Auswirkungen erhöhter pCO2-Werte auf benthische Foraminiferenaus der süd-westlichen Ostsee

Increasing atmospheric CO2 concentrations have a strong impact on the marine carbonate chemistry leading to a phenomenon called ocean acidification. Excess CO2 dissolves in the surface water of the ocean, thereby the seawater pCO2 increases, whereas the [CO3 2-] and pH decrease. Reduced CO3 2- concentrations may affect marine, especially calcifying, organisms such as benthic foraminifera, in that their ability to form calcareous tests might be affected. In comparison to open oceans, water pCO2 levels are often not in equilibrium with the atmosphere in coastal regions, which are characterized by high CO2 variability during the seasonal cycle. This has also been observed for the southwestern Baltic, an eutrophic marginal sea, where bacterial degradation of large amounts of organic matter cause O2 depletion and CO2 enrichment in the bottom water. In the frame of this thesis, the impact of elevated pCO2, temperature and salinity changes on the survival and calcification ability of the benthic foraminiferal species Ammonia aomoriensis was investigated in mid-term and long-term laboratory experiments. Under laboratory conditions, foraminifera were either isolated from the sediment or remained in their natural microhabitat. Further, the natural carbonate system variability and its impact on foraminiferal communities were monitored in a one-year field study. Specimens of Ammonia aomoriensis were isolated from their natural sediment. They exhibited reduced survival and growth rates with increasing pCO2 of up to 3130 μatm under laboratory conditions. At pCO2 levels above 1800 μatm, dissolution caused a decrease of test diameter, and at the highest pCO2, only the inner organic lining remained. Testing the combined effects of ocean acidification, temperature and salinity on living Ammonia aomoriensis, a significant reduction of test diameter was observed at a pCO2 >1200 μatm (Ωcalc<1). Tests were mainly affected by undersaturation of calcite. This effect was partly compensated by a temperature rise, which increased Ωcalc and led to lower test degradation. In contrast, salinity did not have a significant effect on test growth. These results revealed that Ammonia ammoriensis exhibited a high sensitivity to elevated pCO2 and accompanying calcium carbonate undersaturation when the specimens were kept without their protective sedimentary habitat. During the field survey, large seasonal fluctuations of pCO2 from 465 up to 3429 μatm were encountered in the bottom water of Flensburg Fjord in the southwestern Baltic Sea. The pCO2 in the sediment pore water reached even higher values ranging from 1244 to 3324 μatm. However, and as a consequence of higher alkalinity (AT), the calcium carbonate saturation state of the sediment pore water remained slightly supersaturated with respect to calcite for most of the year. Accordingly, during the monitoring period, no dynamic responses of foraminiferal population density and diversity to elevated sediment pore water pCO2 were recognized. Benthic foraminifera may indeed cope with a high sediment pore water pCO2 as long as the sediment pore water remains calcite supersaturated. This evidence from the field study was also supported by the results of a long-term laboratory experiment, in which a complete foraminiferal fauna in their natural sediment was exposed to elevated pCO2 levels. Similar to field observations, the sediment pore water exhibited higher alkalinity and consequently higher saturation state of Ωcalc in comparison to the overlying seawater. Thereby the sediment chemistry created a microhabitat, which sustained the