meltwater discharge around Greenland. *Nat. Commun.* 9, 3256. doi: 10.1038/s41467-018-05488-8

IPCC (2022). "Impacts of 1.5°C Global Warming on Natural and Human Systems," in *Global Warming of 1.5°C: IPCC Special Report on Impacts of Global Warming of 1.5°C* Above Pre-industrial Levels in Context of Strengthening Response to Climate Change, Sustainable Development, and Efforts to Eradicate Poverty (Cambridge: Cambridge University Press). doi: 10.1017/9781009157940

Jacquot, J. E., and Moffett, J. W. (2015). Copper distribution and speciation across the International GEOTRACES Section GA03. *Deep Sea Res. Part II: Topical Stud. Oceanography* 116, 187–207. doi: 10.1016/j.dsr2.2014.11.013

Jakobsson, M. (2002). Hypometry and volume of the Arctic Ocean and its constituent seas. *Geochemistry Geophysics Geosystems* 3, 1–18. doi: 10.1029/2001GC000302

Jensen, L. T., Cullen, J. T., Jackson, S. L., Gerringa, L. J. A., Bauch, D., Middag, R., et al. (2022). A refinement of the processes controlling dissolved copper and nickel biogeochemistry: insights from the pan-arctic. *J. Geophys Res. Oceans* 127. doi: 10.1029/2021JC018087

Jensen, L. T., Lanning, N. T., Marsay, C. M., Buck, C. S., Aguilar-Islas, A. M., Rember, R., et al. (2021). Biogeochemical cycling of colloidal trace metals in the arctic cryosphere. *J. Geophys Res. Oceans* 126. doi: 10.1029/2021JC017394

Kattner, G. (2014). Nutrients measured on water bottle samples during POLARSTERN cruise ARK-XXVII/3 (IceArc) in 2012. *PANGAEA*. doi: 10.1594/PANGAEA.834081

Kattner, G., Lobbes, J. M., Fitznar, H. P., Engbrodt, R., Nöthig, E.-M., and Lara, R. J. (1999). Tracing dissolved organic substances and nutrients from the Lena River through Laptev Sea (Arctic). *Mar. Chem.* 65, 25–39. doi: 10.1016/S0304-4203(99)00008-0

Klunder, M. B., Laan, P., Middag, R., De Baar, H. J. W., and Bakker, K. (2012). Dissolved iron in the Arctic Ocean: Important role of hydrothermal sources, shelf input and scavenging removal. *J. Geophys Res. Oceans* 117, 1–17. doi: 10.1029/2011JC007135

König-Langlo, G. (2015). *Meteorological Observations During POLARSTERN cruise PS94 (ARK-XXIX/3)* (Bremerhaven: Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research). doi: 10.1594/PANGAEA.854304

Kramer, C. J. M. (1986). Apparent copper complexation capacity and conditional stability constants in north atlantic waters. *Mar. Chem.* 18, 335–349. doi: 10.1016/0304-4203(86)90016-2

Krembs, C., Eicken, H., Junge, K., and Deming, J. W. (2002). High concentrations of exopolymeric substances in Arctic winter sea ice: implications for the polar ocean carbon cycle and cryoprotection of diatoms. *Deep Sea Res. Part I: Oceanographic Res. Papers* 49, 2163–2181. doi: 10.1016/S0967-0637(02)00122-X

Krisch, S., Hopwood, M. J., Roig, S., Gerringa, L. J. A., Middag, R., Rutgers van der Loeff, M. M., et al. (2022). Arctic – atlantic exchange of the dissolved micronutrients iron, manganese, cobalt, nickel, copper and zinc with a focus on fram strait. *Global Biogeochem Cycles* 36. doi: 10.1029/2021GB007191

Krumpen, T., Belter, H. J., Boetius, A., Damm, E., Haas, C., Hendricks, S., et al. (2019). Arctic warming interrupts the Transpolar Drift and affects long-range transport of sea ice and ice-rafted matter. *Sci. Rep.* 9, 5459. doi: 10.1038/s41598-019-41456-y

Kruskal, W. H., and Wallis, W. A. (1952). Use of ranks in one-criterion variance analysis. *J. Am. Stat. Assoc.* 47, 583–621. doi: 10.1080/01621459.1952.10483441

Laglera, L. M., Sukekava, C., Slagter, H. A., Downes, J., Aparicio-Gonzalez, A., and Gerringa, L. J. A. (2019). First quantification of the controlling role of humic substances in the transport of iron across the surface of the arctic ocean. *Environ. Sci. Technol.* 53, 13136–13145. doi: 10.1021/acs.est.9b04240

Laglera, L. M., and van den Berg, C. M. G. (2003). Copper complexation by thiol compounds in estuarine waters. *Mar. Chem.* 82, 71–89. doi: 10.1016/S0304-4203(03)00053-7

