Natural cycles in South Pacific Gyre strength and the Southern Annular Mode.

The South Pacific Gyre (SPG) plays a vital role in regulating Southern Hemisphere climate and ecosystems. The SPG has been intensifying since the twentieth century due to changes in large scale wind forcing. These changes result from variability in the Southern Annular Mode (SAM), causing warming along the eastern SPG which affects local ecosystems. However, our understanding of SPG variability on timescales greater than several decades is poor due to limited observations. Marine sediment cores are traditionally used to determine if recent ocean trends are anomalous, but rarely capture centennial variability in the southwest Pacific and limit our understanding of SPG variability. Here we capture centennial SPG dynamics using a novel high-resolution paleocirculation archive: radiocarbon reservoir ages (R) and local reservoir corrections (∆R) in SPG deep-sea black corals. We find black coral R and ∆R correlates with SAM reconstructions over 0-1000 cal BP and 2000-3000 cal BP. We propose this correlation indicates varying transport of well-ventilated subtropical waters resulting from SPG and SAM interactions. We reconstruct several 'spin up' cycles reminiscent of the recent gyre intensification, which has been attributed to anthropogenic causes. This implies gyre strength and SAM show natural co-variability on anthropogenic timescales which should factor into future climate projections.

Assessing multiproxy approaches (Sr/Ca, U/Ca, Li/Mg, and B/Mg) to reconstruct sea surface temperature from coral skeletons throughout the Great Barrier Reef.

Due to the increasing concerns of global warming and short instrumental records of sea surface temperature (SST), coral-based proxies, such as δ18O, Sr/Ca, U/Ca, and Li/Mg have been developed and applied to reconstruct SST in paleoclimate studies. However, these proxies are not universally applicable in different environments, because they are affected by coral physiology and various environmental factors. In this study, seven long-lived Porites corals were collected from the southern sector of the Great Barrier Reef (GBR) off the coast of Gladstone and the central sector of the GBR within the Whitsunday Islands in 2017 and 2018. Coral sites were selected to cover a wide latitudinal range with different annual temperature ranges. Century-long geochemical records (Li/Ca, B/Ca, Mg/Ca, Sr/Ca, and U/Ca) were generated using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) at weekly resolution. This study has tested the robustness of two traditional temperature proxies (Sr/Ca and U/Ca), a recently developed temperature proxy (Li/Mg), and an additional potential temperature proxy (B/Mg). U/Ca was found to be the most robust and stable temperature proxy for corals from the GBR over long-term timescales. Sr/Ca is a close second, however due to the lower response of Sr fractionation per 1 °C, it is more sensitive to analytical methods and less sensitive to annual SST changes than U/Ca. Li/Mg and B/Mg have clearer periodicity compared to Li/Ca and B/Ca. Both Li/Mg and B/Mg are strongly correlated with SST, which is due to the cancellation of temperature-independent commonality. Empirical calibrations established from this multi-proxy approach increase the certainty of temperature reconstruction when a single proxy does not perform well. These site- and colony-specific SST calibrations also provide an opportunity to revisit the universal multi-trace element calibration of sea surface temperatures (UMTECS) model, which does not require the knowledge of local SST for calibration.

Sediment controls dynamic behavior of a Cordilleran Ice Stream at the Last Glacial Maximum.

The uncertain response of marine terminating outlet glaciers to climate change at time scales beyond short-term observation limits models of future sea level rise. At temperate tidewater margins, abundant subglacial meltwater forms morainal banks (marine shoals) or ice-contact deltas that reduce water depth, stabilizing grounding lines and slowing or reversing glacial retreat. Here we present a radiocarbon-dated record from Integrated Ocean Drilling Program (IODP) Site U1421 that tracks the terminus of the largest Alaskan Cordilleran Ice Sheet outlet glacier during Last Glacial Maximum climate transitions. Sedimentation rates, ice-rafted debris, and microfossil and biogeochemical proxies, show repeated abrupt collapses and slow advances typical of the tidewater glacier cycle observed in modern systems. When global sea level rise exceeded the local rate of bank building, the cycle of readvances stopped leading to irreversible retreat. These results support theory that suggests sediment dynamics can control tidewater terminus position on an open shelf under temperate conditions delaying climate-driven retreat.

Early tropical crop production in marginal subtropical and temperate Polynesia.

