Atlantic Fjord Research Articles

Fjords Are Potential Hotspots of Refractory Dissolved Organic Matter Production: Insights From 1 Year of Weekly Time‐Series Observations of Fluorescent Dissolved Organic Matter in the Bedford Basin, a Northwestern Atlantic Fjord

AbstractFjords are representative marine ecosystems that play an important role in regulating coastal carbon cycling. As fingerprints of the dissolved organic matter (DOM) pool, fluorescent DOM (FDOM) is widely used to study the ocean carbon cycle. Here, we report on 1‐year of weekly observations of FDOM (from May 2018 to May 2019) in the Bedford Basin, a well‐studied northwestern Atlantic fjord. Results showed that differences in FDOM indices (biological index, fluorescence index, and humification indices) between the euphotic and aphotic layers changed during the investigation period, suggesting that classical definitions of these indices may not apply consistently. Spearman rank correlations showed that the surface FDOM was affected by physical and biological factors, while water mass renewal was the major control for the deeper layer. Humic‐like FDOM (FDOMH) changed following the Atlantic deep‐water intrusion, indicating that FDOMH may be used to trace water mass movements in this region. FDOMH shows a significantly positive linear correlation with apparent oxygen utilization (AOU). Their slopes were higher than those from the open ocean, suggesting that the Bedford Basin is a hotspot of RDOM production. Hence, we proposed a possible carbon sequestration mechanism that fjords play as “RDOM producing hot spots” and that the produced RDOM is then transported to the open ocean via water mass movement and finally stored in the ocean for extended periods of time. The proposed biogeochemical processes may also occur, more generally, in the global coastal ocean.

Temporal dynamics of carbon sequestration in coastal North Atlantic fjord system as seen through dissolved organic matter characterisation

Fjord systems in higher latitudes are unique coastal water ecosystems that facilitate the study of dissolved organic matter (DOM) dynamics from surface to deeper waters. The current work was undertaken in the Trondheim fjord characterized by North Atlantic waters, and compared DOM fractions from three depths - surface (3 m), intermediate (225 m) and deep (440 m) in four seasons, from late spring to winter in 2017. The high-resolution mass spectrometry data showed that DOM composition varies significantly in different seasons rather than in different depths in the fjord systems. The bacterial community composition was comparable except at spring surface and summer intermediate depths. Bacterial production was minimal below the euphotic layer, even with sufficient availability of inorganic nutrients. The bacterial production rate in the surface waters was about 7 times and over 50 times higher than that of the aphotic zone in the winter and the summer seasons, respectively. The surface heterotrophic microbial communities might have rapidly consumed the available labile DOM, with the production of more refractory DOM limiting bacterial production in aphotic layers. The greater number of CRAM-like formulas determined in the surface waters compared to other depths supports our hypothesis. The refractory DOM sequestered in the water column may either be exported into sediments attached to particulate matter and marine gels, or may escape into the atmosphere as carbon dioxide/monoxide during the photochemical oxidation pathways, suggesting that it is involved in climate change scenarios.

Organic Matter Sources in North Atlantic Fjord Sediments

AbstractTo better constrain the global carbon cycle fundamental knowledge of the role of carbon cycling on continental margins is crucial. Fjords are particularly important shelf areas for carbon burial due to relatively high sedimentation rates and high organic matter fluxes. As terrigenous organic matter is more resistant to remineralization than marine organic matter, a comprehensive knowledge of the carbon source is critical to better constrain the efficiency of organic carbon burial in fjord sediments. Here we investigated highly productive fjords in northern Norway and compare our results with both existing and new organic carbon to organic nitrogen ratios and carbon stable isotope compositions from fjords in mid‐Norway, west Svalbard, and east Greenland. The marine organic carbon contribution varies significantly between these fjords, and the contribution of marine organic carbon in Norwegian fjords is much larger than previously suggested for fjords in NW Europe and also globally. Additionally, northern Norwegian fjords show very high marine carbon burial rates (73.6 gC · m‐2 · year‐1) suggesting that these fjords are probably very distinct carbon burial hotspots. We argue that the North Atlantic Current inflow sustains these high burial rates and changes in the current strength due to ongoing climate change are likely to have a pronounced effect on carbon burial in North Atlantic fjords.

A 3-year time series of volatile organic iodocarbons in Bedford Basin, Nova Scotia: a northwestern Atlantic fjord

Abstract. We report weekly observations of volatile organic iodocarbons (CH3I, CH2ClI and CH2I2) over the time period May 2015 to December 2017 from four depths in Bedford Basin, a coastal fjord (70 m deep) on the Atlantic coast of Canada. The fjord is subject to wintertime mixing, seasonal stratification and bloom dynamics, subsurface oxygen depletion, local input of freshwater, and occasional intrusions of higher-density water from the adjacent continental shelf. Near-surface concentrations showed strong seasonal and sub-seasonal variability, which is compared with other coastal time series. The vertical variation of CH2I2 and CH2ClI within the upper 10 m is consistent with rapid photolysis of CH2I2. Average annual sea-to-air fluxes (46.7 nmol m−2 day−1) of total volatile organic iodine were similar to those observed in other coastal and shelf time series, and polyiodinated compounds contributed 80 % of the total flux. Fluxes were subject to strong interannual variability (a factor of 2) mainly due to wind speed variability. Near-surface net production of CH3I averaged 1 pmol L−1 day−1 and was similar to rates in the English Channel but an order of magnitude higher than in shallow waters of the Kiel Fjord, Germany, possibly due to higher microbial degradation in the latter. The near-bottom (60 m) time series showed evidence of CH3I production associated with organic matter degradation and a possible “switch” from the production of CH3I via an alkylation pathway to the production of CH2I2 by a haloform-type reaction. Near-bottom CH3I production varied strongly between years but was generally ca. 20 times lower than near-surface production.