Liguori, B. T. P., Ehlert, C., and Pahnke, K. (2020). The influence of water mass mixing and particle dissolution on the silicon cycle in the central arctic ocean. *Front. Mar. Sci.* 7. doi: 10.3389/fmars.2020.00202

Lin, H., Wang, C., Zhao, H., Chen, G., and Chen, X. (2020). A subcellular level study of copper speciation reveals the synergistic mechanism of microbial cells and EPS involved in copper binding in bacterial biofilms. *Environ. Pollut.* 263, 114485. doi: 10.1016/j.envpol.2020.114485

Lorenzo, J. I., Nieto-Cid, M., Álvarez-Salgado, X. A., Pérez, P., and Beiras, R. (2007). Contrasting complexing capacity of dissolved organic matter produced during the onset, development and decay of a simulated bloom of the marine diatom Skeletonema costatum. *Mar. Chem.* 103, 61–75. doi: 10.1016/j.marchem.2006.05.009

Maldonado, M. T., Allen, A. E., Chong, J. S., Lin, K., Leus, D., Karpenko, N., et al. (2006). Copper-dependent iron transport in coastal and oceanic diatoms. *Limnol Oceanogr* 51, 1729–1743. doi: 10.4319/lo.2006.51.4.1729

Middag, R., de Baar, H. J. W., Laan, P., and Klunder, M. B. (2011). Fluvial and hydrothermal input of manganese into the Arctic Ocean. *Geochim Cosmochim Acta* 75, 2393–2408. doi: 10.1016/j.gca.2011.02.011

Millero, F. J., Woosley, R., Ditrolio, B., and Waters, J. (2009). Effect of ocean acidification on the speciation of metals in seawater. *Oceanography* 22, 72–85. doi: 10.2307/24861025

Moffett, J. W., and Dupont, C. (2007). Cu complexation by organic ligands in the sub-arctic NW Pacific and Bering Sea. *Deep-Sea Res. I* 54, 586–595. doi: 10.1016/j.dsr.2006.12.013

Muller, F. L. L., and Batchelli, S. (2013). Copper binding by terrestrial versus marine organic ligands in the coastal plume of River Thurso, North Scotland. *Estuar. Coast. Shelf Sci.* 133, 137–146. doi: 10.1016/j.ecss.2013.08.024

Nixon, R. L., Jackson, S. L., Cullen, J. T., and Ross, A. R. S. (2019). Distribution of copper-complexing ligands in Canadian Arctic waters as determined by immobilized copper(II)-ion affinity chromatography. *Mar. Chem.* 103673. doi: 10.1016/j.marchem.2019.103673

Ober, S., Rijkenberg, M. J. A., and Gerringa, L. J. A. (2016). Physical oceanography measured on water bottle samples with ultra clean CTD/Water sampler-system during POLARSTERN cruise PS94 (ARK-XXIX/3). *PANGAEA*. doi: 10.1594/PANGAEA.859561

Omanović, D., Garnier, C., and Pižeta, I. (2015). ProMCC: An all-in-one tool for trace metal complexation studies. *Mar. Chem.* 173, 25–39. doi: 10.1016/j.marchem.2014.10.011

Opsahl, S., Benner, R., and Amon, R. M. W. (1999). Major flux of terrigenous dissolved organic matter through the Arctic Ocean. *Limnol Oceanogr* 44, 2017–2023. doi: 10.4319/lo.1999.44.8.2017

Paffrath, R., Laukert, G., Bauch, D., Rutgers van der Loeff, M., and Pahnke, K. (2021). Separating individual contributions of major Siberian rivers in the Transpolar Drift of the Arctic Ocean. *Sci. Rep.* 11, 8216. doi: 10.1038/s41598-021-86948-y

Paulsen, M. L., Müller, O., Larsen, A., Møller, E. F., Middelboe, M., Sejr, M. K., et al. (2019). Biological transformation of Arctic dissolved organic matter in a NE Greenland fjord. *Limnol Oceanogr* 64, 1014–1033. doi: 10.1002/lno.11091

Peterson, B. J., Holmes, R. M., McClelland, J. W., Vörösmarty, C. J., Lammers, R. B., Shiklomanov, A. I., et al. (2002). Increasing river discharge to the arctic ocean. *Sci.* (1979) 298, 2171–2173. doi: 10.1126/science.1077445

Rabe, B., Schauer, U., Ober, S., Horn, M., Hopmann, M., Korhonen, M., et al. (2016). Physical oceanography during POLARSTERN cruise PS94 (ARK-XXIX/3). *PANGAEA*. doi: 10.1594/PANGAEA.859558

Rijkenberg, M. J. A., de Baar, H. J. W., Bakker, K., Gerringa, L. J. A., Keijzer, E., Laan, M., et al. (2015). PRISTINE", a new high volume sampler for ultraclean sampling of trace metals and isotopes. *Mar. Chem.* 177, 501–509. doi: 10.1016/j.marchem.2015.07.001

