Mineral dust deposition is an important supply mechanism for trace elements in the low-latitude ocean. Our understanding of the controls of such inputs has been mostly built on laboratory and surface ...ocean studies. The lack of direct observations and the tendency to focus on near-surface waters prevent a comprehensive evaluation of the role of dust in oceanic biogeochemical cycles. In the frame of the PEACETIME project (ProcEss studies at the Air-sEa Interface after dust deposition in the MEditerranean sea), the responses of the aluminum (Al) and iron (Fe) cycles to two dust wet deposition events over the central and western Mediterranean Sea were investigated at a timescale of hours to days using a comprehensive dataset gathering dissolved and suspended particulate concentrations, along with sinking fluxes.
In the ocean, remineralization rate associated with sinking particles is a
crucial variable. Since the 1990s, particulate biogenic barium (Baxs) has been used as an indicator of carbon ...remineralization by applying a transfer function relating Baxs to O2 consumption (Dehairs's
transfer function, Southern Ocean-based). Here, we tested its validity in
the Mediterranean Sea (ANTARES/EMSO-LO) for the first time by investigating connections between Baxs, prokaryotic heterotrophic
production (PHP) and oxygen consumption (JO2-Opt; optodes measurement). We show that (1) higher Baxs (409 pM; 100–500 m) occurs in situations where integrated PHP (PHP100/500=0.90) is located deeper, (2) higher Baxs occurs with increasing JO2-Opt, and (3) there is similar magnitude between JO2-Opt (3.14 mmol m−2 d−1; 175–450 m) and JO2-Ba (4.59 mmol m−2 d−1; transfer function). Overall,
Baxs, PHP and JO2 relationships follow trends observed earlier in the Southern Ocean. We conclude that such a transfer function could apply in the Mediterranean Sea.
We report on the sub-basin variability in particulate organic carbon (POC)
remineralization in the western and central Mediterranean Sea in late spring
during the PEACETIME (ProcEss studies at the
...Air–sEa Interface after dust deposition in the MEditerranean sea) cruise. POC remineralization rates were estimated using
the excess biogenic particulate barium (Baxs) inventories in the
mesopelagic layers (100–1000 m depth) and compared with prokaryotic
heterotrophic production (PHP). Baxs-based mesopelagic remineralization
rates (MRs) ranged from 25±2 to 306±70 mgCm-2d-1.
MRs were larger in the Algero-Provençal (ALG) Basin than in the
Tyrrhenian (TYR) and Ionian (ION) basins. Our Baxs inventories and
integrated PHP data also indicated that significant mesopelagic
remineralization occurred down to 1000 m depth in the ALG Basin in contrast
to the ION and TYR basins, where remineralization was mainly located above
500 m depth. We propose that the higher and deeper MRs in the ALG
Basin were sustained by an additional particle export event driven by deep
convection. The TYR Basin (in contrast to the ALG and ION basins) presented
the impact of a previous dust event, as reflected by our particulate Al water
column concentrations. The ION and TYR basins showed small-scale
heterogeneity in remineralization processes, reflected by our Baxs
inventories and integrated PHP data at the Tyrr long-duration station.
This heterogeneity was linked to the mosaic of blooming and non-blooming
patches reported in this area during the cruise. In contrast to the western
Mediterranean Sea (ALG Basin), the central Mediterranean Sea (ION and TYR
basins) showed lower remineralization rates restricted to the upper
mesopelagic layer during the late spring PEACETIME cruise.
