Description: We analyze the contribution of the Agulhas Current on the central water masses of the Benguela upwelling system (BUS) over the last decades in a high-resolution ocean simulation driven by atmospheric reanalysis. The BUS is an Eastern Boundary Upwelling System where upwelling of cold nutrient-rich water favors biomass growth. The two distinct subregions, North and South Benguela, differ in nutrient and oxygen properties of the upwelling water mass. Our analysis indicates that the contribution of Agulhas water to the upwelling is very strong in both subregions. Although the water masses feeding the upwelling have a common origin, their pathways are distinct in both regions. Whereas for the central waters of South Benguela the path is rather direct from where it is formed, the central waters of North Benguela takes a longer route through the equatorial current system. Not only the travel time from the Agulhas Current to the BUS is longer but also the central water mass is twice as old for the northern part when compared to the southern. Our analysis traces the pathways, history, and origin of the central water masses feeding upwelling in the BUS and emphasizes the direct impact of the Agulhas Current on the upwelling region. The variability of that link between the Indian Ocean and the South Atlantic is likely to change the nutrient and oxygen content, as well as temperature and salinity of the water masses in the upwelling region.

Description: The geological evolution of the western margin of South America has long been a challenge to geologists interested in convergent plate tectonics. Late in 1986, scientists on the ODP drillship JOIDES Resolution confirmed that the upper slope of the Peruvian margin consists of continental crust whereas the lower slope comprises an accretionary complex. An intricate history of horizontal and vertical movements can be detected, and the locations of ancient centers of upwelling appear to have varied, partly due to tectonic movements of the margin. In this review of Leg 112, the three scientific leaders on this cruise discuss their results.

Description: The present study examines sedimentation rates in the eastern Gotland Basin using a variety of methods that reveal considerable heterogeneity in the rates, both spatially and temporally. High-resolution seismic recordings and correlation with long sediment cores indicate increased thickness of strata and higher sedimentation rates (0.75 mm a-1) in the eastern part of the basin than in the western part (0.23 mm a-1) since the Littorina transgression some 8000 14C years BP. This difference is apparently a consequence of a counterclockwis e near-bottom circulation in the basin with periodically high current speeds that cause winnowing on the steep SE slope of the basin and differential settling of sediments in areas of low current speeds. On shorter time scales, recent sediment accumulation rates based on radiometric dating (210Pb) are in general twice as high as those observed 25 years ago using the same method. The higher modern rates, compared to those of the 1970s, may partly be due to increased eutrophication, as more carbon is buried in the sediment, and partly due to increased erosion in shallow water areas. However, strong lateral variations are evident. The average sediment accumulation rates vary between 119 and 340 gm-2 a-1 (corresponding to sedimentation rates of 2.1–2.5 mm a-1) in the deepest part of the basin. Very high rates (6100 g m-2 a-1, corresponding to sedimentation rates of 30 mm a-1) are observed on an intraslope basin site (offshore Latvia) at a water depth of only 70 m. The radiometrically determined sediment accumulation rates are up to three times higher than those estimated from average water column concentrations of suspended matter and from sediment trap flux rates. The discrepancy suggests that sedimentation in the deep basin may have a substantial contribution from near-bottom lateral transport.

Description: Rising stable nitrogen isotope ratios (δ15N) in dated sediment records of the German Bight/SE North Sea track river-induced coastal eutrophication over the last 2 centuries. Fully exploiting their potential for reconstructions of pristine conditions and quantitative analysis of historical changes in the nitrogen cycle from these sediment records requires knowledge on processes that alter the isotopic signal in non-living organic matter (OM) of sinking particles and sediments. In this study, we analyze the isotopic composition of particulate nitrogen (PN) in the water column during different seasons, in surface sediments, and in sediment cores to assess diagenetic influences on the isotopic composition of OM. Amino acid (AA) compositions of suspended matter, surface sediments, and dated cores at selected sites of the German Bight serve as indicators for quality and degradation state of PN. The δ15N of PN in suspended matter had seasonal variances caused by two main nitrate sources (oceanic and river) and different stages of nitrate availability during phytoplankton assimilation. Elevated δ15N values (〉 20‰) in suspended matter near river mouths and the coast coincide with a coastal water mass receiving nitrate with elevated isotope signal (δ15N 〉 10‰) derived from anthropogenic input. Particulate nitrogen at offshore sites fed by oceanic nitrate having a δ15N between 5 and 6‰ had low δ15N values (〈 2‰), indicative of an incipient phytoplankton bloom. Surface sediments along an offshore–onshore transect also reflect the gradient of low δ15N of nitrate in offshore sites to high values near river mouths, but the range of values is smaller than between the end members listed above and integrates the annual δ15N of detritus. Sediment cores from the coastal sector of the gradient show an increasing δ15N trend (increase of 2.5‰) over the last 150 years. This is not related to any change in AA composition and thus reflects eutrophication. The δ15N signals from before AD 1860 represent a good estimation of pre-industrial isotopic compositions with minimal diagenetic overprinting. Rising δ13C in step with rising δ15N in these cores is best explained by increasing productivity caused by eutrophication.

