Quantification of the interaction between river discharge and tides is vital to characterize fluvio-deltaic systems, to identify diagnostic elements of tidal signatures in the rock record, and to reconstruct paleogeographies. In modern systems, even microtides can significantly influence delta morphodynamics; yet, many fundamental processes, particularly in prodeltaic settings, remain elusive. Here, by combining a unique process-product data set acquired during a flood event of the Po River (Italy) with numerical modeling, we show that tidal signatures are recorded in the open-water prodelta zone of a microtidal system. Based on the analyses of box-cores collected before and after a flood off the main distributary channel, we interpreted storm beds, tide-modulated flood strata of alternating normal and inverse graded beds, and rapid bioturbation. Modeling of the river discharge indicates that, at the peak of the flood, the steepening of the water-surface profile forced by 0.15 m lowering of sea level during low tides generated an 8% increase in river flow velocity. The alternation of profile steepness and associated cyclicity in flow strength during consecutive tidal cycles controlled the sediment load of the plume and, consequently, led to the deposition of tidal-modulated strata. Formation of microtidal signals appears to be enhanced in fluvio-deltaic successions characterized by multiple distributaries and in basins where river floods are out of phase with storm-wave activity. Bioturbation of sediment, which can start during the waning stage of the flow, and erosion by storm waves hamper the preservation of tidal signals, unless rapid burial occurs. The recognition of tidal-modulated strata in river-dominated settings may facilitate the characterization of mudstone reservoirs and reconstruction of paleogeographic conditions during deposition.

Time-series analyses of satellite images reveal that sea ice extent in the Ross Sea has experienced significant changes over the last 40 years, likely triggered by large-scale atmospheric anomalies. However, resolving how sea ice in the Ross Sea has changed over longer timeframes has until now remained more elusive. Here we used a laminated sediment piston core (14.6 m) collected from the Edisto inlet (Western Ross Sea) to reconstruct fast ice dynamics over the last 2.6 ka. Our goal was to first understand the climate expression of selected well-defined sediment laminae and then use these characteristics for reconstructing past sea ice behaviour across the whole sedimentary sequence. We used the recently established sea ice diatom biomarker proxy IPSO25 in combination with diatom census counts and bulk analyses. Analyses performed on a suite of discrete laminae revealed statistically significant differences between dark and light laminae reflecting different depositional conditions. Based on their respective biogeochemical fingerprints, we infer that dark laminae accumulated during sea ice thaws in early summer. Under these conditions, laminae contain relatively high concentrations of IPSO25 and display an enriched delta C-13 composition for the bulk organic matter (OM). While diatom assemblages in dark laminae are relatively homogenous, as the thaw continues later in the summer, Corethron pennatum becomes the dominant diatom species, resulting in the formation of light laminae characterized by low IPSO25 concentrations. Since C. pennatum can migrate vertically through the water column to uptake nutrients and avoid competition in oligotrophic waters, its high concentration likely reflects stratified and ice-free surface waters typical of late summer. Down-core trends show that the correlation between sediment brightness and geochemical fingerprint (i.e., IPSO25 and delta C-13) holds throughout the record. Based on the knowledge gained at lamina level, our down-core high-resolution reconstruction shows that the summer fast ice coverage changed dramatically during the late Holocene. Specifically, we conclude that the Edisto inlet experienced regular early summer opening between 2.6 ka, and ca. 0.7 ka, after which, coastal fast ice persisted during summer months and ice-free conditions became less frequent. Comparison with previous regional ice core data suggests that the sudden cooling recorded over the Victoria Land Coast region since 0.7 ka might potentially explain our observation of persistent summer fast ice in the Western Ross Sea. Our study has shown that multi-proxy data derived from laminated sediments can provide hitherto unknown detail regarding past summer sea ice dynamics in coastal Antarctic regions. (C) 2020 Elsevier Ltd. All rights reserved.

