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Salinity-driven density stratification of the upper Arctic Ocean isolates sea-ice cover and cold, nutrient-poor surface waters from underlying warmer, nutrient-rich waters. Recently, stratification has strengthened in the western Arctic but has weakened in the eastern Arctic; it is unknown if these trends will continue. Here we present foraminifera-bound nitrogen isotopes from Arctic Ocean sediments since 35,000 years ago to reconstruct past changes in nutrient sources and the degree of nutrient consumption in surface waters, the latter reflecting stratification. During the last ice age and early deglaciation, the Arctic was dominated by Atlantic-sourced nitrate and incomplete nitrate consumption, indicating weaker stratification. Starting at 11,000 years ago in the western Arctic, there is a clear isotopic signal of Pacific-sourced nitrate and complete nitrate consumption associated with the flooding of the Bering Strait. These changes reveal that the strong stratification of the western Arctic relies on low-salinity inflow through the Bering Strait. In the central Arctic, nitrate consumption was complete during the early Holocene, then declined after 5,000 years ago as summer insolation decreased. This sequence suggests that precipitation and riverine freshwater fluxes control the stratification of the central Arctic Ocean. Based on these findings, ongoing warming will cause strong stratification to expand into the central Arctic, slowing the nutrient supply to surface waters and thus limiting future phytoplankton productivity., Nature Geoscience, 14 (9), ISSN:1752-0908, ISSN:1752-0894

Changes to the carbon content of the deep ocean, the largest reservoir in the surficial carbon cycle, are capable of altering atmospheric carbon dioxide concentrations and thereby Earth's climate. While the role of the deep ocean's carbon inventory in the last ice age has been thoroughly investigated, comparatively little is known about whether the deep ocean contributed to the change in the pacing and intensity of ice ages around 1 million years ago during the Mid‐Pleistocene Transition (MPT). Qin et al. (2022, https://doi.org/10.1029/2021GL097121) provide new reconstructions of deep ocean carbonate ion saturation, a proxy for carbon content, from the deep Pacific Ocean across the MPT. Intriguingly, their results show that a reduction in deep Pacific carbonate ion saturation across the MPT occurred at different intervals from carbonate ion saturation decline in the deep Atlantic Ocean. These results suggest a more nuanced contribution of whole‐ocean carbon sequestration to the climate changes reconstructed across the MPT., Plain Language Summary: Earth's periodic ice ages became longer and more intense around 1 million years ago. While the underlying reasons for this climate change remain debated, it is widely understood that the deep ocean may have played an important role by storing the potent greenhouse gas carbon dioxide away from the atmosphere. New research by Qin et al. (2022, https://doi.org/10.1029/2021gl097121) shows that the deep Pacific Ocean did indeed accumulate additional carbon around the time of this million‐year old climate transition. However, the new results also show that Pacific Ocean accumulated carbon over different intervals than the Atlantic Ocean, deepening the mystery around how and why this carbon uptake occurred., Key Points: The deep Atlantic and Pacific Oceans accumulated carbon at different intervals during the mid‐Pleistocene transition., National Science Foundation http://dx.doi.org/10.13039/100000001, https://doi.org/10.1029/2021GL097121

