Search

Atlantification, known as impacts of high-latitude Atlantic water inflows on the Arctic Ocean has strengthened owing to climate change, corresponding to the rapid ice retreat in the Arctic. The relationship between phytoplankton and environmental changes in the Arctic on the interannual scale is unclear because of the lack of long-time series data. In this study, we discuss the ecological response to Atlantic water intrusion in the Kongsfjorden,Svalbard. We measured chlorophyll a and photosynthesis pigments for the water column samples from a fixed section along the Kongsfjorden to study the response of phytoplankton biomass and communities to Atlantic water intrusion in the summer season from 2007 to 2018. The results showed that dinoflagellates, prasinophytes, cryptophytes, and chlorophytes consistently accounted for over 50% of the total biomass, with the distinct annual variation of chlorophyll a. Bioavailable nitrogen was the main limiting factor on phytoplankton growth in the study area, as inferred by its concentration and nutrients ratios. The relationship between phytoplankton and water mass analysis suggested that the intrusion of Atlantic water in Kongsfjorden may cause interannual variability of the phytoplankton biomass and community structure by influencing the nutrient supply and water stratification in the fjord region. Our study provides insights into the ongoing impact of Atlantification on the phytoplankton community in the Arctic fjord., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Subsurface chlorophyll maxima (SCM) layers are becoming more important to the Arctic shelf ecosystem as phytoplankton growing season and ice‐free water increase. We measured size‐fractionated pigments and environmental variables on the western Arctic shelf during the open‐water season in 2014, to study the spatial pattern and mechanisms of the phytoplankton community at the SCM. The SCM layers accumulated approximately 50% of the chlorophyll a (Chl a) standing stock in the water column, and the contribution increased to >70% for high‐biomass areas, suggesting the biological importance of the summer SCM in the shelf ecosystem. The spatial difference in phytoplankton biomass was caused mainly by bioavailable nitrogen concentrations, and the spatial difference in diatom size may be the result of differences in predominant species. High biomass and large diatoms dominated in the SCM layers, making the south and north of the Chukchi shelf a biological hotspot for the ecosystem's food chain and benthos of the western Arctic shelf in summer. Plain Language Summary: Subsurface chlorophyll maxima (SCM) play an increasingly important role in shelf ecosystems in the western Arctic Ocean. The correlations between the subsurface phytoplankton community and environmental variables were examined to gain insight into the mechanisms underlying phytoplankton distribution in SCM layers. Spatial variability of the chlorophyll a (Chl a) standing stock showed a high phytoplankton biomass in the south Bering shelf (SBS), south Chukchi shelf (SCS), and north Chukchi shelf (NCS). Small diatoms dominated the phytoplankton community in the SBS, whereas large diatoms dominated in the SCS and NCS. The spatial difference in phytoplankton biomass was caused mainly by bioavailable nitrogen concentrations, and the spatial difference in diatom size may be the result of differences in predominant species. Summer SCM accumulate a large number of large diatoms in the water column, making the south and north of the Chukchi shelf a biological hotspot for the marine ecosystem on the western Arctic shelf in summer. Key Points: Summer SCM accumulate ~50% of the total water column chlorophyll aNitrate availability causes the spatial difference in phytoplankton biomassHigh biomass and dominance of large diatoms make the south and north of the Chukchi shelf a biological hotspot in summer [ABSTRACT FROM AUTHOR]

The southern Yellow Sea (SYS) shows extensive spatial variations in water masses, particularly YS Warm Current Water (YSWCW) and YS Coastal Current Water in cold and YS Bottom Cold Water (YSBCW) and Changjiang Diluted Water in warm seasons. These hydrographic processes result in significant spatial changes in nutrients, stratification, and turbidity, which may highly regulate phytoplankton distribution in the SYS. Here, we provide high spatial resolution data sets of phytoplankton in the SYS in all seasons during 2011–2012. Diatoms thrived in eutrophic Changjiang Diluted Water and YS Coastal Current Water regions. Notably, benthic/meroplanktonic diatoms, including Paralia sulcata and Rhaphoneis spp., were dominant near the Changjiang Estuary and Subei Shoal. However, cryptophytes and haptophytes were dominant in oligotrophic offshore regions controlled by YSWCW and YSBCW. Phytoplankton abundance and chlorophyll a were considerably lower in the YSWCW and YSBCW than in other regions, and the community composition varied significantly among regions. Algal blooms were observed off the SYS coast in spring and near the Changjiang Estuary in summer, which were characterized by abundant nutrients, low turbidity, and a relatively stable water column. Canonical correspondence analysis demonstrated that stratification in cold and nutrients in warm seasons were most important variables correlated with phytoplankton community. Variation partitioning analysis confirmed that spatial changes in phytoplankton community composition were largely structured by nutrients rather than by physical factors in all seasons except winter. Our findings highlight the significance of water column stability and nutrients associated with water mass variation in shaping spatial changes of phytoplankton community in the SYS. Key Points: Spatial changes in phytoplankton community were largely regulated by water column stability in cold and nutrients in warm seasonsSpring and summer algal blooms were found in the regions characterized by abundant nutrients, low turbidity, and a stable water columnBenthic/meroplanktonic diatoms, including Paralia sulcata and Rhaphoneis spp., were dominant near the Changjiang Estuary and Subei Shoal [ABSTRACT FROM AUTHOR]

