Modeled Impacts of Sea Ice Exchange Processes on Arctic Ocean Carbon Uptake and Acidification (1980–2015)

Abstract

A regional Arctic ice ocean model incorporating biogeochemical processes occurring inside the sea ice and water column is used to assess changes to the Arctic Ocean's carbon system, including oceanic carbon uptake and ocean acidification, over the recent period of Arctic sea ice decline (1980–2015). Two novel modifications are the following: (1) incorporation of carbon uptake by sea ice algae and (2) modification of the sea ice carbon pump to allow for vertical transport by brine plumes with high concentrations of dissolved inorganic carbon (DIC) and total alkalinity (TA) to the bottom of the mixed layer. The simulated carbon uptake north of 66.5°N increases by 20%, from 110 to 135 Tg C yr−1 from 1980–2015, and the mean pan‐Arctic sea surface pH decreases from 8.1 to 8.0. There is substantial regional and seasonal variability, highlighting potential problems with interpolating sparse measurements. Two sensitivity studies assess the effects of modifications to the near‐surface carbonate system. First, excluding the sea ice carbon pump results in a marked decrease in seasonal variability of pan‐Arctic‐mean sea surface DIC (∼25% less than the standard run) and TA (∼10% less), suggesting that neglecting the ice carbon pump results in models overestimating the saturation state in summer. Second, neglecting the sea ice algae results in an underestimation of the Arctic Ocean's annual carbon uptake (∼3% per year), indicating that the accumulating year‐on‐year underestimation of annual carbon uptake, as a result of neglecting sea ice algae, would lead to increasing error over multidecadal runs of polar ocean models.

Increase in CO2 Uptake Capacity in the Arctic Chukchi Sea During Summer Revealed by Satellite‐Based Estimation

“…To reduce the uncertainty rising from limited observations, great efforts have been made by the oceanographic community to extend the spatial and temporal coverage of p CO 2 on the Chukchi shelf. Approaches such as interpolation (Evans et al., 2015), ocean‐biogeochemistry coupled model (Manizza et al., 2019; Mortenson et al., 2020), and artificial neural network‐based self‐organizing map (SOM) technique (Laruelle et al., 2017; Roobaert et al., 2019; Yasunaka et al., 2016) have been proposed to create monthly or annual climatology of ∆ p CO 2 in western Arctic coastal ocean. These approaches provide general variability in biogeochemical characteristics within this broad and rapidly changing polar coastal ocean, however, their applicability in the Chukchi Sea may have limitations.…”

PREPRINT OF MANUSCRIPT ACCEPTED AT ELEMENTA: SCIENCE OF THE ANTHROPOCENE "The MOSAiC Distributed Network: observing the coupled Arctic system with multidisciplinary, coordinated platforms"

“…In addition to complex autonomous instruments, the distributed deployment of position-tracking buoys has provided information about the localized and aggregate ice dynamics, allowing relationships to the wind and ocean forcing to be identified. The corresponding time period, when the Central Observatory was unattended, was a critical time to complete our observations of the full seasonal cycle of the ice within the DN, including optical measurements of biology and chemistry, all subject to changing rapidly with climate change (Bluhm et al, 2020;Mortenson et al, 2020). Hence, there is a continuous need for more telemetered, autonomous observations, such as those of the DN.…”

The impact of sea ice melt on the evolution of surface pCO2 in a polar ocean basin

“…Due to the high solubility of CO 2 in low-temperature waters, the Arctic Ocean and its adjacent marginal seas serve as a significant CO 2 sink (Anderson and Kaltin, 2016;Yasunaka et al, 2018). Observations and model simulations have indicated that the Arctic Ocean absorbs 58-180 Tg C per year, accounting for 2%-7% of the global oceanic carbon sink (Manizza et al, 2013;Yasunaka et al, 2016;Mortenson et al, 2020). In recent decades, rapid and diverse changes, for example the increased seawater temperature, ice sheet melt, and an extended ice-free period, have occurred in Arctic ecosystems (Screen and Simmonds, 2010;Shepherd et al, 2012;Jeong et al, 2018).…”