K. A. Hughen

Woods Hole Oceanographic Institution, Falmouth, Massachusetts, United States

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Publications (141)541.69 Total impact

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    ABSTRACT: Lake Titicaca leaf wax shows South American monsoon variability over past 60 kyr.•Leaf wax well correlated with nearby 19-kyr ice core record.•Central Andes wetter during last glacial period compared to Holocene.•Andean hydrologic changes linked to North Atlantic events during last deglaciation.•Precessional forcing only apparent during Holocene, not last glacial period.
    Earth and Planetary Science Letters 12/2014; 408. · 4.72 Impact Factor
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    ABSTRACT: Global climate change and anthropogenic activities are threatening the future survival of coral reef ecosystems. The ability of reef-building zooxanthellate coral to survive these stressors may be determined through fundamental differences within their symbiotic dinoflagellates (Symbiodinium sp.). We define the in vitro apoptotic response of 2 evolutionarily distant Symbiodinium sp., subtypes B2 and C1, to determine the synergistic effects of disease and temperature on cell viability using flow cytometry. The putative yellow band disease (YBD) consortium of Vibrio spp. bacteria and temperature (33°C) had a positive synergistic effect on C1 apoptosis, while B2 displayed increased apoptosis to elevated temperature (29 and 33°C), the Vibrio consortium, and a lone virulent strain of V. alginolyticus, but no synergistic effects. Additionally, heat shock protein 60 expression revealed differential cell-mediated temperature sensitivity between subtypes via western blotting. This result marks the first evidence of Symbiodinium sp. apoptotic variations to YBD pathogens and emphasizes the potential impact of synergistic stress on globally distributed coral−Symbiodinium symbioses.
    Diseases of Aquatic Organisms 12/2014; 112:149-159. · 1.73 Impact Factor
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    ABSTRACT: Abstract
    Quaternary Science Reviews 12/2014; 105:195-208. · 4.57 Impact Factor
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    ABSTRACT: Paired strontium-to-calcium (Sr/Ca) and δ18O measurements for two Porites lutea corals recovered from Hon Tre Island, Vietnam, are strongly correlated to sea surface temperature (SST) and precipitation at monthly to interannual time-scales. Least squares linear regression of monthly Sr/Ca to SST shows a strong, significant correlation (r2 = 0.77, p < .0001), with root mean square residuals of 0.9 °C. 3-year averaged (binned) Sr/Ca for wet (Sep–Nov) and dry (Jan–Mar) seasons separately captures SST variability at interannual time scales (Sr/Ca RMSR = 0.42 °C and 0.70 °C for wet and dry seasons, respectively). Coral δ18O correlates weakly to SST at seasonal and interannual time scales for wet and dry seasons, with significant anomalies (δ18O RMSR = 2.4 °C and 1.65 °C, respectively). Correcting the SST influence on coral δ18O using paired Sr/Ca values provides estimates of δ18O of seawater (δ18Osw). 3-year averaged δ18Osw during the wet season shows a significant correlation to local precipitation (r2 = 0.54, p = 0.01). These results show that coral Sr/Ca in this location accurately reflects SST at a number of timescales, and that seawater δ18O composition in the wet season is controlled by local precipitation, largely unmodified by ocean circulation during the winter monsoon. This study highlights the sensitivity and utility of coral geochemistry in this region for reliably reconstructing SST and monsoonal precipitation.
    Palaeogeography Palaeoclimatology Palaeoecology 06/2014; 410:233-243. · 2.75 Impact Factor
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    ABSTRACT: As sea surface temperatures rise and the global human population increases, large-scale field observations of marine organism health and water quality are increasingly necessary. We investigated the health of corals from the family Fungiidae using visual observations in relation to water quality and microbial biogeochemistry parameters along 1300 km of the Red Sea coast of Saudi Arabia. At large scales, incidence of lesions caused by unidentified etiology showed consistent signs, increasing significantly from the northern to southern coast and positively correlated to annual mean seawater temperatures. Lesion abundance also increased to a maximum of 96% near the populous city of Jeddah. The presence of lesioned corals in the region surrounding Jeddah was strongly correlated with elevated concentrations of ammonium and changes in microbial communities that are linked to decreased water quality. This study suggests that both high seawater temperatures and nutrient pollution may play an indirect role in the formation of lesions on corals.
    Marine Environmental Research. 01/2014;
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    Timothy J Heaton, Konrad A Hughen, Edouard Bard
