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Between 14.5 and 5 ka, the Sahara was vegetated owing to a wet climate during the African humid period. However, the climatic factors sustaining the “green Sahara” are still a matter of debate. Particularly the role of winter precipitation is poorly understood. Using the stable hydrogen isotopic composition (δD, where D stands for deuterium) of high molecular weight (HMW) n-alkanoic acids in a marine sediment core from the eastern Mediterranean, we provide a continuous record for winter precipitation in the Nile river delta spanning the past 18 kyr. Pairing the data with δD records from HMW n-alkanes from the same core, we show that HMW n-alkanoic acids constantly derived from the delta, while the HMW n-alkanes also received significant contributions from the headwaters between ∼ 15–1 ka when fluvial runoff enhanced. This enables us to reconstruct the evolution of Mediterranean (winter) and monsoonal (summer) rainfall in the Nile river watershed in parallel. In the delta, the Heinrich stadial 1 (HS1) evolved in two phases, with a dry episode between ∼ 17.5–16.0 ka, followed by wet conditions between ∼ 16–14.5 ka. Winter rainfall enhanced substantially between 11–6 ka, lagging behind the intensification of the summer monsoon by ca. 3 kyr. Heavy winter rainfall resulted from a southern position of the Atlantic storm track combined with elevated sea surface temperatures in the eastern Mediterranean, reinforcing local cyclogenesis. We show that during the green Sahara, monsoon precipitation and Mediterranean winter rainfall were both enhanced and infer that the winter rainfall zone extended southwards, delivering moisture to the Sahara. Our findings corroborate recent hypotheses suggesting that winter rains that extended southward were a crucial addition to the northward displacement of the summer monsoon in helping to sustain a green Sahara.

The last deglaciation is the most recent relatively well-documented period of pronounced and fast climate warming, and, as such, it holds important information for our understanding of the climate system. Notably, while research into terrestrial organic carbon reservoirs has been instrumental in exploring the possible sources of atmospheric carbon dioxide during periods of rapid change, the underlying mechanisms are not fully understood. Here we investigate the mobilization of organic matter to the Bay of Biscay, located in the north-eastern Atlantic Ocean off the coasts of France and Spain. Specifically, we focus on the area that was the mouth of the Channel River during the last deglaciation, where an enhanced terrigenous input has been reported for the last glacial–interglacial transition. We conducted a comprehensive suite of biomarker analyses (e.g. n-alkanes, hopanes and n-alkanoic acids) and isotopic investigations (radiocarbon dating and δ13C measurements) on a high-resolution sedimentary archive. The present study provides the first direct evidence for the fluvial supply of immature and ancient terrestrial organic matter to the core location. Moreover, our results reveal the possibility of permafrost carbon export to the ocean, driven by processes such as deglacial warming and glacial erosion. These findings are consistent with observations from other regions characterized by present or past permafrost conditions on land, which have shown that permafrost thaw and glacial erosion can lead to carbon remobilization, potentially influencing atmospheric carbon dioxide levels.

The reconstruction of past sea-ice distribution in the Southern Ocean is crucial for an improved understanding of ice–ocean–atmosphere feedbacks and the evaluation of Earth system and Antarctic ice sheet models. The Antarctic Peninsula (AP) has been experiencing a warming since the start of regular monitoring of the atmospheric temperature in the 1950s. The associated decrease in sea-ice cover contrasts the trend of growing sea-ice extent in East Antarctica. To reveal the long-term sea-ice history at the northern Antarctic Peninsula (NAP) under changing climate conditions, we examined a marine sediment core from the eastern basin of the Bransfield Strait covering the last Deglacial and the Holocene. For sea-ice reconstructions, we focused on the specific sea-ice biomarker lipid IPSO25, a highly branched isoprenoid (HBI), and sea-ice diatoms, whereas a phytoplankton-derived HBI triene (C25:3) and warmer open-ocean diatom assemblages reflect predominantly ice-free conditions. We further reconstruct ocean temperatures using glycerol dialkyl glycerol tetraethers (GDGTs) and diatom assemblages and compare our sea-ice and temperature records with published marine sediment and ice core data. A maximum ice cover is observed during the Antarctic Cold Reversal 13 800–13 000 years before present (13.8–13 ka), while seasonally ice-free conditions permitting (summer) phytoplankton productivity are reconstructed for the late Deglacial and the Early Holocene from 13 to 8.3 ka. An overall decreasing sea-ice trend throughout the Middle Holocene coincides with summer ocean warming and increasing phytoplankton productivity. The Late Holocene is characterized by highly variable winter sea-ice concentrations and a sustained decline in the duration and/or concentration of spring sea ice. Overall diverging trends in GDGT-based TEX86L and RI-OH' subsurface ocean temperatures (SOTs) are found to be linked to opposing spring and summer insolation trends, respectively.

Rapid Arctic warming accelerates permafrost thaw, causing an additional release of terrestrial organic matter (OM) into rivers and, ultimately, after transport via deltas and estuaries, to the Arctic Ocean nearshore. The majority of our understanding of nearshore OM dynamics and fate has been developed from freshwater rivers despite the likely impact of highly dynamic estuarine and deltaic environments on the transformation, storage, and age of OM delivered to coastal waters. Here, we studied particulate organic carbon (POC) dynamics in the Lena River delta and compared them with POC dynamics in the Lena River main stem along a ∼ 1600 km long transect from Yakutsk, downstream to the delta. We measured POC, total suspended matter (TSM), and carbon isotopes (δ13C and Δ14C) in POC to compare riverine and deltaic OM composition and changes in OM source and fate during transport offshore. We found that TSM and POC concentrations decreased by 70 % during transit from the main stem to the delta and Arctic Ocean. We found deltaic POC to be strongly depleted in 13C relative to fluvial POC. Dual-carbon (Δ14C and δ13C) isotope mixing model analyses indicated a significant phytoplankton contribution to deltaic POC (∼ 68 ± 6 %) and suggested an additional input of permafrost-derived OM into deltaic waters (∼ 18 ± 4 % of deltaic POC originates from Pleistocene deposits vs. ∼ 5 ± 4 % in the river main stem). Despite the lower concentration of POC in the delta than in the main stem (0.41 ± 0.10 vs. 0.79 ± 0.30 mg L−1, respectively), the amount of POC derived from Yedoma deposits in deltaic waters was almost twice as large as the amount of POC of Yedoma origin in the main stem (0.07 ± 0.02 and 0.04 ± 0.02 mg L−1, respectively). We assert that estuarine and deltaic processes require consideration in order to correctly understand OM dynamics throughout Arctic nearshore coastal zones and how these processes may evolve under future climate-driven change.

