Description: The Late Quaternary variability of the South Asian (or Indian) monsoon has been linked with glacial-interglacial and millennial scale climatic changes but past rainfall intensity in the river catchments draining into the Andaman Sea remains poorly constrained. Here we use radiogenic Sr, Nd, and Pb isotope compositions of the detrital clay-size fraction and clay mineral assemblages obtained from sediment core NGHP Site 17 in the Andaman Sea to reconstruct the variability of the South Asian monsoon during the past 60 kyr. Over this time interval eNd values changed little, generally oscillating between 27.3 and 25.3 and the Pb isotope signatures are essentially invariable, which is in contrast to a record located further northeast in the Andaman Sea. This indicates that the source of the detrital clays did not change significantly during the last glacial and deglaciation suggesting the monsoon was spatially stable. The most likely source region is the Irrawaddy river catchment including the Indo-Burman Ranges with a possible minor contribution from the Andaman Islands. High smectite/(illite1chlorite) ratios (up to 14), as well as low 87Sr/86Sr ratios (0.711) for the Holocene period indicate enhanced chemical weathering and a stronger South Asian monsoon compared to marine oxygen isotope stages 2 and 3. Short, smectite-poor intervals exhibit markedly radiogenic Sr isotope compositions and document weakening of the South Asian monsoon, which may have been linked to short-term northern Atlantic climate variability on millennial time scales.

Description: We interpret the sedimentologic evolution of a deep-water channel-levee deposit in Green Canyon Block 955 (deep-water Gulf of Mexico) by analyzing hydrate-bearing pressure cores and nonpressure cores collected during The University of Texas-Gulf of Mexico 2-1 (UT-GOM2-1) Hydrate Pressure Coring Expedition that preserve remarkable sedimentary structures. The levee is composed of alternating beds of sandy silt and clayey silt that range from millimeters to meters in thickness. We interpret that each couplet of sandy silt and clayey silt records a single turbidity current flow in which the upper part of the flow overtops the levee and is deposited along its flank. The sandy silt is coarser, its beds are thicker, and the fraction of sandy silt to clayey silt (net-to-gross) is greater near the base of the levee. We interpret that as the levee grew, the channel depth increased and a smaller fraction of the flow overtopped the levee. An increase in net-to-gross, both at the base and near the top of the cored section, may record an increase in the size of turbidity current flows or a decrease in the relative height of the levee. Based on the limited core recovery, we infer that the lithology of the bounding unit immediately above the hydrate-bearing unit is thinner bedded and has lower net-to-gross than the hydrate reservoir. The bounding unit below the hydrate-bearing interval is similarly thinner bedded, yet contains high saturations of hydrate. This study illuminates the lithologic architecture of leveed-channel turbidite reservoirs at core scale and provides insight into how lithology controls hydrate distribution and concentration.

Description: Background: A composite biological structure, such as an insect head or abdomen, contains many internal structures with distinct functions. Composite structures are often used in RNA-seq studies, though it is unclear how expression of the same gene in different tissues and structures within the same structure affects the measurement (or even utility) of the resulting patterns of gene expression. Here we determine how complex composite tissue structure affects measures of gene expression using RNA-seq. Results: We focus on two structures in the honey bee (the sting gland and digestive tract) both contained within one larger structure, the whole abdomen. For each of the three structures, we used RNA-seq to identify differentially expressed genes between two developmental stages, nurse bees and foragers. Based on RNA-seq for each structure-specific extraction, we found that RNA-seq with composite structures leads to many false negatives (genes strongly differentially expressed in particular structures which are not found to be differentially expressed within the composite structure). We also found a significant number of genes with one pattern of differential expression in the tissue-specific extraction, and the opposite in the composite extraction, suggesting multiple signals from such genes within the composite structure. We found these patterns for different classes of genes including transcription factors. Conclusions: Many RNA-seq studies currently use composite extractions, and even whole insect extractions, when tissue and structure specific extractions are possible. This is due to the logistical difficultly of micro-dissection and unawareness of the potential errors associated with composite extractions. The present study suggests that RNA-seq studies of composite structures are prone to false negatives and difficult to interpret positive signals for genes with variable patterns of local expression. In general, our results suggest that RNA-seq on large composite structures should be avoided unless it is possible to demonstrate that the effects shown here do not exist for the genes of interest.