German Research Vessel Polarstern Research Articles

Geophysical insights on the crustal structure of Greenland's northern continental margin towards the Morris Jesup Spur

During expedition PS115/1, the German research vessel Polarstern acquired seismic refraction data along a 102-km-long profile crossing Greenland's northern continental margin and extending up to the southwestern limit of the Morris Jesup Spur. A P–wave velocity model is obtained and validated by gravity modelling. A nearby seismic reflection line provides insights on the structures within the sedimentary cover. Beneath a 2-km-thick sedimentary cover with velocities of 1.8 km/s to 3.4 km/s, an up to 1.5-km-thick layer is characterized by velocities of 4.2 km/s and is interpreted to consist of volcanic rocks. This is consistent with proposed volcanic activity on the Morris Jesup Spur and exposed volcano-sedimentary rocks of the nearby Kap Washington Group. Below the volcanic rocks, an up to 7 km-thick unit with velocities of 4.4 to 5.8 km/s is interpreted to consist of metasedimentary rocks still belonging to the deformed units of the Franklinian Basin. The seismic reflection data image a tectonic overprint of the acoustic basement and the lowermost sedimentary layers. Tectonic faults indicating the tectonic overprint do not reach to the uppermost sedimentary layers. This hints at an older fracture zone that is also observed in the velocity model and aligns well with observed anomalies in the regional gravity and magnetic fields. The seismic velocity model reveals a highly extended continental crust that shows a magmatic overprint at all crustal levels. The upper crust is 5 km thick with a velocity of 6.0 km/s. However, in three distinct zones its thickness is up to 8 km and the velocity increases to 6.3 km/s. These zones are interpreted as magmatic intrusions into the upper crust. The lower crust represents a 9-km-thick high-velocity layer (7.2 km/s) that is interpreted as magmatic underplating or lower crustal sill intrusions. Such a high-velocity lower crust is not present in models of adjacent Arctic margins.PACS: 0000, 11112000 MSC: 0000, 1111

Aerosol measurements with a shipborne Sun–sky–lunar photometer and collocated multiwavelength Raman polarization lidar over the Atlantic Ocean

Abstract. A shipborne Sun–sky–lunar photometer of type CE318-T was tested during two trans-Atlantic cruises aboard the German research vessel Polarstern from 54∘ N to 54∘ S in May/June and December 2018. The continuous observations of the motion-stabilized shipborne CE318-T enabled the first-time observation of a full diurnal cycle of aerosol optical depth (AOD) and column-mean Ångström coefficient of a mixed dust–smoke episode. The latitudinal distribution of the AOD from the shipborne CE318-T, Raman lidar and MICROTOPS II shows the same trend with highest values in the dust belt from 0 to 20∘ N and overall low values in the Southern Hemisphere. The linear-regression coefficients of determination between MICROTOPS II and the CE318-T were 0.988, 0.987, 0.994 and 0.994 for AODs at 380, 440, 500 and 870 nm and 0.896 for the Ångström exponent at 440–870 nm. The root-mean-squared differences of AOD at 380, 440, 500 and 870 nm were 0.015, 0.013, 0.010 and 0.009, respectively.

On the Reliability of Surface Current Measurements by X-Band Marine Radar

Real-time quality-controlled surface current data derived from X-Band marine radar (MR) measurements were evaluated to estimate their operational reliability. The presented data were acquired by the standard commercial off-the-shelf MR-based sigma s6 WaMoS® II (WaMoS® II) deployed onboard the German Research vessel Polarstern. The measurement reliability is specified by an IQ value obtained by the WaMoS® II real-time quality control (rtQC). Data which pass the rtQC without objection are assumed to be reliable. For these data sets accuracy and correlation with corresponding vessel-mounted acoustic Doppler current profiler (ADCP) measurements are determined. To reduce potential misinterpretation due to short-term oceanic variability/turbulences, the evaluation of the WaMoS® II accuracy was carried out based on sliding means over 20 min of the reliable data only. The associated standard deviation σ W a M o S = 0.02 m/s of the mean WaMoS® II measurements reflect a high precision of the measurement and the successful rtQC during different wave, current and weather conditions. The direct comparison of 7272 WaMoS® II/ADCP northward and eastward velocity data pairs yield a correlation of r ≥ 0.94 , with | b i a s Δ | ≤ 0.06 m/s and σ S = 0.05 m/s. This confirms that the MR-based surface current measurements are accurate and reliable.