Observing systems are the tool to study climate change when they provide the basic information to assess changes: time-series of good quality data. Marine observatories historically involved the collection of physical data as seawater temperature and salinity, but, in relative recent time, timeseries have been improved with relevant data about C fluxes and other climate related variables., e.g. nutrients, DMS or dissolved CO2, also thanks to improved technology of measurements. Parallel to data collection by moored instruments, time-series are also derived from regular hydrological survey and CTD casts. Although these CTD surveys do not have the robust time coverage of moorings, they are often replicated on a regular basis, resulting in a time-series. The marine observing system in Ny-Ålesund provides a full coverage of the major ocean variables relevant to monitor climate-related changes in Arctic sea water properties. It has been built around the permanent mooring Dirigibile Italia and has been improved with other measurements and observations. Italian moorings were first deployed at sea in September 2000 and 2001 in a site that was in the innermost part of the fjord at that time (Aliani et al., 2004). Melting of tidewater glaciers' ice tongues produced in big changes in Ny-Ålesund and the mooring Dirigibile Italia, which is the core of the present-day observing system, has been positioned close to the inner moraine. Sediment traps and new sensors were added to the traditional CT recorders and regular CTD surveys were performed within FIKO project during moorings maintenance, resulting in a large data set every year since September 2010 when the mooring was first deployed. These data after Quality Control will be delivered to the CNR Arctic Data Center and available for modelling. Taking advantage of the presence of Dirigibile Italia marine observatory, experiments have been performed in Ny-Ålesund about the microbial communities in seawater and about the technological exploitation of autonomous vehicles for measuring in extreme and very dangerous environments as the glacier's front, which successfully brought an instrumented AUV to touch Kronebreen glacier (Zappalà et al., 2016, 2017). Time-series of thermohaline properties from the mooring Dirigibile Italia (MDI) revealed a large seasonal variability (? = -1.82 / 6.26°C, S = 34 / 35) and from the beginning of the time-series an increasing trend in temperature (0.07 °C y-1) was measured showing constant minima, and progressively higher warm peaks. An average total mass flux (TMF) of about 20 g m-2 d-1, with the highest peaks recorded in summer-fall months (avg. flux, ~100 g m-2 d-1) and reduced fluxes in autumn-winters (avg. flux, ~7 g m-2 day-1). The terrestrial input due to the melting of glacier terminations generated an increase of the detritus, and the surface runoff introduced debris into the sea from the permafrost surface layer erosion (D'Angelo et al., 2018). All this variability may affect prokaryotic and phytoplanktonic biomass and microbial remineralization rates over short time scales (Azzaro et al., 2017; Caroppo et al., 2017). Nowadays, the Italian marine experimental platform has two pillars. The first is the marine observatory centered on the mooring(s) MDI which will deliver oceanographic data to IADC. The second pillar is the experimental platform that derives from the presence of the marine observatory, which is used for dedicated experiments. Together with Climate Change Tower atmospheric measurements, they are a solid and multidisciplinary approach to monitoring climate change in the Arctic.

Climate warming is expected to destabilize permafrost carbon (PF-C) by thaw-erosion and deepening of the seasonally thawed active layer and thereby promote PF-C mineralization to CO2 and CH4. A similar PF-C remobilization might have contributed to the increase in atmospheric CO2 during deglacial warming after the last glacial maximum. Using carbon isotopes and terrestrial biomarkers (Delta C-14, delta C-13, and lignin phenols), this study quantifies deposition of terrestrial carbon originating from permafrost in sediments from the Chukchi Sea (core SWERUS-L2-4-PC1). The sediment core reconstructs remobilization of permafrost carbon during the late Allerod warm period starting at 13,000 cal years before present (BP), the Younger Dryas, and the early Holocene warming until 11,000 cal years BP and compares this period with the late Holocene, from 3,650 years BP until present. Dual-carbon-isotope-based source apportionment demonstrates that Ice Complex Deposit-ice- and carbon-rich permafrost from the late Pleistocene (also referred to as Yedoma)-was the dominant source of organic carbon (66 +/- 8%; mean +/- standard deviation) to sediments during the end of the deglaciation, with fluxes more than twice as high (8.0 +/- 4.6 g.m(-2).year(-1)) as in the late Holocene (3.1 +/- 1.0 g.m(-2).year(-1)). These results are consistent with late deglacial PF-C remobilization observed in a Laptev Sea record, yet in contrast with PF-C sources, which at that location were dominated by active layer material from the Lena River watershed. Release of dormant PF-C from erosion of coastal permafrost during the end of the last deglaciation indicates vulnerability of Ice Complex Deposit in response to future warming and sea level changes.

