Abstract
The Ross Sea, one of the most productive regions in the Southern Ocean, plays a significant role in deep water formation and carbon cycling. Dissolved organic carbon (DOC) concentrations and chromophoric dissolved organic matter (CDOM) absorption and fluorescence (FDOM) properties were studied in conjunction with biophysical properties during austral summer. Elevated values of both DOC (mean 47.82 ± 5.70 μM) and CDOM (absorption coefficient at 325 nm, acdom325: mean 0.31 ± 0.18 m–1) observed in the upper shelf waters in the southwest (SW), north of the Ross Ice Shelf (RIS), the northwest and along a transect inward of the shelf break, suggested in situ production and accumulation linked to the productive spring/summer season. However, regional differences were observed in CDOM with acdom325 higher (0.63 ± 0.19 m–1) and its spectral slope S275–295 lower (24.06 ± 2.93 μm–1) in the SW compared to other regions (0.25 ± 0.08 m–1 and 28.92 ± 2.67 μm–1, respectively). Similarly, the specific UV absorption coefficient or SUVA254 determined at 254 nm was greater (1.85 ± 0.55 m2 mg–1 C) compared to other regions (1.07 ± 0.24 m2 mg–1 C), indicating CDOM of greater molecular weight and aromaticity in the SW. Phytoplankton absorption spectra indicated the shallow mixed layer of SW Ross Sea to be dominated by diatoms (e.g., Fragilariopsis spp.), a preferential food source for grazers such as the Antarctic krill, which in large numbers have been shown to enhance CDOM absorption, a likely source in the SW. Excitation-emission matrix (EEM) fluorescence combined with parallel factor analysis (PARAFAC) retrieved one protein-like and two humic-like FDOM fractions commonly observed in the global ocean. In contrast to acdom325 which was uncorrelated to DOC, we observed weak but significant positive correlations between the humic-like FDOM with salinity and DOC, high value of the biological index parameter BIX and an instance of increasing FDOM with depth at a location with sinking organic matter, suggesting autochthonous production of FDOM. The absorption budget showed a relatively higher contribution by CDOM (70.7 ± 18.3%) compared to phytoplankton (22.5 ± 15.2%) absorption coefficients at 443 nm with implications to ocean color remote sensing. This first study of DOM optical properties provides additional insights on carbon cycling in the Ross Sea.
Highlights
The Ross Sea, a highly productive region of the Southern Ocean, accounts for 25–30% of the annual Southern Ocean primary production and ∼25% of bottom waters formed globally (Orsi et al, 2002; Arrigo et al, 2008; Smith et al, 2014), playing an important role in the marine carbon cycle (DiTullio and Smith, 1996; Arrigo et al, 1999, 2008)
We examine water column Dissolved organic carbon (DOC) concentrations, chromophoric dissolved organic matter (CDOM) absorption and fluorescence (EEMs, parallel factor analysis (PARAFAC) components, BIX) properties in conjunction with biophysical properties obtained during a field campaign in the Ross Sea conducted onboard the Korean ice breaker and research vessel Araon in the austral summer of 2014–2015
Along the main T1 transect, inflow of the modified CDW (MCDW) into the shelf is observed at several locations generally below the low salinity Antarctic Surface Water (AASW) and above the cold and high salinity dense shelf water (DSW), with DSW dominating over the troughs and the MCDW over the banks
Summary
The Ross Sea, a highly productive region of the Southern Ocean, accounts for 25–30% of the annual Southern Ocean primary production and ∼25% of bottom waters formed globally (Orsi et al, 2002; Arrigo et al, 2008; Smith et al, 2014), playing an important role in the marine carbon cycle (DiTullio and Smith, 1996; Arrigo et al, 1999, 2008). Many insights into these bloom dynamics, which are often spatially and temporally distinct, have been obtained from numerous field (DiTullio and Smith, 1996; Smith et al, 1996; DiTullio et al, 2000; Sweeney et al, 2000) and satellite ocean color remote sensing studies (Arrigo et al, 1998a, 1999, 2000; Arrigo and Van Dijken, 2003; Park et al, 2019) These studies reported on two regions within the Ross Sea that exhibit physical and biogeochemical differences: (i) the weakly stratified and deeply mixed central Ross Sea polynya surface waters generally dominated by Phaeocystis antarctica, and (ii) the southwest (SW) marginal ice zone with intense surface stratification and shallow mixed layer depths dominated by diatoms. These recurrent and spatially variable distributions of phytoplankton biomass and taxa have important implications to food-web dynamics (Ainley et al, 2006; Davis et al, 2017), and the fate of dissolved (DOM) and particulate organic matter in the Ross Sea (Asper and Smith, 1999; Carlson et al, 2000; DiTullio et al, 2000; Carlson, 2002; Smith et al, 2011; Smith and Jones, 2015)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