Rijkenberg, M. J. A., Slagter, H. A., van der Loeff, M. R., van Ooijen, J., and Gerringa, L. J. A. (2018). Dissolved Fe in the deep and upper Arctic Ocean with a focus on Fe Limitation in the Nansen Basin. *Front. Mar. Sci.* 5. doi: 10.3389/fmars.2018.00088

Ruacho, A., Richon, C., Whitby, H., and Bundy, R. M. (2022). Sources, sinks, and cycling of dissolved organic copper binding ligands in the ocean. *Commun. Earth Environ.* 3, 263. doi: 10.1038/s43247-022-00597-1

Rudels, B. (2012). Arctic Ocean circulation and variability – advection and external forcing encounter constraints and local processes. *Ocean Sci.* 8, 261–286. doi: 10.5194/ os-8-261-2012

Rudels, B. (2019). "Arctic ocean circulation," in *Encyclopedia of Ocean Sciences (Third Edition)*, eds. J. K. Cochran, H. J. Bokuniewicz and P. L. Yager (Oxford: Elsevier), 262–277. doi: 10.1016/B978-0-12-409548-9.11209-6

Sakamoto, Y., Ishiguro, M., and Kitagawa, G. (1986). Akaike information criterion statistics. *Dordrecht Netherlands: D. Reidel* 81, 26853.

Schauer, U. (2004). Arctic warming through the Fram Strait: Oceanic heat transport from 3 years of measurements. *J. Geophys Res.* 109, C06026. doi: 10.1029/2003JC001823

Schauer, U. (2016). The expedition PS94 of the research vessel POLARSTERN to the central arctic ocean in 2015. *Berichte zur Polar-und Meeresforschung= Rep. polar Mar. Res.* 703. doi: 10.2312/BzPM_0703_2016

Schlosser, P., Kromer, B., Ekwurzel, B., Bönisch, G., McNichol, A., Schneider, R., et al. (1997). The first trans-Arctic 14C section: comparison of the mean ages of the deep waters in the Eurasian and Canadian basins of the Arctic Ocean. *Nucl. Instrum Methods Phys. Res. B* 123, 431–437. doi: 10.1016/S0168-583X(96)00677-5

Schuur, E. A. G., Abbott, B. W., Bowden, W. B., Brovkin, V., Camill, P., Canadell, J. G., et al. (2013). Expert assessment of vulnerability of permafrost carbon to climate change. *Clim Change* 119, 359–374. doi: 10.1007/s10584-013-0730-7

Schuur, E. A. G., McGuire, A. D., Schädel, C., Grosse, G., Harden, J. W., Hayes, D. J., et al. (2015). Climate change and the permafrost carbon feedback. *Nature* 520, 171–179. doi: 10.1038/nature14338

Semeniuk, D. M., Bundy, R. M., Payne, C. D., Barbeau, K. A., and Maldonado, M. T. (2015). Acquisition of organically complexed copper by marine phytoplankton and bacteria in the northeast subarctic Pacific Ocean. *Mar. Chem.* 173, 222–233. doi: 10.1016/j.marchem.2015.01.005

Shank, G. C., Skrabal, S. A., Whitehead, R. F., and Kieber, R. J. (2004). Strong copper complexation in an organic-rich estuary: the importance of allochthonous dissolved organic matter. *Mar. Chem.* 88, 21–39. doi: 10.1016/j.marchem.2004.03.001

Shank, G. C., Whitehead, R. F., Smith, M. L., Skrabal, S. A., and Kieber, R. J. (2006). Photodegradation of strong copper-complexing ligands in organic-rich estuarine waters. *Limnol Oceanogr* 51, 884–892. doi: 10.4319/lo.2006.51.2.0884

Slagter, H. A., Laglera, L. M., Sukekava, C., and Gerringa, L. J. A. (2019). Fe-binding organic ligands in the humic-rich transPolar drift in the surface arctic ocean using multiple voltammetric methods. *J. Geophys Res. Oceans* 124, 1491–1508. doi: 10.1029/ 2018JC014576

Slagter, H. A., Reader, H. E., Rijkenberg, M. J. A., Rutgers van der Loeff, M., de Baar, H. J. W., and Gerringa, L. J. A. (2017). Organic Fe speciation in the Eurasian Basins of the Arctic Ocean and its relation to terrestrial DOM. *Mar. Chem.* 197, 11–25. doi: 10.1016/j.marchem.2017.10.005
meltwater discharge around Greenland. *Nat. Commun.* 9, 3256. doi: 10.1038/s41467-018-05488-8

IPCC (2022). "Impacts of 1.5°C Global Warming on Natural and Human Systems," in *Global Warming of 1.5°C: IPCC Special Report on Impacts of Global Warming of 1.5°C* Above Pre-industrial Levels in Context of Strengthening Response to Climate Change, Sustainable Development, and Efforts to Eradicate Poverty (Cambridge: Cambridge University Press). doi: 10.1017/9781009157940