86 pages, 33 figures, 2 tables, 1 appendix.-- Data Availability Statement: The majority of the dissolved data were sourced from the GEOTRACES Intermediate Data Products in 2014 (Mawji et al., 2015) and 2017 (Schlitzer et al., 2018), and citations to the primary data sources are given in the caption for each figure. Data sources for Figure 1 are given below. Figure 1: Iron: Conway & John, 2014a (Atlantic); Conway & John, 2015a (Pacific); Abadie et al., 2017 (Southern). Zinc: Conway & John, 2014b (Atlantic); Conway & John, 2015a (Pacific); R. M. Wang et al., 2019 (Southern). Copper: Little et al., 2018 (Atlantic); Takano et al., 2017 (Pacific); Boye et al., 2012 (Southern). Cadmium: Conway and John, 2015b (Atlantic); Conway & John, 2015a (Pacific); Abouchami et al., 2014 (Southern). Molybdenum: Nakagawa et al., 2012 (all basins). Barium: Bates et al., 2017 (Atlantic); Geyman et al., 2019 (Pacific); Hsieh & Henderson, 2017 (Southern). Nickel: Archer et al., 2020 (Atlantic); Takano et al., 2017 (Pacific); R. M. Wang et al., 2019 (Southern). Chromium: Goring-Harford et al., 2018 (Atlantic); Moos & Boyle, 2019 (Pacific); Rickli et al., 2019 (Southern). Silver: Fischer et al., 2018 (Pacific); Boye et al., 2012 (Southern), Phytoplankton productivity and export sequester climatically significant quantities of atmospheric carbon dioxide as particulate organic carbon through a suite of processes termed the biological pump. Constraining how the biological pump operated in the past is important for understanding past atmospheric carbon dioxide concentrations and Earth's climate history. However, reconstructing the history of the biological pump requires proxies. Due to their intimate association with biological processes, several bioactive trace metals and their isotopes are potential proxies for past phytoplankton productivity, including iron, zinc, copper, cadmium, molybdenum, barium, nickel, chromium, and silver. Here, we review the oceanic distributions, driving processes, and depositional archives for these nine metals and their isotopes based on GEOTRACES-era datasets. We offer an assessment of the overall maturity of each isotope system to serve as a proxy for diagnosing aspects of past ocean productivity and identify priorities for future research. This assessment reveals that cadmium, barium, nickel, and chromium isotopes offer the most promise as tracers of paleoproductivity, whereas iron, zinc, copper, and molybdenum do not. Too little is known about silver to make a confident determination. Intriguingly, the trace metals that are least sensitive to productivity may be used to track other aspects of ocean chemistry, such as nutrient sources, particle scavenging, organic complexation, and ocean redox state. These complementary sensitivities suggest new opportunities for combining perspectives from multiple proxies that will ultimately enable painting a more complete picture of marine paleoproductivity, biogeochemical cycles, and Earth's climate history, This contribution grew (and grew) out of a joint workshop between GEOTRACES and Past Global Changes (PAGES) held in Aix-en-Provence in December 2018. The workshop was funded by the U.S. National Science Foundation (NSF) through the GEOTRACES program, the international PAGES project, which received support from the Swiss Academy of Sciences and NSF, and the French program Les Envelopes Fluides et l'Environnement. [...] T. J. Horner acknowledges support from NSF; S. H. Little from the UK Natural Environment Research Council (NE/P018181/1); T. M. Conway from the University of South Florida; and, J. R. Farmer from the Max Planck Society, the Tuttle Fund of the Department of Geosciences of Princeton University, the Grand Challenges Program of the Princeton Environmental Institute, and the Andlinger Center for Energy and the Environment of Princeton University. [...] With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S)

International audience; Introduction 5 Sedimentology 11 Biostratigraphy 20 Paleomagnetism 22 Geochemistry 25 Physical properties 31 Downhole measurements 32 Stratigraphic correlation 34 References

Assessing the physicochemical variability of the deeper ocean is currently hampered by limited instrumental time series and proxy records. Bamboo corals (Isididae) form a cosmopolitan family of calcitic deep sea corals that could fill this information gap via geochemical information recorded in their skeletons. Here we evaluate the suitability of high-resolution chemical imaging of bamboo coral skeletons for temperature and nutrient reconstruction. The applied elemental mapping techniques allow to verify the suitability of the chosen transect on the sample section for paleo-reconstructions and enhance the statistical precision of the reconstruction. We measured Mg/Ca via electron microprobe at 1 µm resolution and Ba/Ca via laser ablation ICP-MS at 35 µm resolution in a historic specimen of Keratoisis grayi from the Blake Plateau off Eastern Florida. Long-term growth temperatures of 7.1 ± 3.4 °C (± 2 SD) that are in agreement with recent ambient temperature range can be reconstructed from Mg/Ca ratios provided that anomalously Mg-enriched structural features around the central axis and isolated features related to tissue attachment are avoided for reconstruction. Skeletal Ba/Ca measurements reflect mean seawater barium [Ba]SW concentrations ([Ba]SW = 51 ± 24 nmol kg-1 (± 2 SD)), in agreement with instrumental data (47 nmol kg-1). We show for the first time that Ba/Ca forms concentric structures in a bamboo coral skeleton section. Our investigations suggest that, while bamboo coral skeletons do record environmental parameters in their mean chemical composition, the magnitude of environmental variability reconstructed from high-resolution chemical maps exceeds that expected from instrumental time series. This necessitates additional investigation of the factors driving bamboo coral skeletal composition.