Nutrient and phytoplankton pigment data were collected during summer cruises in 2008–2014 to examine how the Beaufort Gyre (BG) affected regional differences in nutrient stocks and the phytoplankton community. The results showed a gradual decrease in nutrient concentrations and increasing depth of the chlorophyll maxima toward the center of the gyre. A horizontal map of nitrate at a depth of 50 m indicated nitrogen deficiency in the gyre compared with that in the surroundings. Biogeochemical model simulations suggested that an increased freshwater convergence, driven by the strengthened BG and sea ice retreat, was primarily responsible for the decrease in nutrient stocks. In the BG zone, the contribution of diatoms to the phytoplankton community decreased, accompanied by the increased contribution of small flagellates. The current state of the BG under anticyclonic winds negatively affected the diatom biomass and biological carbon pump. The possible rotation of wind regimes from anticyclonic to cyclonic might relieve the nitrogen deficiency for phytoplankton growth in the western Arctic Ocean. [ABSTRACT FROM AUTHOR]

Photosynthesis pigments and size-fractionated chlorophyll a were determined during the Chinese CHINARE Arctic cruise in summer 2010, to study the phytoplankton community in response to different Pacific water masses in the Eastern Chukchi Shelf (ECS). In the summer, the phytoplankton biomass was high with large diatoms dominated in the shelf, which might in favor to well-stratified water conditions and adequate nutrient supply of Pacific waters. However, nitrate-poor Alaska Coastal Water (ACW) altered the phytoplankton community structure in the east part of Chukchi shelf, as dinoflagellate and chrysophyte biomass significantly increased. It was shown that in ACW-influenced area, the Chl a concentration was an order of magnitude lower (0.41 µg/dm 3 in averaged) compared to that in the entire ECS, with the community mainly consisting of nano- and pico-phytoplankton. The result indicated that the diatom-dominated shelf was greatly impact by the spreading pathway of ACW. Thus, the future enhancement of ACW and subsequent ecological impact need further concern. [ABSTRACT FROM AUTHOR]

The inflow of Alaska Coastal Water (ACW) acts as a source of heat and freshwater for the Arctic Ocean, and contributes to ecosystem succession as well as phytoplankton change. To explore the mechanisms and patterns of the phytoplankton composition in response to the ACW, diagnostic pigments and environmental parameters were analyzed along three similar transects from shelf to basin in the Arctic Ocean during summer in 2008–2016. The results showed that the incursion of the ACW reduced the chlorophyll a (Chl a) concentration in the shelf areas, but favored phytoplankton growth in basin areas, especially that of small prasinophytes and chrysophytes. A possible explanation is the change in nutrient status, because during its northward flow, the ACW dissipates heat and receives nutrients from the surrounding cold water. The concentrations of Prasino and Chl b (the diagnostic pigments of prasinophytes) increase from barely detected in 2008 to higher than 15 ng/dm3 (Prasino) and 65 ng/dm3 (Chl b) respectively in 2014 and 2016, which occurred synchronously with presence of ACW and an increase in subsurface nitrate reservoirs. These findings indicate that the incursion of the ACW brings nutrients into subsurface basin layers, which could favor the growth of small phytoplankton in the western Arctic Ocean. [ABSTRACT FROM AUTHOR]

Highlights • First report on HBI-III and P III IP 25 in sinking particles in the western Arctic Ocean. • HBI-III in sinking particles suggests ice edge rather than ice-free production of this compound at our site. • Sedimentary IP 25 shows a positive correlation with HBI-III. • Sedimentary P B IP 25 and P III IP 25 both exhibit a linear relationship with spring sea ice cover. Abstract Sediment traps were deployed at 870 m water-depth from August 2008 to September 2009 at station DM in the Chukchi Sea (western Arctic Ocean) in an area covered by sea ice in winter to determine seasonal fluxes of HBIs and phytoplankton sterols in order to improve our understanding of sea ice proxies. HBI-III fluxes and P III IP 25 are for the first time documented in the Arctic Ocean to evaluate their significance for paleoclimate reconstructions. Highest mass fluxes were found from mid-July 2009 to September 2009 contrasting with low values during all other months (i.e., December 2008 to early July 2009). Indeed, during the winter months IP 25 was not detected but increased by a factor of nine over summer 2009 reflecting sea ice algae and pelagic phytoplankton production at the sea ice edge. High HBIs and low sterol fluxes at the end of summer 2008 are consistent with the complete melting of sea ice and post-bloom conditions. We found that HBI-III was more abundant in the early stage of sea ice retreat that characterizes the marginal ice zone. These sea ice biomarkers were also measured in surface sediments across a wide range of sea ice cover in the western Arctic region. Higher IP 25 values were found in the southeastern Chukchi Sea and decreased westwards where sea ice conditions are less severe. Stronger positive linear relationship were found between the sea ice proxy indexes P B IP 25 and P III IP 25 and spring sea ice concentrations than with IP 25 in agreement with earlier findings from other Arctic and sub-Arctic regions. [ABSTRACT FROM AUTHOR]