Table of Contents, Volume 10, 2012

January

Eneko Bachiller, Jose Antonio Fernandes, Xabier Irigoien
Improving semiautomated zooplankton classification using an internal control and different imaging devices
2012, 10:1-9
Abstract | PDF

Adrian M. Bass, Michael I. Bird, Marshall J. Morrison, Jeremy Gordon
CADICA: Continuous Automated Dissolved Inorganic Carbon Analyzer with application to aquatic carbon cycle science
2012, 10:10-19
Abstract | PDF

Ryan D. Batt, Stephen R. Carpenter
Free-water lake metabolism: addressing noisy time series with a Kalman filter
2012, 10:20-30
Abstract | PDF

Tomas Feseker, Gero Wetzel, Bernd Heesemann
Introducing the T-Stick: A new device for high precision in situ sediment temperature profile measurements
2012, 10:31-40
Abstract | PDF

Heidi R. Mack, Joseph D. Conroy, Karen A. Blocksom, Roy A. Stein, Stuart A. Ludsin
A comparative analysis of zooplankton field collection and sample enumeration methods
2012, 10:41-53
Abstract | PDF

Lindsay P. Scheef, Daniel E. Pendleton, Stephanie E. Hampton, Stephen L. Katz, Elizabeth E. Holmes, Mark D. Scheuerell, David G. Johns
Assessing marine plankton community structure from long-term monitoring data with multivariate autoregressive (MAR) models: a comparison of fixed station versus spatially distributed sampling data
2012, 10:54-64
Abstract | PDF

A.L. Forrest, M.E. Wittmann, V. Schmidt, N.A. Raineault, A. Hamilton, W. Pike, S.G. Schladow, J.E. Reuter, B.E. Laval, A.C. Trembanis
Quantitative assessment of invasive species in lacustrine environments through benthic imagery analysis
2012, 10:65-74
Abstract | PDF

February

Danny C. P. Lau, Kenneth M. Y. Leung, David Dudgeon
Preservation effects on C/N ratios and stable isotope signatures of freshwater fishes and benthic macroinvertebrates
2012, 10:75-89
Abstract | PDF

Intercalibration Special Issue Article
Carl H. Lamborg, Chad R. Hammerschmidt, Gary A. Gill, Robert P. Mason, Susan Gichuki
An intercomparison of procedures for the determination of total mercury in seawater and recommendations regarding mercury speciation during GEOTRACES cruises
2012, 10:90-100
Abstract | PDF (Open Access)

Torsten Mayr, Birgit Ungerböck, Günter Mistlberger, Sergey M. Borisov, Ingo Klimant
A simple method to reduce optical cross-talk effects in chemical imaging with planar optodes
2012, 10:101-109
Abstract | PDF

March

Brittany E. Huntington, Diego Lirman
Coral species richness estimates are sensitive to differences in reef size and regional diversity
2012, 10:110-116
Abstract | PDF

Ryan J. Bell, William B. Savidge, Strawn K. Toler, Robert H. Byrne, R. Timothy Short
In situ determination of porewater gases by underwater flow-through membrane inlet mass spectrometry
2012, 10:117-128
Abstract | PDF

Richard A. Wildman Jr., Markus Huettel
Acoustic detection of gas bubbles in saturated sands at high spatial and temporal resolution
2012, 10:129-141
Abstract | PDF (Open Access)

Kevin Oxborough, C. Mark Moore, David J. Suggett, Tracy Lawson, Hoi Ga Chan, Richard J. Geider
Direct estimation of functional PSII reaction center concentration and PSII electron flux on a volume basis: a new approach to the analysis of Fast Repetition Rate fluorometry (FRRf) data
2012, 10:142-154
Abstract | PDF (Open Access)

Xavier Mari, Emma Rochelle-Newall, Jean-Pascal Torréton, Olivier Pringault, Yvan Bettarel, Chiaki Motegi, and Markus G. Weinbauer
Production of individual marine organic aggregates using Paramagnetic Microspheres: A new tool for examining microbial associations with aggregates
2012, 10:155-166
Abstract | PDF (Open Access)

Matheus C. Carvalho, Bradley D. Eyre
Measurement of planktonic CO2 respiration in the light
2012, 10:167-178
Abstract | PDF