Seabed images from Southern Ocean shelf regions off the northern Antarctic Peninsula and in the southeastern Weddell Sea

Abstract. Recent advances in underwater imaging technology allow for the gathering of invaluable scientific information on seafloor ecosystems, such as direct in situ views of seabed habitats and quantitative data on the composition, diversity, abundance, and distribution of epibenthic fauna. The imaging approach has been extensively used within the research project DynAMo (Dynamics of Antarctic Marine Shelf Ecosystems) at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research Bremerhaven (AWI), which aimed to comparatively assess the pace and quality of the dynamics of Southern Ocean benthos. Within this framework, epibenthic spatial distribution patterns have been comparatively investigated in two regions in the Atlantic sector of the Southern Ocean: the shelf areas off the northern tip of the Antarctic Peninsula, representing a region with above-average warming of surface waters and sea-ice reduction, and the shelves of the eastern Weddell Sea as an example of a stable high-Antarctic marine environment that is not (yet) affected by climate change. The AWI Ocean Floor Observation System (OFOS) was used to collect seabed imagery during two cruises of the German research vessel Polarstern, ANT-XXIX/3 (PS81) to the Antarctic Peninsula from January to March 2013 and ANT-XXXI/2 (PS96) to the Weddell Sea from December 2015 to February 2016. Here, we report on the image and data collections gathered during these cruises. During PS81, OFOS was successfully deployed at a total of 31 stations at water depths between 29 and 784 m. At most stations, series of 500 to 530 pictures ( > 15 000 in total, each depicting a seabed area of approximately 3.45 m2 or 2.3 × 1.5 m) were taken along transects approximately 3.7 km in length. During PS96, OFOS was used at a total of 13 stations at water depths between 200 and 754 m, yielding series of 110 to 293 photos (2670 in total) along transects 0.9 to 2.6 km in length. All seabed images taken during the two cruises, including metadata, are available from the data publisher PANGAEA via the two persistent identifiers at https://doi.org/10.1594/PANGAEA.872719 (for PS81) and https://doi.org/10.1594/PANGAEA.862097 (for PS96).

Mini neutron monitor measurements at the Neumayer III station and on the German research vessel Polarstern

Neutron monitors (NMs) are ground-based devices to measure the variation of cosmic ray intensities, and although being reliable they have two disadvantages: their size as well as their weight. As consequence, [1] suggested the development of a portable, and thus much smaller and lighter, calibration neutron monitor that can be carried to any existing station around the world [see 2; 3]. But this mini neutron monitor, moreover, can also be installed as an autonomous station at any location that provides ’’office” conditions such as a) temperatures within the range of around 0 to less than 40 degree C as well as b) internet and c) power supply. However, the best location is when the material above the NM is minimized. In 2011 a mini Neutron Monitor was installed at the Neumayer III station in Antarctica as well as the German research vessel Polarstern, providing scientific data since January 2014 and October 2012, respectively. The Polarstern, which is in the possession of the Federal Republic of Germany represented by the Ministry of Education and Research and operated by the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research and managed by the shipping company Laeisz, was specially designed for working in the polar seas and is currently one of the most sophisticated polar research vessels worldwide. It spends almost 310 days a year at sea usually being located in the waters of Antarctica between November and March while spending the northern summer months in Arctic waters. Therefore, the vessel scans the rigidity range below the atmospheric threshold and above 10 GV twice a year. In contrast to spacecraft measurements NM data are influenced by variations of the geomagnetic field as well as the atmospheric conditions. Thus, in order to interpret the data a detailed knowledge of the instrument sensitivity with geomagnetic latitude (rigidity) and atmospheric pressure is essential. In order to determine the atmospheric response data from the Neumayer III station here we will perform comparisons to other polar stations, resulting in an atmospheric pressure coefficient of 7.5‰/hPa, while the rigidity dependence will be determined experimentally by utilizing several latitude scans. Thereby, the atmospheric pressure and temperature correction will be discussed in more detail and the results of the latitude scan performed between October 2012 and March 2013 will be presented. Moreover, we will show that this latitude scan can also be described by using the yield function of [4].