Ongoing permafrost thaw in the Arctic may remobilize large amounts of old organic matter. Upon transport to the Siberian shelf seas, this material may be degraded and released to the atmosphere, exported off-shelf, or buried in the sediments. While our understanding of the fate of permafrost-derived organic matter in shelf waters is improving, poor constraints remain regarding degradation in sediments. Here we use an extensive data set of organic carbon concentrations and isotopes (n=109) to inventory terrigenous organic carbon (terrOC) in surficial sediments of the Laptev and East Siberian Seas (LS + ESS). Of these similar to 2.7 Tg terrOC about 55% appear resistant to degradation on a millennial timescale. A first-order degradation rate constant of 1.5 kyr(-1) is derived by combining a previously established relationship between water depth and cross-shelf sediment-terrOC transport time with mineral-associated terrOC loadings. This yields a terrOC degradation flux of similar to 1.7Gg/year from surficial sediments during cross-shelf transport, which is orders of magnitude lower than earlier estimates for degradation fluxes of dissolved and particulate terrOC in the water column of the LS + ESS. The difference is mainly due to the low degradation rate constant of sedimentary terrOC, likely caused by a combination of factors: (i) the lower availability of oxygen in the sediments compared to fully oxygenated waters, (ii) the stabilizing role of terrOC-mineral associations, and (iii) the higher proportion of material that is intrinsically recalcitrant due to its chemical/molecular structure in sediments. Sequestration of permafrost-released terrOC in shelf sediments may thereby attenuate the otherwise expected permafrost carbon-climate feedback.

Paleoclimatic and paleoenvironmental reconstruction during the last 2ka using geochemical and biological proxies in marine sediments from western Ross Sea (Antarctica)

High-latitude regions are warming faster than other areas due to reduction of snow cover and sea ice loss and changes in atmospheric and ocean circulation. The combination of these processes, collectively known as polar amplification, provides an extraordinary opportunity to document the ongoing thermal destabilisation of the terrestrial cryosphere and the release of land-derived material into the aquatic environment. This study presents a 6-year time series (2010-2016) of physical parameters and particle fluxes collected by an oceanographic mooring in Kongsfjorden (Spitsbergen, Svalbard). In recent decades, Kongsfjorden has been experiencing rapid loss of sea ice coverage and retreat of local glaciers as a result of the progressive increase in ocean and air temperatures. The overarching goal of this study was to continuously monitor the inner fjord particle sinking and to understand to what extent the temporal evolution of particulate fluxes was linked to the progressive changes in both Atlantic and freshwater input. Our data show high peaks of settling particles during warm seasons, in terms of both organic and inorganic matter. The different sources of suspended particles were described as a mixing of glacier carbonate, glacier siliciclastic and autochthonous marine input. The glacier releasing sediments into the fjord was the predominant source, while the sediment input by rivers was reduced at the mooring site. Our time series showed that the seasonal sunlight exerted first-order control on the particulate fluxes in the inner fjord. The marine fraction peaked when the solar radiation was at a maximum in May-June while the land-derived fluxes exhibited a 1-2-month lag consistent with the maximum air temperature and glacier melting. The inter-annual time-weighted total mass fluxes varied by 2 orders of magnitude over time, with relatively higher values in 2011, 2013, and 2015. Our results suggest that the land-derived input will remarkably increase over time in a warming scenario. Further studies are therefore needed to understand the future response of the Kongsfjorden ecosystem alterations with respect to the enhanced release of glacier-derived material.

To understand how the climate change affects the microbial community in the Arctic Sea and the ongoing heating results in cascading effects on the globally delicate climatic equilibrium is an important challenge of recent research performed in vulnerable ecosystems such as the Svalbard Islands. Within the UVASS (Unmanned Vehicles for Autonomous Sensing and Sampling) project, an unmanned marine vehicle (PROTEUS, Portable RObotic TEchnology for Unmanned Surveys), equipped with an automatic water multisampler, designed and built by ISSIA-CNR and IAMC-CNR respectively, were applied to study the response of planktonic communities, particularly prokaryotes, in the extreme environment of Kongsfjorden. During June 2017, seawater samples collected by those automatic systems along three transects located from glaciers to the open sea were analyzed for nutrients, organic matter and its utilization by microbial activity, using Biolog-Ecoplates(TM) and extracellular enzymatic activity rates (leucine aminopeptidase, beta-glucosidase and phosphatase activities). Richness and Shannon-Weaver index and Principal Component Analysis were used to depict differences in the microbial catabolic potential. Variations in organic matter distribution and in the functional diversity of microbial assemblages were observed. Freshwater runoff from ice melting was found to increase the amount of terrestrial organic matter to the fjord and microbial processes allowed organic matter decomposition.

