Abstract
The carbon cycle is a key regulator of Earth’s climate. On geological time-scales, our understanding of particulate organic matter (POM), an important upper ocean carbon pool that fuels ...ecosystems and an integrated part of the carbon cycle, is limited. Here we investigate the relationship of planktonic foraminifera-bound organic carbon isotopes (δ
13
C
org-pforam
) with δ
13
C
org
of POM (δ
13
C
org-POM
). We compare δ
13
C
org-pforam
of several planktonic foraminifera species from plankton nets and recent sediment cores with δ
13
C
org-POM
on a N-S Atlantic Ocean transect. Our results indicate that δ
13
C
org-pforam
of planktonic foraminifera are remarkably similar to δ
13
C
org-POM
. Application of our method on a glacial sample furthermore provided a δ
13
C
org-pforam
value similar to glacial δ
13
C
org-POM
predictions. We thus show that δ
13
C
org-pforam
is a promising proxy to reconstruct environmental conditions in the upper ocean, providing a route to isolate past variations in δ
13
C
org-POM
and better understanding of the evolution of the carbon cycle over geological time-scales.
The use of atmospheric pressure chemical ionisation (APCI) compact mass spectrometry (CMS) was investigated for the analysis of jetsam and museum-archived ambergris and of ambergris components in ...perfumes. The data were compared with those from existing methods. Authentic samples of some individual ambergris constituents (ambrein, coprostanol, epicoprostanol and coprostanone), were also examined. Rapid APCI CMS was achieved using either a solids probe or a probe with solutions held in capillary melting point tubes. Interpretation is made of the spectra of the principal natural product components, the relative ion responses were measured and the elemental composition of key ions in the spectra confirmed using high resolution accurate mass APCI MS. Rapid analysis of ambergris by APCI CMS may prove to be a further convenient method of identifying ambrein, of measuring the relative ratios of ambrein and steroids in ambergris and even of quantifying the latter, with minimal sample preparation.
This study assessed the impact of prescribed burning on the peat properties of moorlands during the post-fire succession in a multi-site study within a major moorland region of Great Britain. Three ...replicate moorland sites were sampled; all were ombrotrophic bogs and had peat soils overlying similar geology and similar vegetation. A chronosequence approach was used to sample soils from a post-fire succession (3–52years since burning) on each site and a number of chemical properties measured. The data on soil chemical properties were analysed using both linear-mixed-effects modelling and multivariate analysis. There were clear differences in some soil properties between moorland sites, but for most soil variables measured there was no change through the post-fire succession. Four variables (available P and Ca; total P and K) showed a significant interaction, i.e. different responses on each moorland site through time. These results suggest that there are complex interactions between nutrient inputs (rainfall and dry deposition which is affected by elevation), storage and cycling within the soil-peat system and losses that differ on the three moorland sites. The most interesting result was the additive response of the C:N ratio which differed between moorland sites; all sites showed the same negative slope with respect to elapsed time since burning, indicating an increased N saturation. This result suggests that the oldest stands sampled here may have either (i) responded to the large N inputs added from the atmosphere in the latter part of the twentieth century, or (ii) the younger ones have had some of this N removed during prescribed burning. This suggestion needs further investigation. Nevertheless, the impacts of prescribed burning on the peat properties during the post-fire succession were relatively small.
•We measured peat chemical properties during post-fire succession on 3 UK moorlands.•Differences in peat chemical properties were found between the 3 moorlands.•There was little change through the succession for most peat chemical properties.•One exception was the C:N which reduced with time since burning.•This suggests either N-saturation (older sites) or N-removal (younger ones).
•Seasonality and cross shelf distribution of DOM and its optical properties were examined in the Celtic Sea.•Strong cross shelf gradients in humic DOM components with significant negative ...correlations with salinity and DOC.•Variability in labile DOM protein components linked to biological productivity.
