Search

Abstract Many aspects of to the vertical and lateral transport of organic matter particles produced in the upper ocean are still not clear. This study documents the production, vertical and lateral displacement of the particulate organic matter fraction formed by dinoflagellate cysts in nepheloid layers present off Cape Blanc in November 2015. The position and extent of cyst production in the upper water column has been assessed by collecting the export rain of cysts with floating sediment traps. This has been compared to cyst associations in different intermediate nepheloid layers in the water column along two onshore-offshore transects. We document that highest cyst export production took place at the rim of a newly formed upwelling eddy/filament. We observed lateral transport up to 130 km off the shelf break into the deeper ocean in the bottom nepheloid layers (BNL) and in intermediate nepheloid layer (INL). The depth of the INL gradually increased from 600 m closest to the shelf break to 1300 m at the most offshore station. Transport in the BNL was observed in the more onshore part between 750 and 2300 m water depth. Cyst associations in both layers were comparable, indicating a common source. The large abundance of living cysts in these layers suggest that this source had a recent origin rather than being the result of resuspension of older sediment. The cyst associations of these samples differed from those of a second INL deeper in the water column as well as from samples from the more offshore part of the BNL. This indicates that the particles in this deeper INL and the offshore part of the BNL had a different origin. This origin could not be identified therefore no conclusions were drawn with respect to the extent to which these particles have been transported vertically or laterally. The cyst associations in the surface sediments differed from those of the nepholoid layers and the upper water column and did not reflect the effects of lateral transport as registered from the water column. The surface sediments contained a higher proportion of cysts that are highly resistant to aerobic degradation than the samples from the water column. This indicates that the former were modified predominantly by species-specific post depositional degradation. Selective degradation altering the cyst associations was not observed for the nepheloid layers. Highlights • Dinoflagellate cysts transport is studied during upwelling off Cape Blanc in November 2015. • Dinoflagellate cysts trace lateral and vertical transport of Particulate Organic Matter. • Lateral cyst transport occurs in intermediate and bottom nepheloid layers. • Lateral cyst transport was restricted to 150 km off the shelf break. • Cysts in the bottom- and upper intermediate nepheloid layers had a common source. [ABSTRACT FROM AUTHOR]

The Transpolar Drift (TPD) is a mechanism for the rapid transport of shelf-modified Siberian river waters across the Arctic Ocean and out through Fram Strait. We present results from three trans-Arctic research cruises in August–September 2014–2016 to investigate the distribution and dynamics of dissolved organic matter (DOM) in the upper waters across the North Pole, from Svalbard to the Mackenzie River mouth, and in two important outflow gateways of the Arctic Ocean (Fram Strait and Lancaster Sound). Fluorescence measurements of DOM obtained using in situ sensor and laboratory-based spectroscopic analyses, coupled with parallel factor analysis (PARAFAC) were used to map components of DOM at high spatial resolution. The optical properties showed a completely different composition with a much stronger humic-like signal observed in surface waters in the Makarov Basin than in the adjacent Canada Basin, likely due to the substantial amount of Siberian runoff transported by the TPD. The high levels of humic-like in TPD-influenced surface waters were traced from southern Makarov shelves up to the Lomonosov Ridge near the North Pole. Lower DOM levels were observed in the eastern Amundsen basin waters, likely the result of mixing with terrestrial-poor DOM Atlantic waters. The annual flux of humic-like C2 transported to the Atlantic through Fram Strait was estimated at 1816 ±926 r.u. km3. This study reveals the importance of shelf processes and TPD in supplying humic-like material to the central Arctic Ocean to Fram Strait. • Significant differences in fluorescence composition were found between the four main Arctic basins. • A much stronger terrigenous signal was observed in Makarov Basin waters than in the adjacent Canada Basin. • The annual flux of humic-like transported to the Atlantic Ocean was estimated at 1816± 926 r.u. km−3 [ABSTRACT FROM AUTHOR]

