Characterization of the Water Masses in the Shelf Region of the Bering and Chukchi Seas With Fluorescent Organic Matter

Abstract

Pacific water is an important nutrient source for sustaining biological production in the Chukchi Sea, western Arctic Ocean, which is one of the productive regions in the world. Therefore, to understand the impacts of future environmental changes on biological production in the sea, it is crucial to understand the origins, modification processes, and spatiotemporal variations of the water masses from the Bering Sea with changes in nutrient concentrations. To improve water mass analysis in the shelf regions of the Bering and Chukchi Seas, we observed levels of humic-like fluorescent organic matter (FOM H ) by using an in situ fluorometer directly connected to a temperature-salinity sensor during a cruise in the early summer of 2013 and evaluated the potential of FOM H as a third parameter of water mass analysis. The levels of FOM H were different among specific water masses in the region, and FOM H seemed to behave semiconservatively in the shelf regions of the Bering and Chukchi Seas during the early summer of 2013. The distributional pattern of FOM H implies that FOM H estimated by the in situ fluorometer has the potential to (1) separate warm water into riverine-affected Alaskan Coastal Water and historically photobleached summer Bering Basin Water; (2) distinguish the Anadyr Water, which has low FOM H levels and high nutrient concentrations, from the Bering Shelf Water; and (3) determine different formation/modification processes of dense shelf water that contains high nutrient concentrations. Plain Language Summary The continental shelves of the northern Bering Sea and the ChukchiSea are known to be the area characterized by a high abundance of organisms from phytoplankton to marine mammals and seabirds. Such a high density of marine organisms is sustained by intensive primary production induced by inputs of enough nutrients. The inputs of nutrients to the region are possibly sensitive to climate change. To project future changes in nutrient supply to the region, the present mechanism of nutrient supply should be quantitatively understood. To date, however, the mechanism is poorly determined because the origin and modification of water masses that convey nutrients have not been well understood. This study measured humic-like fluorescent organic matter, products during the decay and transformation of biogenic remains, in addition to temperature and salinity by in situ sensors to characterize the water masses in the shelf region of the Bering and Chukchi Seas during the early summer of 2013. The levels were clearly different among water masses defined by temperature and salinity and characterized by different concentrations of nutrients, indicating that humic-like fluorescent organic matter is useful to refine the water masses in the region for quantitative understanding of the mechanism of nutrient supply.

Hydrographic Feature Variation Caused Pronounced Differences in Planktonic Ciliate Community in the Pacific Arctic Region in the Summer of 2016 and 2019

“…Biogeographically, the classification of tintinnid genera (Neritic, species largely restricted to nearshore waters; Boreal, species restricted to Arctic and Subarctic waters; Cosmopolitan, species distributed widely in the world ocean) was based on Pierce and Turner (1993) and Dolan and Pierce (2013) . The threshold for Pacific Inflow Water was 4 ° C as Yamashita et al (2019) in our results. Data of total surface heat flux (SHF = net solar radiation + net longwave radiation + sensible heat flux + latent heat flux) were obtained from the European Centre for Medium-Range Weather Forecasts (ECMWF).…”

Long‐term Trends in Dissolved Organic Matter Composition and Its Relation to Sea Ice in the Canada Basin, Arctic Ocean (2007–2017)

“…Optical properties including absorbing and fluorescing properties have been used to assess DOM composition and fate (Coble, 2007; Nelson & Gauglitz, 2016), and trace water masses in Arctic waters (Dainard and Guéguen, 2013; Gonçalves‐Araujo et al., 2016; Guéguen et al., 2014; Logvinova et al., 2015; Stedmon et al., 2011; Walker et al., 2009; Yamashita et al., 2019). Colored DOM (CDOM) is defined as the fraction of DOM (up to 25%; Benner, 2002) that has light absorbing properties in the ultraviolet (UV) and visible regions of the electromagnetic spectrum (Hansell & Carlson, 2002) whereas the fluorescent DOM (FDOM) refers to the DOM pool that fluoresces.…”

“…and Gonçalves-Araujo et al, 2016;Guéguen et al, 2014;Logvinova et al, 2015;Stedmon et al, 2011;Walker et al, 2009;Yamashita et al, 2019). Colored DOM (CDOM) is defined as the fraction of DOM (up to 25%; Benner, 2002) that has light absorbing properties in the ultraviolet (UV) and visible regions of the electromagnetic spectrum (Hansell & Carlson, 2002) whereas the fluorescent DOM (FDOM) refers to the DOM pool that fluoresces.…”

Mass Occurrence of Pacific Copepods in the Southern Chukchi Sea During Summer: Implications of the High-Temperature Bering Summer Water

“…Until recently, various trends in the properties of these water masses have been reported in the Chukchi Sea (Ershova et al, 2015b;Corlett and Pickart, 2017;Danielson et al, 2017;Pickart et al, 2019). In particular, excellent analyses of water masses in this area have been performed by Pickart and colleagues (Pickart and Stossmeister, 2008;Pickart et al, 2010Pickart et al, , 2016Pickart et al, , 2019Brugler et al, 2014;Pickart, 2015, 2016;Pisareva et al, 2015;Corlett and Pickart, 2017;Linders et al, 2017;Lin et al, 2019); many previous studies have cited or applied Pickart's classifications when identifying water masses (e.g., Ershova et al, 2015a;Weingartner et al, 2017;Yamashita et al, 2019). Due to the purpose and region of this study, the water masses were identified with reference to the recent and well-organized methods of classification in Corlett and Pickart (2017) and Pickart et al (2019).…”