Jacquot, J. E., and Moffett, J. W. (2015). Copper distribution and speciation across the International GEOTRACES Section GA03. *Deep Sea Res. Part II: Topical Stud. Oceanography* 116, 187–207. doi: 10.1016/j.dsr2.2014.11.013

Jakobsson, M. (2002). Hypometry and volume of the Arctic Ocean and its constituent seas. *Geochemistry, Geophysics, Geosystems* 3, 1–18. doi: 10.1029/2001GC000302

Jensen, L. T., Cullen, J. T., Jackson, S. L., Gerringa, L. J. A., Bauch, D., Middag, R., et al. (2022). A refinement of the processes controlling dissolved copper and nickel biogeochemistry: insights from the pan-arctic. *J. Geophys Res. Oceans* 127. doi: 10.1029/2021JC018087

Jensen, L. T., Lanning, N. T., Marsay, C. M., Buck, C. S., Aguilar-Islas, A. M., Rember, R., et al. (2021). Biogeochemical cycling of colloidal trace metals in the arctic cryosphere. *J. Geophys Res. Oceans* 126. doi: 10.1029/2021JC017394

Kattner, G. (2014). Nutrients measured on water bottle samples during POLARSTERN cruise ARK-XXVII/3 (IceArc) in 2012. *PANGAEA*. doi: 10.1594/PANGAEA.834081

Kattner, G., Lobbes, J. M., Fitznar, H. P., Engbrodt, R., Nothig, E.-M., and Lara, R. J. (1999). Tracing dissolved organic substances and nutrients from the Lena River through Laptev Sea (Arctic). *Mar. Chem.* 65, 25–39. doi: 10.1016/S0304-4203(99)00008-0

Klunder, M. B., Laan, P., Middag, R., De Baar, H. J. W., and Bakker, K. (2012). Dissolved iron in the Arctic Ocean: Important role of hydrothermal sources, shelf input and scavenging removal. *J. Geophys Res. Oceans* 117, 1–17. doi: 10.1029/2011JC007135

König-Langlo, G. (2015). *Meteorological Observations During POLARSTERN cruise PS94 (ARK-XXIX/3)* (Bremerhaven: Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research). doi: 10.1594/PANGAEA.854304

Kramer, C. J. M. (1986). Apparent copper complexation capacity and conditional stability constants in north atlantic waters. *Mar. Chem.* 18, 335–349. doi: 10.1016/0304-4203(86)90016-2

Krembs, C., Eicken, H., Junge, K., and Deming, J. W. (2002). High concentrations of exopolymeric substances in Arctic winter sea ice: implications for the polar ocean carbon cycle and cryoprotection of diatoms. *Deep Sea Res. Part I: Oceanographic Res. Papers* 49, 2163–2181. doi: 10.1016/S0967-0637(02)00122-X

Krisch, S., Hopwood, M. J., Roig, S., Gerringa, L. J. A., Middag, R., Rutgers van der Loeff, M. M., et al. (2022). Arctic – atlantic exchange of the dissolved micronutrients iron, manganese, cobalt, nickel, copper and zinc with a focus on fram strait. *Global Biogeochem Cycles* 36. doi: 10.1029/2021GB007191

Krumpen, T., Belter, H. J., Boetius, A., Damm, E., Haas, C., Hendricks, S., et al. (2019). Arctic warming interrupts the Transpolar Drift and affects long-range transport of sea ice and ice-rafted matter. *Sci. Rep.* 9, 5459. doi: 10.1038/s41598-019-41456-y

Kruskal, W. H., and Wallis, W. A. (1952). Use of ranks in one-criterion variance analysis. *J. Am. Stat. Assoc.* 47, 583–621. doi: 10.1080/01621459.1952.10483441

Laglera, L. M., Sukekava, C., Slagter, H. A., Downes, J., Aparicio-Gonzalez, A., and Gerringa, L. J. A. (2019). First quantification of the controlling role of humic substances in the transport of iron across the surface of the arctic ocean. *Environ. Sci. Technol.* 53, 13136–13145. doi: 10.1021/acs.est.9b04240

Laglera, L. M., and van den Berg, C. M. G. (2003). Copper complexation by thiol compounds in estuarine waters. *Mar. Chem.* 82, 71–89. doi: 10.1016/S0304-4203(03)00053-7

Liguori, B. T. P., Ehlert, C., and Pahnke, K. (2020). The influence of water mass mixing and particle dissolution on the silicon cycle in the central arctic ocean. *Front. Mar. Sci.* 7. doi: 10.3389/fmars.2020.00202

