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This dataset contains CCN concentrations at five supersaturation levels, averaged to 1 min time resolution, measured during the year-long Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition from October 2019 to September 2020. The measurements were performed in the Swiss container on the D-deck of Research Vessel Polarstern, using the model CCN-100 from Droplet Measurement Technologies (DMT, Boulder, USA). Detailed description of the measurement principle can be found in e.g. Roberts & Nenes (2005). The instrument was located behind an automated valve, which switched hourly between a total and an interstitial air inlet, with upper cutoff sizes of 40 and 1 µm respectively (Heutte et al., Submitted; Beck et al., 2022; Dada et al., 2022). The measurements were performed in 1-h cycles, with a 0.5 L/min sample flow and a 2 L/min make up flow, where the supersaturations 0.15, 0.2, 0.3, 0.5 and 1.0 % were measured. The supersaturation of 0.15 % is measured for 20 min, as it takes longer to equilibrate, and the remaining supersaturations were measured for 10 min each. The instrument was calibrated in July 2019 before the campaign, and in March and April 2020 during the campaign. Based on the inter-variability of the calculated supersaturation levels during these calibrations, we can expect values ranging from 0.15-0.20, 0.20-0.25, 0.29-0.33, 0.43-0.5, 0.78-1.0 % for the nominal supersaturations of 0.15, 0.2, 0.3, 0.5 and 1.0 %, respectively. The counting error for the CCNC is associated with the error in the optical counting of particles and is about 10 %. Data were removed during the cooling cycle (i.e., the time when the measurement cycle starts again and the temperature is cooled to set the lowest supersaturation), which corresponds roughly to the first 10 min of each hour (so 50 % of the 0.15 % supersaturation period). Additionally, the first minute of the transition between supersaturations was removed before averaging the data to 1 min time resolution. During some time periods, a difference pattern of mean and standard deviation of the measurements between even and odd hours was observed, most probably caused by a persistent pressure drop in the inlet lines, resulting in a proportional reduction of the concentration measurements. For correction, the 1-h arithmetic mean of interstitial inlet measurements and the mean of the two adjacent hours of total inlet measurements were subtracted, and the resulting difference was added as a constant to the data points of the interstitial inlet measurements. The dataset contains a pollution mask for local pollution (predominantly exhaust from the Research Vessel Polarstern) with 0 indicating clean, and 1 indicating polluted periods (Beck et al., 2022; Beck et al., 2022).

Changes in marine net primary productivity (PP) and export of particulate organic carbon (EP) are projected over the 21st century with four global coupled carbon cycle-climate models. These include representations of marine ecosystems and the carbon cycle of different structure and complexity. All four models show a decrease in global mean PP and EP between 2 and 20% by 2100 relative to preindustrial conditions, for the SRES A2 emission scenario. Two different regimes for productivity changes are consistently identified in all models. The first chain of mechanisms is dominant in the low- and mid-latitude ocean and in the North Atlantic: reduced input of macro-nutrients into the euphotic zone related to enhanced stratification, reduced mixed layer depth, and slowed circulation causes a decrease in macro-nutrient concentrations and in PP and EP. The second regime is projected for parts of the Southern Ocean: an alleviation of light and/or temperature limitation leads to an increase in PP and EP as productivity is fueled by a sustained nutrient input. A region of disagreement among the models is the Arctic, where three models project an increase in PP while one model projects a decrease. Projected changes in seasonal and interannual variability are modest in most regions. Regional model skill metrics are proposed to generate multi-model mean fields that show an improved skill in representing observation-based estimates compared to a simple multi-model average. Model results are compared to recent productivity projections with three different algorithms, usually applied to infer net primary production from satellite observations.

The reasons for the early Holocene temperature discrepancy between northern hemispheric model simulations and paleoclimate reconstructions—known as the Holocene temperature conundrum—remain unclear. Using hydrogen isotopes of fluid inclusion water extracted from stalagmites from the Milandre Cave in Switzerland, we established a mid-latitude European mean annual temperature reconstruction for the past 14,000 years. Our Milandre Cave fluid inclusion temperature record (MC-FIT) resembles Greenland and Mediterranean sea surface temperature trends but differs from recent reconstructions obtained from biogenic proxies and climate models. The water isotopes are further synchronized with tropical precipitation records, stressing the Northern Hemisphere signature. Our results support the existence of a European Holocene Thermal Maximum and data model temperature discrepancies. Moreover, data-data comparison reveals a significant latitudinal temperature gradient within Europe. Last, the MC-FIT record suggests that seasonal biases in the proxies are not the primary cause of the Holocene temperature conundrum.