We report detailed sections of radium-226 (226Ra, T1/2= 1602 years) activities and barium (Ba) concentrations determined in the North Atlantic (Portugal–Greenland–Canada) in the framework of the ...international GEOTRACES program (GA01 section – GEOVIDE project, May–July 2014). Dissolved 226Ra and Ba are strongly correlated along the section, a pattern that may reflect their similar chemical behavior. Because 226Ra and Ba have been widely used as tracers of water masses and ocean mixing, we investigated their behavior more thoroughly in this crucial region for thermohaline circulation, taking advantage of the contrasting biogeochemical patterns existing along the GA01 section. We used an optimum multiparameter (OMP) analysis to distinguish the relative importance of physical transport (water mass mixing) from nonconservative processes (sedimentary, river or hydrothermal inputs, uptake by particles and dissolved–particulate dynamics) on the 226Ra and Ba distributions in the North Atlantic. Results show that the measured 226Ra and Ba concentrations can be explained by conservative mixing for 58 and 65 % of the samples, respectively, notably at intermediate depth, away from the ocean interfaces. 226Ra and Ba can thus be considered conservative tracers of water mass transport in the ocean interior on the space scales considered here, namely, on the order of a few thousand kilometers. However, regions in which226Ra and Ba displayed nonconservative behavior and in some cases decoupled behaviors were also identified, mostly at the ocean boundaries (seafloor, continental margins and surface waters). Elevated 226Ra and Ba concentrations found in deepwater in the West European Basin suggest that lower Northeast Atlantic Deep Water (NEADWl) accumulates 226Ra and Ba from sediment diffusion and/or particle dissolution during transport. In the upper 1500 m of the West European Basin, deficiencies in 226Ra and Ba are likely explained by their incorporation in planktonic calcareous and siliceous shells, or in barite (BaSO4) by substitution or adsorption mechanisms. Finally, because Ba and 226Ra display different source terms (mostly deep-sea sediments for 226Ra and rivers for Ba), strong decoupling between 226Ra and Ba were observed at the land–ocean boundaries. This is especially true in the shallow stations near the coasts of Greenland and Newfoundland where high 226Ra / Ba ratios at depth reflect the diffusion of 226Ra from sediment and low 226Ra / Ba ratios in the upper water column reflect the input of Ba associated with meteoric waters.
Based on an unprecedented dissolved barium (D_Ba) data set collected in the Mediterranean Sea during a zonal transect between the Lebanon coast and Gibraltar (M84/3 cruise, April 2011), we decompose ...the D_Ba distribution to isolate the contribution of biogeochemical processes from the impact of the oceanic circulation. We have built a simple parametric water mass analysis (Parametric Optimum Multiparameter analysis) to reconstruct the contribution of the different Mediterranean water masses to the thermohaline structure. These water mass fractions have then been used to successfully reconstruct the background vertical gradient of D_Ba reflecting the balance between the large‐scale oceanic circulation and the biological activity over long time scales. Superimposed on the background field, several D_Ba anomalies have been identified. Positive anomalies are associated with topographic obstacles and may be explained by the dissolution of particulate biogenic barium (P_Ba barite) of material resuspended by the local currents. The derived dissolution rates range from 0.06 to 0.21 μmol m−2 d−1. Negative anomalies are present in the mesopelagic region of the western and eastern basins (except in the easternmost Levantine basin) as well as in the abyssal western basin. This represents the first quantification of the nonconservative component of the D_Ba signal. These mesopelagic anomalies could reflect the subtraction of D_Ba during P_Ba barite formation occurring during organic carbon remineralization. The deep anomalies may potentially reflect the transport of material toward the deep sea during winter deep convection and the subsequent remineralization. The D_Ba subtraction fluxes range from −0.07 to −1.28 μmol m−2 d−1. D_Ba‐derived fluxes of P_Ba barite (up to 0.21 μmol m−2 d−1) and organic carbon (13 to 29 mmol C m−2 d−1) are in good agreement with other independent measurements suggesting that D_Ba can help constrain remineralization horizons. This study highlights the importance of quantifying the impact of the large‐scale oceanic circulation in order to better understand the biogeochemical cycling of elements and to build reliable geochemical proxies.
Key Points
Background D_Ba distribution reflects the balance between the overturning circulation and biogeochemical processes over long time scales
Significant depletion compared with the D_Ba background in the mesopelagic interior indicates organic carbon remineralization horizons
Water mass framework is a powerful tool to better understand biogeochemical elements distribution and build robust geochemical tracers
The dissolved barium (D_Ba) data set for the Mediterranean Sea is here expanded with data from a large-scale transect sampled in April 2011 (M84/3 cruise) at high resolution. A total of 833 seawater ...samples have been analyzed for D_Ba. Over the basin the D_Ba content ranges from 38 to 85nmolkg−1 with local deep D_Ba maxima reaching up to 172nmolkg−1. Deep D_Ba maxima are associated with near bottom waters influenced by benthic processes and brine waters. The water column is largely undersaturated with respect to barite (BaSO4, the main phase of particulate biogenic barium P_Ba), with water column barite saturation state ranging between 0.2 and 0.6 over the basin. This new D_Ba dataset shows that the general zonal distribution of D_Ba is impacted by the large-scale Mediterranean circulation, as evidenced by the Levantine Intermediate Water zonal and meridional progression as well as by the eastward flow of surface Atlantic Water. However biogeochemical processes are also at play, as suggested by an elevated D_Ba content of deep waters and by local lower D_Ba contents in intermediate waters. These features could be attributed to active cycling between the particulate and dissolved Ba phases. Since P_Ba barite has been recognized in previous studies as a proxy for particulate organic carbon remineralization at intermediate depths, the significance of local changes in the water column D_Ba patterns may be the key to better constrain the Ba and carbon dynamics in the Mediterranean Sea.