April

Intercalibration Special Issue Article
Robert F. Anderson, Martin Q. Fleisher, Laura F. Robinson, R. Lawrence Edwards, John A. Hoff, S. Bradley Moran, Michiel Rutgers van der Loeff, Alexander L. Thomas, Matthieu Roy-Barman, Roger Francois
GEOTRACES intercalibration of 230Th, 232Th, 231Pa, and prospects for 10Be
2012, 10:179-213
Abstract | PDF (Open Access)

Stefan G.H. Simis, Hanna M. Kauko
In vivo mass-specific absorption spectra of phycobilipigments through selective bleaching
2012, 10:214-226
Abstract | PDF (Open Access)

Bente Aa. Lomstein, Bo Barker Jørgensen
Pre-column liquid chromatographic determination of dipicolinic acid from bacterial endospores
2012, 10:227-233
Abstract | PDF

Intercalibration Special Issue Article
Tina van de Flierdt, Katharina Pahnke, GEOTRACES intercalibration participants: Hiroshi Amakawa, Per Andersson, Chandranath Basak, Barry Coles, Christophe Colin, Kirsty Crocket, Martin Frank, Norbert Frank, Steven L. Goldstein, Vineet Goswami, Brian A. Haley, Ed C. Hathorne, Sidney R. Hemming, Gideon M. Henderson, Catherine Jeandel, Kevin Jones, Katharina Kreissig, Francois Lacan, Myriam Lambelet, Ellen E. Martin, Derrick R. Newkirk, Haijme Obata, Leopoldo Pena, Alexander M. Piotrowski, Catherine Pradoux, Howie D. Scher, Hans Schöberg, Sunil Kumar Singh,Torben Stichel, Hirofumi Tazoe, Derek Vance, Jingjing Yang
GEOTRACES intercalibration of neodymium isotopes and rare earth element concentrations in seawater and suspended particles. Part 1: reproducibility of results for the international intercomparison
2012, 10:234-251
Abstract | PDF (Open Access)

Intercalibration Special Issue Article
Katharina Pahnke, Tina van de Flierdt, Kevin M. Jones, Myriam Lambelet, Sidney R. Hemming, Steven L. Goldstein
GEOTRACES intercalibration of neodymium isotopes and rare earth element concentrations in seawater and suspended particles. Part 2: Systematic tests and baseline profiles
2012, 10:252-269
Abstract | PDF (Open Access)

Intercalibration Special Issue Article
C. M. Zurbrick, P. L. Morton, C. Gallon, A. M. Shiller, W.M. Landing, A.R. Flegal
Intercalibration of Cd and Pb concentration measurements in the northwest Pacific Ocean
2012, 10:270-277
Abstract | PDF (Open Access)

Emily A. Moberg, Heidi M. Sosik
Distance maps to estimate cell volume from two-dimensional plankton images
2012, 10:278-288
Abstract | PDF (Open Access)

May

Catherine McGavigan
A quantitative method for sampling littoral zooplankton in lakes: The Active Tube
2012, 10:289-295
Abstract | PDF (Open Access)

Intercalibration Special Issue Article
Per S. Andersson, Hans Schöberg
Determination of 232Th and 230Th in seawater using a chemical separation procedure and thermal ionization mass spectrometry
2012, 10:296-303
Abstract | PDF (Open Access)

Lindsay Chipman, Markus Huettel, Peter Berg, Volker Meyer, Ingo Klimant, Ronnie Glud, Frank Wenzhoefer
Oxygen optodes as fast sensors for eddy correlation measurements in aquatic systems
2012, 10:304-316
Abstract | PDF (Open Access)

Torben Gentz, Michael Schlüter
Underwater cryotrap-membrane inlet system (CT-MIS) for improved in situ analysis of gases
2012, 10:317-328
Abstract | PDF

Andrew M. P. McDonnell, Ken O. Buesseler
A new method for the estimation of sinking particle fluxes from measurements of the particle size distribution, average sinking velocity, and carbon content
2012, 10:329-346
Abstract | PDF

Aron Stubbins, Thorsten Dittmar
Low volume quantification of dissolved organic carbon and dissolved nitrogen
2012, 10:347-352
Abstract | PDF

Eli K. Moore, Brook L. Nunn, Jessica F. Faux, David R. Goodlett, H. Rodger Harvey
Evaluation of electrophoretic protein extraction and database-driven protein identification from marine sediments
2012, 10:353-366
Abstract | PDF

