Search

This study analyzes the molecular composition of dissolved organic matter (DOM) in Prydz Bay by Fourier Transform Ion Cyclotron Resonance mass spectrometry to probe the carbon sequestration capacity in the continental shelf system. Concentrations of particulate organic carbon (POC), particulate nitrogen and dissolved organic carbon (DOC) with water depth show that POC could be mainly decomposed into DOC and/or microbially degraded. Highly labile DOC is further degraded and remineralized by microorganisms within the upper 200 m, as evidenced by a downward enrichment of 13CPOC and increases in the average molecular weight, oxygen atom number (O) and double bond equivalents of DOM molecules, indicating that biodegradation is the main driver for particulate organic matter and DOM evolution with water depth. Semi‐quantitative calculation demonstrates that ∼83% of POC was transformed to DOC as well as dissolved inorganic carbon (DIC), and ∼30% of DOC further to DIC via microbial degradation within the upper 200 m in summer, resulting in a relatively low total organic carbon content in sediments of Prydz Bay. The newly transformed DIC and residue DOC can be preserved in the deep layer due to the formation of well stratified and stable water body in summer of Prydz Bay, ultimately entering the regional circulation system instead of being released back into the atmosphere. This could be one of the most important processes determining the atmosphere CO2 uptake in the continental shelf system of Southern Ocean. Plain Language Summary: The continental shelf system in the Southern Ocean, especially with the development of polynyas, plays a critical role in the global carbon cycle and disproportionally accounts for almost half of the anthropogenic CO2 uptake by the biological pump, with ensuing deep‐sea sequestration by the form of particulate and dissolved organic carbon, and even CO2 due to microbial degradation of primary productivity. However, complex interactions between physical, chemical and biological processes significantly affect the fate of organic carbon through the water column, resulting in an uncertainty of vertical carbon export. In this study, we conduct an investigation on the dissolved organic matter sources and evolution with water depth in summer of Prydz Bay, a typical polynya‐developed continental shelf system in the East Antarctica. The results clearly show that biodegradation is the main factor controlling organic carbon mineralization and mainly occurs within the upper 200 m of water column, with a transformation into dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC). Integrated with regional circulation system and hydrological characteristics, our study further indicates that newly formed DIC and DOC can be preserved in the deep layer of Prydz Bay, then into the regional circulation system rather back to the atmosphere. Key Points: Novel evidence at molecular level shows the vital role of biodegradation during carbon sink in Prydz BayThe conversion of POC into DOC/DIC mainly occurs within the upper 200 m of water columnHighlighting regional circulation's contribution to carbon transport and sequestration in the Southern Ocean [ABSTRACT FROM AUTHOR]

To examine seasonal and regional variabilities in metabolic status and the coupling of net community production (NCP) and air‐sea CO2 fluxes in the western Arctic Ocean, we collected underway measurements of surface O2/Ar and partial pressure of CO2 (pCO2) in the summers of 2016 and 2018. With a box‐model, we demonstrate that accounting for local sea ice history (in addition to wind history) is important in estimating NCP from biological oxygen saturation (Δ(O2/Ar)) in polar regions. Incorporating this sea ice history correction, we found that most of the western Arctic exhibited positive Δ(O2/Ar) and negative pCO2 saturation, Δ(pCO2), indicative of net autotrophy but with the relationship between the two parameters varying regionally. In the heavy ice‐covered areas, where air‐sea gas exchange was suppressed, even minor NCP resulted in relatively high Δ(O2/Ar) and low pCO2 in water due to limited gas exchange. Within the marginal ice zone, NCP and CO2 flux magnitudes were strongly inversely correlated, suggesting an air to sea CO2 flux induced primarily by biological CO2 removal from surface waters. Within ice‐free waters, the coupling of NCP and CO2 flux varied according to nutrient supply. In the oligotrophic Canada Basin, NCP and CO2 flux were both small, controlled mainly by air‐sea gas exchange. On the nutrient‐rich Chukchi Shelf, NCP was strong, resulting in great O2 release and CO2 uptake. This regional overview of NCP and CO2 flux in the western Arctic Ocean, in its various stages of ice‐melt and nutrient status, provides useful insight into the possible biogeochemical evolution of rapidly changing polar oceans. Key Points: Accounting for the local sea ice history (in addition to wind history) is important in estimating net community production from Δ(O2/Ar)Coupling of sea surface Δ(O2/Ar) and Δ(pCO2) and related NCP and CO2 flux vary regionally as sea ice cover changesPacific Water greatly affects the regional NCP and CO2 flux in the western Arctic Ocean in summer [ABSTRACT FROM AUTHOR]

Oceanic dimethyl sulfide (DMS) is of interest due to its critical influence on atmospheric sulfur compounds in the marine atmosphere and its hypothesized significant role in global climate. High-resolution shipboard underway measurements of surface seawater DMS and the partial pressure of carbon dioxide ( pCO2) were conducted in the Atlantic Ocean and Indian Ocean sectors of the Southern Ocean (SO), the southeast Indian Ocean, and the northwest Pacific Ocean from February to April 2014 during the 30th Chinese Antarctic Research Expedition. The SO, particularly in the region south of 58°S, had the highest mean surface seawater DMS concentration of 4.1 ± 8.3 nM (ranged from 0.1 to 73.2 nM) and lowest mean seawater pCO2 level of 337 ± 50 μatm (ranged from 221 to 411 μatm) over the entire cruise. Significant variations of surface seawater DMS and pCO2 in the seasonal ice zone (SIZ) of SO were observed, which are mainly controlled by biological process and sea ice activity. We found a significant negative relationship between DMS and pCO2 in the SO SIZ using 0.1° resolution, [DMS] seawater = −0.160 [ pCO2] seawater + 61.3 ( r2 = 0.594, n = 924, p < 0.001). We anticipate that the relationship may possibly be utilized to reconstruct the surface seawater DMS climatology in the SO SIZ. Further studies are necessary to improve the universality of this approach. [ABSTRACT FROM AUTHOR]

Characteristics of the pCO2 distribution in surface water of the Bering Abyssal Plain and their relationships with the ambient hydrological conditions were discussed using variations of the partial pressure of CO2 in surface water of the Bering Abyssal Plain and the Chukchi Sea. Data in this study are from a field investigation during the First Chinese National Arctic Research Expedition in 1999. Compared to the high productivity in the Bering Continental Shelf, much lower levels of chlorophyll a were observed in the Bering Abyssal Plain. The effect of hydrological factors on the pCO2 distribution in surface seawater of the Plain in summer has become a major driving force and dominated over biological factors. The Plain also presents a High Nutrient Low Chlorophyll (HNLC). In addition, the pCO2 distribution in the Bering Abyssal Plain has also been found to be influenced from the Bering Slope Current which would transform to the Anadyr Current when it inflows northwestward over the Plain. The Anadyr Current would bring a high nutrient water to the western Arctic Ocean where local nutrients are almost depleted in the surface water during the summer time. Resupplying nutrients would stimulate the growth of phytoplankton and enhance capacity of absorbing atmospheric CO2 in the surface water. Otherwise, in the Bering Sea the dissolved inorganic carbon brought from freshwater are not deposited down to the deep sea water but most of them would be transported into the western Arctic Ocean by the Alaska Coastal Current to form a carbon sink there. Therefore, the two carbon sinks in the western Arctic Ocean, one carried by the Anadyr Current and another by the Alaska Costal Current, will implicate the western Arctic Ocean in global change. [ABSTRACT FROM AUTHOR]