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    ABSTRACT: We consider a general methodology for the transferral of chronologies from a master reference record contain-ing direct dating information to an undated record of interest that does not. Transferral is achieved through the identification, by an expert, of a series of tie-points within both records that are believed to correspond to approximately contemporaneous events. Through tying of the 2 records together at these points, the reference chronology is elastically deformed onto the undated record. The method consists of 3 steps: creation of an age-depth model for the reference record using its direct dating information; selection of the tie-points and translation of their age estimates from the reference to the undated record; and finally, creation of an age-depth model for the undated record using these uncertain tie-point age estimates. Our method takes full account of the uncertainties involved in all stages of the process to create a final chronology within the undated record that allows joint age estimates to be found together with their credible intervals. To achieve computational practicality, we employ a Gaussian process to create our age-depth models. Calculations can then be performed exactly without resort to extremely slow Monte Carlo methods involving multiple independent model fits that would be required by other age-depth models.
    Radiocarbon 11/2013; 55(4):1975-1997. · 1.07 Impact Factor
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    ABSTRACT: Geological records of past sea ice, such as those contained in Arctic marine sediments, offer an opportunity to strengthen our understanding of long-term sea ice variability, provided unambiguous paleo-sea ice proxies can be developed. One such recently proposed proxy is IP25, a highly branched isoprenoid alkene biosynthesized exclusively by sea-ice dwelling diatoms (Haslea spp.), which is well preserved in marine sediments and could be used to reconstruct past changes in spring sea-ice extent. However, little is known about regional-scale controls on IP25 production in sea ice, limiting its wider applicability as a paleo-sea-ice proxy. To address this issue we examined the distributions of IP25 and the marine productivity biomarkers dinosterol and brassicasterol in a suite of surface sediment samples distributed across the Arctic. We find a statistically significant, logarithmic relationship between IP25 and spring sea ice cover in sediment samples from arctic and subarctic sites in the Pacific (n = 96, R2 = 0.67, P < 0.0001) and the Atlantic n = 25, R2 = 0.50, P < 0.0001), though the absolute concentrations of IP25 are generally higher in the Atlantic (1.6-166.4 μg/g OC) than in the Pacific (0-38.5 μg/g OC) for equivalent sea-ice cover, and there are regional and basin-specific differences in the slope of the IP25 - sea ice relationship. Using the PDIP25 index, which also includes a biomarker for marine productivity (e.g., dinosterol) the relationship with sea ice cover is improved in all of the study areas (R2 = 0.86 and R2 = 0.75 for Atlantic and Pacific, respectively) and most basin specific differences in the proxy-sea ice relationships are significantly reduced. However, there remain differences in the absolute magnitudes of the PDIP25 index for equivalent amounts of sea ice cover between the Atlantic and the Pacific, and with previously published data from Fram Strait. Nevertheless, this work demonstrates that the PDIP25 index can provide a valuable tool for sea ice reconstructions at local and regional scales.
    Quaternary Science Reviews 11/2013; · 4.57 Impact Factor
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    ABSTRACT: High-quality data from appropriate archives are needed for the continuing improvement of radiocarbon cali- bration curves. We discuss here the basic assumptions behind 14C dating that necessitate calibration and the relative strengths and weaknesses of archives from which calibration data are obtained. We also highlight the procedures, problems, and uncertainties involved in determining atmospheric and surface ocean 14C/12C in these archives, including a discussion of the various methods used to derive an independent absolute timescale and uncertainty. The types of data required for the current IntCal database and calibration curve model are tabulated with examples.
    Radiocarbon 11/2013; 55(4):1923-1945. · 1.07 Impact Factor
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    ABSTRACT: Understanding the causes and potential ecological and environmental impacts of recent and future temperature changes in the Arctic requires a better understanding of long term climate variability. Amongst the most promising new geochemical tools for sedimentary paleotemperature reconstructions are those based on the glycerol diakyl glycerol tetraethers (GDGTs). Although a number of studies have recently developed empirical calibrations for the temperature sensitivity of isoprenoid GDGTs (i.e., the TEX86 index) and the branched GDGTs (i.e., the MBT/CBT index) in mid and low latitude lakes, there is very little data from lakes in the Arctic. Here, we examine the temperature and environmental controls on GDGT abundances in a transect of small lakes (n = 59) distributed across Baffin Island in the eastern Canadian