The boron concentration (B/Ca ratio) and isotopic composition (δ11B) of biogenic calcite are widely applied to reconstruct past changes in seawater carbonate chemistry. Knowledge of B incorporation pathways into calcite is critical for these applications and for improving the theoretical basis of B proxies. While the canonical interpretation of δ11B holds that B in calcite predominantly derives from dissolved borate anion in seawater, recent studies of the B content, coordination, and isotopic composition in calcite suggest more complex B incorporation pathways. To provide new insights into these pathways, here we present δ11B of inorganic calcite precipitated from saline solutions of varying pH, calcium and dissolved inorganic carbon (DIC) concentration for which B/Ca data were previously reported by Uchikawa et al. (2015). Results show that calcite δ11B significantly increases with increasing pH and decreases with increasing [Ca2+] and [DIC]. In combination, these experiments show that the difference in δ11B between solid calcite and aqueous borate linearly decreases with increasing calcite precipitation rate. To interpret these data, we present the first application of surface kinetic modeling (SKM) to boron incorporation. The SKM can simultaneously explain rate-dependent B/Ca and δ11B patterns observed in our and previously published inorganic calcite precipitation experiments when both aqueous borate and boric acid contribute to boron in inorganic calcite. If the B incorporation mechanism shown here for inorganic calcite is applicable to biogenic calcite, precipitation rate variations could modify δ11B patterns by changing the contributions of aqueous boric acid and borate to boron in calcite. However, better knowledge of biogenic calcite precipitation mechanisms and rates is needed to assess the importance of this effect for applications of B proxies in biogenic carbonates.

We evaluate the potential utility of Mg/Ca in the ostracode genera Sarsicytheridea and Paracyprideis as a paleotemperature proxy for continental shelf and upper slope waters of the Arctic Ocean and adjacent seas. Using sediment core-top and surface sediment samples, shells of three species, S. bradii, S. punctillata, and P. pseudopunctillata, were analyzed from Arctic Ocean sites in water depth from 7 to 200 m and bottom-water temperatures (BWT) of −1.5 °C to 12 °C. Mg/Ca values range from 4 to 9 mmol/mol. These results are in excellent agreement with the range of Mg/Ca obtained in a previous study ( Ingram, 1998 ) of shells of Sarsicytheridea from the sub-polar North Atlantic Ocean region with BWT ranging from 1 to 11.4 °C. Unlike this study of Sarsicytheridea, and work on the Arctic ostracode marine genus Krithe showing strong correlations between Mg/Ca and BWT, analysis of Mg/Ca in this study are not correlated with BWT below 0 °C. We hypothesize that this primarily has to do with uncertainty regarding the actual ambient BWT at the time of shell secretion. As with many continental shelf sites, individual sites used in the study have large interannual and seasonal variations in BWT (≥5–8 °C). Thus, there is difficulty in assigning a shell secretion temperature and assessing the utility of Sarsicytheridea Mg/Ca ratios as a paleotemperature proxy below 0 °C. The calibration of Mg/Ca results from temperatures above 0 °C justifies continued evaluation of this potential paleothermometer for Arctic continental shelf and upper slope environments.

