the sediment–water interface, for example, lake‐level lowstands during glacials/stadials; (v) diatomaceous muds were deposited during the early beginning of the lake as a fresh water system; and (vi) fluvial sands and gravels indicating the initial flooding of the lake basin. The recurrence of lithologies (i) to (iv) follows the past five glacial/interglacial cycles. A 20 m thick disturbed unit reflects an interval of major tectonic activity in Lake Van at ca 414 ka bp . Although local environmental processes such as tectonic and volcanic activity influenced sedimentation, the lithostratigraphic pattern and organic matter content clearly reflect past global climate changes, making Lake Van an outstanding terrestrial archive of unprecedented sensitivity for the reconstruction of the regional climate over the last 600 000 years.  相似文献   

Spectral scan of the star-forming region DR21(OH). Observations and LTE analysis     

S. V. Kalenskii  L. E. B. Johansson 《Astronomy Reports》2010,54(4):295-316

Seventy-eight molecules have been detected as a result of a spectral survey of the star-forming region DR21(OH) at 84–115 GHz. The abundances of most molecules are typical of those in the dense cores of molecular clouds. The rotational temperatures derived using the lines of most molecules fall in the range 9–56 K, which is also typical for dense cores. However, emission from high-lying levels of methanol and sulfur dioxide was detected; since the rotational temperatures for methanol and sulfur dioxide are 252 and 186 K, this indicates the presence of hot regions. Another fact indicating the existence of hot regions is the detection of CH₃OCHO, CH₃CH₂OH, and CH₃OCH₃, which have thus far been observed only in hot cores and shock-heated regions. An interesting result is the tentative detection of the J = 2 − 1, v = 1 SiO line, with the upper level energy of 1775 K. This is probably a maser line, similar to but weaker than the well-known SiO masers in the star-forming regions Orion-KL,W51(N), and Sgr B2(N).  相似文献   

Spectral survey of the star-forming region W51 e1/e2 at 3 mm     

S. V. Kalenskii  L. E. B. Johansson 《Astronomy Reports》2010,54(12):1084-1104

A spectral survey of the W51 e1/e2 star-forming region at 84–115 GHz has yielded detections of 105 molecules and their isotopic species, from simple diatomic or triatomic molecules, such as CO, CS, HCN, up to complex organic compounds, such as CH₃OCH₃, CH₃COCH₃, and C₂H₅OOCH. Ninety-three lines that are absent from the Lovas list of molecular lines observed from space were detected, and approximately half of these were identified. A significant number of the detectedmolecules are typical for hot cores. These include the neutral molecules CH₃OCHO, C₂H₅OH, CH₃COCH₃ etc., which are currently believed to exist in the gas phase only in hot cores and shock-heated gas. In addition, vibrationally excited SiO, C₄H, HCN, l-C₃H, HCCCN, CH₃CN, CH₃OH, H₂O, and SO₂ lines with upper-level temperatures of several hundred Kelvin were found. Such lines can arise only in hot gas with temperatures of the order of 100 K or higher. Apart from neutral molecules, various molecular ions were also detected. Some of these (N₂H⁺, HCO⁺, HCS⁺) usually exist in molecular clouds with high visual extinctions A _V . At the same time, the CF⁺ ion should be observed in photon-dominated regions with A _V values of about unity or lower. An interesting result is the tentative detection of two molecules that have thus far been observed only in the atmospheres of late-type giant stars—MgCN and NaCN. This suggests that the conditions in the hottest W51 regions (probably, in the vicinities of protostars) are close to those in the atmospheres of giant stars. It would be desirable to search for other lines of these molecules to verify these tentative detections. Analysis of the radial velocities of the detected molecules suggests that the contribution from the e2 core dominates the emission of some O-bearing molecules (CH₃OCHO, CH₃CH₂OH), while the contribution of the e1 core dominates the emission of some N-bearing molecules (e.g., CH₃CH₂CN). Thus, the molecular composition of the e2 core may be closer to the composition of the “Compact Ridge” in OMC-1, while the composition of the e1 core is closer to that for the “Hot Core” in the same cloud.  相似文献