growth and development of the foraminiferal community even at highly elevated pCO2. The dominant species Ammonia aomoriensis exhibited growth and several reproduction events during the incubation time. Nevertheless, dissolution was observed on dead, empty tests of Ammonia aomoriensis, whereas tests of the second-ranked species Elphidium incertum stayed intact at high pCO2 and Ωcalc<1. This species-specific response could be due to differences in elemental composition and ultrastructure of the test walls. Benthic foraminifera in their natural, sedimentary habitat tolerate elevated pCO2 under laboratory conditions and the current high sedimentary pore water pCO2, which prevails in the southwestern Baltic Sea. In this environment, organic-rich mud influences the carbonate chemistry, and thereby provides a suitable habitat for benthic foraminifera. Consequently, the calcifying Ammonia aomoriensis plays an important role in benthic carbonate production and accumulation in this area. These results emphasize the importance of understanding the carbonate chemistry in the natural environment of benthic foraminifera, which depends upon sediment composition and remineralization processes. It is expected that enhanced future CO2 uptake in the water column will cause a further rise of sedimentary pore water pCO2 levels. As a consequence, undersaturation with respect to calcite will occur more frequently even in the sediment. This will most probably affect the dominant species Ammonia aomoriensis, which might induce changes in the benthic foraminiferal communities and their carbonate production in the southwestern Baltic Sea.Der Anstieg der atmosphärischen CO2-Konzentration hat einen starken Einfluss auf das Karbonatsystem der Ozeane und führt zur sogenannten Ozeanversauerung. Dabei führt die CO2- Aufnahme des Oberflächenwassers zu steigenden pCO2 Werten und gleichzeitig zu einer Abnahme der [CO3 2-] und des pH-Wertes im Wasser. Die verringerte Konzentration an CO3 2--Ionen kann negative Auswirkungen auf die marine Fauna haben, wobei insbesondere kalzifizierende Organismen, wie benthische Foraminiferen bei der Schalenbildung beeinträchtigt werden könnten. Allerdings sind, im Gegensatz zum offenen Ozean, die CO2-Konzentrationen in vielen küstennahen Meeresregionen, mitunter nicht im Gleichgewicht mit der Atmosphäre. Diese Gebiete sind durch saisonale CO2-Schwankungen und teilweise sehr hohe pCO2 Werte im Meerwasser charakterisiert. Dies trifft auch für das Untersuchungsgebiet der süd-westlichen Ostsee zu, wobei es sich hier um ein eutrophes Randmeer mit hohem bakteriellen Abbau von organischem Material handelt, welches zu einem starken O2-Verbrauch und CO2-Anreicherung im Bodenwasser führt. Im Rahmen dieser Arbeit wurden die Effekte erhöhter pCO2-Werte, Temperatur- und Salinitätsschwankungen auf das Überleben und die Kalzifizierung der benthischen Foraminifere Ammonia aomoriensis in Experimenten mit mittlerer und langer Inkubationszeit untersucht. In diesen wurden die Foraminiferen entweder aus dem Sediment isoliert oder in ihrem gewohnten Mikrohabitat gehältert. Weiterhin wurden die natürlichen Karbonatsystemvariabilitäten und deren Auswirkungen auf die Foraminiferen-Gemeinschaft in einer einjährigen Feldstudie untersucht. Im Experiment zeigte Ammonia aomoriensis, wenn sie aus dem natürlichen Sediment isoliert wurde, eine deutliche Abnahme der Wachstum- und Überlebensraten mit steigendem pCO2 bis 3130 μatm. Ab einem pCO2 von mehr als 1800 μatm und gleichzeitiger Untersättigung von Kalzit führte die Auflösung der Schale zu einer deutlichen Abnahme des Gehäusedurchmessers. Unter sehr hohem pCO2 blieb nur die innere organische Membran der Gehäuse