We studied organic matter in the central Black Sea and its northeastern and northwestern shelf break within three weeks in November 2013 to test the hypothesis that in situ production could explain lateral and vertical variability in its composition and distribution. The wide spatial coverage over a short period of time achieved during this study revealed longitudinal variability in organic matter characteristics reflecting productivity at the Black Sea surface. Particulate organic matter was dominantly autochthonous in the central Black Sea. Allochthonous influence of river discharge was only traced on the northwestern shelf by high concentrations but low freshness of particulate organic matter. Compared to the NW shelf break and central Black Sea, primary production was high near the NE shelf break, likely fueled by input from the Azov Sea. Vertical patterns were similar throughout the deep Black Sea and appeared to also be governed by in situ processes rather than reflect variability in the surface water. As concentrations of organic matter decreased with depth, its elemental and isotopic composition indicated chemoautotrophic production at the oxic-anoxic interface and organic matter degradation in the benthic boundary layer. Though profiles of dissolved organic carbon indicated a minor source in anoxic deep water, likely linked to chemosynthesis and reflux from sediments, a negative deviation of concentrations from a conservative mixing line between two endmembers suggested net removal of labile dissolved organic carbon. [ABSTRACT FROM AUTHOR]

234 Th-derived carbon export fluxes were measured in the Atlantic Ocean under the GEOTRACES framework to evaluate basin-scale export variability. Here, we present the results from the northern half of the GA02 transect, spanning from the equator to 64°N. As a result of limited site-specific C/ 234 Th ratio measurements, we further combined our data with previous work to develop a basin wide C/ 234 Th ratio depth curve. While the magnitude of organic carbon fluxes varied depending on the C/ 234 Th ratio used, latitudinal trends were similar, with sizeable and variable organic carbon export fluxes occurring at high latitudes and low to negligible fluxes occurring in oligotrophic waters. Our results agree with previous studies, except at the boundaries between domains, where fluxes were relatively enhanced. Three different models were used to obtain satellite-derived net primary production (NPP). In general, NPP estimates had similar trends along the transect, but there were significant differences in the absolute magnitude depending on the model used. Nevertheless, organic carbon export efficiencies were generally < 25%, with the exception of a few stations located in the transition area between the riverine and the oligotrophic domains and between the oligotrophic and the temperate domains. Satellite-derived organic carbon export models from Dunne et al. (2005) (D05), Laws et al. (2011) (L11) and Henson et al. (2011) (H11) were also compared to our 234 Th-derived carbon exports fluxes. D05 and L11 provided estimates closest to values obtained with the 234 Th approach (within a 3-fold difference), but with no clear trends. The H11 model, on the other hand, consistently provided lower export estimates. The large increase in export data in the Atlantic Ocean derived from the GEOTRACES Program, combined with satellite observations and modeling efforts continue to improve the estimates of carbon export in this ocean basin and therefore reduce uncertainty in the global carbon budget. However, our results also suggest that tuning export models and including biological parameters at a regional scale is necessary for improving satellite-modeling efforts and providing export estimates that are more representative of in situ observations. [ABSTRACT FROM AUTHOR]

The transport and fate of organic matter (OM) sources within the Avilés submarine canyon (Cantabrian Sea, Southern Bay of Biscay) were studied using carbon and nitrogen stable isotope ratios. The isotopic composition of settling particles and deep bottom sediments closely resembled that of surface particulate OM, and there were no marked differences in the isotopic composition of settling particles inside and outside of the AC. This indicates that the Avilés Canyon (AC) receives inputs of sinking OM mostly from the upper water column and less through advective near-bottom down-canyon transport. Sinking OM fluxes are of marine and terrestrial origin in proportions which vary seasonally. Analysis of δ 13 C in the canyon fauna indicates a dependence on OM mainly produced by marine phytoplankton. A tight coupling of isotopic signatures between pelagic organisms and benthic suspension feeders reflects an active biological vertical transport of OM from the surface to the deep-sea. The food web presented seasonal variations in the trophic niche width and the amplitude of the primary carbon sources, reflecting seasonality in the availability of fresh particulate OM. Those seasonal changes are larger for benthic organisms of lower trophic levels. [ABSTRACT FROM AUTHOR]