The burial of terrestrial organic carbon (terrOC) in marine sediments contributes to the regulation of atmospheric CO2 on geological timescales and may mitigate positive feedback to present-day climate warming. However, the fate of terrOC in marine settings is debated, with uncertainties regarding its degradation during transport. Here, we employ compound-specific radiocarbon analyses of terrestrial biomarkers to determine cross-shelf transport times. For the World's largest marginal sea, the East Siberian Arctic shelf, transport requires 3600 +/- 300 years for the 600 km from the Lena River to the Laptev Sea shelf edge. TerrOC was reduced by similar to 85% during transit resulting in a degradation rate constant of 2.4 +/- 0.6 kyr(-1). Hence, terrOC degradation during cross-shelf transport constitutes a carbon source to the atmosphere over millennial time. For the contemporary carbon cycle on the other hand, slow terrOC degradation brings considerable attenuation of the decadal-centennial permafrost carbon-climate feedback caused by global warming.

The Siberian Arctic Sea shelf and slope is a key region for the degradation of terrestrial organic material transported from the organic-carbon-rich permafrost regions of Siberia. We report on sediment carbon mineralization rates based on O2 microelectrode profiling; intact sediment core incubations; 35S-sulfate tracer experiments; pore-water dissolved inorganic carbon (DIC); 13CDIC; and iron, manganese, and ammonium concentrations from 20 shelf and slope stations. This data set provides a spatial overview of sediment carbon mineralization rates and pathways over large parts of the outer Laptev and East Siberian Arctic shelf and slope and allows us to assess degradation rates and efficiency of carbon burial in these sediments. Rates of oxygen uptake and iron and manganese reduction were comparable to temperate shelf and slope environments, but bacterial sulfate reduction rates were comparatively low. In the topmost 50cm of sediment, aerobic carbon mineralization dominated degradation and comprised on average 84% of the depth-integrated carbon mineralization. Oxygen uptake rates and anaerobic carbon mineralization rates were higher in the eastern East Siberian Sea shelf compared to the Laptev Sea shelf. DICoNH4+ ratios in pore waters and the stable carbon isotope composition of remineralized DIC indicated that the degraded organic matter on the Siberian shelf and slope was a mixture of marine and terrestrial organic matter. Based on dual end-member calculations, the terrestrial organic carbon contribution varied between 32 and 36%, with a higher contribution in the Laptev Sea than in the East Siberian Sea. Extrapolation of the measured degradation rates using isotope end-member apportionment over the outer shelf of the Laptev and East Siberian seas suggests that about 16TgCyr'1 is respired in the outer shelf seafloor sediment. Of the organic matter buried below the oxygen penetration depth, between 0.6 and 1.3TgCyr'1 is degraded by anaerobic processes, with a terrestrial organic carbon contribution ranging between 0.3 and 0.5Tgyr'1.

Recent Arctic studies suggest that sea ice decline and permafrost thawing will affect phytoplankton dynamics and stimulate heterotrophic communities. However, in what way the plankton composition will change as the warming proceeds remains elusive. Here we investigate the chemical signature of the plankton-dominated fraction of particulate organic matter (POM) collected along the Siberian Shelf. POM (>10 mu m) samples were analysed using molecular biomarkers (CuO oxidation and IP25 ) and dual-carbon isotopes (delta C-13 and Delta C-14). In addition, surface water chemical properties were integrated with the POM (>10 mu m) dataset to understand the link between plankton composition and environmental conditions.