Intercalibration Special Issue Article
Hélène Planquette, Robert M. Sherrell
Sampling for particulate trace element determination using water sampling bottles: methodology and comparison to in situ pumps
2012, 10:367-388
Abstract | PDF (Open Access)

Henrik Stahl, Kent W. Warnken, Lukasz Sochaczewski, Ronnie N. Glud, William Davison, Hao Zhang
A combined sensor for simultaneous high resolution 2-D imaging of oxygen and trace metals fluxes
2012, 10:389-401
Abstract | PDF (Open Access)

June

Ryan Alexander, Peter Gikuma-Njuru, Jörg Imberger
Identifying spatial structure in phytoplankton communities using multi-wavelength fluorescence spectral data and principal component analysis
2012, 10:402-415
Abstract | PDF

Matthew H. Long, Jennie E. Rheuban, Peter Berg, Joseph C. Zieman
A comparison and correction of light intensity loggers to photosynthetically active radiation sensors
2012, 10:416-424
Abstract | PDF (Open Access)

Intercalibration Special Issue Article
Gregory A. Cutter, Kenneth W. Bruland
Rapid and noncontaminating sampling system for trace elements in global ocean surveys
2012, 10:425-436
Abstract | PDF (Open Access)

Intercalibration Special Issue Article
Jessica N. Fitzsimmons, Edward A. Boyle
An intercalibration between the GEOTRACES GO-FLO and the MITESS/Vanes sampling systems for dissolved iron concentration analyses (and a closer look at adsorption effects)
2012, 10:437-450
Abstract | PDF (Open Access)

Intercalibration Special Issue Article
Matthew A. Charette, Henrieta Dulaiova, Meagan E. Gonneea, Paul B. Henderson, Willard S. Moore, Jan C. Scholten, M.K. Pham
GEOTRACES radium isotopes interlaboratory comparison experiment
2012, 10:451-463
Abstract | PDF | Erratum

July

Intercalibration Special Issue Article
Maureen E. Auro, Laura F. Robinson, Andrea Burke, Louisa I. Bradtmiller, Martin Q. Fleisher, Robert F.Anderson
Improvements to 232-thorium, 230-thorium, and 231-protactinium analysis in seawater arising from GEOTRACES intercalibration
2012, 10:464-474
Abstract | PDF (Open Access)

Helmut Maske, José Ochoa, César Almeda Jáureguí, Andrés Carrasco Avendaño
Free-rising, tethered CTD profiler: increased vertical resolution and near surface profiling
2012, 10:475-482
Abstract | PDF

Xiaogang Xing, Hervé Claustre, Stéphane Blain, Fabrizio D?Ortenzio, David Antoine, Josephine Ras, Christophe Guinet
Quenching correction for in vivo chlorophyll fluorescence acquired by autonomous platforms: A case study with instrumented elephant seals in the Kerguelen region (Southern Ocean)
2012, 10:483-495
Abstract | PDF

Intercalibration Special Issue Article
Kristen N. Buck, James Moffett, Katherine A. Barbeau, Randelle M. Bundy, Yoshiko Kondo, Jingfeng Wu
The organic complexation of iron and copper: an intercomparison of competitive ligand exchange?adsorptive cathodic stripping voltammetry (CLE-ACSV) techniques
2012, 10:496-515
Abstract | PDF (Open Access)

Gustavo Fonseca, Karin H. Fehlauer-Ale
Three in one: fixing marine nematodes for ecological, molecular, and morphological studies
2012, 10:516-523
Abstract | PDF  

Hannes K. Imhof, Johannes Schmid, Reinhard Niessner, Natalia P. Ivleva, Christian Laforsch
A novel, highly efficient method for the separation and quantification of plastic particles in sediments of aquatic environments
2012, 10:524-537
Abstract | PDF

Christine M. Thompson, Matthew P. Hare, Scott M. Gallager
Semi-automated image analysis for the identification of bivalve larvae from a Cape Cod estuary
2012, 10:538-554
Abstract | PDF

Kunshan Gao, Juntian Xu, Yangqiao Zheng, Caihuan Ke
Measurement of benthic photosynthesis and calcification in flowing-through seawater with stable carbonate chemistry
2012, 10:555-559
Abstract | PDF