Remineralization of organic matter in the mesopelagic zone (ca. 150–700 m) is a key controlling factor of carbon export to the deep ocean. By using a tracer conservation model applied to climatological data of oxygen, dissolved inorganic carbon (DIC) and nitrate, we computed mesopelagic respiration near the ESTOC (European Station for Time-Series in the Ocean, Canary Islands) site, located in the Eastern boundary region of the North Atlantic subtropical gyre. The tracer conservation model included vertical Ekman advection, geostrophic horizontal transport and vertical diffusion, and the biological remineralization terms were diagnosed by assuming steady state. Three different approaches were used to compute reference velocities used for the calculation of geostrophic velocities and flux divergences: a no-motion level at 3000 m, surface geostrophic velocities computed from the averaged absolute dynamic topography field, and surface velocities optimized from the temperature model. Mesopelagic respiration rates computed from the model were 2.8–8.9 mol O 2 m 2 y −1 , 2.0–3.1 mol C m 2 y −1 and 0.6–1.0 mol N m 2 y −1 , consistent with remineralization processes occurring close to Redfield stoichiometry. Model estimates were in close agreement with respiratory activity, derived from electron transport system (ETS) measurements collected in the same region at the end of the winter bloom period (3.61±0.48 mol O 2 m −2 y −1 ). According to ETS estimates, 50% of the respiration in the upper 1000 m took place below 150 m. Model results showed that oxygen, DIC and nitrate budgets were dominated by lateral advection, pointing to horizontal transport as the main source of organic carbon fuelling the heterotrophic respiration activity in this region. [ABSTRACT FROM AUTHOR]

The dominance of Oxygen Minimum Zone in the eastern part of the Arabian Sea (ASOMZ) instead of the more bio-productive and likely more oxygen consuming western part is the first part of the paradox. The sources of oxygen to the ASOMZ were evaluated through the distributions of different water masses using the extended optimum multiparameter (eOMP) analysis, whereas the sinks of oxygen were evaluated through the organic matter remineralization, using the apparent oxygen utilization (AOU). The contributions of major source waters to the Arabian Sea viz. Indian Deep water (dIDW), Indian Central water (ICW), Persian Gulf Water (PGW) and Red Sea Water (RSW) have been quantified through the eOMP analysis which shows that the PGW and RSW are significant for the eastward shift of ASOMZ instead of voluminous ICW and dIDW. The distribution of Net Primary Production (NPP) and AOU clearly suggest the transport of organic detritus from the highly productive western Arabian Sea to its eastern counterpart which adds to the eastward shifting of ASOMZ. A revised estimate of the seasonal variation of areal extent and volume occupied by ASOMZ through analysis of latest available data reveals a distinct intensification of ASOMZ by 30% and increase in its volume by 5% during the spring-summer transition. However, during this seasonal transition the productivity in the Arabian Sea shows 100% increase in mean NPP. This disparity between ASOMZ and monsoonal variation of productivity is the other part of the paradox, which has been constrained through apparent oxygen utilization, Net Primary Production along with a variation of core depths of source waters. This study reveals a subtle balance between the circulation of marginal oxygen-rich water masses from the western Arabian Sea and organic matter remineralization in the eastern Arabian Sea in different seasons that explains the maintenance of ASOMZ throughout the year. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • 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. [ABSTRACT FROM AUTHOR]

Time-series sediment traps were deployed at 4 depths in the eastern Fram Strait from July 2007 to June 2008 to investigate variations in the magnitude and composition of the sinking particulate matter from upper waters to the seafloor. Sediment traps were deployed at 196 m in the Atlantic Water layer, at 1296 and 2364 m in the intermediate and deep waters, and at 2430 m on a benthic lander in the near-bottom layer. Fluxes of total particulate matter, particulate organic carbon, particulate organic nitrogen, biogenic matter, lithogenic matter, biogenic particulate silica, calcium carbonate, dominant phytoplankton cells, and zooplankton fecal pellets increased with depth, indicating the importance of lateral advection on fluxes in the deep Fram Strait. The lateral supply of particulate matter was further supported by the constant fluxes of biomarkers such as brassicasterol, alkenones, campesterol, β-sitosterol, and IP 25 at all depths sampled. However, enhanced fluxes of diatoms and appendicularian fecal pellets from the upper waters to the seafloor in the presence of ice during spring indicated the rapid export (15–35 days) of locally-produced large particles that likely contributed most of the food supply to the benthic communities. These results show that lateral supply and downward fluxes are both important processes influencing the transport of particulate matter to the seafloor in the deep eastern Fram Strait, and that particulate matter size dictates the prevailing sinking process. [ABSTRACT FROM AUTHOR]

