Summer Surface CO₂ Dynamics on the Bering Sea and Eastern Chukchi Sea Shelves From 1989 to 2019

Abstract

By compiling boreal summer (June to October) CO2 measurements from 1989 to 2019 on the Bering and eastern Chukchi Sea shelves, we find that the study areas act as a CO2 sink except when impacted by river runoff and wind‐driven upwelling. The CO2 system in this area is seasonally dominated by the biological pump especially in the northern Bering Sea and near Hanna Shoal, while wind‐driven upwelling of CO2‐rich bottom water can cause episodic outgassing. Seasonal surface ΔfCO2 (oceanic fCO2 – air fCO2) is dominantly driven by temperature only during periods of weak CO2 outgassing in shallow nearshore areas. However, after comparing the mean summer ΔfCO2 during the periods of 1989–2013 and 2014–2019, we suggest that temperature does drive long‐term, multi‐decadal patterns in ΔfCO2. In the northern Chukchi Sea, rapid warming concurrent with reduced seasonal sea‐ice persistence caused the regional summer CO2 sink to decrease. By contrast, increasing primary productivity caused the regional summer CO2 sink on the Bering Sea shelf to increase over time. While additional time series are needed to confirm the seasonal and annual trajectory of CO2 changes and ocean acidification in these dynamic and spatially complex ecosystems, this study provides a meaningful mechanistic analysis of recent changes in inorganic carbonate chemistry. As high‐resolution time series of inorganic carbonate parameters lengthen and short‐term variations are better constrained in the coming decades, we will have stronger confidence in assessing the mechanisms contributing to long‐term changes in the source/sink status of regional sub‐Arctic seas.

Seasonal Water Mass Evolution and Non‐Redfield Dynamics Enhance CO2 Uptake in the Chukchi Sea

“…To focus on the Chukchi shelf, data used for this study were limited from 66°N to 74°N to a maximum of 120 m to exclude deep waters from the Canada Basin. We adopted the water mass classification used by several previous studies (Table 2 ; Corlett and Pickart et al., 2017 ; Gong & Pickart, 2015 ; Pacini et al., 2019 ; Pickart et al., 2019 ; Wang et al., 2022 ). The coldest water is known as Newly‐Ventilated Winter Water (NVWW; T < −1.6°C), which is typically observed from spring to early‐summer over the entire shelf.…”

A decade of marine inorganic carbon chemistry observations in the northern Gulf of Alaska – insights into an environment in transition

“…The northern Gulf of Alaska (NGA) is a predominantly downwelling system (Royer and Emery, 1987) with seasonal exceptions. When the onshore surface Ekman transport relaxes in the summer, deep, nutrient-rich, cold water can inundate the continental shelf below the surface layer near the shore (Weingartner et al, 2005). The new intermediate water, also enriched in CO 2 , causes the saturation horizon for both aragonite and calcite minerals to shoal to within 100 and 250 m from the surface respectively (Feely et al, 2004).…”

Early Wintertime CO2 Uptake in the Western Arctic Ocean

“…Wang et al. (2022) have examined summer surface‐water CO 2 dynamics in the Bering Sea and Chukchi Shelf using SOCAT fCO 2 and fCO 2 data collected by unmanned surface vehicles. Wang et al.…”

“…Wang et al (2022) have examined summer surface-water CO 2 dynamics in the Bering Sea and Chukchi Shelf using SOCAT fCO 2 and fCO 2 data collected by unmanned surface vehicles. Wang et al (2022) have found that in early summer, high net primary productivity sustained by nutrients supplied via Bering Summer Water maintains a strong summer CO 2 sink, whereas in late summer, strong upwelling and vertical mixing induced by northerly winds results in CO 2 outgassing. In summary, recent studies have indicated that there are distinct differences of spatiotemporal variations of the CO 2 sink between shelf (Chukchi Shelf) and basin (Canada Basin) and that expansion of open sea due to sea ice loss does not necessarily lead to increases of CO 2 uptake.…”

“…Zheng et al (2021) have found that these factors also control interannual variations of the CO 2 flux but in ways that differ seasonally. Wang et al (2022) have examined summer surface-water CO 2 dynamics in the Bering Sea and Chukchi Shelf using SOCAT fCO 2 and fCO 2 data collected by unmanned surface vehicles. Wang et al (2022) have found that in early summer, high net primary productivity sustained by nutrients supplied via Bering Summer Water maintains a strong summer CO 2 sink, whereas in late summer, strong upwelling and vertical mixing induced by northerly winds results in CO 2 outgassing.…”