Arctic warming and sea level change will lead to widespread permafrost thaw and subsequent mobilization. Sedimentary records of past warming events during the Last Glacial–interglacial transition can be used to study the conditions under which permafrost mobilization occurs and which changes in vegetation on land are associated with such warming. The Amur and Yukon rivers discharging into the Okhotsk and Bering seas, respectively, drain catchments that have been, or remain until today, covered by permafrost. Here we study two marine sediment cores recovered off the mouths of these rivers. We use lignin phenols as biomarkers, which are excellently suited for the reconstruction of terrestrial higher plant vegetation, and compare them with previously published lipid biomarker data. We find that in the Yukon basin, vegetation change and wetland expansion began already in the early deglaciation (ED; 14.6–19 ka). This timing is different from observed changes in the Okhotsk Sea reflecting input from the Amur basin, where wetland expansion and vegetation change occurred later in the Pre-Boreal (PB). In the two basins, angiosperm contribution and wetland extent all reached maxima during the PB, both decreasing and stabilizing after the PB. The permafrost of the Amur basin began to become remobilized in the PB. Retreat of sea ice coupled with increased sea surface temperatures in the Bering Sea during the ED might have promoted early permafrost mobilization. In modern Arctic river systems, lignin and n-alkanes are transported from land to the ocean via different pathways, i.e., surface runoff vs. erosion of deeper deposits, respectively. However, accumulation rates of lignin phenols and lipids are similar in our records, suggesting that under conditions of rapid sea level rise and shelf flooding, both types of terrestrial biomarkers are delivered by the same transport pathway. This finding suggests that the fate of terrigenous organic matter in the Arctic differs on both temporal and spatial scales.

We present a global atlas of downcore foraminiferal oxygen and carbon isotope ratios available at https://doi.org/10.1594/PANGAEA.936747 (Mulitza et al., 2021a). The database contains 2106 published and previously unpublished stable isotope downcore records with 361 949 stable isotope values of various planktic and benthic species of Foraminifera from 1265 sediment cores. Age constraints are provided by 6153 uncalibrated radiocarbon ages from 598 (47 %) of the cores. Each stable isotope and radiocarbon series is provided in a separate netCDF file containing fundamental metadata as attributes. The data set can be managed and explored with the free software tool PaleoDataView. The atlas will provide important data for paleoceanographic analyses and compilations, site surveys, or for teaching marine stratigraphy. The database can be updated with new records as they are generated, providing a live ongoing resource into the future.

Organic carbon (OC) stored in Arctic permafrost represents one of Earth's largest and most vulnerable terrestrial carbon pools. Amplified climate warming across the Arctic results in widespread permafrost thaw. Permafrost deposits exposed at river cliffs and coasts are particularly susceptible to thawing processes. Accelerating erosion of terrestrial permafrost along shorelines leads to increased transfer of organic matter (OM) to nearshore waters. However, the amount of terrestrial permafrost carbon and nitrogen as well as the OM quality in these deposits is still poorly quantified. We define the OM quality as the intrinsic potential for further transformation, decomposition and mineralisation. Here, we characterise the sources and the quality of OM supplied to the Lena River at a rapidly eroding permafrost river shoreline cliff in the eastern part of the delta (Sobo-Sise Island). Our multi-proxy approach captures bulk elemental, molecular geochemical and carbon isotopic analyses of Late Pleistocene Yedoma permafrost and Holocene cover deposits, discontinuously spanning the last ∼52 kyr. We showed that the ancient permafrost exposed in the Sobo-Sise cliff has a high organic carbon content (mean of about 5 wt %). The oldest sediments stem from Marine Isotope Stage (MIS) 3 interstadial deposits (dated to 52 to 28 cal ka BP) and are overlaid by last glacial MIS 2 (dated to 28 to 15 cal ka BP) and Holocene MIS 1 (dated to 7–0 cal ka BP) deposits. The relatively high average chain length (ACL) index of n-alkanes along the cliff profile indicates a predominant contribution of vascular plants to the OM composition. The elevated ratio of iso- and anteiso-branched fatty acids (FAs) relative to mid- and long-chain (C ≥ 20) n-FAs in the interstadial MIS 3 and the interglacial MIS 1 deposits suggests stronger microbial activity and consequently higher input of bacterial biomass during these climatically warmer periods. The overall high carbon preference index (CPI) and higher plant fatty acid (HPFA) values as well as high C/N ratios point to a good quality of the preserved OM and thus to a high potential of the OM for decomposition upon thaw. A decrease in HPFA values downwards along the profile probably indicates stronger OM decomposition in the oldest (MIS 3) deposits of the cliff. The characterisation of OM from eroding permafrost leads to a better assessment of the greenhouse gas potential of the OC released into river and nearshore waters in the future.

Proxies based on long-chain alkane-1, mid-chain diols (diol for short) are obtaining increasing interest to reconstruct past upper ocean temperature and productivity. Here we evaluate performance of the sea surface temperature proxies (long-chain diol index (LDI), diol saturation index (DSI), and diol chain length index (DCI)), productivity and upwelling intensity proxies (two diol indices DIR and DIW and the combined diol index (CDI)), and the nutrient diol index (NDI) as a proxy for phosphate and nitrate levels. This evaluation is based on comparison of the diols in sediment trap samples from the upwelling region off NW Africa collected at 1.28 km water depth with daily satellite-derived sea surface temperatures (SSTs), subsurface temperatures, productivity, the plankton composition from the trap location, monthly phosphate and nitrate concentrations, wind speed, and wind direction from the nearby Nouadhibou airport. The diol-based SST reconstructions are also compared the long-chain-alkenone-based SST reconstructions. The alkenone SSTs correlate best with satellite SST (r2= 0.60). Amplitude and absolute values agree very well as do the flux-corrected time series averages. For the diol proxies the situation is more complicated. Diol proxies including 1,14 diols lag trade wind speed by 30 d. Since wind is nearly always from the NNE to NNW and induces the upwelling, we relate the variability in these proxies to upwelling-induced processes. Correlation with the abundance of upwelling species and wind speed is best for the NDI and the 1,14 diol-based DCI and DSI. The DIR, DIW, and CDI perform comparatively poorly. A negative correlation between DSI and wind speed may suggest that the DSI reflects wind-speed-forced upwelling-related reductions in temperature rather than irradiation-induced temperatures. The nutrient proxy NDI shows no significant correlation to monthly phosphate and nitrate concentrations in the upper waters and a negative correlation with both wind-induced upwelling (r2=0.28 and lagging 32 d) and the abundance of upwelling species (r2=0.38). It is suggested that this proxy reflects upwelling intensity rather than upper ocean nutrient concentrations. At the trap site, satellite SST lags wind-speed-forced upwelling by about 4 months. The 1,13 and 1,15 diol-based LDI-derived SSTs lag satellite SSTs by 41 d but correlate poorly (r2= 0.17). Absolute as well as flux-corrected LDI SSTs are on average 3 ∘C too high and rather reflect values prevailing during the more oligotrophic summer period. We attribute outliers to low LDI SST to 1,13 diols added during short upwelling-related events. The use of the LDI in regions with higher productivity is therefore not recommended. It appears thus that at the trap site the 1,14 diols primarily reflect conditions relating to upwelling whereas the 1,15C30 and to a lesser extent the 1,13 diols seem to reflect the conditions of the more oligotrophic ocean.

This study reports the discovery of dense sponge gardens across the peaks of permanently ice-covered, extinct volcanic seamounts of the Langseth Ridge and on the remnants of a now extinct seep ecosystem. Using approaches to sample and infer food and energy sources to this ice-covered community, the authors suggest that the sponges use refractory organic matter trapped in the extinct seep community on which they sit.

