The Middle to Late Miocene “Carbonate Crash” in the Equatorial Indian Ocean

We integrate benthic foraminiferal stable isotopes, X‐ray fluorescence elemental ratios, and carbonate accumulation estimates in a continuous sedimentary archive recovered at International Ocean Discovery Program Site U1443 (Ninetyeast Ridge, Indian Ocean) to reconstruct changes in carbonate deposition and climate evolution over the interval 13.5 to 8.2 million years ago. Declining carbonate percentages together with a marked decrease in carbonate accumulation rates after ~13.2 Ma signal the onset of a prolonged episode of reduced carbonate deposition. This extended phase, which lasted until ~8.7 Ma, coincides with the middle to late Miocene carbonate crash, originally identified in the eastern equatorial Pacific Ocean and the Caribbean Sea. Interocean comparison reveals that intense carbonate impoverishment at Site U1443 (~11.5 to ~10 Ma) coincides with prolonged episodes of reduced carbonate deposition in all major tropical ocean basins. This implies that global changes in the intensity of chemical weathering and riverine input of calcium and carbonate ions into the ocean reservoir were instrumental in driving the carbonate crash. An increase in U1443 Log (Ba/Ti) together with a change in sediment color from red to green indicate a rise in organic export flux to the sea floor after ~11.2 Ma, which predates the global onset of the biogenic bloom. This early rise in export flux from biological production may have been linked to increased advection of nutrients and intensification of upper ocean mixing, associated with changes in the seasonality and intensity of the Indian Monsoon

Asian monsoon modulation of nonsteady state diagenesis in hemipelagic marine sediments offshore of Japan

We have identified millennial-scale variations in magnetic mineral diagenesis from Pacific Ocean sediments offshore of Japan that we correlate with changes in organic carbon burial that were likely driven by Asian monsoon fluctuations. The correlation was determined by identifying offsets between the positions of fossil diagenetic fronts and climatically induced variations in organic carbon burial inferred from magnetic and geochemical analyses. Episodes of intense monsoon activity and attendant sediment magnetic mineral diagenesis also appear to correlate with Heinrich events, which supports the existence of climatic telecommunications between Asia and the North Atlantic region. Several lines of evidence support our conclusions: (1) fluctuations in down-core magnetic properties and diagenetic pyrite precipitation are approximately coeval; (2) localized stratigraphic intervals with relatively stronger magnetic mineral dissolution are linked to enhanced sedimentary organic carbon contents that gave rise to nonsteady state diagenesis; (3) down-core variations in elemental S content provide a proxy for nonsteady state diagenesis that correlate with key records of Asian monsoon variations; and (4) relict titanomagnetite that is preserved as inclusions within silicate particles, rather than secondary authigenic phases (e.g., greigite), dominates the strongly diagenetically altered sediment intervals and are protected against sulfidic dissolution. We suggest that such millennial-scale environmental modulation of nonsteady state diagenesis (that creates a temporal diagenetic filter and relict magnetic mineral signatures) is likely to be common in organic-rich hemipelagic sedimentary settings with rapidly varying depositional conditions. Our work also demonstrates the usefulness of magnetic mineral inclusions for recording important environmental magnetic signal

North Atlantic Midlatitude Surface-Circulation Changes Through the Plio-Pleistocene Intensification of Northern Hemisphere Glaciation

The North Atlantic Current (NAC) transports warm salty water to high northern latitudes, with important repercussions for ocean circulation and global climate. A southward displacement of the NAC and Subarctic Front, which separate subpolar and subtropical water masses, is widely suggested for the Last Glacial Maximum (LGM) and may have acted as a positive feedback in glacial expansion at this time. However, the role of the NAC during the intensification of Northern Hemisphere glaciation (iNHG) at ~3.5 to 2.5 Ma is less clear. Here we present new records from Integrated Ocean Drilling Program Site U1313 (41°N) spanning ~2.8–2.4 Ma to trace the influence of Subarctic Front waters above this mid‐latitude site. We reconstruct surface and permanent pycnocline temperatures and seawater δ18O using paired Mg/Ca‐δ18O measurements on the planktic foraminifers Globigerinoides ruber and Globorotalia crassaformis and determine abundances of the subpolar foraminifer Neogloboquadrina atlantica. We find that the first significant glacial incursions of Subarctic Front surface waters above Site U1313 did not occur until ~2.6 Ma. At no time during our study interval was (sub)surface reorganization in the midlatitude North Atlantic analogous to the LGM. Our findings suggest that LGM‐like processes sensu stricto cannot be invoked to explain interglacial‐glacial cycle amplification during iNHG. They also imply that increased glacial productivity at Site U1313 during iNHG was not only driven by southward deflections of the Subarctic Front. We suggest that nutrient injection from cold‐core eddies and enhanced glacial dust delivery may have played additional roles in increasing export productivity in the midlatitude North Atlantic from 2.7 Ma.t. Funding for this research was provided by IODP France (C. T. B.) and the German Research Foundation (DFG) (grant OF 2544/2 to O. F.). I. B. is grateful to the UK IODP for financial support for shipboard and post-cruise participation in IODP Exp. 306. C. T. B., K. T., T. D. G., L. V., C. S., and M. E. acknowledge OSU Pythéas. M. M. R. acknowledges support by the USGS Land Change Science Program

