ESSDD Earth System Science Data Discussions ESSDD Earth Syst. Sci. Data Discuss. 1866-3591 Göttingen, Germany 10.5194/essd-2025-585 ABCFlux v2: Arctic&ndash;boreal CO<sub>2</sub> and CH<sub>4</sub> monthly flux observations and ancillary information across terrestrial and freshwater ecosystems Virkkala Anna-Maria 1 186 Wargowsky Isabel https://orcid.org/0000-0001-6654-1414 1 186 Vogt Judith https://orcid.org/0000-0003-2502-7560 2 186 Kuhn McKenzie A. 3 1 186 Madaan Simran 2 O'Keefe Richard 1 Windholz Tiffany 1 Arndt Kyle A. https://orcid.org/0000-0003-4158-2054 1 Rogers Brendan M. https://orcid.org/0000-0001-6711-8466 1 Watts Jennifer D. 1 Kent Kelcy 1 Göckede Mathias https://orcid.org/0000-0003-2833-8401 2 Olefeldt David https://orcid.org/0000-0002-5976-1475 80 Rocher-Ros Gerard https://orcid.org/0000-0001-7853-2531 54 Schuur Edward A. G. 14 Bastviken David https://orcid.org/0000-0003-0038-2152 82 Aalstad Kristoffer https://orcid.org/0000-0002-2475-3731 74 Aho Kelly https://orcid.org/0000-0002-1992-6378 35 Ala-Könni Joonatan 118 Alcock Haley 67 Althuizen Inge https://orcid.org/0000-0003-3485-9609 149 Arp Christopher D. 181 Asanuma Jun https://orcid.org/0000-0003-1258-5491 177 Attermeyer Katrin https://orcid.org/0000-0002-6503-9497 64 180 Aurela Mika https://orcid.org/0000-0002-4046-7225 96 Balathandayuthabani Sivakiruthika https://orcid.org/0000-0002-9058-3048 82 167 Barr Alan 105 Barret Maialen https://orcid.org/0000-0003-1583-4502 136 Batkhishig Ochirbat 126 Biasi Christina 55 60 Björkman Mats P. https://orcid.org/0000-0001-5768-1976 34 106 Black Andrew https://orcid.org/0000-0002-7494-9767 93 Blanc-Betes Elena 122 Bodmer Pascal 50 Boike Julia https://orcid.org/0000-0002-5875-2112 7 115 Bolek Abdullah 2 Bouchard Frédéric 19 28 Bussmann Ingeborg https://orcid.org/0000-0002-1197-7461 83 Cabrol Lea 6 141 Canfora Eleonora 23 Carey Sean https://orcid.org/0000-0002-3316-228X 160 Castro-Morales Karel https://orcid.org/0000-0003-1245-3982 101 Chae Namyi 129 Christen Andres https://orcid.org/0000-0003-3864-1703 89 Christensen Torben R. 57 182 Christiansen Casper T. 38 Chu Housen https://orcid.org/0000-0002-8131-4938 22 Clark Graham 41 Clayer Francois 151 Crill Patrick https://orcid.org/0000-0003-1110-3059 71 Cunada Christopher 107 Davidson Scott J. https://orcid.org/0000-0001-8327-2121 49 26 Dean Joshua F. https://orcid.org/0000-0001-9058-7076 163 Dengel Sigrid 137 Detto Matteo 113 Dieleman Catherine 162 Domine Florent https://orcid.org/0000-0001-6438-6879 166 Dyukarev Egor https://orcid.org/0000-0002-7019-4459 130 185 Edgar Colin https://orcid.org/0000-0002-7026-8358 123 Elberling Bo https://orcid.org/0000-0002-6023-885X 73 Emmerton Craig A. https://orcid.org/0000-0001-9511-9191 31 Euskirchen Eugenie https://orcid.org/0000-0002-0848-4295 123 Falvo Grant 14 Friborg Thomas https://orcid.org/0000-0001-5633-6097 73 Garneau Michelle https://orcid.org/0000-0002-1956-9243 103 Giamberini Mariasilvia 128 Glagolev Mikhail V. 94 125 Gonzalez-Meler Miquel A. 32 Granath Gustaf https://orcid.org/0000-0002-3632-9102 53 Guðmundsson Jón 92 Happonen Konsta 98 Harazono Yoshinobu 133 Harris Lorna 183 Hashemi Josh 7 Hasson Nicholas 172 Heerah Janna 78 Heffernan Liam https://orcid.org/0000-0003-0145-2167 46 Helbig Manuel 78 104 Helgason Warren https://orcid.org/0000-0002-7068-5717 20 Heliasz Michal 18 Henry Greg 3 Hensgens Geert 8 46 Hiyama Tetsuya 121 Hock Macall https://orcid.org/0009-0005-9786-1521 37 174 Holl David https://orcid.org/0000-0002-9269-7030 131 Holmes Beth 48 Holst Jutta 77 Holst Thomas 77 Hould-Gosselin Gabriel 67 Humphreys Elyn https://orcid.org/0000-0002-5397-2802 65 Hung Jacqueline 1 Huotari Jussi 91 139 Ikawa Hiroki 142 Ilyasov Danil V. 168 Ishikawa Mamoru 114 Iwahana Go https://orcid.org/0000-0003-4628-1074 9 133 