The importance of Antarctic sea ice and Southern Ocean warming has come into the focus of polar research during the last couple of decades. Especially around West Antarctica, where warm water masses approach the continent and where sea ice has declined, the distribution and evolution of sea ice play a critical role in the stability of nearby ice shelves. Organic geochemical analyses of marine seafloor surface sediments from the Antarctic continental margin allow an evaluation of the applicability of biomarker-based sea-ice and ocean temperature reconstructions in these climate-sensitive areas. We analysed highly branched isoprenoids (HBIs), such as the sea-ice proxy IPSO25 and phytoplankton-derived HBI-trienes, as well as phytosterols and isoprenoidal glycerol dialkyl glycerol tetraethers (GDGTs), which are established tools for the assessment of primary productivity and ocean temperatures respectively. The combination of IPSO25 with a phytoplankton marker (i.e. the PIPSO25 index) permits semi-quantitative sea-ice reconstructions and avoids misleading over- or underestimations of sea-ice cover. Comparisons of the PIPSO25-based sea-ice distribution patterns and TEX86L- and RI-OH′-derived ocean temperatures with (1) sea-ice concentrations obtained from satellite observations and (2) instrument measurements of sea surface and subsurface temperatures corroborate the general capability of these proxies to determine oceanic key variables properly. This is further supported by model data. We also highlight specific aspects and limitations that need to be taken into account for the interpretation of such biomarker data and discuss the potential of IPSO25 as an indicator for the former occurrence of platelet ice and/or the export of ice-shelf water.

The present study examines the formation history and cryolithological properties of the late-Pleistocene Yedoma Ice Complex (IC) and its Holocene cover in the eastern Lena delta on Sobo-Sise Island. The sedimentary sequence was continuously sampled at 0.5 m resolution at a vertical Yedoma cliff starting from 24.2 m above river level (a.r.l.). The sequence differentiates into three cryostratigraphic units: Unit A, dated from ca. 52 to 28 cal kyr BP; Unit B, dated from ca. 28 to 15 cal kyr BP; Unit C, dated from ca. 7 to 0 cal kyr BP. Three chronologic gaps in the record are striking. The hiatus during the interstadial marine isotope stage (MIS) 3 (36–29 cal kyr BP) as well as during stadial MIS 2 (20–17 cal kyr BP) might be related to fluvial erosion and/or changed discharge patterns of the Lena river caused by repeated outburst floods from the glacial Lake Vitim in southern Siberia along the Lena river valley towards the Arctic Ocean. The hiatus during the MIS 2–1 transition (15–7 cal kyr BP) is a commonly observed feature in permafrost chronologies due to intense thermokarst activity of the deglacial period. The chronologic gaps of the Sobo-Sise Yedoma record are similarly found at two neighbouring Yedoma IC sites on Bykovsky Peninsula and Kurungnakh-Sise Island and are most likely of regional importance. The three cryostratigraphic units of the Sobo-Sise Yedoma exhibit distinct signatures in properties of their clastic, organic, and ice components. Higher permafrost aggradation rates of 1 m kyr−1 with higher organic-matter (OM) stocks (29 ± 15 kg C m−3, 2.2 ± 1.0 kg N m−3; Unit A) and mainly coarse silt are found for the interstadial MIS 3 if compared to the stadial MIS 2 with 0.7 m kyr−1 permafrost aggradation, lower OM stocks (14 ± 8 kg C m−3, 1.4 ± 0.4 kg N m−3; Unit B), and pronounced peaks in the coarse-silt and medium-sand fractions. Geochemical signatures of intra-sedimental ice reflect the differences in summer evaporation and moisture regime by higher ion content and less depleted ratios of stable δ18O and stable δD isotopes but lower deuterium excess (d) values during interstadial MIS 3 if compared to stadial MIS 2. The δ18O and δD composition of MIS 3 and MIS 2 ice wedges shows characteristic well-depleted values and low d values, while MIS 1 ice wedges have elevated mean d values between 11 ‰ and 15 ‰ and surprisingly low δ18O and δD values. Hence, the isotopic difference between late-Pleistocene and Holocene ice wedges is more pronounced in d than in δ values. The present study of the permafrost exposed at the Sobo-Sise Yedoma cliff provides a comprehensive cryostratigraphic inventory, insights into permafrost aggradation, and degradation over the last approximately 52 kyr as well as their climatic and morphodynamic controls on the regional scale of the central Laptev Sea coastal region in NE Siberia.

In the last decades, changing climate conditions have had a severe impact on sea ice at the western Antarctic Peninsula (WAP), an area rapidly transforming under global warming. To study the development of spring sea ice and environmental conditions in the pre-satellite era we investigated three short marine sediment cores for their biomarker inventory with a particular focus on the sea ice proxy IPSO25 and micropaleontological proxies. The core sites are located in the Bransfield Strait in shelf to deep basin areas characterized by a complex oceanographic frontal system, coastal influence and sensitivity to large-scale atmospheric circulation patterns. We analyzed geochemical bulk parameters, biomarkers (highly branched isoprenoids, glycerol dialkyl glycerol tetraethers, sterols), and diatom abundances and diversity over the past 240 years and compared them to observational data, sedimentary and ice core climate archives, and results from numerical models. Based on biomarker results we identified four different environmental units characterized by (A) low sea ice cover and high ocean temperatures, (B) moderate sea ice cover with decreasing ocean temperatures, (C) high but variable sea ice cover during intervals of lower ocean temperatures, and (D) extended sea ice cover coincident with a rapid ocean warming. While IPSO25 concentrations correspond quite well to satellite sea ice observations for the past 40 years, we note discrepancies between the biomarker-based sea ice estimates, the long-term model output for the past 240 years, ice core records, and reconstructed atmospheric circulation patterns such as the El Niño–Southern Oscillation (ENSO) and Southern Annular Mode (SAM). We propose that the sea ice biomarker proxies IPSO25 and PIPSO25 are not linearly related to sea ice cover, and, additionally, each core site reflects specific local environmental conditions. High IPSO25 and PIPSO25 values may not be directly interpreted as referring to high spring sea ice cover because variable sea ice conditions and enhanced nutrient supply may affect the production of both the sea-ice-associated and phytoplankton-derived (open marine, pelagic) biomarker lipids. For future interpretations we recommend carefully considering individual biomarker records to distinguish between cold sea-ice-favoring and warm sea-ice-diminishing environmental conditions.

The temperature proxies U37K′, LDI, TEX86H, and RI-OH are derived from lipid biomarkers, namely long-chain alkenones from coccolithophorids and long-chain diols ascribed tentatively to eustigmatophytes, as well as glycerol dialkyl glycerol tetraethers (GDGTs) and OH-GDGTs produced by Archaea. The applicability of these proxies in the South China Sea (SCS) has been investigated previously. However, in each study only one or two of the proxies were compared, and the recently updated calibrations or new calibrating methods such as BAYSPAR and BAYSPLINE were not applied. Here, we investigate four proxies in parallel in a set of surface sediment samples from the northern SCS shelf and relate them to local sea surface temperature (SST), which allows for us to compare and assess similarities and differences between them and also help improve regional multiproxy seawater temperature reconstructions. Our results indicate that U37K′ reflects annual mean SST with a slight bias toward the warm season. Terrestrial inputs appear to have a significant impact on LDI, TEX86H, and RI-OH proxies near the coast, leading to colder LDI- and TEX86H-derived temperatures but a warmer RI-OH temperature estimate. After excluding samples influenced by terrestrial materials, we find that LDI-derived temperature agrees well with annual SST, while TEX86H- and RI-OH-derived temperature estimates are close to SSTs in seasons dominated by the East Asian winter monsoon and summer monsoon, respectively. The different seasonal biases of these temperature proxies provide valuable tools to reconstruct regional SSTs under different monsoonal conditions.