The Antarctic Circumpolar Current (ACC), the world’s strongest zonal current system, connects all three major ocean basins of the global ocean and therefore integrates and responds to global climate variability. Its flow is largely driven by strong westerly winds and is constricted to its narrowest extent in the Drake Passage. Fresh and cold Pacific surface and intermediate water flowing through the Drake Passage (cold-water route) and warm Indian Ocean water masses flowing through the Agulhas region (warm-water route) are critical for the South Atlantic contribution to Meridional Overturning Circulation changes. Furthermore, physical and biological processes associated with the ACC affect the strength of the ocean carbon pump and therefore are critical to feedbacks linking atmospheric CO2 concentrations, ocean circulation, and climate/cryosphere on a global scale. In contrast to the Atlantic and Indian sectors of the ACC, and with the exception of drill cores from the Antarctic continental margin and off New Zealand, there are no deep-sea drilling paleoceanographic records from the Pacific sector of the ACC. To advance our understanding of Miocene to Holocene atmosphere-ocean-cryosphere dynamics in the Pacific and their implications for regional and global climate and atmospheric CO2, International Ocean Discovery Program Expedition 383 recovered sedimentary sequences at (1) three sites in the central South Pacific (CSP) (U1539, U1540, and U1541), (2) two sites at the Chilean margin (U1542 and U1544), and (3) one site from the pelagic eastern South Pacific (U1543) close to the entrance to the Drake Passage. Because of persistently stormy conditions and the resulting bad weather avoidance, we were not successful in recovering the originally planned Proposed Site CSP-3A in the Polar Frontal Zone of the CSP. The drilled sediments at Sites U1541 and U1543 reach back to the late Miocene, and those at Site U1540 reach back to the early Pliocene. High sedimentation rate sequences reaching back to the early Pleistocene (Site U1539) and the late Pleistocene (Sites U1542 and U1544) were recovered in both the CSP and at the Chilean margin. Taken together, the sites represent a depth transect from ~1100 m at Chilean margin Site U1542 to ~4070 m at CSP Site U1539 and allow investigation of changes in the vertical structure of the ACC, a key issue for understanding the role of the Southern Ocean in the global carbon cycle. The sites are located at latitudes and water depths where sediments will allow the application of a wide range of siliciclastic-, carbonate-, and opal-based proxies to address our objectives of reconstructing, with unprecedented stratigraphic detail, surface to deep-ocean variations and their relation to atmosphere and cryosphere changes.

JWBR received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant Agreement No. 805246) and from the Natural Environmental Research Council (NERC) grant NE/N011716/1. Boron isotopes in marine carbonates are increasingly used to reconstruct seawater pH and atmospheric pCO2 through Earth’s history. While isotope ratio measurements from individual laboratories are often of high quality, it is important that records generated in different laboratories can equally be compared. Within this Boron Isotope Intercomparison Project (BIIP), we characterised the boron isotopic composition (commonly expressed in δ11B) of two marine carbonates: Geological Survey of Japan carbonate reference materials JCp‐1 (coral Porites) and JCt‐1 (giant clam Tridacna gigas). Our study has three foci: (a) to assess the extent to which oxidative pre‐treatment, aimed at removing organic material from carbonate, can influence the resulting δ11B; (b) to determine to what degree the chosen analytical approach may affect the resultant δ11B; and (c) to provide well‐constrained consensus δ11B values for JCp‐1 and JCt‐1. The resultant robust mean and associated robust standard deviation (s*) for un‐oxidised JCp‐1 is 24.36 ± 0.45‰ (2s*), compared with 24.25 ± 0.22‰ (2s*) for the same oxidised material. For un‐oxidised JCt‐1, respective compositions are 16.39 ± 0.60‰ (2s*; un‐oxidised) and 16.24 ± 0.38‰ (2s*; oxidised). The consistency between laboratories is generally better if carbonate powders were oxidatively cleaned prior to purification and measurement. Publisher PDF

Biological productivity in the ocean directly influences the partitioning of carbon between the atmosphere and ocean interior, thereby controlling the distributions of many elements and their isoto...

Bamboo corals are calcitic octocorals dwelling in a broad range of water depths and in all ocean basins. Their skeletons could give insight into the temporal variability of environmental parameters at their growth locations, in areas where long-time observations are often lacking. A thorough understanding of calcification mechanisms is essential to interpret the chemical composition of their high-magnesium calcite skeleton regarding environmental fluctuations of the deeper ocean. To address this issue, we employed electron microprobe analysis, confocal Raman spectroscopy, laser ablation-ICPMS and solution based multi collector-ICPMS that together provide insights into the fine-scale spatial heterogeneity of the coral chemical composition. We investigate the spatial distribution of Na, S, and Ca, as well as organic matter in skeletal sections of specimens of Keratoisis grayi (family Isididae) from the Atlantic Ocean. Two bamboo coral samples from the Atlantic and Pacific Ocean were further used to create laser ablation-based maps of δ11B and boron to carbon ratios (B/C) over the sample radii. These maps are compared with results obtained via solution based δ11B analyses on drilled samples.An inverse correlation between Na and S is observed while S seems to be positively correlated with organic matter. We will discuss the ability of a qualitative physicochemical model to explain the observed Na and S distribution and the potential role of organic matter and amorphous calcium carbonate. Our results indicate that skeletal Na/Ca in bamboo corals is largely driven by physiological processes rather than environmental salinity variability. The spatial distribution of δ11B shows a positive correlation with B/C. The observed range of bulk δ11B - partly falling below the theoretical borate fractionation curve in seawater - is larger than the conventional measured δ11B of the calcite fraction alone. The latter cannot be explained with a spatial smoothing of the distribution during sample drilling but is rather associated with a loss of an isotopically highly variable B fraction during sample bleaching. Potential reasons for the observed differences in B isotopic range and their implications will be presented. We conclude that skeletal δ11B as a proxy for pHSW is dependent on the applied technique and investigated material fraction.

