Variability in transport of terrigenous material on the shelves and the deep Arctic Ocean during the Holocene

Arctic coastal zones serve as a sensitive filter for terrigenous matter input onto the shelves via river discharge and coastal erosion. This material is further distributed across the Arctic by ocean currents and sea ice. The coastal regions are particularly vulnerable to changes related to recent climate change. We compiled a pan-Arctic review that looks into the changing Holocene sources, transport processes and sinks of terrigenous sediment in the Arctic Ocean. Existing palaeoceanographic studies demonstrate how climate warming and the disappearance of ice sheets during the early Holocene initiated eustatic sea-level rise that greatly modified the physiography of the Arctic Ocean. Sedimentation rates over the shelves and slopes were much greater during periods of rapid sea-level rise in the early and middle Holocene, as a result of the relative distance to the terrestrial sediment sources. However, estimates of suspended sediment delivery through major Arctic rivers do not indicate enhanced delivery during this time, which suggests enhanced rates of coastal erosion. The increased supply of terrigenous material to the outer shelves and deep Arctic Ocean in the early and middle Holocene might serve as analogous to forecast changes in the future Arctic.Peer reviewe

Variability in transport of terrigenous material on the shelves and the deep Arctic Ocean during the Holocene

Arctic coastal zones serve as a sensitive filter for terrigenous matter input onto the shelves via river discharge and coastal erosion. This material is further distributed across the Arctic by ocean currents and sea ice. The coastal regions are particularly vulnerable to changes related to recent climate change. We compiled a pan-Arctic review that looks into the changing Holocene sources, transport processes and sinks of terrigenous sediment in the Arctic Ocean. Existing palaeoceanographic studies demonstrate how climate warming and the disappearance of ice sheets during the early Holocene initiated eustatic sea-level rise that greatly modified the physiography of the Arctic Ocean. Sedimentation rates over the shelves and slopes were much greater during periods of rapid sea-level rise in the early and middle Holocene, as a result of the relative distance to the terrestrial sediment sources. However, estimates of suspended sediment delivery through major Arctic rivers do not indicate enhanced delivery during this time, which suggests enhanced rates of coastal erosion. The increased supply of terrigenous material to the outer shelves and deep Arctic Ocean in the early and middle Holocene might serve as analogous to forecast changes in the future Arctic.Peer reviewe

Palaeoceanographic changes in Hornsund Fjord (Spitsbergen, Svalbard) over the last millennium: new insights from ancient DNA

International audienceThis paper presents a reconstruction of climate-driven environmental changes over the last millennium in Hornsund Fjord (Svalbard), based on sedimentological and micropalaeontological records. Our palaeo-investigation was supported by an analysis of foraminiferal ancient DNA (aDNA), focusing on the non-fossilized monothalamous species. The main climatic fluctuations during the last millennium were the Medieval Warm Period (MWP, AD 1000– 1600), the Little Ice Age (LIA, AD 1600–1900) and the modern warming (MW, AD 1900 to present). Our study indicates that the environmental conditions in Hornsund during the MWP and the early LIA (before ∼ AD 1800) were relatively stable. The beginning of the LIA (∼ AD 1600) was poorly evidenced by the micropalaeontological record but was well marked in the aDNA data by an increased proportion of monothalamous foraminifera, especially Bathysiphon sp. The early LIA (∼ 1600 to ∼ AD 1800) was marked by an increase in the abundance of sequences of Hippocrepinella hirudinea and Cedhagenia saltatus. In the late LIA (after ∼ AD 1800), the conditions in the fjord became glacier-proximal and were characterized by increased meltwater out-flows, high sedimentation and a high calving rate. This coincided with an increase in the percentages of sequences of Micrometula sp. and Vellaria pellucidus. During the MW, the major glacier fronts retreated rapidly to the inner bays, which limited the iceberg discharge to the fjord's centre and caused a shift in the foraminiferal community that was reflected in both the fossil and aDNA records. The palaeoceanographic changes in the Hornsund fjord over the last millennium were driven mainly by the inflow of shelf-originated water masses and glacial activity. However , the environmental changes were poorly evidenced in the micropalaeontological record, but they were well documented in our aDNA data. We considerably increased the number of potential proxy species by including monothala-mous foraminifera in the palaeoecological studies

Present and past flow regime on contourite drifts west of Spitsbergen: preliminary results from Eurofleet 2 PREPARED cruise (June 2014).

Eurofleets-2 PREPARED cruise was conducted during June 5–15, 2014 on board the Norwegian R/V G.O. Sars to investigate the present and past oceanographic flow regime and patterns around two contourite drifts located in the eastern side of the Fram Strait (south-western margin of Spitsbergen). To achieve the main objective of the project, a full range of time scaled measurements was planned, from instantaneous (CTD) and seasonal (moorings) oceanographic measurements, to the recent (Box corer) and geologic (Calypso core) past record. The successful cruise recovered about 2780 km of underway measurements (hull-mounted ADCP and thermosalinograph); 60 CTD sites along 5 main transects; 22 sites for water sampling at different depths for biogeochemical characterization of water masses; 13 meso-zooplankton samplings carried out by vertical hauls (WP2 net) and 20 by horizontal hauls (Manta net) for the study of the present biological productivity of the area; about 120 km of site survey including high-resolution multibeam map and sub-bottom profiles for the identification of current related structures; 5 Box cores; and 2 Calypso piston cores 19.67 and 17.37 m long with an excellent sediment recovery up to 92%. In addition, 3 moorings were deployed for seasonal measurements of water currents direction and velocity, water mass temperature and salinity and to determine the annual amount of local sediment input. Preliminary onboard analyses outlined the presence of a cold-oxygenated and low salinity water mass moving in the deep northern part of the Storfjorden Trough under the effect of the Corilis force and tide configuration considerably affecting the velocity and bottom distribution of the cold water mass. The long Calypso cores contain the record of the past 20 ka with an exceptionally expanded Holocene sequence (over 5 m-thick) that will allow us to obtain very-high resolution palaeoceanographic and palaeoenvironmental reconstructions in the area