Tantulocarida (Crustacea) from the Southern Ocean deep sea, and the description of three new species of Tantulacus Huys, Andersen & Kristensen, 1992

During the expedition ANT XIX/3 meiofauna samples were collected from the German research vessel Polarstern near the Shackleton Fracture Zone. During sorting of the samples 86 tantulus larvae were found. Extensive examination of the larvae revealed a high diversity of tantulocaridans in the Southern Ocean deep sea (33 species). A remarkable proportion of these were new species of Tantulacus Huys, Andersen & Kristensen, 1992. The present paper reports the discovery of three new Antarctic tantulocarids which are referred to Tantulacus. The affiliation of T. longispinosus n. sp., T. karolae n. sp. and T. dieteri n. sp. to Tantulacus is straightforward: all representatives of the Tantulocarida are characterised by the presence of 1-2 slender setae on the endopod of the second to fifth thoracopods, but in none of the hitherto described genera, other than Tantulacus, are these elements modified. Tantulacus hoegi Huys, Andersen & Kristensen, 1992 and the three new species share the possession of a distal rigid spine on the endopod of the second to fifth thoracopods as a synapomorphy and thus can be readily distinguished from other tantulocaridans. This is the first record of free-living sediment-inhabiting tantulus larvae from this area, although this probably reflects the degree of undersampling.

Description of two new deep-water species of the genus Brookula Iredale, 1912(Mollusca, Gastropoda, Trochoidea), with a revision of the genus for the Subantarcticand Arctic Sector of the Atlantic Ocean

Among benthic mollusc samples from the deep Southern Atlantic Ocean collected during various expeditions of the German Research Vessel Polarstern were several representatives of the genus Brookula, of which four new deep water records are presented herein. Two of the species, B. bohni sp. nov. and B. charleenae sp. nov. are described and differences to congeners are given. For Brookula argentina (Zelaya, Absalão & Pimenta, 2006) and B. exquisita Clarke, 1961 range extensions are provided. The problematic use of the genus Benthobrookula instead of the genus Brookula is discussed and the use of the genus name Benthobrookula is discouraged until more detailed data on morphology and anatomy are available. For the first time the soft part gross morphology of Brookula pfefferi Powell, 1951 has been investigated and illustrated. Brookula decussata (Pelseneer, 1903) has to be regarded as a potential senior synonym of B. pfefferi. Examination of the type material has shown that B. antarctica Dell, 1990 does not differ from B. strebeli Powell, 1951 and the former becomes a junior synonym of B. strebeli. Morphometric data for all Brookula species from the Subantarctic and Antarctic waters of the Southern Atlantic Ocean are also provided, allowing a total of nine species to be included in this sector.

Ship-borne measurements of erythemal UV irradiance and ozone content in various climate zones

Ship-borne measurements of spectral as well as biologically effective UV irradiance have been performed on the German research vessel Polarstern during the Atlantic transect from Bremerhaven, Germany (53.5 degrees N, 8.5 degrees E), to Cape Town, South Africa (33.6 degrees S, 18.3 degrees E), from 13 October to 17 November 2005. Such measurements are required to study UV effects on marine organisms. They are also necessary to validate satellite-derived surface UV irradiance. Cloud free radiative transfer calculations support the investigation of this latitudinal dependence. Input parameters, such as total ozone column and aerosol optical depth have been measured on board as well. Using these measured parameters, the modelled cloudless noontime UVA irradiance (320-400 nm) shows the expected dependence on varying minimum solar zenith angles (SZA) at different latitudes. The modelled cloudless noontime UVB irradiance (290-320 nm) does not show this clear dependence on SZA due to the strong influence of ozone absorption in this spectral range. The maximum daily dose of erythemal irradiance of 5420 J m(-1) was observed on 14 November 2005, when the ship was in the tropical Atlantic south of the equator. The expected UV maximum should have been observed with the sun in the zenith during local noon (11 November). Stratiform clouds reduced the dose to 3835 J m(-1). In comparison, the daily erythemal doses in the mid-latitudinal Bay of Biscay only reached values between 410 and 980 J m(-1) depending on cloud conditions. The deviation in daily erythemal dose derived from different instruments is around 5%. The feasibility to perform ship-borne measurements of spectral UV irradiance is demonstrated.

