Characteristics of the surface water DMS and pCO₂ distributions and their relationships in the Southern Ocean, southeast Indian Ocean, and northwest Pacific Ocean

Abstract

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.

First High-Frequency Underway Observation of DMS Distribution in the Southern Ocean during Austral Autumn

“…However, in these previous studies, no elevated DMS concentrations (e.g., >5 nM) or DMS hotspots were observed. The regional significant enhancement of DMS concentrations in this study could be attributed to (i) high-resolution detection of DMS hotspots or (ii) up-to-date enhanced production with increasing terrestrial nutrients via melting glaciers and ice in recent years [12,13].…”

“…The discrepancies (in the range of 1 to 17 nM) between observed and climatological estimates were mainly attributed to the mismatch of spatial (in situ observation point and 1 • × 1 • gridded mean) and temporal (6-h mean and monthly mean) resolution. The much larger discrepancy in the Amundsen Sea (early April) relative to the Antarctic Peninsula (end of April) could be associated with the local DMS sources transported outward from the polynyas (Figure 4), where the high production occurred during the austral summer [6,12,13]. Therefore, the MIZ (early April) of the Amundsen Sea appears to show a particularly large error between observed and climatological data (Figure 4).…”

“…pared to the open ocean [12,13]. More recently, substantially higher DMS concentrations were also observed in Arctic melt ponds for the first time [14].…”

Measurements of atmospheric &#x00394;¹⁴CO₂ along the R/V <i>Xuelong</i> cruise track from Zhongshan Station &#x00028;Antarctica&#x00029; to Shanghai

“…Large-scale upwelling of deep water is evident at latitudes south of 50.0 S, characterised by the 34.5 psu salinity contour that protrudes up to $200 m below the ocean surface. Previous studies have measured high levels of pCO 2 that correspond to this regional CDW upwelling (Poisson et al, 1993;Metzl et al, 1999;Zhang et al, 2017). Moreover, the horizontal gradients of those high levels of pCO 2 display mesoscale features attributable to the nearby Kerguelen Plateau (Poisson et al, 1993).…”

The grazing of abundant microzooplankton causes ultrahigh seawater dimethylsulfide during Southern Ocean algal blooms

“…Compared with those in mid-and low-latitude regions (concentrations mainly below 5 nM), ultrahigh seawater DMS levels, up to hundreds of nM, were observed in the Southern Ocean during the austral spring and summer (Lana et al 2011). And, these ultrahigh DMS concentrations were associated with the high phytoplankton biomass (Arrigo et al 1997;Arrigoet al 1998), which mainly occurred in marginal sea ice zone (Inomata et al 2006;Zhang et al 2017), coastal polynya (Tortell et al 2011;Tortell et al 2012;Kim et al 2017) or even sea ice (Asher et al 2011). However, in other similar high-productivity regions at mid-and low-latitudes, such as the eastern boundary upwelling regions (Chavez & Messié 2009), coral reef waters (Deschaseaux et al 2016) or coastal areas (Yanget al 2012), the seawater DMS concentrations generally do not reach extreme values.…”