In this study, we have used stable isotopes of megafauna, microbial mats and particulate organic matter to examine the effect of depth and vent fluid composition on the carbon sources at two proximal, chemically distinct hydrothermal vent fields along the Mid-Cayman Rise. The basalt hosted Piccard vent field (4980 m) is twice as deep as the ultramafic hosted Von Damm vent field (2300 m) and has very different faunal assemblages. Of particular note is the presence of seep-associated fauna, Escarpia and Lamellibrachia tubeworms, at the Von Damm vent field. We identify a greater range of carbon sources and a suggestion of increased photosynthetic inputs to the Von Damm vent field compared to Piccard vent field. Rimicaris hybisae shrimp are the only abundant species shared between the two vent fields with δ 13 C values ranging between −22.7 and −10.1‰. Higher concentrations of hydrogen sulfide in the vent fluids at Piccard is proposed to be responsible for varying the relative contributions of the carbon fixation cycles used by their epibionts. Seep-associated fauna at Von Damm rely on elevated, thermogenic hydrocarbon content of the vent fluids for their carbon source (δ 13 C values ranging from −21.3 to 11.6‰). They also derive energy from hydrogen sulfide formed by the microbial reduction of sulfide (δ 34 S values ranging from −10.2 to −6.9‰). The tubeworms have very short roots (buried at most a centimeter into rubble), suggesting that microbial sulfate reduction must be occurring either in the shallow subsurface and/or in the anterior part of the tube. Overall, megafauna at Von Damm vent field appear to have a smaller food chain length (smaller δ 15 N range) but a greater breadth of trophic resources compared to the megafauna at the Piccard vent field. [ABSTRACT FROM AUTHOR]

The trophic relationships of 21 species from an oceanic zooplankton community were studied using stable isotopes of carbon and nitrogen. Zooplankton and suspended particulate organic matter (POM) were sampled in three different water types in the western Tasman Sea: inner shelf (IS), a cold core eddy (CCE) and a warm core eddy (WCE). δ 15 N values ranged from 3.9‰ for the parasitic copepod Sapphirina augusta to 10.2‰ for the euphausiid, Euphausia spinifera. δ 13 C varied from −22.6 to −19.4‰ as a result of the copepod Euchirella curticauda and E. spinifera. The isotopic composition of POM varied significantly among water types; as did the trophic enrichment of zooplankton over POM, with the lowest enrichment in the recently upwelled IS water type (0.5‰) compared to the warm core eddy (1.6‰) and cold core eddy (2.7‰). The WCE was an oligotrophic environment and was associated with an increased trophic level for omnivorous zooplankton (copepods and euphausiids) to a similar level as carnivorous zooplankton (chaetognaths). Therefore carnivory in zooplankton can increase in response to lower abundance and reduced diversity in their phytoplankton and protozoan prey. Trophic niche width comparisons across three zooplankton species: the salp Thalia democratica , the copepod Eucalanus elongatus and the euphausiid Thysanoessa gregaria , indicated that both niche partitioning and competition can occur within the zooplankton community. We have shown that trophic relationships among the zooplankton are dynamic and respond to different water types. The changes to the zooplankton isotopic niche, however, were still highly variable as result of oceanographic variation within water types. [ABSTRACT FROM AUTHOR]