Bamboo corals represent an intriguing paleoceanographic archive with the potential to reconstruct variations throughout the water column over multiple centuries. Realizing this potential partially depends on if, and at what resolution, timeseries of variability can be generated. Recent work demonstrates that bamboo coral growth temperature, averaged over its entire lifespan, can be derived from linear correlations in its carbon and oxygen isotope composition (δ13C, δ18O) when the apparent equilibrium fractionations for a coral's growth rate and calcifying pH are used. Building on this method, this study applies it to coeval coral skeleton to assess the possibility of extracting paleoceanographic timeseries from bamboo coral skeletons. Using boron isotope (δ11B) based pH estimates, micromilled samples yield accurate paleotemperatures with uncertainties of 2 °C. This is attributed to the inability to measure δ13C and δ18O in exactly the same skeleton, as is the case for micromilled samples. A micromilled sampling strategy is therefore likely the most practical means of applying the method. Carbonate clumped isotopes (∆47) estimate temperatures slightly warmer than observed, suggesting they may not accurately record the subtle variations of the latest Holocene. When interpreted in conjunction, δ18O, δ11B and ∆47 data suggest that pH up-regulation plays a role in generating linear δ13C-δ18O trends. However, oxygen isotope fractionation and ∆47 are lower than would be predicted by pH alone. Potential explanations for this discrepancy include biological processes that favor the incorporation of carbonate ion into coral skeleton, uncertainties in the δ11B-pH proxy, the influence of magnesium on calcite-fluid isotope fractionation, or uncertainties in the fractionation factors used to calculate apparent equilibrium. Despite some remaining uncertainties, the method can resolve many observed decadal-scale thermocline temperature anomalies, suggesting that appropriately located bamboo corals could help constrain the behavior of similar temporal variability prior to instrumental monitoring.

Measurements of boron isotopes (δ11B) in marine carbonates are an important tool for reconstructing past ocean acidity and atmospheric carbon dioxide levels, but are challenging to obtain due to low boron concentrations and the presence of only two stable boron isotopes. Previous studies have observed differences in absolute δ11B values of marine carbonates measured via negative thermal ionization mass spectrometry (N-TIMS) and multicollector inductively coupled mass spectrometry (MC-ICP-MS) that are relatively large compared to magnitudes of δ11B variability in paleoceanographic studies. Here we investigate the cause of these δ11B offsets and implications for paleo-pH reconstructions by performing N-TIMS and MC-ICP-MS measurements within the same laboratory on a suite of eighteen homogenized samples, including inorganic calcites grown under controlled pH conditions and Quaternary planktic foraminifera. Results show that δ11B values between both measurement techniques are highly correlated (R2 > 0.99), but calcite δ11B values are ~ 0.5 to 2.7‰ lower when measured by MC-ICP-MS compared to N-TIMS. The δ11B offset between techniques cannot be attributed to procedural blank contribution, but the magnitude of offset moderately correlates with indicators of sample chemical composition, including B/Ca, Mg/Ca and δ18O (R2 = 0.39 to 0.50). N-TIMS δ11B does not change with calcium addition to a biogenic carbonate sample, suggesting that varying calcium abundance between samples and standards is not the reason for N-TIMS “matrix effects”. Correlation between δ18O and the δ11B offset is particularly apparent for calcites (R2 = 0.71); the origin of this relationship is not clear, but is not likely due to 17O interference. Although identifying the origin of measurement offsets requires further study, we demonstrate that such offsets do not affect the validity of δ11B data: The sensitivity of δ11B in inorganic calcite to pH is the same when measured by either technique, and paleo-pH reconstructed from δ11B measurements in planktic foraminifera is equivalent within uncertainty when a technique-specific constant offset is applied. Our results strongly indicate that δ11B measurements from both measurement techniques (N-TIMS and MC-ICP-MS) can be employed for paleo-pH reconstructions with equal confidence.

