1,447 research outputs found
Calcium isotopic composition of high-latitude proxy carrier Neogloboquadrina pachyderma (sin.)
The accurate reconstruction of sea surface temperature (SST) history in climate-sensitive regions (e.g. tropical and polar oceans) became a challenging task in palaeoceanographic research. Biogenic shell carbonate SST proxies successfully developed for tropical regions often fail in cool water environments. Their major regional shortcomings and the cryptic diversity now found within the major high latitude proxy carrier Neogloboquadrina pachyderma (sin.) highlight an urgent need to explore complementary SST proxies for these cool-water regions. Here we incorporate the genetic component into a calibration study of a new SST proxy for the high latitudes. We found that the calcium isotopic composition (δ44/40Ca) of calcite from genotyped net catches and core-top samples of the planktonic foraminifera Neogloboquadrina pachyderma (sin.) is related to temperature and unaffected by genetic variations. The temperature sensitivity has been found to be 0.17 (±0.02)‰ per 1°C, highlighting its potential for downcore applications in open marine cool-water environments. Our results further indicate that in extreme polar environments, below a critical threshold temperature of 2.0 (±0.5)°C associated with salinities below 33.0 (±0.5)‰, a prominent shift in biomineralization affects the δ44/40Ca of genotyped and core-top N. pachyderma (sin.), becoming insensitive to temperature. These findings highlight the need of more systematic calibration studies on single planktonic foraminiferal species in order to unravel species-specific factors influencing the temperature sensitivity of Ca isotope fractionation and to validate the proxies' applicability
Out With the Old, In With the New: Are Western Commodity Producers Ready for Buyouts?
Agricultural and Food Policy,
Field Dependent Phase Diagram of the Quantum Spin Chain (CH3)2NH2CuCl3
Although (CH3)2NH2CuCl3 (MCCL) was first examined in the 1930's [1], there
are open questions regarding the magnetic dimensionality and nature of the
magnetic properties. MCCL is proposed to be a S=1/2 alternating ferromagnetic
antiferromagnetic spin chain alternating along the crystalline a-axis [2,3].
Proposed ferromagnetic (JFM =1.3 meV) and antiferromagnetic (JAFM =1.1 meV)
exchange constants make this system particularly interesting for experimental
study. Because JFM and JAFM are nearly identical, the system should show
competing behavior between S=1/2 (AFM) and S=1(FM) effects. We report low
temperature magnetic field dependent susceptibility, chi(H), and specific heat,
Cp, of MCCL. These provide an initial magnetic-field versus temperature phase
diagram. A zero-field phase transition consistent with long range magnetic
order is observed at T=0.9 K. The transition temperature can be reduced via
application of a magnetic field. We also present comparisons to a FM/AFM dimer
model that accounts for chi(T,H=0) and Cp(H,T).Comment: 2 pages, 1 figure included in text. Submitted to proceedings of 24th
International Conference on Low Temperature Physics, August 200
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