The Whittard Canyon (NE Atlantic) is one of the largest canyon systems on the northern Bay of Biscay margin. It likely receives a high input of organic matter from the productive overlying surface waters, and part of this organic matter may eventually be transferred down the canyon into the Whittard Channel extending from the canyon mouth onto the Biscay Abyssal Plain. To establish if substantial transport of organic matter takes place from the canyon into the deep-sea channel we: (1) deployed a benthic lander in the Whittard Channel for a period of one year to measure near-bottom particulate matter transport and deposition rates; (2) collected surface sediment samples from the Whittard Channel and adjacent areas to assess possible organic matter enrichment in the channel (3) surveyed transects across the channel and adjacent areas with towed video camera to assess distribution of benthic megafauna potentially indicating enhanced flux of fresh organic material. The video surveys revealed massive occurrence of elpidiid holothurians in the proximal Whittard Channel, whilst only low numbers were counted further down the channel and on areas adjacent to the channel. We speculate that these deposit-feeding holothurians were attracted by the elevated content of relatively fresh organic matter in surface sediments of the proximal channel, as indicated by analysis of the surface sediment samples. Yet, whilst we expected that organic matter enrichment in the channel could be attributed to down-canyon transport through the Whittard Canyon, this could not be confirmed by data recorded by the benthic lander. During most of the 1-year deployment period, the net near-bottom currents and suspended particulate matter transport was directed in up-channel direction. During two sediment-gravity flow events recorded in March and July 2011, most likely originating from the Whittard Canyon, substantial deposition of particulate matter did occur in the Whittard Channel. However, the material deposited during those events consisted largely of inorganic sediment and was relatively poor in fresh organic material, and hence could not have substantially contributed to the organic matter enrichment observed in the channel. The highest deposition flux of fresh organic matter, recorded in May 2011, was not associated with any down-channel flow and more likely was derived from local settling of phytodetritus produced during the spring phytoplankton bloom. Based on our observations we infer that the organic enrichment observed in the proximal Whittard Channel is due to redistribution of phytodetritus by bottom currents, and accumulation of this material in the topographic depression formed by the Whittard Channel. The mobility of the elpidiid holothurians allows them to exploit these localised food sources. [ABSTRACT FROM AUTHOR]

We analyze a two-year time-series of chromophoric dissolved organic matter (CDOM) light absorption measurements in the upper 400m of the water column at the BOUSSOLE site in the NW Mediterranean Sea. The seasonal dynamics of the CDOM light absorption coefficients at 440nm (acdom(440)) is essentially characterized by (i) subsurface maxima forming in spring and progressively reinforcing throughout summer, (ii) impoverishment in the surface layer throughout summer and (iii) vertical homogeneity in winter. Seasonal variations of the spectral dependence of CDOM absorption, as described by the exponential slope value (Scdom), are characterized by highest values in summer and autumn at the surface and low values at the depths of acdom(440) subsurface maxima or just below them. Variations of acdom(440) are likely controlled by microbial digestion of phytoplankton cells, which leads to CDOM production, and by photochemical destruction (photobleaching), which leads to CDOM degradation. Photobleaching is also the main driver of Scdom variations. Consistently with previous observations, acdom(440) for a given chlorophyll a concentration is higher than expected from Case I waters bio-optical models. The total non-water light absorption budget shows that surface waters at the BOUSSOLE site are largely dominated by CDOM during all seasons but the algal bloom in March and April. These results improve the knowledge of CDOM absorption dynamics in the Mediterranean Sea, which is scarcely documented. In addition, they open the way to improved algorithms for the retrieval of CDOM absorption from field or satellite radiometric measurements. [ABSTRACT FROM AUTHOR]

Abstract: Decapods were sampled with a 1m2 MOCNESS (mainly upper 1000m) in the northern Benguela Current during three cruises in December 2009, September/October 2010 and February 2011. Although pelagic decapods are abundant members of the micronekton community, information about their ecophysiology is very limited. Species-specific regional distribution limits were detected for various decapod species (e.g. Plesionika carinata, Sergestes arcticus, Pasiphaea semispinosa). Significant diel vertical migration patterns were determined for three caridean and three penaeiodean species. Biomass was variable and ranged from 23 to 2770mg dry mass m−2 with highest values for P. semispinosa. Fatty acid and stable isotope analyses revealed that the examined decapod species are omnivorous to carnivorous except for the herbivorous to omnivorous species P. carinata. Calanid copepods such as Calanoides carinatus were identified as an important prey item especially for caridean species. Community consumption rates of pelagic decapods derived from respiration rates ranged from 7mgCm−2 d−1 (23°S) to >20mgCm−2 d−1 (19°S, 17°S). A potential active respiratory carbon flux was calculated for migrating pelagic decapods with 4.4mgCm−2 d−1 for the upper 200m and with 2.6mgCm−2 d−1 from the base of the euphotic zone to a depth of 600m. Overall, pelagic decapods apparently play a more prominent role in the northern Benguela Current ecosystem than previously assumed and may exert a substantial predation impact on calanid copepods (up to 13%d−1 of standing stock). [Copyright &y& Elsevier]