Iwata Hiroki 61 120 Jackowicz-Korczynski Marcin Antoni https://orcid.org/0000-0002-6574-5703 56 Jansen Joachim https://orcid.org/0000-0001-5965-7662 118 Järveoja Järvi https://orcid.org/0000-0001-6317-660X 63 Jassey Vincent E. J. https://orcid.org/0000-0002-1450-2437 170 Jensen Rasmus 57 Jentzsch Katharina 7 Jespersen Robert G. 169 Johannesson Carl-Fredrik https://orcid.org/0000-0002-2651-7505 73 150 Jones Chersity P. 44 Jonsson Anders 54 Jung Ji Young 135 Juutinen Sari 97 Kane Evan 24 Karlsson Jan 54 Karsanaev Sergey 119 Kasak Kuno https://orcid.org/0000-0002-0810-2154 70 Kelly Julia https://orcid.org/0000-0002-7370-1401 18 Kempton Kasha https://orcid.org/0009-0003-7465-1359 80 Klaus Marcus https://orcid.org/0000-0003-0747-3524 63 Kling George W. https://orcid.org/0000-0002-6349-8227 52 Kljun Natacha https://orcid.org/0000-0001-9650-2184 18 Knutson Jacqueline https://orcid.org/0000-0001-7976-6321 151 Kobayashi Hideki https://orcid.org/0000-0001-9319-0621 134 Kochendorfer John 148 Kohonen Kukka-Maaria https://orcid.org/0000-0001-9258-1225 62 118 Kolari Pasi 175 Korkiakoski Mika https://orcid.org/0000-0001-6875-9978 96 Korrensalo Aino https://orcid.org/0000-0002-0320-8689 60 147 Kortelainen Pirkko 95 Koster Egle 59 Koster Kajar 59 Kotani Ayumi https://orcid.org/0000-0003-0350-0775 109 Krishnan Praveena 148 Kurbatova Juliya 4 Kutzbach Lars https://orcid.org/0000-0003-2631-2742 131 Kwon Min Jung https://orcid.org/0000-0002-7330-2320 132 135 Kyzivat Ethan D. 43 Lagroix Jessica 173 Langhorst Theodore 176 Lapshina Elena https://orcid.org/0000-0001-5571-7787 168 Larmola Tuula https://orcid.org/0000-0002-9350-6689 146 Larsen Klaus S. https://orcid.org/0000-0002-1421-6182 73 Laurion Isabelle https://orcid.org/0000-0001-8694-3330 16 19 Ledman Justin 14 Lee Hanna https://orcid.org/0000-0002-2003-4377 36 Leffler A. Joshua 76 Lesack Lance 84 Lindroth Anders 77 Lipson David 37 Lohila Annalea https://orcid.org/0000-0003-3541-672X 96 López-Blanco Efrén 56 58 St. Louis Vincent L. 31 Lundin Erik https://orcid.org/0000-0002-3785-8305 5 Luoto Misha https://orcid.org/0000-0001-6203-5143 72 Machimura Takashi 110 Magnani Marta 127 Malhotra Avni https://orcid.org/0000-0002-7850-6402 11 Maljanen Marja 60 Mammarella Ivan https://orcid.org/0000-0002-8516-3356 118 Männistö Elisa 153 Marchesini Luca Belelli https://orcid.org/0000-0001-8408-4675 99 Marsh Phil https://orcid.org/0000-0002-3618-6893 184 Martkainen Pertti J. 60 Marushchak Maija E. https://orcid.org/0000-0002-2308-5049 60 Mastepanov Mikhail https://orcid.org/0000-0002-5543-0302 56 152 Mavrovic Alex https://orcid.org/0000-0003-4314-4461 12 19 171 Maximov Trofim 119 Minions Christina 1 Montemayor Marco https://orcid.org/0009-0006-3373-837X 1 Morishita Tomoaki 100 Murphy Patrick 1 Nadeau Daniel F. 40 Nicholls Erin 47 Nilsson Mats B. https://orcid.org/0000-0003-3765-6399 63 Niyazova Anastasia 168 Nordén Jenni 150 Noumonvi Koffi Dodji https://orcid.org/0000-0002-3305-174X 63 Nykanen Hannu 60 Oechel Walter https://orcid.org/0000-0002-3504-026X 37 Ojala Anne 146 Okadera Tomohiro 143 Pal Sujan https://orcid.org/0000-0001-6503-0014 90 Panov Alexey V. 179 Papakyriakou Tim 17 Papale Dario https://orcid.org/0000-0001-5170-8648 144 Park Sang-Jong 135 Parmentier Frans-Jan W. https://orcid.org/0000-0003-2952-7706 13 Pastorello Gilberto https://orcid.org/0000-0002-9387-3702 164 Peacock Mike https://orcid.org/0000-0002-3086-2854 29 66 Peichl Matthias https://orcid.org/0000-0002-9940-5846 63 Petrov Roman 119 St. Pierre Kyra https://orcid.org/0000-0003-0981-920X 42 Pirk Norbert https://orcid.org/0000-0002-8137-2329 74 Plein Jessica https://orcid.org/0000-0002-4505-8527 37 Preskienis Vilmantas 16 19 27 112 Prokushkin Anatoly https://orcid.org/0000-0001-8721-2142 179 Pumpanen Jukka