Record of Little Ice Age sea surface temperatures at Bermuda using a growth-dependent calibration of coral Sr/Ca

Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 20 (2005): PA4016, doi:10.1029/2005PA001140.Strontium to calcium ratios (Sr/Ca) are reported for a massive brain coral Diploria labyrinthiformis collected from the south shore of Bermuda and are strongly correlated with both sea surface temperature (SST) and mean annual skeletal growth rate. High Sr/Ca ratios correspond with cold SSTs and slow skeletal growth rate and vice versa. We provide a quantitative calibration of Sr/Ca to extension rate and SST along the axis of maximum growth and derive a growth-dependent Sr/Ca–SST calibration equation to reconstruct western subtropical North Atlantic SSTs for the past 223 years. When the influence of growth rate is excluded from the calibration, Sr/Ca ratios yield SSTs that are too cold during cool anomalies and too warm during warm anomalies. Toward the end of the Little Ice Age (∼1850), SST changes derived using a calibration that is not growth-dependent are exaggerated by a factor of 2 relative to those from the growth-corrected model that yields SSTs ∼1.5°C cooler than today. Our results indicate that incorporation of growth rate effects into coral Sr/Ca calibrations may improve the accuracy of SSTs derived from living and fossil corals.A Stanley Watson Foundation Fellowship (N.F.G.), and grants from NSF (OCE-0402728) and WHOI (K.A.H., A.L.C., and M.S.M.) supported this work

Two centuries of limited variability in subtropical North Atlantic thermocline ventilation

© The Author(s), 2012. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nature Communications 3 (2012): 803, doi:10.1038/ncomms1811.Ventilation and mixing of oceanic gyres is important to ocean-atmosphere heat and gas transfer, and to mid-latitude nutrient supply. The rates of mode water formation are believed to impact climate and carbon exchange between the surface and mid-depth water over decadal periods. Here, a record of 14C/12C (1780–1940), which is a proxy for vertical ocean mixing, from an annually banded coral from Bermuda, shows limited inter-annual variability and a substantial Suess Effect (the decrease in 14C/12C since 1900). The Sargasso Sea mixing rates between the surface and thermocline varied minimally over the past two centuries, despite changes to mean-hemispheric climate, including the Little Ice Age and variability in the North Atlantic Oscillation. This result indicates that regional formation rates of sub-tropical mode water are stable over decades, and that anthropogenic carbon absorbed by the ocean does not return to the surface at a variable rate.Funding provided by NSF’s Chemical Oceanography Program OCE - 0526463 and 0961980 and the Stephen Hui Trust Fund

Technical and clinical validation of commercial automated volumetric MRI tools for dementia diagnosis-a systematic review

Developments in neuroradiological MRI analysis offer promise in enhancing objectivity and consistency in dementia diagnosis through the use of quantitative volumetric reporting tools (QReports). Translation into clinical settings should follow a structured framework of development, including technical and clinical validation steps. However, published technical and clinical validation of the available commercial/proprietary tools is not always easy to find and pathways for successful integration into the clinical workflow are varied. The quantitative neuroradiology initiative (QNI) framework highlights six necessary steps for the development, validation and integration of quantitative tools in the clinic. In this paper, we reviewed the published evidence regarding regulatory-approved QReports for use in the memory clinic and to what extent this evidence fulfils the steps of the QNI framework. We summarize unbiased technical details of available products in order to increase the transparency of evidence and present the range of reporting tools on the market. Our intention is to assist neuroradiologists in making informed decisions regarding the adoption of these methods in the clinic. For the 17 products identified, 11 companies have published some form of technical validation on their methods, but only 4 have published clinical validation of their QReports in a dementia population. Upon systematically reviewing the published evidence for regulatory-approved QReports in dementia, we concluded that there is a significant evidence gap in the literature regarding clinical validation, workflow integration and in-use evaluation of these tools in dementia MRI diagnosis

Environmental assessment of metal exposure to corals living in Castle Harbour, Bermuda