Lin, H., Wang, C., Zhao, H., Chen, G., and Chen, X. (2020). A subcellular level study of copper speciation reveals the synergistic mechanism of microbial cells and EPS involved in copper binding in bacterial biofilms. *Environ. Pollut.* 263, 114485. doi: 10.1016/j.envpol.2020.114485

Lorenzo, J. I., Nieto-Cid, M., Álvarez-Salgado, X. A., Pérez, P., and Beiras, R. (2007). Contrasting complexing capacity of dissolved organic matter produced during the onset, development and decay of a simulated bloom of the marine diatom Skeletonema costatum. *Mar. Chem.* 103, 61–75. doi: 10.1016/j.marchem.2006.05.009

Maldonado, M. T., Allen, A. E., Chong, J. S., Lin, K., Leus, D., Karpenko, N., et al. (2006). Copper-dependent iron transport in coastal and oceanic diatoms. *Limnol Oceanogr* 51, 1729–1743. doi: 10.4319/lo.2006.51.4.1729

Middag, R., de Baar, H. J. W., Laan, P., and Klunder, M. B. (2011). Fluvial and hydrothermal input of manganese into the Arctic Ocean. *Geochim Cosmochim Acta* 75, 2393–2408. doi: 10.1016/j.gca.2011.02.011

Millero, F. J., Woosley, R., Ditrolio, B., and Waters, J. (2009). Effect of ocean acidification on the speciation of metals in seawater. *Oceanography* 22, 72–85. doi: 10.2307/24861025

Moffett, J. W., and Dupont, C. (2007). Cu complexation by organic ligands in the sub-arctic NW Pacific and Bering Sea. *Deep-Sea Res. I* 54, 586–595. doi: 10.1016/j.dsr.2006.12.013

Muller, F. L. L., and Batchelli, S. (2013). Copper binding by terrestrial versus marine organic ligands in the coastal plume of River Thurso, North Scotland. *Estuar. Coast. Shelf Sci.* 133, 137–146. doi: 10.1016/j.ecss.2013.08.024

Nixon, R. L., Jackson, S. L., Cullen, J. T., and Ross, A. R. S. (2019). Distribution of copper-complexing ligands in Canadian Arctic waters as determined by immobilized copper(II)-ion affinity chromatography. *Mar. Chem.* 103673. doi: 10.1016/j.marchem.2019.103673

Ober, S., Rijkenberg, M. J. A., and Gerringa, L. J. A. (2016). Physical oceanography measured on water bottle samples with ultra clean CTD/Water sampler-system during POLARSTERN cruise PS94 (ARK-XXIX/3). *PANGAEA*. doi: 10.1594/PANGAEA.859561

Omanović, D., Garnier, C., and Pižeta, I. (2015). ProMCC: An all-in-one tool for trace metal complexation studies. *Mar. Chem.* 173, 25–39. doi: 10.1016/j.marchem.2014.10.011

Opsahl, S., Benner, R., and Amon, R. M. W. (1999). Major flux of terrigenous dissolved organic matter through the Arctic Ocean. *Limnol Oceanogr* 44, 2017–2023. doi: 10.4319/lo.1999.44.8.2017

Paffrath, R., Laukert, G., Bauch, D., Rutgers van der Loeff, M., and Pahnke, K. (2021). Separating individual contributions of major Siberian rivers in the Transpolar Drift of the Arctic Ocean. *Sci. Rep.* 11, 8216. doi: 10.1038/s41598-021-86948-y

Paulsen, M. L., Müller, O., Larsen, A., Møller, E. F., Middelboe, M., Sejr, M. K., et al. (2019). Biological transformation of Arctic dissolved organic matter in a NE Greenland fjord. *Limnol Oceanogr* 64, 1014–1033. doi: 10.1002/lno.11091

Peterson, B. J., Holmes, R. M., McClelland, J. W., Vörösmarty, C. J., Lammers, R. B., Shiklomanov, A. I., et al. (2002). Increasing river discharge to the arctic ocean. *Sci.* (1979) 298, 2171–2173. doi: 10.1126/science.1077445

Rabe, B., Schauer, U., Ober, S., Horn, M., Hopmann, M., Korhonen, M., et al. (2016). Physical oceanography during POLARSTERN cruise PS94 (ARK-XXIX/3). *PANGAEA*. doi: 10.1594/PANGAEA.859558

Rijkenberg, M. J. A., de Baar, H. J. W., Bakker, K., Gerringa, L. J. A., Keijzer, E., Laan, M., et al. (2015). PRISTINE", a new high volume sampler for ultraclean sampling of trace metals and isotopes. *Mar. Chem.* 177, 501–509. doi: 10.1016/j.marchem.2015.07.001

Rijkenberg, M. J. A., Slagter, H. A., van der Loeff, M. R., van Ooijen, J., and Gerringa, L. J. A. (2018). Dissolved Fe in the deep and upper Arctic Ocean with a focus on Fe Limitation in the Nansen Basin. *Front. Mar. Sci.* 5. doi: 10.3389/fmars.2018.00088