Armando Sepulveda-Jauregui, Karla Martinez-Cruz, Amy Strohm, Katey M. Walter Anthony, Frédéric Thalasso
A new method for field measurement of dissolved methane in water using infrared tunable diode laser absorption spectroscopy
2012, 10:560-567
Abstract | PDF

August

Intercalibration Special Issue Article
Louise Aastrup Zimmer, Gregory A. Cutter
High resolution determination of nanomolar concentrations of dissolved reactive phosphate in ocean surface waters using long path liquid waveguide capillary cells (LWCC) and spectrometric detection
2012, 10:568-580
Abstract | PDF (Open Access)

Thomas Brey
A multi-parameter artificial neural network model to estimate macrobenthic invertebrate productivity and production
2012, 10:581-589
Abstract | PDF

Intercalibration Special Issue Article
Timothy C. Kenna, Pere Masqué, José Luís Mas, Patricia Camara-Mor, Elena Chamizo, Jan Scholten, Mats Eriksson, Joan-Albert Sanchez-Cabeza, Janine Gastaud, Isabelle Levy, Jürgen Herrmann, Patric Lindahl, Gi-Hoon Hong, Sven Nielsen
Intercalibration of selected anthropogenic radionuclides for the GEOTRACES Program
2012, 10:590-607
Abstract | PDF (Open Access)

Qinghui Huang, Karl Kaiser, Ronald Benner
A simple high performance liquid chromatography method for the measurement of nucleobases and the RNA and DNA content of cellular material
2012, 10:608-616
Abstract | PDF (Open Access)

Matthew A. Charette, Henrieta Dulaiova, Meagan E. Gonneea, Paul B. Henderson, Willard S. Moore, Jan C. Scholten, M.K. Pham
Erratum: GEOTRACES radium isotopes interlaboratory comparison experiment
2012, 10:617
PDF (Open Access)

September

Intercalibration Special Issue Article
Mukul Sharma, Cynthia Chen, Tim Blazina
Osmium contamination of seawater samples stored in polyethylene bottles
2012, 10:618-630
Abstract | PDF (Open Access)

Intercalibration Special Issue Article
Kanchan Maiti, Ken O. Buesseler, Steven M. Pike, Claudia Benitez-Nelson, Pinghe Cai, Weifang Chen, Kirk Cochran, Minhan Dai, Frank Dehairs, Beat Gasser, Roger P. Kelly, Pere Masque, Lisa A. Miller, Juan Carlos Miquel, S. Bradley Moran, Paul J. Morris, Florian Peine, Frederic Planchon, Alisha A. Renfro, Michiel Rutgers van der Loeff, Peter H. Santschi, Robert Turnewitsch, James T. Waples, Chen Xu
Intercalibration studies of short-lived thorium-234 in the water column and marine particles
2012, 10:631-644
Abstract | PDF (Open Access)

Greg M. Silsbe, Jacco C. Kromkamp
Modeling the irradiance dependency of the quantum efficiency of photosynthesis
2012, 10:645-652
Abstract | PDF

Intercalibration Special Issue Article
Edward A. Boyle, Seth John, Wafa Abouchami, Jess F. Adkins, Yolanda Echegoyen-Sanz, Michael Ellwood, A. Russell Flegal, Kyrstin Fornace, Celine Gallon, Steve Galer, Melanie Gault-Ringold, Francois Lacan, Amandine Radic, Mark Rehkamper, Olivier Rouxel, Yoshiki Sohrin, Claudine Stirling, Claire Thompson, Derek Vance, Zichen Xue, Ye Zhao
GEOTRACES IC1 (BATS) contamination-prone trace element isotopes Cd, Fe, Pb, Zn, Cu, and Mo intercalibration
2012, 10:653-665
Abstract | PDF (Open Access)

Mariona Segura-Noguera, Dolors Blasco, José-Manuel Fortuño
An improved energy-dispersive X-ray microanalysis method for analyzing simultaneously carbon, nitrogen, oxygen, phosphorus, sulfur, and other cation and anion concentrations in single natural marine microplankton cells
2012, 10:666-680
Abstract | PDF

Intercalibration Special Issue Article
James K.B. Bishop, Phoebe J. Lam, Todd J. Wood
Getting good particles: Accurate sampling of particles by large volume in-situ filtration
2012, 10:681-710
Abstract | PDF (Open Access)