erhalten. Gleiche Ergebnisse wurden in einer weiteren Studie erzielt, in welcher die kombinierten Effekte von Ozeanversauerung, Temperatur- und Salinitätsschwankungen auf die gleiche Art untersucht wurden. Diese zeigt wiederum eine deutliche Reduktion des Gehäusedurchmessers bei einem pCO2 >1200 μatm (ΩKalzit <1). Gleichzeitig führte eine erhöhte Temperatur zu einer Zunahme des ΩKalzit, welches die Schalenauflösung entsprechend verringerte. Demgegenüber hatte die Salinität keinen nachweisbaren Einfluss auf das Wachstum. Diese Ergebnisse verdeutlichen, dass wenn die Individuen aus ihrem Sedimenthabitat isoliert wurden, Ammonia ammoriensis eine hohe Sensitivität gegenüber erhöhten pCO2-Werten zeigt, insbesondere bei starker Untersättigung von Kalzit. Während der Feldstudie wurden hohe saisonale pCO2-Schwankungen von 465 bis 3429 μatm im Bodenwasser der süd-westlichen Ostsee in der Flensburger Förde beobachtet. Der pCO2 im Sedimentporenwasser war im Mittel noch höher und variierte zwischen 1244 und 3324 μatm. Jedoch führten die hohen Alkalinitäten dazu, dass das Sedimentporenwasser für die meiste Zeit im Jahr leicht an Kalzit übersättigt war. Demzufolge waren die Auswirkungen des erhöhten pCO2 im Sedimentporenwasser auf die Populationsdichten und Diversität der Foraminiferen-Gemeinschaft gering. Diese Erkenntnisse machen deutlich, dass benthische Foraminiferen mit einem erhöhten pCO2 im Sedimenporenwasser gut zurechtkommen, solange CaCO3-Übersättigung besteht. Die Ergebnisse der Freilandstudie wurden durch ein weiterführendes Langzeit-Experiment bestätigt. In diesem wurde die Foraminiferen-Gemeinschaft in ihrem natürlichen Sediment erhöhten pCO2-Bedingungen ausgesetzt. Wie bereits in der Feldstudie beobachtet, wies das Porenwasser des Sedimentes höhere Alkalinitäten und dementsprechend höhere ΩKalzit-Werte im Vergleich zum darüber liegenden Bodenwasser auf. Hierdurch schaffte die Porenwasserchemie ein Mikrohabitat, welches das Wachstum und die Entwicklung der benthischen Foraminiferen-Gemeinschaft, auch bei stark erhöhtem pCO2 fördert. So zeigte die dominante Art Ammonia aomoriensis im Verlauf der Inkubationszeit ein ausgeprägtes Wachstum und mehrere Reproduktionsereignisse. Lediglich bei sehr hohem pCO2, beziehungsweise ΩKalzit <1 wurde Schalenlösung an leeren Gehäusen beobachtet. Gehäuse von Elphidium incertum blieben jedoch unbeeinflusst. Diese art-spezifische Reaktion könnte in einem unterschiedlichen Elementaufbau und einer verschiedenen Ultrastruktur der Wandung begründet sein. In ihrem natürlichen Habitat tolerierten benthische Foraminiferen erhöhte pCO2-Werte, sowohl unter simulierten Laborbedingungen, als auch unter erhöhten Sedimentporenwasser pCO2 in der süd-westlichen Ostsee. In dieser Umgebung beeinflusst das organikreiche Bodensediment die Karbonatchemie und schafft dabei ein geeignetes Habitat für benthische Foraminiferen. Unter diesen Bedingungen nimmt die kalzifizierende Ammonia aomoriensis eine bedeutende Rolle in der Karbonatproduktion ein. Die Ergebnisse unterstreichen die Notwendigkeit des Verständnisses der Karbonatchemie in der natürlichen Umgebung der Foraminiferen, und welche Sedimentzusammensetzung und Remineralisierungsprozesse ihr zugrunde liegen. Bedingt durch die zukünftig steigende CO2-Aufnahme der Ozeane werden die pCO2-Werte im Sedimentporenwasser weiterhin ansteigen. Als Folge davon könnte die Kalzit-Untersättigung im Sedimentporenwasser zunehmen, welche zu einer drastischen Verschlechterung der Lebensbedingungen für die derzeit dominante Art Ammonia aomoriensis führen dürfte. Dies könnte wiederum zu tiefgreifenden Veränderungen innerhalb der benthischen Foraminiferen-Fauna in der südwestlichen Ostsee führen