Pleistocene ice complex permafrost deposits contain roughly a quarter of the organic carbon (OC) stored in permafrost (PF) terrain. When permafrost thaws, its OC is remobilized into the (aquatic) environment where it is available for degradation, transport or burial. Aquatic or coastal environments contain sedimentary reservoirs that can serve as archives of past climatic change. As permafrost thaw is increasing throughout the Arctic, these reservoirs are important locations to assess the fate of remobilized permafrost OC. We here present compound-specific deuterium (delta H-2) analysis on leaf waxes as a tool to distinguish between OC released from thawing Pleistocene permafrost (ice complex deposits; ICD) and from thawing Holocene permafrost (from near-surface soils). Bulk geochemistry (%OC; delta C-13; % total nitrogen, TN) was analyzed as well as the concentrations and delta H-2 signatures of long-chain n-alkanes (C-21 to C-33) and midto long-chain n-alkanoic acids (C-16 to C-30) extracted from both ICD-PF samples (n = 9) and modern vegetation and Ohorizon (topsoil-PF) samples (n = 9) from across the northeast Siberian Arctic. Results show that these topsoil-PF samples have higher %OC, higher OC/TN values and more depleted delta(COC)-C-13 values than ICD-PF samples, suggesting that these former samples trace a fresher soil and/or vegetation source. Whereas the two investigated sources differ on the bulk geochemical level, they are, however, virtually indistinguishable when using leaf wax concentrations and ratios. However, on the molecular isotope level, leaf wax biomarker delta H-2 values are statistically different between topsoil PF and ICD PF. For example, the mean delta H-2 value of C-29 n-alkane was -246 +/- 13% (mean +/- SD) for topsoil PF and -280 +/- 12 parts per thousand for ICD PF. With a dynamic isotopic range (difference between two sources) of 34 to 50 parts per thousand; the isotopic fingerprints of individual, abundant, biomarker molecules from leaf waxes can thus serve as endmembers to distinguish between these two sources. We tested this molecular delta H-2 tracer along with another source-distinguishing approach, dual-carbon (delta C-13-Delta C-14) isotope composition of bulk OC, for a surface sediment transect in the Laptev Sea. Results show that general offshore patterns along the shelfslope transect are similar, but the source apportionment between the approaches vary, which may highlight the advan-tages of either. This study indicates that the application of delta H-2 leaf wax values has potential to serve as a complementary quantitative measure of the source and differential fate of OC thawed out from different permafrost compartments.

The formation of Eastern Mediterranean sapropels has periodically occurred during intensification of northern hemisphere monsoon precipitation over North Africa. However, the large-scale response of the Eastern Mediterranean thermohaline circulation during these monsoon-fuelled freshening episodes is poorly constrained. Here, we investigate the formation of the youngest sapropel (S1) along an across slope transect in the Adriatic Sea. Foraminifera-based oxygen index, redox-sensitive elements and biogeochemical parameters reveal - for the first time - that the Adriatic S1 was synchronous with the deposition of south-eastern Mediterranean S1 beds. Proxies of paleo thermohaline currents indicate that the bottom-hugging North Adriatic Dense Water (NAdDW) suddenly decreased at the sapropel onset simultaneously with the maximum freshening of the Levantine Sea during the African Humid Period. We conclude that the lack of the "salty" Levantine Intermediate Water hampered the preconditioning of the northern Adriatic waters necessary for the NAdDW formation prior to the winter cooling. Consequently, a weak NAdDW limited in turn the Eastern Mediterranean Deep Water (EMDWAdriatic) formation with important consequences for the ventilation of the Ionian basin as well. Our results highlight the importance of the Adriatic for the deep water ventilation and the interdependence among the major eastern Mediterranean water masses whose destabilization exerted first-order control on S1 deposition. (C) 2017 Elsevier Ltd. All rights reserved.

Recent hypotheses, based on atmospheric records and models, suggest that permafrost carbon (PF-C) accumulated during the last glaciation may have been an important source for the atmospheric CO2 rise during post-glacial warming. However, direct physical indications for such PF-C release have so far been absent. Here we use the Laptev Sea (Arctic Ocean) as an archive to investigate PF-C destabilization during the last glacial-interglacial period. Our results show evidence for massive supply of PF-C from Siberian soils as a result of severe active layer deepening in response to the warming. Thawing of PF-C must also have brought about an enhanced organic matter respiration and, thus, these findings suggest that PF-C may indeed have been an important source of CO2 across the extensive permafrost domain. The results challenge current paradigms on the post-glacial CO2 rise and, at the same time, serve as a harbinger for possible consequences of the present-day warming of PF-C soils.

