Barium isotopes reveal role of ocean circulation on barium cycling in the Atlantic

We diagnose the relative influences of local-scale biogeochemical cycling and regional-scale ocean circulation on Atlantic barium cycling by analysing four new depth profiles of dissolved Ba concentrations and isotope compositions from the South and tropical North Atlantic. These new profiles exhibit systematic vertical, zonal and meridional variations that reflect the influence of both local-scale barite cycling and large-scale ocean circulation. Epipelagic decoupling of dissolved Ba and Si reported previously in the tropics is also found to be associated with significant Ba isotope heterogeneity. As such, we contend that this decoupling originates from the depth segregation of opal and barite formation but is exacerbated by weak vertical mixing. Zonal influence from isotopically-‘heavy’ water masses in the western North Atlantic evidence the advective inflow of Ba-depleted Upper Labrador Sea Water, which is not seen in the eastern basin or the South Atlantic. Meridional variations in Atlantic Ba isotope systematics below 2000 m appear entirely controlled by conservative mixing. Using an inverse isotopic mixing model, we calculate the Ba isotope composition of the Ba-poor northern end-member as +0.45 ‰ and the Ba-rich southern end-member +0.26 ‰, relative to NIST SRM 3104a. The near-conservative behaviour of Ba below 2000 m indicates that Ba isotopes can serve as an independent tracer of the provenance of northern- versus southern-sourced water masses in the deep Atlantic Ocean. This finding may prove useful in palaeoceanographic studies, should appropriate sedimentary archives be identified, and offers new insights into the processes that cycle Ba in seawater

Teasing Apart Impacts of Human Activity and Regional Drought on Madagascar's Large Vertebrate Fauna: Insights From New Excavations at Tsimanampesotse and Antsirafaly

Madagascar experienced a major faunal turnover near the end of the first millenium CE that particularly affected terrestrial, large-bodied vertebrate species. Teasing apart the relative impacts of people and climate on this event requires a focus on regional records with good chronological control. These records may document coeval changes in rainfall, faunal composition, and human activities. Here we present new paleontological and paleoclimatological data from southwestern Madagascar, the driest part of the island today. We collected over 1500 subfossil bones from deposits at a coastal site called Antsirafaly and from both flooded and dry cave deposits at Tsimanampesotse National Park. We built a chronology of Late Holocene changes in faunal assemblages based on 65 radiocarbon-dated specimens and subfossil associations. We collected stalagmites primarily within Tsimanampesotse but also at two additional locations in southern Madagascar. These provided information regarding hydroclimate variability over the past 120,000 years. Prior research has supported a primary role for drought (rather than humans) in triggering faunal turnover at Tsimanampesotse. This is based on evidence of: (1) a large freshwater ecosystem west of what is now the hypersaline Lake Tsimanampesotse, which supported freshwater mollusks and waterfowl (including animals that could not survive on resources offered by the hypersaline lake today); (2) abundant now-extinct terrestrial vertebrates; (3) regional decline or disappearance of certain tree species; and (4) scant local human presence. Our new data allow us to document the hydroclimate of the subarid southwest during the Holocene, as well as shifts in faunal composition (including local extirpations, large-vertebrate population collapse, and the appearance of introduced species). These records affirm that climate alone cannot have produced the observed vertebrate turnover in the southwest. Human activity, including the introduction of cattle, as well as associated changes in habitat exploitation, also played an important role

Insights Into Changing Interglacial Conditions in Subarctic Canada From MIS 11 Through MIS 5e From Seasonally Resolved Speleothem Records

Abstract High‐resolution records from past interglacial climates help constrain future responses to global warming, yet are rare. Here, we produce seasonally resolved climate records from subarctic‐Canada using micron‐scale measurements of oxygen isotopes (δ18O) in speleothems with apparent annual growth bands from three interglacial periods—Marine Isotope Stages (MIS) 11, 9, and 5e. We find 3‰ lower δ18O values during MIS 11 than MIS 5e, despite MIS 11 likely being warmer. We explore controls on high‐latitude speleothem δ18O and suggest low MIS 11 δ18O values reflect greater contribution of cold‐season precipitation to dripwater from longer annual ground thaw durations. Other potential influences include changes in precipitation source and/or increased fraction of cold‐season precipitation from diminished sea ice in MIS 11. Our study highlights the potential for high‐latitude speleothems to yield detailed isotopic records of Northern Hemisphere interglacial climates beyond the reach of Greenland ice cores and offers a framework for interpreting them

