Beschreibung: Marine carbonate chemistry measurements have been carried out annually since 2009 during UK research cruises along the Extended Ellett Line (EEL), a hydrographic transect in the northeast Atlantic Ocean. The EEL intersects several water masses that are key to the global thermohaline circulation, and therefore the cruises sample a region in which it is critical to monitor secular physical and biogeochemical changes. We have combined results from these EEL cruises with existing quality-controlled observational data syntheses to produce a hydrographic time series for the EEL from 1981 to 2013. This reveals multidecadal increases in dissolved inorganic carbon (DIC) throughout the water column, with a near-surface maximum rate of 1.800.45 mu molkg(-1)yr(-1). Anthropogenic CO2 accumulation was assessed, using simultaneous changes in apparent oxygen utilization (AOU) and total alkalinity (TA) as proxies for the biogeochemical processes that influence DIC. The stable carbon isotope composition of DIC (C-13(DIC)) was also determined and used as an independent test of our method. We calculated a volume-integrated anthropogenic CO2 accumulation rate of 2.80.4mgCm(-3)yr(-1) along the EEL, which is about double the global mean. The anthropogenic CO2 component accounts for only 316% of the total DIC increase. The remainder is derived from increased organic matter remineralization, which we attribute to the lateral redistribution of water masses that accompanies subpolar gyre contraction. Output from a general circulation ecosystem model demonstrates that spatiotemporal heterogeneity in the observations has not significantly biased our multidecadal rate of change calculations and indicates that the EEL observations have been tracking distal changes in the surrounding North Atlantic and Nordic Seas.

Beschreibung: We present labile (L-pTM) and refractory (R-pTM) particulate trace metal distributions of Fe, Mn, Al, Ti, Co, Zn, Cd, Ni, Pb, Cu, and P for a transect along the southwest African shelf and an off-shore section at 3°S of the GEOTRACES GA08 section cruise. Particle sources and biogeochemical cycling processes are inferred using particle-type proxies and elemental ratios. Enhanced concentrations of bio-essential L-pTMs (Zn, Cu, Ni, Cd, Co, and P) were observed in the Benguela upwelling region, attributed to enhanced primary production. Bio-essential pTM stoichiometric ratios (normalized to pP) were consistent with phytoplankton biomass across the transect, except for Fe and Mn, which included adsorbed and labile oxide phases. Low pP lability (∼41%) suggests a potential refractory biogenic source on the Benguela shelf. Variable labilities observed between stations along the transect indicated potentially different biogenic pP labilities among different plankton groups. Benthic resuspension was prevalent in (near-)bottom waters along the transect and formed an important source of Fe and Mn oxides. Lithogenic particles along the entire shelf were Mn deficient and particles on the Benguela shelf were enriched in Fe, consistent with regional sediment compositions. Enhanced available-Fe (dissolved + labile particulate Fe) concentrations (up to 39.6 nM) were observed in oxygen-deficient (near-)bottom waters of the Benguela shelf coinciding with low L-pMn. This was attributed to the faster oxidation kinetics of Fe, allowing Fe-oxide precipitation and retention on the shelf, while Mn oxidation was slower. Enhanced L-pFe in the Congo River plume, which comprised as much as 93% of the available-Fe pool, was attributed to increased scavenging and formation of Fe oxides. Increased scavenging of other particle-reactive trace metals (TMs) (Mn, Al, and Pb) was also apparent in Congo-influenced waters. However, particles did not play a significant role in transporting TMs off-shelf within Congo plume waters. Key Points: • Different oxidation kinetics lead to decoupled Fe and Mn oxide redox cycling within oxygen-depleted waters on the Benguela Shelf • Lower lability of particulate phosphorus (∼41%) indicate potential refractory biogenic source on Benguela shelf • Nepheloid particles formed important sources of Fe and Mn oxides that adsorb trace metals (TMs), and serve as potential TM sources from shelf to open ocean