This paper is not subject to U.S. copyright. The definitive version was published in Marine Chemistry 154 (2013): 55–66, doi:10.1016/j.marchem.2013.05.002.Environmental contamination in Castle Harbour, Bermuda, has been linked to the dissolution and leaching of contaminants from the adjacent marine landfill. This study expands the evidence for environmental impact of leachate from the landfill by quantitatively demonstrating elevated metal uptake over the last 30 years in corals growing in Castle Harbour. Coral Pb/Ca, Zn/Ca and Mn/Ca ratios and total Hg concentrations are elevated relative to an adjacent control site in John Smith's Bay. The temporal variability in the Castle Harbour coral records suggests that while the landfill has increased in size over the last 35 years, the dominant input of metals is through periodic leaching of contaminants from the municipal landfill and surrounding sediment. Elevated contaminants in the surrounding sediment suggest that resuspension is an important transport medium for transferring heavy metals to corals. Increased winds, particularly during the 1990s, were accompanied by higher coral metal composition at Castle Harbour. Coupled with wind-induced resuspension, interannual changes in sea level within the Harbour can lead to increased bioavailability of sediment-bound metals and subsequent coral metal assimilation. At John Smith's Bay, large scale convective mixing may be driving interannual metal variability in the coral record rather than impacts from land-based activities. Results from this study provide important insights into the coupling of natural variability and anthropogenic input of contaminants to the nearshore environment.This work was supported by a grant from a postdoctoral scholarship to N.G. Prouty from the Woods Hole Oceanographic Institution and grants from the NSF (OCE-0402728; K. Hughen) and the Cove Point Foundation (C. Lamborg)

Hippocampal profiling: Localized magnetic resonance imaging volumetry and T2 relaxometry for hippocampal sclerosis

Objective: Hippocampal sclerosis (HS) is the most common cause of drug‐resistant temporal lobe epilepsy, and its accurate detection is important to guide epilepsy surgery. Radiological features of HS include hippocampal volume loss and increased T2 signal, which can both be quantified to help improve detection. In this work, we extend these quantitative methods to generate cross‐sectional area and T2 profiles along the hippocampal long axis to improve the localization of hippocampal abnormalities. Methods: T1‐weighted and T2 relaxometry data from 69 HS patients (32 left, 32 right, 5 bilateral) and 111 healthy controls were acquired on a 3‐T magnetic resonance imaging (MRI) scanner. Automated hippocampal segmentation and T2 relaxometry were performed and used to calculate whole‐hippocampal volumes and to estimate quantitative T2 (qT2) values. By generating a group template from the controls, and aligning this so that the hippocampal long axes were along the anterior‐posterior axis, we were able to calculate hippocampal cross‐sectional area and qT2 by a slicewise method to localize any volume loss or T2 hyperintensity. Individual patient profiles were compared with normative data generated from the healthy controls. Results: Profiling of hippocampal volumetric and qT2 data could be performed automatically and reproducibly. HS patients commonly showed widespread decreases in volume and increases in T2 along the length of the affected hippocampus, and focal changes may also be identified. Patterns of atrophy and T2 increase in the left hippocampus were similar between left, right, and bilateral HS. These profiles have potential to distinguish between sclerosis affecting volume and qT2 in the whole or parts of the hippocampus, and may aid the radiological diagnosis in uncertain cases or cases with subtle or focal abnormalities where standard whole‐hippocampal measurements yield normal values. Significance: Hippocampal profiling of volumetry and qT2 values can help spatially localize hippocampal MRI abnormalities and work toward improved sensitivity of subtle focal lesions

FLAIR-only joint volumetric analysis of brain lesions and atrophy in clinically isolated syndrome (CIS) suggestive of multiple sclerosis

Background: MRI assessment in multiple sclerosis (MS) focuses on the presence of typical white matter (WM) lesions. Neurodegeneration characterised by brain atrophy is recognised in the research field as an important prognostic factor. It is not routinely reported clinically, in part due to difficulty in achieving reproducible measurements. Automated MRI quantification of WM lesions and brain volume could provide important clinical monitoring data. In general, lesion quantification relies on both T1 and FLAIR input images, while tissue volumetry relies on T1. However, T1-weighted scans are not routinely included in the clinical MS protocol, limiting the utility of automated quantification. Objectives: We address an aspect of this important translational challenge by assessing the performance of FLAIR-only lesion and brain segmentation, against a conventional approach requiring multi-contrast acquisition. We explore whether FLAIR-only grey matter (GM) segmentation yields more variability in performance compared with two-channel segmentation; whether this is related to field strength; and whether the results meet a level of clinical acceptability demonstrated by the ability to reproduce established biological associations. Methods: We used a multicentre dataset of subjects with a CIS suggestive of MS scanned at 1.5T and 3T in the same week. WM lesions were manually segmented by two raters, ‘manual 1′ guided by consensus reading of CIS-specific lesions and ‘manual 2′ by any WM hyperintensity. An existing brain segmentation method was adapted for FLAIR-only input. Automated segmentation of WM hyperintensity and brain volumes were performed with conventional (T1/T1 + FLAIR) and FLAIR-only methods. Results: WM lesion volumes were comparable at 1.5T between ‘manual 2′ and FLAIR-only methods and at 3T between ‘manual 2′, T1 + FLAIR and FLAIR-only methods. For cortical GM volume, linear regression measures between conventional and FLAIR-only segmentation were high (1.5T: α = 1.029, R2 = 0.997, standard error (SE) = 0.007; 3T: α = 1.019, R2 = 0.998, SE = 0.006). Age-associated change in cortical GM volume was a significant covariate in both T1 (p = 0.001) and FLAIR-only (p = 0.005) methods, confirming the expected relationship between age and GM volume for FLAIR-only segmentations. Conclusions: FLAIR-only automated segmentation of WM lesions and brain volumes were consistent with results obtained through conventional methods and had the ability to demonstrate biological effects in our study population. Imaging protocol harmonisation and validation with other MS phenotypes could facilitate the integration of automated WM lesion volume and brain atrophy analysis as clinical tools in radiological MS reporting