Arctic. Isoprenoid and branched GDGTs are ubiquitous in these lakes. The temperature control on the isoprenoid GDGT distributions is weak, although there is a significant relationship between the branched GDGT distributions and warm season temperature. Furthermore, published relationships developed between branched GDGTs and mean annual air temperatures in tropical lakes yield reconstructed temperatures from Arctic lakes that are consistent with Arctic summer air temperature. This suggests that empirical calibrations from branched GDGTs in lakes reflect the seasonality of branched GDGT production. For example, at low latitudes there is little seasonality in temperature, and branched GDGT production records air temperatures throughout the year. In the Arctic however, branched GDGTs are likely produced in summer, when the temperatures are warmest, sunlight hours are greatest and ice cover is diminished. Due to the extreme seasonality and short window of Arctic productivity, the use of branched GDGTs for summer paleotemperature reconstructions likely remains robust back through time. However, interpretations of paleotemperatures from branched GDGTs in temperate lakes may require careful consideration about potential changes in the seasonal timing of branched GDGT production.
    Organic Geochemistry 11/2013; 64:119–128. · 2.52 Impact Factor
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    ABSTRACT: The hydrogen isotope composition of plant waxes preserved in lacustrine sediments is a potentially valuable tool for reconstructing paleoenvironmental changes in the Arctic. However, in contrast to the mid- and low-latitudes, significantly less effort has been directed towards understanding the factors controlling D/H fractionation in high latitude plant waxes and the impact of these processes on the interpretation of sedimentary leaf wax δD records. To better understand these processes, we examined the D/H ratios of long chain fatty acids in lake surface sediments spanning a temperature and precipitation gradient on Baffin Island in the eastern Canadian Arctic. D/H ratios of plant waxes increase with increasing temperature and aridity, with values ranging from -240‰ to -160‰ over the study area. Apparent fractionation factors between n-alkanoic acids in Arctic lake sediments and precipitation(ɛFA-ppt) are less negative than those of mid-latitude lakes and modern plants by 25‰ to 65‰, consistent with n-alkane data from modern Arctic plants (Yang et al., 2011). Furthermore, ɛFA-ppt values from Arctic lakes become systematically more positive with increasing evaporation, in contrast to mid-latitude sites, which show little to no change in fractionation with aridity. These data are consistent with enhanced water loss and isotope fractionation at higher latitude in the Arctic summer, when continuous sunlight supports increased daily photosynthesis. The dominant control on δDFA variations on Baffin Island is temperature. However, changing ɛFA-ppt result in steeper δDFA-temperature relationships than observed for modern precipitation. The application of this δDFA-based paleotemperature calibration to existing δDFA records from Baffin Island produces much more realistic changes in late Holocene temperature and highlights the importance of these effects in influencing the interpretation of Arctic δDFA records. A better understanding of the controls on hydrogen isotope fractionation in high latitude leaf waxes will be essential to the proper interpretation of isotope records from sedimentary plant waxes in the Arctic.
    Geochimica et Cosmochimica Acta 10/2013; 119:286 - 301. · 3.88 Impact Factor
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    ABSTRACT: The Sr/Ca ratio of coral aragonite is used to reconstruct past sea surface temperature (SST). Twenty-one laboratories took part in an interlaboratory study of coral Sr/Ca measurements. Results show interlaboratory bias can be significant, and in the extreme case could result in a range in SST estimates of 7° C. However, most of the data fall within a narrower range and the Porites coral reference material JCp- 1 is now characterized well enough to have a certified Sr/Ca value of 8.838 mmol/mol with an expanded uncertainty of 0.089 mmol/mol following International Association of Geoanalysts (IAG) guidelines. This uncertainty, at the 95% confidence level, equates to 1.5 °C for SST estimates using Porites, so is approaching fitness for purpose. The comparable median within laboratory error is <0.5 °C. This difference in uncertainties illustrates the interlaboratory bias component that should be reduced through the use of reference materials like the JCp-1. There are many potential sources contributing to biases in comparative methods but traces of Sr in Ca standards and uncertainties in reference solution composition can account for half of the combined uncertainty. Consensus values that fulfil the requirements to be certified values were also obtained for Mg/Ca in JCp-1 and for Sr/Ca and Mg/Ca ratios in the JCt-1 giant clam reference material. Reference values with variable fitness for purpose have also been obtained for Li/Ca, B/Ca, Ba/Ca, and U/Ca in both reference materials. In future, studies reporting coral element/Ca data should also report the average value obtained for a reference material such as the JCp-1.