Experimental salt marsh islands: a model system for novel metacommunity experiments

Shallow tidal coasts are characterised by shifting tidal flats and emerging or eroding islands above the high tide line. Salt marsh vegetation colonising new habitats distant from existing marshes are an ideal model to investigate metacommunity theory. We installed a set of 12 experimental salt marsh islands made from metal cages on a tidal flat in the German Wadden Sea to study the assembly of salt marsh communities in a metacommunity context. Experimental plots at the same elevation were established within the adjacent salt marsh on the island of Spiekeroog. For both, experimental islands and salt marsh enclosed plots, the same three elevational levels were realised while creating bare patches open for colonisation and vegetated patches with a defined transplanted community. One year into the experiment, the bare islands were colonised by plant species with high fecundity although with a lower frequency compared to the salt marsh enclosed bare plots. Initial plant community variations due to species sorting along the inundation gradient were evident in the transplanted vegetation. Competitive exclusion was not observed and is only expected to unfold in the coming years. Our study highlights that spatially and temporally explicit metacommunity dynamics should be considered in salt marsh plant community assembly and disassembly

The benthic foraminiferal community in a naturally CO2-rich coastal habitat in the southwestern Baltic Sea

It is expected that the calcification of foraminifera will be negatively affected by the ongoing acidification of the oceans. Compared to the open oceans, these organisms are subjected to much more adverse carbonate system conditions in coastal and estuarine environments such as the southwestern Baltic Sea, where benthic foraminifera are abundant. This study documents the seasonal changes of carbonate chemistry and the ensuing response of the foraminiferal community with bi-monthly resolution in Flensburg Fjord. In comparison to the surface pCO2, which is close to equilibrium with the atmosphere, we observed large seasonal fluctuations of pCO2 in the bottom and sediment pore waters. The sediment pore water pCO2 was constantly high during the entire year ranging from 1244 to 3324 μatm. Nevertheless, in contrast to the bottom water, sediment pore water was slightly supersaturated with respect to calcite as consequence of higher alkalinity (AT) for the most time of the year. Foraminiferal assemblages were dominated by two calcareous species, Ammonia aomoriensis and Elphidium incertum, and the agglutinated Ammotium cassis. The one year-cycle was characterized by seasonal community shifts. Our results revealed that there is no dynamic response of foraminiferal population density and diversity to elevated sediment pore water pCO2. Surprisingly, the fluctuations of sediment pore water undersaturation (Ωcalc) co-vary with the population densities of living Ammonia aomoriensis. Further, we observed that most of the tests of living calcifying specimens were intact. Only Ammonia aomorienis showed dissolution and recalcification structures on the tests, especially at undersaturated conditions. Therefore, the benthic community is subjected to constantly high pCO2 and tolerates elevated levels as long as sediment pore water remains supersaturated. Model calculations inferred that increasing atmospheric CO2 concentrations will finally lead to a perennial undersaturation in sediment pore waters. Whereas benthic foraminifera indeed may cope with a high sediment pore water pCO2, the steady undersaturation of sediment pore waters would likely cause a significant higher mortality of the dominating Ammonia aomoriensis. This shift may eventually lead to changes in the benthic foraminiferal communities in Flensburg Fjord, as well as in other regions experiencing naturally undersaturated Ωcalc levels