The Celtic Sea is a productive temperate sea located on the Northwest European Shelf. It is an important pathway for the delivery of land-derived material to the North Atlantic Ocean, including dissolved organic matter (DOM). The aim of this study was to determine the seasonal and spatial variability in the magnitude, source and composition of DOM at three sites representing on shelf, central shelf and shelf edge regions in the Celtic Sea, using observations collected during the UK Shelf Sea Biogeochemistry (SSB) research programme (November 2014 – August 2015). The concentration of dissolved organic carbon (DOC) alongside DOM absorbance and fluorescence indices were measured and fluorescence Excitation and Emission Matrices (EEMs) combined with Parallel Factor Analysis (PARAFAC) were used to assess DOM composition and lability. The PARAFAC model identified four unique fluorescent components for autumn (November 2014), winter (March 2015), spring (April 2015) and summer (July 2015) consisting of two humic-like components attributed to terrestrial (C1) and marine sources (C2), and two protein components identified as tyrosine-like (C3) and tryptophan-like (C4) attributed to in situ production. DOC varied seasonally and there were strong cross shelf trends. The protein components (C3 and C4) exhibited large seasonal and within season variability particularly during productive periods. In contrast, there were persistent cross shelf gradients in the CDOM absorption coefficient at 305 nm (a305), the UV specific absorbance at 280 nm (SUVA280), the humification index (HIX), and the humic-like fluorescent components (C1 and C2), which were higher in the on shelf region and decreased towards the shelf edge. The humic-like components and the slope ratio (SR) were significantly correlated with salinity throughout all seasons, indicating a strong influence of terrestrially-derived organic matter in the Celtic Sea, with potentially up to 35% of DOC in the central shelf during winter originating from terrestrial inputs. Results from this study illustrate the importance of monitoring DOM quantitatively and qualitatively for a better understanding of the supply, production, cycling and export of this dynamic organic carbon pool in shelf seas.
•Seasonal dissolved and particulate organic matter pools examined in the Celtic Sea.•Organic carbon (C) concentrations highest in spring and lowest in autumn.•Nutrient (C, N and P) dynamics decoupled ...with seasons and during bloom events.•Dissolved organic matter always carbon-rich relative to particulates.•DOC dominates downward C flux in summer, POC dominates downward flux in spring.
Organic matter (OM) plays an important role in productive shelf seas and their contribution to global carbon (C) and nutrient cycles. We investigated dissolved and particulate OM (DOM and POM, respectively) dynamics over a seasonal cycle in the Celtic Sea. The quantity of OC was largest during the spring bloom and lowest in autumn. DOM was always C rich relative to the POM pool and the Redfield ratio (106C:16N:P). There was clear decoupling between C, N and P and the response of OM composition to different seasons and nutrient statuses of the microbial community. The C:P stoichiometry was much more variable than the C:N stoichiometry, which was near constant. Downward OC fluxes were dominated by POM during bloom events and DOM during the stratified summer. In terms of partitioning, 92–96% of OC was in the DOM pool throughout sampling, which given its high C:N (12.4–17) suggests it was an efficient vehicle for potential off-shelf export of C during winter mixing.
•A first look at the intergenerational impact of krill exposed to nanoplastics.•Nanoplastic spheres (50 nm) were found in digested krill embryos.•Maternal exposure of krill to nanoplastic did not ...affect lipid metabolism of embryos.•Direct exposure of krill embryos to nanoplastic did not impact energy reserves.