Effects of the invasive red king crab on food web structure and ecosystem properties in an Atlantic fjord

Effects of the invasive red king crab on food web structure and ecosystem properties in an Atlantic fjord

Divergent Chemosymbiosis-Related Characters in Thyasira cf. gouldi (Bivalvia: Thyasiridae)

Within the marine bivalve family Thyasiridae, some species have bacterial chemosymbionts associated with gill epithelial cells while other species are asymbiotic. Although the abundance of symbionts in a particular thyasirid species may vary, the structure of their gills (i.e., their frontal-abfrontal thickening) does not. We examined gill structure in a species tentatively identified as Thyasira gouldi from a Northwest Atlantic fjord (Bonne Bay, Newfoundland) and found remarkable differences among specimens. Some individuals had thickened gill filaments with abundant symbionts, while others had thin filaments and lacked symbionts. We could differentiate symbiotic and asymbiotic specimens based on the size and outline of their shell as well as 18S rRNA, 28S rRNA and CO1 sequences. The wide morphological, genetic and symbiosis-related disparity described herein suggests that chemosymbiosis may influence host divergence, and that Thyasira gouldi forms a cryptic species complex.

Strong Seasonality and Interannual Recurrence in Marine Myovirus Communities

The temporal community dynamics and persistence of different viral types in the marine environment are still mostly obscure. Polymorphism of the major capsid protein gene, g23, was used to investigate the community composition dynamics of T4-like myoviruses in a North Atlantic fjord for a period of 2 years. A total of 160 unique operational taxonomic units (OTUs) were identified by terminal restriction fragment length polymorphism (TRFLP) of the gene g23. Three major community profiles were identified (winter-spring, summer, and autumn), which resulted in a clear seasonal succession pattern. These seasonal transitions were recurrent over the 2 years and significantly correlated with progression of seawater temperature, Synechococcus abundance, and turbidity. The appearance of the autumn viral communities was concomitant with the occurrence of prominent Synechococcus blooms. As a whole, we found a highly dynamic T4-like viral community with strong seasonality and recurrence patterns. These communities were unexpectedly dominated by a group of persistently abundant viruses.

Fjord stratigraphy and processes – evidence from the NE Atlantic Fensfjorden system

ABSTRACTFjords commonly hold sediment basins with high temporal resolution that mirror land‐ and marine‐based processes and depositional environments during a glacial–interglacial cycle. Here, we present TOPAS seismic profiles, with a vertical resolution of <30 cm, bathymetric records and a gravity core from Fensfjorden, west Norway, which allow a detailed study of sedimentary processes and depositional environments in a NE Atlantic fjord system. Fensfjorden hosts a sediment volume of 0.70 km3 and the sediment basins evolved reach a maximum thickness of 100 m. The basins are characterized by a lower acoustically well‐laminated glacimarine unit, of Allerød and Younger Dryas age. This unit is overlain by several acoustically transparent lenses, interpreted to be slide debrites. We suggest these slide debrites to be a result of recurrent mass failures that occurred between 11 500 and 2100 cal a BP. A thin late Holocene hemipelagic unit drapes the slide debrites. During the late Holocene the sedimentation rates in Fensfjorden decreased from 0.110 to 0.040 cm a−1 and two turbidity currents occurred in the 2040–1190 cal a BP time period. This ability to map fjord processes in more detail has, furthermore, made it possible to revise the established stratigraphical framework for NE Atlantic fjords. Copyright © 2013 John Wiley & Sons, Ltd.

Differences between Arctic and Atlantic fjord systems on bioaccumulation of persistent organic pollutants in zooplankton from Svalbard

Differences in bioaccumulation of persistent organic pollutants (POPs) between fjords characterized by different water masses were investigated by comparing POP concentrations, patterns and bioaccumulation factors (BAFs) in seven species of zooplankton from Liefdefjorden (Arctic water mass) and Kongsfjorden (Atlantic water mass), Svalbard, Norway. No difference in concentrations and patterns of POPs was observed in seawater and POM; however higher concentrations and BAFs for certain POPs were found in species of zooplankton from Kongsfjorden. The same species were sampled in both fjords and the differences in concentrations of POPs and BAFs were most likely due to fjord specific characteristics, such as ice cover and timing of snow/glacier melt. These confounding factors make it difficult to conclude on water mass (Arctic vs. Atlantic) specific differences and further to extrapolate these results to possible climate change effects on accumulation of POPs in zooplankton. The present study suggests that zooplankton do biomagnify POPs, which is important for understanding contaminant uptake and flux in zooplankton, though consciousness regarding the method of evaluation is important.

Environmental effects on phytoplankton production in a Northeast Atlantic fjord, Faroe Islands

Primary production in the fjords of the Faroe Islands is usually high. Results of productivity measurements in a typical Faroese fjord (Kaldbaksfjord) in 2006 and 2007 reveal values of about 335 g C m 22 year 21 , which is two to three times higher than reported from neighboring regions, such as Icelandic, west Norwegian and west Scottish fjords. The causal mechanism is high flushing rate of the euphotic zone and high influx of nutrients, relative to the surface area. On average, the majority of the production is based on new production. The productive season is from late March to early April until October. It is controlled by irradiance and occurs when the critical depth extends below the halocline. The system is highly dynamic and the plankton productivity is largely influenced by short-term fluctuations in horizontal flow and vertical mixing, influencing vertical as well as temporal variability in P/B ratio and f-ratio. Fast repetition rate fluorescence profiles revealed that Fv/Fm decreases below 0.5 when the light intensity is above 200 m Em 22 s 21 or when the nitrate þ ammonium concentrations were below a threshold between 0.8 and 2 mM.