https://orcid.org/0000-0003-4879-3663 60 Rains Hilary A. 154 Rakos Niklas https://orcid.org/0000-0002-5268-5799 5 Räsänen Aleski https://orcid.org/0000-0002-3629-1837 102 Rautakoski Helena https://orcid.org/0000-0002-5297-286X 97 Rinnan Riika https://orcid.org/0000-0001-7222-700X 38 Rinne Janne https://orcid.org/0000-0003-1168-7138 146 Rocha Adrian 33 Roulet Nigel https://orcid.org/0000-0001-9571-1929 140 Roy Alexandre https://orcid.org/0000-0002-1472-3619 19 171 Rutgersson Anna https://orcid.org/0000-0001-7656-1881 45 Sabrekov Aleksandr F. https://orcid.org/0000-0002-6501-912X 168 Sachs Torsten https://orcid.org/0000-0002-9959-4771 104 Sahlée Erik 45 Salazar Alejandro https://orcid.org/0000-0002-0798-882X 92 Sawakuchi Henrique Oliveira https://orcid.org/0000-0002-6815-7261 82 Schulze Christopher https://orcid.org/0000-0002-6579-0360 67 80 Seco Roger https://orcid.org/0000-0002-2078-9956 124 Sepulveda-Jauregui Armando https://orcid.org/0000-0001-7777-4520 79 138 Serikova Svetlana 54 Serrone Abbey 21 34 Silvennoinen Hanna M. 150 Sjogersten Sofie 159 Skeeter June 3 145 Snöälv Jo 69 Sobek Sebastian 53 75 Sonnentag Oliver 67 Stanley Emily H. https://orcid.org/0000-0003-4922-8121 15 Strack Maria 178 Strom Lena 77 Sullivan Patrick https://orcid.org/0000-0002-8015-3036 88 Sullivan Ryan https://orcid.org/0000-0002-3500-1842 90 Sytiuk Anna 170 Tagesson Torbern 77 Taillardat Pierre 10 Talbot Julie 67 Tank Suzanne E. https://orcid.org/0000-0002-5371-6577 31 Tenuta Mario 81 Terenteva Irina 68 Thalasso Frederic https://orcid.org/0000-0003-2246-2372 39 Thiboult Antoine 40 Thorgeirsson Halldor 117 Garcia Tigreros Fenix https://orcid.org/0000-0001-8694-9046 111 Torn Margaret 22 Townsend-Small Amy https://orcid.org/0000-0002-6107-0833 161 Treat Claire https://orcid.org/0000-0002-1225-8178 7 155 Tremblay Alain 116 Trotta Carlo https://orcid.org/0000-0001-6377-0262 23 Tuittila Eeva-Stiina https://orcid.org/0000-0001-8861-3167 153 Turetsky Merritt 51 Ueyama Masahito https://orcid.org/0000-0002-4000-4888 108 Umair Muhammad https://orcid.org/0000-0002-7651-9015 67 Vähä Aki 118 van Delden Lona https://orcid.org/0000-0003-4332-3160 7 van Hardenbroek Maarten 25 Varlagin Andrej 4 Varner Ruth K. https://orcid.org/0000-0002-3571-6629 44 71 Veretennikova Elena 130 165 Vesala Timo 175 Virtanen Tarmo 87 Voigt Carolina https://orcid.org/0000-0001-8589-1428 7 67 132 Vonk Jorien E. 46 Wagner Robert 37 Walter Anthony Katey 181 Wang Qinxue https://orcid.org/0000-0001-7723-5412 143 Watanabe Masataka 158 Webb Hailey 51 157 Welker Jeffrey M. 30 86 Westergaard-Nielsen Andreas 73 Westermann Sebastian 13 White Jeffrey R. https://orcid.org/0000-0002-7541-3737 85 Wille Christian 104 Williamson Scott N. 156 Zolkos Scott 1 Zona Donatella https://orcid.org/0000-0002-0003-4839 37 Natali Susan M. 1 Woodwell Climate Research Center, Falmouth, MA, USA Max Planck Institute for Biogeochemistry, Jena, Germany Department of Geography, University of British Columbia, Vancouver, Canada A.N. 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N. Sukachev Institute of forest, Siberian Branch of the Russian Academy of Sciences, Russia WasserCluster Lunz, Biologische Station, Dr. Carl Kupelwieser Promenade 5, 3293 Lunz am See, Austria Water and Environmental Research Center, University of Alaska Fairbanks, Fairbanks, AK, USA Water, energy and environmental engineering research unit, Oulu University, Finland Independent Researcher Wilfred Laurier University, Canada Yugra State University, Russia shared first-authorship 20 10 2025 2025 1 86 Copyright: © 2025 Anna-Maria Virkkala et al. 2025 This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/ This article is available from https://essd.copernicus.org/preprints/essd-2025-585/ The full text article is available as a PDF file from https://essd.copernicus.org/preprints/essd-2025-585/essd-2025-585.pdf