Enhanced tropospheric BrO over Antarctic sea ice in mid winter observed by MAX-DOAS on board the research vessel Polarstern

Abstract. We present Multi AXis-Differential Optical Absorption Spectroscopy (MAX-DOAS) observations of tropospheric BrO carried out on board the German research vessel Polarstern during the Antarctic winter 2006. Polarstern entered the area of first year sea ice around Antarctica on 24 June 2006 and stayed within this area until 15 August 2006. For the period when the ship cruised inside the first year sea ice belt, enhanced BrO concentrations were almost continuously observed. Outside the first year sea ice belt, typically low BrO concentrations were found. Based on back trajectory calculations we find a positive correlation between the observed BrO differential slant column densities (ΔSCDs) and the duration for which the air masses had been in contact with the sea ice surface prior to the measurement. While we can not completely rule out that in several cases the highest BrO concentrations might be located close to the ground, our observations indicate that the maximum BrO concentrations might typically exist in a (possibly extended) layer around the upper edge of the boundary layer. Besides the effect of a decreasing pH of sea salt aerosol with altitude and therefore an increase of BrO with height, this finding might be also related to vertical mixing of air from the free troposphere with the boundary layer, probably caused by convection over the warm ocean surface at polynyas and cracks in the ice. Strong vertical gradients of BrO and O3 could also explain why we found enhanced BrO levels almost continuously for the observations within the sea ice. Based on our estimated BrO profiles we derive BrO mixing ratios of several ten ppt, which is slightly higher than many existing observations. Our observations indicate that enhanced BrO concentrations around Antarctica exist about one month earlier than observed by satellite instruments. From detailed radiative transfer simulations we find that MAX-DOAS observations are up to about one order of magnitude more sensitive to near-surface BrO than satellite observations. In contrast to satellite observations the MAX-DOAS sensitivity hardly decreases for large solar zenith angles and is almost independent from the ground albedo. Thus this technique is very well suited for observations in polar regions close to the solar terminator. For large periods of our measurements the solar elevation was very low or even below the horizon. For such conditions, most reactive Br-compounds might exist as Br2 molecules and ozone destruction and the removal of reactive bromine compounds might be substantially reduced.

Latitudinal Gradient of Airborne Polyfluorinated Alkyl Substances in the Marine Atmosphere between Germany and South Africa (53° N−33° S)

Neutral, volatile polyfluorinated alkyl substances (PFAS) were determined in high-volume air samples collected onboard the German research vessel Polarstern during cruise ANTXXIII-1 between Bremerhaven, Germany (53 degrees N) and Capetown, Republic of South Africa (33 degrees S) in fall 2005. An optimized and validated analytical protocol was used for the determination of several fluorotelomer alcohols (FTOHs) as well as N-alkylated fluorooctane sulfonamides and sulfonamidoethanols (FOSAs/FOSEs). Quantitative analyses were done by gas chromatography-mass spectrometry. This study provides the first concentration data of airborne PFAS from the Southern Hemisphere. Results indicate a strongly decreasing concentration gradient from the European continent toward less industrialized regions. The study confirms that airborne PFAS are mainly restricted to the Northern Hemisphere with a maximum concentration of 190 pg/m3 (8:2 FTOH) in the first sample collected in the channel between the European mainland and the UK. However, south of the equator, trace amounts of several FTOHs and FOSAs with a maximum of 14 pg/m3 (8:2 FTOH) could still be detected. Furthermore, a selection of ionic PFAS including perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) were determined in the particulate phase of high-volume air samples by liquid chromatography-mass spectrometry. Levels of ionic PFAS were almost 2 orders of magnitude lower than those of neutral PFAS, with maximum concentrations in the first sample of 2.5 pg/m3 (PFOS) and 2.0 pg/m3 (PFOA).