Impact of seawater carbonate chemistry on the calcification of marine bivalves

Bivalve calcification, particularly of the early larval stages, is highly sensitive to the change in ocean carbonate chemistry resulting from atmospheric CO2 uptake. Earlier studies suggested that declining seawater [CO32−] and thereby lowered carbonate saturation affect shell production. However, disturbances of physiological processes such as acid-base regulation by adverse seawater pCO2 and pH can affect calcification in a secondary fashion. In order to determine the exact carbonate system component by which growth and calcification are affected it is necessary to utilize more complex carbonate chemistry manipulations. As single factors, pCO2 had no effects and [HCO3-] and pH had only limited effects on shell growth, while lowered [CO32−] strongly impacted calcification. Dissolved inorganic carbon (CT) limiting conditions led to strong reductions in calcification, despite high [CO32−], indicating that [HCO3-] rather than [CO32−] is the inorganic carbon source utilized for calcification by mytilid mussels. However, as the ratio [HCO3-] / [H+] is linearly correlated with [CO32−] it is not possible to differentiate between these under natural seawater conditions. An equivalent of about 80 μmol kg−1 [CO32−] is required to saturate inorganic carbon supply for calcification in bivalves. Below this threshold biomineralization rates rapidly decline. A comparison of literature data available for larvae and juvenile mussels and oysters originating from habitats differing substantially with respect to prevailing carbonate chemistry conditions revealed similar response curves. This suggests that the mechanisms which determine sensitivity of calcification in this group are highly conserved. The higher sensitivity of larval calcification seems to primarily result from the much higher relative calcification rates in early life stages. In order to reveal and understand the mechanisms that limit or facilitate adaptation to future ocean acidification, it is necessary to better understand the physiological processes and their underlying genetics that govern inorganic carbon assimilation for calcification

Response of benthic foraminifera to ocean acidification in their natural sediment environment: a long-term culturing experiment

Calcifying foraminifera are expected to be endangered by ocean acidification, However, the response of a complete community kept in natural sediment and over multiple generations under controlled laboratory conditions has not been constrained to date. During 5 six month incubation, foraminiferal assemblages were treated with pCO2 enriched seawater of 430, 907, 1865 and 3247 μatm pCO2. The fauna was dominated by Ammonia aomoriensis and Elphidium species, whereas agglutinated species were rare. After 6 months incubation, pore water alkalinity was much higher in comparison to the overlying seawater. Consequently, the saturation state of Òcalc was much higher in the sedi10 ment than in the water column in all pCO2 treatments and remained close to saturation. As a result, the life cycle of living assemblages was largely unaffected by the tested pCO2 treatments. Growth rates, reproduction and mortality, and therefore population densities and size-frequency distribution of Ammonia aomoriensis varied markedly during the experimental period. Growth rates varied between 25 and 50 μm per month, 15 which corresponds to an addition of 1 or 2 new chambers per month. According to the size-frequency distribution, foraminifera start reproduction at a diameter of 250 μm. Mortality of large foraminifera was recognized, commencing at a test size of 285 μm at a pCO2 ranging from 430 to 1865 μatm, and of 258 μm at 3247 μatm. The total organic content of living Ammonia aomoriensis has been determined to be 4.3% of dry 20 weight. Living individuals had a calcium carbonate production rate of 0.47 gm−2 yr−1, whereas dead empty tests accumulated at a rate of 0.27 gm−2a−1. Although Òcalc was close to 1, some empty tests of Ammonia aomoriensis showed dissolution features at the end of incubation. In contrast, tests of the subdominant species, Elphidium incertum, stayed intact. This species specific response could be explained by differences in 25 the elemental test composition, in particular the higher Mg-concentrations in Ammonia aomoriensis tests. Our results emphasize that the sensitivity to ocean acidification of endobenthic foraminifera in their natural sediment habitat is much lower compared to the experimental response of specimens isolated from the sediment