Measurements of surface-atmosphere carbon dioxide (CO<sub>2</sub>) and methane (CH<sub>4</sub>) fluxes have been relatively sparse across the Arctic tundra and boreal biomes, causing significant uncertainties in carbon budget estimates from the region. While the availability of Arctic-boreal carbon flux data has increased substantially over the past decade, the data have remained spread across different repositories, scientific articles, and unpublished sources, making it difficult to leverage. Here we present a new dataset of monthly Arctic-boreal carbon fluxes (ABCFlux v2) across terrestrial (wetlands and uplands) and freshwater (lakes and rivers) ecosystems compiled from previous syntheses including the Arctic-boreal CO<sub>2</sub> flux database (ABCFlux v1), the Boreal-Arctic Wetland and Lake Methane Dataset (BAWLD-CH4), and the Global River Methane Database (GRiMeDB). In addition, we consider data from general-purpose (e.g., Zenodo) and flux network repositories, literature, and site principal investigators. The dataset includes surface-atmosphere CO<sub>2</sub> fluxes of gross primary production (GPP), ecosystem respiration (Reco), and net ecosystem exchange (NEE), alongside CH<sub>4</sub> fluxes. For aquatic ecosystems, we split CH<sub>4</sub> fluxes into diffusive and ebullitive flux pathways, and included potential emissions from transient storage in the water column (&ldquo;storage fluxes&rdquo;), alongside CO<sub>2</sub> and CH<sub>4</sub> concentrations dissolved in the surface water. Fluxes are measured through a variety of methods including chamber and eddy covariance techniques alongside bubble traps, ice-surveys, and concentration-based turbulence-driven modelling in aquatic ecosystems. The monthly flux data are reported together with supporting methodological and environmental metadata. The resulting ABCFlux v2 has 23,656 flux site-months, 8,182 concentration site-months, and 199 seasonal observations from 1,024 sites, and includes 55,560 reported fluxes (i.e. sum of GPP, Reco, NEE, and CH<sub>4</sub> fluxes) from the years 1984 to 2024. The majority of monthly observations occurred after 1999. Wetlands had the highest number of site-month observations (8,641), followed by boreal forest (6,981), lotic ecosystems (6,275), lentic ecosystems (3,725) and upland tundra (3,308). Measurements of CO<sub>2</sub> dominated the dataset across most ecosystem types (25,101) except for lentic ecosystems, where CH<sub>4</sub> flux site-months (3,024) were more frequent than CO<sub>2</sub> flux site-months (2,858). Overall, ABCFlux v2 includes 158 % more site-months for terrestrial CO<sub>2</sub> flux data compared to ABCFlux v1. Integrating and updating BAWLD-CH4 flux data from growing season averages to monthly fluxes resulted in 5,671 site-months of chamber CH<sub>4</sub> data compared to 762 site-years. This collaborative initiative, involving contributions from over 260 researchers, provides a comprehensive overview of the current state of the Arctic-boreal carbon flux network and its data, and serves as an important step in reducing uncertainties in Arctic-boreal carbon budgets and in enhancing our understanding of climate feedbacks. The data can be accessed at ORNL DAAC at <a href="https://doi.org/10.3334/ORNLDAAC/2448" target="_blank" rel="noopener">https://doi.org/10.3334/ORNLDAAC/2448</a> (Virkkala et al., 2025b).

 TED Audacious Project- Permafrost Pathways Gordon and Betty Moore Foundation grant no. 8414 European Research Council grant agreement no. 951288, Q-Arctic HORIZON EUROPE Climate, Energy and Mobility grant agreement no. 101056921, GreenFeedBack Natural Sciences and Engineering Research Council of Canada DGECR-2025-00337