Ice wedges in the Yana Highlands of interior Yakutia – the most continental region of the Northern Hemisphere – were investigated to elucidate changes in winter climate and continentality that have taken place since the Middle Pleistocene. The Batagay megaslump exposes ice wedges and composite wedges that were sampled from three cryostratigraphic units: the lower ice complex of likely pre-Marine Isotope Stage (MIS) 6 age, the upper ice complex (Yedoma) and the upper sand unit (both MIS 3 to 2). A terrace of the nearby Adycha River provides a Late Holocene (MIS 1) ice wedge that serves as a modern reference for interpretation. The stable-isotope composition of ice wedges in the MIS 3 upper ice complex at Batagay is more depleted (mean δ18O about −35 ‰) than those from 17 other ice-wedge study sites across coastal and central Yakutia. This observation points to lower winter temperatures and therefore higher continentality in the Yana Highlands during MIS 3. Likewise, more depleted isotope values are found in Holocene wedge ice (mean δ18O about −29 ‰) compared to other sites in Yakutia. Ice-wedge isotopic signatures of the lower ice complex (mean δ18O about −33 ‰) and of the MIS 3–2 upper sand unit (mean δ18O from about −33 ‰ to −30 ‰) are less distinctive regionally. The latter unit preserves traces of fast formation in rapidly accumulating sand sheets and of post-depositional isotopic fractionation.

Organic geochemical and micropaleontological analyses of surface sediments collected in the southern Drake Passage and the Bransfield Strait, Western Antarctic Peninsula, enable a proxy-based reconstruction of recent sea ice conditions in this climate-sensitive area. We study the distribution of the sea ice biomarker IPSO25, and biomarkers of open marine environments such as more unsaturated highly branched isoprenoid alkenes and phytosterols. Comparison of the sedimentary distribution of these biomarker lipids with sea ice data obtained from satellite observations and diatom-based sea ice estimates provide for an evaluation of the suitability of these biomarkers to reflect recent sea surface conditions. The distribution of IPSO25 supports earlier suggestions that the source diatom seems to be common in near-coastal environments characterized by annually recurring sea ice cover, while the distribution of the other biomarkers is highly variable. Offsets between sea ice estimates deduced from the abundance of biomarkers and satellite-based sea ice data are attributed to the different time intervals recorded within the sediments and the instrumental records from the study area, which experienced rapid environmental changes during the past 100 years. To distinguish areas characterized by permanently ice-free conditions, seasonal sea ice cover and extended sea ice cover, we apply the concept of the PIP25 index from the Arctic Ocean to our data and introduce the term PIPSO25 as a potential sea ice proxy. While the trends in PIPSO25 are generally consistent with satellite sea ice data and winter sea ice concentrations in the study area estimated by diatom transfer functions, more studies on the environmental significance of IPSO25 as a Southern Ocean sea ice proxy are needed before this biomarker can be applied for semi-quantitative sea ice reconstructions.

The relative abundance of individual archaeal membrane lipids, namely of glycerol dialkyl glycerol tetraethers (GDGTs) with different numbers of cyclopentane rings, varies with temperature, which enables their use as a paleotemperature proxy index. The first GDGT-based index in marine sediments called TEX86 is believed to reflect mean annual sea surface temperature (maSST). The TEX86L is an alternative temperature proxy for “low-temperature” regions ( ∘C), where the original TEX86 proxy calibration shows a larger scatter. However, TEX86L-derived temperatures still display anomalous estimates in polar regions. In order to elucidate the potential cause of the disagreement between the TEX86L estimate and SST, we analyzed GDGT fluxes and TEX86L-derived temperatures in sinking particles collected with time-series sediment traps in high-northern- and high-southern-latitude regions. At 1296 m depth in the eastern Fram Strait (79∘ N), a combination of various transporting mechanisms for GDGTs might result in seasonally different sinking velocities for particles carrying these lipids, resulting in strong variability in the TEX86L signal. The similarity of flux-weighted TEX86L temperatures from sinking particles and surface sediments implies an export of GDGTs without alteration in the Fram Strait. The estimated temperatures correspond to temperatures in water depths of 30–80 m, where nitrification might occur, indicating the favorable depth habitat of Thaumarchaeota. In the Antarctic Polar Front of the Atlantic sector (50∘ S), TEX86L-derived temperatures displayed warm and cold biases compared to satellite-derived SSTs at 614 m depth, and its flux-weighted mean signal differs from the deep signal at 3196 m. TEX86L-derived temperatures at 3196 m depth and the surface sediment showed up to 7 ∘C warmer temperatures relative to satellite-derived SST. Such a warm anomaly might be caused by GDGT contributions from Euryarchaeota, which are known to dominate archaeal communities in the circumpolar deep water of the Antarctic Polar Front. The other reason might be that a linear calibration is not appropriate for this frontal region. Of the newly suggested SST proxies based on hydroxylated GDGTs (OH-GDGTs), only those with OH-GDGT–0 and crenarchaeol or the ring index (RI) of OH-GDGTs yield realistic temperature estimates in our study regions, suggesting that OH-GDGTs could be applied as a potential temperature proxy in high-latitude oceans.

Long-chain diols (LCDs) occur widespread in marine environments and also in lakes and rivers. Transport of LCDs from rivers may impact the distribution of LCDs in coastal environments, however relatively little is known about the distribution and biological sources of LCDs in river systems. In this study, we investigated the distribution of LCDs in suspended particulate matter (SPM) of three river systems (Godavari, Danube, and Rhine) in relation with precipitation, temperature, and source catchments. The dominant long-chain diol is the C32 1,15-diol followed by the C30 1,15-diol in all studied river systems. In regions influenced by marine waters, such as delta systems, the fractional abundance of the C30 1,15-diol is substantially higher than in the river itself, suggesting different LCD producers in marine and freshwater environments. A change in the LCD distribution along the downstream transects of the rivers studied was not observed. However, an effect of river flow is observed; i.e., the concentration of the C32 1,15-diol is higher in stagnant waters such as reservoirs and during seasons with river low stands. A seasonal change in the LCD distribution was observed in the Rhine, likely due to a change in the producers. Eukaryotic diversity analysis by 18S rRNA gene sequencing of SPM from the Rhine showed extremely low abundances of sequences (i.e., < 0.32 % of total reads) related to known algal LCD producers. Furthermore, incubation of the river water with 13C-labeled bicarbonate did not result in 13C incorporation into LCDs. This indicates that the LCDs present are mainly of fossil origin in the fast-flowing part of the Rhine. Overall, our results suggest that the LCD producers in rivers predominantly reside in lakes or side ponds that are part of the river system.

Due to the high sensitivity of southern Africa to climate change, a reliable understanding of its hydrological system is crucial. Recent studies of the regional climatic system have revealed a highly complex interplay of forcing factors on precipitation regimes. This includes the influence of the tropical easterlies, the strength of the southern hemispheric westerlies as well as sea surface temperatures along the coast of the subcontinent. However, very few marine records have been available in order to study the coupling of marine and atmospheric circulation systems. Here we present results from a marine sediment core, recovered in shallow waters off the Gouritz River mouth on the south coast of South Africa. Core GeoB18308-1 allows a closer view of the last ∼ 4 kyr. Climate sensitive organic proxies, like the distribution and isotopic composition of plant-wax lipids as well as indicators for sea surface temperatures and soil input, give information on oceanographic and hydrologic changes during the recorded time period. Moreover, the micropaleontology, mineralogical and elemental composition of the sediments reflect the variability of the terrigenous input to the core site. The combination of down-core sediment signatures and a catchment-wide provenance study indicate that the Little Ice Age ( ∼ 300–650 cal yr BP) was characterized by climatic conditions favorable to torrential flood events. The Medieval Climate Anomaly ( ∼ 950–650 cal yr BP) is expressed by lower sea surface temperatures in the Mossel Bay area and humid conditions in the Gouritz River catchment. These new results suggest that the coincidence of humid conditions and cooler sea surface temperatures along the south coast of South Africa resulted from a strengthened and more southerly anticyclonic circulation. Most probably, the transport of moisture from the Indian Ocean by strong subtropical easterlies was coupled with Agulhas Bank upwelling pulses, which were initiated by an increase in Agulhas Current strength.