Polynesians introduced the tropical crop taro (Colocasia esculenta) to temperate New Zealand after 1280 CE, but evidence for its cultivation is limited. This contrasts with the abundant evidence for big game hunting, raising longstanding questions of the initial economic and ecological importance of crop production. Here we compare fossil data from wetland sedimentary deposits indicative of taro and leaf vegetable (including Sonchus and Rorippa spp.) cultivation from Ahuahu, a northern New Zealand offshore island, with Raivavae and Rapa, both subtropical islands in French Polynesia. Preservation of taro pollen on all islands between 1300 CE and 1550 CE indicates perennial cultivation over multiple growing seasons, as plants rarely flower when frequently harvested. The pollen cooccurs with previously undetected fossil remains of extinct trees, as well as many weeds and commensal invertebrates common to tropical Polynesian gardens. Sedimentary charcoal and charred plant remains show that fire use rapidly reduced forest cover, particularly on Ahuahu. Fires were less frequent by 1500 CE on all islands as forest cover diminished, and short-lived plants increased, indicating higher-intensity production. The northern offshore islands of New Zealand were likely preferred sites for early gardens where taro production was briefly attempted, before being supplanted by sweet potato (Ipomoea batatas), a more temperate climate-adapted crop, which was later established in large-scale cultivation systems on the mainland after 1500 CE.

Age structure of the Australian lungfish (Neoceratodus forsteri).

The Australian lungfish has been studied for more than a century without any knowledge of the longevity of the species. Traditional methods for ageing fish, such as analysis of otolith (ear stone) rings is complicated in that lungfish otoliths differ from teleost fish in composition. As otolith sampling is also lethal, this is not appropriate for a protected species listed under Australian legislation. Lungfish scales were removed from 500 fish from the Brisbane, Burnett and Mary rivers. A sub-sample of scales (85) were aged using bomb radiocarbon techniques and validated using scales marked previously with oxytetracycline. Lungfish ages ranged from 2.5-77 years of age. Estimated population age structures derived using an Age Length Key revealed different recruitment patterns between river systems. There were statistically significant von Bertalanffy growth model parameters estimated for each of the three rivers based on limited sample sizes. In addition, length frequency distributions between river systems were also significantly different. Further studies will be conducted to review drivers that may explain these inter-river differences.

Radiocarbon evidence for alternating northern and southern sources of ventilation of the deep Atlantic carbon pool during the last deglaciation.

Recent theories for glacial-interglacial climate transitions call on millennial climate perturbations that purged the deep sea of sequestered carbon dioxide via a "bipolar ventilation seesaw." However, the viability of this hypothesis has been contested, and robust evidence in its support is lacking. Here we present a record of North Atlantic deep-water radiocarbon ventilation, which we compare with similar data from the Southern Ocean. A striking coherence in ventilation changes is found, with extremely high ventilation ages prevailing across the deep Atlantic during the last glacial period. The data also reveal two reversals in the ventilation gradient between the deep North Atlantic and Southern Ocean during Heinrich Stadial 1 and the Younger Dryas. These coincided with periods of sustained atmospheric CO2 rise and appear to have been driven by enhanced ocean-atmosphere exchange, primarily in the Southern Ocean. These results confirm the operation of a bipolar ventilation seesaw during deglaciation and underline the contribution of abrupt regional climate anomalies to longer-term global climate transitions.

Subarctic weathering of mineral wastes provides a sink for atmospheric CO(2).

The mineral waste from some mines has the capacity to trap and store CO(2) within secondary carbonate minerals via the process of silicate weathering. Nesquehonite [MgCO(3)·3H(2)O] forms by weathering of Mg-silicate minerals in kimberlitic mine tailings at the Diavik Diamond Mine, Northwest Territories, Canada. Less abundant Na- and Ca-carbonate minerals precipitate from sewage treatment effluent deposited in the tailings storage facility. Radiocarbon and stable carbon and oxygen isotopes are used to assess the ability of mine tailings to trap and store modern CO(2) within these minerals in the arid, subarctic climate at Diavik. Stable isotopic data cannot always uniquely identify the source of carbon stored within minerals in this setting; however, radiocarbon isotopic data provide a reliable quantitative estimate for sequestration of modern carbon. At least 89% of the carbon trapped within secondary carbonate minerals at Diavik is derived from a modern source, either by direct uptake of atmospheric CO(2) or indirect uptake though the biosphere. Silicate weathering at Diavik is trapping 102-114 g C/m(2)/y within nesquehonite, which corresponds to a 2 orders of magnitude increase over the background rate of CO(2) uptake predicted from arctic and subarctic river catchment data.

Fixation and fate of C and N in the cyanobacterium Trichodesmium using nanometer-scale secondary ion mass spectrometry.