•D_Ba is investigated along a high resolution and quasi-zonal transect in the MedSea.•The D_Ba content ranges from 38 to 85nmolkg−1 with local deep D_Ba maxima reaching up to 172nmolkg−1.•The water column is largely undersaturated with respect to barite (0.2<SI<0.6).•The D_Ba distribution is impacted by the large-scale Mediterranean circulation and biogeochemical processes.•Local changes in the D_Ba patterns may be the key to better constrain the C dynamics in the MedSea.
We performed scanning electron microscopy and electron microprobe analysis on the eucritic meteorites Errachidia 002 and Northwest Africa 11911, with a focus on the metallic iron disseminated in ...them, in order to constrain the processes involved in its formation, and discuss its implication for their parent body collisional history. Errachidia 002 is a polymict eucrite that consists of basaltic and noritic (diogenite) clasts set in a fragmental matrix. Fe-metals in this meteorite contain <0.04 wt% Ni, and 0.06 wt% Co, and they are mostly associated with silica in pyroxene. This suggests formation by decomposition of troilite, which generated S-vapors (S2) that subsequently reacted with FeO in pyroxene during an impact event, producing pure Fe-metal and silica, with escape of SO2 from the rock. The presence of late-stage phases in proximity of a few Fe-metal grains, as well as low Fe/Mn coupled with high Fe/Mg in pyroxene indicate a different scenario in which pure Fe-metal in this meteorite formed by reduction from a residual melt. NWA 11911 is also a polymict eucrite composed mainly of unequilibrated and equilibrated eucritic clasts set in a clastic groundmass. Here, metallic iron is either enclosed in the fragmental matrix, or within a vitrophyric impact melt clast. Its Ni and Co contents are ∼2.8 and 0.6 wt%, implying an exogenous origin, namely contamination by an iron-bearing impactor. Our results point out the major role impacts played in controlling the surface features and mineral compositions of early formed bodies in the solar system such as (4) Vesta.
Display omitted
•We investigate metallic iron in two brecciated eucrites to constrain the collisional history of the asteroid (4) Vesta.•The polymict eucrite Errachidia 002 is a breccia within a breccia consisting of various eucritic and noritic fragments.•The polymict eucrite NWA 11911 is composed mainly of eucritic clasts and impact melts.•Fe-metal in Errachidia 002 formed through reduction of FeO in pyroxene, or by reduction from a residual melt.•The presence of FeNi metal in NWA 11911 indicates contamination by metal-bearing impactors.
Reducing stigma is key to improving the wellbeing of people with albinism in Tanzania. This study aimed to obtain more insight into the effects of two radio interventions with regard to ...albinism-related stigma: a radio drama and a radio interview. Assessment of the radio interventions was based on two attitude measurement instruments (The Albinism Explanatory Model Interview Catalogue Community Stigma Scale and the Albinism Social Distance Scale), an entertainment scale, and two informal (group) interviews. In total, 111 community members participated in the assessment prior to the radio drama, and 65 after. In the case of the radio interview, 123 community members participated in the assessment prior to the radio show, and 77 after. Following the radio drama, a significant reduction was found in terms of community stigma, and a reduction in social distance was found after both interventions. The entertainment score for both interventions was high, but significantly higher for the radio drama. The respondents indicated that they had gained more understanding of albinism as a result of the interventions, and were positive about this type of education. The current study shows that a radio show in which the listener interacts with someone with albinism can contribute to a reduction in stigma, and demonstrates that different types of radio intervention can have different outcomes.
Points of interest
Reducing discrimination is key to improving the wellbeing of people with albinism in Tanzania.