Antarctic krill (Euphausia superba) plays a central role in the Antarctic marine food web and biogeochemical cycles and has been identified as a species that is potentially vulnerable to plastic pollution. While plastic pollution has been acknowledged as a potential threat to Southern Ocean marine ecosystems, the effect of nanoplastics (<1000 nm) is poorly understood. Deleterious impacts of nanoplastic are predicted to be higher than that of larger plastics, due to their small size which enables their permeation of cell membranes and potentially provokes toxicity. Here, we investigated the intergenerational impact of exposing Antarctic krill to nanoplastics. We focused on whether embryonic energy resources were affected when gravid female krill were exposed to nanoplastic by determining lipid and fatty acid compositions of embryos produced in incubation. Embryos were collected from females who had spawned under three different exposure treatments (control, nanoplastic, nanoplastic + algae). Embryos collected from each maternal treatment were incubated for a further 6 days under three nanoplastic exposure treatments (control, low concentration nanoplastic, and high concentration nanoplastic). Nanoplastic additions to seawater did not impact lipid metabolism (total lipid or fatty acid composition) across the maternal or direct embryo treatments, and no interactive effects were observed. The provision of a food source during maternal exposure to nanoplastic had a positive effect on key fatty acids identified as important during embryogenesis, including higher total polyunsaturated fatty acids (PUFA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) when compared to the control and nanoplastic treatments. Whilst the short exposure time was ample for lipids from maternally digested algae to be incorporated into embryos, we discuss why the nanoplastic-fatty acid relationship may be more complex. Our study is the first to scope intergeneration effects of nanoplastic on Antarctic krill lipid and fatty acid reserves. From this, we suggest directions for future research including long term exposures, multi-stressor scenarios and exploring other critical energy reserves such as proteins.
Inputs of detritus from the surface ocean are an important driver of community dynamics in the deep sea. The assessment of the flow of carbon through the benthic food web gives insight into how the ...community is sustained, and its resilience to fluctuations in food supply. We used a linear inverse model to compare the carbon flow through the food webs on an abyssal hill and the nearby plain at the Porcupine Abyssal Plain sustained observatory (4850 m water depth; northeast Atlantic), to examine the partitioning of detrital input in these substantially different megafaunal communities. We found minimal variation in carbon flows at the plain over two years, but differences in the detrital inputs and in the processing of that carbon input between the hill and plain habitats. Suspension feeding dominated metazoan carbon processing on the hill, removing nearly all labile detritus input to the system. By contrast, half of all labile detritus was deposited and available for deposit feeders on the abyssal plain. This suggests that the biomass on the hill is dependent on a more variable carbon supply than the plain. The presence of millions of abyssal hills globally suggests that the high benthic biomass and respiration, and reduced deposition of detritus may be pervasive, albeit with varying intensity.
Zooplankton form an integral component of epi- and mesopelagic ecosystems, and there is a need to better understand their role in ocean biogeochemistry. The export and remineralisation of particulate ...organic matter at depth plays an important role in controlling atmospheric CO2 concentrations. Pelagic mesozooplankton and micronekton communities may influence the fate of organic matter in a number of ways, including: the consumption of primary producers and export of this material as fast-sinking faecal pellets, and the active flux of carbon by animals undertaking diel vertical migration (DVM) into the mesopelagic. We present day and night vertical biomass profiles of mesozooplankton and micronekton communities in the upper 500 m during three visits to an ocean observatory station (P3) to the NW of South Georgia (Scotia Sea, South Atlantic) in austral spring, alongside estimates of their daily rates of ingestion and respiration throughout the water column. Day and night community biomass estimates were dominated by copepods >330 μm, including the lipid-rich species, Calanoides acutus and Rhincalanus gigas. We found little evidence of synchronised DVM, with only Metridia spp. and Salpa thompsoni showing patterns consistent with migratory behaviour. At depths below 250 m, estimated community carbon ingestion rates exceeded those of metabolic costs, supporting the understanding that food quality in the mesopelagic is relatively poor, and organisms have to consume a large amount of food in order to fulfil their nutritional requirements. By contrast, estimated community rates of ingestion and metabolic costs at shallower depths were approximately balanced, but only when we assumed that the animals were predominantly catabolising lipids (i.e. respiratory quotient = 0.7) and had relatively high absorption efficiencies. Our work demonstrates that it is possible to balance the metabolic budgets of mesopelagic animals to within observational uncertainties, but highlights the need for a better understanding of the physiology of lipid-storing animals and how it influences carbon budgeting in the pelagic.