The Amazon River transports large amounts of terrestrial organic carbon (OCterr) from the Andean and Amazon neotropical forests to the Atlantic Ocean. In order to compare the biogeochemical characteristics of OCterr in the fluvial sediments from the Amazon drainage basin and in the adjacent marine sediments, we analysed riverbed sediments from the Amazon mainstream and its main tributaries as well as marine surface sediments from the Amazon shelf and fan for total organic carbon (TOC) content, organic carbon isotopic composition (δ13CTOC), and lignin phenol compositions. TOC and lignin content exhibit positive correlations with Al ∕ Si ratios (indicative of the sediment grain size) implying that the grain size of sediment discharged by the Amazon River plays an important role in the preservation of TOC and leads to preferential preservation of lignin phenols in fine particles. Depleted δ13CTOC values (−26.1 to −29.9 ‰) in the main tributaries consistently correspond with the dominance of C3 vegetation. Ratios of syringyl to vanillyl (S ∕ V) and cinnamyl to vanillyl (C ∕ V) lignin phenols suggest that non-woody angiosperm tissues are the dominant source of lignin in the Amazon basin. Although the Amazon basin hosts a rich diversity of vascular plant types, distinct regional lignin compositions are not observed. In the marine sediments, the distribution of δ13CTOC and Λ8 (sum of eight lignin phenols in organic carbon (OC), expressed as mg/100 mg OC) values implies that OCterr discharged by the Amazon River is transported north-westward by the North Brazil Current and mostly deposited on the inner shelf. The lignin compositions in offshore sediments under the influence of the Amazon plume are consistent with the riverbed samples suggesting that processing of OCterr during offshore transport does not change the encoded source information. Therefore, the lignin compositions preserved in these offshore sediments can reliably reflect the vegetation in the Amazon River catchment. In sediments from the Amazon fan, low lignin content, relatively depleted δ13CTOC values and high (Ad ∕ Al)V ratios indicating highly degraded lignin imply that a significant fraction of the deposited OCterr is derived from petrogenic (sourced from ancient rocks) sources.

Little is known about the climate evolution on the Kamchatka Peninsula during the last glacial–interglacial transition as existing climate records do not reach beyond 12 ka BP. In this study, a summer temperature record for the past 20 kyr is presented. Branched glycerol dialkyl glycerol tetraethers, terrigenous biomarkers suitable for continental air temperature reconstructions, were analyzed in a sediment core from the western continental margin off Kamchatka in the marginal northwest Pacific (NW Pacific). The record suggests that summer temperatures on Kamchatka during the Last Glacial Maximum (LGM) equaled modern temperatures. We suggest that strong southerly winds associated with a pronounced North Pacific High pressure system over the subarctic NW Pacific accounted for the warm conditions. A comparison with an Earth system model reveals discrepancies between model and proxy-based reconstructions for the LGM temperature and atmospheric circulation in the NW Pacific realm. The deglacial temperature development is characterized by abrupt millennial-scale temperature oscillations. The Bølling–Allerød warm phase and the Younger Dryas cold spell are pronounced events, suggesting a connection to North Atlantic climate variability.

Particle fluxes at the Cape Verde Ocean Observatory (CVOO) in the eastern tropical North Atlantic for the period December 2009 until May 2011 are discussed based on bathypelagic sediment trap time-series data collected at 1290 and 3439 m water depth. The typically oligotrophic particle flux pattern with weak seasonality is modified by the appearance of a highly productive and low oxygen (minimum concentration below 2 µmol kg−1 at 40 m depth) anticyclonic modewater eddy (ACME) in winter 2010. The eddy passage was accompanied by unusually high mass fluxes of up to 151 mg m−2 d−1, lasting from December 2009 to May 2010. Distinct biogenic silica (BSi) and organic carbon flux peaks of ∼ 15 and 13.3 mg m−2 d−1, respectively, were observed in February–March 2010 when the eddy approached the CVOO. The flux of the lithogenic component, mostly mineral dust, was well correlated with that of organic carbon, in particular in the deep trap samples, suggesting a tight coupling. The lithogenic ballasting obviously resulted in high particle settling rates and, thus, a fast transfer of epi-/meso-pelagic signatures to the bathypelagic traps. We suspect that the two- to three-fold increase in particle fluxes with depth as well as the tight coupling of mineral dust and organic carbon in the deep trap samples might be explained by particle focusing processes within the deeper part of the eddy. Molar C : N ratios of organic matter during the ACME passage were around 18 and 25 for the upper and lower trap samples, respectively. This suggests that some productivity under nutrient (nitrate) limitation occurred in the euphotic zone of the eddy in the beginning of 2010 or that a local nitrogen recycling took place. The δ15N record showed a decrease from 5.21 to 3.11 ‰ from January to March 2010, while the organic carbon and nitrogen fluxes increased. The causes of enhanced sedimentation from the eddy in February/March 2010 remain elusive, but nutrient depletion and/or an increased availability of dust as a ballast mineral for organic-rich aggregates might have contributed. Rapid remineralisation of sinking organic-rich particles could have contributed to oxygen depletion at shallow depth. Although the eddy formed in the West African coastal area in summer 2009, no indications of coastal flux signatures (e.g. from diatoms) were found in the sediment trap samples, confirming the assumption that the suboxia developed within the eddy en route. However, we could not detect biomarkers indicative of the presence of anammox (anaerobic ammonia oxidation) bacteria or green sulfur bacteria thriving in photic zone suboxia/hypoxia, i.e. ladderane fatty acids and isorenieratene derivatives, respectively. This could indicate that suboxic conditions in the eddy had recently developed and/or the respective bacterial stocks had not yet reached detection thresholds. Another explanation is that the fast-sinking organic-rich particles produced in the surface layer did not interact with bacteria from the suboxic zone below. Carbonate fluxes dropped from ∼ 52 to 21.4 mg m−2 d−1 from January to February 2010, respectively, mainly due to reduced contribution of shallow-dwelling planktonic foraminifera and pteropods. The deep-dwelling foraminifera Globorotalia menardii, however, showed a major flux peak in February 2010, most probably due to the suboxia/hypoxia. The low oxygen conditions forced at least some zooplankton to reduce diel vertical migration. Reduced “flux feeding” by zooplankton in the epipelagic could have contributed to the enhanced fluxes of organic materials to the bathypelagic traps during the eddy passage. Further studies are required on eddy-induced particle production and preservation processes and particle focusing.