Abstract: The relationship between surface-derived particulate organic matter (POM) and deep-sea sediment bacterial abundance, community structure and composition was investigated in two different sediment layers from two zones of contrasting surface water productivity in the southern Indian Ocean. Bacterial sediment communities from high chlorophyll (HC) and low chlorophyll (LC) sites were characterized and compared using direct counts, clone library construction, denaturing gradient gel electrophoresis (DGGE) and fluorescence in situ hybridization (FISH). Of the 1566 bacterial clones generated from the sediment communities, 1010 matched published 16S rDNA sequences at ≥97% identity. A comparison of surface sediment clone libraries showed that at least one third of all identified operational taxonomic units (OTUs) were common to both HC and LC sites. DGGE community profiles were consistent (82% similar) and evenness of the major phylogenetic groups was 96% similar between surface sediment communities, where gamma- and alpha-Proteobacteria were dominant. Sediment communities shared similarly high biodiversity, while species richness was marginally higher at the LC site. Intra-site shifts in bacterial abundance and composition were observed with increasing sediment depth. Despite the differences in organic matter input between sites, the consistency observed between HC and LC sediment communities pointed to (1) the extent of remineralisation by mega and meio-fauna as a potential factor affecting the quantity and quality of POM available to sediment bacteria, (2) sampling during the early ‘nutrient assimilation phase’ of the bacterial response to freshly deposited POM or (3) that the action of bacteria in the water column could affect the quantity and quality of POM available to sediment bacteria. Although factors other than these may explain the observed similarities, this first comparison of such deep-sea sediment communities in relation to surface-derived productivity may be useful in further elucidating the role of sediment bacteria in carbon remineralisation in the deep-sea environment. [Copyright &y& Elsevier]

Abstract: The accumulation of anthropogenic CO2 in the oceans is altering seawater carbonate chemistry. Investigation and monitoring of the carbonate parameters is therefore necessary to understand potential impacts on ocean ecosystems. Total alkalinity (AT) and dissolved inorganic carbon (CT) were sampled across the Rockall Trough in Feb 2009 (CE0903) and Feb 2010 (CE10002) as part of a baseline study of inorganic carbon chemistry in Irish shelf waters. The results have been compared with data from WOCE surveys A01E (Sept 1991), A01 (Dec 1994), AR24 (Nov 1996) and A24 (June 1997). The 2009 and 2010 datasets provide a snapshot of the biogeochemical parameters which can act as a baseline of inorganic carbon and acidity levels in surface waters of the Rockall Trough in late winter for future comparison since previous surveys in the area have been affected by biological activity. The dataset also offers the possibility to compare decadal changes in subsurface waters. The temporal evolution of anthropogenic carbon (ΔCant) between the 1990s and 2010 was evaluated using two separate methods; (i) a comparison of the concentrations of C T between surveys, after correcting it for remineralisation of organic material and formation and dissolution of calcium carbonate (ΔC T-abio) and (ii) an extended Multiple Linear Regression was used to calculate the ΔCant (). There was an increase in ΔC T-abio and of 18±4μmolkg−1 and 19±4μmolkg−1, respectively, in the subsurface waters between 1991 and 2010, equivalent to a decrease of 0.040±0.003 pH units over the 19 year period. There was an increase in both ΔC T-abio and of 8±4μmolkg−1 in Labrador Sea Water (LSW) in the Trough between 1991 and 2010, and LSW has acidified by 0.029±0.002 pH units over the same time period. A reduction in calcite and aragonite saturation states was observed, which may have implications for calcifying organisms in the region. [Copyright &y& Elsevier]

