A four-year record of UK'37- and TEX86-derived sea surface temperature estimates from sinking particles in the filamentous upwelling region off Cape Blanc, Mauritania

Lipid biomarker records from sinking particles collected by sediment traps are excellent tools to study the seasonality of biomarker production as well as processes of particle formation and settling, ultimately leading to the preservation of the biomarkers in sediments. Here we present records of the biomarker indices UK'37 based on alkenones and TEX86 based on isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs), both used for the reconstruction of sea surface temperatures (SST). These records were obtained from sinking particles collected using a sediment trap moored in the filamentous upwelling zone off Cape Blanc, Mauritania, at approximately 1300 water depth during a four-year time interval between 2003 and 2007. Mass and lipid fluxes are highest during peak upwelling periods between October and June. The alkenone and GDGT records both display pronounced seasonal variability. Sinking velocities calculated from the time lag between measured SST maxima and minima and corresponding index maxima and minima in the trap samples are higher for particles containing alkenones (14-59 m/d) than for GDGTs (9-17 m/d). It is suggested that GDGTs are predominantly exported from shallow waters by incorporation in opal-rich particles. SST estimates based on the UK'37 index faithfully record observed fluctuations in SST during the study period. Temperature estimates based on TEX86 show smaller seasonal amplitudes, which can be explained with either predominant production of GDGTs during the warm season, or a contribution of GDGTs exported from deep waters carrying GDGTs in a distribution that translates to a high TEX86 signal.

Sediment volume variations inferred from DGPS measurements within Bossons glacier proglacial area (Mont-Blanc massif, France)

This dataset presents Differential Global Positioning System data (DGPS) acquired within the Bossons glacier proglacial area. Bossons glacier is a rapidly retreating glacier and its proglacial area is deglaciated for ~30 years. Bossons stream is one of the outlets of the subglacial drainage system. It starts as a 800 m steep cascade reach, then flows through an area with gentler slope : the Plan des Eaux (PdE). PdE is a 300 m long, 50 m wide proglacial alluvial plain with an increasing channel mobility in the downstream direction but decreasing slope gradient and incision. As it may act a sediment trap, studying periglacial and proglacial erosion processes in the Bossons catchment requires to quantify PdE sediment volume evolution. A several meter-sized block located within Bossons proglacial area was set up as GPS base : its location was measured by one antenna (Topcon Hyper Pro) by performing 600 consecutive measurements throughout one day. A second antenna (Topcon Hyper Pro) was then used to measure XYZ location of points in the proglacial area with a ~2 m grid. Radio communication between the two antennas allowed differential calculations to be automatically carried out on field using the Topcon FC-250 hand controller. This methodology yields 3 cm XY and 1.5 cm Z uncertainties. DGPS data have been acquired through 10 campaigns from 2004 to 2014; campaigns from 2004 to 2008 cover a smaller area than those from 2010 to 2014. Digital Elevation Model (DEM) have been interpolated from DGPS data and difference between two DEMs yields deposited and eroded volume within PdE. Maps of PdE volume variation between two campaigns show that incision mainly occurs in the upper and lower sections where as deposition dominates in the middle section. Deposition, denudation and net rate (deposition rate - denudation rate) are calculated by normalizing volumes by DEM areas. Deposition dominates results with a mean net rate of 29 mm/yr. However, strong inter-annual variability exists and some years are dominated by denudation : -36 mm/yr and -100 mm/yr for 2006 and 2011, respectively. Nonetheless, oldest campaigns (2004 to 2008) were carried out on the lower part part of the alluvial plain and ruling them out to keep only complete DEM (2010 to 2014) yields a mean net rate of ~15 mm/yr. This results is coherent with field observations of both strong deposition (e.g. flood deposits) and strong erosion (e.g. 30 cm incision) evidences. Bossons glacier proglacial area is thus dynamic with year-to-year geormorphological changes but may leans toward increasing its mean elevation through a deposition dominated system.

Hydro-sedimentary parameters measurements within the proglacial area of the Bossons glacier (Mont-Blanc massif, France)

This dataset presents hydro-sedimentary data within the Bossons glacier proglacial area. Bossons glacier is rapidly retreating and its proglacial area is deglaciated for ~ 30 years. It is an intriguing location to study periglacial, proglacial and subglacial erosion processes which requires estimating Total Dissolved Solid (TDS) and Total Suspended Solid (TSS) concentrations, and discharge. Measurements were performed at three distinct locations within Bosson glacier watershed : Bossons downstream (BDS), Bossons upstream (BUS) and Crosette (CRO). The latter is located at the glacier termini whereas BDS and BUS stations are farther downstream from the glacier, at 1.5 and 1.15 km, respectively .