MAX‐DOAS measurements of BrO and NO2 in the marine boundary layer

During a cruise of the German research vessel Polarstern from Bremerhaven, Germany to Capetown, South Africa in October 2000 mid latitude tropospheric bromine oxide (BrO) and nitrogen dioxide (NO2) abundances were investigated by ground‐based MAX‐DOAS (scattered light Multi Axis Differential Optical Absorption Spectroscopy). By comparing the slant column densities of absorbers measured at different elevation angles above the horizon (5° to 90°) it is possible to draw conclusions regarding the vertical distribution of the investigated absorbers (i.e., BrO and NO2). During a period of 2 days in the region north of the Canary Islands (around 35°N, 13°W) significant boundary layer BrO in the 1 ppt range was found. For the remaining time all data points ranged below the detection limit. Boundary layer NO2 was found near Europe and the Canary Islands with mixing ratios in the range of several ppb. In the remote marine air south west of Africa upper limits were derived.

Small-Sized Benthic Organisms of the Alpha Ridge, Central Arctic Ocean

Abundance, biomass and activity of the small-sized benthic organisms (bacteria to meiofauna, includingforaminifera) was studied in summer 1998 during the expedition ARK XIV/1a to the Amerasian area of theperennially ice covered central Arctic Ocean. With the help of two icebreakers, the German research vesselPOLARSTERN and the Russian nuclear-powered ARCTICA, it was possible to reach this remote, heavilyice-covered region in order to carry out the first benthic investigations. These focus on effects on the benthiccommunity of the expected low food availability under perennial ice coverage. Bacterial and meiofaunalabundances were determined by direct counting. Biomass determinations on bacteria and nematodes wereundertaken by size-imaging techniques. In addition biochemical analyses were carried out to estimate foodavailability (as sediment-bound chloroplastic pigments indicating phytodetritus) at the sea floor, the total microbialbiomass (TMB; i.e. the total amount of sediment inhabiting bacteria, flagellata, protozoa and small metazoa,estimated by phospholipid quantification) and the potential bacterial activity (turnover rates of ester-cleavingexoenzymes). Concentrations of chloroplastic pigment equivalents (CPE) in the main target area (Alpa-Ridge)ranged between 0.10 ± 0.02 and 0.17 ± 0.04 g/ml. A 2-3 times higher concentration was determined at astation on the Lomonosov Ridge crest (0.40 ± 0.15 g/ml). The standing stock of meiobenthic organisms(including foraminiferans) was extremely low and varied between 72 ± 17 individuals 10 cm-2 in the deepMakarov Basin (3,170 m) and 190 ± 56 individuals 10 cm-2 on the Alpha Ridge (1,470 m). Significantly highernumbers (U-test, p = 0.049) were found on the Lomonosov Ridge (297 ± 82 individuals 10 cm-2). Meiobenthicabundances from the area of investigations, were up to ten times lower than those reported from non-ice covereddeep-sea regions. However a significant water depth depending decrease of meiobenthic abundances was stilldetectable.A comparison of biomass data determined by volumetric measurements and biochemical methods showed thatabout 67% of the TMB are held by organisms of nanofauna size (2-32 m), approx. 32% belongs to bacteria.Only 0.5-1.5% of the TMB were held by metazoan meiofauna.

Peroxy radical and related trace gas measurements in the boundary layer above the Atlantic Ocean

Measurements of peroxy radicals (RO2* = HO2 + ∑RO2, where HO2 is the hydroperoxyl radical and R is an organic group) were made using the chemical amplifier technique (PERCA) during the Air chemistry and Lidar studies of tropospheric and stratospheric species on the Atlantic Ocean (ALBATROSS) campaign on board the German research vessel Polarstern (cruise ANT XIV/1, 1996). The data obtained are compared to previous results from an earlier cruise in 1991 (ANT X/1). Reasonable agreement between the two data sets was observed, indicating the reliability of these measurements. Both data sets take into account the sensitivity of the radical amplifier to the presence of ambient water vapor. Maximum RO2* mixing ratios around noon between 40 and 80 pptv were measured. Nighttime signals were observed on many days. Air masses in different latitude regions in the North and South Atlantic could be characterized using back trajectories. In spite of the fact that the RO2* is relatively short lived, its mixing ratio appears to be influenced by the path traveled by the air mass somewhat higher levels being associated with sources of pollution. A box model based on CH4 and CO oxidation chemistry describes RO2* reasonably well but could not explain the persistent nighttime signals and the HCHO observed. An additional source of HCHO is required, indicating the importance of nonmethane hydrocarbon (NMHC) chemistry in the remote Atlantic boundary layer. Both back trajectories and variations of trace gas concentrations indicate that biomass burning, ship, and natural emissions are likely responsible for the observed deviations from the assumed chemistry.