Ruacho, A., Richon, C., Whitby, H., and Bundy, R. M. (2022). Sources, sinks, and cycling of dissolved organic copper binding ligands in the ocean. *Commun. Earth Environ.* 3, 263. doi: 10.1038/s43247-022-00597-1

Rudels, B. (2012). Arctic Ocean circulation and variability – advection and external forcing encounter constraints and local processes. *Ocean Sci.* 8, 261–286. doi: 10.5194/os-8-261-2012

Rudels, B. (2019). "Arctic ocean circulation," in *Encyclopedia of Ocean Sciences (Third Edition)*, eds. J. K. Cochran, H. J. Bokuniewicz and P. L. Yager (Oxford: Elsevier), 262–277. doi: 10.1016/B978-0-12-409548-9.11209-6

Sakamoto, Y., Ishiguro, M., and Kitagawa, G. (1986). Akaike information criterion statistics. *Dordrecht Netherlands: D. Reidel* 81, 26853.

Schauer, U. (2004). Arctic warming through the Fram Strait: Oceanic heat transport from 3 years of measurements. *J. Geophys Res.* 109, C06026. doi: 10.1029/2003JC001823

Schauer, U. (2016). The expedition PS94 of the research vessel POLARSTERN to the central arctic ocean in 2015. *Berichte zur Polar-und Meeresforschung= Rep. polar Mar. Res.* 703. doi: 10.2312/BzPM_0703_2016

Schlosser, P., Kromer, B., Ekwurzel, B., Bönisch, G., McNichol, A., Schneider, R., et al. (1997). The first trans-Arctic 14C section: comparison of the mean ages of the deep waters in the Eurasian and Canadian basins of the Arctic Ocean. *Nucl. Instrum Methods Phys. Res. B* 123, 431–437. doi: 10.1016/S0168-583X(96)00677-5

Schuur, E. A. G., Abbott, B. W., Bowden, W. B., Brovkin, V., Camill, P., Canadell, J. G., et al. (2013). Expert assessment of vulnerability of permafrost carbon to climate change. *Clim Change* 119, 359–374. doi: 10.1007/s10584-013-0730-7

Schuur, E. A. G., McGuire, A. D., Schädel, C., Grosse, G., Harden, J. W., Hayes, D. J., et al. (2015). Climate change and the permafrost carbon feedback. *Nature* 520, 171–179. doi: 10.1038/nature14338

Semeniuk, D. M., Bundy, R. M., Payne, C. D., Barbeau, K. A., and Maldonado, M. T. (2015). Acquisition of organically complexed copper by marine phytoplankton and bacteria in the northeast subarctic Pacific Ocean. *Mar. Chem.* 173, 222–233. doi: 10.1016/j.marchem.2015.01.005

Shank, G. C., Skrabal, S. A., Whitehead, R. F., and Kieber, R. J. (2004). Strong copper complexation in an organic-rich estuary: the importance of allochthonous dissolved organic matter. *Mar. Chem.* 88, 21–39. doi: 10.1016/j.marchem.2004.03.001

Shank, G. C., Whitehead, R. F., Smith, M. L., Skrabal, S. A., and Kieber, R. J. (2006). Photodegradation of strong copper-complexing ligands in organic-rich estuarine waters. *Limnol Oceanogr* 51, 884–892. doi: 10.4319/lo.2006.51.2.0884

Slagter, H. A., Laglera, L. M., Sukekava, C., and Gerringa, L. J. A. (2019). Fe-binding organic ligands in the humic-rich transPolar drift in the surface arctic ocean using multiple voltammetric methods. *J. Geophys Res. Oceans* 124, 1491–1508. doi: 10.1029/2018JC014576

Slagter, H. A., Reader, H. E., Rijkenberg, M. J. A., Rutgers van der Loeff, M., de Baar, H. J. W., and Gerringa, L. J. A. (2017). Organic Fe speciation in the Eurasian Basins of the Arctic Ocean and its relation to terrestrial DOM. *Mar. Chem.* 197, 11–25. doi: 10.1016/j.marchem.2017.10.005
Stedmon, C. A., Amon, R. M. W., Rinehart, A. J., and Walker, S. A. (2011). The supply and characteristics of colored dissolved organic matter (CDOM) in the Arctic Ocean: Pan Arctic trends and differences. *Mar. Chem.* 124, 108–118. doi: 10.1016/j.marchem.2010.12.007

Stockdale, A., Tipping, E., Lofts, S., and Mortimer, R. J. G. (2016). Effect of ocean acidification on organic and inorganic speciation of trace metals. *Environ. Sci. Technol.* 50, 1906–1913. doi: 10.1021/acs.est.5b05624