Over the past three million years, Earth’s climate oscillated between warmer interglacials with reduced terrestrial ice volume and cooler glacials with expanded polar ice sheets. These climate cycles, as reflected in benthic foraminiferal oxygen isotopes, transitioned from dominantly 41-kyr to 100-kyr periodicities during the mid-Pleistocene 1,250 to 700 kyr ago (ka). Because orbital forcing did not shift at this time, the ultimate cause of this mid-Pleistocene transition remains enigmatic. Here we present foraminiferal trace element (B/Ca, Cd/Ca) and Nd isotope data that demonstrate a close linkage between Atlantic Ocean meridional overturning circulation and deep ocean carbon storage across the mid-Pleistocene transition. Specifically, between 950 and 900 ka, carbonate ion saturation decreased by 30 µmol kg−1 and phosphate concentration increased by 0.5 µmol kg−1 coincident with a 20% reduction of North Atlantic Deep Water contribution to the abyssal South Atlantic. These results demonstrate that the glacial deep Atlantic carbon inventory increased by approximately 50 Gt during the transition to 100-kyr glacial cycles. We suggest that the coincidence of our observations with evidence for increased terrestrial ice volume reflects how weaker overturning circulation and Southern Ocean biogeochemical feedbacks facilitated deep ocean carbon storage, which lowered the atmospheric partial pressure of CO2 and thereby enabled expanded terrestrial ice volume at the mid-Pleistocene transition. Deep Atlantic carbon storage increased and the meriodional overturning circulation weakened at the mid-Pleistocene transition to 100,000-year glacial–interglacial cycles, according to analyses of foraminifera trace elements and Nd isotopes.

Radiocarbon ( 14 C) measurements are an important tool for determining growth rates of bamboo corals, a cosmopolitan group of calcitic deep-sea corals. Published growth rate estimates for bamboo corals are highly variable, with potential environmental or ecological drivers of this variability poorly constrained. Here we systematically investigate the application of 14 C for growth rate determinations in bamboo corals using 55 14 C dates on the calcite and organic fractions of six bamboo corals (identified as Keratoisis sp.) from the western North Atlantic Ocean. Calcite 14 C measurements on the distal surface of these corals and five previously published bamboo corals exhibit a strong one-to-one relationship with the 14 C of dissolved inorganic carbon (DI 14 C) in ambient seawater ( r 2 =0.98), confirming the use of Keratoisis sp. calcite 14 C as a proxy for seawater 14 C activity. Radial growth rates determined from 14 C age-depth regressions, 14 C plateau tuning and bomb 14 C reference chronologies range from 12 to 78 µm y −1 , in general agreement with previously published radiometric growth rates. We document potential biases to 14 C growth rate determinations resulting from water mass variability, bomb radiocarbon, secondary infilling (ontogeny), and growth rate nonlinearity. Radial growth rates for Keratoisis sp. specimens do not correlate with ambient temperature, suggesting that additional biological and/or environmental factors may influence bamboo coral growth rates.

The ocean is currently absorbing excess carbon from anthropogenic emissions, leading to reduced seawater-pH (termed ‘ocean acidification’). Instrumental records of ocean acidification are unavailable from well-ventilated areas of the deep ocean, necessitating proxy records to improve spatio-temporal understanding on the rate and magnitude of deep ocean acidification. Here we investigate boron, carbon, and oxygen isotopes on live-collected deep-sea bamboo corals (genus Keratoisis) from a pHtot range of 7.5–8.1. These analyses are used to explore the potential for using bamboo coral skeletons as archives of past deep-sea pH and to trace anthropogenic acidification in the subsurface North Atlantic Ocean (850–2000 m water depth). Boron isotope ratios of the most recently secreted calcite of bamboo coral skeletons are close to the calculated isotopic composition of borate anion in seawater (δ11Bborate) for North Atlantic corals, and 1–2‰ higher than δ11Bborate for Pacific corals. Within individual coral skeletons, carbon and oxygen isotopes correlate positively and linearly, a feature associated with vital effects during coral calcification. δ11B variability of 0.5–2‰ is observed within single specimens, which exceeds the expected anthropogenic trend in modern North Atlantic corals. δ11B values are generally elevated in Pacific corals relative to δ11Bborate, which may reflect pH-driven physiological processes aiding coral calcification in environments unfavorable for calcite precipitation. Elevated δ11B values are also observed proximal to the central axis in multiple Atlantic and Pacific specimens, relative to δ11Bborate, which might reflect ontogenetic variability in calcification rates. Although the observed boron isotope variability is too large to resolve the present anthropogenic ocean acidification signal at the studied depths in the North Atlantic (∼0.03–0.07 pH units), pH changes ⩾0.1 units might still be reconstructed using δ11B measurements in bamboo corals.