    Geochemistry Geophysics Geosystems 09/2013; 14:3730-3750. · 2.94 Impact Factor
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    ABSTRACT: 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.
    Marine Chemistry 08/2013; 154:55–66. · 3.00 Impact Factor
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    ABSTRACT: Endozoicomonas bacteria were found highly associated with the coral Stylophora pistillata, and these bacteria are also ubiquitously associated with diverse corals worldwide. Novel Endozoicomonas-specific probes revealed that Endozoicomonas bacteria were abundant in the endodermal tissues of S. pistillata and appear to have an intimate relationship with the coral.
    Applied and Environmental Microbiology 05/2013; 79(15):4759. · 3.95 Impact Factor
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    ABSTRACT: During the last glacial period, the North Atlantic regionexperienced pronounced, millennial-scale alternations between cold, stadial conditions and milder interstadial conditions--commonly referred to as Dansgaard-Oeschger oscillations--as well as periods of massive iceberg discharge known as Heinrich events. Changes in Northern Hemisphere temperature, as recorded in Greenland, are thought to have affected the location of the Atlantic intertropical convergence zone and the strength of the Indian summer monsoon. Here we use high-resolution records of sediment colour--a measure of terrigenous versus biogenic content--from the Cariaco Basin off the coast of Venezuela and the Arabian Sea to assess teleconnections with the North Atlantic climate system during the last glacial period. The Cariaco record indicates that the intertropical convergence zone migrated seasonally over the site during mild stadial conditions, but was permanently displaced south of the basin during peak stadials and Heinrich events. In the Arabian Sea, we find evidence of a weak Indian summer monsoon during the stadial events. The tropical records show a more variable response to North Atlantic cooling than the Greenland temperature records. We therefore suggest that Greenland climate is especially sensitive to variations in the North Atlantic system--in particular sea-ice extent--whereas the intertropical convergence zone and Indian monsoon system respond primarily to variations in mean Northern Hemisphere temperature.
    Nature Geoscience 03/2013; 6(3):213-217. · 11.67 Impact Factor
  • Amy Apprill, Konrad Hughen, Tracy Mincer
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    ABSTRACT: Cultivation-based studies have demonstrated that yellow-band disease (YBD), a lesion-producing ailment affecting diverse species of coral, is caused by a consortium of Vibrio spp. This study takes the first cultivation-independent approach to examine the whole bacterial community associated with YBD-like lesioned corals. Two species of Fungiidae corals, Ctenactis crassa and Herpolitha limax, displaying YBD-like lesions were examined across diverse reefs throughout the Red Sea. Using a pyrosequencing approach targeting the V1-V3 regions of the SSU rRNA gene, no major differences in bacterial community composition or diversity were identified between healthy and lesioned corals of either species. Indicator species analysis did not find Vibrio significantly associated with the lesioned corals. However, operational taxonomic units belonging to the Ruegeria genus of Alphaproteobacteria and NS9 marine group of Flavobacteria were significantly associated with the lesioned corals. The most striking trend of this dataset was that reef location was found to be the most significant influence on the coral-bacterial community. It is possible that more pronounced lesion-specific bacterial signatures might have been concealed by the strong influence of environmental conditions on coral-bacteria. Overall, this study demonstrates inconsistencies between cultivation-independent and cultivation-based studies regarding the role of specific bacteria in coral diseases.
    Environmental Microbiology 02/2013; · 6.24 Impact Factor

Publication Stats

5k Citations
541.69 Total Impact Points

Institutions

  • 2000–2014
    • Woods Hole Oceanographic Institution
      • Department of Marine Chemistry and Geochemistry
      Falmouth, Massachusetts, United States
  • 2011
    • National Cheng Kung University
      • Department of Earth Sciences
      Tainan, Taiwan, Taiwan
  • 2008
    • University of Illinois, Urbana-Champaign
      Urbana, Illinois, United States
  • 2003
    • University of California, Santa Barbara
      • Marine Science Institute
      Santa Barbara, CA, United States
  • 2001
    • University of Miami
      • Rosenstiel School of Marine and Atmospheric Science
      Coral Gables, FL, United States
    • ETH Zurich
      • Department of Earth Sciences
      Zürich, ZH, Switzerland
    • Universität Bern
      • Physikalisches Institut
      Bern, BE, Switzerland
  • 1999–2001
    • Harvard University
      • Department of Earth and Planetary Sciences
      Cambridge, Massachusetts, United States