Ocean circulation and biogeochemistry moderate interannual and decadal surface water pH changes in the Sargasso Sea

© The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geophysical Research Letters 42 (2015): 4931–4939, doi:10.1002/2015GL064431.The oceans absorb anthropogenic CO2 from the atmosphere, lowering surface ocean pH, a concern for calcifying marine organisms. The impact of ocean acidification is challenging to predict as each species appears to respond differently and because our knowledge of natural changes to ocean pH is limited in both time and space. Here we reconstruct 222 years of biennial seawater pH variability in the Sargasso Sea from a brain coral, Diploria labyrinthiformis. Using hydrographic data from the Bermuda Atlantic Time-series Study and the coral-derived pH record, we are able to differentiate pH changes due to surface temperature versus those from ocean circulation and biogeochemical changes. We find that ocean pH does not simply reflect atmospheric CO2 trends but rather that circulation/biogeochemical changes account for >90% of pH variability in the Sargasso Sea and more variability in the last century than would be predicted from anthropogenic uptake of CO2 alone.Funding to N.F.G. was provided by the University of Hong Kong and the National Research Foundation Singapore under its Singapore NRF Fellowship scheme (National Research Fellow Award NRF-RF2012-03), as administered by the Earth Observatory of Singapore and the Singapore Ministry of Education under the Research Centres of Excellence initiative. S.C.D. and K.A.H. acknowledge support from the National Science Foundation and Woods Hole Oceanographic Institution

Natural and anthropogenic forcing of multi-decadal to centennial scale variability of sea surface temperature in the South China Sea

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Goodkin, N. F., Samanta, D., Bolton, A., Ong, M. R., Hoang, P. K., Vo, S. T., Karnauskas, K. B., & Hughen, K. A. Natural and anthropogenic forcing of multi-decadal to centennial scale variability of sea surface temperature in the South China Sea. Paleoceanography and Paleoclimatology, 36(10), (2021): e2021PA004233, https://doi.org/10.1029/2021PA004233.Four hundred years of reconstructed sea surface temperatures (SSTs) from a coral located off the coast of Vietnam show significant multi-decadal to centennial-scale variability in wet and dry seasons. Wet and dry season SST co-vary significantly at multi-decadal timescales, and the Interdecadal Pacific Oscillation (IPO) explains the majority of variability in both seasons. A newly reconstructed wet season IPO index was compared to other IPO reconstructions, showing significant long-term agreement with varying amplitude of negative IPO signals based on geographic location. Dry season SST also correlates to sea level pressure anomalies and the East Asian Winter Monsoon, although with an inverse relationship from established interannual behavior, as previously seen with an ocean circulation proxy from the same coral. Centennial-scale variability in wet and dry season SST shows 300 years of near simultaneous changes, with an abrupt decoupling of the records around 1900, after which the dry season continues a long-term cooling trend while the wet season remains almost constant. Climate model simulations indicate greenhouse gases as the largest contributor to the decoupling of the wet and dry season SSTs and demonstrate increased heat advection to the western South China Sea in the wet season, potentially disrupting the covariance in seasonal SST.This research was supported by a Singapore National Research Fellowship to N.F. Goodkin (NRFF-2012-03) as administered by the Earth Observatory of Singapore and by a Singapore Ministry of Education Academic Research Fund Tier 2 award to N.F. Goodkin, K.A. Hughen, and K.B. Karnauskas (MOE-2016-T2-1-016). D. Samanta was partially supported by a Singapore Ministry of Education Tier 3 award (MOE2019-T3-1-004)

