4,472 research outputs found
An evaluation of physical and biogeochemical processes regulating perennial suboxic conditions in the water column of the Arabian Sea
Monthly oxygen budgets for the subsurface Arabian Sea (100-1000 m) are constructed on the basis of Modular Ocean Model and recently collected oxygen data. The model results are in agreement with the observed pattern. The model results revealed that Oxygen Minimum Zone (OMZ) in the Arabian Sea is regulated largely by physical processes in association with biogeochemical cycling of oxygen. This results in perennial suboxic conditions in the water column with no significant seasonal variability. Maintenance of OMZ during non-monsoon seasons, when oligotrophic conditions prevail in surface layers, occurs through low supply of oxygen by physical pump aided by continued oxygen consumption in the oxidation of organic matter produced during monsoons. On the other hand, formation of anoxic conditions during monsoons, when higher sinking fluxes of carbon occur, is prevented by higher flux of oxygen by the physical pump. Hence, suboxic conditions in the Arabian Sea are maintained by physical pump with moderation from monsoonal biological pump. The residence time of the Arabian Sea intermediate waters (100-1000 m) was computed to be 6.5 years with rapid replacement during monsoons. The oxygen consumption rates are also high during monsoons compared with non-monsoon seasons. The carbon regeneration rates computed based on the water mass-mixing model, bacterial carbon demand, and electron transport system activity in the subsurface layers are in agreement with oxygen consumption rates estimated based on this model
Searching for a Supersolid in Cold Atom Optical Lattices
We suggest a technique for the observation of a predicted supersolid phase in
extended Bose-Hubbard models which are potentially realizable in cold atom
optical lattice systems. In particular, we discuss important subtleties arising
from the existence of the trapping potential which leads to an externally
imposed (as opposed to spontaneous) breaking of translational invariance. We
show, by carefully including the trapping potential in our theoretical
formalism, that noise correlations could prove instrumental in identifying the
supersolid and density wave phases. We also find that the noise correlation
peak width scales inversely with the relative size of trapped Mott domains.Comment: 5 pages, 4 figure
Spin Polarization Dependence of Carrier Effective Mass in Semiconductor Structures: Spintronic Effective Mass
We introduce the concept of a spintronic effective mass for spin-polarized
carriers in semiconductor structures, which arises from the strong
spin-polarization dependence of the renormalized effective mass in an
interacting spin-polarized electron system. The majority-spin many-body
effective mass renormalization differs by more than a factor of 2 at rs=5
between the unpolarized and the fully polarized two-dimensional system, whereas
the polarization dependence (~15%) is more modest in three dimensions around
metallic densities (rs~5). The spin-polarization dependence of the carrier
effective mass is of significance in various spintronic applications.Comment: Final versio
Ground-state of graphene in the presence of random charged impurities
We calculate the carrier density dependent ground state properties of
graphene in the presence of random charged impurities in the substrate taking
into account disorder and interaction effects non-perturbatively on an equal
footing in a self-consistent theoretical formalism. We provide detailed
quantitative results on the dependence of the disorder-induced spatially
inhomogeneous two-dimensional carrier density distribution on the external gate
bias, the impurity density, and the impurity location. We find that the
interplay between disorder and interaction is strong, particularly at lower
impurity densities. We show that for the currently available typical graphene
samples, inhomogeneity dominates graphene physics at low (
cm) carrier density with the density fluctuations becoming larger than
the average density.Comment: Final version, accepted for publication in Phys. Rev. Let
Condensates induced by interband coupling in a double-well lattice
We predict novel inter-band physics for bosons in a double-well lattice. An
intrinsic coupling between the s and px band due to interaction gives rise to
larger Mott regions on the phase diagram at even fillings than the ones at odd
fillings. On the other hand, the ground state can form various types of
condensates, including a mixture of single-particle condensates of both bands,
a mixture of a single-particle condensate of one band and a pair-condensate of
the other band, and a pair-condensate composed of one particle from one band
and one hole from the other band. The predicted phenomena should be observable
in current experiments on double-well optical lattices.Comment: Published versio
Increase of total alkalinity due to shoaling of aragonite saturation horizon in the Pacific and Indian Oceans: influence of anthropogenic carbon inputs
Aragonite Saturation Horizon (ASH) shallowed significantly by 25 to 155 m and 16 to 124 m in the Pacific and Indian Ocean respectively in two decades. Apparent Oxygen Utilization (AOU) increased by 3 to 34 and 0.5 to 31.5 μmol kg−1 in the Pacific and Indian Ocean respectively at the depth of ASH during this period. DIC increased by 12.5 to 36.8 and 5.5 to 32 μmol kg−1 in the vicinity of ASH in the Pacific and Indian Ocean respectively due to combined effect of increased anthropogenic CO2 and change in AOU. TA increased significantly by 5 to 10 and 4 to 9.2 μmol kg−1 in the Pacific and Indian Oceans respectively at the ASH most likely as a result of aragonite dissolution. The upward migration of ASH solely due to anthropogenic CO2 amounted to 6 to 58 m in the Pacific and 4 to 44 m in the Indian Ocean
Observed changes in ocean acidity and carbon dioxide exchange in the coastal Bay of Bengal – a link to air pollution
Variations in surface water hydrographic properties and Dissolved Inorganic Carbon (DIC) were evaluated in the coastal Bay of Bengal using observations carried out during March–April 1991 and 2011, including 8 yr monthly time-series observations during 2005 and 2013. The coastal Bay of Bengal is characterised by relatively fresher, more basic and lower pCO2 in 1991 compared to 2011. The rates of decrease in pH, increase in DIC and pCO2 per decade were consistent with global trends in the Southwestern (SW) coastal Bay of Bengal, whereas rates in the Northwestern (NW) coastal Bay of Bengal were observed to be 3–5 times higher. The associated recent increase in sulphate and nitrogen aerosol loadings over NW Bay of Bengal from the Indo-Gangetic Plain and Southeast Asia during winter and spring may be mainly responsible for the increased acidity in recent years. Thus, this region, which was previously considered to be a significant sink for atmospheric CO2, now seems to have become a source of CO2 to the atmosphere
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