During Termination 1, millennial-scale weakening events of the Atlantic meridional overturning circulation (AMOC) supposedly produced major changes in sea surface temperatures (SSTs) of the western South Atlantic, and in mean air temperatures (MATs) over southeastern South America. It has been suggested, for instance, that the Brazil Current (BC) would strengthen (weaken) and the North Brazil Current (NBC) would weaken (strengthen) during slowdown (speed-up) events of the AMOC. This anti-phase pattern was claimed to be a necessary response to the decreased North Atlantic heat piracy during periods of weak AMOC. However, the thermal evolution of the western South Atlantic and the adjacent continent is so far largely unknown. Here we address this issue, presenting high-temporal-resolution SST and MAT records from the BC and southeastern South America, respectively. We identify a warming in the western South Atlantic during Heinrich Stadial 1 (HS1), which is followed first by a drop and then by increasing temperatures during the Bølling–Allerød, in phase with an existing SST record from the NBC. Additionally, a similar SST evolution is shown by a southernmost eastern South Atlantic record, suggesting a South Atlantic-wide pattern in SST evolution during most of Termination 1. Over southeastern South America, our MAT record shows a two-step increase during Termination 1, synchronous with atmospheric CO2 rise (i.e., during the second half of HS1 and during the Younger Dryas), and lagging abrupt SST changes by several thousand years. This delay corroborates the notion that the long duration of HS1 was fundamental in driving the Earth out of the last glacial.

Particulate organic matter (POM) derived from permafrost soils and transported by the Lena River represents a quantitatively important terrestrial carbon pool exported to Laptev Sea sediments (next to POM derived from coastal erosion). Its fate in a future warming Arctic, i.e., its remobilization and remineralization after permafrost thawing as well as its transport pathways to and sequestration in marine sediments, is currently under debate. We present one of the first radiocarbon (14C) data sets for surface water POM within the Lena Delta sampled in the summers of 2009–2010 and spring 2011 (n = 30 samples). The bulk Δ14C values varied from −55 to −391 ‰ translating into 14C ages of 395 to 3920 years BP. We further estimated the fraction of soil-derived POM to our samples based on (1) particulate organic carbon to particulate nitrogen ratios (POC : PN) and (2) on the stable carbon isotope (δ13C) composition of our samples. Assuming that this phytoplankton POM has a modern 14C concentration, we inferred the 14C concentrations of the soil-derived POM fractions. The results ranged from −322 to −884 ‰ (i.e., 3060 to 17 250 14C years BP) for the POC : PN-based scenario and from −261 to −944 ‰ (i.e., 2370 to 23 100 14C years BP) for the δ13C-based scenario. Despite the limitations of our approach, the estimated Δ14C values of the soil-derived POM fractions seem to reflect the heterogeneous 14C concentrations of the Lena River catchment soils covering a range from Holocene to Pleistocene ages better than the bulk POM Δ14C values. We further used a dual-carbon-isotope three-end-member mixing model to distinguish between POM contributions from Holocene soils and Pleistocene Ice Complex (IC) deposits to our soil-derived POM fraction. IC contributions are comparatively low (mean of 0.14) compared to Holocene soils (mean of 0.32) and riverine phytoplankton (mean of 0.55), which could be explained with the restricted spatial distribution of IC deposits within the Lena catchment. Based on our newly calculated soil-derived POM Δ14C values, we propose an isotopic range for the riverine soil-derived POM end member with Δ14C of −495 ± 153 ‰ deduced from our δ13C-based binary mixing model and δ13C of −26.6 ± 1 ‰ deduced from our data of Lena Delta soils and literature values. These estimates can help to improve the dual-carbon-isotope simulations used to quantify contributions from riverine soil POM, Pleistocene IC POM from coastal erosion, and marine POM in Siberian shelf sediments.

The Lena River in central Siberia is one of the major pathways translocating terrestrial organic matter (OM) from its vast catchment area to the coastal zone of the Laptev Sea and the Arctic Ocean. The permafrost soils of its far south-stretching catchment, which store huge amounts of OM, will most likely respond differently to climate warming and remobilize previously frozen OM with distinct properties specific for the source vegetation and soil. To characterize the material discharged by the Lena River, we analyzed the lignin phenol composition in total suspended matter (TSM) from surface water collected in spring and summer, surface sediments from Buor Khaya Bay along with soils from the Lena Delta's first (Holocene) and third terraces (Pleistocene ice complex), and plant samples. Our results show that lignin-derived cinnamyl : vanillyl (C / V) and syringyl : vanillyl (S / V) ratios are > 0.14 and 0.25, respectively, in TSM and surface sediments, whereas in delta soils they are > 0.16 and > 0.51, respectively. These lignin compositions are consistent with significant inputs of organic matter from non-woody angiosperm sources mixed with organic matter derived from woody gymnosperm sources. We applied a simple linear mixing model based on the C / V and S / V ratios, and the results indicate the organic matter in delta TSM samples and Buor Khaya Bay surface sediments contain comparable contributions from gymnosperm material, which is primarily derived from the taiga forests south of the delta, and angiosperm material typical for tundra vegetation. Considering the small catchment area covered by tundra (~ 12%), the input is substantial and tundra-derived OM input is likely to increase in a warming Arctic. The similar and high acid to aldehyde ratios of vanillyl and syringyl (Ad / AlV, S) in Lena Delta summer TSM (> 0.7 and > 0.5, respectively) and Buor Khaya Bay surface sediments (> 1.0 and > 0.9, respectively) suggest that the OM is highly degraded and Lena River summer TSM could be a possible source of the surface sediments. The Ad / AlV, S ratios of the first and third delta terraces were generally lower (mean ratios > 0.4 and > 0.4, respectively) than summer TSM and surface sediments. This implies that TSM contains additional contributions from a more degraded OM source (southern catchment and/or finer more degraded particle size). Alternatively, OM degradation on land after permafrost thawing and subaqueously during transport and sedimentation could be considerable. Despite the high natural heterogeneity of OM stored in delta soils and exported by the Lena River, the catchment-characteristic vegetation is reflected by the lignin biomarker composition. Climate-warming-related changes in the Lena River catchment may be detectable in changing lignin biomarker composition and diagenetic alteration.

Chloropigments and their derivative pheopigments preserved in sediments can directly be linked to photosynthesis. Their carbon and nitrogen stable isotopic compositions have been shown to be a good recorder of recent and past surface ocean environmental conditions tracing the carbon and nitrogen sources and dominant assimilation processes of the phytoplanktonic community. In this study we report results from combined compound-specific radiocarbon and stable carbon and nitrogen isotope analysis to examine the time-scales of synthesis and fate of chlorophyll-a and its degradation products pheophytin-a, pyropheophytin-a, and 132,173-cyclopheophorbide-a-enol until burial in Black Sea core-top sediments. The pigments are mainly of marine phytoplanktonic origin as implied by their stable isotopic compositions. Pigment δ15N values indicate nitrate as the major uptake substrate but 15N-depletion towards the open marine setting indicates either contribution from N2-fixation or direct uptake of ammonium from deeper waters. Radiocarbon concentrations translate into minimum and maximum pigment ages of approximately 40 to 1200 years. This implies that protective mechanisms against decomposition such as association with minerals, storage in deltaic anoxic environments, or eutrophication-induced hypoxia and light limitation are much more efficient than previously thought. Moreover, seasonal variations of nutrient source, growth period, and habitat and their associated isotopic variability are likely at least as strong as long-term trends. Combined triple isotope analysis of sedimentary chlorophyll and its primary derivatives is a powerful tool to delineate biogeochemical and diagenetic processes in the surface water and sediments, and to assess their precise time-scales.

