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 (CO2) 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 CO2 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 CO2 (pCO2) distribution, which manifested as an increase in pCO2 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 CO2 uptake. In contrast, the uptake of CO2 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 CO2 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 CO2. It stresses the need for high-resolution 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.
Highlights
The Arctic is currently 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 biodiversity of Arctic waters and land vegetation (Serreze and Barry, 2011; Bhatt et al, 2010)
The negative sea-ice concentration anomaly was strongest to the east of the study area, while the total anomaly for the whole Arctic Ocean was −0.5 million km2 compared to the mean coverage during the 1981–2010 time period
It should be noted that pressure of CO2 (pCO2) was higher in the deep regions of the Laptev and East Siberian seas than in the deep regions of the Kara Sea, even if the river discharge is higher in the Kara Sea than in the East Siberian Arctic seas (ESAS). This is likely a combination of the dominating flow of the river plume and the source pCO2 in the water that mixes with the runoff; the water in the Kara Sea comes from the Barents Sea with its low pCO2, while the Laptev Sea is dominated by inflow from the Kara Sea. This 3-year study of the outer shelf and the continental slope waters of the Eurasian Arctic seas has revealed a general trend in the surface pCO2 distribution, which manifested as an increase in pCO2 values eastward, from the surface waters of the highly productive Barents Sea to the poorly productive eastern Laptev Sea and western East Siberian Sea, which are strongly influenced by terrestrial runoff and coastal/sub-sea permafrost erosion
Summary
The Arctic is currently 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 biodiversity of Arctic waters and land vegetation (Serreze and Barry, 2011; Bhatt et al, 2010). The changes being observed today will probably become more intense in the coming decades through positive feedback, causing further changes in atmospheric circulation, river discharge, the carbon cycle, vegetation, conditions of terrestrial and submarine permafrost, and many other natural processes; the consequences will be noticed within, as well as outside of, the Arctic region (Serreze and Barry, 2011; Anderson et al, 1998; Macdonald et al, 2008; Semiletov et al, 2000, 2016; Shakhova et al, 2014) These changes refer to a “new condition” of the Arctic climate (Kattsov et al, 2010; Jeffries et al, 2013; Wood et al, 2015). The melt season has lengthened by 1–2 weeks per decade, and with continued Arctic warming it will expand further (Stroeve et al, 2014)
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