This paper provides a synthesis of available in situ primary production (PP) measurements from the Pacific Arctic Region (PAR), collected between 1950 and 2012. Seasonal integrated primary production ...(IPP) across the PAR was calculated from 524 profiles, 340 of which were also analyzed to determine the average vertical distribution of PP rates for spring, summer and fall months. The Chirikov Basin and Chukchi Shelf were the most productive areas, with the East Siberian Sea, Chukchi Plateau and Canada Basin the lowest. Decadal-scale changes were indicated in the southern Chukchi Sea, and across Hanna Shoal. In the southern Chukchi Sea in August, IPP increased significantly from 113±35mgCm-2 d-1 in 1959 and 1960 to 833±307mgCm-2 d-1 in the 2000s. Increases in the magnitude of IPP were accompanied by variations in the vertical distribution, the subsurface peak observed in the 1959/60 was not present in the 2000s. The mechanism behind this change was undetermined but could have included changes in stratification, mixing or surface distribution of water masses as well as methodological differences. Over Hanna Shoal, the phytoplankton surface bloom now occurs earlier by several weeks compared to 1993, linked to increases in light due to earlier sea- ice retreat. In 1993 with sea ice still present in the region the surface bloom occurred in August, in 2002 and 2004 this same period was characterized by open water and low surface PP and strong subsurface production. This dataset provides a region-wide quantification of IPP and decadal trends and highlights the need for a cooperative monitoring program to observe the long-term impacts of climate change in the Arctic ecosystem.
For photosynthetic microbial eukaryotes, the rate-limiting step in NO
assimilation is its reduction to nitrite (NO
), which is catalyzed by assimilatory nitrate reductase (NR). Oceanic productivity ...is primarily limited by available nitrogen and, although nitrate is the most abundant form of available nitrogen in oceanic waters, little is known about the identity of microbial eukaryotes that take up nitrate. This lack of knowledge is especially severe for ice-covered seas that are being profoundly affected by climate change. To address this, we examined the distribution and diversity of NR genes in the Arctic region by way of clone libraries and data mining of available metagenomes (total of 4.24 billion reads). We directly compared NR clone phylogenies with the V4 region of the 18S rRNA gene (DNA pool) and 18S rRNA (RNA pool) at two ice-influenced stations in the Canada Basin (Beaufort Sea). The communities from the two nucleic acid templates were similar at the level of major groups, and species identified by way of NR gene phylogeny and microscopy were a subset of the 18S results. Most NR genes from arctic clone libraries matched diatoms and chromist nanoflagellates, including novel clades, while the NR genes in arctic eukaryote metagenomes were dominated by chlorophyte NR, in keeping with the ubiquitous occurrence of Mamiellophyceae in the Arctic Ocean. Overall, these data suggest that a dynamic and mixed eukaryotic community utilizes nitrate across the Arctic region, and they show the potential utility of NR as a tool to identify ongoing changes in arctic photosynthetic communities.
To better understand the diversity of primary producers in the Arctic Ocean, we targeted a nitrogen cycle gene, NR, which is required for phytoplankton to assimilate nitrate into organic forms of nitrogen macromolecules. We compared this to the more detailed taxonomy from ice-influenced stations using a general taxonomic gene (18S rRNA). NR genes were ubiquitous and could be classified as belonging to diatoms, dinoflagellates, other flagellates, chlorophytes, and unknown microbial eukaryotes, suggesting novel diversity of both species and metabolism in arctic phytoplankton.