The present paper is the result of a workshop sponsored by the DFG Research Center/Cluster of Excellence MARUM "The Ocean in the Earth System", the International Graduate College EUROPROX, and the Alfred Wegener Institute for Polar and Marine Research. The workshop brought together specialists on organic matter degradation and on proxy-based environmental reconstruction. The paper deals with the main theme of the workshop, understanding the impact of selective degradation/preservation of organic matter (OM) in marine sediments on the interpretation of the fossil record. Special attention is paid to (A) the influence of the molecular composition of OM in relation to the biological and physical depositional environment, including new methods for determining complex organic biomolecules, (B) the impact of selective OM preservation on the interpretation of proxies for marine palaeoceanographic and palaeoclimatic reconstruction, and (C) past marine productivity and selective preservation in sediments. It appears that most of the factors influencing OM preservation have been identified, but many of the mechanisms by which they operate are partly, or even fragmentarily, understood. Some factors have not even been taken carefully into consideration. This incomplete understanding of OM breakdown hampers proper assessment of the present and past carbon cycle as well as the interpretation of OM based proxies and proxies affected by OM breakdown. To arrive at better proxy-based reconstructions "deformation functions" are needed, taking into account the transport and diagenesis-related molecular and atomic modifications following proxy formation. Some emerging proxies for OM degradation may shed light on such deformation functions. The use of palynomorph concentrations and selective changes in assemblage composition as models for production and preservation of OM may correct for bias due to selective degradation. Such quantitative assessment of OM degradation may lead to more accurate reconstruction of past productivity and bottom water oxygenation. Given the cost and effort associated with programs to recover sediment cores for paleoclimatological studies, as well as with generating proxy records, it would seem wise to develop a detailed sedimentological and diagenetic context for interpretation of these records. With respect to the latter, parallel acquisition of data that inform on the fidelity of the proxy signatures and reveal potential diagenetic biases would be of clear value.

Purpose: Endoluminal vacuum sponge therapy has dramatically improved the treatment of anastomotic leaks in esophageal surgery. However, the blind insertion of vacuum sponge kits like Eso-Sponge® via an overtube and a pusher can be technically difficult., Methods: We therefore insert our sponges under direct visual control by a nonstandard "piggyback" technique that was initially developed for the self-made sponge systems preceding these commercially available kits., Results: Using this technique, we inserted or changed 56 Eso-Sponges® in seven patients between 2018 and 2023. Apart from one secondary sponge dislocation, no intraprocedural complications were encountered. One patient died due to unrelated reasons. In all others, the defects healed and they were dismissed from the hospital. Long-term follow-up showed three strictures that were successfully treated by dilatation., Conclusion: We conclude that sponge placement via piggyback technique is a fast, safe, and successful alternative to the standard method of insertion., (© 2024. The Author(s).)

The changes in atmospheric pCO 2 provide evidence for the release of large amounts of ancient carbon during the last deglaciation. However, the sources and mechanisms that contributed to this process remain unresolved. Here, we present evidence for substantial ancient terrestrial carbon remobilization in the Canadian Arctic following the Laurentide Ice Sheet retreat. Glacial-retreat-induced physical erosion of bedrock has mobilized petrogenic carbon, as revealed by sedimentary records of radiocarbon dates and thermal maturity of organic carbon from the Canadian Beaufort Sea. Additionally, coastal erosion during the meltwater pulses 1a and 1b has remobilized pre-aged carbon from permafrost. Assuming extensive petrogenic organic carbon oxidation during the glacial retreat, a model-based assessment suggests that the combined processes have contributed 12 ppm to the deglacial CO 2 rise. Our findings suggest potentially positive climate feedback of ice-sheet retreat by accelerating terrestrial organic carbon remobilization and subsequent oxidation during the glacial-interglacial transition., (© 2022. The Author(s).)

The Central Arctic Ocean is one of the most oligotrophic oceans on Earth because of its sea-ice cover and short productive season. Nonetheless, across the peaks of extinct volcanic seamounts of the Langseth Ridge (87°N, 61°E), we observe a surprisingly dense benthic biomass. Bacteriosponges are the most abundant fauna within this community, with a mass of 460 g C m -2 and an estimated carbon demand of around 110 g C m -2 yr -1 , despite export fluxes from regional primary productivity only sufficient to provide <1% of this required carbon. Observed sponge distribution, bulk and compound-specific isotope data of fatty acids suggest that the sponge microbiome taps into refractory dissolved and particulate organic matter, including remnants of an extinct seep community. The metabolic profile of bacteriosponge fatty acids and expressed genes indicate that autotrophic symbionts contribute significantly to carbon assimilation. We suggest that this hotspot ecosystem is unique to the Central Arctic and associated with extinct seep biota, once fueled by degassing of the volcanic mounts., (© 2022. The Author(s).)

The Arctic is nutrient limited, particularly by nitrogen, and is impacted by anthropogenic global warming which occurs approximately twice as fast compared to the global average. Arctic warming intensifies thawing of permafrost-affected soils releasing their large organic nitrogen reservoir. This organic nitrogen reaches hydrological systems, is remineralized to reactive inorganic nitrogen, and is transported to the Arctic Ocean via large rivers. We estimate the load of nitrogen supplied from terrestrial sources into the Arctic Ocean by sampling in the Lena River and its Delta. We took water samples along one of the major deltaic channels in winter and summer in 2019 and sampling station in the central delta over a one-year cycle. Additionally, we investigate the potential release of reactive nitrogen, including nitrous oxide from soils in the Delta. We found that the Lena transported nitrogen as dissolved organic nitrogen to the coastal Arctic Ocean and that eroded soils are sources of reactive inorganic nitrogen such as ammonium and nitrate. The Lena and the Deltaic region apparently are considerable sources of nitrogen to nearshore coastal zone. The potential higher availability of inorganic nitrogen might be a source to enhance nitrous oxide emissions from terrestrial and aquatic sources to the atmosphere., (© 2021. The Author(s).)

Arctic warming is causing ancient perennially frozen ground (permafrost) to thaw, resulting in ground collapse, and reshaping of landscapes. This threatens Arctic peoples' infrastructure, cultural sites, and land-based natural resources. Terrestrial permafrost thaw and ongoing intensification of hydrological cycles also enhance the amount and alter the type of organic carbon (OC) delivered from land to Arctic nearshore environments. These changes may affect coastal processes, food web dynamics and marine resources on which many traditional ways of life rely. Here, we examine how future projected increases in runoff and permafrost thaw from two permafrost-dominated Siberian watersheds-the Kolyma and Lena, may alter carbon turnover rates and OC distributions through river networks. We demonstrate that the unique composition of terrestrial permafrost-derived OC can cause significant increases to aquatic carbon degradation rates (20 to 60% faster rates with 1% permafrost OC). We compile results on aquatic OC degradation and examine how strengthening Arctic hydrological cycles may increase the connectivity between terrestrial landscapes and receiving nearshore ecosystems, with potential ramifications for coastal carbon budgets and ecosystem structure. To address the future challenges Arctic coastal communities will face, we argue that it will become essential to consider how nearshore ecosystems will respond to changing coastal inputs and identify how these may affect the resiliency and availability of essential food resources., (© 2021. The Author(s).)

The recent expansion of Atlantic waters into the Arctic Ocean represents undisputable evidence of the rapid changes occurring in this region. Understanding the past variability of this “Atlantification” is thus crucial in providing a longer perspective on the modern Arctic changes. Here, we reconstruct the history of Atlantification along the eastern Fram Strait during the past 800 years using precisely dated paleoceanographic records based on organic biomarkers and benthic foraminiferal data. Our results show rapid changes in water mass properties that commenced in the early 20th century—several decades before the documented Atlantification by instrumental records. Comparison with regional records suggests a poleward expansion of subtropical waters since the end of the Little Ice Age in response to a rapid hydrographic reorganization in the North Atlantic. Understanding of this mechanism will require further investigations using climate model simulations.