Description: Under the EC sponsored research project ODER (Oder Discharge-Environmental Response) first investigations have been carried out to estimate the chlorinated biphenyls (CB) input into Oderhaff via the Oder river. For this purpose, vertical profiles of CB content and composition were analysed on samples of three sediment cores. In two water samples, the content of suspended particulate material as weil as the particulate CB content and congener-specific composition were measured. In the Oderhaff the CB concentrations of particulate material were between 700 to 800 pg/dm3. Significant differences in the composition of the components were not observed. In sediments, CB contents were as high as 17 to 24 ngig dry weight in near surface sediment layers. They decreased with increasing sediment depth and were below detection limits at 15 to 21 cm depth. Based on the size of the 49 accumulation area and related hydrographic conditions, we estimated an input of 95 kg into the Oderhaff for the last 65 years since the onset of CB production. Applying the present prevailing conditions, we calculated an average transport of about 825 kg CB by the Oder river during this period. Comparing these two estimates, we observed that at least 15 % of the CB transported by the Oder river was deposited in the Oderhaff. The remaining 85 % (-730 kg), have been further transported into the South Pomeranian Bight and Southern Baltic Sea.

Description: Cruise POS-199 was a first expedition under Project ODER to investigate the geological and sedimentological situation in an area east of the island of Riigen, where the submarine valley of the river Oder discharges into the southern Arkona-Basin. Using acoustic methods (3.5 kHz, Boomer, and Sidescan Sonar) in a closely-spaced grid of survey lines (2 sm apart in E-W trending profiles), we located accumulations of mud (Schlick) in an area characterized generally by sand deposition and -redeposition. Mud deposition is restricted to the deepest parts of the pre-transgressional river valley and to water depths below 20 mbsl. These accumulations of mud were sampled by box coring and gravity coring (where successful) and subsampled onboard ship for investigation of physical properties and subsequent analyses in shorebased laboratories. Future analyses will include sedimentological, radiochemical, micropaleontological and geochemical analyses to establish the dispersal, sedimentation and transformation of natural and manmade substances in the Oder depositional system.

Description: Cruise GOBEX-III was the second expedition mounted by the IOW Marine Geology Group under Project GOBEX to investigate the geochemical and sedimentological environment in the Gotland Basin of the Central Baltic Sea. The cruise concentrated on improving the coverage with shallow seismic profiles (GEOCHIRP sonar), shallow sediment cores (Multicorer) and long gravity and Kasten cores of various depths in the Gotland Deep and adjacent basins. Using acoustic methods, we mapped the local accumulations of mud (Schlick) in basin-normal and along-strike profiles. The accumulations of mud and underlying lacustrine clays were sampled by shallow multi-coring and gravity coring (to 12 m, maximum or 10.5 m recovery). Cores were subsampled onboard ship for porewater, sedimentolngical, and magnetic analyses in shorebased laboratories. A first exploratory survey of sediments was carried out in the Gdansk Basin by seismic soLmdings, surface sediment sampling, and gravity coring. Two gravity cores were taken in the Arkona Basin.

Description: The effect of the supply of chlorinated biphenyls by the river Oder into some adjacent areas of Baltic Sea was studied in nine sediment cores and in 10 suspended matter samples. Congener-specific analysis was carried out on 28 individual chlorobiphenyls (CBs). ∑CB concentrations in suspension ranged from 2.4 pg dm-3 in the southern Bornholm Basin to 986 pg dm-3 in the Achterwasser. ∑CB contents in surface sediment decreased with increasing distance from the river mouth. Highest contents were found in the Oderhaff (18 ng g-1 dw) decreasing to 2 ng g-1 dw in the Bornholm Basin. The ∑CB contents generally decreased more or less regularly with increasing depth. The compositions of the CB mixtures in surficial sediment and suspension samples were rather similar, suggesting a common source. Compositions of the CB mixtures in the sediment cores showed distinct differences. These may reflect variations in source strength over time. Mass balance considerations on the basis of the 28 CBs resulted in an estimation of a total storage of approximate 733±158 kg ∑CBs in the Oderhaff, Achterwasser, Greifswalder Bodden, Oder Rinne, Arkona Basin and Bornholm Basin in the past 65 years, covering the time period since CBs were first produced. Based on river data about 500 kg of ∑CBs were supplied during this time by river Oder, that may thus be the major source of these compounds for the southern Baltic Sea.

Description: Laufzeit des Vorhabens: 01.07.2016 bis 30.06.2018, Berichtszeitraum: 01.07.2016 bis 30.06.2018

Description: Arabian Sea sediments record changes in the upwelling system off Arabia, which is driven by the monsoon circulation system over the NW Indian Ocean. In accordance with climate models, and differing from other large upwelling areas of the tropical ocean, a 500,000-yr record of productivity at ODP Site 723 shows consistently stronger upwelling during interglaciations than during glaciations. Sea-surface temperatures (SSTs) reconstructed from the alkenone unsaturation index (U K′ 37) are high (up to 27°C) during interglaciations and low (22-24°C) during glaciations, indicating a glacial-interglacial temperature change of 〉3°C in spite of the dampening effect of enhanced or weakened upwelling. The increased productivity is attributed to stronger monsoon winds during interglacial times relative to glacial times, whereas the difference in SSTs must be unrelated to upwelling and to the summer monsoon intensity. The winter (NE) monsoon was more effective in cooling the Arabian Sea during glaciations then it is now.