Fluvial discharge and coastal erosion of the permafrost-dominated East Siberian Arctic delivers large quantities of terrigenous organic carbon (Terr-OC) to marine waters. The composition and fate of the remobilized Terr-OC needs to be better constrained as it impacts the potential for a climate-carbon feedback. In the present study, the bulk isotope (delta C-13 and Delta C-14) and macromolecular (lignin-derived phenols) composition of the cross-shelf exported organic carbon (OC) in different marine pools is evaluated. For this purpose, as part of the SWERUS-C3 expedition (July-September 2014), sediment organic carbon (SOC) as well as water column (from surface and near-bottom seawater) dissolved organic carbon (DOC) and particulate organic carbon (POC) samples were collected along the outer shelves of the Kara Sea, Laptev Sea and East Siberian Sea. The results show that the Lena River and the DOC may have a preferential role in the transport of Terr-OC to the outer shelf. DOC concentrations (740-3600 mu g L-1) were 1 order of magnitude higher than POC (20-360 mu g L-1), with higher concentrations towards the Lena River plume. The delta C-13 signatures in the three carbon pools varied from -23.9 +/- 1.9 parts per thousand in the SOC, 26.1 +/- 1.2 parts per thousand in the DOC and 27.1 +/- 1.9 parts per thousand in the POC. The Delta C-14 values ranged between 395 +/- 83 (SOC), 226 +/- 92 (DOC) and 113 +/- 122 parts per thousand(POC). These stable and radiocarbon isotopes were also different between the Laptev Sea and the East Siberian Sea. Both DOC and POC showed a depleted and younger trend off the Lena River plume. Further, the Pacific inflow and the sea-ice coverage, which works as a barrier preventing the input of "young" DOC and POC, seem to have a strong influence in these carbon pools, presenting older and more enriched delta C-13 signatures under the sea-ice extent. Lignin phenols exhibited higher OC-normalized concentrations in the SOC (0.10-2.34 mg g(-1) OC) and DOC (0.08-2.40 mg g(-1) OC) than in the POC (0.03-1.14 mg g(-1) OC). The good relationship between lignin and Delta C-14 signatures in the DOC suggests that a significant fraction of the outer-shelf DOC comes from " young" Terr-OC. By contrast, the slightly negative correlation between lignin phenols and Delta C-14 signatures in POC, with higher lignin concentrations in older POC from near-bottom waters, may reflect the off-shelf transport of OC from remobilized permafrost in the nepheloid layer. Syringyl/vanillyl and cinnamyl/vannillyl phenol ratios presented distinct clustering between DOC, POC and SOC, implying that those pools may be carrying different Terr-OC of partially different origin. Moreover, 3,5-dihydroxybenzoic acid to vanillyl phenol ratios and p-coumaric acid to ferulic acid ratios, used as a diagenetic indicators, enhanced in POC and SOC, suggesting more degradation within these pools. Overall, the key contrast between enhanced lignin yields both in the youngest DOC and the oldest POC samples reflects a significant decoupling of terrestrial OC sources and pathways.

Ongoing global warming in high latitudes may cause an increasing supply of permafrost-derived organic carbon through both river discharge and coastal erosion to the Arctic shelves. Mobilized permafrost carbon can be either buried in sediments, transported to the deep sea or degraded to CO2 and outgassed, potentially constituting a positive feedback to climate change. br>br> This study aims to assess the fate of terrigenous organic carbon (TerrOC) in the Arctic marine environment by exploring how it changes in concentration, composition and degradation status across the wide Laptev Sea shelf. We analyzed a suite of terrestrial biomarkers as well as source-diagnostic bulk carbon isotopes (I/13C, 14C) in surface sediments from a Laptev Sea transect spanning more than 800km from the Lena River mouth (10m water depth) across the shelf to the slope and rise (2000-3000m water depth). These data provide a broad view on different TerrOC pools and their behavior during cross-shelf transport. The concentrations of lignin phenols, cutin acids and high-molecular-weight (HMW) wax lipids (tracers of vascular plants) decrease by 89-99% along the transect. Molecular-based degradation proxies for TerrOC (e.g., the carbon preference index of HMW lipids, the HMW acid?oalkanes ratio and the acidoaldehyde ratio of lignin phenols) display a trend to more degraded TerrOC with increasing distance from the coast. We infer that the degree of degradation of permafrost-derived TerrOC is a function of the time spent under oxic conditions during protracted cross-shelf transport. Future work should therefore seek to constrain cross-shelf transport times in order to compute a TerrOC degradation rate and thereby help to quantify potential carbon-climate feedbacks.