Wei-Jen Huang, Yongchen Wang, Wei-Jun Cai
Assessment of sample storage techniques for total alkalinity and dissolved inorganic carbon in seawater
2012, 10:711-717
Abstract | PDF (Open Access)

Laurence Lin, J. R. Webster
Sensitivity analysis of a pulse nutrient addition technique for estimating nutrient uptake in large streams
2012, 10:718-727
Abstract | PDF

October

Masaya Shinki, Magnus Wendeberg, Svein Vagle, Jay T. Cullen, Dennis K. Hore
Characterization of adsorbed microlayer thickness on an oceanic glass plate sampler
2012, 10:728-735
Abstract | PDF

Greg. M. Silsbe, Robert E. Hecky, Ralph E.H. Smith
Improved estimation of carbon fixation rates from active flourometry using spectral fluorescence in light-limited environments
2012, 10:736-751
Abstract | PDF

M. Becker, N. Andersen, B. Fiedler, P. Fietzek, A. Körtzinger, T. Steinhoff, G. Friedrichs
Using cavity ringdown spectroscopy for continuous monitoring of d13C(CO2) and ?CO2 in the surface ocean
2012, 10:752-766
Abstract | PDF

Bryan D. Downing, Brian A. Pellerin, Brian A. Bergamaschi, John Franco Saraceno, Tamara E.C. Kraus
Seeing the light: The effects of particles, dissolved materials, and temperature on in situ measurements of DOM fluorescence in rivers and streams
2012, 10:767-775
Abstract | PDF (Open Access)

Intercalibration Special Issue Article
Thomas Church, Sylvain Rigaud, Mark Baskaran, Anupam Kumar, Jana Friedrich, Pere Masque, Viena Puigcorbé, Guebuem Kim, Olivier Radakovitch, Gi Hong, Hiu Choi, Gillian Stewart
Intercalibration studies of 210Po and 210Pb in dissolved and particulate seawater samples
2012, 10:776-789
Abstract | PDF (Open Access)

Intercalibration Special Issue Article
Clifton S. Buck, Adina Paytan
Evaluation of commonly used filter substrates for the measurement of aerosol trace element solubility
2012, 10:790-806
Abstract | PDF (Open Access)

Michel Lunven, Jose Maria Landeira, Michel LehaĆ®tre, Raffaele Siano, Christian Podeur, Marie Madeleine Daniélou, Erwan Le Gall, Patrick Gentien, Marc Sourisseau
In situ video and fluorescence analysis (VFA) of marine particles: applications to phytoplankton ecological studies
2012, 10:807-823
Abstract | PDF (Open Access)

November

Iris E. Hendriks, Salud Deudero, Giacomo Tavecchia
Recapture probability underwater: predicting the detection of the threatened noble pen shell in seagrass meadows
2012, 10:824-831
Abstract | PDF

Tomas Remenyi, Pavel Nesterenko, Andrew Bowie, Edward Butler, Paul Haddad
Reversed phase high performance liquid chromatographic determination of dissolved aluminium in open ocean seawater
2012, 10:832-839
Abstract | PDF (Open Access)

Daniel G. Boyce, Marlon Lewis, Boris Worm
Integrating global chlorophyll data from 1890 to 2010
2012, 10:840-852
Abstract | PDF

Rich Pawlowicz, Rainer Feistel
Limnological applications of the Thermodynamic Equation of Seawater 2010 (TEOS-10)
2012, 10:853-867
Abstract | PDF

Darcy A.A. Taniguchi, Peter J.S. Franks, Michael R. Landry
Estimating size-dependent growth and grazing rates and their associated errors using the dilution method
2012, 10:868-881
Abstract | PDF

Sarah A. Spaulding, David H. Jewson, Rebecca J. Bixby, Harry Nelson, Diane M. McKnight
Automated measurement of diatom size
2012, 10:882-890
Abstract | PDF (Open Access)

Stephanie J. Christensen, Thomas K. Hemscheidt, Henry Trapido-Rosenthal, Edward A. Laws, Robert R. Bidigare
Detection and quantification of β-methylamino-L-alanine in aquatic invertebrates
2012, 10:891-898
Abstract | PDF (Open Access)