The marine cyanobacterium Trichodesmium is ubiquitous in tropical and subtropical seas and is an important contributor to global N and C cycling. We sought to characterize metabolic uptake patterns in individual Trichodesmium IMS-101 cells by quantitatively imaging (13)C and (15)N uptake with high-resolution secondary ion mass spectrometry (NanoSIMS). Trichodesmium fix both CO(2) and N(2) concurrently during the day and are, thus, faced with a balancing act: the O(2) evolved during photosynthesis inhibits nitrogenase, the key enzyme in N(2) fixation. After performing correlated transmission electron microscopy (TEM) and NanoSIMS analysis on trichome thin-sections, we observed transient inclusion of (15)N and (13)C into discrete subcellular bodies identified as cyanophycin granules. We speculate that Trichodesmium uses these dynamic storage bodies to uncouple CO(2) and N(2) fixation from overall growth dynamics. We also directly quantified both CO(2) and N(2) fixation at the single cell level using NanoSIMS imaging of whole cells in multiple trichomes. Our results indicate maximal CO(2) fixation rates in the morning, compared with maximal N(2) fixation rates in the afternoon, bolstering the argument that segregation of CO(2) and N(2) fixation in Trichodesmium is regulated in part by temporal factors. Spatial separation of N(2) and CO(2) fixation may also have a role in metabolic segregation in Trichodesmium. Our approach in combining stable isotope labeling with NanoSIMS and TEM imaging can be extended to other physiologically relevant elements and processes in other important microbial systems.

Extreme longevity in proteinaceous deep-sea corals.

Deep-sea corals are found on hard substrates on seamounts and continental margins worldwide at depths of 300 to approximately 3,000 m. Deep-sea coral communities are hotspots of deep ocean biomass and biodiversity, providing critical habitat for fish and invertebrates. Newly applied radiocarbon age dates from the deep water proteinaceous corals Gerardia sp. and Leiopathes sp. show that radial growth rates are as low as 4 to 35 mum year(-1) and that individual colony longevities are on the order of thousands of years. The longest-lived Gerardia sp. and Leiopathes sp. specimens were 2,742 years and 4,265 years, respectively. The management and conservation of deep-sea coral communities is challenged by their commercial harvest for the jewelry trade and damage caused by deep-water fishing practices. In light of their unusual longevity, a better understanding of deep-sea coral ecology and their interrelationships with associated benthic communities is needed to inform coherent international conservation strategies for these important deep-sea habitat-forming species.

Imaging and 3D elemental characterization of intact bacterial spores by high-resolution secondary ion mass spectrometry.

We present a quantitative, imaging technique based on nanometer-scale secondary ion mass spectrometry for mapping the 3D elemental distribution present in an individual micrometer-sized Bacillus spore. We use depth profile analysis to access the 3D compositional information of an intact spore without the additional sample preparation steps (fixation, embedding, and sectioning) typically used to access substructural information in biological samples. The method is designed to ensure sample integrity for forensic characterization of Bacillus spores. The minimal sample preparation/alteration required in this methodology helps to preserve sample integrity. Furthermore, the technique affords elemental distribution information at the individual spore level with nanometer-scale spatial resolution and high (microg/g) analytical sensitivity. We use the technique to map the 3D elemental distribution present within Bacillus thuringiensis israelensis spores.

Carbon and nitrogen fixation and metabolite exchange in and between individual cells of Anabaena oscillarioides.

Filamentous nitrogen fixing cyanobacteria are key players in global nutrient cycling, but the relationship between CO2- and N2-fixation and intercellular exchange of these elements remains poorly understood in many genera. Using high-resolution nanometer-scale secondary ion mass spectrometry (NanoSIMS) in conjunction with enriched H13CO3- and 15N2 incubations of Anabaena oscillarioides, we imaged the cellular distributions of C, N and P and 13C and 15N enrichments at multiple time points during a diurnal cycle as proxies for C and N assimilation. The temporal and spatial distributions of the newly fixed C and N were highly heterogeneous at both the intra- and inter-cellular scale, and indicative of regions performing active assimilation and biosynthesis. Subcellular components such as the neck region of heterocycts, cell division septae and putative cyanophycin granules were clearly identifiable by their elemental composition. Newly fixed nitrogen was rapidly exported from heterocysts and was evenly allocated among vegetative cells, with the exception of the most remote vegetative cells between heterocysts, which were N limited based on lower 15N enrichment. Preexisting functional heterocysts had the lowest levels of 13C and 15N enrichment, while heterocysts that were inferred to have differentiated during the experiment had higher levels of enrichment. This innovative approach, combining stable isotope labeling and NanoSIMS elemental and isotopic imaging, allows characterization of cellular development (division, heterocyst differentiation), changes in individual cell composition and cellular roles in metabolite exchange.