Increasing carbon inventory of the intermediate layers of the Arctic Ocean

Abstract

Concentrations of dissolved inorganic carbon (DIC), total alkalinity (TA), nutrients, and oxygen in subsurface waters of the central Arctic Ocean have been investigated for conceivable time trends over the last two decades. Data from six cruises that cover the Nansen, Amundsen, and Makarov Basins were included in this analysis. In waters deeper than 2000 m, no statistically significant trend could be observed for DIC, TA, phosphate, or nitrate, but a small rate of increase in apparent oxygen utilization (AOU) was noticeable. For the individual stations, differences in concentration of each property were computed between the mean concentrations in the Arctic Atlantic Water (AAW) or the upper Polar Deep Water (uPDW), i.e., between about 150 and 1400 m depth, and in the deep water (assumed invariable over time). In these shallower water layers, we observe significant above-zero time trends for DIC, in the range of 0.6-0.9 lmol kg 21 yr 21 (for AAW) and 0.4-0.6 mmol kg 21 yr 21 (for uPDW). No time trend in nutrients could be observed, indicating no change in the rate of organic matter mineralization within this depth range. Consequently, the buildup of DIC is attributed to increasing concentrations of anthropogenic carbon in the waters flowing into these depth layers of the Arctic Ocean. The resulting rate of increase of the column inventory of anthropogenic CO 2 is estimated to be between 0.6 and 0.9 mol C m 22 yr 21 , with distinct differences between basins.

Origin and Accumulation of an Anthropogenic CO2 and 13C Suess Effect in the Arctic Ocean

“…An AOU increase of ~20 μmol kg −1 caused by a temperature decrease of 2.5 °C between the Iceland Sea and the Arctic IW was applied for the calculation of the preformed DIC in the Arctic. The estimated DIC time rate of change for the Arctic IW is consistent with a range of 0.6–0.9 μmol kg −1 yr −1 estimated in the intermediate layers of the Nansen and Amundsen Basins in the Arctic Ocean (Ericson et al, ), the rate of 1.0 μmol kg −1 yr −1 in the Norwegian Atlantic Current over the period 1981–2005 (Skjelvan et al, ), and rate of 0.9 μmol kg −1 yr −1 in the Atlantic domain of the Nordic Sea (Olsen et al, ).…”

Rapid Changes in Anthropogenic Carbon Storage and Ocean Acidification in the Intermediate Layers of the Eurasian Arctic Ocean: 1996–2015

“…The inclusion of either O 2 or AOU to the variables in equations resulted in highly scattered results with both depth and in space. Neither nutrient changed the statistical fit considerably; however, NO 3 and Si best supported the notion of invariable deep waters with respect to changes in physical and biogeochemical variables over the considered period of time in this study (Ericson et al, ). For the MLRs, a robust regression routine was used (MATLAB routine “robustfit”) following Carter et al ().…”

“…Secondary quality control was applied on Eurasian Basin Deep Water (>2,500 m) by offset analysis using multiple linear regression (MLR) for each parameter (Jutterström et al, ). There is little variation in Eurasian Basin Deep Water properties as a result of long residence time (Tanhua et al, ) with small impact from biogeochemical processes, such as organic matter remineralization and the temporal variability of calcium carbonate dissolution (Ericson et al, ). According to Jutterström et al (), the offset (supporting information Figure S1) should be greater than 4 μ mol/kg for DIC, 6 μ mol/kg for TA, 2% for nutrients and oxygen, and 0.01 for salinity for an adjustment to be made.…”

Measuring pH in the Arctic Ocean: Colorimetric method or SeaFET?

“…Due to the intense ventilation of its subsurface layers, the Arctic Ocean is estimated to contain nearly two times the global mean concentration of anthropogenic CO 2 (Tanhua et al, 2009). Important increases of anthropogenic carbon concentrations have recently been estimated in the intermediate layers of the Arctic Ocean (Ericson et al, 2014), leading to a significant acidification of these water masses. In order to determine ongoing changes in the carbonate chemistry of the Arctic Ocean, it is essential to expand observational capacity.…”