Controls on the Silicon Isotope Composition of Diatoms in the Peruvian Upwelling

The upwelling area off Peru is characterized by exceptionally high rates of primary productivity, mainly dominated by diatoms, which require dissolved silicic acid (dSi) to construct their frustules. The silicon isotope compositions of dissolved silicic acid (δ 30 Si dSi ) and biogenic silica (δ 30 Si bSi ) in the ocean carry information about dSi utilization, dissolution, and water mass mixing. Diatoms are preserved in the underlying sediments and can serve as archives for past nutrient conditions. However, the factors influencing the Si isotope fractionation between diatoms and seawater are not fully understood. More δ 30 Si bSi data in today’s ocean are required to validate and improve the understanding of paleo records. Here, we present the first δ 30 Si bSi data (together with δ 30 Si dSi ) from the water column in the Peruvian Upwelling region. Samples were taken under strong upwelling conditions and the bSi collected from seawater consisted of more than 98% diatoms. The δ 30 Si dSi signatures in the surface waters were higher (+1.7‰ to +3.0‰) than δ 30 Si bSi (+1.0‰ to +2‰) with offsets between diatoms and seawater (Δ 30 Si) ranging from −0.4‰ to −1.0‰. In contrast, δ 30 Si dSi and δ 30 Si bSi signatures were similar in the subsurface waters of the oxygen minimum zone (OMZ) as a consequence of a decrease in δ 30 Si dSi . A strong relationship between δ 30 Si bSi and [dSi] in surface water samples supports that dSi utilization of the available pool (70 and 98%) is the main driver controlling δ 30 Si bSi . A comparison of δ 30 Si bSi samples from the water column and from underlying core-top sediments (δ 30 Si bSi_ sed. ) in the central upwelling region off Peru (10°S and 15°S) showed good agreement (δ 30 Si bSi_ sed. = +0.9‰ to +1.7‰), although we observed small differences in δ 30 Si bSi depending on the diatom size fraction and diatom assemblage. A detailed analysis of the diatom assemblages highlights apparent variability in fractionation among taxa that has to be taken into account when using δ 30 Si bSi data as a paleo proxy for the reconstruction of dSi utilization in the region

Naturally acidified habitat selects for ocean acidification–tolerant mussels

Ocean acidification severely affects bivalves, especially their larval stages. Consequently, the fate of this ecologically and economically important group depends on the capacity and rate of evolutionary adaptation to altered ocean carbonate chemistry. We document successful settlement of wild mussel larvae (Mytilus edulis) in a periodically CO2-enriched habitat. The larval fitness of the population originating from the CO2-enriched habitat was compared to the response of a population from a nonenriched habitat in a common garden experiment. The high CO2–adapted population showed higher fitness under elevated Pco2 (partial pressure of CO2) than the non-adapted cohort, demonstrating, for the first time, an evolutionary response of a natural mussel population to ocean acidification. To assess the rate of adaptation, we performed a selection experiment over three generations. CO2 tolerance differed substantially between the families within the F1 generation, and survival was drastically decreased in the highest, yet realistic, Pco2 treatment. Selection of CO2-tolerant F1 animals resulted in higher calcification performance of F2 larvae during early shell formation but did not improve overall survival. Our results thus reveal significant short-term selective responses of traits directly affected by ocean acidification and long-term adaptation potential in a key bivalve species. Because immediate response to selection did not directly translate into increased fitness, multigenerational studies need to take into consideration the multivariate nature of selection acting in natural habitats. Combinations of short-term selection with long-term adaptation in populations from CO2-enriched versus nonenriched natural habitats represent promising approaches for estimating adaptive potential of organisms facing global change

The impact of ocean acidification on the functional morphology of foraminifera

This work was supported by the NERC UK Ocean Acidification Research Programme grant NE/H017445/1. WENA acknowledges NERC support (NE/G018502/1). DMP received funding from the MASTS pooling initiative (The Marine Alliance for Science and Technology for Scotland). MASTS is funded by the Scottish Funding Council (grant reference HR09011) and contributing institutions.Culturing experiments were performed on sediment samples from the Ythan Estuary, N. E. Scotland, to assess the impacts of ocean acidification on test surface ornamentation in the benthic foraminifer Haynesina germanica. Specimens were cultured for 36 weeks at either 380, 750 or 1000 ppm atmospheric CO2. Analysis of the test surface using SEM imaging reveals sensitivity of functionally important ornamentation associated with feeding to changing seawater CO2 levels. Specimens incubated at high CO2 levels displayed evidence of shell dissolution, a significant reduction and deformation of ornamentation. It is clear that these calcifying organisms are likely to be vulnerable to ocean acidification. A reduction in functionally important ornamentation could lead to a reduction in feeding efficiency with consequent impacts on this organism’s survival and fitness.Publisher PDFPeer reviewe