Sunda, W. G., and Lewis, J. A. M. (1978). Effect of complexation by natural organic ligands on the toxicity of copper to a unicellular alga, Monochrysis lutheri. *Limnol Oceanogr* 23, 870–876. doi: 10.4319/lo.1978.23.5.0870

Thuróczy, C. E., Gerringa, L. J. A., Klunder, M., Laan, P., Le Guitton, M., and de Baar, H. J. W. (2011). Distinct trends in the speciation of iron between the shallow shelf seas and the deep basins of the Arctic Ocean. *J. Geophys Res.* 116, C10009. doi: 10.1029/2010JC006835

Tomczak, M., and Godfrey, J. S. (2001). "Arctic oceanography: the Path of North Atlantic Deep Water," in *Regional Oceanography: an Introduction*. Eds. M. Tomczak and J. S. Godfrey (Oxford: Pergamon), 83–103.

Tovar-Sánchez, A., Duarte, C. M., Alonso, J. C., Lacorte, S., Tauler, R., and Galbán-Malagón, C. (2010). Impacts of metals and nutrients released from melting multiyear Arctic sea ice. *J. Geophys Res.* 115, C07003. doi: 10.1029/2009JC005685

Twining, B. S., and Baines, S. B. (2013). The trace metal composition of marine phytoplankton. *Ann. Rev. Mar. Sci.* 5, 191–215. doi: 10.1146/annurev-marine-121211-172322

Uhlig, C., Damm, E., Peeken, I., Krumpen, T., Rabe, B., Korhonen, M., et al. (2019). Sea ice and water mass influence dimethylsulfide concentrations in the central arctic ocean. *Front. Earth Sci. (Lausanne)* 7. doi: 10.3389/feart.2019.00179

van den Berg, C. M. G. (1982). Determination of copper complexation with natural organic ligands in seawater by equilibration with MnO2 II. Experimental procedures

and application to surface seawater. *Mar. Chem.* 11, 323–342. doi: 10.1016/0304-4203 (82)90029-9

van Ooijen, J. C., Rijkenberg, M. J. A., Gerringa, L. J. A., Rabe, B., and Rutgers van der Loeff, M. M. (2016). Inorganic nutrients measured on water bottle samples during POLARSTERN cruise PS94 (ARK-XXIX/3). *PANGAEA*. doi: 10.1594/PANGAEA.868396

Vernet, M., Ellingsen, I. H., Seuthe, L., Slagstad, D., Cape, M. R., and Matrai, P., A. (2019). Influence of phytoplankton advection on the productivity along the atlantic water inflow to the arctic ocean. *Front. Mar. Sci.* 6. doi: 10.3389/fmars.2019.00583

Whitby, H., Hollibaugh, J. T., and van den Berg, C. M. G. (2017). Chemical speciation of copper in a salt marsh estuary and bioavailability to thaumarchaeota. *Front. Mar. Sci.* 4. doi: 10.3389/fmars.2017.00178

Whitby, H., Posacka, A. M., Maldonado, M. T., and van den Berg, C. M. G. (2018). Copper-binding ligands in the NE pacific. *Mar. Chem.* 204, 36–48. doi: 10.1016/j.marchem.2018.05.008

Whitby, H., and van den Berg, C. M. G. (2015). Evidence for copper-binding humic substances in seawater. *Mar. Chem.* 173, 282–290. doi: 10.1016/j.marchem.2014.09.011

Williford, T., Amon, R. M. W., Kaiser, K., Benner, R., Stedmon, C., Bauch, D., et al. (2022). Spatial complexity in dissolved organic matter and trace elements driven by hydrography and freshwater input across the arctic ocean during 2015 arctic GEOTRACES expeditions. *J. Geophys Res. Oceans* 127. doi: 10.1029/2022JC018917

Wisotzki, A., and Bakker, K. (2008). *Hydrochemistry Measured on Water Bottle Samples During POLARSTERN cruise ARK-XXII/2*. PANGAEA. doi: 10.1594/PANGAEA.759286

Wiwit, Wong, K. H., Fukuda, H., Ogawa, H., Mashio, A. S., Kondo, Y., et al. (2021). Wide-range detection of Cu-binding organic ligands in seawater using reverse titration. *Mar. Chem.* 230, 103927. doi: 10.1016/j.marchem.2021.103927

Wong, K. H., Obata, H., Kim, T., Kondo, Y., and Nishioka, J. (2021). New insights into the biogeochemical cycling of copper in the subarctic Pacific: Distributions, size fractionation, and organic complexation. *Limnol Oceanogr* 66, 1424–1439. doi: 10.1002/lno.11695
Stedmon, C. A., Amon, R. M. W., Rinehart, A. J., and Walker, S. A. (2011). The supply and characteristics of colored dissolved organic matter (CDOM) in the Arctic Ocean: Pan Arctic trends and differences. *Mar. Chem.* 124, 108–118. doi: 10.1016/j.marchem.2010.12.007