This research investigated the use of radio shows to change attitudes towards people with albinism within the community; two types of radio show were tested: a radio drama and a radio interview.
Through the shows the respondents got into contact with someone with albinism.
The shows were valued by the community members as an attractive means of education.
The shows proved to be effective in terms of improving peoples' knowledge about, and attitude towards people with albinism.
People enjoyed the radio drama more than the radio interview. The radio drama was also more effective than the radio interview in improving peoples' attitudes towards people with albinism.
This research offers recommendations for organisations that are working to raise awareness with regard to albinism.
We report on the zonal variability of mesopelagic particulate organic carbon remineralization and deep carbon transfer potential during the Kerguelen Ocean and Plateau compared Study 2 expedition ...(KEOPS 2; October-November 2011) in an area of the polar front supporting recurrent massive blooms from natural Fe fertilization. Mesopelagic carbon remineralization (MR) was assessed using the excess, non-lithogenic particulate barium (Baxs) inventories in mesopelagic waters and compared with bacterial production (BP), surface primary production (PP) and export production (EP). Results for this early season study are compared with the results obtained during a previous study (2005; KEOPS 1) for the same area at a later stage of the phytoplankton bloom. Our results reveal the patchiness of the seasonal advancement and of the establishment of remineralization processes between the plateau (A3) and polar front sites during KEOPS 2. For the Kerguelen plateau (A3 site) we observe a similar functioning of the mesopelagic ecosystem during both seasons (spring and summer), with low and rather stable remineralization fluxes in the mesopelagic column (150-400 m). The shallow water column (~500 m), the lateral advection, the zooplankton grazing pressure and the pulsed nature of the particulate organic carbon (POC) transfer at A3 seem to drive the extent of MR processes on the plateau. For deeper stations (>2000 m) located on the margin, inside a polar front meander, as well as in the vicinity of the polar front, east of Kerguelen, remineralization in the upper 400 m in general represents a larger part of surface carbon export. However, when considering the upper 800 m, in some cases, the entire flux of exported carbon is remineralized. In the polar front meander, where successive stations form a time series, two successive events of particle transfer were evidenced by remineralization rates: a first mesopelagic and deep transfer from a past bloom before the cruise, and a second transfer expanding at mesopelagic layers during the cruise. Regarding the deep carbon transfer efficiency, it appeared that above the plateau (A3 site) the mesopelagic remineralization was not a major barrier to the transfer of organic matter to the seafloor (close to 500 m). There, the efficiency of carbon transfer to the bottom waters (>400 m) as assessed by PP, EP and MR fluxes comparisons reached up to 87% of the carbon exported from the upper 150 m. In contrast, at the deeper locations, mesopelagic remineralization clearly limited the transfer of carbon to depths of >400 m. For sites at the margin of the plateau (station E-4W) and the polar front (station F-L), mesopelagic remineralization even exceeded upper 150 m export, resulting in a zero transfer efficiency to depths >800 m. In the polar front meander (time series), the capacity of the meander to transfer carbon to depth >800 m was highly variable (0 to 73%). The highest carbon transfer efficiencies in the meander are furthermore coupled to intense and complete deep (>800 m) remineralization, resulting again in a near-zero, deep (>2000 m) carbon sequestration efficiency there.
Albinism in Tanzania causes fierce health-related stigma. Little research has focused on the impact of stigma reduction strategies aiming to reduce albinism related stigma. Therefore, this research ...assessed the impact of two short video interventions among high school students in Tanzania on their attitude towards people with albinism: a contact intervention (n = 95) and an education intervention (n = 97). A mixed method design was used. Directly before and after the interventions impact was measured among all participants through the Albinism Social Distance Scale for Adolescents (ASDS-A), knowledge items, and entertainment items. After these measurements focus group discussions were conducted, 16 in total (n = 80). Both interventions caused a significant increase in the levels of correct knowledge about albinism. The education intervention entailed a significant positive change in attitude measured through the ASDS-A, whereas the contact intervention did not have a significant effect. In terms of entertainment value, the respondents were more enthusiastic about the contact intervention. The study suggests that education interventions on their own can be a successful tool in decreasing albinism related stigma. Additionally, qualitative findings show many positive outcomes for the contact intervention. Therefore, we would recommend using a combination of these two interventions, which has also proved successful in the past. However, more research on the effect of a combination of the two strategies is recommended.
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