Thawing Arctic permafrost causes massive fluvial and erosional releases of dissolved and particulate organic carbon (DOC and POC) to coastal waters. Here we investigate how different sources and degradation of remobilized terrestrial carbon may affect large-scale carbon cycling, by comparing molecular and dual-isotope composition of waterborne high molecular weight DOC (>1 kD, aka colloidal OC), POC, and sedimentary OC (SOC) across the East Siberian Arctic Shelves. Lignin phenol fingerprints demonstrate a longitudinal trend in relative contribution of terrestrial sources to coastal OC. Wax lipids and cutins were not detected in colloidal organic carbon (COC), in contrast to POC and SOC, suggesting that different terrestrial carbon pools partition into different aquatic carrier phases. The ?14C signal suggests overwhelmingly contemporary sources for COC, while POC and SOC are dominated by old C from Ice Complex Deposit (ICD) permafrost. Monte Carlo source apportionment (?13C, ?14C) constrained that COC was dominated by terrestrial OC from topsoil permafrost (65%) and marine plankton (25%) with smaller contribution ICD and other older permafrost stocks (9%). This distribution is likely a result of inherent compositional matrix differences, possibly driven by organomineral associations. Modern OC found suspended in the surface water may be more exposed to degradation, in contrast to older OC that preferentially settles to the seafloor where it may be degraded on a longer timescale. The different sources which partition into DOC, POC, and SOC appear to have vastly different fates along the Eurasian Arctic coastal margin and may possibly respond on different timescales to climate change.

The Southern Adriatic is an area of dense shelf water (DSW) cascading and open-ocean convection. The impact of DSW cascading events in transferring organic matter to the deep benthic community and in producing a wide range of bedforms along the continental margin has been highlighted in recent years. In order to improve our knowledge on the interannual variability of the DSW cascading with the ultimate goal to understand timing of DSW formation and transport as well as the cascading process, its variability in intensity and duration, and the ultimate impact of the dense water on the deep sea, in March 2009 we deployed an instrumented mooring in a field of sediment waves (860 m depth) located down current to the Bari canyon. In March 2010, a second mooring was installed in the northern channel of the canyon. Winters 2009, 2010 and 2011 were mild and particularly wet and the Po river discharge remained relatively high throughout the whole winter. Hence, we expected weak dense shelf water formation associated with a shallow shelf water overflowing off the Adriatic shelf. By contrast, in winter 2012, the North Adriatic experienced a severe cold wave with NE Bora winds and reduced fresh water input. These weather conditions allowed the formation of extremely dense shelf water. Three additional moorings were quickly deployed during this cold event in the Southern Adriatic Sea to investigate the spatial variability of particle and organic matter fluxes exiting from the Adriatic continental shelf under the influence of a strong DSW cascading event. Slow near-bottom currents, never exceeding 40 cm s(-1), were recorded between March 2009 and February 2012. Water temperatures depicted minor negative shifts. Total mass fluxes (TMFs) were low (annual avg., 1.7-2.8 g m(-2) d(-1) and 0.3-0.6 g m(-2) d(-1) in the canyon and in the sediment wave field, respectively; and peak values g m(-2) d(-1)), but showed significant seasonal and interannual variability. Fluxes in the canyon were higher than those measured in the sediment wave field at deeper water depth. Mass flux peaks during the 2112-DSW cascading were up to 5 times higher than the peaks of previous years (up to 18.70 g m(-2) d(-1)), with a spatial variability mainly driven by the localized pathways of DSW cascading. In the canyon, near-bottom currents exceeded 70 cm s(-1) and temperature dropped to 12.2 degrees C while current speeds were high also at 1200 m depth (similar to 60 cm s(-1)) in the moat surrounding the Dauno seamount. Surprisingly, mass flux peaks occurred from the 16th February to the 1st of March, 3-4 weeks ahead of the usual DSW occurrence, suggesting an early arrival of the DSW. The deep DSW cascading was the main process driving the particle transfer across the southern Adriatic margin during late winter-spring 2012. Mooring data showed a NW-SE gradient of temperature and kinetic energy from upslope to basin floor, indicating slope transverse flow modulated by local obstruction caused by the rugged sea floor topography. Bari canyon is one of the sites of DSW flow and in this area we have the possibility to extend observations back in time using continuous mooring data since 2009 and previous published materials; this approach allowed evaluation of additional mechanisms of particle transport (e.g., open-ocean convection, storm-driven downward transport, shallow dense water cascading) that are particularly relevant in years when the DSW formation is less vigorous and cascading processes are sluggish. The small amplitude of total mass flux peaks, the weak currents and the relatively high and constant temperatures recorded during 2009, 2010 and 2011 springs are consistent with an enhanced vertical particle rain from a mid-water nepheloid layer, triggered in turn by a shallow cascading of not-particularly dense shelf water detaching from the seafloor when reaches its neutral buoyancy. Thus, the intensity of DSW cascading (shallow vs. deep) plays a first order control on the particulate fluxes through the western margin of the Southern Adriatic, while storm-induced sediment transport can occasionally be relevant too. (C) 2015 Elsevier B.V. All rights reserved.