The terrestrial potassium layer (75–110 km) between 71°S and 54°N: Observations and modeling

Observations of the nighttime atmospheric potassium layer were performed on the German research vessel Polarstern from March to June 1996. K density profiles were obtained between 71°S and 45°N. The nightly mean peak densities ranged from 140 cm−3 in the equatorial region to 10 cm−3 in the Antarctic, and the column abundances decreased from 1.2 × 108 to 1.3 × 107 cm−2 going from low to high latitudes. High peak densities and column abundances were also commonly observed together with sporadic K layers. The global mean peak height of the normal (background) K layer was found to be 88.3 km. After the Polarstern campaign, observations were continued at Kühlungsborn (54°N). The summer and winter K layers, observed during July 1996 and January 1997, were quite different in shape but had similar peak densities and column abundances. A one‐dimensional model of the K layer was developed which includes meteoric deposition, vertical transport through eddy diffusion, and a full chemical scheme. This model was able to reproduce very satisfactorily the seasonal behavior of the K layer at 54°N if the wintertime deposition flux of the metal was reduced by 30% compared to the summer. The midlatitude ratio of K to Na was about 1%, much less than either the chondritic or cosmic ratios of the two metals (≈8 or 6%, respectively). The most likely reason is that potassium vaporizes less efficiently from meteoroids than sodium, in agreement with a thermodynamic model of a nonideal chondritic magma and observations in the exosphere of Mercury. Finally, the model was generally very successful in reproducing the latitudinal variations in the K layer.

Determination of Monomethylcadmium in the Environment by Differential Pulse Anodic Stripping Voltammetry

A differential pulse anodic stripping voltammetric (DPASV) method was used to differentiate between the cadmium species Cd(2+) and MeCd(+) (Me = methyl) in aquatic systems. These two species show peaks in the DPASV voltammogram which differ by 112 mV. In model experiments, it was demonstrated that monomethylcadmium is not stable at pH 2, but under higher pH conditions, normally found in fresh and ocean water samples, the identity of MeCd(+) was verified by different investigations, including cyclic voltammetry, selective extraction of a complex of diethyldithiocarbamate with MeCd(+) into n-hexane, and photochemical dissociation of MeCd(+) by UV irradiation. It was also shown that humic acids do not influence the voltammetric determination of monomethylcadmium. For the first time, it was possible to analyze MeCd(+) in environmental samples. During different expeditions with the German research vessel Polarstern, monomethylcadmium could be determined above the detection limit of 470 pg L(-1) in nearly all surface water samples of the South Atlantic with spot concentrations of up to about 700 pg L(-1), whereas in the North Atlantic only 15-30% of the total samples showed MeCd(+) concentrations above this limit. The existence of MeCd(+) in the remote area of the South Atlantic, as well as positive correlations with the local bioactivity in the ocean, indicates biomethylation as the most probable formation process for this methylated cadmium species. This assumption is supported by the simultaneous occurrence of other methylated heavy metal compounds, such as Me(3)Pb(+). Up to 48% of the total cadmium was found to be monomethylcadmium in some Arctic meltwater ponds.

Shipborne FT-IR Measurements of Atmospheric Trace Gases on a South (33°S) to North (53°N) Atlantic Traverse

For the first time solar and lunar IR absorption measurements have been performed by means of an FT-IR spectrometer on a lengthy ship cruise. These measurements were performed in May and June 1994 on board the German research vessel Polarstern between Cape Town (33°S) and Bremerhaven (53°N). Spectral analysis of the obtained spectra allowed retrieval of the total zenith columns of a number of trace gases in the atmosphere and study of the latitudinal dependence of the column densities of these trace gases.