Fractionation of silicon (Si) isotopes was measured in seven species (nine strains) of polar and sub-polar marine diatoms grown in semi-continuous unialgal cultures under optimal irradiance and ...temperature for each diatom strain. Results from this work provide the first evidence that Si isotope fractionation by diatoms is species-dependent. The greatest difference in the Si isotope fractionation factor (ε) was observed between two Southern Ocean diatoms, Fragilariopsis kerguelensis (−0.54‰, average for two strains) and Chaetoceros brevis (−2.09‰). The ε for the other species, both polar and sub-polar, ranged from −0.72‰ to −1.21‰. The two remaining polar diatoms had ε values of −0.74±0.05‰ for Thalassiosira antarctica, and −1.21±0.04‰ for Thalassiosira nordenskioeldii, while the sub-polar species had ε values of −0.72±0.04‰ for Thalassiosira weissflogii, −0.88±0.06‰ for Thalassiosira pseudonana (CCCM58), −0.97±0.14‰ for Thalassiosira pseudonana (CCMP1014), and −1.15±0.03‰ for Porosira glacialis. The range in ε for the diatoms evaluated in this study may be large enough to significantly impact the Si isotope composition measured in diatom opal (δ30Si-bSiO2) from marine sediments and its subsequent interpretation. To test the influence of diatom taxonomic composition on δ30Si-bSiO2, we developed a model that considered the relative abundance of diatom species and the ε values (from this study) for each species present within the sediment core (i.e. weighted-average ε). The model was applied to records from a Southern Ocean sediment core (TN057-13) where both diatom abundance and δ30Si-bSiO2 data were available. The analysis indicated that 67% of the variation in δ30Si-bSiO2 could be explained by species-dependent Si isotope fractionation. We suggest that future work should assess phytoplankton taxonomic composition when using δ30Si-bSiO2 as a proxy for Si utilization.
We present measurements of the silicon isotopic composition of silicic acid (δ30Si‐Si(OH)4) from seawater collected along a transect following one of the main flow paths of Pacific‐origin waters ...through the Arctic Ocean during the Canadian Arctic GEOTRACES and Distributed Biological Observatory expeditions in the summer of 2015. The δ30Si‐Si(OH)4 signals track the modification of Pacific‐origin waters as they transit from west to east, and reflect the distribution of water masses, the dissolution of biogenic silica (bSiO2), and the biological utilization of Si in surface waters. Pacific‐origin waters have lower δ30Si‐Si(OH)4 values than the surrounding water masses and are closely linked with a tongue of nutrient‐rich cold water that can be traced back to the Bering Strait. The δ30Si‐Si(OH)4 measurements indicate that the high Si(OH)4 in the deep waters of Baffin Bay are driven entirely by dissolution of exported bSiO2. Using an open‐system model, we estimate the biogenic Si isotope effect (30ε) for the Bering and Chukchi Seas, and the Canadian Arctic Archipelago to be 30ε = −1.18 ± 0.02‰ (1SE), which agrees very well with laboratory and field estimates. In contrast, the isotope systematics in the Canada Basin and Baffin Bay are better represented by a closed‐system model. We also present an approach to estimate production by sea‐ice algae using δ30Si‐Si(OH)4 signals, though a better understanding of the sea‐ice/water column Si systematics in the Arctic is needed to confirm the viability of this approach.
Key Points
The dissolved silicon isotope distribution in the Arctic exhibits close association with major water masses
Dissolved silicon isotope signals track the production of biogenic silica in Pacific‐origin waters on their transit through the Arctic
Biogenic silica dissolution determines the dissolved silicon isotope signatures of the isolated deep waters of Baffin Bay
During the International Polar Year (IPY), large international research programs provided a unique opportunity for assessing the current state and trends in major components of arctic marine ...ecosystems at an exceptionally wide spatio-temporal scale: sampling covered most regions of the Canadian Arctic (IPY-Canada’s Three Oceans project), and the coastal and offshore areas of the southeastern Beaufort Sea were monitored over almost a full year (IPY-Circumpolar Flaw Lead project). The general goal of these projects was to improve our understanding of how the response of arctic marine ecosystems to climate warming will alter the productivity and structure of the food web and the ecosystem services it provides to Northerners. The present paper summarizes and discusses six key findings related to primary production (PP), which determines the amount of food available to consumers. (1) Offshore, the warming and freshening of the surface layer is leading to the displacement of large nanophytoplankton species by small picophytoplankton cells, with potentially profound bottom-up effects within the marine food web. (2) In coastal areas, PP increases as favourable winds and the deeper seaward retreat of ice promote upwelling. (3) Multiple upwelling events repeatedly provide food to herbivores throughout the growth season. (4) A substantial amount of pelagic PP occurs under thinning ice and cannot be detected by orbiting sensors. (5) Early PP in the spring does not imply a trophic mismatch with key herbivores. (6) The epipelagic ecosystem is very efficient at retaining carbon in surface waters and preventing its sedimentation to the benthos. While enhanced PP could result in increased fish and marine mammal harvests for Northerners, it will most likely be insufficient for sustainable large-scale commercial fisheries in the Canadian Arctic.