Cherisse Du Preez, Verena Tunnicliffe
A new video survey method of microtopographic laser scanning (MiLS) to measure small-scale seafloor bottom roughness
2012, 10:899-909
Abstract | PDF (Open Access)

Jason R. Graff, Allen J. Milligan, Michael J. Behrenfeld
The measurement of phytoplankton biomass using flow-cytometric sorting and elemental analysis of carbon
2012, 10:910-920
Abstract | PDF (Open Access)

Henry C. Bittig, Björn Fiedler, Tobias Steinhoff, Arne Körtzinger
A novel electrochemical calibration setup for oxygen sensors and its use for the stability assessment of Aanderaa optodes
2012, 10:921-933
Abstract | PDF (Open Access)

Yanwu Zhang, John P. Ryan, James G. Bellingham, Julio B. J. Harvey, Robert S. McEwen
Autonomous detection and sampling of water types and fronts in a coastal upwelling system by an autonomous underwater vehicle
2012, 10:934-951
Abstract | PDF (Open Access)

R. Blaine McCleskey, D. Kirk Nordstrom, Joseph N. Ryan
Comparison of electrical conductivity calculation methods for natural waters
2012, 10:952-967
Abstract | PDF (Open Access)

December

Clinton A. Oakley, Brian M. Hopkinson, Gregory W. Schmidt
A modular system for the measurement of CO2 and O2 gas flux and photosynthetic electron transport in microalgae
2012, 10:968-977
Abstract | PDF

Chee-Loon Ng, Schuyler Senft-Grupp, Harold F. Hemond
A multi-platform optical sensor for in situ sensing of water chemistry
2012, 10:978-990
Abstract | PDF

Rick Hennekam, Gert de Lange
X-ray fluorescence core scanning of wet marine sediments: methods to improve quality and reproducibility of high-resolution paleoenvironmental records
2012, 10:991-1003
Abstract | PDF (Open Access)

Elizabeth Ryder, Eleanor Jennings, Elvira de Eyto, Mary Dillane, Caitriona NicAonghusa, Donald C. Pierson, Karen Moore, Martin Rouen, Russell Poole
Temperature quenching of CDOM fluorescence sensors: temporal and spatial variability in the temperature response and a recommended temperature correction equation
2012, 10:1004-1010
Abstract | PDF

Griet Neukermans, Kevin Ruddick, Hubert Loisel, Patrick Roose
Optimization and quality control of suspended particulate matter concentration measurement using turbidity measurements
2012, 10:1011-1023
Abstract | PDF (Open Access)

Robert van Geldern, Johannes A.C. Barth
Optimization of instrument setup and post-run corrections for oxygen and hydrogen stable isotope measurements of water by isotope ratio infrared spectroscopy (IRIS)
2012, 10:1024-1036
Abstract | PDF (Open Access)

Charles Verpoorter, Tiit Kutser, Lars Tranvik
Automated mapping of water bodies using Landsat multispectral data
2012, 10:1037-1050
Abstract | PDF (Open Access)

Diego A. Ibarra, Allan Cembella, Jon Grant
Attenuation of sunlight measured from moored radiometers to assess depletion of suspended particles caused by bivalve aquaculture
2012, 10:1051-1069
Abstract | PDF

Peter S. Wilson, Kay Vopel
Estimating the in situ distribution of acid volatile sulfides from sediment profile images
2012, 10:1070-1077
Abstract | PDF (Open Access)

A. Venti, D. Kadko, A. J. Andersson, C. Langdon, N. R. Bates
A multi-tracer model approach to estimate reef water residence times
2012, 10:1078-1095
Abstract | PDF

D.W. Murphy, D.R. Webster, J. Yen
A high-speed tomographic PIV system for measuring zooplanktonic flow
2012, 10:1096-1112
Abstract | PDF

Please Note

Articles are added to the Table of Contents throughout the year. The month of publication is shown as a convenient guide to locating the most recent articles. Open Access articles are freely available for download. Other articles require an institutional or individual subscription.

Quicklinks

Volume 1, 2003
Volume 2, 2004
Volume 3, 2005
Volume 4, 2006
Volume 5, 2007
Volume 6, 2008
Volume 7, 2009
Volume 8, 2010
Volume 9, 2011
Volume 10, 2012
Volume 11, 2013
Volume 12, 2014
Intercalibration Special Issue