Large reserves of carbon are preserved under conditions of subsea permafrost in the bottom sediments of the Arctic shelf. The existence of permafrost has created the necessary conditions for the thermodynamic stability of methane hydrates. Using a mathematical model that describes the thermal state of the sediment, we analyzed the dynamics of the permafrost and methane hydrates stability zone of the Arctic shelf bottom sediments for 100 thousand years in the future. Climate changes are considered under an idealized scenario of CO2 emissions into the atmosphere and changes in the parameters of the earth's orbit. The simulations for the next 100 kyr found that at the middle and shallow parts of the shelf the subsea permafrost survives, at least, for 9 kyr after the emission onset or even for several tens of kiloyears. Model estimates of methane emission from the Arctic shelf sediments to the water amounts up to 10 g/m2 per year.
The changes in the characteristics of submarine permafrost within the ocean shelf have been analyzed using a mathematical model describing the thermal state of the soil and supplemented with the salt diffusion equation. The model is complemented with reconstructions of climate changes at the Arctic shelf over the past 400 thousand years with two combinations of air temperature and sea level reconstructions. The estimates of the subsea permafrost sensitivity to the uncertainty of paleoclimatic reconstructions of air temperature and ocean level have been obtained. The time scales of the Arctic shelf submarine permafrost response to climate change in the glacial cycles have been estimated. The temporal scale of the propagation of the thermal signal in the permafrost layer of the shelf sediment amounted to 4-12 thousand years.
On the base of numerical experiments with the general circulation climatic model MIROC-ESM and climate model of intermediate complexity IAP RAS CM it was shown that the sign of the time lag between changes in global temperature T and atmospheric carbon dioxide content qCO2 depends on the type and the time scale of the external forcing applied to the Earth system. In particular, modern climate models are able to reproduce the qCO2 lagging behind T under conditions that are valid for the pre-industrial Holocene, so it does not contradict the idea of the importance of anthropogenic contribution to modern climate change.
The estimates of the uncertainty for the model simulated subsea permafrost characteristics relative to the uncertainty of paleoclimatic reconstructions of ocean level are obtained. This is done by using the model for thermophysical processes in the subsea sediments. This model is driven by four time series of temperature at the sediment top, TB, which is constructed for the last 400 kyr by using different combinations of the same reconstruction of the past surface air temperature but different sea level reconstructions. At each time instant t and each variable Y, the uncertainty metric is defined as a ratio ▵Y (t) / Ym(t), where ▵Y (t) is spread of the values of Y for different TB time series, and Ym(t) is the mean of Y over different realizations corresponding to different TB. The root-mean-square calculated value of thus defined metric for different time intervals is ≤ 50% for permafrost base depth with the exception of isolated time intervals and / or the deepest part of the shelf. This uncertainty is not symmetric with respect to the sign of the sea level uncertainty. In turn, uncertainty for the hydrate stability zone thickness is small for shallow shelf but becomes pronounced for intermediate and deep shelves. The most uncertainty is due to uncertainty of dates for oceanic regressions and transgressions.
Climate model developed at the A.M. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences (IAP RAS CM) includes modules describing the state of the atmosphere, the ocean, the active land layer, biogeochemical cycles, processes associated with atmospheric electricity and atmospheric chemistry. It belongs to the class of climate models of intermediate complexity (EMICs) and participates in relevant international comparison projects. A specifics of the model is the parameterisation of synoptic variability in the atmosphere and ocean, which allows reducing the computation cost by two orders of magnitude. The model rather realistically reproduces climate change over a period of instrumental measurements and is used to estimate past and future climate changes on a ten-year and longer time scale.
Amplitude-phase characteristics (APCs) of surface air temperature (SAT) annual cycle (SAT) are analyzed. From meteorological observations from the XX century and meteorological reanalyses for its second half it is found that alongside with the well-known negative correlation of SAT AC amplitude Ts,1 with annual mean SAT Ts,m a peculiarity in the North Pacific exists where Ts,1 and Ts,m are positively intercorrelated. In contrast, SAT AC phase characteristics show more regional behavior. In particular southward of the characteristic annual mean position of the snow-ice boundary (SIB) SAT AC is harmonized under climate warming while northward it is deharmonized. In the Far East (southward about 50 degree(s)N) SAT AC shifts as a whole with its extrema occurring earlier with increasing annual mean SAT. From the energy-balance climate considerations these tendencies of change of the SAT AC APCs in the middle and high latitudes are associated to the influence of the albedo-SAT feedback due to the SIB movement and in the Far East - to the interannual cloudiness variability. Tendencies of change for SAT AC related to the SIB movement are simulated reasonably well by the climate model of intermediate complexity in the experiments with greenhouse gases atmospheric loading. In contrast, the tendencies resulting from the cloudiness variability are not reproduced by this model.
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