Abstract: Sinking particle fluxes during two strong El Niño events (1997/98 and 2009/10) were monitored at a station (10°30´N, 131°20´W) located in the 10°N thermocline ridge area (9°–13°N, 105°–140°W) of the northeastern equatorial Pacific. The 1997/98 El Niño event resulted in two- to fourfold higher organic carbon and biogenic silica fluxes than the non-ENSO levels. In combination, these findings suggest an increase in the productivity of surface waters. The strengthening of the North Equatorial Countercurrent, due to intensified westerlies and the resulting shoaling of the thermocline, likely induced upwelling of nutrient-enriched subsurface water and enhanced biological productivity. In contrast, the 2009/10 El Niño event was only accompanied by a substantial increase in planktonic foraminifera, with minor increases in organic carbon and biogenic silica fluxes. The distinct differences in the particle composition and the biological response of the marine ecosystem during the two El Niño events are attributed to different oceanographic and atmospheric conditions generated by two different types of El Niño: the cold-tongue (CT) type and the warm-pool (WP) type. Our results, together with the findings of a previous study of the 1982/83 strong El Niño event, suggest that enhanced biological productivity occurs in the 10°N thermocline ridge area under strong El Niño conditions. Our study also provides insight into equatorial biological dynamics under the extreme CT- and WP-type El Niño conditions. This is important because the WP-type El Niño conditions are projected to increase in frequency in the future. [Copyright &y& Elsevier]

Abstract: The transit time distribution method was applied to dichlorodifluoromethane and sulfur hexafluoride measurements from four cruises to the tropical North Atlantic between 2006 and 2009 in order to estimate anthropogenic carbon () concentrations. By assuming an Inverse Gaussian distribution of the transit time distribution the best fit to the data was achieved with the ratio of mean age to width equals 1. Significant differences in the mean age and concentrations between the equatorial belt (5°S–5°N) and the Guinea dome area (5°–15°N) was found. Mean ages are higher and concentrations are lower in the Guinea dome area than at same depths, or densities, in the equatorial belt. The mean column inventories in the upper 1200m are higher by about 3molm−2 in the equatorial belt compared to the Guinea dome area. The mean column inventory of , for the whole water column, in the tropical Atlantic is 32.2molm−2 (error range: 30.6–45.2molm−2), which is significantly lower than the previous estimates. The total inventory in the eastern tropical Atlantic is 2.5Pg (error range: 2.3–3.5Pg) for an area of 6×106 km2, comprising the Guinea dome region and the equatorial belt. The equatorial belt has 40% higher storage of compared to the Guinea dome area which reflects the occurrence of relatively young deep waters at the equator, being high in anthropogenic carbon. Our tracer based estimates were compared to concentrations calculated with the TrOCA method applied to measurements conducted in 1999. The TrOCA based estimates are significantly higher than our tracer based estimates. Comparison between tracer measurements in 1999 and the 2006–2009 time-frame revealed possible speed-up of ventilation in the upper water column, increasing the concentration in this depth range at a faster rate and a increase of in the tropical surface water was found. [Copyright &y& Elsevier]