Rapid changes in ocean circulation and climate have been observed in marine-sediment and ice cores over the last glacial period and deglaciation, highlighting the non-linear character of the climate system and underlining the possibility of rapid climate shifts in response to anthropogenic greenhouse gas forcing. To date, these rapid changes in climate and ocean circulation are still not fully explained. One obstacle hindering progress in our understanding of the interactions between past ocean circulation and climate changes is the difficulty of accurately dating marine cores. Here, we present a set of 92 marine sediment cores from the Atlantic Ocean for which we have established age-depth models that are consistent with the Greenland GICC05 ice core chronology, and computed the associated dating uncertainties, using a new deposition modeling technique. This is the first set of consistently dated marine sediment cores enabling paleoclimate scientists to evaluate leads/lags between circulation and climate changes over vast regions of the Atlantic Ocean. Moreover, this data set is of direct use in paleoclimate modeling studies.

Eastern boundary upwelling systems (EBUSs) are among the most productive marine environments in the world. The Canary Current upwelling system off the coast of Mauritania and Morocco is the second most productive of the four EBUS, where nutrient-rich waters fuel perennial phytoplankton blooms, evident by high chlorophyll a concentrations off Cape Blanc, Mauritania. High primary production leads to eutrophic waters in the surface layers, whereas sinking phytoplankton debris and horizontally dispersed particles form nepheloid layers (NLs) and hypoxic waters at depth. We used Catalyzed Reporter Deposition Fluorescence In Situ Hybridization (CARD-FISH) in combination with fatty acid (measured as methyl ester; FAME) profiles to investigate the bacterial and archaeal community composition along transects from neritic to pelagic waters within the "giant Cape Blanc filament" in two consecutive years (2010 and 2011), and to evaluate the usage of FAME data for microbial community studies. We also report the first fatty acid profile of Pelagibacterales strain HTCC7211 which was used as a reference profile for the SAR11 clade. Unexpectedly, the reference profile contained low concentrations of long chain fatty acids 18:1 cis11, 18:1 cis11 11methyl, and 19:0 cyclo11-12 fatty acids, the main compounds in other Alphaproteobacteria. Members of the free-living SAR11 clade were found at increased relative abundance in the hypoxic waters in both years. In contrast, the depth profiles of Gammaproteobacteria (including Alteromonas and Pseudoalteromonas), Bacteroidetes, Roseobacter, and Synechococcus showed high abundances of these groups in layers where particle abundance was high, suggesting that particle attachment or association is an important mechanisms of dispersal for these groups. Collectively, our results highlight the influence of NLs, horizontal particle transport, and low oxygen on the structure and dispersal of microbial communities in upwelling systems., (© 2018 The Authors. MicrobiologyOpen published by John Wiley & Sons Ltd.)

The mobilization of glacial permafrost carbon during the last glacial-interglacial transition has been suggested by indirect evidence to be an additional and significant source of greenhouse gases to the atmosphere, especially at times of rapid sea-level rise. Here we present the first direct evidence for the release of ancient carbon from degrading permafrost in East Asia during the last 17 kyrs, using biomarkers and radiocarbon dating of terrigenous material found in two sediment cores from the Okhotsk Sea. Upscaling our results to the whole Arctic shelf area, we show by carbon cycle simulations that deglacial permafrost-carbon release through sea-level rise likely contributed significantly to the changes in atmospheric CO 2 around 14.6 and 11.5 kyrs BP.

Membrane lipids of marine planktonic archaea have provided unique insights into archaeal ecology and paleoceanography. However, past studies of archaeal lipids in suspended particulate matter (SPM) and sediments mainly focused on a small class of fully saturated glycerol dibiphytanyl glycerol tetraether (GDGT) homologues identified decades ago. The apparent low structural diversity of GDGTs is in strong contrast to the high diversity of metabolism and taxonomy among planktonic archaea. Furthermore, adaptation of archaeal lipids in the deep ocean remains poorly constrained. We report the archaeal lipidome in SPM from diverse oceanic regimes. We extend the known inventory of planktonic archaeal lipids to include numerous unsaturated archaeal ether lipids (uns-AELs). We further reveal (i) different thermal regulations and polar headgroup compositions of membrane lipids between the epipelagic (≤ 100 m) and deep (>100 m) populations of archaea, (ii) stratification of unsaturated GDGTs with varying redox conditions, and (iii) enrichment of tetra-unsaturated archaeol and fully saturated GDGTs in epipelagic and deep oxygenated waters, respectively. Such stratified lipid patterns are consistent with the typical distribution of archaeal phylotypes in marine environments. We, thus, provide an ecological context for GDGT-based paleoclimatology and bring about the potential use of uns-AELs as biomarkers for planktonic Euryarchaeota., (© 2016 Society for Applied Microbiology and John Wiley & Sons Ltd.)

Intense debate persists about the climatic mechanisms governing hydrologic changes in tropical and subtropical southeast Africa since the Last Glacial Maximum, about 20,000 years ago. In particular, the relative importance of atmospheric and oceanic processes is not firmly established. Southward shifts of the intertropical convergence zone (ITCZ) driven by high-latitude climate changes have been suggested as a primary forcing, whereas other studies infer a predominant influence of Indian Ocean sea surface temperatures on regional rainfall changes. To address this question, a continuous record representing an integrated signal of regional climate variability is required, but has until now been missing. Here we show that remote atmospheric forcing by cold events in the northern high latitudes appears to have been the main driver of hydro-climatology in southeast Africa during rapid climate changes over the past 17,000 years. Our results are based on a reconstruction of precipitation and river discharge changes, as recorded in a marine sediment core off the mouth of the Zambezi River, near the southern boundary of the modern seasonal ITCZ migration. Indian Ocean sea surface temperatures did not exert a primary control over southeast African hydrologic variability. Instead, phases of high precipitation and terrestrial discharge occurred when the ITCZ was forced southwards during Northern Hemisphere cold events, such as Heinrich stadial 1 (around 16,000 years ago) and the Younger Dryas (around 12,000 years ago), or when local summer insolation was high in the late Holocene, that is, during the past 4,000 years.

The Sahara Desert is the largest source of mineral dust in the world. Emissions of African dust increased sharply in the early 1970s (ref. 2), a change that has been attributed mainly to drought in the Sahara/Sahel region caused by changes in the global distribution of sea surface temperature. The human contribution to land degradation and dust mobilization in this region remains poorly understood, owing to the paucity of data that would allow the identification of long-term trends in desertification. Direct measurements of airborne African dust concentrations only became available in the mid-1960s from a station on Barbados and subsequently from satellite imagery since the late 1970s: they do not cover the onset of commercial agriculture in the Sahel region approximately 170 years ago. Here we construct a 3,200-year record of dust deposition off northwest Africa by investigating the chemistry and grain-size distribution of terrigenous sediments deposited at a marine site located directly under the West African dust plume. With the help of our dust record and a proxy record for West African precipitation we find that, on the century scale, dust deposition is related to precipitation in tropical West Africa until the seventeenth century. At the beginning of the nineteenth century, a sharp increase in dust deposition parallels the advent of commercial agriculture in the Sahel region. Our findings suggest that human-induced dust emissions from the Sahel region have contributed to the atmospheric dust load for about 200 years.