Pre-twentieth century sea level (SL) variability remains poorly understood due to limits of tide gauge records, low temporal resolution of tidal marsh records, and regional anomalies caused by dynamic ocean processes, notably multidecadal changes in Atlantic Meridional Overturning Circulation (AMOC). We examined SL and AMOC variability along the eastern United States over the last 2000 years, using a SL curve constructed from proxy sea surface temperature (SST) records from Chesapeake Bay, and twentieth century SL-sea surface temperature (SST) relations derived from tide gauges and instrumental SST. The SL curve shows multidecadal-scale variability (20–30 years) during the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA), as well as the twentieth century. During these SL oscillations, short-term rates ranged from 2 to 4 mm yr−1, roughly similar to those of the last few decades. These oscillations likely represent internal modes of climate variability related to AMOC variability and originating at high latitudes, although the exact mechanisms remain unclear. Results imply that dynamic ocean changes, in addition to thermosteric, glacio-eustatic, or glacio-isostatic processes are an inherent part of SL variability in coastal regions, even during millennial-scale climate oscillations such as the MCA and LIA and should be factored into efforts that use tide gauges and tidal marsh sediments to understand global sea level rise.

A new instrumental setup, combining laser ablation (LA) with accelerator mass spectrometry (AMS), has been investigated for the online radiocarbon (14C) analysis of carbonate records. Samples were placed in an in-house designed LA-cell and CO2 gas was produced by ablation using a 193 nm ArF excimer laser. The 14C/12C abundance ratio of the gas was then analyzed by gas ion source AMS. This configuration allows flexible and time resolved acquisition of 14C profiles in contrast to conventional measurements, where only the bulk composition of discrete samples can be obtained. Three different measurement modes, i.e. discrete layer analysis, survey scans and precision scans, were investigated and compared using a stalagmite sample and, subsequently, applied to terrestrial and marine carbonates. Depending on the measurement mode, a precision of typically 1-5 % combined with a spatial resolution of 100 µm can be obtained. Prominent 14C features, such as the atomic bomb 14C peak, can be resolved by scanning several cm of a sample within one hour. Stalagmite, deep-sea coral and mollusk shell samples yielded comparable signal intensities, which again were comparable to those of conventional gas measurements. The novel LA-AMS setup allowed rapid scans on a variety of sample materials with high spatial resolution.

In the Arctic Ocean, the cold and relatively fresh water beneath the sea ice is separated from the underlying warmer and saltier Atlantic Layer by a halocline. Ongoing sea ice loss and warming in t ...

[1] The reconstruction of deep-sea bottom water temperature (BWT) is important to assess the ocean's response to and role in orbital- and millennial-scale climate change. Deep-sea paleothermometry employs magnesium to calcium (Mg/Ca) ratios in calcitic benthic microfaunas (foraminifera, ostracodes) as a primary proxy method. Mg/Ca paleothermometry may, however, be complicated by bottom water carbonate ion chemistry, which might affect Mg/Ca ratios in shells. To address temperature and carbonate ion influence on Mg/Ca ratios, we studied Mg/Ca ratios in the benthic ostracode genus Krithe in the North Atlantic and Arctic oceans using a 686-specimen core top collection, including 412 previously unpublished analyses. Mg/Ca ratios are positively correlated to temperature in multiple species from the North Atlantic [BWT = (0.885 × Mg/Ca) − 5.69, r2 = 0.73] and for K. glacialis in the Arctic Ocean and Nordic Seas [BWT = (0.439 × Mg/Ca) − 5.14, r2 = 0.50], consistent with previously published calibrations. We found no evidence for a relationship between Krithe Mg/Ca and carbonate ion saturation in the North Atlantic Ocean, Nordic Seas, and Arctic Ocean, supporting the use of Krithe Mg/Ca for reconstructing past BWT.