Individual foraminiferal analysis (IFA) geochemical data was generated for the Recent (mudline) and climatic maxima of Marine Isotope Stages (MISs) 9e, 11c and 12 aged sediments from IODP Site 359-U1467. All samples were measured on a Thermo Electron Delta+ Advantage mass spectrometer integrated with a Kiel carbonate III automated extraction line. Species measured: Globigerinoides ruber (white) and Trilobatus sacculifer (with sac-like final chamber) from the 355-400 μm size fraction.

Past millennial-scale changes in atmospheric CO2 (CO2,atm) levels have often been attributed to variations in the overturning timescale of the ocean that result in changes in the marine carbon inventory. There remains a paucity of proxy evidence that documents changes in marine carbon storage globally, and that links them to distinct abrupt climate variability in the northern hemi-sphere that involve perturbations of the Atlantic Meridional Overturning Circulation (AMOC). The last two glacial periods were suggested to differ in the extent and sensitivity of the AMOC to changes, and therefore provide an opportunity to study their role in marine carbon cycling. Here, we reconstruct variations in respired carbon storage (via oxygenation) and the AMOC 'geometry' (via carbonate ion saturation) in the deep South Atlantic during the past two glacial periods. We infer decreases in deep South Atlantic respired carbon levels at times of weakened AMOC and rising CO2,atm concentrations during both glacial periods. These findings suggest a consistent pat-tern of increased Southern Ocean convection and/or air-sea CO2 fluxes during northern-hemisphere stadials accompanying AMOC perturbations and promoting a rise in CO2,atm levels, despite potential differences in the magnitude of the forcing, the climate (and hence, AMOC) background conditions and the rate of ocean-atmospheric CO2 fluxes. We find that net ocean car-bon loss, and hence the magnitude of CO2,atm rise, during a glacial is largely determined by the stadial duration. North Atlantic climate anomalies may therefore significantly affect Southern Ocean carbon cycling through oceanic (e.g., 'ventilation' seesaw) and/or atmospheric processes (e.g., Ekman pumping).

Stable isotope ratios from tree rings are important proxies of past climate variations. We have access to a calendar-dated wood material from wood collected at glacier forefields and peat bog sites located in the Alps. They are of two species, larch (Larix decidua) and cembran pine (Pinus cembra). All the wood samples were collected at high altitudes in the Swiss and Tyrol Alps, they cover the whole Holocene period and belong to the Eastern Alpine Conifer Chronology Dataset (Nicolussi et al., 2009; doi:10.1177/0959683609336565). We analysed the δ13C, δ18O and δ2H isotope ratios of alpha cellulose obtained from blocks of 5 annual rings from 203 trees. Cellulose was extracted following the modified Jayme-Wise method (Boettger et al., 2007; doi:10.1021/ac0700023). The isotopes values were determined using conventional Isotope Ratio Mass Spectrometry (Isoprime 100) coupled to a pyrolysis unit (HEKAtech GmbH, Germany), which is similar to the previously used TC/EA (for technical details see (Leuenberger 2007). This approach was extended to measurements of non-exchangeable hydrogen of alpha-cellulose using the on-line equilibration method (Filot et al., 2006 (doi:10.1002/rcm.2743); Loader et al., 2015(doi:10.1021/ac502557x)). The results are reported in per mil (‰) relative to the Vienna Pee Dee Belemnite (VPDB) for carbon and to Vienna Standard Mean Ocean Water (VSMOW) for hydrogen and oxygen (Coplen 1994; doi:10.1351/pac199466020273). For all the δ13C values after 1000 CE we applied the factor described in Leuenberger (2007; doi:10.1016/S1936-7961(07)01014-7) to correct for the δ13C depletion of CO2 caused by the Industrial Revolution from about 1850 onwards (Leuenberger, 2007).

Lake Towuti is a tectonic basin, surrounded by ultramafic rocks. Lateritic soils form through weathering and deliver abundant iron (oxy)hydroxides but very little sulfate to the lake and its sediment. To characterize the sediment biogeochemistry, we collected cores at three sites with increasing water depth and decreasing bottom water oxygen concentrations. Microbial cell densities were highest at the shallow site - a feature we attribute to the availability of labile organic matter and the higher abundance of electron acceptors due to oxic bottom water conditions. At the two other sites, OM degradation and reduction processes below the oxycline led to partial electron acceptor depletion. Genetic information preserved in the sediment as extracellular DNA provides information on aerobic and anaerobic heterotrophs related to Actinobacteria, Nitrospirae, Chloroflexi and Thermoplasmatales. These taxa apparently played a significant role in the degradation of sinking organic matter. However, extracellular DNA concentrations rapidly decrease with core depth. Despite very low sulfate concentrations, sulfate-reducing bacteria were present and viable in sediments at all three sites, as confirmed by measurement of potential sulfate reduction rates. Microbial community fingerprinting supported the presence of taxa related to Deltaproteobacteria and Firmicutes with demonstrated capacity for iron and sulfate reduction. Concomitantly, sequences of Ruminococcaceae, Clostridiales and Methanomicrobiales indicated potential for fermentative hydrogen and methane production. Such first insights into ferruginous sediments show that microbial populations perform successive metabolisms related to sulfur, iron and methane. In theory, iron reduction could reoxidize reduced sulfur compounds and desorb OM from iron minerals to allow remineralization to methane. Overall, we found that biogeochemical processes in the sediments can be linked to redox differences in the bottom waters of the three sites, like oxidant concentrations and the supply of labile OM. At the scale of the lacustrine record, our geomicrobiological study should provide a means to link the extant subsurface biosphere to past environments.