Enhanced Late Miocene Chemical Weathering and Altered Precipitation Patterns in the Watersheds of the Bay of Bengal Recorded by Detrital Clay Radiogenic Isotopes

The late Miocene was a period of declining CO2 levels and extensive environmental changes, which likely had a large impact on monsoon strength as well as on the weathering and erosion intensity in the South Asian Monsoon domain. To improve our understanding of these feedback systems, detrital clays from the southern Bay of Bengal (International Ocean Discovery Program Site U1443) were analyzed for the radiogenic isotope compositions of Sr, Nd, and Pb to reconstruct changes in sediment provenance and weathering regime related to South Asian Monsoon rainfall from 9 to 5 Ma. The 100 kyr resolution late Miocene to earliest Pliocene record suggests overall low variability in the provenance of clays deposited on the Ninetyeast Ridge. However, at 7.3 Ma, Nd and Pb isotope compositions indicate a switch to an increased relative contribution from the Irrawaddy River (by ∼10%). This shift occurred during the global benthic δ13C decline, and we suggest that global cooling and increasing aridity resulted in an eastward shift of precipitation patterns leading to a more focused erosion of the Indo‐Burman Ranges. Sr isotope compositions were decoupled from Nd and Pb isotope signatures and became more radiogenic between 6 and 5 Ma. Grassland expansion generating thick, easily weatherable soils may have led to an environment supporting intense chemical weathering, which is likely responsible for the elevated detrital clay 87Sr/86Sr ratios during this time. This change in Sr isotope signatures may also have contributed to the late Miocene increase of the global seawater Sr isotope composition

The Middle to Late Miocene “Carbonate Crash” in the Equatorial Indian Ocean

金沢大学理工研究域地球社会基盤学系We integrate benthic foraminiferal stable isotopes, X-ray fluorescence elemental ratios, and carbonate accumulation estimates in a continuous sedimentary archive recovered at International Ocean Discovery Program Site U1443 (Ninetyeast Ridge, Indian Ocean) to reconstruct changes in carbonate deposition and climate evolution over the interval 13.5 to 8.2 million years ago. Declining carbonate percentages together with a marked decrease in carbonate accumulation rates after ~13.2 Ma signal the onset of a prolonged episode of reduced carbonate deposition. This extended phase, which lasted until ~8.7 Ma, coincides with the middle to late Miocene carbonate crash, originally identified in the eastern equatorial Pacific Ocean and the Caribbean Sea. Interocean comparison reveals that intense carbonate impoverishment at Site U1443 (~11.5 to ~10 Ma) coincides with prolonged episodes of reduced carbonate deposition in all major tropical ocean basins. This implies that global changes in the intensity of chemical weathering and riverine input of calcium and carbonate ions into the ocean reservoir were instrumental in driving the carbonate crash. An increase in U1443 Log (Ba/Ti) together with a change in sediment color from red to green indicate a rise in organic export flux to the sea floor after ~11.2 Ma, which predates the global onset of the biogenic bloom. This early rise in export flux from biological production may have been linked to increased advection of nutrients and intensification of upper ocean mixing, associated with changes in the seasonality and intensity of the Indian Monsoon. ©2019. American Geophysical Union. All Rights Reserved.Embargo Period 6 month

Secular and orbital-scale variability of equatorial Indian Ocean summer monsoon winds during the late Miocene

