144 research outputs found
The importance of northern peatlands in global carbon systems during the Holocene
We applied an inverse model to simulate global carbon (C) cycle dynamics during the Holocene period using atmospheric carbon dioxide (CO2) concentrations reconstructed from Antarctic ice cores and prescribed C accumulation rates of Northern Peatlands (NP) as inputs. Previous studies indicated that different sources could contribute to the 20 parts per million by volume (ppmv) atmospheric CO2 increase over the past 8000 years. These sources of C include terrestrial release of 40–200 petagram C (PgC, 1 petagram=1015 gram), deep oceanic adjustment to a 500 PgC terrestrial biomass buildup early in this interglacial period, and anthropogenic land-use and land-cover changes of unknown magnitudes. Our study shows that the prescribed peatland C accumulation significantly modifies our previous understanding of Holocene C cycle dynamics. If the buildup of the NP is considered, the terrestrial pool becomes the C sink of about 160–280 PgC over the past 8000 years, and the only C source for the terrestrial and atmospheric C increases is presumably from the deep ocean due to calcium carbonate compensation. Future studies need to be conducted to constrain the basal times and growth rates of the NP C accumulation in the Holocene. These research endeavors are challenging because they need a dynamically-coupled peatland simulator to be constrained with the initiation time and reconstructed C reservoir of the NP. Our results also suggest that the huge reservoir of deep ocean C explains the major variability of the glacial-interglacial C cycle dynamics without considering the anthropogenic C perturbation
Interior of Distorted Black Holes
We study the interior of distorted static axisymmetric black holes. We obtain
a general interior solution and study its asymptotics both near the horizon and
singularity. As a special example, we apply the obtained results to the case of
the so-called `caged' black holes.Comment: 12 pages, 16 figure
Distorted charged dilaton black holes
We construct exact static, axisymmetric solutions of Einstein-Maxwell-dilaton
gravity presenting distorted charged dilaton black holes. The thermodynamics of
such distorted black holes is also discussed.Comment: 14 pages, latex; v2 typos corrected, references adde
Distorted 5-dimensional vacuum black hole
In this paper we study how the distortion generated by a static and neutral
distribution of external matter affects a 5-dimensional
Schwarzschild-Tangherlini black hole. A solution representing a particular
class of such distorted black holes admits an RxU(1)xU(1) isometry group. We
show that there exists a certain duality transformation between the black hole
horizon and a stretched singularity surfaces. The space-time near the distorted
black hole singularity has the same topology and Kasner exponents as those of a
5-dimensional Schwarzschild-Tangherlini black hole. We calculate the maximal
proper time of free fall of a test particle from the distorted black hole
horizon to its singularity and find that, depending on the distortion, it can
be less, equal to, or greater than that of a Schwarzschild-Tangherlini black
hole of the same horizon area. This implies that due to the distortion, the
singularity of a Schwarzschild-Tangherlini black hole can come close to its
horizon. A relation between the Kretschmann scalar calculated on the horizon of
a 5-dimensional static, asymmetric, distorted black hole and the trace of the
square of the Ricci tensor of the horizon surface is derived.Comment: 20 pages, 9 figure
Dynamical Horizons and their Properties
A detailed description of how black holes grow in full, non-linear general
relativity is presented. The starting point is the notion of dynamical
horizons. Expressions of fluxes of energy and angular momentum carried by
gravitational waves across these horizons are obtained. Fluxes are local and
the energy flux is positive. Change in the horizon area is related to these
fluxes. A notion of angular momentum and energy is associated with
cross-sections of the horizon and balance equations, analogous to those
obtained by Bondi and Sachs at null infinity, are derived. These in turn lead
to generalizations of the first and second laws of black hole mechanics. The
relation between dynamical horizons and their asymptotic states --the isolated
horizons-- is discussed briefly. The framework has potential applications to
numerical, mathematical, astrophysical and quantum general relativity.Comment: 44 pages, 2 figures, RevTeX4. Minor typos corrected. Final PRD
versio
Sea-ice production over the Laptev Sea shelf inferred from historical summer-to-winter hydrographic observations of 1960s-1990s
The winter net sea-ice production (NSIP) over the Laptev Sea shelf is inferred from continuous summer-to-winter historical salinity records of 1960s–1990s. While the NSIP strongly depends on the assumed salinity of newly formed ice, the NSIP quasi-decadal variability can be linked to the wind-driven circulation anomalies in the Laptev Sea region. The increased wind-driven advection of ice away from the Laptev Sea coast when the Arctic Oscillation (AO) is positive implies enhanced coastal polynya sea-ice production and brine release in the shelf water. When the AO is negative, the NSIP and seasonal salinity amplitude tends to weaken. These results are in reasonable agreement with sea-ice observations and modeling
Isolated Horizons: Hamiltonian Evolution and the First Law
A framework was recently introduced to generalize black hole mechanics by
replacing stationary event horizons with isolated horizons. That framework is
significantly extended. The extension is non-trivial in that not only do the
boundary conditions now allow the horizon to be distorted and rotating, but
also the subsequent analysis is based on several new ingredients. Specifically,
although the overall strategy is closely related to that in the previous work,
the dynamical variables, the action principle and the Hamiltonian framework are
all quite different. More importantly, in the non-rotating case, the first law
is shown to arise as a necessary and sufficient condition for the existence of
a consistent Hamiltonian evolution. Somewhat surprisingly, this consistency
condition in turn leads to new predictions even for static black holes. To
complement the previous work, the entire discussion is presented in terms of
tetrads and associated (real) Lorentz connections.Comment: 56 pages, 1 figure, Revtex; Final Version, to appear in PR
Stationary Black Holes as Holographs
Smooth spacetimes possessing a (global) one-parameter group of isometries and
an associated Killing horizon in Einstein's theory of gravity are investigated.
No assumption concerning the asymptotic structure is made, thereby, the
selected spacetimes may be considered as generic distorted stationary black
holes. First, spacetimes of arbitrary dimension, , with matter
satisfying the dominant energy condition and allowing non-zero cosmological
constant are investigated. In this part complete characterisation of the
topology of the event horizon of ``distorted'' black holes is given. It is
shown that the topology of the event horizon of ``distorted'' black holes is
allowed to possess a much larger variety than that of the isolated black hole
configurations. In the second part, 4-dimensional (non-degenerate) electrovac
distorted black hole spacetimes are considered. It is shown that the spacetime
geometry and the electromagnetic field are uniquely determined in the black
hole region once the geometry of the bifurcation surface and one of the
electromagnetic potentials are specified there. Conditions guaranteeing the
same type of determinacy, in a neighbourhood of the event horizon, on the {\it
domain of outer communication} side are also investigated. In particular, they
are shown to be satisfied in the analytic case.Comment: 31 pages, LaTeX; typos corrected, new references added, to appear in
CQ
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