The spatial and interannual dynamics of the surface water carbonate system and air–sea CO<sub>2</sub> fluxes in the outer shelf and slope of the Eurasian Arctic Ocean

Abstract

Abstract. The Arctic is undergoing dramatic changes which cover the entire range of natural processes, from extreme increases in the temperatures of air, soil, and water, to changes in the cryosphere, the biodiversity of Arctic waters, and land vegetation. Small changes in the largest marine carbon pool, the dissolved inorganic carbon pool, can have a profound impact on the carbon dioxide (CO 2 ) flux between the ocean and the atmosphere, and the feedback of this flux to climate. Knowledge of relevant processes in the Arctic seas improves the evaluation and projection of carbon cycle dynamics under current conditions of rapid climate change.Investigation of the CO 2 system in the outer shelf and continental slope waters of the Eurasian Arctic seas (the Barents, Kara, Laptev, and East Siberian seas) during 2006, 2007, and 2009 revealed a general trend in the surface water partial pressure of CO 2 (pCO 2 ) distribution, which manifested as an increase in pCO 2 values eastward. The existence of this trend was defined by different oceanographic and biogeochemical regimes in the western and eastern parts of the study area; the trend is likely increasing due to a combination of factors determined by contemporary change in the Arctic climate, each change in turn evoking a series of synergistic effects. A high-resolution in situ investigation of the carbonate system parameters of the four Arctic seas was carried out in the warm season of 2007; this year was characterized by the next-to-lowest historic sea-ice extent in the Arctic Ocean, on satellite record, to that date. The study showed the different responses of the seawater carbonate system to the environment changes in the western vs. the eastern Eurasian Arctic seas. The large, open, highly productive water area in the northern Barents Sea enhances atmospheric CO 2 uptake. In contrast, the uptake of CO 2 was strongly weakened in the outer shelf and slope waters of the East Siberian Arctic seas under the 2007 environmental conditions. The surface seawater appears in equilibrium or slightly supersaturated by CO 2 relative to atmosphere because of the increasing influence of river runoff and its input of terrestrial organic matter that mineralizes, in combination with the high surface water temperature during sea-ice-free conditions. This investigation shows the importance of processes that vary on small scales, both in time and space, for estimating the air-sea exchange of CO 2 . It stresses the need for highresolution coverage of ocean observations as well as time series. Furthermore, time series must include multi-year studies in the dynamic regions of the Arctic Ocean during these times of environmental change.

Answer to reviewer #1

“…1). Samples from this region collected during this cruise have also been studied for DOC (Alling et al, 2010;Bröder et al, 2016;Karlsson et al, 2016;Salvadó et al, 2017), dissolved inorganic carbon , POC (Karlsson et al, 2016;Sánchez-García et al, 2011), nutrients and alkalinity (Anderson et al, 2009;Pipko et al, 2017), and stable O isotopes (Rosén et al, 2015).…”

“…Carbon-iron cycling is complex, and stable Fe-isotope data show that the isotopic compositions might be used to investigate chemical pathways for Fe and Fe bound to OC during weathering and estuarine mixing in the boreal-Arctic region Escoube et al, 2015Escoube et al, , 2009Ilina et al, 2013;Ingri et al, 2006;Mulholland et al, 2015;Poitrasson, 2006;Poitrasson et al, 2014)…”

The role of river runoff in the Kara Sea surface layer acidification and carbonate system changes

“…Especially the Canadian and American sectors of the Arctic are well studied (Bates et al 2009, Mathis et al 2011, Bates et al 2013, Robbins et al 2013, Azetsu-Scott et al 2014. The current acidification state of the East Siberian shelf seas (Laptev and East Siberian) is known from (Semiletov et al 2016, Pipko et al 2017. Based on the published data, the acidification process is quite intense in these seas.…”

Dynamics of dissolved inorganic carbon and co2 fluxes between water and atmosphere in the main channel of the ob river

“…Но из-за сравнительно небольшой площади, занимаемой реками на поверхности Земли, они редко рассматриваются в качестве потенциально важного количественного компонента углеродного цикла в глобальной или региональной шкале. Однако последние исследования показали, что эмиссия углекислого газа из наземных водных экосистем играет важную роль в углеродном цикле [1], а геохимический сигнал крупнейших си-бирских рек прослеживается на шельфе/склоне Северного Ледовитого океана [2][3][4].…”

“…С поверхностного и придонного горизонтов были отобраны пробы речной воды для определения гидрохимических параметров -общей щёлочности TA, рН, растворённого кислорода, окрашенной фракции растворённого органического вещества и хлорофилла "а". Эти характеристики измерялись в судовой лаборатории, и методы их определения приведены в [2][3][4]6]. Концентрации форм растворённого неорганического углерода (CO 2 , НСО 3…”