In the modern northern Indian Ocean, biological productivity is intimately linked to near-surface oceanographic dynamics forced by the South Asian, or Indian, monsoon. In the late Pleistocene, this strong seasonal signal is transferred to the sedimentary record in the form of strong variance in the precession band (19–23 kyr), because precession dominates low-latitude insolation variations and drives seasonal contrast in oceanographic conditions. In addition, internal climate system feedbacks (e.g. ice-sheet albedo, carbon cycle, topography) play a key role in monsoon variability. Little is known about orbital-scale monsoon variability in the pre-Pleistocene, when atmospheric CO2 levels and global temperatures were higher. In addition, many questions remain open regarding the timing of the initiation and intensification of the South Asian monsoon during the Miocene, an interval of significant global climate change that culminated in bipolar glaciation. Here, we present new high-resolution (<1 kyr) records of export productivity and sediment accumulation from International Ocean Discovery Program Site U1443 in the southernmost part of the Bay of Bengal spanning the late Miocene (9 to 5 million years ago). Underpinned by a new orbitally tuned benthic isotope stratigraphy, we use X-ray fluorescence-derived biogenic barium variations to discern productivity trends and rhythms. Results show strong eccentricity-modulated precession-band productivity variations throughout the late Miocene, interpreted to reflect insolation forcing of summer monsoon wind strength in the equatorial Indian Ocean. On long timescales, our data support the interpretation that South Asian monsoon winds were already established by 9 Ma in the equatorial sector of the Indian Ocean, with no apparent intensification over the latest Miocene

Individual common variants exert weak effects on the risk for autism spectrum disorders.

While it is apparent that rare variation can play an important role in the genetic architecture of autism spectrum disorders (ASDs), the contribution of common variation to the risk of developing ASD is less clear. To produce a more comprehensive picture, we report Stage 2 of the Autism Genome Project genome-wide association study, adding 1301 ASD families and bringing the total to 2705 families analysed (Stages 1 and 2). In addition to evaluating the association of individual single nucleotide polymorphisms (SNPs), we also sought evidence that common variants, en masse, might affect the risk. Despite genotyping over a million SNPs covering the genome, no single SNP shows significant association with ASD or selected phenotypes at a genome-wide level. The SNP that achieves the smallest P-value from secondary analyses is rs1718101. It falls in CNTNAP2, a gene previously implicated in susceptibility for ASD. This SNP also shows modest association with age of word/phrase acquisition in ASD subjects, of interest because features of language development are also associated with other variation in CNTNAP2. In contrast, allele scores derived from the transmission of common alleles to Stage 1 cases significantly predict case status in the independent Stage 2 sample. Despite being significant, the variance explained by these allele scores was small (Vm&lt; 1%). Based on results from individual SNPs and their en masse effect on risk, as inferred from the allele score results, it is reasonable to conclude that common variants affect the risk for ASD but their individual effects are modest

Genome-Wide Analyses of Exonic Copy Number Variants in a Family-Based Study Point to Novel Autism Susceptibility Genes

The genetics underlying the autism spectrum disorders (ASDs) is complex and remains poorly understood. Previous work has demonstrated an important role for structural variation in a subset of cases, but has lacked the resolution necessary to move beyond detection of large regions of potential interest to identification of individual genes. To pinpoint genes likely to contribute to ASD etiology, we performed high density genotyping in 912 multiplex families from the Autism Genetics Resource Exchange (AGRE) collection and contrasted results to those obtained for 1,488 healthy controls. Through prioritization of exonic deletions (eDels), exonic duplications (eDups), and whole gene duplication events (gDups), we identified more than 150 loci harboring rare variants in multiple unrelated probands, but no controls. Importantly, 27 of these were confirmed on examination of an independent replication cohort comprised of 859 cases and an additional 1,051 controls. Rare variants at known loci, including exonic deletions at NRXN1 and whole gene duplications encompassing UBE3A and several other genes in the 15q11–q13 region, were observed in the course of these analyses. Strong support was likewise observed for previously unreported genes such as BZRAP1, an adaptor molecule known to regulate synaptic transmission, with eDels or eDups observed in twelve unrelated cases but no controls (p = 2.3×10−5). Less is known about MDGA2, likewise observed to be case-specific (p = 1.3×10−4). But, it is notable that the encoded protein shows an unexpectedly high similarity to Contactin 4 (BLAST E-value = 3×10−39), which has also been linked to disease. That hundreds of distinct rare variants were each seen only once further highlights complexity in the ASDs and points to the continued need for larger cohorts