Timing and lock-in effect of the Laschampgeomagnetic excursion in Chinese Loess

The Laschamp geomagnetic excursion (LGE, at 41 ka) is a critical age control for hemispherical comparison of paleoclimate records from various kinds of geological archives (e.g., ice core, marine, and lake sediments). The timing of the LGE in Chinese Loess, however, remains poorly constrained due to the lack of a reliable chronology and the complex acquisition processes of natural remanent magnetization. Here, we systematically compare the paleomagnetic results of three optically stimulated luminescence dated loess sequences on the Chinese Loess Plateau. Our results indicate that the timing of the LGE in the northwestern Loess Plateau is slightly older than the absolute radiometric age determination and the timing inferred from Greenland ice core (10Be flux) and marine (i.e., relative paleointensity and authogenic 10Be/9Be stack) records, but younger than the counterparts in the central Loess Plateau. We attribute the different timing of the LGE in the three loess sections to a progressive southeastward increase in the lock-in depth caused by the combined effects of postdepositional processes (e.g., surface mixing, chemical weathering, and lock-in delay) on the remanence acquisition process. We conclude that caution is needed to use the LGE in Chinese Loess as a reliable tie-event for highresolution chronological correlation to marine and ice core records, only if the potential lock-in effect can be precisely determined.</p

Iron fertilisation and biogeochemical cycles in the sub-Arctic northwest Pacific during the late Pliocene intensification of northern hemisphere glaciation

Increases in the low-field mass-specific magnetic susceptibility (chi), dropstones and the terrigenous sediment component from Ocean Drilling Program (ODP) Site 882 (similar to 45 degrees N) have been interpreted to indicate a major onset of ice-rafting to the sub-Arctic northwest Pacific Ocean during marine isotope stage (MIS) G6 (from similar to 2.75 Ma). In contrast, studies of the terrigenous content of sediments cored downwind of ODP Site 882 indicate that dust and disseminated volcanic ash deposition in the sub-Arctic Pacific increased markedly during MIS G6. To investigate the relative contribution of dust, volcanic ash and ice rafting to the Pliocene chi increase, we present new high-resolution environmental magnetic and ice-rafted debris records from ODP Sites 882 and 885. Our results demonstrate that the chi increase at both sites across MIS G6 is predominantly controlled by a previously overlooked mixture of aeolian dust and volcanic ash. Our findings call into question the reliability of chi as a proxy for ice-rafting to the North Pacific. They also highlight a previously undocumented link between iron fertilisation and biogeochemical cycling in the North Pacific at a key stage during intensification of late Pliocene northern hemisphere glaciation.</p

Quantifying the dietary potassium requirement of juvenile grass carp (Ctenopharyngodon idellus)

A growth trial lasting for 12 weeks was conducted in a semi flow-through system to determine the dietary potassium requirement of juvenile grass carp (Ctenopharyngodon idellus) with an initial body weight of 4.8 g. Seven isonitrogenous and isoenergetic semi-purified diets were compounded with different dietary potassium levels: 1.50, 2.32, 3.28, 5.30, 7.12, 9.45 and 10.44 g kg(-1) diet. The results showed that specific growth rate and feed efficiency of grass carp were significantly (P 0.05). The Na+-K+ ATPase activity value in the gills varied significantly (P 0.05). Body potassium and moisture contents increased and lipid content decreased with dietary potassium content, while ash content in fish body increased first and then decreased as potassium content increased (P 0.05). The Na+-K+ ATPase activity value in the gills varied significantly (P 0.05). Body potassium and moisture contents increased and lipid content decreased with dietary potassium content, while ash content in fish body increased first and then decreased as potassium content increased (P < 0.05). Body protein in the 10.44 g kg(-1) group was significantly lowered (P < 0.05). However, calcium, magnesium, phosphorus and sodium contents in dry matter were not affected by dietary potassium level. When the potassium content of water was 1.86-3.10 mg L-1, judging from the polynomial regression analysis for the specific growth rate of fish and the Na+-K+ ATPase activity in the gill, and the broken-line analysis for body potassium content, the optimal dietary potassium content for juvenile grass carp was 4.65, 7.27 and 5.98 g kg(-1) diet respectively. (C) 2014 Elsevier B.V. All rights reserved

Dominant 100,000-year precipitation cyclicity in a lateMiocene lake from northeast Tibet

East Asian summer monsoon (EASM) precipitation received by northern China over the past 800 thousand years (ky) is characterized by dominant 100-ky periodicity, mainly attributed to CO2 and Northern Hemisphere insolation-driven ice sheet forcing. We established an EASM record in the Late Miocene from lacustrine sediments in the Qaidam Basin, northern China, which appears to exhibit a dominant 100-ky periodicity similar to the EASM records during the Late Quaternary. Because evidence suggests that partial or ephemeral ice existed in the Northern Hemisphere during the Late Miocene, we attribute the 100-ky cycles to CO2 and Southern Hemisphere insolation-driven Antarctic ice sheet forcing. This indicates a &gt;6-million year earlier onset of the dominant 100-ky Asian monsoon and, likely, glacial and CO2 cycles and may indicate dominant forcing of Northern Hemisphere climate by CO2 and Southern Hemisphere ice sheets in a warm world