Atmospheric nitrate concentrations and isotope composition for samples collected in the marine boundary layer in 2006 and 2007

The comprehensive isotopic composition of atmospheric nitrate (i.e., the simultaneous measurement of all its stable isotope ratios: 15N/14N, 17O/16O and 18O/16O) has been determined for aerosol samples collected in the marine boundary layer (MBL) over the Atlantic Ocean from 65°S (Weddell Sea) to 79°N (Svalbard), along a ship-borne latitudinal transect. In nonpolar areas, the d15N of nitrate mostly deriving from anthropogenically emitted NOx is found to be significantly different (from 0 to 6 per mil) from nitrate sampled in locations influenced by natural NOx sources (-4 ± 2) per mil. The effects on d15N(NO3-) of different NOx sources and nitrate removal processes associated with its atmospheric transport are discussed. Measurements of the oxygen isotope anomaly (D17O = d17O - 0.52 × d18O) of nitrate suggest that nocturnal processes involving the nitrate radical play a major role in terms of NOx sinks. Different D17O between aerosol size fractions indicate different proportions between nitrate formation pathways as a function of the size and composition of the particles. Extremely low d15N values (down to -40 per mil) are found in air masses exposed to snow-covered areas, showing that snowpack emissions of NOx from upwind regions can have a significant impact on the local surface budget of reactive nitrogen, in conjunction with interactions with active halogen chemistry. The implications of the results are discussed in light of the potential use of the stable isotopic composition of nitrate to infer atmospherically relevant information from nitrate preserved in ice cores.

(Table 1) Conditions of vertical near-bottom profiling and the main parameters of the benthic boundary layer in several regions of the Black Sea shelf

Measurements of 14 vertical profiles of currents and hydrological parameters in the near-bottom layer with depth resolution of 0.1 m were carried out in several regions of the Black Sea shelf, at five points over the continental slope, and in three deep water regions. The upper boundary of the benthic boundary layer (BBL) was reliably determined at a point at distance from 5-7 to 35-40 m from the bottom where the gradients of density and current velocity changed. Experimental data obtained were used to determine the coefficient of bottom friction, friction velocity, coefficients of vertical diffusion of momentum and density, and vertical fluxes of temperature and salinity in the BBL.

Seawater carbonate chemistry and concentration boundary layers around complex assemblages of macroalgae in a laboratory experiment

Metabolic processes have the potential to modulate the effects of ocean acidification (OA) in nearshore macroalgal beds. We investigated whether natural mixed assemblages of the articulate coralline macroalgae Arthrocardia corymbosa and understory crustose coralline algae (CCA) altered pH and O2 concentrations within and immediately above their canopies. In a unidirectional flume, we tested the effect of water velocity (0-0.1 m/s), bulk seawater pH (ambient pH 8.05, and pH 7.65), and irradiance (photosynthetically saturating light and darkness) on pH and O2 concentration gradients, and the derived concentration boundary layer (CBL) thickness. At bulk seawater pH 7.65 and slow velocities (0 and 0.015 m/s), pH at the CCA surface increased to 7.90-8.00 in the light. Although these manipulations were short term, this indicates a potential daytime buffering capacity that could alleviate the effects of OA. Photosynthetic activity also increased O2 concentrations at the surface of the CCA. However, this moderating capacity was flow dependent; the CBL thickness decreased from an average of 26.8 mm from the CCA surface at 0.015 m/s to 4.1 mm at 0.04 m/s. The reverse trends occurred in the dark, with respiration causing pH and O2 concentrations to decrease at the CCA surface. At all flow velocities the CBL thicknesses (up to 68 mm) were much greater than those previously published, indicating that the presence of canopies can alter the CBL substantially. In situ, the height of macroalgal canopies can be an order of magnitude larger than those used here, indicating that the degree of buffering to OA will be context dependent.

Concentration and composition of aerosols in the near-water atmosphere layer above the Laptev Sea in July-September 1995

During the ARK-XI/1 expedition of R/V Polarstern in July-September 1995 12 samples of aerosols were collected in lower atmosphere layer over the Laptev Sea by filtration of air through AFA-HA filters. Element composition of the samples was determined by instrumental neutron activation analysis. Average atmospheric concentrations of Cr, Mn, Fe, Co, Zn and As are higher than in other regions of the Arctic. This can be explained by natural reasons: (1) by input of particles from the surface microlayer of sea water enriched by many chemical elements, (2) by atmospheric transfer of organic matter and lithogenic material from the land, and (3) by resuspension of particles from ice-rafted sediments. In some samples anthropogenic pollution was registered.

Natural fluctuations and gradients in the experimental design:research bias in the field of ocean acidification

These data form the basis of an analysis of a prevalent research bias in the field of ocean acidification, notably the ignoring of natural fluctuations and gradients in the experimental design. The data are extracted from published work and own experiments.

Physical oceanography from the TRACTOR project

Primary Objectives - Describe and quantify the present strength and variability of the circulation and oceanic processes of the Nordic Seas regions using primarily observations of the long term spread of a tracer purposefully released into the Greenland Sea Gyre in 1996. - Improve our understanding of ocean processes critical to the thermaholine circulation in the Nordic Seas regions so as to be able to predict how this region may respond to climate change. - Assess the role of mixing and ageing of water masses on the carbon transport and the role of the thermohaline circulation in carbon storage using water transports and mixing coefficients derived from the tracer distribution. Specific Objectives Perform annual hydrographic, chemical and SF6 tracer surveys into the Nordic regions in order to: - Measure lateral and diapycnal mixing rates in the Greenland Sea Gyre and in the surrounding regions. - Document the depth and rates of convective mixing in the Greenland Sea using the SF6 and the water masses characteristics. - Measure the transit time and transport of water from the Greenland Sea to surrounding seas and outflows. Document processes of water mass transformation and entrainment occurring to water emanating from the central Greenland Sea. - Measure diapycnal mixing rates in the bottom and margins of the Greenland Sea basin using the SF6 signal observed there. Quantify the potential role of bottom boundary-layer mixing in the ventilation of the Greenland Sea Deep Water in absence of deep convection. Monitor the variability of the entrainment of water from the Greenland Sea using time series auto-sampler moorings at strategic positions i.e., sill of the Denmark Strait, Labrador Sea, Jan Mayen fracture zone and Fram Strait. Relate the observed variability of the tracer signal in the outflows to convection events in the Greenland Sea and local wind stress events. Obtain a better description of deepwater overflow and entrainment processes in the Denmark Strait and Faeroe Bank Channel overflows and use these to improve modelling of deepwater overflows. Monitor the tracer invasion into the North Atlantic using opportunistic SF6 measurements from other cruises: we anticipate that a number of oceanographic cruises will take place in the north-east Atlantic and the Labrador Sea. It should be possible to get samples from some cruises for SF6 measurements. Use process models to describe the spread of the tracer to achieve better parameterisation for three-dimensional models. One reason that these are so resistant to prediction is that our best ocean models are as yet some distance from being good enough, to predict climate and climate change.