Power plants originally designed to be decommissioned at 20-30 years are extending their service life by removing/replacing major power plant components. This requirement is contrary to the original floor and workspace designs engineered for power plants. Feedwater heaters, casks, heat exchangers, and other very large (50’ +) and heavy (20-100 ton) components can overcome floor and space restrictions by using a combination of air casters and cranes. This proven methodology saves in excess of 75% the cost of a standard crane-only operation and significantly reduces the possibility of permanent floor damage. Air caster transport systems are low profile and easily insert under industrial heaters, exchangers, transformers, etc. The casters raise components and carry them across the floor, spreading the multi-ton weight across the surface area without damage to the floor or component. Air casters are frictionless even with the heaviest loads, and significantly reduce ergonomic risk while also providing the benefit of requiring a reduced workforce to move the component across the floor. Controlled drive systems allow a single operator to easily move components omnidirectionally without wheels or rails, and into position within .5 inches/13mm accuracy. Proven effective in existing nuclear plants as noted in the ICONE paper presented by Tokyo Power. Air casters, often coupled with cranes, significantly lower material handling costs associated with new installation and repair/refurbishment of components up to and over 5000 tons. Air casters operate on normal compressed air and have very few moving parts, resulting in low ongoing maintenance costs. INTRODUCTION Early prior research demonstrated the superiority of ceramics for bearings (1, 2) and the existence of elastohydrodynamic (ehd) lubricant films at ball and roller contacts (3), the calculation of which is now an accepted part of bearing engineering. These new concepts are now used in the design of lubrication systems with solid lubricants that operate in much more severe environments than oils and greases (4, 5). Proprietary computer codes and unique patented bearing configurations for optimizing the performance of bearing/solidlubricant systems have been developed (6, 7 and 8). In this way, patented self-contained solid-lubricated all-steel and hybrid-ceramic ball and roller bearings are now available for environments that do not contribute to their lubrication, such as in air or vacuum. NOMENCLATURE Put nomenclature here. Put body of the paper here. Put body of the paper here. Put body of the paper here. Put body of the paper here. Put body of the paper here. Put body of the paper here. Put body of the paper here. Put body of the paper here. Put body of the paper here. Put body of the paper here. Put body of the paper here. Put body of the paper here. ACKNOWLEDGMENTS Put acknowledgments here.

The kinematic analysis and design of an articulated twin body, four-wheel, robotic vehicle is presented. The mobility of the vehicle is improved by connecting the two bodies with a four-bar linkage rather than the standard revolute-jointed body connection used in earlier designs. When properly proportioned, the new linkage design passively minimizes vehicle off-tracking by allowing the rear wheels to closely track the path of the front wheels. This significantly improves the ability of the vehicle to deal with cluttered environments. We outline the theoretical kinematic model of the four-bar linkage as applied to a twin-bodied, differentially driven vehicle. This model is validated through computer simulation as well as experimentation on a fully operational robotic vehicle. The kinematic model provides the foundation for an actively-controlled, linkage-based tracking system.Copyright © 2009 by ASME

This paper presents an algorithm for solving three challenges of autonomous navigation: sensor signal processing, sensor integration, and path-finding. The algorithm organizes these challenges into three steps. The first step involves converting the raw data from each sensor to a form suitable for real-time processing. Emphasis in the first step is on image processing. In the second step, the processed data from all sensors is integrated into a single map. Using this map as input, during the third step the algorithm calculates a goal and finds a suitable path from robot to the goal. The method presented in this paper completes these steps in this order and the steps repeat indefinitely. The robotic platform designed for testing the algorithm is a six-wheel mid-wheel drive system using differential steering. The robot, called Anassa II, has an electric wheelchair base and a custom-built top and it is designed to participate in the Intelligent Ground Vehicle Competition (IGVC). The sensors consist of a laser scanner, a video camera, a Differential Global Positioning System (DGPS) receiver, a digital compass, and two wheel encoders. Since many intelligent vehicles have similar sensors, the approach presented here is general enough for many types of autonomous mobile robots.

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