The mesopelagic zooplankton community plays an important role in the cycling and sequestration of carbon via the biological pump. However, little is known about the physiology and ecology of key taxa ...found within this region, hindering our understanding of their influence on the pathways of energy and organic matter cycling. We sampled the eight most abundant zooplankton (Calanoides acutus, Rhincalanus gigas, Paraeuchaeta spp., Chaetognatha, Euphausia triacantha, Thysanoessa spp., Themisto gaudichaudii and Salpa thompsoni) from within the mesopelagic zone in the Scotia Sea during a sinking diatom bloom and investigated their physiological ecology using lipid biomarkers and stable isotopic signatures of nitrogen. Data suggest that the large calanoid copepods, C. acutus and R. gigas, were in, or emerging from, a period of metabolic inactivity during the study period (November 15th – December 15th, 2017). Abundant, but decreasing lipid reserves in the predominantly herbivorous calanoid copepods, suggest these animals may have been metabolising previously stored lipids at the time of sampling, rather than deriving energy solely from the diatom bloom. This highlights the importance of understanding the timing of diapause of overwintering species as their feeding is likely to have an impact on the turnover of particulate organic matter (POM) in the upper mesopelagic. The δ15N signatures of POM became enriched with increasing depth, whereas all species of zooplankton except T. gaudichaudii did not. This suggests that animals were feeding on fresher, surface-derived POM, rather than reworked particles at depth, likely influencing the quantity and quality of organic matter leaving the upper mesopelagic. Our study highlights the complexity of mesopelagic food webs and suggests that the application of broad trophic functional types may lead to an incorrect understanding of ecosystem dynamics.
•Calanoides acutus and Rhincalanus gigas use stored lipids for energy not ingestion.•Actively feeding zooplankton consumed fresh POM, not reworked particles at depth.•Decoupling between zooplankton feeding dynamics and ambient POM in the upper 500m.
Cold-water corals (CWCs) are important ecosystem engineers in the deep sea that provide habitat for numerous species and can form large coral mounds. These mounds influence surrounding currents and ...induce distinct hydrodynamic features, such as internal waves and episodic downwelling events that accelerate transport of organic matter towards the mounds, supplying the corals with food. To date, research on organic matter distribution at coral mounds has focussed either on seasonal timescales or has provided single point snapshots. Data on food distribution at the timescale of a diurnal tidal cycle is currently limited. Here, we integrate physical, biogeochemical, and biological data throughout the water column and along a transect on the south-eastern slope of Rockall Bank, Northeast Atlantic Ocean. This transect consisted of 24-h sampling stations at four locations: Bank, Upper slope, Lower slope, and the Oreo coral mound. We investigated how the organic matter distribution in the water column along the transect is affected by tidal activity. Repeated CTD casts indicated that the water column above Oreo mound was more dynamic than above other stations in multiple ways. First, the bottom water showed high variability in physical parameters and nutrient concentrations, possibly due to the interaction of the tide with the mound topography. Second, in the surface water a diurnal tidal wave replenished nutrients in the photic zone, supporting new primary production. Third, above the coral mound an internal wave (200 m amplitude) was recorded at 400 m depth after the turning of the barotropic tide. After this wave passed, high quality organic matter was recorded in bottom waters on the mound coinciding with shallow water physical characteristics such as high oxygen concentration and high temperature. Trophic markers in the benthic community suggest feeding on a variety of food sources, including phytodetritus and zooplankton. We suggest that there are three transport mechanisms that supply food to the CWC ecosystem. First, small phytodetritus particles are transported downwards to the seafloor by advection from internal waves, supplying high quality organic matter to the CWC reef community. Second, the shoaling of deeper nutrient-rich water into the surface water layer above the coral mound could stimulate diatom growth, which form fast-sinking aggregates. Third, evidence from lipid analysis indicates that zooplankton faecal pellets also enhance supply of organic matter to the reef communities. This study is the first to report organic matter quality and composition over a tidal cycle at a coral mound and provides evidence that fresh high-quality organic matter is transported towards a coral reef during a tidal cycle.
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•We measured physical conditions and food supply at a cold-water coral reef over 24h.•Large variability in environmental conditions and food supply over the tidal cycle.•Internal waves transport fresh organic matter to the cold-water coral reef.•Organic matter delivered to the cold-water coral reef is of high quality.•The reef community feeds on variety of sources, but depends on surface production.
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