Food availability outweighs ocean acidification effects in juvenileMytilus edulis: laboratory and field experiments

Ocean acidification is expected to decrease calcification rates of bivalves. Nevertheless in many coastal areas high pCO2 variability is encountered already today. Kiel Fjord (Western Baltic Sea) is a brackish (12-20 g kg-1) and CO2 enriched habitat, but the blue mussel Mytilus edulis dominates the benthic community. In a coupled field and laboratory study we examined the annual pCO2 variability in this habitat and the combined effects of elevated pCO2 and food availability on juvenile M. edulis growth and calcification. In the laboratory experiment, mussel growth and calcification were found to chiefly depend on food supply, with only minor impacts of pCO2 up to 3350 μatm. Kiel Fjord was characterized by strong seasonal pCO2 variability. During summer, maximal pCO2 values of 2500 μatm were observed at the surface and >3000 μatm at the bottom. However, the field growth experiment revealed seven times higher growth and calcification rates of M. edulis at a high pCO2 inner fjord field station (mean pCO2 ca. 1000 μatm) in comparison to a low pCO2 outer fjord station (ca. 600 μatm). In addition, mussels were able to outcompete the barnacle Amphibalanus improvisus at the high pCO2 site. High mussel productivity at the inner fjord site was enabled by higher particulate organic carbon concentrations. Kiel Fjord is highly impacted by eutrophication, which causes bottom water hypoxia and consequently high seawater pCO2. At the same time, elevated nutrient concentrations increase the energy availability for filter feeding organisms such as mussels. Thus M. edulis can dominate over a seemingly more acidification resistant species such as A. improvisus. We conclude that benthic stages of M. edulis tolerate high ambient pCO2 when food supply is abundant and that important habitat characteristics such as species interactions and energy availability need to be considered to predict species vulnerability to ocean acidification

Trace Metals and Their Isotopes in the Tropical Atlantic Ocean - Cruise No. M81/1, February 04 – March 08, 2010, Las Palmas (Canary Islands, Spain) – Port of Spain (Trinidad & Tobago)

Summary Meteor Cruise M81/1 was dedicated to the investigation of the distribution of dissolved and particulate trace metals and their isotopic compositions (TEIs) in the full water column of the tropical Atlantic Ocean and their driving factors including main external inputs and internal cycling and ocean circulation. The research program is embedded in the international GEOTRACES program (e.g. Henderson et al., 2007), which this cruise was an official part of and thus corresponds to GEOTRACES cruise GA11. This cruise was completely dedicated to the trace metal clean and contamination-free sampling of waters and particulates for subsequent analyses of the TEIs in the home laboratories of the national and international participants. Besides a standard rosette for the less contaminant prone metals, trace metal clean sampling was realized by using a dedicated and coated trace metal clean rosette equipped with Teflon-coated GO-FLO bottles operated via a polyester coated cable from a mobile winch that was thankfully made available by the U.S. partners of the GEOTRACES program for this cruise. The particulate samples were also collected under trace metal clean conditions using established in-situ pump systems. The cruise track led the cruise southward from the Canary Islands to 11°S and then continued northwestward along the northern margin of South America until it reached Port of Spain, Trinidad & Tobago. The track crossed areas of major external inputs including exchange with the volcanic Canary Islands, the Saharan dust plume, as well as the plume of the Amazon outflow. In terms of internal cycling the equatorial high biological productivity band, as well as increased productivity associated with the Amazon Plume were covered. All major water masses contributing the Atlantic Meridional Overturning Circulation, as well as the distinct narrow equatorial surface and subsurface east-west current bands were sampled. A total of 17 deep stations were sampled for the different dissolved TEIs, which were in most cases accompanied by particulate sampling. In addition, surface waters were continuously sampled under trace metal clean conditions using a towed fish