The climate around the Western Antarctic Peninsula (WAP) is rapidly changing and dramatically affecting marine coastal waters. Increases in air and seawater temperatures, not matter how small, can ...alter coastal biological communities due to both temperature increases as well as salinity reduction from glacier melting. The aim of this study was to evaluate the individual and combined effects of elevated sea surface temperature (+4 °C) and decreased salinity (−4) on growth and assemblage composition of natural summer phytoplankton from Potter Cove (King George Island, South Shetlands, northern WAP), using an outdoor microcosm experiment. Pigment composition was analyzed by high performance liquid chromatography (HPLC/Chemtax) and species composition by light and electron microscopy. Increases in phytoplankton biomass during the first 3 days at elevated-temperatures coincided with an increase in the abundance and the specific growth rate of small centric diatoms (Chaetoceros socialis and Shionodiscus gaarderae, mostly observed in temperate waters) and unidentified small phytoflagellates <5 μm. In contrast, pennate diatoms significantly decreased. At the end of the experiment on day 7, under nitrate and phosphate limitation, chlorophytes abundances increased under low salinity whereas prasinophytes decreased in all treatments. This study suggests that climate change could notably affect Antarctic phytoplankton composition by favouring temperate-water species previously undetected in Antarctic waters, such us S. gaarderae. Moreover, the observed changes in phytoplankton structure, associated with an increase of nano- over micro-size taxa, could have important implications for future Antarctic food webs.
•Experimental response of phytoplankton to increased temperature and reduced salinity•Phytoplankton assemblage characterization by HPLC, light and electron microscopy•Dominance of nano-diatoms and phytoflagellates on high temperature and low salinity•Sub-polar species previously undetected in Antarctica favoured by climate change•The first report of Shionodiscus gaarderae (sub-Antarctic species) in Antarctica
Details of the design and implementation of an open-source platform for studying the adhesion of cells attached to solid substrata are provided. The hardware is based on a laser-cut flow channel ...connected to a programmable syringe pump. The software automates all aspects of the flow rate profile, data acquisition and image analysis. An example of the pelagic diatom Thalassiosira rotula adhered to poly(dimethyl siloxane) surfaces is provided. The procedure described enables the shear rate to be converted to drag force for arbitrary-shaped objects, of utility to the study of many cell species, especially ones that are obviously non-spherical. It was determined that 90% of cells are removed with the application of drag forces <
N, and that this value is relatively independent of the incubation time on the surface. This result is important to understand how marine species interact with polymer surfaces that are used in electrical insulator applications.
Abstract
Phytoplankton are the base of nearly all marine food webs and mediate the interactions of biotic and abiotic components in marine systems. Understanding the spatial and temporal changes in ...phytoplankton growth requires comprehensive biological, physical, and chemical information. Long-term datasets are an invaluable tool to study these changes, but they are rare and often include only a small set of measurements. Here, we present biological, physical and chemical oceanographic data measured periodically between March 2010 and November 2017 from the euphotic zone of Saanich Inlet, a temperate fjord on the west coast of British Columbia, Canada. The dataset includes measurements of dissolved macronutrients, total and size-fractionated chlorophyll-a, particulate carbon, nitrogen and biogenic silica, and carbon and nitrate uptake rates. This collection describes phytoplankton dynamics and the distribution of biologically-available macronutrients over time in the upper water column of Saanich Inlet. We establish a baseline for future investigations in Saanich Inlet and provide a data collection protocol that can be applied to similar productive coastal regions.
•Summer phytoplankton assemblages were described in 5 Arctic and Subarctic domains.•Average abundance of total phytoplankton (>2 µm) varied ∼10-fold among domains.•Average total carbon (C) of ...phytoplankton (>2 µm) varied ∼20-fold among domains.•Spatial variation in C biomass was driven mainly by diatoms and dinoflagellates.•Estimates of C biomass are highly sensitive to the cellular C:vol equations used.
