999 resultados para Total mass
Resumo:
Investigations of lithogenic and biogenic particle fluxes using long-term sediment traps are still very rare in the northern high latitudes and restricted to the arctic marginal seas and sub-arctic regions. Here, for the first time, data on the variability of fluxes of lithogenic matter, carbonate, opal, and organic carbon as well as biomarker composition from the central Arctic Ocean are presented for a one-year period. The study has been carried out on material obtained from a long-term mooring system equipped with two multi-sampling-traps (150 and 1550 m water depth) and deployed on the southern Lomonosov Ridge close to the Laptev Sea continental margin from September 1995 to August 1996. In addition, data from surface-sediments were included in the study to get more information about the flux and sedimentation of organic carbon in this area. Annual fluxes of lithogenic matter, carbonate, opal, and particulate organic carbon are 3.9 g/m**2/y, 0.8 g/m**2/y, 2.6 g/m**2/y, 1.5 g/m**2/y, respectively, at the shallow trap and 11.3 g/m**2/y, 0.5 g/m**2/y, 2.9 g/m**2/y, 1.05 g/m**2/y, respectively, at the deep trap. Both the shallow as well as the deep trap show significant differences in vertical flux values over the year. Higher values were found from mid-July to end of October (total flux of 75-130 mg/m**2/d in the shallow trap and 40-225 mg/m**2/d in the deep trap, respectively). During all other months, fluxes were fairly low in both traps (most total flux values <10 mg/m**2/d1). The interval of increased fluxes can be separated into (1) a mid-July/August maximum caused by increased primary production as documented in high abundances of marine biomarkers and diatoms, and (2) a September/October (absolute) maximum caused by increased influence of Lena river discharge indicated by maximum lithogenic flux and high portions of terrigenous/fluvial biomarkers in both traps. Here, total fluxes in the deep trap were significantly higher than in the shallow trap, suggesting a lateral sediment flux at greater depth. The lithogenic flux data also support the importance of sediment input from the Laptev Sea for the sediment accumulation on the Lomonosov Ridge on geological time scales, as indicated in sedimentary records from this region.
Resumo:
Substantial retreat or disintegration of numerous ice shelves have been observed on the Antarctic Peninsula. The ice shelf in the Prince Gustav Channel retreated gradually since the late 1980's and broke-up in 1995. Tributary glaciers reacted with speed-up, surface lowering and increased ice discharge, consequently contributing to sea level rise. We present a detailed long-term study (1993-2014) on the dynamic response of Sjögren Inlet glaciers to the disintegration of Prince Gustav Ice Shelf. We analyzed various remote sensing datasets to observe the reactions of the glaciers to the loss of the buttressing ice shelf. A strong increase in ice surface velocities was observed with maximum flow speeds reaching 2.82±0.48 m/d in 2007 and 1.50±0.32 m/d in 2004 at Sjögren and Boydell glaciers respectively. Subsequently, the flow velocities decelerated, however in late 2014, we still measured about two times the values of our first measurements in 1996. The tributary glaciers retreated 61.7±3.1 km² behind the former grounding line of the ice shelf. In regions below 1000 m a.s.l., a mean surface lowering of -68±10 m (-3.1 m/a) was observed in the period 1993-2014. The lowering rate decreased to -2.2 m/a in recent years. Based on the surface lowering rates, geodetic mass balances of the glaciers were derived for different time steps. High mass loss rate of -1.21±0.36 Gt/a was found in the earliest period (1993-2001). Due to the dynamic adjustments of the glaciers to the new boundary conditions the ice mass loss reduced to -0.59±0.11 Gt/a in the period 2012-2014, resulting in an average mass loss rate of -0.89±0.16 Gt/a (1993-2014). Including the retreat of the ice front and grounding line, a total mass change of -38.5±7.7 Gt and a contribution to sea level rise of 0.061±0.013 mm were computed. Analysis of the ice flux revealed that available bedrock elevation estimates at Sjögren Inlet are too shallow and are the major uncertainty in ice flux computations. This temporally dense time series analysis of Sjögren Inlet glaciers shows that the adjustments of tributary glaciers to ice shelf disintegration are still going on and provides detailed information of the changes in glacier dynamics.
