ALBERT

Description: Sub-micron marine aerosol particles (PM1) were collected over the period 22 June–21 July 2011 during the RV MARIA S. MERIAN cruise MSM 18/3, which travelled from the Cape Verdean island of São Vicente to Gabon, in the process crossing the tropical Atlantic Ocean with its equatorial upwelling regime. According to air mass origin and the chemical composition of the sampled aerosol particles, three main regimes could be established. Aerosol particles in the first part of the cruise were mainly of marine origin (Region I). In the second part of the cruise, marine influences mixed with increasing influence from biomass burning (Region II). In the final part of the cruise, which approached the African mainland, the biomass burning influence became dominant (Region III). Generally, aerosol particles were dominated by sulfate (caverage = 2.0 μg m−3) and ammonium ions (caverage = 0.7 μg m−3), which were well-correlated and increased slightly over the duration of the cruise. High concentrations of water-insoluble organic carbon (WISOC; caverage = 0.4 μg m−3) were found, most likely as a result of the high oceanic productivity in this region. Water-soluble organic carbon (WSOC) concentrations increased from 0.26 μg m−3 in Region I to 2.3 μg m−3 in Region III, most likely as a result of biomass burning influences. The major organic aerosol constituents were oxalic acid, methanesulfonic acid (MSA), and aliphatic amines. MSA concentrations were quite constant during the cruise (caverage = 42 ng m−3). Aliphatic amines were most abundant in Region I, with concentrations of ~ 20 ng m−3. Oxalic acid showed the opposite trend, with average concentrations of 12 ng m−3 in Region I and 158 ng m−3 in Region III. The α-dicarbonyl compounds glyoxal and methylglyoxal were detected in the aerosol particles in the low ng m−3 range and were closely correlated with oxalic acid. MSA and aliphatic amines arise from biogenic marine sources, whereas oxalic acid and the α-dicarbonyl compounds were attributed to biomass burning. Concentrations of n-alkanes increased from 0.8 to 4.7 ng m−3 over the duration of the cruise. PAHs and hopanes were abundant only in Region III (caverage of PAHs = 0.13 ng m−3; caverage of hopanes = 0.19 ng m−3). Levoglucosan was identified in several samples obtained in Region III, with caverage = 1.9 ng m−3, which points to (aged) biomass burning influences. The organic compounds quantified in this study could explain 8.3 % of WSOC in Regions I, where aliphatic amines and MSA dominated, 3.7 % of WSOC in Region II and 2.5 % of WSOC in Region III, where oxalic acid dominated.

Description: Particle fluxes at the Cape Verde Ocean Observatory (CVOO) in the eastern tropical North Atlantic for the period December 2009 until May 2011 are discussed based on bathypelagic sediment trap time-series data collected at 1290 and 3439 m water depth. The typically oligotrophic particle flux pattern with weak seasonality is modified by the appearance of a highly productive and low oxygen (minimum concentration below 2 µmol kg**-1 at 40 m depth) anticyclonic modewater eddy (ACME) in winter 2010. The eddy passage was accompanied by unusually high mass fluxes of up to 151 mg m**-2 d**-1, lasting from December 2009 to May 2010. Distinct biogenic silica (BSi) and organic carbon flux peaks of ~15 and 13.3 mg m**-2 d**-1, respectively, were observed in February-March 2010 when the eddy approached the CVOO. The flux of the lithogenic component, mostly mineral dust, was well correlated with that of organic carbon, in particular in the deep trap samples, suggesting a tight coupling. The lithogenic ballasting obviously resulted in high particle settling rates and, thus, a fast transfer of epi-/meso-pelagic signatures to the bathypelagic traps. We suspect that the two- to three-fold increase in particle fluxes with depth as well as the tight coupling of mineral dust and organic carbon in the deep trap samples might be explained by particle focusing processes within the deeper part of the eddy. Molar C : N ratios of organic matter during the ACME passage were around 18 and 25 for the upper and lower trap samples, respectively. This suggests that some productivity under nutrient (nitrate) limitation occurred in the euphotic zone of the eddy in the beginning of 2010 or that a local nitrogen recycling took place. The d15N record showed a decrease from 5.21 to 3.11 per mil from January to March 2010, while the organic carbon and nitrogen fluxes increased. The causes of enhanced sedimentation from the eddy in February/March 2010 remain elusive, but nutrient depletion and/or an increased availability of dust as a ballast mineral for organic-rich aggregates might have contributed. Rapid remineralisation of sinking organic-rich particles could have contributed to oxygen depletion at shallow depth. Although the eddy formed in the West African coastal area in summer 2009, no indications of coastal flux signatures (e.g. from diatoms) were found in the sediment trap samples, confirming the assumption that the suboxia developed within the eddy en route. However, we could not detect biomarkers indicative of the presence of anammox (anaerobic ammonia oxidation) bacteria or green sulfur bacteria thriving in photic zone suboxia/hypoxia, i.e. ladderane fatty acids and isorenieratene derivatives, respectively. This could indicate that suboxic conditions in the eddy had recently developed and/or the respective bacterial stocks had not yet reached detection thresholds. Another explanation is that the fast-sinking organic-rich particles produced in the surface layer did not interact with bacteria from the suboxic zone below. Carbonate fluxes dropped from -52 to 21.4 mg m**-2 d**-1 from January to February 2010, respectively, mainly due to reduced contribution of shallow-dwelling planktonic foraminifera and pteropods. The deep-dwelling foraminifera Globorotalia menardii, however, showed a major flux peak in February 2010, most probably due to the suboxia/hypoxia. The low oxygen conditions forced at least some zooplankton to reduce diel vertical migration. Reduced "flux feeding" by zooplankton in the epipelagic could have contributed to the enhanced fluxes of organic materials to the bathypelagic traps during the eddy passage. Further studies are required on eddy-induced particle production and preservation processes and particle focusing.