Coral-based proxy calibrations constrain ENSO-driven sea surface temperature and salinity gradients in the Western Pacific Warm Pool

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Mohtar, A. T., Hughen, K. A., Goodkin, N. F., Streanga, I., Ramos, R. D., Samanta, D., Cervino, J., & Switzer, A. D. Coral-based proxy calibrations constrain ENSO-driven sea surface temperature and salinity gradients in the Western Pacific Warm Pool. Palaeogeography Palaeoclimatology Palaeoecology, 561, (2021): 110037, doi:10.1016/j.palaeo.2020.110037.Constraining past variability in ocean conditions in the Western Pacific Warm Pool (WPWP) and examining how it has been influenced by the El-Niño Southern Oscillation (ENSO) is critical to predicting how these systems may change in the future. To characterize the spatiotemporal variability of the WPWP and ENSO during the past three decades, we analyzed climate proxies using coral cores sampled from Porites spp. from Kosrae Island (KOS) and Woleai Atoll (WOL) in the Federated States of Micronesia. Coral skeleton samples drilled along the major growth axis were analyzed for oxygen isotopes (δ18Oc) and trace element ratios (Sr/Ca), used to reconstruct sea surface salinity and temperature (SSS and SST). Pseudocoral δ18O time series (δ18Opseudo) were calculated from gridded instrumental observations and compared to δ18Oc, followed by fine-tuning using coral Sr/Ca and gridded SST, to produce age models for each coral. The thermal component of δ18Oc was removed using Sr/Ca for SST, to derive δ18O of seawater (δ18Osw), a proxy for SSS. The Sr/Ca, and δ18Osw records were compared to instrumental SST and SSS to test their fidelity as regional climate recorders. We found both sites display significant Sr/Ca-SST calibrations at monthly and interannual (dry season, wet season, mean annual) timescales. At each site, δ18Osw also exhibited significant calibrations to SSS across the same timescales. The difference between normalized dry season SST (Sr/Ca) anomalies from KOS and WOL generates a zonal SST gradient (KOSWOLSST), capturing the east-west WPWP migration observed during ENSO events. Similarly, the average of normalized dry season δ18Osw anomalies from both sites produces an SSS index (KOSWOLSSS) reflecting the regional hydrological changes. Both proxy indices, KOSWOLSST and KOSWOLSSS, are significantly correlated to regional ENSO indices. These calibration results highlight the potential for extending the climate record, revealing spatial hydrological gradients within the WPWP and ENSO variability back to the end of the Little Ice Age.We also thank the crew of the M/V Alucia for assistance during the 2012 coral drilling expedition to FSM, funded by the Dalio Family Foundation through a WHOI Access to The Sea grant to KAH (#25110104). Geochemical analysis was funded by Singapore Ministry of Education Academic Research Fund Tier-2 (# MOE2016-T2-1016) to NFG and KAH, and by the WHOI Summer Student Fellowship Program (00450400) and Coastal Preservation Network 501c to IMS

East Asian Monsoon variability since the sixteenth century

Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters, 46(9), (2019):4790-4798, doi:10.1029/2019GL081939.The East Asian Monsoon (EAM) impacts storms, freshwater availability, wind energy production, coal consumption, and subsequent air quality for billions of people across Asia. Despite its importance, the EAM's long‐term behavior is poorly understood. Here we present an annually resolved record of EAM variance from 1584 to 1950 based on radiocarbon content in a coral from the coast of Vietnam. The coral record reveals previously undocumented centennial scale changes in EAM variance during both the summer and winter seasons, with an overall decline from 1600 to the present. Such long‐term variations in monsoon variance appear to reflect independent seasonal mechanisms that are a combination of changes in continental temperature, the strength of the Siberian High, and El Niño–Southern Oscillation behavior. We conclude that the EAM is an important conduit for propagating climate signals from the tropics to higher latitudes.Thanks go to G. Williams, W. Tak‐Cheung, and J. Ossolinski. Thanks also go to V. Lee, S. H. Ng for coral sampling, and B. Buckley for conversations. This research was supported by the National Research Foundation Singapore NRF Fellowship scheme awarded to N. Goodkin (National Research Fellowship award NRFF‐2012‐03) and administered by the Earth Observatory of Singapore and the Singapore Ministry of Education under the Research Centers of Excellence initiative. The research was also supported by the Singapore Ministry of Education Academic Research Fund Tier 2 (award MOE2016‐T2‐1‐016). Data are available in Table S1 and the NOAA paleoclimate database