Abstract: Surface-tethered particle interceptor traps (PITs) were deployed at 50 and 100m (1–3 days) on ten occasions in the Cariaco Basin between March 2007 and November 2009 to measure the settling fluxes of biogenic particles at 50m (the base of the euphotic zone—Ez) and 100m. Fluxes at these two depths were compared to concurrent fluxes estimated with moored sediment traps at 150, 225 and 410m from the CARIACO Ocean Time-Series program. We measured particulate organic carbon (POC), particulate organic nitrogen (PON), calcium carbonate, biogenic silica and terrigenous material concentrations in samples collected with both the drifting and moored traps. We also estimated the fluxes of foraminifera shells and coccolithophore cells at 50 and 100m using drifting traps samples. Surface chlorophyll a and primary production observations during each sampling period were examined to quantify the relationship between the magnitude and geochemical composition of the vertical flux and overlying production. Surface chlorophyll a concentrations and primary production rates were highest during months of upwelling (2.58−1.35mgm−3 and 3.6−1.4g Cm−2 d−1, respectively). The fluxes of POC, PON, calcite and silica measured during the upwelling season (December–May) were typically higher than during the period of non-upwelling (August–November), when surface waters are more strongly stratified. POC fluxes measured with the drifting traps (50 and 100m) varied between 0.95 (upwelling) and 0.14gm−2 d−1 (non-upwelling), compared with those from the moored traps (150, 225 and 410m) which ranged from 0.21 to 0.01gm−2 d−1. Similarly, the fluxes of biogenic opal in the upper 100m ranged from 1.12 and 0.18gm−2 d−1, and those at greater depths varied from 0.27gm−2 d−1 during upwelling to values near zero during stratification periods. The fluxes of POC, PON, calcite and silica in the upper 100m decreased by an order of magnitude at the depth of the oxic–anoxic interface (>200m). The sinking organic matter collected with the floating traps within the upper 100m was significantly correlated with surface chlorophyll a concentrations (r=0.68, p<0.05) as a result of close coupling between the flux of biogenic particles and primary production. In contrast, there was no clear relationship between surface chlorophyll/primary production and fluxes measured below 150m depth. [Copyright &y& Elsevier]

Abstract: Biomarker distributions and organic carbon and nitrogen isotopic signatures of organic matter (OM) produced in surface waters around the Crozet Plateau (Southern Ocean) are significantly different between a Fe-fertilised region (north) and a high nutrient low chlorophyll region (HNLC, south). If these OM signatures are exported to and preserved in surface sediments, they could potentially be used as palaeo-proxies for identifying Fe-fertilisation events in the past. Here, we assess the alteration of the OM signature through the water column and at the sediment–water interface by comparing organic signatures in surface waters, sediment traps and surface sediments. Our results suggest that there is significant degradation of OM during transport to the sea floor, which causes reduced fluxes of biomarkers to sediments north and east of the Crozet Plateau. Sterols, alkenones and C27 and C29 12-hydroxymethyl alkanoates, and C28 1,14-diols appear to be less labile than total organic carbon (TOC), except to the north, where alkenones and sterols are more rapidly degraded than TOC. Sedimentary bulk and compound specific δ13C values also reflect surface water productivity patterns, with elevated values occurring in sediments underlying the Fe-fertilised waters. In contrast, δ15N values appear to be strongly biased by degradation and grazing during export and burial. Thus, only some of the differences observed in surface waters between the Fe- fertilised and HNLC areas are exported to deep waters and preserved in the sedimentary record, suggesting that caution is required in the application of these proxies to studies of ocean palaeoproductivity. [Copyright &y& Elsevier]

Abstract: Mixed-layer CO2 fluxes in the 1980s (1979–1983) and the 2000s (1998–2001) are assessed in the Mediterranean Sea. The analysis uses an array of one-dimensional physical–biological–chemical coupled models covering all areas where depth is greater than 300m. These models are driven by surface heat fluxes and wind stress, and surface chlorophyll concentrations. This approach provides estimations of basin-scale oceanic CO2 levels over two time periods separated by a 14-year gap and allows characterizing differences between these two periods. The results indicate that the Mediterranean Sea was more biologically productive (by about 16gCm−2 y−1) during the 2000s, with an increase of carbon export to deep layers by about 7gCm−2 y−1 as compared to the 1980s. The consecutive modification of CO2 fluxes toward deep layers did not, however, strongly modify the oceanic CO2 levels, which differ by only ∼5–10μatm between the two periods. The reason is the increase of atmospheric CO2 levels by 30μatm between the two periods, which led to an increase of the CO2 flux from the atmosphere to the ocean. The Mediterranean Sea was a CO2 source to the atmosphere in the 1980s (about 1.5×1012 molCy−1). It is close to equilibrium with the atmosphere in the 2000s (slight sink of about −0.2×1012 molCy−1). [Copyright &y& Elsevier]