Description: The data involves annotations with the MBARI VARS annotation software of pelagic HD video transects obtained by the pelagic in situ observations system PELAGIOS. PELAGIOS is a newly developed towed camera system for deep-sea biological exploration and performance of video transects for diversity and distribution data. The data was collected in 2015 during cruise MSM49 on R/V MARIA S. MERIAN, from 20 to 950 m, during day (187 minutes) and night (292 minutes) transects on the northwestern slope of Senghor Seamount (17°14.2'N, 22°00.7'W; bottom depth of approximately 1000 m). The annotated organisms include fishes, crustaceans and gelatinous zooplankton. One file includes the transect length at each depth at day or night and another file has all individual annotated taxa observed at a particular depth at day or night. The Figure 4 is made with this data. A third file involves the data we used to make Figure 3 which is the comparison between the observations of Poeobius observed in PELAGIOS and UVP5 to calculate sample volume.

Description: We present measurements of pCO2, O2 concentration, biological oxygen saturation (Delta O2/Ar) and N2 saturation (Delta N2) in Southern Ocean surface waters during austral summer, 2010-2011. Phytoplankton biomass varied strongly across distinct hydrographic zones, with high chlorophyll a (Chla) concentrations in regions of frontal mixing and sea-ice melt. pCO2 and Delta O2 /Ar exhibited large spatial gradients (range 90 to 450 µatm and -10 to 60%, respectively) and co-varied strongly with Chla. However, the ratio of biological O2 accumulation to dissolved inorganic carbon (DIC) drawdown was significantly lower than expected from photosynthetic stoichiometry, reflecting the differential time-scales of O2 and CO2 air-sea equilibration. We measured significant oceanic CO2 uptake, with a mean air-sea flux (~ -20 mmol m-2 d-1) that significantly exceeded regional climatological values. N2 was mostly supersaturated in surface waters (mean Delta N2 of +2.5 %), while physical processes resulted in both supersaturation and undersaturation of mixed layer O2 (mean Delta O2phys = 2.1 %). Box model calculations were able to reproduce much of the spatial variability of Delta N2 and Delta O2phys along the cruise track, demonstrating significant effects of air-sea exchange processes (e.g. atmospheric pressure changes and bubble injection) and mixed layer entrainment on surface gas disequilibria. Net community production (NCP) derived from entrainment-corrected surface Delta O2 /Ar data, ranged from ~ -40 to 〉 300 mmol O2 m-2 d-1 and showed good coherence with independent NCP estimates based on seasonal mixed layer DIC deficits. Elevated NCP was observed in hydrographic frontal zones and regions of sea-ice melt with shallow mixed layer depths, reflecting the importance of mixing in controlling surface water light and nutrient availability.

Description: The distribution of the mean oceanic oxygen concentration results from a balance between ventilation and consumption. In the eastern tropical Pacific and Atlantic, this balance creates extended oxygen minimum zones (OMZ) at intermediate depth. Here, we analyze hydrographic and velocity data from shipboard and moored observations, which were taken along the 23°W meridian cutting through the Tropical North East Atlantic (TNEA) OMZ, to study the distribution and generation of oxygen variability. By applying the extended Osborn-Cox model, the respective role of mesoscale stirring and diapycnal mixing in producing enhanced oxygen variability, found at the southern and upper boundary of the OMZ, is quantified. From the well-ventilated equatorial region toward the OMZ core a northward eddy-driven oxygen flux is observed whose divergence corresponds to an oxygen supply of about 2.4 µmol kg-1 year-1 at the OMZ core depth. Above the OMZ core, mesoscale eddies act to redistribute low- and high-oxygen waters associated with westward and eastward currents, respectively. Here, absolute values of the local oxygen supply 〉10 mmol kg-1 year-1 are found, likely balanced by mean zonal advection. Combining our results with recent studies, a refined oxygen budget for the TNEA OMZ is derived. Eddy-driven meridional oxygen supply contributes more than 50 % of the supply required to balance the estimated oxygen consumption. The oxygen tendency in the OMZ, as given by the multidecadal oxygen decline, is maximum slightly above the OMZ core and represents a substantial imbalance of the oxygen budget reaching about 20 % of the magnitude of the eddy-driven oxygen supply.