Evaluating the Drivers of Quaternary Dust Fluxes to the Western North Pacific: East Asian Dustiness and Northern Hemisphere Gustiness

Quantifying variability in, and identifying the mechanisms behind, East Asian dust production and transport across the last several million years is essential for constraining future dust emissions and deposition. Our current understanding of East Asian dust dynamics through the Quaternary is primarily limited to low-resolution records from the North Pacific Ocean, those from the Chinese Loess Plateau (CLP), and paleoenvironmental reconstructions from arid basins. All are susceptible to sediment winnowing and focusing as well as input of poorly constrained or unidentified non-dust detrital material. To avoid these limitations, we examine high-resolution, constant flux proxy-derived dust fluxes from the North Pacific and find evidence for higher glacial dust fluxes in the late Pliocene-early Pleistocene compared to the late Pleistocene-Holocene. Our results suggest decreasing dust transported to the mid-latitude North Pacific Ocean from eastern Asia across the Quaternary. This observation is ostensibly at odds with previous dust records from marine sediments and the CLP, and with the perception of higher East Asian dust production and transport during the late Pleistocene associated with the amplification of glaciations. We provide three possible scenarios to describe the ∼2,700-ky evolution of eastern Asia glacial dust dynamics, and discuss them in the context of sediment production, availability, and atmospheric circulation. Our data and proposed driving mechanisms not only raise questions about the framework typically used to interpret dust archives from East Asia and the North Pacific Ocean, but also provide a roadmap for hypothesis testing and future work necessary to produce better-constrained records of paleo-dust fluxes

Monsoon-driven Saharan dust variability over the past 240,000 years.

Reconstructions of past Saharan dust deposition in marine sediments provide foundational records of North African climate over time scales of 103 to 106 years. Previous dust records show primarily glacial-interglacial variability in the Pleistocene, in contrast to other monsoon records showing strong precessional variability. Here, we present the first Saharan dust record spanning multiple glacial cycles obtained using 230Th normalization, an improved method of calculating fluxes. Contrary to previous data, our record from the West African margin demonstrates high correlation with summer insolation and limited glacial-interglacial changes, indicating coherent variability in the African monsoon belt throughout the late Pleistocene. Our results demonstrate that low-latitude Saharan dust emissions do not vary synchronously with high- and mid-latitude dust emissions, and they call into question the use of existing Plio-Pleistocene dust records to investigate links between climate and hominid evolution

Identification of homozygous WFS1 mutations (p.Asp211Asn, p.Gln486*) causing severe Wolfram syndrome and first report of male fertility

Wolfram syndrome (WFS) is a neurodegenerative genetic condition characterized by juvenile-onset of diabetes mellitus and optic atrophy. We studied clinical features and the molecular basis of severe WFS (neurodegenerative complications) in two consanguineous families from Iran. A clinical and molecular genetic investigation was performed in the affected and healthy members of two families. The clinical diagnosis of WFS was confirmed by the existence of diabetes mellitus and optic atrophy in the affected patients, who in addition had severe neurodegenerative complications. Sequencing of WFS1 was undertaken in one affected member from each family. Targeted mutations were tested in all members of relevant families. Patients had most of the reported features of WFS. Two affected males in the first family had fathered unaffected children. We identified two homozygous mutations previously reported with apparently milder phenotypes: family 1: c.631G>A (p.Asp211Asn) in exon 5, and family 2: c.1456C>T (p.Gln486*) in exon 8. Heterozygous carriers were unaffected. This is the first report of male Wolfram patients who have successfully fathered children. Surprisingly, they also had almost all the complications associated with WFS. Our report has implications for genetic counseling and family planning advice for other affected families