In the summers of 2007 and 2008, we studied assemblages of nano- and microphytoplankton from the subsurface chlorophyll maximum (SCM) across five broad oceanographic domains in the seas surrounding northern North America. These domains are the eastern Subarctic North Pacific (ESNP), Bering and Chukchi Seas (BE-CH), Beaufort Sea and Canada Basin (BS-CB), Canadian Arctic Archipelago (CAA), and Baffin Bay and Labrador Sea (BB-LS). Average abundance and total carbon biomass (C) of phytoplankton (>2 µm) varied ∼10-fold and ∼20-fold, respectively, across the five domains. In the BE-CH, CAA and BB-LS, diatoms averaged 35–70% and dinoflagellates 11–45% of total phytoplankton C (>2 µm), whereas in the ESNP and BS-CB, unidentified flagellates/coccoids (2–8 µm) represented a greater proportion of total C (27% and 39% respectively) than in the other domains.
In the BE-CH and BB-LS, phytoplankton C (>2 µm) was dominated by dinoflagellates of the genus Gymnodinium, centric diatoms including Thalassiosira spp. and Chaetoceros spp., unidentified flagellates/coccoids (2–8 µm), and cryptomonads. In contrast, diatoms such as Thalassiosira spp. and its resting spores dominated C in the CAA, with dinoflagellates being less significant than in the BE-CH and BB-LS. Unidentified flagellates/coccoids (2–8 µm), Gymnodinium spp., and cryptomonads dominated in the ESNP, and particularly in the BS-CB, where diatoms contributed only 18% of the very low levels of total phytoplankton C (>2 µm).
Phytoplankton C (>2 µm) to chlorophyll a ratios (phyto C:chl a) averaged only 31 g C g chl a−1 in the oligotrophic BS-CB domain, and 51–150 g C g chl a−1 in the other domains, whereas ratios of biogenic silica to phytoplankton C (>2 µm) (bSi:phyto C) were lowest in the eastern domains. Estimates of phytoplankton C were highly sensitive to the choice of C to cell volume equations (C:vol) adopted in the calculations, particularly in diatom-rich areas.
This study highlights how diatoms and dinoflagellates are the main drivers of large-scale variations in C biomass for phytoplankton (> 2 µm), whereas unidentified flagellates/coccoids (2–8 µm) make a significant contribution to C biomass in oligotrophic domains, such as BS-CB, where diatoms and dinoflagellates are less abundant. Reduced surface water density (σT) was associated with deeper SCM layers, and with decreased C biomass of unidentified flagellates/coccoids (2–8 µm). These observations confirm recent studies highlighting the role of surface water stratification caused by melting sea ice in shaping nano- and microphytoplankton assemblages.
Simultaneous and precise measurements of primary and secondary productivity are required when examining energy transfer from phytoplankton to zooplankton. We examined the relationship between primary ...and crustacean productivity over 2 yr in Saanich Inlet, British Columbia, Canada, to determine how temporal variations in primary productivity influence crustacean productivity and trophic transfer efficiency (TTE). Primary productivity was measured via the 13C tracer method, while the crustacean moulting enzyme chitobiase was used to estimate community-level somatic crustacean productivity. Peak primary productivity occurred much earlier in 2010 (late April; 9.17 g C m−2 d−1) than in 2011 (mid-June; 5.01 g C m−2 d−1) due to a higher abundance of diatoms. Fatty acid analyses revealed that one of the dominant copepods, Calanus marshallae, was feeding on a higher proportion of diatoms than dinoflagellates (lowest DHA:EPA ratios) in May 2010 and June 2011. Crustacean productivity ranged between 0.01 and 0.65 g C m−2 d−1 over both sampling years. Average TTE was 14% in 2010 and 8% in 2011, indicating that the earlier peak in primary productivity in 2010 resulted in more efficient energy transfer from phytoplankton to crustacean zooplankton compared to 2011. Results from this study highlight the need for incorporating routine field estimates of crustacean productivity into oceanographic studies with the same resolution as primary productivity measurements. Together, these estimates are critical in terms of investigating the impact of a potential increase in the occurrence of mismatches between lower and higher trophic levels in predicted future warming scenarios.
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