Provenance of Aerosol Black Carbon over Northeast Indian Ocean and South China Sea and Implications for Oceanic Black Carbon Cycling.

Aerosol black carbon (BC) is a short-lived climate pollutant. The poorly constrained provenance of tropical marine aerosol BC hinders the mechanistic understanding of extreme climate events and oceanic carbon cycling. Here, we collected PM2.5 samples during research cruise NORC2016-10 through South China Sea (SCS) and Northeast Indian Ocean (NEIO) and measured the dual-carbon isotope compositions (δ13C-Δ14C) of BC using hydrogen pyrolysis technique. Aerosol BC exhibits six different δ13C-Δ14C isotopic spaces (i.e., isotope provinces). Liquid fossil fuel combustion, from shipping emissions and adjacent land, is the predominant source of BC over isotope provinces "SCS close to Chinese Mainland" (53.5%), "Malacca Strait" (53.4%), and "Open NEIO" (40.7%). C3 biomass burning is the major contributor to BC over isotope provinces "NEIO close to Southeast Asia" (55.8%), "Open NEIO" (41.3%), and "Open SCS" (40.0%). Coal combustion and C4 biomass burning show higher contributions to BC over "Sunda Strait" and "Open SCS" than the others. Overall, NEIO near the Bay of Bengal, Malacca Strait, and north SCS are three hot spots of fossil fuel-derived BC; the first two areas are also hot spots of biomass-derived BC. The comparable δ13C-Δ14C between BC in aerosol and dissolved BC in surface seawater may suggest atmospheric BC deposition as a potential source of oceanic dissolved BC.

A global carbon and nitrogen isotope perspective on modern and ancient human diet.

Stable carbon and nitrogen isotope analyses are widely used to infer diet and mobility in ancient and modern human populations, potentially providing a means to situate humans in global food webs. We collated 13,666 globally distributed analyses of ancient and modern human collagen and keratin samples. We converted all data to a common "Modern Diet Equivalent" reference frame to enable direct comparison among modern human diets, human diets prior to the advent of industrial agriculture, and the natural environment. This approach reveals a broad diet prior to industrialized agriculture and continued in modern subsistence populations, consistent with the human ability to consume opportunistically as extreme omnivores within complex natural food webs and across multiple trophic levels in every terrestrial and many marine ecosystems on the planet. In stark contrast, isotope dietary breadth across modern nonsubsistence populations has compressed by two-thirds as a result of the rise of industrialized agriculture and animal husbandry practices and the globalization of food distribution networks.

Author Correction: Savanna in equatorial Borneo during the late Pleistocene.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

A rapid throughput technique to isolate pyrogenic carbon by hydrogen pyrolysis for stable isotope and radiocarbon analysis.

RATIONALE: Rapid, reliable isolation of pyrogenic carbon (PyC; also known as char, soot, black carbon, or biochar) for the determination of stable carbon isotope (δ13 C) composition and radiocarbon (14 C) dating is needed across multiple fields of research in geoscience, environmental science and archaeology. Many current techniques do not provide reliable isolation from contaminating organics and/or are relatively time-consuming. Hydrogen pyrolysis (HyPy) does provide reliable isolation of PyC, but the current methodology is time consuming. METHODS: We explored the potential for subjecting multiple samples to HyPy analysis by placing up to nine individual samples in custom-designed borosilicate sample vessels in a single reactor run. We tested for cross-contamination between samples in the same run using materials with highly divergent radiocarbon activities (~0.04-116.3 pMC), δ13 C values (-11.9 to -26.5‰) and labile carbon content. We determined 14 C/13 C using accelerator mass spectrometry and δ13 C values using an elemental analyser coupled to a continuous flow isotope ratio mass spectrometer. RESULTS: Very small but measurable transfer between samples of highly divergent isotope composition was detectable. For samples having a similar composition, this cross-contamination is considered negligible with respect to measurement uncertainty. For samples having divergent composition, we found that placing a sample vessel loaded with silica mesh adsorbent between samples eliminated measurable cross-contamination in all cases for both 14 C/13 C and δ13 C values. CONCLUSIONS: It is possible to subject up to seven samples to HyPy in the same reactor run for the determination of radiocarbon content and δ13 C value without diminishing the precision or accuracy of the results. This approach enables an increase in sample throughput of 300-600%. HyPy process background values are consistently lower than the nominal laboratory process background for quartz tube combustion in the NERC Radiocarbon Laboratory, indicating that HyPy may also be advantageous as a relatively 'clean' radiocarbon pre-treatment method.

Savanna in equatorial Borneo during the late Pleistocene.

Equatorial Southeast Asia is a key region for global climate change. Here, the Indo-Pacific Warm Pool (IPWP) is a critical driver of atmospheric convection that plays a dominant role in global atmospheric circulation. However, fluctuating sea-levels during the Pleistocene produced the most drastic land-sea area changes on Earth, with the now-drowned continent of Sundaland being exposed as a contiguous landmass for most of the past 2 million years. How vegetation responded to changes in rainfall that resulted from changing shelf exposure and glacial boundary conditions in Sundaland remains poorly understood. Here we use the stable carbon isotope composition (δ13C) of bat guano and High Molecular Weight n-alkanes, from Saleh Cave in southern Borneo to demonstrate that open vegetation existed during much the past 40,000 yrs BP. This location is at the southern equatorial end of a hypothesized 'savanna corridor' and the results provide the strongest evidence yet for its existence. The corridor would have operated as a barrier to east-west dispersal of rainforest species, and a conduit for north-south dispersal of savanna species at times of lowered sea level, explaining many modern biogeographic patterns. The Saleh Cave record also exhibits a strong correspondence with insolation and sea surface temperatures of the IPWP, suggesting a strong sensitivity of vegetation to tropical climate change on glacial/interglacial timeframes.

Australian tropical cyclone activity lower than at any time over the past 550-1,500 years.

The assessment of changes in tropical cyclone activity within the context of anthropogenically influenced climate change has been limited by the short temporal resolution of the instrumental tropical cyclone record (less than 50 years). Furthermore, controversy exists regarding the robustness of the observational record, especially before 1990. Here we show, on the basis of a new tropical cyclone activity index (CAI), that the present low levels of storm activity on the mid west and northeast coasts of Australia are unprecedented over the past 550 to 1,500 years. The CAI allows for a direct comparison between the modern instrumental record and long-term palaeotempest (prehistoric tropical cyclone) records derived from the (18)O/(16)O ratio of seasonally accreting carbonate layers of actively growing stalagmites. Our results reveal a repeated multicentennial cycle of tropical cyclone activity, the most recent of which commenced around AD 1700. The present cycle includes a sharp decrease in activity after 1960 in Western Australia. This is in contrast to the increasing frequency and destructiveness of Northern Hemisphere tropical cyclones since 1970 in the Atlantic Ocean and the western North Pacific Ocean. Other studies project a decrease in the frequency of tropical cyclones towards the end of the twenty-first century in the southwest Pacific, southern Indian and Australian regions. Our results, although based on a limited record, suggest that this may be occurring much earlier than expected.