Stockdale, A., Tipping, E., Lofts, S., and Mortimer, R. J. G. (2016). Effect of ocean acidification on organic and inorganic speciation of trace metals. *Environ. Sci. Technol.* 50, 1906–1913. doi: 10.1021/acs.est.5b05624

Sunda, W. G., and Lewis, J. A. M. (1978). Effect of complexation by natural organic ligands on the toxicity of copper to a unicellular alga, Monochrysis lutheri. *Limnol Oceanogr* 23, 870–876. doi: 10.4319/lo.1978.23.5.0870

Thuróczy, C. E., Gerringa, L. J. A., Klunder, M., Laan, P., Le Guitton, M., and de Baar, H. J. W. (2011). Distinct trends in the speciation of iron between the shallow shelf seas and the deep basins of the Arctic Ocean. *J. Geophys Res.* 116, C10009. doi: 10.1029/2010JC006835

Tomczak, M., and Godfrey, J. S. (2001). "Arctic oceanography: the Path of North Atlantic Deep Water," in *Regional Oceanography: an Introduction*. Eds. M. Tomczak and J. S. Godfrey (Oxford: Pergamon), 83–103.

Tovar-Sánchez, A., Duarte, C. M., Alonso, J. C., Lacorte, S., Tauler, R., and Galbán-Malagón, C. (2010). Impacts of metals and nutrients released from melting multiyear Arctic sea ice. *J. Geophys Res.* 115, C07003. doi: 10.1029/2009JC005685

Twining, B. S., and Baines, S. B. (2013). The trace metal composition of marine phytoplankton. *Ann. Rev. Mar. Sci.* 5, 191–215. doi: 10.1146/annurev-marine-121211-172322

Uhlig, C., Damm, E., Peeken, I., Krumpen, T., Rabe, B., Korhonen, M., et al. (2019). Sea ice and water mass influence dimethylsulfide concentrations in the central arctic ocean. *Front. Earth Sci. (Lausanne)* 7. doi: 10.3389/feart.2019.00179

van den Berg, C. M. G. (1982). Determination of copper complexation with natural organic ligands in seawater by equilibration with MnO2 II. Experimental procedures

and application to surface seawater. *Mar. Chem.* 11, 323–342. doi: 10.1016/0304-4203 (82)90029-9

van Ooijen, J. C., Rijkenberg, M. J. A., Gerringa, L. J. A., Rabe, B., and Rutgers van der Loeff, M. M. (2016). Inorganic nutrients measured on water bottle samples during POLARSTERN cruise PS94 (ARK-XXIX/3). *PANGAEA*. doi: 10.1594/PANGAEA.868396

Vernet, M., Ellingsen, I. H., Seuthe, L., Slagstad, D., Cape, M. R., and Matrai, P., A. (2019). Influence of phytoplankton advection on the productivity along the atlantic water inflow to the arctic ocean. *Front. Mar. Sci.* 6. doi: 10.3389/fmars.2019.00583

Whitby, H., Hollibaugh, J. T., and van den Berg, C. M. G. (2017). Chemical speciation of copper in a salt marsh estuary and bioavailability to thaumarchaeota. *Front. Mar. Sci.* 4. doi: 10.3389/fmars.2017.00178

Whitby, H., Posacka, A. M., Maldonado, M. T., and van den Berg, C. M. G. (2018). Copper-binding ligands in the NE pacific. *Mar. Chem.* 204, 36–48. doi: 10.1016/j.marchem.2018.05.008

Whitby, H., and van den Berg, C. M. G. (2015). Evidence for copper-binding humic substances in seawater. *Mar. Chem.* 173, 282–290. doi: 10.1016/j.marchem.2014.09.011

Williford, T., Amon, R. M. W., Kaiser, K., Benner, R., Stedmon, C., Bauch, D., et al. (2022). Spatial complexity in dissolved organic matter and trace elements driven by hydrography and freshwater input across the arctic ocean during 2015 arctic GEOTRACES expeditions. *J. Geophys Res. Oceans* 127. doi: 10.1029/2022JC018917

Wisotzki, A., and Bakker, K. (2008). *Hydrochemistry Measured on Water Bottle Samples During POLARSTERN cruise ARK-XXII/2*. PANGAEA. doi: 10.1594/PANGAEA.759286

Wiwit, Wong, K. H., Fukuda, H., Ogawa, H., Mashio, A. S., Kondo, Y., et al. (2021). Wide-range detection of Cu-binding organic ligands in seawater using reverse titration. *Mar. Chem.* 230, 103927. doi: 10.1016/j.marchem.2021.103927

Wong, K. H., Obata, H., Kim, T., Kondo, Y., and Nishioka, J. (2021). New insights into the biogeochemical cycling of copper in the subarctic Pacific: Distributions, size fractionation, and organic complexation. *Limnol Oceanogr* 66, 1424–1439. doi: 10.1002/lno.11695