A latitudinal survey of mesospheric and upper stratospheric water vapor

As part of the LAtitudinal DIstribution of Middle Atmosphere Structure (LADIMAS) campaign, measurements of mesospheric and upper stratospheric water vapor concentration were made over a latitudinal range from 53 N to 63 S. The 22-GHz emission line of water vapor was observed by a new, portable, cryogenically cooled microwave radiometer that was carried on board the German research vessel Polarstern as it sailed from Bremerhaven, Germany, to the Antarctic during November and December, 1991. Water vapor profiles were obtained at approximately 5 deg latitude intervals for an altitude range of 40 to 80 km.

Emissions of light nonmethane hydrocarbons from the Atlantic into the atmosphere

During two Atlantic cruises of the German research vessel Polarstern, 1988 and 1989, the concentrations of light nonmethane hydrocarbons (NMHC) in seawater were measured. On the basis of a simple budget analysis, the oceanic mixed layer represents a NMHC reservoir with an internal production and a major loss by emission into the atmosphere. As a consequence, the concentrations of NMHC depend on the rates of ocean‐atmosphere exchange: high exchange rates reduce the concentrations and vice versa. With the prevailing transfer velocities the emission rates were calculated according to ocean‐atmosphere exchange models. The regional averages of the alkene emission rates vary by 1 order of magnitude. For ethene the maximum value was 5×108 molecules cm−2 s−1. The emissions of the various alkanes were generally below 1×108 molecules cm−2s−1. The total C2‐C4 hydrocarbon emissions during both cruises average 6×108 molecules cm−2 s−1, 70 % of which are alkene emissions, with ethene alone contributing 42 % to the total. No indications for enhanced emissions of NMHC at high phytoplankton concentrations or in the proximity to coastlines were observed. Thus we regard the emissions as representative for the mid‐Atlantic and the season of the investigations, August to October. The calculated emission rates of the shortlived alkenes are validated by comparison with atmospheric measurements of NMHC. The emission rates are substantially lower than the majority of reported oceanic emission estimates by up to about 2 orders of magnitude.

Hydrogen peroxide measurements in the marine atmosphere

Hydrogen peroxide, one of the key compounds in multiphase atmospheric chemistry, was measured on an Atlantic cruise (ANT VII/1) of the German research vessel Polarstern from 15 September to 9 October 1988, in rain and ambient air by a chemiluminescence technique. For gas phase H2O2 cryogenic sampling was employed. The presented results show an increase of gas-phase mixing ratios of about 45 pptv per degree latitude between 50° N and 0°, and a maximum of 3.5 ppbv around the equator. Generally higher mixing ratios were observed in the Southern Hemisphere, with a clear diurnal variation. The H2O2 mixing ratio is correlated to the UV radiation intensity and to the temperature difference between air and ocean surface water.

The distribution of light nonmethane hydrocarbons over the mid-Atlantic: Results of the Polarstern cruise ANT VII/1

During the cruise ANT VII/1 (September/October 1988) of the German research vessel Polarstern the latitudinal distributions of several nonmethane hydrocarbons were measured over the Atlantic between 45°N and 30°S by in-situ gas chromatography.On the average, the highest mixing ratios of ethane, propane, i- and n-butane, ethene and acetylene were observed in the Northern Hemisphere around 40° N and just north of the intertropical convergence zone, respectively. South of the equator, a bulge in the mixing ratios of ethane and acetylene was observed indicating aged biomass burning emissions. This observation coincided with enhanced tropospheric ozone found in this region at this season. On the average ethane and acetylene mixing ratios were around 500 and 100 ppt, respectively, whereas the levels of the other NMHC were in the range of some ppt up to 100 ppt.compared with the results of the cruise ANT V/5 (March/April, 1987), the ethane mixing ratios in September/October proved to be a factor of 3 lower in the Northern Hemisphere and a factor of 2 higher in the Southern Hemisphere, probably due to seasonal effects. Possible causes are the higher OH radical concentrations in summer, which result in a faster removal of ethane or stronger emission from biomass burning which also peaks in the dry season.The relative pattern of the hydrocarbons just north of the ITCZ was very similar for both measurement series. In this region, the NMHC were advected by long-range transport from the continent, whereas generally the ocean itself acts as a major NMHC source. This is supported by the results of a balance calculation between oceanic emissions and atmospheric removal rates.