A feature of Pliocene climate is the occurrence of "permanent El Niño-like" or "El Padre" conditions in the Pacific Ocean. From the analysis of sediment cores in the modern northern Benguela upwelling, we show that the mean oceanographic state off Southwest Africa during the warm Pliocene epoch was also analogous to that of a persistent Benguela "El Niño". At present these events occur when massive southward flows of warm and nutrient-poor waters extend along the coasts of Angola and Namibia, with dramatic effects on regional marine ecosystems and rainfall. We propose that the persistent warmth across the Pliocene in the Benguela upwelling ended synchronously with the narrowing of the Indonesian seaway, and the early intensification of the Northern Hemisphere Glaciations around 3.0-3.5 Ma. The emergence of obliquity-related cycles in the Benguela sea surface temperatures (SST) after 3 Ma highlights the development of strengthened links to high latitude orbital forcing. The subsequent evolution of the Benguela upwelling system was characterized by the progressive intensification of the meridional SST gradients, and the emergence of the 100 ky cycle, until the modern mean conditions were set at the end of the Mid Pleistocene transition, around 0.6 Ma. These findings support the notion that the interplay of changes in the depth of the global thermocline, atmospheric circulation and tectonics preconditioned the climate system for the end of the warm Pliocene epoch and the subsequent intensification of the ice ages.

Background: Parental care, while increasing parental fitness through offspring survival also bears cost to the care-giving parent. Consequentially, trade offs between parental care and other vitally important traits, such as the immune system seem evident. In co-occurring phases of parental care and immunological challenges negative consequences through a resource allocation trade off on both the parental and the offspring conditions can be predicted. While the immune system is reflecting parental stress conditions, parental immunological investments also boost offspring survival via the transfer of immunological substances (trans-generational immune priming). We investigated this relationship adult and juvenile mouth brooding East African cichlid Astotatilapia burtoni. Prior to mating, females were exposed to an immunological activation, while others remained immunologically naive. Correspondingly, immunological status of females was either examined directly after reproduction or after mouth brooding had ceased. Offspring from both groups were exposed to immunological challenges to assess the extent of trans-generational immune priming. As proxy for immune status, cellular immunological activity and gene expression were determined. Results: Both reproducing and mouthbrooding females allocate their resources towards reproduction. While upon reproduction the innate immune system was impeded, mouthbrooding females showed an attenuation of inflammatory components and an elevated stress levels. Juveniles from immune challenged mouthbrooding females showed downregulation of immune and life history candidate genes, implying a limitation of trans-generational plasticity when parents experience stress during the costly reproductive phase. Conclusion: Our results provide evidence that parental investment via mouthbrooding is beneficial for the offspring. However, both parental investment and the rise of the immunological activity upon an immune challenge are costly traits. If applied simultaneously, not only mothers seem to be impacted in their performance, but also offspring are impeded in their ability to react upon a potentially virulent pathogen exposure.

This study presents simulations of Greenland surface melt for the Eemian interglacial period (∼130 000 to 115 000 years ago) derived from regional climate simulations with a coupled surface energy balance model. Surface melt is of high relevance due to its potential effect on ice core observations, e.g., lowering the preserved total air content (TAC) used to infer past surface elevation. An investigation of surface melt is particularly interesting for warm periods with high surface melt, such as the Eemian interglacial period. Furthermore, Eemian ice is the deepest and most compressed ice preserved on Greenland, resulting in our inability to identify melt layers visually. Therefore, simulating Eemian melt rates and associated melt layers is beneficial to improve the reconstruction of past surface elevation. Estimated TAC, based on simulated melt during the Eemian, could explain the lower TAC observations. The simulations show Eemian surface melt at all deep Greenland ice core locations and an average of up to ∼30 melt days per year at Dye-3, corresponding to more than 600 mm water equivalent (w.e.) of annual melt. For higher ice sheet locations, between 60 and 150 mmw.e.yr-1 on average are simulated. At the summit of Greenland, this yields a refreezing ratio of more than 25 % of the annual accumulation. As a consequence, high melt rates during warm periods should be considered when interpreting Greenland TAC fluctuations as surface elevation changes. In addition to estimating the influence of melt on past TAC in ice cores, the simulated surface melt could potentially be used to identify coring locations where Greenland ice is best preserved.