This study seeks an improved understanding of how matrix association affects the redistribution and degradation of terrigenous organic carbon (TerrOC) during cross-shelf transport in the Siberian margin. Sediments were collected at increasing distance from two river outlets (Lena and Kolyma Rivers) and one coastal region affected by erosion. Samples were fractionated according to density, size, and settling velocity. The chemical composition in each fraction was characterized using elemental analyses and terrigenous biomarkers. In addition, a dual-carbon-isotope mixing model (C-13 and C-14) was used to quantify the relative TerrOC contributions from active layer (Topsoil) and Pleistocene Ice Complex Deposits (ICD). Results indicate that physical properties of particles exert first-order control on the redistribution of different TerrOC pools. Because of its coarse nature, plant debris is hydraulically retained in the coastal region. With increasing distance from the coast, the OC is mainly associated with fine/ultrafine mineral particles. Furthermore, biomarkers indicate that the selective transport of fine-grained sediment results in mobilizing high-molecular weight (HMW) lipid-rich, diagenetically altered TerrOC while lignin-rich, less degraded TerrOC is retained near the coast. The loading (mu g/m(2)) of lignin and HMW wax lipids on the fine/ultrafine fraction drastically decreases with increasing distance from the coast (98% and 90%, respectively), which indicates extensive degradation during cross-shelf transport. Topsoil-C degrades more readily (903.5%) compared to the ICD-C (6011%) during transport. Altogether, our results indicate that TerrOC is highly reactive and its accelerated remobilization from thawing permafrost followed by cross-shelf transport will likely represent a positive feedback to climate warming.

Destabilization and degradation of permafrost carbon in the Arctic regions could constitute a positive feedback to climate change. A better understanding of its fate upon discharge to the Arctic shelf is therefore needed. In this study, bulk carbon isotopes as well as terrigenous and marine biomarkers were used to construct two centennial records in the East Siberian Sea. Differences in topsoil and Pleistocene Ice Complex Deposit permafrost concentrations, modeled using ?13C and ?14C, were larger between inner and outer shelf than the changes over time. Similarly, lignin-derived phenol and cutin acid concentrations differed by a factor of ten between the two stations, but did not change significantly over time, consistent with the dual-carbon isotope model. High molecular weight (HMW) n-alkane and n-alkanoic acid concentrations displayed a smaller difference between the two stations (factor of 3-6). By contrast, the fraction for marine OC drastically decreased during burial with a half-life of 19-27 years. Vegetation and degradation proxies suggested supply of highly degraded gymnosperm wood tissues. Lipid Carbon Preference Index (CPI) values indicated more extensively degraded HMW n-alkanes on the outer shelf with no change over time, whereas n-alkanoic acids appeared to be less degraded toward the core top with no large differences between the stations. Taken together, our results show larger across-shelf changes than down-core trends. Further investigation is required to establish whether the observed spatial differences are due to different sources for the two depositional settings or, alternatively, a consequence of hydrodynamic sorting combined with selective degradation during cross-shelf transport.